Performance analysis of an Earth-Air Heat Exchanger applied to the ventilation of a near Zero Energy Building

Performance analysis of an Earth-Air Heat Exchanger applied to the ventilation of a near Zero Energy Building | 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 Article Performance analysis of an Earth-Air Heat Exchanger applied to the ventilation of a near Zero Energy Building Salmen Ghorbel, Hatem Bentaher, Ana Tejero-Gonzalez, Mossaad Ben Ayed, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1925622/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 Introducing near Zero Energy Buildings (nZEBs) in the European Union involves integrating new renewable energy technologies into buildings. Geothermal energy is one of them that can be exploited through the application of the Earth-Air Heat Exchanger (EAHX). It is basically constituted of a series of pipes buried underground at a particular depth. It utilizes the soil as a heat source or sinks to supply cooling or heating to the building. This type of exchanger can offer many advantages in terms of energy savings for the air-conditioning requirements and for assuring the indoor thermal comfort. This paper presents a performance analysis of an EAHX applied to the ventilation of a near Zero Energy Building situated in Spain. The proposed considered the thermo-physical proprieties of the soil in the region under investigation. The purpose is to study the effect of changing the depth in the ground, the pipe length, the pipe diameter, and the air velocity on the outlet air temperature. The mean efficiency of the EAHX is detailed then. The numerical model is implemented using Matlab environment. Results showed that, for specific parameters, the daily average cooling capacity can reach 1.7 KWh, and the EAHX can provide an energy saving of approximately 152 MWh for one year. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction At the European Union level, commercial and residential buildings account for more than 40% of the total global primary energy consumption, contributing to approximately 24% of European greenhouse gas emissions 1 . As a result, reducing the building's energy needs could lead to a 20% reduction in their environmental impacts 2 . The European Union (EU) introduced specific measures to reduce energy consumption in the construction sector with the Energy Performance of Buildings Directive (EPBD) in 2002 3 . Therefore, near Zero Energy Buildings (nZEBs) appear to have a much higher energy performance than conventional buildings. Many studies 45 proved that the nZEB reduces energy consumption and helps decrease the environmental pollution. Many countries or institutions with ambitious goals for future energy consumption are trying to adopt nZEBs as the main target for their future building energy, such as the US Department of Energy's Building Technology Program and the European Union's Buildings Energy Performance Directive 67 . The building energy consumption for cooling and heating has increased in the last years. For that, the Heating, Ventilation and Air-Conditioning (HVAC) systems are responsible for about half of the energy consumed in buildings 8 . When the ambient air temperature decreases during winter or rises during summer to an undesirable value, it's important to consider an energy source for improving the thermal comfort by maintaining the indoor air temperature between 22 and 27°C 9 . Various passive heating and cooling systems are available for building thermal management to reduce this important air-conditioning demand. These systems are characterized by their advantage of consuming almost negligible energy compared to conventional ones. We mention, among them, the Earth Air Heat Exchanger (EAHX), which has the benefits of reducing both the energy consumption for space cooling and heating and the CO2 emission in the sector of buildings. Its capital cost is high, but its operating cost is lower than the conventional active HVAC system. Therefore, the EAHX can yield considerable savings during the system lifecycle 10 . As its name suggests, this exchanger uses the earth as a heat source. This device consists of generally many pipes buried at a certain depth underground where the soil temperature remains fairly constant over the year. The ambient air is pumped into the underground pipes by a fan or a pump. During its passage along the pipes, it loses/absorbs the heat in exchange with the soil surrounding the pipes. Therefore, the air temperature becomes lower/higher. This heat exchange produces cooling effect in summer and heating effect in winter 11 . The performance of an EAHX depends on the following properties: the diameter and length of the pipes, the depth of the system burial, the flow rate of the air, the pipes' material, and the soil's thermal characteristics 1213 . Throughout the year, the underground temperature remains relatively constant below a certain depth due to the soil's high thermal inertia. Moreover, as the depth increases, the effect of the ground surface temperature fluctuations is reduced. Also, at a sufficient depth, the underground temperature is always higher than the temperature of the outside air in winter and lower than in summer. This is due to the time lag between the temperature variations at the ground's surface and below the ground 14 . In summer, warm air releases heat to buried pipes by convection, which will be dissipated to the ground by conduction. Afterward, cool air flows from the heat exchanger into the building space to create the desired thermal conditions. In winter, a heat transfer will be occurred from the surrounding ground to the pipes by conduction, and then when the cold air flows through the buried