Methodology and Performance Analysis of the Portuguese Window Energy Labelling System

Methodology and Performance Analysis of the Portuguese Window Energy Labelling System | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Methodology and Performance Analysis of the Portuguese Window Energy Labelling System Nuno Simões, Joana Prata, Rita Garcia, Paulo Santos, Bruna Morais This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7012970/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Energy labelling is a tool for reducing building operational energy use by offering transparent, comparable performance data. While well established for appliances, labelling of construction products, particularly windows remains rare. In Portugal, the CLASSE + system, managed by ADENE and based on Itecons’ methodology, has issued over 745,000 window labels in the past decade. This paper details the CLASSE + methodology and analyzes data from the first 500,000 labels to uncover product performance trends and system behavior. A residential case study is used to evaluate the practical impact of window replacement on building energy performance, illustrating that the most efficient label rating is not universally optimal. This work provides a robust, data-driven foundation for refining window labelling schemes. It critically reviews the current classification scale and offers recommendations, including new indicators such as safety, sustainability and alignment with the EU Taxonomy, thereby supporting national and European policy goals. Windows Energy labelling Buildings Energy performance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 1. INTRODUCTION The construction sector accounts for 40% of energy consumption in the European Union (EU) and 36% of greenhouse gas emissions [1], which led the creating of European policies to help reduce these values. The proposal to revise the Energy Performance of Buildings Directive aims to gradually reduce greenhouse gas emissions (GHG) and energy consumption in the EU's construction sector, with the goal of achieving climate neutrality by 2050. To achieve this, there is a need to transition to higher performance standards in buildings, namely nearly zero-energy buildings (nZEB) and zero-carbon buildings (ZEB) [2]. Therefore, selecting construction solutions with higher thermal performance for building envelopes is essential [3]. Windows are one of the weakest thermal elements of the building envelope, accounting for 20% to 60% of energy loss in buildings, depending on their age, type, and size ([4]-[9]). In summer, windows can promote a house's heat gain up to 80% [10]. High thermal transmittance (U w ) values lead to increased energy consumption for heating, while high solar factor (g) values lead to higher cooling energy needs. Thus, the energy performance of windows depends on the proper combination of both factors ([11]-[14]). The relationship between the glazed area, its orientation, and the thermal performance of a building is significant. Studies indicate that larger windows facing south, east, and west, combined with smaller areas facing north, reduce heating needs [4]. Window size has a greater impact on heating needs than on cooling needs. While large glazed surfaces improve winter performance, they also increase peak thermal loads during this season [4]. North-facing windows, when energy-efficient, can vary in size without significantly affecting energy performance [7]. Shading also influences window performance. Research shows that selective shading is crucial for improving summer performance without compromising winter efficiency [6]. An optimized glazed window can save up to 24% of energy [5]. According to some studies, heating load is more sensitive to window size and type compared to cooling load ([4],[5]). Choosing high-performance windows is a valuable improvement opportunity for both new buildings and renovation projects [15], as it contributes to reducing building energy consumption, lowering heating and cooling needs, while enhancing natural lighting and ventilation. However, selecting energy-efficient windows requires clear and comparable performance information, enabling designers and end consumers to make informed product choices. An energy classification system, similar to that used for household appliances and lighting systems, not only provides clear and accurate information on window performance but also promotes improved quality among products on the market [19]. The International Standard ISO 18292:2011 [16] outlines guidelines for assessing the energy performance of fenestration systems. It establishes methods for calculating heating and cooling energy consumption in residential buildings, covering aspects such as calculation approaches, preparation of weather data, and key characteristics of buildings and windows. According to this standard, the energy performance of fenestration systems must be presented in terms of annual energy requirements, based on a national reference building and reference climate conditions. Different levels of information [17] are available to support the development of a window energy rating scheme. In most countries, the energy performance of windows is evaluated as a linear combination of solar energy transmittance, thermal transmittance, and the influence of air permeability characteristics. The information provided by an energy performance label can be categorized into three levels. Level 1 (L1) includes basic physical data of the product and is independent from climate, orientation and use conditions. Level 2 (L2) provides energy performance information calculated using Level 1 data and a standard window size of 1.23 x 1.48 m² [18]. The energy performance (EP) is determined by the formula (EP = A w .g - B.(U + L f )), where g represents solar thermal transmittance, U is the thermal transmittance of the fenestration (W/m²ºC), L f is an air leakage factor related to air permeability, and A and B are constants reflecting climate conditions, calculated for specific climate zone. A W denotes the window area. Level 3 (L3) offers comprehensive data on the window's energy performance, considering its actual dimensions within a reference building to evaluate its impact on the building's overall energy behaviour. There is no international reference building so it must be established at national level, as stated in ISO 18292:2011. This level is highly detailed and intended for use by architects and engineers [16]. Several countries have been pioneers in this field and have established window energy rating systems [20], each adopting a specific level of information: Sweden (L1), South Korea (L1), Canada (L2), Denmark (L2), the United Kingdom (L2), Finland (L2), New Zealand (L3), and Australia (L2). While energy labelling is generally voluntary, it is mandatory in certain countries like Iran, where window manufacturers are required to specify the energy performance index and label for the windows they produce [20]. Window performance strongly depends on climate, geographical location [21], and solar radiation [10]. Some European organizations support the introduction of an EU label for windows reflecting multiple climate zones [22]. However, the idea is not unanimous. Some critics claim that such a label may be inadequate from both consumer and environmental perspectives, as it may not effectively guide consumers to the most energy- and cost-efficient products across different European climates and building types, reducing its effectiveness [23]. In the meantime, to facilitate the selection of more efficient windows, several countries in Europe have established their own national window certification systems [19], including Portugal. ADENE – the Portuguese Energy Agency – created the CLASSE+ energy labelling system. This system is based on a calculation methodology developed by Itecons “Institute for Research and Technological Development in Construction, Energy, Environment and Sustainability (https://www.itecons.uc.pt/)” in accordance with ISO 18292:2011 standard [16] and described in this paper. The growing adoption of the CLASSE+ energy labelling system reflects a positive response from the window sector, with the participation of more than 770 companies and the issuance of over 745 000 window labels. This growth is also driven by the label being a mandatory requirement for access to certain financial incentive programs. The CLASSE+ system was revised in 2017 to include Class A+, which is now the highest efficiency rating. In the CLASSE+ methodology, the energy class of windows depends on several factors: thermal transmittance, solar factor, and air permeability class of the window, all of which strongly affect the thermal performance of building envelopes. The label also provides additional information on the glass’s light transmission and the window’s acoustic attenuation (Rw) and indicates a comfort level for summer and winter. Issuing a Classe+ label requires detailed technical information, including the glass technical data sheet and test reports verifying compliance with national and European standards: U w -value report (thermal transmittance determined following EN ISO 10077-1 [24] and EN ISO 10077-2 [25] or ISO 12567:2000 [26]), AEV report (air permeability, water tightness, and wind resistance, determined in accordance with EN 1026 [27], EN 1027 [28], and EN 12211 [29]), and acoustic report (sound insulation determined under EN ISO 10140-2 procedure [30]). A major limitation of the CLASSE+ system is the lack of comprehensive studies quantifying how different window classes affect building energy performance and certification. This gap makes it difficult to evaluate whether higher-rated windows consistently deliver better energy efficiency. Current window energy labelling programs prioritize thermal performance during the use phase but overlook life-cycle environmental impacts. Including Life Cycle Assessment (LCA) in labelling would help consumers choose products with lower environmental and cost impacts, promote sustainable innovation, and support climate policies ([31]-[33]). There are challenges in including LCA information in labelling, namely related to the complexity of LCA, which requires special expertise, the fact that it is a data intensive assessment, and the need for standardized criteria to enable a fair comparison of environmental performance ([34],[35]). The new Construction Products Regulation [36], which has included new sustainability requirements for construction products, will likely incentivise the generation of life-cycle environmental information, and it is key that labelling programs are at the forefront of this new paradigm. Future efforts in labelling should, therefore, focus on building on readily available environmental data, namely Environmental Product Declarations (EPD), defining specific environmental metrics, and influencing regulatory incentives to improve sustainable window labelling. This study evaluates the CLASSE+ energy labelling system for windows, examining its effectiveness and identifying areas for improvement. It outlines the system’s methodology, analyses issued labels to explore relationships between energy classification and window characteristics and includes a case study on how different window ratings impact a residential building energy performance based on Portuguese energy performance calculation method (regulation published in the Decree-Law no. 101-D/2020). The findings highlight the need to update energy classification levels and incorporate additional parameters related to safety, sustainability, and European taxonomy alignment. 2. METHODOLOGY 2.1. Introduction According to ISO 18292:2011 [16], in order to create a rating system, the energy performance of fenestration systems should be based on indices that represent the energy requirements for heating and cooling, P E,H,w and P H,w , measured in kWh/m². Based on the methodology described in ISO 13790:2008 [37], which focuses on assessing the thermal and energy performance of buildings, ISO 18292:2011 introduces a range of methods with varying levels of detail. These methods serve as the basis for calculating a building's heating and cooling demands, covering energy balance calculations on seasonal, monthly, and hourly scales. The methodology used in the Portuguese window energy labelling system is based on the hourly method and involves the four main steps established by ISO 18292:2011: 1. Selecting the climate data ; 2. Defining the reference building ; 3. Preparing window thermal properties ; 4. Calculating energy performance . 2.1.1. CLIMATE data Climate data for different Portuguese climate zones were obtained from SolTerm, a software tool provided by the National Energy and Geology Laboratory (LNEG). According to national regulations, Portugal is divided into six distinct climate zones - three for heating (winter climate zones: I1, I2, I3) and three for cooling (summer climate zones: V1, V2, V3). Figure 1 shows the distribution of climate zones in Portugal as defined in the year the methodology was developed. Energy simulations conducted during the development of the window labelling methodology covered all climate zones. For this purpose, three Portuguese cities representative of these zones were selected to obtain results reflecting the entire national territory. The cities analysed are identified in Figure 1 and listed in Table 1. Table 1: Portuguese cities considered in energy simulations. Climate Zone Portuguese City Conditions Winter I1 Évora Mild winter I2 Porto Moderate winter I3 Bragança Severe winter Summer V1 Porto Mild summer V2 Bragança Moderate summer V3 Évora Severe summer 2.1.2. REFERENCE BUILDING The energy simulations were performed for a reference building with specific geometry and thermophysical properties, as defined in ISO 13790:2008 [37] and detailed in ISO 13791:2004 [38]. The reference building used in the simulations was modelled with: - A single window with a window floor area (WFA) of 18%; - Adiabatic boundary conditions for all walls except the one with the window, eliminating external thermal gains or heat losses through other surfaces; - No internal heat sources, ensuring that all energy gains or losses result only from the interaction of the window with the external environment. Figure 2 illustrates the building geometry, while Table 2 provides thermophysical property details. The dimensions shown in Figure 2 represent the interior measurements of the compartment and do not account for the thickness of the construction solutions. Table 2: Thermophysical properties of the reference building envelope. Structure S [m] λ [W/(m.K)] Ρ [kg/m 3 ] C p [kJ/(kg.K)] External Wall Outer layer 0.0115 0.99 1800 0.85 Insulation layer 0.06 0.04 30 0.85 Masonry 0.175 0.79 1600 0.85 Internal plastering 0.015 0.70 1400 0.85 Internal Wall Gypsum Plaster 0.012 0.21 900 0.85 Insulation layer 0.10 0.04 30 0.85 Gypsum Plaster 0.012 0.21 900 0.85 Ceiling / Floor Plastic covering 0.004 0.23 1500 1.50 Cement floor 0.06 1.40 2000 0.85 Insulation layer 0.04 0.04 50 0.85 Concrete 0.18 2.10 2400 0.85 2.1.3. Window’s thermal properties Table 3 presents the different window solutions considered in the methodology development. A wide range of fenestration designs was evaluated, varying the window thermal transmittance (U w -value), the total solar energy transmittance of the glazing (g-value), and the air permeability level of the windows. The modelled U-values ranged from 0.5 W/(m²·°C) to 4 W/(m²·°C), reflecting commercially available options, while the g-values were adjusted from 0.3 to 0.8 to simulate different levels of solar gain. Two air permeability classes were selected: Class 4, with an air leakage of 3 m³/(m²·h) at a pressure difference of 100 Pa, and Class 2, with an air leakage of 27 m³/(m²·h) under the same conditions. Table 3: Window solutions considered in the methodology development. Window solution - Case study Thermal transmittance, U [W/(m 2 .K] Solar energy transmittance, g Air permeability 1 0.5 0.3 Class 2/ Class 4 2 0.5 0.8 3 1.0 0.7 4 2.5 0.3 5 2.5 0.8 6 3.0 0.7 7 4.0 0.3 8 4.0 0.8 2.1.4. Energy Performance Simulations In the step four of the Portuguese window labelling system methodology, the impact of window characteristics (air permeability, global area and thermal properties) on the annual heating and cooling energy needs of a reference building was evaluated, considering different climate zones and window orientations. The analysis was performed for the different window solutions presented in Table 3. The annual energy needs were determined hourly through dynamic simulations using EnergyPlus software with the DesignBuilder graphical interface. The simulations were conducted with constant indoor temperatures of 20°C for heating and 25°C for cooling. Cooling needs were evaluated from June to September, accounting for both sensible and latent heat, while heating needs were evaluated from October to May, considering only sensible heat. Four different window orientations were simulated: north, east, south, and west. The weighted average of the heating and cooling needs were then analysed. Effect of window air permeability Two window performance levels for air permeability were analysed: classes 4 and 2. Simulations used steady ventilation rates based on EN 12207:1999 guidelines. At a reference pressure difference of 100 Pa, airflow rates were 27 m³/(m²·h) for class 2 and 3 m³/(m²·h) for class 4. At 6 Pa, these corresponded to air exchange rates of 0.26 air changes per hour (h⁻¹) for class 2 and 0.03 for class 4. First, heating and cooling needs were calculated for each climate scenario (Table 1) using a ventilation rate of 0.03 h⁻¹, corresponding to Class 4 windows. Figure 3 illustrates the annual heating and