pipes, this heat will be transferred to the air by convection, increasing the supply air temperature. As the air rises, it dissipates heat into the building rooms. The difference between the outside air temperature and the ground temperature is considered as a pre-heating mechanism in winter and pre-cooling in summer 9 . If the outgoing air temperature is relatively sufficient and the EAHX is well designed, it can be used directly for space heating/cooling. However, it can be further heated/cooled by either passing through conventional air conditioners or other HVAC systems 14 . The EAHX has many advantages, mentioned among them: long-term cost-effectiveness, high efficiency, good air quality, simple equipment required, easy control, stable capacity, low maintenance costs, noise-free, and environment friendly 15 . The estimation of the heat transfer rate and maximum air temperature are two essential indicators of the EAHX efficient working during the summer. The heat transfer rate and the large temperature drops improve the viability of the EAHX also. Thus, there must be a methodology to obtain the highest air temperature drop for space cooling applications. Derbel and Kanoun 9 observed that the temperature difference between the inlet and outlet air of the EAHX increases by raising the pipe length, but the temperature change rate decreases. It was also observed that, by increasing the length of pipe, the heat transfer does not increase after a certain length, defined as saturation length 16 that increases by increasing the air flow rate. Ahmed et al. defined in a parametric study that the length of the pipe is a dominating parameter among the other parameters (the diameter, the depth, the material, and the air velocity) that affect the EAHX thermal performance. It was identified in many studies that the drop/rise in air temperature increases by increasing the pipe length, but the effect of pipe length on temperature drop/rise decreases after a certain extent 17 . The difference between inlet and outlet air temperature decreases by increasing the airflow velocity. Moreover, the flowing air velocity significantly influences the EAHX system's performance 18 Niu et al. 19 used the flowing flow velocities for cooling operations 0.5, 1.0, 1.5, 2, and 2.5 m/s, and they obtained that the drop rate of the air temperature was maximal at 0.5 m/s, and that's due to the high time of contact between air and pipe through the low velocity. For winter heating application, Bansal et al. 20 used these airflow velocities of 2, 3, 4, and 5 m/s and found that the temperature rise is obtained at the lowest velocity. However, 5 m/s corresponds to the maximum hourly heat gain. For a summer cooling study, Bansal et al. 21 found that the maximum air temperature drop is observed at ai velocity of 2 m/s and maximum hourly cooling at 5 m/s. Wu et al. 22 obtained similar results for cooling operations. The air temperature at the outlet increases by increasing the airflow velocity from 1 to 4 m/s, but the increase in the rate of mass flow guides to increasing heat transfer rate. Dubey et al. 23 found that the air temperature drops from 8 to 4°C, and COP (Coefficient Of Performance) also decreased from 6 to 3 by increasing the air velocity from 4 to 11 m/s. Bisoniya et al. 24 considered three different values of velocities (2, 3.5, and 5 m/s) for a 19.2 m length and 0.1 m diameter of an EAHX pipe. The observed minimum and maximum drops in air temperature were 11.3 and 12.9°C at 5 and 2 m/s airflow velocities. Yusof et al. 25 used different input parameters (airflow rate from 0.03 to 0.07 kg/s, ground temperature from 23 to 25°C, and inlet air temperature from 31 to 35°C) for the simulation of an EAHX exchanger under specific conditions. It was obtained that the maximal temperature drop was at the ground temperature of 23°C and the airflow rate of 0.03 kg/s, while at the ground temperature of 23°C, the air flow rate of 0.07 kg/s, the highest heat transfer rate (558.3 W) was achieved. The inlet air temperature plays an important role because the heat transfer rate between air and soil is governed by the temperature difference between ground and air. Kumar et al. 26 observed that the increase of the ambient air temperature leads to the rise of the outlet air temperature, but the amplitude significantly decreases. The outlet temperature varied from 23.8 to 27.9°C, while the inlet temperature varied from 27 to 45.9°C for an 80 m pipe length. Elminshawy et al. 27 used a laboratory-scale EAHX experimental setup under controlled operating parameters such as air flow rate, induced air temperature, and soil bulk temperature at three different compaction levels. It was observed that the cooling capacity of the EAHX system increases by 227% when the inlet air temperature is increased from 40 to 55°C. Niu et al. 19 studied the impact of the inlet air temperature on the EAHX performance through a control volume model of 1-D steady-state. It was observed that the air temperature decline rate in EAHX was higher when the inlet air temperature was high. For the inlet air temperature 26, 28, 30, 32, and 34°C the lowest and highest air temperature decline rate was found for respectively 26 and 34°C. Vidhi et al. 28 presented an EAHX application condenser cooling of a supercritical Rankine cycle (SRC) power generation. A 2-D model was developed to analyze the effect of different parameters on air cooling in EAHX and the thermodynamic cycle efficiency. The diameter, the length and the installation depth were kept as respectively 25–50 cm, 25-75m, and 1–4 m. It was found that the SRC efficiency increases by increasing the length and depth of the pipe. However, the improvement rate in SRC efficiency is very low after a certain limit. The constructal design has been used widely to search for the optimal geometries that lead to the best performances. Rodrigues et al. 29 presented a numerical investigation based on the constructal design of various geometrical configurations of an EAHX to achieve the highest thermal potential. The results showed that the thermal potential improved up to 73% and 115% respectively, for cooling and heating by increasing the number of pipes for the same mass flow rate of air and the same occupied area. This paper provides a parametric study of an EAHX implemented in the near Zero Energy Building LUCIA situated in the city of Valladolid, Spain. Four main parameters were chosen, which are the depth in the soil, the pipe length, the pipe diameter, and the air velocity, in order to analyses their effects on the daily average cooling/heating potential over the whole year and the mean efficiency of the EAHX. The final aim is to find the maximal energy savings that can be reached using this exchanger in function of these parameters. Case Study The studied Earth-Air Heat Exchanger (EAHX) is integrated in LUCIA building as one of the energy-efficient renewable energy systems that makes the LUCIA building considered as a nZEB. It has a useful space of 7500 \({m}^{2}\) that is committed to research and development through laboratories, spaces for spin-offs and research areas. The LUCIA building of the University of Valladolid (UVA) has obtained certifications that endorse it as the most sustainable building in Europe, the entire Northern Hemisphere, and the second in the world. The sustainability of the building began with its own design, with a reduction in energy demand of up to 41 percent, to which have been added efficient systems to consume only the necessary energy. It also has "clean energy" generation systems such as geothermal, through Canadian wells that treat air, photovoltaic, or biomass cogeneration system. The building (see Fig. 1 ) is at the forefront of energy technologies, with many systems that provide this characteristic, allowing it to be used as a model to achieve the objectives using only renewable sources. It can be said that the building has a zero CO2 balance. The objective of the building is validated with a reduction of energy demand by more than 50% because of its bioclimatic design, increased insulation, passive ventilation, and other strategies. Compared to a standard building with similar characteristics, the savings produced in demand for electricity and gas reach 60%. In addition, it is important to highlight the transferring surplus energy possibility to neighboring buildings that facilitates the savings of these buildings that benefit from this energy input. Energy generation is based on a tri-generation system with biomass, through four rectified motors to work with poor gas, plus one that is in reserve, each with 112 kW of power, to which additionally, photovoltaic panels exist for the complete production of electricity using different technologies. The building's air conditioning system is covered by an Air Treatment Unit (ATU) that provides heating and cooling, along with the ventilation of the building. The dissipation system is made of 4-pipes fan coils that supply heating or cooling to each space of the building. There is the ability to use free-cooling in the ATU when demand is cold, and the ambient temperature is lower than that of the interior air of the building, increasing the systems thermal efficiency and reducing consumption through the geothermal exchanger EAHX. Additionally, free cooling can be provided by the night ventilation of the building. Therefore, the air conditioning of the building can be with or without free-cooling, and the same also for the EAHX. The EAHX system (see photos in Fig. 2 ) consists of 52 tubes of 200 mm diameter, in "staggered" disposition, equivalent to a total area of 0,031 m2 with a length of 16 meters, providing a total passage section for all tubes of 1,63 \({m}^{2}\) and a total exchange length of 832 m, circulating an average airflow of 15 000 m3/h. They are buried at a depth of 2.02, 2,72 and 3,42 m. The EAHX is designed to provide an estimated input in summer of 62 000 kWh/year and winter of 50 740 kWh/year. This will reduce emissions estimated at 21 000 kg CO2 during the 6264 hours of the building operation per year. Table 1 Thermo-physical properties of the air, soil, and pipe used in the simulation Material Density ( \({K}{g}/{{m}}^{3})\) Heat capacity \({J}/{K}{g}.{C}\) Thermal conductivity \(({W}/{m}.{C})\) Air 1,225 1006,43 0,0242 Soil 3200 840 8,7 Pipe 950 1900 0,5 The ground where the EAHX tubes are positioned has a sufficient extension to provide the necessary heat recovery energy to facilitate energy reduction and project toward an efficiency improvement. This system allows for acclimating the outdoor air naturally before introducing it in the Air Treatment Unit. It is considered a bioclimatic device for renewable energy production. Table 1 represents the thermos-physical proprieties that are the density, the heat capacity and the thermal conductivity of the ambient air, the soil in the region where the study was carried out, and the pipe materiel. A. Modeling of the earth air heat exchanger EAHX The soil temperature mathematical model is based on the theory of the heat conduction applied to a homogenous semi-infinite solid. The following differential equation gives the heat conduction in the ground: $$\frac{{\partial }^{2}T}{\partial {Z}^{2}}-\frac{1}{\alpha }\times \frac{\partial T}{\partial t}=0$$ 1 Where \(\alpha\) is the thermal diffusivity of the soil in \({m}^{2}{s}^{-1}\) which is given by: $$\alpha = \frac{{\lambda }_{soil}}{{\rho }_{soil}\times {C}_{p soil}}$$ \({\lambda }_{soil}\) is the thermal conductivity of the soil in \(W{m}^{-1}{^\circ C}^{-1}\) , \({C}_{p soil}\) is the soil specific heat in \(J{Kg}^{-1}{^\circ C}^{-1}\) , \({\rho }_{soil}\) is the density of the soil in \(Kg{m}^{-3}\) , and z is the depth below the ground surface. The corresponding boundary conditions at z = 0 is the following: $$T\left(0,t\right)= {T}_{mean}+ {A}_{s}\times \text{c}\text{o}\text{s}\left(\omega \left(t -{t}_{0}\right)\right)$$ 2 Where \(\omega\) is the frequency of the annual temperature wave and for the infinite depth z \(\to \infty\) , we obtain: $${T\left(\infty ,t\right)= T}_{mean}$$ 3 $$\text{T}(\text{z},\text{t})={\text{T}}_{\text{mean }}+{\text{A}}_{\text{s}}\times \text{E}\text{x}\text{p}\left(-\left(\text{z}\right)\sqrt{\frac{\pi }{365\alpha }}\right)\times \text{c}\text{o}\text{s}\left(\frac{2\pi }{365}\times \left(\text{t}-{\text{t}}_{0}\right)-\left(\frac{\text{z}}{2}\right)\times \sqrt{\frac{365}{\frac{\text{T}}{\alpha }}}\right)$$ 4 \({T}_{mean}\) is the mean annual soil temperature, which can be calculated approximately from well water at a specific location, \({A}_{s}\) is the temperature wave amplitude of the temperature at the soil surface (z = 0), t is the day of the year and \({t}_{0}\) is the day of the maximum temperature at the soil surface. The coefficient of the convective heat transfer in a pipe is defined by: $${\text{h}}_{\text{c}\text{o}\text{n}\text{v}}=\frac{\text{N}\text{u}\times \lambda }{\text{D}}$$ 5 The following equation calculates the Nusselt number: $$\text{N}\text{u}=\text{0,0214}\times \left({\text{R}\text{e}}^{\text{0,8}}-100\right)\times {\text{P}\text{r}}^{\text{0,4}}$$ 6 The Reynolds number and Prandtl number of the air inside the pipe are calculated by: $$\text{R}\text{e}=\frac{{\text{V}}_{\text{a}\text{i}\text{r}}\times {\text{D}}_{\text{i}}}{v}$$ 7 $$Pr=\frac{v\times \rho \times \text{C}\text{p}}{\lambda }$$ 8 The following correlation gives the transferred heat: $$\varphi =\dot{\text{m}}\times {\text{C}\text{p}}_{\text{f}}\times \text{d}\text{T}\left(\text{x}\right)=\frac{\text{d}\text{x}}{{\text{R}}_{\text{conv }}+{\text{R}}_{\text{pipe }}+{\text{R}}_{\text{soil }}}\times \left(\text{T}\right(\text{z},\text{t})-\text{T}(\text{x}\left)\right)$$ 9 The soil and pipe thermal resistance are expressed respectively as: $${\text{R}}_{\text{soil }}=\frac{1}{{\lambda }_{\text{soil }}\times 2\times \pi }\times \text{l}\text{n}\left({\text{R}}_{(\text{z},\text{t})}/{\text{r}}_{\text{e}}\right)$$ 10 $${\text{R}}_{\text{pipe }}=\frac{1}{{\lambda }_{\text{pipe }}\times 2\times \pi }\times \text{l}\text{n}\left({\text{r}}_{\text{e}}/{\text{r}}_{\text{i}}\right)$$ 11 While the convective thermal resistance between the air in the pipe and the internal surface of the pipe is expressed as: $${\text{R}}_{\text{c}\text{o}\text{n}\text{v}}=\frac{1}{{r}_{i}\times {\text{h}}_{\text{c}\text{o}\text{n}\text{v}}\times 2\times \pi }$$ 12 The EAHX total thermal conductance is then defined by: $${G}_{Tot}= \frac{1}{{R}_{conv}+{R}_{pipe}+{R}_{soil}}$$ 13 The energy balance is obtained by combining the two equations ( 9 ) and ( 13 ): $$\frac{dT\left(x\right)}{T(z,t)-T\left(x\right)}=\frac{{G}_{Tot}}{\dot{m}\times {C}_{pf}}\times dx$$ 14 By making the integral of the Eq. ( 14 ), we obtain: $$-\text{l}\text{n}\left(\text{T}\right(\text{z},\text{t})-\text{T}(\text{x}\left)\right)=\frac{{\text{G}}_{\text{T}\text{o}\text{t}}}{\text{m}\times {\text{C}\text{p}}_{\text{f}}}\times \text{x}+\text{ Cte}$$ 15 For the boundary condition at the surface of the ground, the temperature is given by: $$T\left(0\right)= {T}_{amb}$$ 16 We obtain by replacing "Cte" by its expression found from the boundary equation in Eq. ( 15 ): $$\text{l}\text{n}\left(\text{T}\left(\text{x}\right)-\text{T}(\text{z},\text{t})/\left({\text{T}}_{\text{a}\text{m}\text{b}}-\text{T}(\text{z},\text{t})\right)\right)=\frac{-{\text{G}}_{\text{T}\text{o}\text{t}}}{\dot{\text{m}}\times {\text{C}\text{p}}_{\text{f}}}\times \text{x}$$ 17 At the outlet of the pipe, the air temperature is given by the following expression: $${\text{T}}_{\text{s}}={\text{T}}_{\text{a}\text{m}\text{b}}+\left(\text{T}(\text{z},\text{t})-{\text{T}}_{\text{a}\text{m}\text{b}}\right)\times \left(1-Exp(\frac{-{\text{G}}_{\text{T}\text{o}\text{t}}\times \text{m}\times \text{f}}{\text{m}}\times \text{x})\right)$$ 18 The mass flow rate of the air is expressed as follows: $$\dot{m}= {\rho }_{a}{V}_{a}\pi {D}_{i}^{2}/4$$ 19 By using the Fourier series, the ambient temperature daily variation is as follows: $${\text{T}}_{\text{a}\text{m}\text{b}}\left(\text{t}\right)=\frac{{\text{T}}_{max}+{\text{T}}_{min}}{2}+\frac{{\text{T}}_{max}-{\text{T}}_{min}}{2}\text{cos}\left(\frac{\pi }{12}\left(t-14\right)\right)$$ 20 The following equation gives the mean daily thermal efficiency of the EAHX: $${\eta }_{\text{mean }}=\frac{\sum _{\text{i}=1}^{24} \left({\text{T}}_{\text{a}\text{m}\text{b}}\left(\text{i}\right)-{\text{T}}_{\text{out }}\left(\text{i}\right)\right)}{\sum _{\text{i}=1}^{24} \left({\text{T}}_{\text{a}\text{m}\text{b}}\left(\text{i}\right)-{\text{T}}_{\text{soil }}\right)}$$ 21 The average daily cooling potential is calculated according to the following equation: $${\text{Q}}_{\text{c}\text{o}\text{o}\text{l}}=\sum _{\text{i}=1}^{24} \dot{\text{m}}\text{C}\text{p}\left({\text{T}}_{\text{a}\text{m}\text{b}}\left(\text{i}\right)-{\text{T}}_{\text{out }}\left(\text{i}\right)\right)$$ 22 The pipe is divided into 45 sections along the length, and all the previous equations are solved sequentially through sections from the inlet to the outlet of the EAHX. B. MODEL VALIDATION The model was validated using experimental data before carrying out the parametric