cooling needs, expressed in kWh per square meter of window area, for the climate zone of Évora (mild winter (I1) and severe summer (V3)), considering different window orientations. These results are based on a ventilation rate of 0.03 h⁻¹ and assume a window-to-floor area ratio of 18%. Then, the impact of increased ventilation was evaluated by comparing these results with those from Class 2 windows, which have a ventilation rate of 0.26 h⁻¹ (Figure 4). The results indicated that total energy needs are generally greater for Class 2 windows compared to Class 4 windows. An exception occurs with south-facing façades featuring low thermal transmittance values, where Class 4 windows exhibit slightly higher energy needs. The results also revealed that east and west-facing façades have similar energy consumption patterns, whereas south-facing façades demonstrate greater variability in energy needs. This suggests that the thermal properties of windows are more critical for south-facing orientation. In contrast, north-facing windows exhibit relatively stable energy performance across most cases, showing the lowest thermal demands overall, except in two instances where low solar thermal transmittance leads to increased needs. Effect of Window Area The study analysed how window area affects the overall energy performance of the reference building. Simulations were conducted for various window floor area ratios (20%, 40%, 60%, and 80%), considering the different window orientations (north, east, south, and west). Four scenarios were modelled, varying the U-value and the g-value (Table 4). Table 4: Window solutions used to evaluate the effect of window area. Thermal transmittance, U [W/(m 2 .K] Solar energy transmittance, g 1 0.7 4 0.7 2.5 0.3 2.5 0.8 Figure 5 a) and Figure 5 b) give the total needs for Évora climate, for north and east orientation, respectively. Total needs are the sum of annual heating and cooling needs. The results are given in kWh per floor area (in m2). The results showed a linear relationship between energy needs and window area, with larger windows increasing both heating and cooling demands. This pattern was consistent across all window solutions analysed, with the extent of variation depending on the window's thermal properties. The effect was more pronounced in orientations with higher solar gains. Weighted Average Results Finally, the energy performance results were summarized by presenting the weighted average of the heating and cooling needs for the three cities analyzed (Table 1). This analysis highlights the combined effects of window design, ventilation rates, and climate conditions on energy efficiency. The weighted average was calculated for heating and cooling needs, considering energy demands over eight months of heating (October to May) and four months of cooling (June to September), following the national energy calculations recommendations. To provide a more accurate assessment of overall energy performance, the calculation was based on the typical window distribution across building orientations, using the weighting factors shown in Table 5, defined assuming the national statistics. Table 5: Weighting factors for each orientation. Orientation Weighting factor North 0.15 East 0.25 South 0.35 West 0.25 Figure 6 shows the heating and cooling weighted average needs of each window solution, at each location (Bragança, Porto and Évora). A clear increase in heating needs is observed for Bragança, which is associated with its colder winter climate. Cooling needs varies less between climate zones compared to heating needs, with higher cooling needs observed in locations with more extreme summer climates (Évora). Figure 7 shows the weighted average of the total annual energy needs (heating and cooling) for all locations. The lowest total energy needs are associated with windows that have both a low thermal transmittance coefficient (U = 0.5 W/(m²·°C)) and low solar thermal transmittance (g = 0.3). Higher heating needs are typically linked to windows with low g-value, while higher cooling needs are associated with windows with higher g-value. When the U-value remains constant, reducing the g-value decreases cooling and total energy needs but increases heating needs. If solar thermal transmittance remains high, lowering the U-value slightly reduces total energy needs, increases cooling needs, and decreases heating needs. Conversely, when the g-value is low, reducing the U-value slightly increases cooling needs while decreasing both total energy and heating needs. CONCLUSIONS Based on the simulation results, the following conclusions were drawn: - Air Leakage: Higher air permeability (Class 2) significantly increases total energy needs, except for some south-facing windows with low U-values. - Orientation Sensitivity: South-facing windows were most affected by thermal properties, while north-facing ones had the lowest energy needs. East and west orientations displayed similar, stable energy demands. - Window Area Impact: A linear increase in energy needs was observed with larger window areas, highlighting the importance of optimizing window-to-floor area ratios. - Thermal and Solar Transmittance: Reducing U-values (thermal transmittance) decreased heating needs but had mixed effects on cooling demands, depending on g-values. Reducing g-values (solar transmittance) lowered cooling and total energy needs but increased heating requirements. Optimizing window design, orientation, and size is essential for maximizing energy efficiency. Selecting windows with low U-values and g-values significantly reduces overall energy demand, though careful consideration is required to balance heating and cooling requirements. 2.2. Portuguese WINDOWs ENERGY Rating The results obtained with the methodology described before formed the basis of the Portuguese energy labelling system (known as Classe+ energy labelling). The classification reflects the overall energy performance of windows, considering heating and cooling needs. Energy classification limits were established based on the simulations of the reference room, considering different windows solutions (varying the U-value and g-value) and different air permeability classes 1 to 4. Although the simulations covered a year, the rating was based on monthly results to reduce variations caused by solar thermal transmittance. January and August, the months with the highest energy demand, were selected. Figure 7 shows the results of energy needs when the window’s air permeability is class 4. The Classe+ energy classification system for windows uses intervals ranging from A+ (most energy-efficient product) to F (least energy-efficient product). Table 6 presents the current energy classes for windows and the maximum total energy requirements assigned to each class. These limits have already undergone a review phase, as the initial version of the scale extended only up to Class A. Table 6: Current energy classes for windows and their corresponding maximum total energy requirements. Energy Class (CLASSE+ System) Maximum Total Energy Requirements [kWh/(m²·month)] A+ 16.65 A 18.50 B 22.20 C 25.90 D 29.60 E 33.30 F 37.00 Additionally, the Portuguese window classification methodology defines 10 comfort levels - less comfort (1) to more comfort (10) - for summer and winter, based on the energy needs for cooling (Nc) and heating (Nh), respectively. Table 8 shows the ranges of energy requirements associated with each of the comfort levels for the summer and winter situation. Table 7: Portuguese window energy labelling - comfort levels. Comfort levels 1 2 3 4 5 6 7 8 9 10 Summer Nc [kWh/(m 2 .month)] Nc ≥ 13.7 12.9 ≤ Nc < 13.7 12.2 ≤ Nc < 13.9 11.5 ≤ Nc < 12.2 10.7 ≤ Nc < 11.5 10.0 ≤ Nc < 10.7 9.3 ≤ Nc < 10.0 8.5 ≤ Nc < 9.3 7.8 ≤ Nc < 8.5 Nc < 7.8 Winter Nh [kWh/(m 2 .month)] Nh ≥ 20.7 18.2 ≤ Nh < 20.7 15.7 ≤ Nh < 18.2 13.2 ≤ Nh < 15.7 10.7 ≤ Nh < 13.2 8.2 ≤ Nh < 10.7 5.7 ≤ Nh < 8.2 3.2 ≤ Nh < 5.7 0.7 ≤ Nc < 3.2 Nc < 0.7 3. Analysis of the Portuguese labeling Data This section presents the key findings from the analysis of data provided by ADENE regarding the national energy labelling system for windows, known as CLASSE+. CLASSE+ System Data Overview Considering the dataset of the first 500 000 labelled windows, 91.4% are rated A+, 6.8% are rated A, and 1.6% are rated B. Lower energy efficiency classes (C, D, E, and F) account for only 0.2% of the labelled windows. Furthermore, 95.9% of the labelled windows have an air permeability class of 4, 3.9% are classified as class 3, and just 0.2% fall into classes 1 or 2. It is important to note that participation in the CLASSE+ system is voluntary, which explains why companies predominantly label their highest-performing products. Thermal Transmittance (Uw) Analysis Figure 8 shows the distribution of energy labels by thermal transmittance (Uw) ranges. About 40% of A+ windows have a Uw between 1.4 and 1.6 W/m²°C (around 182 000 windows), while 25% fall between 1.2 and 1.4 W/m²°C. Only 1.0% have Uw values between 1.8 and 2.0 W/m²°C. For A-rated windows, 29% have a Uw between 1.6 and 1.8 W/m²°C, and 27% between 1.8 and 2.0 W/m²°C. Notably, 25% of E-rated windows fall within 1.2 to 1.4 W/m²°C, accounting for 12 labels, and these also have low solar factors and air permeability classifications. Solar Factor (g) Analysis Figure 9 shows the distribution of energy labels by solar factor (g) ranges. Most windows have a g-value between 0.4 and 0.7. Of the windows with g-values in this range, 82% are rated A+ and 4% are rated A. About 40% fall between 0.4 and 0.5 (around 194 000 labels), 37% between 0.6 and 0.7 (about 179 600 labels), and 11% between 0.5 and 0.6. Frame Material Analysis The CLASSE+ data also indicates that the majority of windows with energy ratings of A+, A, or B use PVC frames. More than 450 000 labelled windows have PVC frames, followed by approximately 33 000 thermal Break aluminium windows. Other frame materials account for less than 1% of the total windows labelled under the CLASSE+ system. 4. Impact of WINDOW’s replacement on the energy performance of a residential building This study analyzed the impact of replacing existing windows with higher energy-labelled ones on the thermal and energy performance of a single-family home. Heat losses through the building envelope and annual energy needs (useful and primary) were calculated using a seasonal methodology, considering different window energy classes. The study also evaluated window replacement combined with other thermal improvements, including various insulation solutions for the vertical opaque envelope and different climate zones: I3, V2 (Zone A); I2, V2 (Zone B); and I1, V3 (Zone C). The calculations followed the guidelines of Decree-Law No. 101-D/2020 of December [ 39 ]. 4.1. Case Study Description The case study corresponds to an existing four-bedroom single-family dwelling (Fig. 11 ), with a usable floor area of 315 m², an intermediate thermal inertia class, and façades oriented to the NE, SE, SW, and NW. For climate control of all main spaces and circulation areas, an air-to-air heat pump system was installed, with a SCOP of 4.0 and a SEER of 6.4. The study evaluated three insulation solutions for the vertical opaque envelope, including external walls and structural thermal bridges: no insulation, External Thermal Insulated Composite Systems (ETICS) with 4 cm of Expanded Polystyrene (EPS), and ETICS with 8 cm of EPS. Table 8 presents the U-values calculated based on the building materials and their thermal properties, as specified in [ 40 ]. Table 8 Constructive solutions comprising the opaque exterior envelope. Type U [W/m 2 .°C] Without insulation ETICS | EPS 4 cm ETICS | EPS 8 cm External wall 1,02 0,52 0,35 External wall (Thermal Bridge) 2,93 0,78 0,45 For the glazed envelope, various scenarios with different Uw values were analyzed to assess the impact of installing windows with energy classes D, C, B, A, and A+. The goal was to evaluate the effect of replacing class D windows with higher-rated ones. An air permeability class of 4 and a solar factor of 0.5 for the glass were assumed in all scenarios. 4.2. Results Figure 12 shows the heat losses through the windows (in W/°C) for each window energy class and the three thermal insulation solutions. The graphs indicate that replacing class D windows with class A + or class A windows reduces heat losses through the windows to less than half. A similar reduction occurs when class C windows are replaced with class A + windows. Figure 13 shows the windows' contribution to total heat losses through the building's exterior envelope (%), considering different window and insulation solutions. Better window energy classes reduce heat losses. When class D windows are replaced with class A + windows, this contribution decreases by more than 40%, and the reduction can exceed 50% in envelopes without thermal insulation. With an ETICS system (8 cm of EPS) and class D windows, 52% of the heat loss occurs through the windows. Upgrading to class A + reduces this to 27%. Figure 14 shows the annual energy needs for heating (Nic) and cooling (Nvc) based on window energy class, climate zones (I3, V2 – Zone A; I2, V2 – Zone B; I1, V3 – Zone C) and insulation solutions. Replacing class D windows with higher-rated ones significantly reduces Nic by up to 48% in highly insulated envelopes and 38% in uninsulated ones. However, better-rated windows increase Nvc, with rises of up to 44% in climate zone V2, though only about 5% in climate zone V3. Figure 15 shows the ratio of annual primary energy needs to reference energy needs (Ntc/Nt) for the different scenarios when changing window energy classes and insulation solutions (no insulation, ETICS with 4 cm of EPS, and ETICS with 8 cm of EPS). It also displays the maximum limits for each building energy class, indicating the class achieved in each scenario. The building’s classes are those defined by the national energy certification scheme (defined in the Decree-Law No. 101-D/2020 of December 7). The results show that the impact of window energy class depends on the building's location and envelope type. In the analysed building, upgrading from class A to A + windows did not change its energy class due to the window class range. For a highly insulated envelope, class B is enough to achieve building energy class B, regardless of location - this was the highest class reached in the analysis. In an uninsulated envelope and a colder climate zone (I3), replacing class C windows with class B or higher can raise the building's energy class from C to B-. 5. recommendations for the EVOLUTION OF the WINDOW energy LABELING system Based on the study's results, this section proposes revising the CLASSE + energy labeling system for windows in Portugal by adding new criteria and parameters, including safety, sustainability, and compliance with European requirements. The information below comprises a set of recommendations that have been proposed to ADENE for implementation in an upcoming revision of the labelling scheme. 5.1. Update of the Energy Classification Scale The CLASSE + system for energy labelling of construction products includes seven energy classes, from A+ (most efficient) to F (least efficient). For windows, this classification is based on the total monthly energy needs for climate control in a reference compartment. An analysis of CLASSE + data shows that 91.5% of window labels are class A+. About 96% of labeled windows have class 4 air permeability, while the remaining 4% have class 3. Most labeled windows have a thermal transmittance (Uw) between 1.2 and 1.8 W/m²·°C, with 40% of A + windows falling between 1.4 and 1.6 W/m²·°C. Regarding the solar factor (g), 40% of all labeled windows fall between 0.4 and 0.5, and 37% between 0.6 and 0.7. For air permeability classes 3 and 4, A + windows can have Uw values up to 2.0 W/m²·°C, depending on the glass's solar factor. Windows with class 4 air permeability and Uw ≤ 1.4 W/m²·°C always meet the A + standard, regardless of the solar factor. The Uw and g ranges for achieving an A + class are much broader than for class A, especially for windows with class 4 air permeability, which represents most labelled windows. This analysis suggests an opportunity to tighten the criteria for achieving an A + rating, promoting windows with better thermal performance. Any revisions should reflect the reality of the national market and current Portuguese regulations. It is also important to note that European standards, such as those in the European Taxonomy and certifications like Passivhaus and Minergie, set stricter Uw limits (e.g., Uw ≤ 1.0 W/m²·°C). Although this criterion may not suit Mediterranean climates, the label must include information on whether the window meets this criterion. 5.2. New Parameters and Information for the Label The current energy label provides the window's energy class, summer and winter comfort levels, thermal transmittance (Uw), solar factor, light transmission, air permeability class, and acoustic attenuation. However, adding information on safety, sustainability, and compliance with stricter thermal standards like the European Taxonomy is recommended. Table 9 outlines the suggested new parameters for the updated label. Table 9 Parameters and new information to be provided through the label Indicator Parameter / information Thermal performance and alignment with the European Taxonomy Information on compliance with the technical criterion of the European Taxonomy (Uw ≤ 1.0 W/m².