study. The LUCIA building is equipped with measuring probes of energy variables such temperature, humidity, enthalpy, radiation, energy consumption, etc... The monitoring system allows a data recording with a frequency of taking measurements between 5 and 10 minutes, which provides a wide database for further analysis. Thanks to this dynamic monitoring management system, it is possible to determine the monthly, daily, or even hourly energy savings provided by the different energy systems installed, positioning the LUCIA building as a benchmark for avant-garde energy technology. Before carrying out the parametric analysis, the model is validated using the experimental data reported from some data logger installed at the inlet and the outlet of the EAHX. Table 2 represents the relative error and the outlet temperature for the experimental and the numerical results. As it can be observed that the relative error is below 4.3%. It was calculated through the following equation: \({\epsilon }\) = \(\frac{\left|{{T}{o}{u}{t}}_{{e}{x}{p}}-{{T}{o}{u}{t}}_{{s}{i}{m}}\right|}{{{T}{o}{u}{t}}_{{e}{x}{p}}} \times 100\) (23) Thus, we can conclude that the thermal performance of the EAHX can be predicted by our model. Table 2 Model validation with the obtained experimental results \({{T}{i}{n}}_{ }\) \({{T}{o}{u}{t}}_{{e}{x}{p}}\) (°C) \({{T}{o}{u}{t}}_{{s}{i}{m}}\) (°C) Relative error \({\epsilon }\) (%) 5 11.1 11.4 2.63 10 12.5 12.3 1.6 15 13.7 13.2 3.64 20 14.2 14.5 2.06 25 16.1 16.8 4.34 30 18.3 18.5 1.09 Results And Discussion In this section, a deep discussion about the performance of the proposed exchanger is detailed. Figure 3 shows the soil's temperature in the Valladolid region at different depths. We observed that the soil temperature sine wave decreases by rising the underground depth until the temperature becomes relatively constant at a depth of 8 m, allowing us to use the ground as a heat source. Figure 4 shows the air temperature variation along the length of the pipe at different depths. In the beginning, the air temperature decreases until it becomes equal to the temperature of the soil. It is noted at a depth of 8 m (Z = 8) that the temperature of air drops from the maximum ambient air temperature corresponding to July, which is around 29 ° C to reach the temperature of the soil, which is about 13°C in the region of Valladolid. Moreover, the air temperature at the outlet becomes lower as the depth is increased. At a depth of 1 m, the difference of the air temperature between the EAHX inlet and outlet is about 3°C that is not sufficient for the cooling of the building. It is also noticed that the air temperature inside the pipe is constant at a certain length (L = 20 m). As we can see in Fig. 4 , the difference in the air temperature between the outlet and inlet of the EAHX as a function of heat exchanger tube length at a maximum ambient air temperature of 29°C in July. As can be seen in Fig. 5 , the difference in the air temperature between the entrance and exit of the EAHX increases significantly over the entire pipe length. Still, starting from a length of around 20 m, the increase in the temperature difference is no longer significant, and it becomes almost constant (16°C). Figure 6 shows the variation of the outlet air temperature along the pipe length for different pipe diameters at a depth of 8 m. As can be seen in this figure, the diameter has an important impact on the outlet temperature. We deduced that the smaller diameter corresponds to the longer pipe length needed to reach the soil temperature at the outlet of the EAHX and vice versa. Figure 7 shows the average efficiency of the geothermal heat exchanger as a function of the length of the underground piping at a depth of 8 m. In this figure, it is observed that at the beginning, the two parameters rise in length significantly, but after 20 m, the increase is no more significant almost. We observe also that, more the pipe diameter is higher, more than the mean efficiency reaches its maximum at a shorter pipe length. We can deduce that the EAHX performance that is considered a device for the air conditioning is principally influenced by the temperature of the soil and the temperature of the air ambient since these two values of temperature change from month to month. Figure 8 shows the monthly variation of the ambient air temperature over a year, the air at the outlet, and the difference between both. It can be deduced also that the maximal difference of the air temperature between the inlet and outlet air is around 8.2°C and 7.3°C for respectively July and August, while the minimal difference is around 0.6°C and 0.8°C for respectively November and March. We can conclude from these results that the EAHX is efficient in the summer and winter, while it is not for the spring and autumn. It can be seen from Fig. 9 that the temperature difference between the outlet and the inlet decreases with the increasing of the air velocity inside the pipes. This drop is due to the diminution of the thermal transfer time between the pipe surface and the air passed through it. Figure 10 presents the monthly temperature of the ambient air and cooling/heating performance potential for EAHX over a year. It can be observed that the daily cooling capacity potential peaks at 1.75 kWh, corresponding to July when the ambient air temperature is at its highest. In October, the cooling performance potential for EAHX was a minimum of 0.16 kWh. The negative values for cooling potential shown in the figure represent the potential for daily heating when the ambient air temperature is lower than the soil temperature. The maximum daily heating potential values are 1.4 and 1.5 kWh, respectively, corresponding to December and January, when the ambient air temperature is the lowest. In addition, the corresponding thermal potential minimums in October and May are 0.25 and 0.3 kWh, respectively. Conclusion In the Valladolid region in Spain, the optimum depth for the EAHX used in the air conditioning applications is 8 m, which was determined using a special MATLAB program based meanly on the criteria of a constant ground temperature per year. The EAHX is then simulated using Valladolid climate conditions. The developed model was firstly validated by using the experimental results taken by the monitoring system installed in the Air Treatment Unit. Then, a parametric analysis was carried out to study and evaluate the effect of the buried pipe length and diameter on the outlet air temperature. We can summarize the main conclusions here: In the beginning, the air temperature in the pipe dropped and decreased significantly along the pipe until it became equal to the ground temperature at about 20 m. At 8 m depth, the air temperature drops from a maximal ambient air temperature value 29°C, corresponding to July, until it reaches a constant temperature of around 12°C. In August, the maximum difference between ambient air temperature and the outlet air temperature of the EAHX reached approximately 12°C. The EAHX used in this analysis had a maximal value of the daily cooling potential of about 1.75 kWh in July. Thanks to the EAHX, the cooling/heating energy savings for one year is approximately 152 MWh. It complements the energy sustainability of the building and directly implies a significant reduction in CO2 emissions to the atmosphere and contribute to a significant reduction in environmental pollution. Declarations ACKNOWLEDGMENTS The authors extend their appreciation to the Deputyship for Research and Innovation, Ministry of Education in Saudi Arabia for funding this research work through the project number “IF_2022_nbu_4093. The authors gratefully thank the Prince Faisal bin Khalid bin Sultan Research Chair in Renewable Energy Studies and Applications (PFCRE) at Northern Border University for their support and assistance. AVAILABILITY OF DATA AND MATERIALS The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request. References Eurostat T. Final energy consumption by sector. Dostupno na https//www econdb com/dataset/TSDPC320/ [Pristupljeno 26-lip-2018] . Published online 2014. D’Agostino D. 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A critical review of combined natural ventilation techniques in sustainable buildings. Renew Sustain Energy Rev. 2021;141:110795. Derbel HBJ, Kanoun O. Investigation of the ground thermal potential in tunisia focused towards heating and cooling applications. Appl Therm Eng. 2010;30(10):1091–1100. Agrawal KK, Agrawal G Das, Misra R, Bhardwaj M, Jamuwa DK. A review on effect of geometrical, flow and soil properties on the performance of Earth air tunnel heat exchanger. Energy Build. 2018;176:120–138. Ahmed SF, Liu G, Mofijur M, Azad AK, Hazrat MA, Chu Y-M. Physical and hybrid modelling techniques for earth-air heat exchangers in reducing building energy consumption: Performance, applications, progress, and challenges. Sol Energy. 2021;216:274–294. Agrawal KK, Yadav T, Misra R, Agrawal G Das. Effect of soil moisture contents on thermal performance of earth-air-pipe heat exchanger for winter heating in arid climate: In situ measurement. Geothermics. 2019;77:12–23. Mihalakakou G, Souliotis M, Papadaki M, et al. Applications of earth-to-air heat exchangers: A holistic review. Renew Sustain Energy Rev. Published online 2021:111921. Congedo PM, Baglivo C, Bonuso S, D’Agostino D. Numerical and experimental analysis of the energy performance of an air-source heat pump (ASHP) coupled with a horizontal earth-to-air heat exchanger (EAHX) in different climates. Geothermics. 2020;87:101845. Jakhar S, Misra R, Soni MS, Gakkhar N. Parametric simulation and experimental analysis of earth air heat exchanger with solar air heating duct. Eng Sci Technol an Int J. 2016;19(2):1059–1066. Benhammou M, Draoui B. Parametric study on thermal performance of earth-to-air heat exchanger used for cooling of buildings. Renew Sustain Energy Rev. 2015;44:348–355. Ghosal MK, Tiwari GN. Modeling and parametric studies for thermal performance of an earth to air heat exchanger integrated with a greenhouse. Energy Convers Manag. 2006;47(13–14):1779–1798. Kabashnikov VP, Danilevskii LN, Nekrasov VP, Vityaz IP. Analytical and numerical investigation of the characteristics of a soil heat exchanger for ventilation systems. Int J Heat Mass Transf. 2002;45(11):2407–2418. Niu F, Yu Y, Yu D, Li H. Heat and mass transfer performance analysis and cooling capacity prediction of earth to air heat exchanger. Appl Energy. 2015;137:211–221. Bansal V, Misra R, Agrawal G Das, Mathur J. Performance analysis of earth–pipe–air heat exchanger for winter heating. Energy Build. 2009;41(11):1151–1154. Bansal V, Misra R, Agrawal G Das, Mathur J. Performance analysis of earth–pipe–air heat exchanger for summer cooling. Energy Build. 2010;42(5):645–648. Wu H, Wang S, Zhu D. Modelling and evaluation of cooling capacity of earth–air–pipe systems. Energy Convers Manag. 2007;48(5):1462–1471. Dubey MK, Bhagoria J, Atullanjewar A. Earth air heat exchanger in parallel connection. Int J Eng Trends Technol. 2013;4(6):2463–2467. Bisoniya TS, Kumar A, Baredar P. Cooling potential evaluation of earth-air heat exchanger system for summer season. Int J Eng Tech Res. 2014;2(4):309–316. Yusof TM, Ibrahim H, Azmi WH, Rejab MRM. Thermal analysis of earth-to-air heat exchanger using laboratory simulator. Appl Therm Eng. 2018;134:130–140. Kumar R, Kaushik SC, Garg SN. Heating and cooling potential of an earth-to-air heat exchanger using artificial neural network. Renew Energy. 