°C) Safety Wind resistance class according with EN 12210:2016 [ 41 ] Sustainability Environmental parameters: Embodied carbon, kg CO₂ eq.m⁻²; Embodied energy, MJp.m⁻² Circularity parameters: Recycled content rate, % Compliance with the European Taxonomy Requirements The EU Taxonomy regulation, approved by the European Union (EU) in June 2020, defines which activities are considered sustainable using a common classification system. The regulation outlines six environmental objectives and stipulates that an activity can be deemed environmentally sustainable if it contributes to one of these objectives without significantly harming the others. To this end, criteria have been defined for different economic activities. Concerning windows, the criterion is to produce highly energy-efficient systems with a thermal transmittance (Uw) of ≤ 1.0 W/m²·°C to help mitigate climate change. While this standard is strict for Mediterranean climates and should not define a window’s energy class, whether the window meets this criterion should be highlighted on the label. Wind Resistance Although wind resistance does not affect a window's energy performance, it is a crucial safety feature, especially during extreme weather events. It measures how much the window deforms under wind pressure, depending on the frame material, profile type, and fitting strength. A performance scale, from least to most resistant, could represent wind resistance, considering both the window's ability to withstand wind pressure and its relative frontal deflection. The wind resistance classification of windows must be determined through testing following EN 12211:2016 [ 29 ] and classified per EN 12210:2016 [ 41 ], ensuring compliance with performance levels for static and dynamic wind loads. Sustainability (Environmental/Circularity Parameters) The current label does not include parameters to distinguish windows according to their environmental performance. The possibility of adding voluntary environmental and circularity parameters was evaluated, focusing on three key factors: embodied carbon, embodied energy, and recycled content rate, calculated using the Life Cycle Assessment (LCA) methodology (ISO 14040:2006 [ 42 ]). These parameters were selected based on: 1. Comparability : As standardized calculation method shall be used to ensure a meaningful comparison of results. 2. Third-party verification : Environmental data shall be verified by an independent party. 3. Public information : Environmental data for the calculation of each parameter should be public whenever possible. 4. Life cycle perspective : The window's life cycle impact should be assessed to avoid the transfer of impacts between life cycle stages, following internationally recommended practices for assessing the environmental sustainability of products. Environmental data from third-party verified Environmental Product Declarations (EPDs) is proposed for the calculation of environmental and circularity indicators in CLASSE + label. EPDs provide transparent, reliable information on a product’s environmental impact throughout its life cycle, following standards such as ISO 14025:2006 [ 43 ], ISO 21930:2017 [ 44 ], EN 15804:2012 [ 45 ], and EN 15942:2000 [ 46 ]. 5.3. The Role of the Window Labeling System in Portugal's Renovation Wave A major challenge in building rehabilitation is the lack of accessible information for owners on renovation options and their long-term benefits. Energy labels are essential tools in this context. They allow consumers to easily compare the performance of different products, supporting informed decisions that enhance energy efficiency and drive market innovation with advanced technologies. In Portugal, the CLASSE + window labelling system plays a central role in the national strategy to improve energy performance in buildings. It is especially relevant under the Recovery and Resilience Plan (PRR), where several funding schemes require the use of windows with a CLASSE + label rated “A” or higher, issued by manufacturers officially registered in the CLASSE + program. However, the energy performance of a window depends on multiple factors, including building orientation, insulation level, and climate zone. As such, the highest-rated windows (class A or A+) is not always the most appropriate or cost-effective choice for every project. For this reason, architects and engineers should adopt a holistic design approach, considering window ratings as part of the overall project. Additionally, the current CLASSE + labelling system does not account for broader sustainability indicators, such as embodied carbon, embodied energy, or the use of recycled materials. Integrating these criteria into the label would support the selection of more sustainable solutions and better aligned with national and EU decarbonisation goals. To support a more flexible and inclusive renovation strategy, funding eligibility should not be limited strictly to class A or A + windows but rather extended to any window product that carries a valid CLASSE + energy label and that meets the regulatory standards. This approach promotes flexibility, inclusivity, and a more accessible market. 6. CONCLUSION This paper outlines the methodology for the Portuguese window labelling system. The process began by selecting climate data from six climate zones in Portugal, with three locations representing winter and summer conditions. A reference building, based on ISO 13790:2008, was used for analysis, with windows making up 18% of the floor area. Key window properties—thermal transmittance (U-value), solar transmittance (g), and air permeability—were varied to assess their impact on energy performance. Using EnergyPlus software through DesignBuilder, simulations calculated hourly heating and cooling demands for different orientations, ventilation rates, and window sizes, providing a comprehensive evaluation of window performance. The study also analyzed the impact of window energy classes on existing buildings and proposed updating the current classification scale. It suggests adding new parameters to the label, such as those related to safety, sustainability, and compliance with European Taxonomy standards. Findings show that a window’s impact on energy performance depends on factors like location and building insulation, meaning A + class windows are not always the best option. Class B windows can provide sufficient performance in some cases. The paper recommends that renovation funding should not be limited to A and A + class windows, as these may have higher initial costs without always offering the best return on investment. Decisions should follow a holistic approach, considering the entire building envelope. While A + class windows are suitable for projects aiming for high energy efficiency or environmental certifications, other sustainability criteria—such as embodied carbon, embodied energy, and recycled content—should also be included. Declarations Author Contribution N.S. was responsible for the development and detailed description of the Classe+ Windows methodology, as well as for supervising and critically reviewing the study.J.P. carried out the case study, drafted the main body of the manuscript, and prepared the figures.R.G. provided recommendations for the evolution of the energy labeling system for windows, with a focus on sustainability indicators.P.S. and B.M. supplied all data required for the analysis of the issued Classe+ labels.All authors contributed to the revision and final approval of the manuscript. Acknowledgement N. Simões, J. Prata and R. Garcia are grateful for the Foundation for Science and Technology's support through funding UIDB/04625/2020 from the research unit CERIS (DOI: 10.54499/UIDB/04625/2020).This research was also supported by R2UTechnologies for the modular system, within the scope of the Mobilizing Agendas/Alliances for Business Innovation, funded by the Recovery and Resilience Plan (RRP) and the Next Generation EU mechanisms, as well as by the P2E project (CENTRO2030-FEDER-01416300), co-financed by the Centro Regional Programme (Centro2030). References European Commission (2020). Energy efficiency in buildings. Available online: https://commission.europa.eu/news/focus-energy-efficiency-buildings-2020-02-17_en (accessed on may 22, 2024). European Parliament. (2023). Carbon emissions reduction: EU targets and policies . Available online: https://www.europarl.europa.eu/topics/pt/article/20180305STO99003/reducao-das-emissoes-de-carbono-metas-e-politicas-da-ue (accessed on May 10, 2025). Nair, G.; Verde, L.; Olofsson, T. (2022). A Review on Technical Challenges and Possibilities on Energy Efficient Retrofit Measures in Heritage Buildings. Energies, 15, 7472. Hassouneh, K., Alshboul, A., Al-Salaymeh, A., Influence of windows on the energy balance of apartment buildings in Amman, Energy Conversion and Management, No. 51, pp 1583-1591, 2010. Jaber, S., Ajib S., Thermal and economic windows design for different climate zones, Energy and Buildings, No. 43, pp 3208-3215, 2011. Gasparella, A., Pernigotto, G., Cappelletti, F., Romagnoni, P., Baggio, P., Analysis and modelling of window and glazing systems energy performance for a well insulated residential building, Energy and Buildings, No. 43, pp 1030-1037, 2010. Person, M., Roos A., Wall, M., Influence of window size on the energy balance of low energy houses, Energy and Buildings, No 38,pp 181-188, 2005. Moghaddam, S.A.; Mattsson, M.; Ameen, A.; Akander, J.; Gameiro Da Silva, M.; Simões, (2021). N. Low-Emissivity Window Films as an Energy Retrofit Option for a Historical Stone Building in Cold Climate. Energies, 14, 7584. Rosa Francesca De Masi, Valentino Festa, Antonio Gigante, Silvia Ruggiero, Giuseppe Peter Vanoli. (2023) The role of windows on building performance under current and future weather conditions of European climates, Energy and Buildings, Volume 292, 1 August 2023, 113177. Quddus Tushar, Muhammed A. Bhuiyan, Guomin Zhang (2022) Energy simulation and modeling for window system: A comparative study of life cycle assessment and life cycle costing, Volume 330, 1 January 2022, 129936 Moghaddam, S.A.; Serra, C.; Gameiro da Silva, M.; Simões, N. (2023). Comprehensive Review and Analysis of Glazing Systems towards Nearly Zero-Energy Buildings: Energy Performance, Thermal Comfort, Cost-Effectiveness, and Environmental Impact Perspectives. Energies, 16, 6283. Wu, W.; Skye, H.M. (2021). Residential net-zero energy buildings: Review and perspective. Renew. Sustain. Energy Rev, 142, 110859. Gasparella, A., Pernigotto, G., Cappelletti, F., Romagnoni, P., Baggio, P. (2010). Analysis and modelling of window and glazing systems energy performance for a well insulated residential building. Energy and Buildings, No. 43, pp 1030-1037. Katerina Tsikaloudaki, Konstantinos Laskos, Theodoros Theodosiou, and Dimitrios Bikas (2015) The energy performance of windows in Mediterranean regions. Energy and Buildings, Volume 92, 1 April 2015, pp 180-187. Karlsson, J., Roos, A. (2003). Evaluation of window energy rating models for different houses and European climates, Solar Energy, No. 76, pp 71-77. International Organization for Standardization (ISO) (2011). ISO 18292:2011, Energy performance of fenestration systems for residential buildings - Calculation procedure. Geneva: ISO. Kragh J., Laustsen, J. B., Svendsen, S., Proposal for Energy Rating System of windows in EU, Technical University of Denmark, CVR-nr: 63 39 30 10, 2008. European Committee for Standardization (CEN) (2006). EN 14351-1: 2006-03 Windows and doors - Product standard, performance characteristics - Part 1: Windows and external pedestrian doorsets without resistance to fire and/or smoke leakage characteristics. Trząski, A., Rucińska, J. (2015). Energy labeling of windows – Possibilities and limitations. Solar Energy, Journal of Cleaner Production, Volume 120, Pages 158-174. Orouji, P., Vakili, A., Behrouz, M.K., Jafari, H.H., Eslami M.R., Vahidnia, M., Sadegh, R.M., Rezaie, M. (2019). Methodology of standardizing the energy labeling and rating of window fenestration in IRAN, Sustainable Energy Technologies and Assessments, Volume 33, Pages 24-33. Saeed Banihashemi, Hamed Golizadeh, M. Reza Hosseini, Mahmoud Shakouri (2015) Climatic, parametric and non-parametric analysis of energy performance of double-glazed windows in different climates, International Journal of Sustainable Built Environment Volume 4, Issue 2, December 2015, Pages 307-322. Glass for Europe (2018). The benefits of Window Energy Labelling. Available online: https://glassforeurope.com/labelling_scheme-windows/#_edn1 (accessed on May 20, 2025). EuroWindoor, EuroWindoor reply to European Commission proposals for EU Energy Labelling for windows from 9/9/2015. 25 th September 2015 (https://www.eurowindoor.eu/wp-content/uploads/2023/02/EuroWindoor_reply_to_WD_on_Delegated_Regulation_for_Energy_Labelling_Windows_1509.pdf). European Committee for Standardization (CEN) (2017). EN ISO 10077-1:2017, Thermal Performance of Windows, Doors and Shutters – Calculation of Thermal Transmittance - Part 1: General. Brussels: CEN. European Committee for Standardization (CEN) (2017). EN ISO 10077-2:2017, Thermal performance of windows, doors and shutters — Calculation of thermal transmittance - Part 2: Numerical method for frames. Brussels: CEN. International Organization for Standardization (ISO) (2000). ISO 12567-1:2000 Thermal performance of windows and doors - Determination of thermal transmittance by hot box method - Part 1: Complete windows and doors. Geneva: ISO European Committee for Standardization (CEN) (2016). EN 1026:2016, Windows and doors - Air permeability - Test method. Brussels: CEN. European Committee for Standardization (CEN) (2016). EN 1027:2016, Windows and doors - Water tightness - Test method. Brussels: CEN. European Committee for Standardization (CEN) (2016). EN 12211:2016, Windows and doors - Resistance to wind load - Test method. Brussels: CEN. European Committee for Standardization (CEN) (2021). ISO 10140-2:2021, Acoustics - Laboratory measurement of sound insulation of building elements - Part 2: Measurement of airborne sound insulation (ISO 10140-2:2021). Brussels: CEN. Gazulla Santos, C. (2014). Using life cycle assessment (LCA) methodology to develop eco-labels for construction and building materials. Eco-Efficient Construction and Building Materials, Pages 84–97 . doi:10.1533/9780857097729.1.84 Roesch, A., Douziech, M., Mann, S., Lansche, J., Gaillard, G. (2025). Consequences of the use or absence of life cycle assessment in novel environmental assessment methods and food ecolabels, Cleaner Production Letters , Volume 8, 100087, https://doi.org/10.1016/j.clpl.2024.100087. Rajagopalan, N., Bilec, M.M. & Landis, A.E. Life cycle assessment evaluation of green product labeling systems for residential construction. Int J Life Cycle Assess 17 , 753–763 (2012). https://doi.org/10.1007/s11367-012-0416-9 Roesch, A., Douziech, M., Mann, S., Lansche, J., Gaillard, G. (2025). Consequences of the use or absence of life cycle assessment in novel environmental assessment methods and food ecolabels, Cleaner Production Letters , Volume 8, 100087, https://doi.org/10.1016/j.clpl.2024.100087. Clift, R. (1993). L ife cycle assessment and ecolabelling. Journal of Cleaner Production, Volume 1, Issues 3-4, Pages 155-159.. doi:10.1016/0959-6526(93)90006-w Regulation (EU) 2024/3110 of the European Parliament and of the Council of 27 November 2024 laying down harmonised rules for the marketing of construction products and repealing Regulation (EU) No 305/2011, http://data.europa.eu/eli/reg/2024/3110/oj International Organization for Standardization (ISO) (2008). ISO 13790:2008 Energy performance of buildings — Calculation of energy use for space heating and cooling. Geneva: ISO. International Organization for Standardization (ISO) (2004). ISO 13791:2004 Thermal performance of buildings - Calculation of internal temperatures of a room in summer without mechanical cooling - General criteria and validation procedures. Geneva: ISO. Portugal. Decree-Law No. 101-D/2020 of December 7th: Establishes the requirements for the energy performance of buildings. Diário da República, 1st series, no. 235 (Supplement), December 7, 2020. Carlos Pina dos Santos (2006) ITE50 – Thermal Transmittance Coefficients of Building Envelope Elements, LNEC publication. European Committee for Standardization (CEN) (2016). European Standard EN 12210:2016 Windows and doors - Resistance to wind load – Classification. Brussels: CEN. International Organization for Standardization (ISO) (2006). ISO 14040:2006 Environmental management — Life cycle assessment — Principles and framework. Geneva: ISO. International Organization for Standardization (ISO) (2006). ISO 14025:2006 Environmental labels and declarations — Type III environmental declarations — Principles and procedures. Geneva: ISO. International Organization for Standardization (ISO) (2017). ISO 21930:2017 Sustainability in buildings and civil engineering works — Core rules for environmental product declarations of construction products and services. Geneva: ISO. European Committee for Standardization (CEN) (2019). EN 15804:2012+A2:2019 Sustainability of construction works - Environmental product declarations - Core rules for the product category of construction products. Brussels: CEN. European Committee for Standardization (CEN) (2021). EN 15942:2021 Sustainability of construction works - Environmental product declarations - Communication format business-to-business. Brussels: CEN. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7012970","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":529903544,"identity":"dc189c88-66f2-4bfc-971a-0c7e088e3e42","order_by":0,"name":"Nuno Simões","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAw0lEQVRIiWNgGAWjYJCCAyCCnyGBVC2SDTAtbMTqMzhArBZz9uMPD92osLE3Pp588ANjmx2DuXwDfi2WPTkGh3POpCVuO/MsWYKxLZnBso2ge3IYDue2HU4wu5FjxsDYdoDB4BghLeefPwBq+W9vPCP/G5FabiQYALUcYNwgkcNGrJY3IL8kJ84488xYIuFcMo9lWwIhh6U//pxTYWfP35788MOHMjs5c+YDBKxBAUDzeQxI0QC1l3Qto2AUjIJRMMwBAMxrRQI9XYWVAAAAAElFTkSuQmCC","orcid":"","institution":"University of Coimbra, CERIS, Department of Civil Engineering","correspondingAuthor":true,"prefix":"","firstName":"Nuno","middleName":"","lastName":"Simões","suffix":""},{"id":529903545,"identity":"7d16526b-1766-4a4c-a602-0ae50e38865e","order_by":1,"name":"Joana Prata","email":"","orcid":"","institution":"Itecons - Institute for Research and Technological Development in Construction, Energy, Environment and Sustainability","correspondingAuthor":false,"prefix":"","firstName":"Joana","middleName":"","lastName":"Prata","suffix":""},{"id":529903547,"identity":"036aedf1-39f9-4700-b151-8a12eb85b2d3","order_by":2,"name":"Rita Garcia","email":"","orcid":"","institution":"Itecons - Institute for Research and Technological Development in Construction, Energy, Environment and Sustainability","correspondingAuthor":false,"prefix":"","firstName":"Rita","middleName":"","lastName":"Garcia","suffix":""},{"id":529903548,"identity":"9ef6404e-8f94-4a95-9511-b2a6d6958ab1","order_by":3,"name":"Paulo Santos","email":"","orcid":"","institution":"ADENE – Agency for Energy","correspondingAuthor":false,"prefix":"","firstName":"Paulo","middleName":"","lastName":"Santos","suffix":""},{"id":529903549,"identity":"dfc450b2-8767-4d06-966e-0a7653709fb0","order_by":4,"name":"Bruna Morais","email":"","orcid":"","institution":"ADENE – Agency for Energy","correspondingAuthor":false,"prefix":"","firstName":"Bruna","middleName":"","lastName":"Morais","suffix":""}],"badges":[],"createdAt":"2025-06-30 17:08:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7012970/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7012970/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":93732403,"identity":"2010d081-b783-4f7b-8f4b-6ceec193177a","added_by":"auto","created_at":"2025-10-17 02:31:22","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1574036,"visible":true,"origin":"","legend":"","description":"","filename":"Classefinal.docx","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/527ad26a4964c700e4d91dec.docx"},{"id":93732402,"identity":"21709184-6bfa-4f62-b753-dcb6839a9333","added_by":"auto","created_at":"2025-10-17 02:31:22","extension":"json","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6833,"visible":true,"origin":"","legend":"","description":"","filename":"281f2f180853411290606a4b6d928a73.json","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/1dd3c30ec85fd4891cf8fc47.json"},{"id":93731248,"identity":"78831db8-20a3-4d53-9ec1-ba9e96bfd531","added_by":"auto","created_at":"2025-10-17 02:23:22","extension":"xml","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":136116,"visible":true,"origin":"","legend":"","description":"","filename":"281f2f180853411290606a4b6d928a731enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/4332c46d27c918d43347e88a.xml"},{"id":93729579,"identity":"8a2dd21d-04bc-4a7d-a062-e1c2bf41e017","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"eps","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":102375,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage10.eps","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/a0323128534a708df809f010.eps"},{"id":93729588,"identity":"35aa8ce5-f0c6-4d91-85c5-db7b9fb1352a","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"eps","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":100185,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage11.eps","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/1e00d554199239fea6fffd3f.eps"},{"id":93729580,"identity":"14de959f-d46e-434e-91a1-bd93f64d5596","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"eps","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":153996,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage3.eps","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/c765149432fc65a2f489c122.eps"},{"id":93731264,"identity":"06744ce7-4674-4083-be4c-46e94e96cb4d","added_by":"auto","created_at":"2025-10-17 02:23:23","extension":"eps","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":152806,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage4.eps","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/720eed1d5696cd974731ad2a.eps"},{"id":93729590,"identity":"0976830b-6ed0-44da-b18f-d45c0b39a7f6","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"eps","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":124151,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage8.eps","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/1a0d72eced3186955a8d117c.eps"},{"id":93729626,"identity":"162dccfc-3bad-4c4c-9ca5-a13bdbe86949","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"eps","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":137081,"visible":true,"origin":"","legend":"","description":"","filename":"drawingimage9.eps","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/8bb906cc4a052e8ead0cd58b.eps"},{"id":93729598,"identity":"2aca23cb-3ae4-4333-b073-641f8575c623","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":295229,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/9091c24c229d8ee8458a9155.png"},{"id":93732405,"identity":"79844e18-f99a-41e1-b121-306f65430408","added_by":"auto","created_at":"2025-10-17 02:31:23","extension":"png","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":9948,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/52d0a64f2fb44ad6c7985aa9.png"},{"id":93732407,"identity":"dc024b54-e71c-4202-8dff-7d08ec3a88fc","added_by":"auto","created_at":"2025-10-17 02:31:23","extension":"png","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":84083,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/21dcf98b3e8e9aad25ef57a1.png"},{"id":93729623,"identity":"846d4c4f-5ca0-467a-b34b-f53113b3902c","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":853752,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/4ca45108c138566a7d163a0d.png"},{"id":93729634,"identity":"0e1d264e-5500-4bd5-99be-c72c1cd0293b","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":18,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":14574,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/02a90fdc8cc19a0a99b94305.png"},{"id":93729592,"identity":"370cc497-7bef-46b9-bdd0-b4fda31a6320","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"png","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":14574,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/82c54971742a0ce43883eaae.png"},{"id":93729594,"identity":"e3ff04bd-1d98-43e3-896c-51b31747ec5d","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"png","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":91857,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/063c17e531f2e0ad2f9d9bd0.png"},{"id":93731257,"identity":"5526d32e-8e06-46f7-9823-f65a4a527396","added_by":"auto","created_at":"2025-10-17 02:23:23","extension":"png","order_by":21,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":33509,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/441171bf7699d98bcc366e16.png"},{"id":93731255,"identity":"12911cd9-5010-4547-9a1d-4f16b628f08a","added_by":"auto","created_at":"2025-10-17 02:23:23","extension":"png","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":31060,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/d71b4ef7dd1b9fb16d6e87b2.png"},{"id":93729599,"identity":"0907912d-2d13-498b-9f3a-76b21a1c2dcf","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":32138,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/1bc9b829d269bb8f0aeed938.png"},{"id":93731263,"identity":"7b548723-73ea-45f2-a258-9522d0c0d9ac","added_by":"auto","created_at":"2025-10-17 02:23:23","extension":"png","order_by":24,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":56158,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/45fa27888fe1761c500dd9b8.png"},{"id":93731267,"identity":"4b59e115-fbd6-4652-b6cf-ee41caa64744","added_by":"auto","created_at":"2025-10-17 02:23:23","extension":"png","order_by":25,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":4314,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/5c258ebc5836e7d152c7ccf8.png"},{"id":93732406,"identity":"cea0ee8f-9b8d-40c2-bd03-69b1cee9a506","added_by":"auto","created_at":"2025-10-17 02:31:23","extension":"png","order_by":26,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":10802,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/944bb43e3aa0baf38f96b93b.png"},{"id":93729624,"identity":"406423a8-3fee-4adb-96f4-e641d827717d","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":27,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":134638,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/6f573eec931b23bdd4e545e2.png"},{"id":93729627,"identity":"f9dd8f39-852d-4392-8bfd-459eba3cb7d1","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":28,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6005,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/da77b042f748e6908b934234.png"},{"id":93729629,"identity":"1d5630d3-7779-4f3c-bb30-7eb45a816425","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":29,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6005,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/45e7e49238a3a0a226f9981e.png"},{"id":93729600,"identity":"fba2efee-57b4-459a-9e03-856e15017ede","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":30,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":33217,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/fb18a88d0376cc0c053b5283.png"},{"id":93729596,"identity":"36db9913-779b-4356-aa2f-877fbd22eb4f","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"png","order_by":31,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":11582,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/4db5cf84d45e1fca08154db8.png"},{"id":93729625,"identity":"b717c13d-73ed-4ee4-a232-6ecf8148cb6e","added_by":"auto","created_at":"2025-10-17 02:15:23","extension":"png","order_by":32,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":10812,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/9ab8d7bb94382c6994eaea5b.png"},{"id":93729597,"identity":"c1d09f90-f6a4-4987-9f11-158635018717","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"png","order_by":33,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":11314,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/dfb538a8c1a6e49ff02be0ee.png"},{"id":93731266,"identity":"977ac498-bca9-48e8-a987-8a3e80c849d1","added_by":"auto","created_at":"2025-10-17 02:23:23","extension":"xml","order_by":34,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":136221,"visible":true,"origin":"","legend":"","description":"","filename":"281f2f180853411290606a4b6d928a731structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/79d405817e143b937329d2b5.xml"},{"id":93731259,"identity":"1f0cd1b9-9ce9-4a02-a659-07b89f532ba8","added_by":"auto","created_at":"2025-10-17 02:23:23","extension":"html","order_by":35,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":150256,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/43c8746f71833e064237952c.html"},{"id":93729570,"identity":"ea5debd0-cbf4-4036-ad1f-2ce91be12300","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":87635,"visible":true,"origin":"","legend":"\u003cp\u003ePortuguese climate zones for a) winter and b) summer\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/db5ce4a5449320ddbe34b614.jpg"},{"id":93731243,"identity":"c4151b70-dbb7-44c6-a364-0656366f2e84","added_by":"auto","created_at":"2025-10-17 02:23:22","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":21826,"visible":true,"origin":"","legend":"\u003cp\u003eReference building geometry\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/9190da934b55d1a2886557a4.jpg"},{"id":93729571,"identity":"343cd4a3-1a1e-47a6-a3e6-61d1bf262342","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":107581,"visible":true,"origin":"","legend":"\u003cp\u003eAnnual cooling and heating needs for different window orientations, with a ventilation rate of 0.03 h-1 and for a window floor area (WFA) of 18%. Climate data for Évora (mild winter; severe summer).\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/9cac2726e7e011d26e31d205.jpg"},{"id":93729574,"identity":"d664cdbf-fde2-4095-9053-f71fa4e75ae5","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":79802,"visible":true,"origin":"","legend":"\u003cp\u003eAnnual cooling and heating needs variation by air leakage influence for a WFA of 18% - Climate data for Évora (mild winter; severe summer).\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/80e02834a1e0cf14ae7edc7e.jpg"},{"id":93731242,"identity":"61d00bb5-f0e6-4210-b001-a96a2238010c","added_by":"auto","created_at":"2025-10-17 02:23:22","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":68139,"visible":true,"origin":"","legend":"\u003cp\u003eTotal energy needs for Évora climate data as a function of window orientation, considering a ventilation rate of 0.03 h-1 and varying window floor area ratios for north (a) and east-facing (b) windows.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/63d93091c305f1be2c9e326d.jpg"},{"id":93729593,"identity":"2d0556fa-c843-4b7b-bda4-6d79e6a45cd7","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":97673,"visible":true,"origin":"","legend":"\u003cp\u003eWeighted average of heating and cooling needs at all locations.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/2bc01ac6531bab8de2a1378f.jpg"},{"id":93729577,"identity":"04847398-1536-4c13-bf5e-3146eb91f64e","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":103346,"visible":true,"origin":"","legend":"\u003cp\u003eWeighted average of the total annual energy needs (heating \u0026amp; cooling) for all locations and orientations.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/f74d3ab1d9a3b48bebdb5f74.jpg"},{"id":93729583,"identity":"b51d4212-dadc-4810-9a87-defde423c29f","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":81453,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of energy consumption of the different solutions considered, for class 4 of air leakage, for the reference room.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/1e1b2fa8a066f87c8516a660.jpg"},{"id":93731252,"identity":"e8cf6bce-ac26-423a-8c52-685da1172cf3","added_by":"auto","created_at":"2025-10-17 02:23:22","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":62080,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of window energy rating with U\u003csub\u003ew\u003c/sub\u003e value.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/c974e961a3f78170c527a5d8.jpg"},{"id":93731247,"identity":"033c14b0-1f8e-46d4-b768-8de1ab845864","added_by":"auto","created_at":"2025-10-17 02:23:22","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":60019,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of window energy rating with g-value.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/5cff6d66f88f3d8a891c07a8.jpg"},{"id":93729586,"identity":"8c2ffc49-2482-4a54-96c0-4a90bb231e36","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":51798,"visible":true,"origin":"","legend":"\u003cp\u003eCase study – existing single-family dwelling.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/517cd12cc66cbdd610ab3f45.jpg"},{"id":93731249,"identity":"a70430b9-2c9c-4893-b40f-04c0129ec7f5","added_by":"auto","created_at":"2025-10-17 02:23:22","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":47679,"visible":true,"origin":"","legend":"\u003cp\u003eHeat losses through the windows (in W/°C).\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/c24681f57b4d0382c120ff11.jpg"},{"id":93731251,"identity":"1bde95b8-815e-49f7-ae76-5c13996713c1","added_by":"auto","created_at":"2025-10-17 02:23:22","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":45907,"visible":true,"origin":"","legend":"\u003cp\u003eContribution of the windows to the heat losses through the building's exterior envelope.\u003c/p\u003e","description":"","filename":"13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/49359026e6440d8c4d74c0e1.jpg"},{"id":93729595,"identity":"0efde61b-1e2d-426c-b250-aa1d78c2b9dc","added_by":"auto","created_at":"2025-10-17 02:15:22","extension":"jpg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":153988,"visible":true,"origin":"","legend":"\u003cp\u003eImpact of energy class of the windows in the variation of the annual nominal energy needs for heating (Nic) and cooling (Nvc), for different climate zones: a) I3, V2 (Zone A); b) I2, V2 (Zone B); c) I1, V3 (Zone C), considering the various thermal insulation solutions.\u003c/p\u003e","description":"","filename":"14.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/6789b41828299dbc5be021c7.jpg"},{"id":93731250,"identity":"6722e16f-20e2-4173-b768-e137a0b8ffad","added_by":"auto","created_at":"2025-10-17 02:23:22","extension":"jpg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":119859,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of the Ntc/Nt ratio with the energy class of the windows, for different climate zones and considering various thermal insulation solutions.\u003c/p\u003e","description":"","filename":"15.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/f817ba7f55e040ca67e7481b.jpg"},{"id":93733143,"identity":"f3286100-3c3b-4cc8-b735-269b5f52aa74","added_by":"auto","created_at":"2025-10-17 02:39:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2321902,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7012970/v1/4ca31bd2-72fd-447e-99d0-8f3710027035.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eMethodology and Performance Analysis of the Portuguese Window Energy Labelling System\u003c/p\u003e","fulltext":[{"header":"1.\tINTRODUCTION","content":"\u003cp\u003eThe construction sector accounts for 40% of energy consumption in the European Union (EU) and 36% of greenhouse gas emissions [1], which led the creating of European policies to help reduce these values. The proposal to revise the Energy Performance of Buildings Directive aims to gradually reduce greenhouse gas emissions (GHG) and energy consumption in the EU\u0026apos;s construction sector, with the goal of achieving climate neutrality by 2050. To achieve this, there is a need to transition to higher performance standards in buildings, namely nearly zero-energy buildings (nZEB) and zero-carbon buildings (ZEB) [2]. Therefore, selecting construction solutions with higher thermal performance for building envelopes is essential [3].\u003c/p\u003e\n\u003cp\u003eWindows are one of the weakest thermal elements of the building envelope, accounting for 20% to 60% of energy loss in buildings, depending on their age, type, and size ([4]-[9]). In summer, windows can promote a house\u0026apos;s heat gain up to 80% [10]. High thermal transmittance (U\u003csub\u003ew\u003c/sub\u003e) values lead to increased energy consumption for heating, while high solar factor (g) values lead to higher cooling energy needs. Thus, the energy performance of windows depends on the proper combination of both factors ([11]-[14]).\u003c/p\u003e\n\u003cp\u003eThe relationship between the glazed area, its orientation, and the thermal performance of a building is significant. Studies indicate that larger windows facing south, east, and west, combined with smaller areas facing north, reduce heating needs [4]. Window size has a greater impact on heating needs than on cooling needs.\u0026nbsp;While large glazed surfaces improve winter performance, they also increase peak thermal loads during this season [4].\u0026nbsp;North-facing windows, when energy-efficient, can vary in size without significantly affecting energy performance\u0026nbsp;[7].\u003c/p\u003e\n\u003cp\u003eShading also influences window performance. Research shows that selective shading is crucial for improving summer performance without compromising winter efficiency [6].\u0026nbsp;An optimized glazed window can save up to 24% of energy [5]. According to some studies, heating load is more sensitive to window size and type compared to cooling load\u0026nbsp;([4],[5]).\u003c/p\u003e\n\u003cp\u003eChoosing high-performance windows is a valuable improvement opportunity for both new buildings and renovation projects [15], as it contributes to reducing building energy consumption, lowering heating and cooling needs, while enhancing natural lighting and ventilation. However, selecting energy-efficient windows requires clear and comparable performance information, enabling designers and end consumers to make informed product choices. An energy classification system, similar to that used for household appliances and lighting systems, not only provides clear and accurate information on window performance but also promotes improved quality among products on the market [19].\u003c/p\u003e\n\u003cp\u003eThe International Standard ISO 18292:2011 [16] outlines guidelines for assessing the energy performance of fenestration systems. It establishes methods for calculating heating and cooling energy consumption in residential buildings, covering aspects such as calculation approaches, preparation of weather data, and key characteristics of buildings and windows. According to this standard, the energy performance of fenestration systems must be presented in terms of annual energy requirements, based on a national reference building and reference climate conditions.\u003c/p\u003e\n\u003cp\u003eDifferent levels of information [17] are available to support the development of a window energy rating scheme. In most countries, the energy performance of windows is evaluated as a linear combination of solar energy transmittance, thermal transmittance, and the influence of air permeability characteristics.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe information provided by an energy performance label can be categorized into three levels.\u0026nbsp;\u003c/p\u003e\n\u003cul class=\"decimal_type\"\u003e\n \u003cli\u003eLevel 1 (L1) includes basic physical data of the product and is independent from climate, orientation and use conditions.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eLevel 2 (L2) provides energy performance information calculated using Level 1 data and a standard window size of 1.23 x 1.48 m\u0026sup2; [18]. The energy performance (EP) is determined by the formula (EP = A\u003csub\u003ew\u003c/sub\u003e.g - B.(U + L\u003csub\u003ef\u003c/sub\u003e)), where g represents solar thermal transmittance, U is the thermal transmittance of the fenestration (W/m\u0026sup2;\u0026ordm;C), L\u003csub\u003ef\u003c/sub\u003e is an air leakage factor related to air permeability, and A and B are constants reflecting climate conditions, calculated for specific climate zone. A\u003csub\u003eW\u003c/sub\u003e denotes the window area.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eLevel 3 (L3) offers comprehensive data on the window\u0026apos;s energy performance, considering its actual dimensions within a reference building to evaluate its impact on the building\u0026apos;s overall energy behaviour. There is no international reference building so it must be established at national level, as stated in ISO 18292:2011. This level is highly detailed and intended for use by architects and engineers [16].\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eSeveral countries have been pioneers in this field and have established window energy rating systems [20], each adopting a specific level of information: Sweden (L1), South Korea (L1), Canada (L2), Denmark (L2), the United Kingdom (L2), Finland (L2), New Zealand (L3), and Australia (L2). While energy labelling is generally voluntary, it is mandatory in certain countries like Iran, where window manufacturers are required to specify the energy performance index and label for the windows they produce [20].\u003c/p\u003e\n\u003cp\u003eWindow performance strongly depends on climate, geographical location [21], and solar radiation [10]. Some European organizations support the introduction of an EU label for windows reflecting multiple climate zones [22]. However, the idea is not unanimous. Some critics claim that such a label may be inadequate from both consumer and environmental perspectives, as it may not effectively guide consumers to the most energy- and cost-efficient products across different European climates and building types, reducing its effectiveness [23].\u003c/p\u003e\n\u003cp\u003eIn the meantime, to facilitate the selection of more efficient windows, several countries in Europe have established their own national window certification systems [19], including Portugal. ADENE \u0026ndash; the Portuguese Energy Agency \u0026ndash; created the CLASSE+ energy labelling system. This system is based on a calculation methodology developed by Itecons \u0026ldquo;Institute for Research and Technological Development in Construction, Energy, Environment and Sustainability (https://www.itecons.uc.pt/)\u0026rdquo; in accordance with ISO 18292:2011 standard [16] and described in this paper.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe growing adoption of the CLASSE+ energy labelling system reflects a positive response from the window sector, with the participation of more than 770 companies and the issuance of over 745 000 window labels. This growth is also driven by the label being a mandatory requirement for access to certain financial incentive programs. The CLASSE+ system was revised in 2017 to include Class A+, which is now the highest efficiency rating.\u003c/p\u003e\n\u003cp\u003eIn the CLASSE+ methodology, the energy class of windows depends on several factors: thermal transmittance, solar factor, and air permeability class of the window, all of which strongly affect the thermal performance of building envelopes. The label also provides additional information on the glass\u0026rsquo;s light transmission and the window\u0026rsquo;s acoustic attenuation (Rw) and indicates a comfort level for summer and winter.\u003c/p\u003e\n\u003cp\u003eIssuing a Classe+ label requires detailed technical information, including the glass technical data sheet and test reports verifying compliance with national and European standards: U\u003csub\u003ew\u003c/sub\u003e-value report (thermal transmittance determined following EN ISO 10077-1 [24] and EN ISO 10077-2 [25] or ISO 12567:2000 [26]), AEV report (air permeability, water tightness, and wind resistance, determined in accordance with EN 1026 [27], EN 1027 [28], and EN 12211 [29]), and acoustic report (sound insulation determined under EN ISO 10140-2 procedure [30]).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA major limitation of the CLASSE+ system is the lack of comprehensive studies quantifying how different window classes affect building energy performance and certification. This gap makes it difficult to evaluate whether higher-rated windows consistently deliver better energy efficiency.\u003c/p\u003e\n\u003cp\u003eCurrent window energy labelling programs prioritize thermal performance during the use phase but overlook life-cycle environmental impacts. Including Life Cycle Assessment (LCA) in labelling would help consumers choose products with lower environmental and cost impacts, promote sustainable innovation, and support climate policies ([31]-[33]). There are challenges in including LCA information in labelling, namely related to the complexity of LCA, which requires special expertise, the fact that it is a data intensive assessment, and the need for standardized criteria to enable a fair comparison of environmental performance ([34],[35]). The new Construction Products Regulation [36], which has included new sustainability requirements for construction products, will likely incentivise the generation of life-cycle environmental information, and it is key that labelling programs are at the forefront of this new paradigm. Future efforts in labelling should, therefore, focus on building on readily available environmental data, namely Environmental Product Declarations (EPD), defining specific environmental metrics, and influencing regulatory incentives to improve sustainable window labelling.\u003c/p\u003e\n\u003cp\u003eThis study evaluates the CLASSE+ energy labelling system for windows, examining its effectiveness and identifying areas for improvement. It outlines the system\u0026rsquo;s methodology, analyses issued labels to explore relationships between energy classification and window characteristics and includes a case study on how different window ratings impact a residential building energy performance based on Portuguese energy performance calculation method (regulation published in the Decree-Law no. 101-D/2020). The findings highlight the need to update energy classification levels and incorporate additional parameters related to safety, sustainability, and European taxonomy alignment.\u003c/p\u003e"},{"header":"2.\tMETHODOLOGY ","content":"\u003cp\u003e2.1. Introduction\u003c/p\u003e\n\u003cp\u003eAccording to ISO 18292:2011 [16], in order to create a rating system, the energy performance of fenestration systems should be based on indices that represent the energy requirements for heating and cooling, P\u003csub\u003eE,H,w\u003c/sub\u003e and P\u003csub\u003eH,w\u003c/sub\u003e, measured in kWh/m\u0026sup2;.\u003c/p\u003e\n\u003cp\u003eBased on the methodology described in ISO 13790:2008 [37], which focuses on assessing the thermal and energy performance of buildings, ISO 18292:2011 introduces a range of methods with varying levels of detail. These methods serve as the basis for calculating a building\u0026apos;s heating and cooling demands, covering energy balance calculations on seasonal, monthly, and hourly scales.\u003c/p\u003e\n\u003cp\u003eThe methodology used in the Portuguese window energy labelling system is based on the hourly method and involves the four main steps established by ISO 18292:2011:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e1. Selecting the \u003cstrong\u003eclimate data\u003c/strong\u003e;\u003c/p\u003e\n\u003cp\u003e2. Defining the \u003cstrong\u003ereference building\u003c/strong\u003e;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e3. Preparing \u003cstrong\u003ewindow thermal properties\u003c/strong\u003e;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e4. Calculating \u003cstrong\u003eenergy performance\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e2.1.1.\u0026nbsp; \u0026nbsp;\u0026nbsp;CLIMATE data\u003c/p\u003e\n\u003cp\u003eClimate data for different Portuguese climate zones were obtained from SolTerm, a software tool provided by the National Energy and Geology Laboratory (LNEG). According to national regulations, Portugal is divided into six distinct climate zones - three for heating (winter climate zones: I1, I2, I3) and three for cooling (summer climate zones: V1, V2, V3). Figure 1 shows the distribution of climate zones in Portugal as defined in the year the methodology was developed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEnergy simulations conducted during the development of the window labelling methodology covered all climate zones. For this purpose, three Portuguese cities representative of these zones were selected to obtain results reflecting the entire national territory. The cities analysed are identified in\u0026nbsp;Figure 1\u0026nbsp;and listed in\u0026nbsp;Table 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;1: Portuguese cities considered in energy simulations.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 285px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eClimate Zone\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePortuguese City\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 157px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eConditions\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 135px;\"\u003e\n \u003cp\u003eWinter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eI1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003e\u0026Eacute;vora\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 157px;\"\u003e\n \u003cp\u003eMild winter\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eI2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003ePorto\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 157px;\"\u003e\n \u003cp\u003eModerate winter\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eI3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eBragan\u0026ccedil;a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 157px;\"\u003e\n \u003cp\u003eSevere winter\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 135px;\"\u003e\n \u003cp\u003eSummer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eV1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003ePorto\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 157px;\"\u003e\n \u003cp\u003eMild summer\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eV2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eBragan\u0026ccedil;a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 157px;\"\u003e\n \u003cp\u003eModerate summer\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003eV3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003e\u0026Eacute;vora\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 157px;\"\u003e\n \u003cp\u003eSevere summer\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e2.1.2. REFERENCE BUILDING\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe energy simulations were performed for a reference building with specific geometry and thermophysical properties, as defined in ISO 13790:2008 [37] and detailed in ISO 13791:2004 [38]. The reference building used in the simulations was modelled with:\u003c/p\u003e\n\u003cp\u003e- A single window with a window floor area (WFA) of 18%;\u003c/p\u003e\n\u003cp\u003e- Adiabatic boundary conditions for all walls except the one with the window, eliminating external thermal gains or heat losses through other surfaces;\u003c/p\u003e\n\u003cp\u003e- No internal heat sources, ensuring that all energy gains or losses result only from the interaction of the window with the external environment.\u003c/p\u003e\n\u003cp\u003eFigure 2 illustrates the building geometry, while Table 2 provides thermophysical property details. The dimensions shown in Figure 2 represent the interior measurements of the compartment and do not account for the thickness of the construction solutions.\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;2: Thermophysical properties of the reference building envelope.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 200px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStructure\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eS [m]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lambda; [W/(m.K)]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Rho; [kg/m\u003csup\u003e3\u003c/sup\u003e]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eC\u003csub\u003ep\u0026nbsp;\u003c/sub\u003e[kJ/(kg.K)]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eExternal Wall\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eOuter layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.0115\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e1800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eInsulation layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eMasonry\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.175\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e1600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eInternal plastering\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e1400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInternal Wall\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eGypsum Plaster\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e900\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eInsulation layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eGypsum Plaster\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e900\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCeiling / Floor\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003ePlastic covering\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e1500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e1.50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eCement floor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e1.