2006;31(8):1139–1155. Elminshawy NAS, Siddiqui FR, Farooq QU, Addas MF. Experimental investigation on the performance of earth-air pipe heat exchanger for different soil compaction levels. Appl Therm Eng. 2017;124:1319–1327. Vidhi R, Goswami DY, Stefanakos E. Supercritical Rankine cycle coupled with ground cooling for low temperature power generation. Energy Procedia. 2014;57:524–532. Rodrigues MK, da Silva Brum R, Vaz J, Rocha LAO, dos Santos ED, Isoldi LA. Numerical investigation about the improvement of the thermal potential of an Earth-Air Heat Exchanger (EAHE) employing the Constructal Design method. Renew Energy. 2015;80:538–551. Additional Declarations No competing interests reported. Supplementary Files AG.jpg 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-1925622","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":131134888,"identity":"335ae862-91bf-4338-9ffd-445ec57295f2","order_by":0,"name":"Salmen Ghorbel","email":"","orcid":"","institution":"National Engineering School of Sfax","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Salmen","middleName":"","lastName":"Ghorbel","suffix":""},{"id":131134889,"identity":"e2452110-9891-4fbb-82da-41d9aabf3a33","order_by":1,"name":"Hatem Bentaher","email":"","orcid":"","institution":"National Engineering School of Sfax","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hatem","middleName":"","lastName":"Bentaher","suffix":""},{"id":131134890,"identity":"d13da70e-df42-4208-bf38-7bd34f741133","order_by":2,"name":"Ana Tejero-Gonzalez","email":"","orcid":"","institution":"University of Valladolid","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ana","middleName":"","lastName":"Tejero-Gonzalez","suffix":""},{"id":131134891,"identity":"ffb8cf30-8651-4ad0-8386-b17dfeb320cb","order_by":3,"name":"Mossaad Ben Ayed","email":"data:image/png;base64,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","orcid":"","institution":"National Engineering School of Sousse, Sousse University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Mossaad","middleName":"Ben","lastName":"Ayed","suffix":""},{"id":131134892,"identity":"6e64bbba-a931-4016-b34b-7af75e442c9b","order_by":4,"name":"Mohamed Fterich","email":"","orcid":"","institution":"Northern Border University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Mohamed","middleName":"","lastName":"Fterich","suffix":""}],"badges":[],"createdAt":"2022-08-03 12:14:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1925622/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1925622/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":25796728,"identity":"c74dd20f-a826-41db-957a-bc9fedf142d8","added_by":"auto","created_at":"2022-08-29 14:26:14","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2243215,"visible":true,"origin":"","legend":"\u003cp\u003enear Zero Energy Building LUCIA\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/763fab2da88b5af47b79b3b3.png"},{"id":25797587,"identity":"ad1639d8-966a-48c4-954c-f973fe9362cd","added_by":"auto","created_at":"2022-08-29 14:36:14","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":156446,"visible":true,"origin":"","legend":"\u003cp\u003eEarth-Air Heat Exchanger (EAHX) Exterior and Interior views\u003c/p\u003e","description":"","filename":"Fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/c094daf27c6e6c620613b27b.jpg"},{"id":25796738,"identity":"7df386bf-36d8-4ba6-ab88-45975778a84b","added_by":"auto","created_at":"2022-08-29 14:26:14","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":50161,"visible":true,"origin":"","legend":"\u003cp\u003eThe temperature of the soil in the region of Valladolid at different depth\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/bb7f11a690b10d5a59a506f4.jpeg"},{"id":25797586,"identity":"263b4f51-5d6b-4489-9c04-61018ae28c60","added_by":"auto","created_at":"2022-08-29 14:36:14","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":45265,"visible":true,"origin":"","legend":"\u003cp\u003eAir temperature along the pipe length at different depth\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/b4e35278ca42c007f609114a.jpeg"},{"id":25797288,"identity":"f7ced100-470e-4ffc-9bc4-926131ab0b5d","added_by":"auto","created_at":"2022-08-29 14:31:14","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":27078,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of the air temperature difference between the inlet and the outlet of the EAHX in function of the pipe length (Tamb = 29 °C, Z = 8 m)\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/a4522e7096c259ef57284cb3.jpeg"},{"id":25796731,"identity":"728f97a2-13c5-4fc5-8b59-70c69215f387","added_by":"auto","created_at":"2022-08-29 14:26:14","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":38928,"visible":true,"origin":"","legend":"\u003cp\u003eInfluence of the pipe diameter on the outlet air temperature for an ambient Temperature 29 °C at a depth of 8 m\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/07d4b3767db0370787837ee9.jpeg"},{"id":25797584,"identity":"302d4cc6-ac48-413c-b99e-d68c71d6e7a2","added_by":"auto","created_at":"2022-08-29 14:36:14","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":39931,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of the mean efficiency of the EAHX in the function of the pipe length for different pipe diameter\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/c6cc3c21a9744c46278514ef.jpeg"},{"id":25796736,"identity":"27e83d0e-7b92-45fb-a02b-d2d15483c072","added_by":"auto","created_at":"2022-08-29 14:26:14","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":37802,"visible":true,"origin":"","legend":"\u003cp\u003eMonthly temperature of the ambient air, outlet air of the EAHX and