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e2000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eInsulation layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eConcrete\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e2.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e2400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e2.1.3.\u0026nbsp; \u0026nbsp;\u0026nbsp;Window\u0026rsquo;s thermal properties\u003c/p\u003e\n\u003cp\u003eTable 3 presents the different window solutions considered in the methodology development. A wide range of fenestration designs was evaluated, varying the window thermal transmittance (U\u003csub\u003ew\u003c/sub\u003e-value), the total solar energy transmittance of the glazing (g-value), and the air permeability level of the windows. The modelled U-values ranged from 0.5 W/(m\u0026sup2;\u0026middot;\u0026deg;C) to 4 W/(m\u0026sup2;\u0026middot;\u0026deg;C), reflecting commercially available options, while the g-values were adjusted from 0.3 to 0.8 to simulate different levels of solar gain. Two air permeability classes were selected: Class 4, with an air leakage of 3 m\u0026sup3;/(m\u0026sup2;\u0026middot;h) at a pressure difference of 100 Pa, and Class 2, with an air leakage of 27 m\u0026sup3;/(m\u0026sup2;\u0026middot;h) under the same conditions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;3:\u0026nbsp;Window solutions considered in the methodology development.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003eWindow solution - Case study\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003eThermal transmittance, U [W/(m\u003csup\u003e2\u003c/sup\u003e.K]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003eSolar energy transmittance, g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003eAir permeability\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"8\" style=\"width: 150px;\"\u003e\n \u003cp\u003eClass 2/ Class 4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 150px;\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e2.1.4.\u0026nbsp; \u0026nbsp;\u0026nbsp;Energy Performance Simulations\u003c/p\u003e\n\u003cp\u003eIn the step four of the Portuguese window labelling system methodology, the impact of window characteristics (air permeability, global area and thermal properties) on the annual heating and cooling energy needs of a reference building was evaluated, considering different climate zones and window orientations.\u003c/p\u003e\n\u003cp\u003eThe analysis was performed for the different window solutions presented in\u0026nbsp;Table 3. The annual energy needs were determined hourly through dynamic simulations using EnergyPlus software with the DesignBuilder graphical interface. The simulations were conducted with constant indoor temperatures of 20\u0026deg;C for heating and 25\u0026deg;C for cooling.\u003c/p\u003e\n\u003cp\u003eCooling needs were evaluated from June to September, accounting for both sensible and latent heat, while heating needs were evaluated from October to May, considering only sensible heat. Four different window orientations were simulated: north, east, south, and west. The weighted average of the heating and cooling needs were then analysed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEffect of window air permeability\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTwo window performance levels for air permeability were analysed: classes 4 and 2. Simulations used steady ventilation rates based on EN 12207:1999 guidelines. At a reference pressure difference of 100 Pa, airflow rates were 27 m\u0026sup3;/(m\u0026sup2;\u0026middot;h) for class 2 and 3 m\u0026sup3;/(m\u0026sup2;\u0026middot;h) for class 4. At 6 Pa, these corresponded to air exchange rates of 0.26 air changes per hour (h⁻\u0026sup1;) for class 2 and 0.03 for class 4.\u003c/p\u003e\n\u003cp\u003eFirst, heating and cooling needs were calculated for each climate scenario (Table 1) using a ventilation rate of 0.03 h⁻\u0026sup1;, corresponding to Class 4 windows. Figure 3 illustrates the annual heating and cooling needs, expressed in kWh per square meter of window area, for the climate zone of \u0026Eacute;vora (mild winter (I1) and severe summer (V3)), considering different window orientations. These results are based on a ventilation rate of 0.03 h⁻\u0026sup1; and assume a window-to-floor area ratio of 18%.\u003c/p\u003e\n\u003cp\u003eThen, the impact of increased ventilation was evaluated by comparing these results with those from Class 2 windows, which have a ventilation rate of 0.26 h⁻\u0026sup1; (Figure 4).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe results indicated that total energy needs are generally greater for Class 2 windows compared to Class 4 windows. An exception occurs with south-facing fa\u0026ccedil;ades featuring low thermal transmittance values, where Class 4 windows exhibit slightly higher energy needs. The results also revealed that east and west-facing fa\u0026ccedil;ades have similar energy consumption patterns, whereas south-facing fa\u0026ccedil;ades demonstrate greater variability in energy needs. This suggests that the thermal properties of windows are more critical for south-facing orientation. In contrast, north-facing windows exhibit relatively stable energy performance across most cases, showing the lowest thermal demands overall, except in two instances where low solar thermal transmittance leads to increased needs.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEffect of Window Area\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe study analysed how window area affects the overall energy performance of the reference building. Simulations were conducted for various window floor area ratios (20%, 40%, 60%, and 80%), considering the different window orientations (north, east, south, and west). Four scenarios were modelled, varying the U-value and the g-value (Table 4).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;4:\u0026nbsp;Window solutions used to evaluate the effect of window area.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003eThermal transmittance, U [W/(m\u003csup\u003e2\u003c/sup\u003e.K]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003eSolar energy transmittance, g\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eFigure 5 a) and Figure 5 b) give the total needs for \u0026Eacute;vora climate, for north and east orientation, respectively. Total needs are the sum of annual heating and cooling needs. The results are given in kWh per floor area (in m2).\u003c/p\u003e\n\u003cp\u003eThe results showed a linear relationship between energy needs and window area, with larger windows increasing both heating and cooling demands. This pattern was consistent across all window solutions analysed, with the extent of variation depending on the window\u0026apos;s thermal properties. The effect was more pronounced in orientations with higher solar gains.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eWeighted Average Results\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFinally, the energy performance results were summarized by presenting the weighted average of the heating and cooling needs for the three cities analyzed (Table 1). This\u0026nbsp;analysis\u0026nbsp;highlights the combined effects of window design, ventilation rates, and climate conditions on energy efficiency.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe weighted average was calculated for heating and cooling needs, considering energy demands over eight months of heating (October to May) and four months of cooling (June to September), following the national energy calculations recommendations. To provide a more accurate assessment of overall energy performance, the calculation was based on the typical window distribution across building orientations, using the weighting factors shown in\u0026nbsp;Table 5, defined assuming the national statistics.\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;5:\u0026nbsp;Weighting factors for each orientation.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOrientation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWeighting factor\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003eNorth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003eEast\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003eSouth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 214px;\"\u003e\n \u003cp\u003eWest\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 212px;\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eFigure 6 shows the heating and cooling weighted average needs of each window solution, at each location (Bragan\u0026ccedil;a, Porto and \u0026Eacute;vora).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA clear increase in heating needs is observed for Bragan\u0026ccedil;a, which is associated with its colder winter climate. Cooling needs varies less between climate zones compared to heating needs, with higher cooling needs observed in locations with more extreme summer climates (\u0026Eacute;vora).\u003c/p\u003e\n\u003cp\u003eFigure 7 shows the weighted average of the total annual energy needs (heating and cooling) for all locations.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe lowest total energy needs are associated with windows that have both a low thermal transmittance coefficient (U = 0.5 W/(m\u0026sup2;\u0026middot;\u0026deg;C)) and low solar thermal transmittance (g = 0.3). Higher heating needs are typically linked to windows with low g-value, while higher cooling needs are associated with windows with higher g-value.\u003c/p\u003e\n\u003cp\u003eWhen the U-value remains constant, reducing the g-value decreases cooling and total energy needs but increases heating needs.\u003c/p\u003e\n\u003cp\u003eIf solar thermal transmittance remains high, lowering the U-value slightly reduces total energy needs, increases cooling needs, and decreases heating needs. Conversely, when the g-value is low, reducing the U-value slightly increases cooling needs while decreasing both total energy and heating needs.\u003c/p\u003e\n\u003ch3\u003eCONCLUSIONS\u003c/h3\u003e\n\u003cp\u003eBased on the simulation results, the following conclusions were drawn:\u003c/p\u003e\n\u003cp\u003e- \u003cstrong\u003eAir Leakage:\u003c/strong\u003e Higher air permeability (Class 2) significantly increases total energy needs, except for some south-facing windows with low U-values.\u003c/p\u003e\n\u003cp\u003e- \u003cstrong\u003eOrientation Sensitivity:\u003c/strong\u003e South-facing windows were most affected by thermal properties, while north-facing ones had the lowest energy needs. East and west orientations displayed similar, stable energy demands.\u003c/p\u003e\n\u003cp\u003e- \u003cstrong\u003eWindow Area Impact:\u003c/strong\u003e A linear increase in energy needs was observed with larger window areas, highlighting the importance of optimizing window-to-floor area ratios.\u003c/p\u003e\n\u003cp\u003e- \u003cstrong\u003eThermal and Solar Transmittance:\u0026nbsp;\u003c/strong\u003eReducing U-values (thermal transmittance) decreased heating needs but had mixed effects on cooling demands, depending on g-values. Reducing g-values (solar transmittance) lowered cooling and total energy needs but increased heating requirements.\u003c/p\u003e\n\u003cp\u003eOptimizing window design, orientation, and size is essential for maximizing energy efficiency. Selecting windows with low U-values and g-values significantly reduces overall energy demand, though careful consideration is required to balance heating and cooling requirements.\u003c/p\u003e\n\u003cp\u003e2.2. Portuguese WINDOWs ENERGY Rating\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe results obtained with the methodology described before formed the basis of the Portuguese energy labelling system (known as Classe+ energy labelling). The classification reflects the overall energy performance of windows, considering heating and cooling needs.\u003c/p\u003e\n\u003cp\u003eEnergy classification limits were established based on the simulations of the reference room, considering different windows solutions (varying the U-value and g-value) and different air permeability classes 1 to 4. Although the simulations covered a year, the rating was based on monthly results to reduce variations caused by solar thermal transmittance. January and August, the months with the highest energy demand, were selected. Figure 7 shows the results of energy needs when the window\u0026rsquo;s air permeability is class 4.\u003c/p\u003e\n\u003cp\u003eThe Classe+ energy classification system for windows uses intervals ranging from A+ (most energy-efficient product) to F (least energy-efficient product).\u0026nbsp;Table 6\u0026nbsp;presents the current energy classes for windows and the maximum total energy requirements assigned to each class. These limits have already undergone a review phase, as the initial version of the scale extended only up to Class A.\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;6:\u0026nbsp;Current energy classes for windows and their corresponding maximum total energy requirements.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eEnergy Class (CLASSE+ System)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eMaximum Total Energy Requirements [kWh/(m\u0026sup2;\u0026middot;month)]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eA+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e16.65\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e18.50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e22.20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e25.90\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e29.60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e33.30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e37.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAdditionally, the Portuguese window classification methodology defines 10 comfort levels - less comfort (1) to more comfort (10) - for summer and winter, based on the energy needs for cooling (Nc) and heating (Nh), respectively. Table 8 shows the ranges of energy requirements associated with each of the comfort levels for the summer and winter situation.\u003c/p\u003e\n\u003cp\u003eTable 7:\u0026nbsp;Portuguese window energy labelling - comfort levels.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eComfort levels\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 49px;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSummer\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eNc [kWh/(m\u003csup\u003e2\u003c/sup\u003e.month)]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003eNc\u0026nbsp;\u0026ge;\u0026nbsp;13.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e12.9 \u0026le;\u0026nbsp;Nc \u0026lt; 13.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e12.2 \u0026le;\u0026nbsp;Nc \u0026lt; 13.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e11.5 \u0026le;\u0026nbsp;Nc \u0026lt; 12.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e10.7 \u0026le;\u0026nbsp;Nc \u0026lt; 11.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e10.0 \u0026le;\u0026nbsp;Nc \u0026lt; 10.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e9.3 \u0026le;\u0026nbsp;Nc \u0026lt; 10.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e8.5 \u0026le;\u0026nbsp;Nc \u0026lt; 9.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e7.8 \u0026le;\u0026nbsp;Nc \u0026lt; 8.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003eNc \u0026lt; 7.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWinter\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eNh [kWh/(m\u003csup\u003e2\u003c/sup\u003e.month)]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003eNh\u0026nbsp;\u0026ge;\u0026nbsp;20.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e18.2 \u0026le;\u0026nbsp;Nh \u0026lt; 20.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e15.7 \u0026le;\u0026nbsp;Nh \u0026lt; 18.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e13.2 \u0026le;\u0026nbsp;Nh \u0026lt; 15.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e10.7 \u0026le;\u0026nbsp;Nh \u0026lt; 13.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e8.2 \u0026le;\u0026nbsp;Nh \u0026lt; 10.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e5.7 \u0026le;\u0026nbsp;Nh \u0026lt; 8.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e3.2 \u0026le;\u0026nbsp;Nh \u0026lt; 5.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e0.7 \u0026le;\u0026nbsp;Nc \u0026lt; 3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003eNc \u0026lt; 0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"3. Analysis of the Portuguese labeling Data","content":"\u003cp\u003eThis section presents the key findings from the analysis of data provided by ADENE regarding the national energy labelling system for windows, known as CLASSE+.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eCLASSE+ System Data Overview\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConsidering the dataset of the first 500\u0026nbsp;000 labelled windows, 91.4% are rated A+, 6.8% are rated A, and 1.6% are rated B. Lower energy efficiency classes (C, D, E, and F) account for only 0.2% of the labelled windows. Furthermore, 95.9% of the labelled windows have an air permeability class of 4, 3.9% are classified as class 3, and just 0.2% fall into classes 1 or 2. It is important to note that participation in the CLASSE+ system is voluntary, which explains why companies predominantly label their highest-performing products.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eThermal Transmittance (Uw) Analysis\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 8 shows the distribution of energy labels by thermal transmittance (Uw) ranges. About 40% of A+ windows have a Uw between 1.4 and 1.6 W/m\u0026sup2;\u0026deg;C (around 182 000 windows), while 25% fall between 1.2 and 1.4 W/m\u0026sup2;\u0026deg;C. Only 1.0% have Uw values between 1.8 and 2.0 W/m\u0026sup2;\u0026deg;C.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor A-rated windows, 29% have a Uw between 1.6 and 1.8 W/m\u0026sup2;\u0026deg;C, and 27% between 1.8 and 2.0 W/m\u0026sup2;\u0026deg;C. Notably, 25% of E-rated windows fall within 1.2 to 1.4 W/m\u0026sup2;\u0026deg;C, accounting for 12 labels, and these also have low solar factors and air permeability classifications.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eSolar Factor (g) Analysis\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 9 shows the distribution of energy labels by solar factor (g) ranges. Most windows have a g-value between 0.4 and 0.7. Of the windows with g-values in this range, 82% are rated A+ and 4% are rated A. About 40% fall between 0.4 and 0.5 (around 194 000 labels), 37% between 0.6 and 0.7 (about 179 600 labels), and 11% between 0.5 and 0.6.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFrame Material Analysis\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe CLASSE+ data also indicates that the majority of windows with energy ratings of A+, A, or B use PVC frames. More than 450 000 labelled windows have PVC frames, followed by approximately 33 000 thermal Break aluminium windows. Other frame materials account for less than 1% of the total windows labelled under the CLASSE+ system.\u003c/p\u003e"},{"header":"4. Impact of WINDOW’s replacement on the energy performance of a residential building","content":"\u003cp\u003eThis study analyzed the impact of replacing existing windows with higher energy-labelled ones on the thermal and energy performance of a single-family home. Heat losses through the building envelope and annual energy needs (useful and primary) were calculated using a seasonal methodology, considering different window energy classes.\u003c/p\u003e\u003cp\u003eThe study also evaluated window replacement combined with other thermal improvements, including various insulation solutions for the vertical opaque envelope and different climate zones: I3, V2 (Zone A); I2, V2 (Zone B); and I1, V3 (Zone C). The calculations followed the guidelines of Decree-Law No. 101-D/2020 of December [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e4.1. Case Study Description\u003c/h2\u003e\u003cp\u003eThe case study corresponds to an existing four-bedroom single-family dwelling (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e11\u003c/span\u003e), with a usable floor area of 315 m\u0026sup2;, an intermediate thermal inertia class, and fa\u0026ccedil;ades oriented to the NE, SE, SW, and NW. For climate control of all main spaces and circulation areas, an air-to-air heat pump system was installed, with a SCOP of 4.0 and a SEER of 6.4.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe study evaluated three insulation solutions for the vertical opaque envelope, including external walls and structural thermal bridges: no insulation, External Thermal Insulated Composite Systems (ETICS) with 4 cm of Expanded Polystyrene (EPS), and ETICS with 8 cm of EPS. Table\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e8\u003c/span\u003e presents the U-values calculated based on the building materials and their thermal properties, as specified in [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab8\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 8\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eConstructive solutions comprising the opaque exterior envelope.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eType\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eU [W/m\u003csup\u003e2\u003c/sup\u003e.\u0026deg;C]\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eWithout insulation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eETICS | EPS 4 cm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eETICS | EPS 8 cm\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eExternal wall\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1,02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0,52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eExternal wall (Thermal Bridge)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2,93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0,78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,45\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFor the glazed envelope, various scenarios with different Uw values were analyzed to assess the impact of installing windows with energy classes D, C, B, A, and A+. The goal was to evaluate the effect of replacing class D windows with higher-rated ones. An air permeability class of 4 and a solar factor of 0.5 for the glass were assumed in all scenarios.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e4.2. Results\u003c/h2\u003e\u003cp\u003eFigure 12 shows the heat losses through the windows (in W/\u0026deg;C) for each window energy class and the three thermal insulation solutions. The graphs indicate that replacing class D windows with class A\u0026thinsp;+\u0026thinsp;or class A windows reduces heat losses through the windows to less than half. A similar reduction occurs when class C windows are replaced with class A\u0026thinsp;+\u0026thinsp;windows.\u003c/p\u003e\u003cp\u003eFigure 13 shows the windows' contribution to total heat losses through the building's exterior envelope (%), considering different window and insulation solutions. Better window energy classes reduce heat losses. When class D windows are replaced with class A\u0026thinsp;+\u0026thinsp;windows, this contribution decreases by more than 40%, and the reduction can exceed 50% in envelopes without thermal insulation. With an ETICS system (8 cm of EPS) and class D windows, 52% of the heat loss occurs through the windows. Upgrading to class A\u0026thinsp;+\u0026thinsp;reduces this to 27%.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e14\u003c/span\u003e shows the annual energy needs for heating (Nic) and cooling (Nvc) based on window energy class, climate zones (I3, V2 \u0026ndash; Zone A; I2, V2 \u0026ndash; Zone B; I1, V3 \u0026ndash; Zone C) and insulation solutions. Replacing class D windows with higher-rated ones significantly reduces Nic by up to 48% in highly insulated envelopes and 38% in uninsulated ones. However, better-rated windows increase Nvc, with rises of up to 44% in climate zone V2, though only about 5% in climate zone V3.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure 15 shows the ratio of annual primary energy needs to reference energy needs (Ntc/Nt) for the different scenarios when changing window energy classes and insulation solutions (no insulation, ETICS with 4 cm of EPS, and ETICS with 8 cm of EPS). It also displays the maximum limits for each building energy class, indicating the class achieved in each scenario. The building\u0026rsquo;s classes are those defined by the national energy certification scheme (defined in the Decree-Law No. 101-D/2020 of December 7).\u003c/p\u003e\u003cp\u003eThe results show that the impact of window energy class depends on the building's location and envelope type. In the analysed building, upgrading from class A to A\u0026thinsp;+\u0026thinsp;windows did not change its energy class due to the window class range. For a highly insulated envelope, class B is enough to achieve building energy class B, regardless of location - this was the highest class reached in the analysis. In an uninsulated envelope and a colder climate zone (I3), replacing class C windows with class B or higher can raise the building's energy class from C to B-.\u003c/p\u003e\u003c/div\u003e"},{"header":"5. recommendations for the EVOLUTION OF the WINDOW energy LABELING system","content":"\u003cp\u003eBased on the study's results, this section proposes revising the CLASSE\u0026thinsp;+\u0026thinsp;energy labeling system for windows in Portugal by adding new criteria and parameters, including safety, sustainability, and compliance with European requirements. The information below comprises a set of recommendations that have been proposed to ADENE for implementation in an upcoming revision of the labelling scheme.\u003c/p\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e5.1. Update of the Energy Classification Scale\u003c/h2\u003e\u003cp\u003eThe CLASSE\u0026thinsp;+\u0026thinsp;system for energy labelling of construction products includes seven energy classes, from A+ (most efficient) to F (least efficient). For windows, this classification is based on the total monthly energy needs for climate control in a reference compartment.\u003c/p\u003e\u003cp\u003eAn analysis of CLASSE\u0026thinsp;+\u0026thinsp;data shows that 91.5% of window labels are class A+. About 96% of labeled windows have class 4 air permeability, while the remaining 4% have class 3. Most labeled windows have a thermal transmittance (Uw) between 1.2 and 1.8 W/m\u0026sup2;\u0026middot;\u0026deg;C, with 40% of A\u0026thinsp;+\u0026thinsp;windows falling between 1.4 and 1.6 W/m\u0026sup2;\u0026middot;\u0026deg;C. Regarding the solar factor (g), 40% of all labeled windows fall between 0.4 and 0.5, and 37% between 0.6 and 0.7.\u003c/p\u003e\u003cp\u003eFor air permeability classes 3 and 4, A\u0026thinsp;+\u0026thinsp;windows can have Uw values up to 2.0 W/m\u0026sup2;\u0026middot;\u0026deg;C, depending on the glass's solar factor. Windows with class 4 air permeability and Uw\u0026thinsp;\u0026le;\u0026thinsp;1.4 W/m\u0026sup2;\u0026middot;\u0026deg;C always meet the A\u0026thinsp;+\u0026thinsp;standard, regardless of the solar factor. The Uw and g ranges for achieving an A\u0026thinsp;+\u0026thinsp;class are much broader than for class A, especially for windows with class 4 air permeability, which represents most labelled windows.\u003c/p\u003e\u003cp\u003eThis analysis suggests an opportunity to tighten the criteria for achieving an A\u0026thinsp;+\u0026thinsp;rating, promoting windows with better thermal performance. Any revisions should reflect the reality of the national market and current Portuguese regulations. It is also important to note that European standards, such as those in the European Taxonomy and certifications like Passivhaus and Minergie, set stricter Uw limits (e.g., Uw\u0026thinsp;\u0026le;\u0026thinsp;1.0 W/m\u0026sup2;\u0026middot;\u0026deg;C). Although this criterion may not suit Mediterranean climates, the label must include information on whether the window meets this criterion.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e5.2. New Parameters and Information for the Label\u003c/h2\u003e\u003cp\u003eThe current energy label provides the window's energy class, summer and winter comfort levels, thermal transmittance (Uw), solar factor, light transmission, air permeability class, and acoustic attenuation. However, adding information on safety, sustainability, and compliance with stricter thermal standards like the European Taxonomy is recommended. Table\u0026nbsp;\u003cspan refid=\"Tab9\" class=\"InternalRef\"\u003e9\u003c/span\u003e outlines the suggested new parameters for the updated label.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab9\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 9\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eParameters and new information to be provided through the label\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIndicator\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eParameter / information\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eThermal performance and alignment with the European Taxonomy\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eInformation on compliance with the technical criterion of the European Taxonomy (Uw\u0026thinsp;\u0026le;\u0026thinsp;1.0 W/m\u0026sup2;.\u0026deg;C)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eSafety\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eWind resistance class according with EN 12210:2016 [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eSustainability\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eEnvironmental parameters: Embodied carbon, kg CO₂ eq.m⁻\u0026sup2;; Embodied energy, MJp.m⁻\u0026sup2;\u003c/p\u003e\u003cp\u003eCircularity parameters: Recycled content rate, %\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eCompliance with the European Taxonomy Requirements\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe EU Taxonomy regulation, approved by the European Union (EU) in June 2020, defines which activities are considered sustainable using a common classification system. The regulation outlines six environmental objectives and stipulates that an activity can be deemed environmentally sustainable if it contributes to one of these objectives without significantly harming the others. To this end, criteria have been defined for different economic activities. Concerning windows, the criterion is to produce highly energy-efficient systems with a thermal transmittance (Uw) of \u0026le;\u0026thinsp;1.0 W/m\u0026sup2;\u0026middot;\u0026deg;C to help mitigate climate change. While this standard is strict for Mediterranean climates and should not define a window\u0026rsquo;s energy class, whether the window meets this criterion should be highlighted on the label.\u003c/p\u003e\u003cp\u003e\u003cb\u003eWind Resistance\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAlthough wind resistance does not affect a window's energy performance, it is a crucial safety feature, especially during extreme weather events. It measures how much the window deforms under wind pressure, depending on the frame material, profile type, and fitting strength. A performance scale, from least to most resistant, could represent wind resistance, considering both the window's ability to withstand wind pressure and its relative frontal deflection. The wind resistance classification of windows must be determined through testing following EN 12211:2016 [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] and classified per EN 12210:2016 [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e], ensuring compliance with performance levels for static and dynamic wind loads.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSustainability (Environmental/Circularity Parameters)\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe current label does not include parameters to distinguish windows according to their environmental performance. The possibility of adding voluntary environmental and circularity parameters was evaluated, focusing on three key factors: embodied carbon, embodied energy, and recycled content rate, calculated using the Life Cycle Assessment (LCA) methodology (ISO 14040:2006 [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]). These parameters were selected based on:\u003c/p\u003e\u003cp\u003e1. \u003cb\u003eComparability\u003c/b\u003e: As standardized calculation method shall be used to ensure a meaningful comparison of results.\u003c/p\u003e\u003cp\u003e2. \u003cb\u003eThird-party verification\u003c/b\u003e: Environmental data shall be verified by an independent party.\u003c/p\u003e\u003cp\u003e3. \u003cb\u003ePublic information\u003c/b\u003e: Environmental data for the calculation of each parameter should be public whenever possible.\u003c/p\u003e\u003cp\u003e4. \u003cb\u003eLife cycle perspective\u003c/b\u003e: The window's life cycle impact should be assessed to avoid the transfer of impacts between life cycle stages, following internationally recommended practices for assessing the environmental sustainability of products.\u003c/p\u003e\u003cp\u003eEnvironmental data from third-party verified Environmental Product Declarations (EPDs) is proposed for the calculation of environmental and circularity indicators in CLASSE\u0026thinsp;+\u0026thinsp;label. EPDs provide transparent, reliable information on a product\u0026rsquo;s environmental impact throughout its life cycle, following standards such as ISO 14025:2006 [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], ISO 21930:2017 [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], EN 15804:2012 [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], and EN 15942:2000 [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e5.3. The Role of the Window Labeling System in Portugal's Renovation Wave\u003c/h2\u003e\u003cp\u003eA major challenge in building rehabilitation is the lack of accessible information for owners on renovation options and their long-term benefits. Energy labels are essential tools in this context. They allow consumers to easily compare the performance of different products, supporting informed decisions that enhance energy efficiency and drive market innovation with advanced technologies.\u003c/p\u003e\u003cp\u003eIn Portugal, the CLASSE\u0026thinsp;+\u0026thinsp;window labelling system plays a central role in the national strategy to improve energy performance in buildings. It is especially relevant under the Recovery and Resilience Plan (PRR), where several funding schemes require the use of windows with a CLASSE\u0026thinsp;+\u0026thinsp;label rated \u0026ldquo;A\u0026rdquo; or higher, issued by manufacturers officially registered in the CLASSE\u0026thinsp;+\u0026thinsp;program.\u003c/p\u003e\u003cp\u003eHowever, the energy performance of a window depends on multiple factors, including building orientation, insulation level, and climate zone. As such, the highest-rated windows (class A or A+) is not always the most appropriate or cost-effective choice for every project. For this reason, architects and engineers should adopt a holistic design approach, considering window ratings as part of the overall project.\u003c/p\u003e\u003cp\u003eAdditionally, the current CLASSE\u0026thinsp;+\u0026thinsp;labelling system does not account for broader sustainability indicators, such as embodied carbon, embodied energy, or the use of recycled materials. Integrating these criteria into the label would support the selection of more sustainable solutions and better aligned with national and EU decarbonisation goals.\u003c/p\u003e\u003cp\u003eTo support a more flexible and inclusive renovation strategy, funding eligibility should not be limited strictly to class A or A\u0026thinsp;+\u0026thinsp;windows but rather extended to any window product that carries a valid CLASSE\u0026thinsp;+\u0026thinsp;energy label and that meets the regulatory standards. This approach promotes flexibility, inclusivity, and a more accessible market.\u003c/p\u003e\u003c/div\u003e"},{"header":"6. CONCLUSION","content":"\u003cp\u003eThis paper outlines the methodology for the Portuguese window labelling system. The process began by selecting climate data from six climate zones in Portugal, with three locations representing winter and summer conditions. A reference building, based on ISO 13790:2008, was used for analysis, with windows making up 18% of the floor area. Key window properties\u0026mdash;thermal transmittance (U-value), solar transmittance (g), and air permeability\u0026mdash;were varied to assess their impact on energy performance. Using EnergyPlus software through DesignBuilder, simulations calculated hourly heating and cooling demands for different orientations, ventilation rates, and window sizes, providing a comprehensive evaluation of window performance.\u003c/p\u003e\u003cp\u003eThe study also analyzed the impact of window energy classes on existing buildings and proposed updating the current classification scale. It suggests adding new parameters to the label, such as those related to safety, sustainability, and compliance with European Taxonomy standards.\u003c/p\u003e\u003cp\u003eFindings show that a window\u0026rsquo;s impact on energy performance depends on factors like location and building insulation, meaning A\u0026thinsp;+\u0026thinsp;class windows are not always the best option. Class B windows can provide sufficient performance in some cases.\u003c/p\u003e\u003cp\u003eThe paper recommends that renovation funding should not be limited to A and A\u0026thinsp;+\u0026thinsp;class windows, as these may have higher initial costs without always offering the best return on investment. Decisions should follow a holistic approach, considering the entire building envelope. While A\u0026thinsp;+\u0026thinsp;class windows are suitable for projects aiming for high energy efficiency or environmental certifications, other sustainability criteria\u0026mdash;such as embodied carbon, embodied energy, and recycled content\u0026mdash;should also be included.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eN.S. was responsible for the development and detailed description of the Classe+ Windows methodology, as well as for supervising and critically reviewing the study.J.P. carried out the case study, drafted the main body of the manuscript, and prepared the figures.R.G. provided recommendations for the evolution of the energy labeling system for windows, with a focus on sustainability indicators.P.S. and B.M. supplied all data required for the analysis of the issued Classe+ labels.All authors contributed to the revision and final approval of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eN. Sim\u0026otilde;es, J. Prata and R. Garcia are grateful for the Foundation for Science and Technology's support through funding UIDB/04625/2020 from the research unit CERIS (DOI: 10.54499/UIDB/04625/2020).This research was also supported by R2UTechnologies for the modular system, within the scope of the Mobilizing Agendas/Alliances for Business Innovation, funded by the Recovery and Resilience Plan (RRP) and the Next Generation EU mechanisms, as well as by the P2E project (CENTRO2030-FEDER-01416300), co-financed by the Centro Regional Programme (Centro2030).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eEuropean Commission (2020). Energy efficiency in buildings. Available online: https://commission.europa.eu/news/focus-energy-efficiency-buildings-2020-02-17_en (accessed on may 22, 2024).\u003c/li\u003e\n\u003cli\u003eEuropean Parliament. (2023). \u003cem\u003eCarbon emissions reduction: EU targets and policies\u003c/em\u003e. Available online: https://www.europarl.europa.eu/topics/pt/article/20180305STO99003/reducao-das-emissoes-de-carbono-metas-e-politicas-da-ue (accessed on May 10, 2025).\u003c/li\u003e\n\u003cli\u003eNair, G.; Verde, L.; Olofsson, T. (2022). A Review on Technical Challenges and Possibilities on Energy Efficient Retrofit Measures in Heritage Buildings. Energies, 15, 7472.\u003c/li\u003e\n\u003cli\u003eHassouneh, K., Alshboul, A., Al-Salaymeh, A., Influence of windows on the energy balance of apartment buildings in Amman, Energy Conversion and Management, No. 51, pp 1583-1591, 2010.\u003c/li\u003e\n\u003cli\u003eJaber, S., Ajib S., Thermal and economic windows design for different climate zones, Energy and Buildings, No. 43, pp 3208-3215, 2011.\u003c/li\u003e\n\u003cli\u003eGasparella, A., Pernigotto, G., Cappelletti, F., Romagnoni, P., Baggio, P., Analysis and modelling of window and glazing systems energy performance for a well insulated residential building, Energy and Buildings, No. 43, pp 1030-1037, 2010.\u003c/li\u003e\n\u003cli\u003ePerson, M., Roos A., Wall, M., Influence of window size on the energy balance of low energy houses, Energy and Buildings, No 38,pp 181-188, 2005.\u003c/li\u003e\n\u003cli\u003eMoghaddam, S.A.; Mattsson, M.; Ameen, A.; Akander, J.; Gameiro Da Silva, M.; Sim\u0026otilde;es, (2021). N. Low-Emissivity Window Films as an Energy Retrofit Option for a Historical Stone Building in Cold Climate. Energies, 14, 7584. \u003c/li\u003e\n\u003cli\u003eRosa Francesca De Masi, Valentino Festa, Antonio Gigante, Silvia Ruggiero, Giuseppe Peter Vanoli. (2023) The role of windows on building performance under current and future weather conditions of European climates, Energy and Buildings, Volume 292, 1 August 2023, 113177.\u003c/li\u003e\n\u003cli\u003eQuddus Tushar, Muhammed A. Bhuiyan, Guomin Zhang (2022) Energy simulation and modeling for window system: A comparative study of life cycle assessment and life cycle costing, Volume 330, 1 January 2022, 129936\u003c/li\u003e\n\u003cli\u003eMoghaddam, S.A.; Serra, C.; Gameiro da Silva, M.; Sim\u0026otilde;es, N. (2023). Comprehensive Review and Analysis of Glazing Systems towards Nearly Zero-Energy Buildings: Energy Performance, Thermal Comfort, Cost-Effectiveness, and Environmental Impact Perspectives. Energies, 16, 6283. \u003c/li\u003e\n\u003cli\u003eWu, W.; Skye, H.M. (2021). Residential net-zero energy buildings: Review and perspective. Renew. Sustain. Energy Rev, 142, 110859.\u003c/li\u003e\n\u003cli\u003eGasparella, A., Pernigotto, G., Cappelletti, F., Romagnoni, P., Baggio, P. (2010). Analysis and modelling of window and glazing systems energy performance for a well insulated residential building. Energy and Buildings, No. 43, pp 1030-1037.\u003c/li\u003e\n\u003cli\u003eKaterina Tsikaloudaki, Konstantinos Laskos, Theodoros Theodosiou, and Dimitrios Bikas (2015) The energy performance of windows in Mediterranean regions. Energy and Buildings, Volume 92, 1 April 2015, pp 180-187.\u003c/li\u003e\n\u003cli\u003eKarlsson, J., Roos, A. (2003). Evaluation of window energy rating models for different houses and European climates, Solar Energy, No. 76, pp 71-77.\u003c/li\u003e\n\u003cli\u003eInternational Organization for Standardization (ISO) (2011). ISO 18292:2011, Energy performance of fenestration systems for residential buildings - Calculation procedure. Geneva: ISO.\u003c/li\u003e\n\u003cli\u003eKragh J., Laustsen, J. B., Svendsen, S., Proposal for Energy Rating System of windows in EU, Technical University of Denmark, CVR-nr: 63 39 30 10, 2008.\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2006). EN 14351-1: 2006-03 Windows and doors - Product standard, performance characteristics - Part 1: Windows and external pedestrian doorsets without resistance to fire and/or smoke leakage characteristics.\u003c/li\u003e\n\u003cli\u003eTrząski, A., Rucińska, J. (2015). Energy labeling of windows \u0026ndash; Possibilities and limitations. Solar Energy, Journal of Cleaner Production, Volume 120, Pages 158-174.\u003c/li\u003e\n\u003cli\u003eOrouji, P., Vakili, A., Behrouz, M.K., Jafari, H.H., Eslami M.R., Vahidnia, M., Sadegh, R.M., Rezaie, M. (2019). Methodology of standardizing the energy labeling and rating of window fenestration in IRAN, Sustainable Energy Technologies and Assessments, Volume 33, Pages 24-33.\u003c/li\u003e\n\u003cli\u003eSaeed Banihashemi, Hamed Golizadeh, M. Reza Hosseini, Mahmoud Shakouri (2015) Climatic, parametric and non-parametric analysis of energy performance of double-glazed windows in different climates, International Journal of Sustainable Built Environment Volume 4, Issue 2, December 2015, Pages 307-322.\u003c/li\u003e\n\u003cli\u003eGlass for Europe (2018). The benefits of Window Energy Labelling. Available online: https://glassforeurope.com/labelling_scheme-windows/#_edn1 (accessed on May 20, 2025).\u003c/li\u003e\n\u003cli\u003eEuroWindoor, EuroWindoor reply to European Commission proposals for EU Energy Labelling for windows from 9/9/2015. 25 th September 2015 (https://www.eurowindoor.eu/wp-content/uploads/2023/02/EuroWindoor_reply_to_WD_on_Delegated_Regulation_for_Energy_Labelling_Windows_1509.pdf).\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2017). EN ISO 10077-1:2017, Thermal Performance of Windows, Doors and Shutters \u0026ndash; Calculation of Thermal Transmittance - Part 1: General. Brussels: CEN.\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2017). EN ISO 10077-2:2017, Thermal performance of windows, doors and shutters \u0026mdash; Calculation of thermal transmittance - Part 2: Numerical method for frames. Brussels: CEN.\u003c/li\u003e\n\u003cli\u003eInternational Organization for Standardization (ISO) (2000). ISO 12567-1:2000 Thermal performance of windows and doors - Determination of thermal transmittance by hot box method - Part 1: Complete windows and doors. Geneva: ISO\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2016). EN 1026:2016, Windows and doors - Air permeability - Test method. Brussels: CEN.\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2016). EN 1027:2016, Windows and doors - Water tightness - Test method. Brussels: CEN.\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2016). EN 12211:2016, Windows and doors - Resistance to wind load - Test method. Brussels: CEN.\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2021). ISO 10140-2:2021, Acoustics - Laboratory measurement of sound insulation of building elements - Part 2: Measurement of airborne sound insulation (ISO 10140-2:2021). Brussels: CEN.\u003c/li\u003e\n\u003cli\u003eGazulla Santos, C. (2014). Using life cycle assessment (LCA) methodology to develop eco-labels for construction and building materials. \u003cem\u003eEco-Efficient Construction and Building Materials, \u003c/em\u003ePages 84\u0026ndash;97\u003cem\u003e.\u003c/em\u003e doi:10.1533/9780857097729.1.84 \u003c/li\u003e\n\u003cli\u003eRoesch, A., Douziech, M., Mann, S., Lansche, J., Gaillard, G. (2025). Consequences of the use or absence of life cycle assessment in novel environmental assessment methods and food ecolabels, \u003cem\u003eCleaner Production Letters\u003c/em\u003e, Volume 8, 100087, https://doi.org/10.1016/j.clpl.2024.100087.\u003c/li\u003e\n\u003cli\u003eRajagopalan, N., Bilec, M.M. \u0026amp; Landis, A.E. Life cycle assessment evaluation of green product labeling systems for residential construction. \u003cem\u003eInt J Life Cycle Assess\u003c/em\u003e \u003cstrong\u003e17\u003c/strong\u003e, 753\u0026ndash;763 (2012). https://doi.org/10.1007/s11367-012-0416-9 \u003c/li\u003e\n\u003cli\u003eRoesch, A., Douziech, M., Mann, S., Lansche, J., Gaillard, G. (2025). Consequences of the use or absence of life cycle assessment in novel environmental assessment methods and food ecolabels, \u003cem\u003eCleaner Production Letters\u003c/em\u003e, Volume 8, 100087, https://doi.org/10.1016/j.clpl.2024.100087.\u003c/li\u003e\n\u003cli\u003eClift, R. (1993). \u003cem\u003eL\u003c/em\u003eife cycle assessment and ecolabelling.\u003cem\u003e Journal of Cleaner Production, Volume 1, Issues 3-4, Pages 155-159..\u003c/em\u003e doi:10.1016/0959-6526(93)90006-w\u003c/li\u003e\n\u003cli\u003eRegulation (EU) 2024/3110 of the European Parliament and of the Council of 27 November 2024 laying down harmonised rules for the marketing of construction products and repealing Regulation (EU) No 305/2011, http://data.europa.eu/eli/reg/2024/3110/oj\u003c/li\u003e\n\u003cli\u003eInternational Organization for Standardization (ISO) (2008). ISO 13790:2008 Energy performance of buildings \u0026mdash; Calculation of energy use for space heating and cooling. Geneva: ISO.\u003c/li\u003e\n\u003cli\u003eInternational Organization for Standardization (ISO) (2004). ISO 13791:2004 Thermal performance of buildings - Calculation of internal temperatures of a room in summer without mechanical cooling - General criteria and validation procedures. Geneva: ISO.\u003c/li\u003e\n\u003cli\u003ePortugal. Decree-Law No. 101-D/2020 of December 7th: Establishes the requirements for the energy performance of buildings. Di\u0026aacute;rio da Rep\u0026uacute;blica, 1st series, no. 235 (Supplement), December 7, 2020.\u003c/li\u003e\n\u003cli\u003eCarlos Pina dos Santos (2006) ITE50 \u0026ndash; Thermal Transmittance Coefficients of Building Envelope Elements, LNEC publication.\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2016). European Standard EN 12210:2016 Windows and doors - Resistance to wind load \u0026ndash; Classification. Brussels: CEN.\u003c/li\u003e\n\u003cli\u003eInternational Organization for Standardization (ISO) (2006). ISO 14040:2006 Environmental management \u0026mdash; Life cycle assessment \u0026mdash; Principles and framework. Geneva: ISO.\u003c/li\u003e\n\u003cli\u003eInternational Organization for Standardization (ISO) (2006). ISO 14025:2006 Environmental labels and declarations \u0026mdash; Type III environmental declarations \u0026mdash; Principles and procedures. Geneva: ISO.\u003c/li\u003e\n\u003cli\u003eInternational Organization for Standardization (ISO) (2017). ISO 21930:2017 Sustainability in buildings and civil engineering works \u0026mdash; Core rules for environmental product declarations of construction products and services. Geneva: ISO.\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2019). EN 15804:2012+A2:2019 Sustainability of construction works - Environmental product declarations - Core rules for the product category of construction products. Brussels: CEN.\u003c/li\u003e\n\u003cli\u003eEuropean Committee for Standardization (CEN) (2021). EN 15942:2021 Sustainability of construction works - Environmental product declarations - Communication format business-to-business. Brussels: CEN.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Windows, Energy labelling, Buildings, Energy performance","lastPublishedDoi":"10.21203/rs.3.rs-7012970/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7012970/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEnergy labelling is a tool for reducing building operational energy use by offering transparent, comparable performance data. While well established for appliances, labelling of construction products, particularly windows remains rare. In Portugal, the CLASSE\u0026thinsp;+\u0026thinsp;system, managed by ADENE and based on Itecons\u0026rsquo; methodology, has issued over 745,000 window labels in the past decade.\u003c/p\u003e\u003cp\u003eThis paper details the CLASSE\u0026thinsp;+\u0026thinsp;methodology and analyzes data from the first 500,000 labels to uncover product performance trends and system behavior. A residential case study is used to evaluate the practical impact of window replacement on building energy performance, illustrating that the most efficient label rating is not universally optimal.\u003c/p\u003e\u003cp\u003eThis work provides a robust, data-driven foundation for refining window labelling schemes. It critically reviews the current classification scale and offers recommendations, including new indicators such as safety, sustainability and alignment with the EU Taxonomy, thereby supporting national and European policy goals.\u003c/p\u003e","manuscriptTitle":"Methodology and Performance Analysis of the Portuguese Window Energy Labelling System","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-17 02:15:17","doi":"10.21203/rs.3.rs-7012970/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a9aeda9a-b7a1-4547-9b21-e8c9fd967b7b","owner":[],"postedDate":"October 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-25T21:23:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-17 02:15:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7012970","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7012970","identity":"rs-7012970","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}