the difference between them (Z = 2 m)\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/5b8efd7ee59baf520450600b.jpeg"},{"id":25796734,"identity":"433df010-8927-4cd3-8e42-2476f933013c","added_by":"auto","created_at":"2022-08-29 14:26:14","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":29177,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of the temperature difference between the EAHX inlet and outlet in function of the air velocity\u003c/p\u003e","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/a30c4994ad4f15075b0bc83d.jpeg"},{"id":25797289,"identity":"07917dfd-1571-4cdd-8664-3c6a820c7c8d","added_by":"auto","created_at":"2022-08-29 14:31:14","extension":"jpeg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":39313,"visible":true,"origin":"","legend":"\u003cp\u003eMonthly daily average cooling/heating potential and ambient temperature over a year\u003c/p\u003e","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/7cb950330bf71a16939c0c8a.jpeg"},{"id":26805520,"identity":"a2aeae67-b8e2-47cd-af1b-dfdda0038cbf","added_by":"auto","created_at":"2022-09-22 06:59:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2266766,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/fe124683-20ec-4010-89f7-7ec87d071f99.pdf"},{"id":25797285,"identity":"90a217bd-7db0-4c4e-91d5-5a6c08887bd4","added_by":"auto","created_at":"2022-08-29 14:31:14","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":233309,"visible":true,"origin":"","legend":"","description":"","filename":"AG.jpg","url":"https://assets-eu.researchsquare.com/files/rs-1925622/v1/d53a870c6cfad83465b5d86d.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Performance analysis of an Earth-Air Heat Exchanger applied to the ventilation of a near Zero Energy Building","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAt the European Union level, commercial and residential buildings account for more than 40% of the total global primary energy consumption, contributing to approximately 24% of European greenhouse gas emissions \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. As a result, reducing the building's energy needs could lead to a 20% reduction in their environmental impacts \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The European Union (EU) introduced specific measures to reduce energy consumption in the construction sector with the Energy Performance of Buildings Directive (EPBD) in 2002 \u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTherefore, near Zero Energy Buildings (nZEBs) appear to have a much higher energy performance than conventional buildings. Many studies \u003csup\u003e45\u003c/sup\u003e proved that the nZEB reduces energy consumption and helps decrease the environmental pollution. Many countries or institutions with ambitious goals for future energy consumption are trying to adopt nZEBs as the main target for their future building energy, such as the US Department of Energy's Building Technology Program and the European Union's Buildings Energy Performance Directive \u003csup\u003e67\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe building energy consumption for cooling and heating has increased in the last years. For that, the Heating, Ventilation and Air-Conditioning (HVAC) systems are responsible for about half of the energy consumed in buildings \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. When the ambient air temperature decreases during winter or rises during summer to an undesirable value, it's important to consider an energy source for improving the thermal comfort by maintaining the indoor air temperature between 22 and 27\u0026deg;C \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eVarious passive heating and cooling systems are available for building thermal management to reduce this important air-conditioning demand. These systems are characterized by their advantage of consuming almost negligible energy compared to conventional ones. We mention, among them, the Earth Air Heat Exchanger (EAHX), which has the benefits of reducing both the energy consumption for space cooling and heating and the CO2 emission in the sector of buildings. Its capital cost is high, but its operating cost is lower than the conventional active HVAC system. Therefore, the EAHX can yield considerable savings during the system lifecycle \u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. As its name suggests, this exchanger uses the earth as a heat source. This device consists of generally many pipes buried at a certain depth underground where the soil temperature remains fairly constant over the year. The ambient air is pumped into the underground pipes by a fan or a pump. During its passage along the pipes, it loses/absorbs the heat in exchange with the soil surrounding the pipes. Therefore, the air temperature becomes lower/higher. This heat exchange produces cooling effect in summer and heating effect in winter \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe performance of an EAHX depends on the following properties: the diameter and length of the pipes, the depth of the system burial, the flow rate of the air, the pipes' material, and the soil's thermal characteristics \u003csup\u003e1213\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThroughout the year, the underground temperature remains relatively constant below a certain depth due to the soil's high thermal inertia. Moreover, as the depth increases, the effect of the ground surface temperature fluctuations is reduced. Also, at a sufficient depth, the underground temperature is always higher than the temperature of the outside air in winter and lower than in summer. This is due to the time lag between the temperature variations at the ground's surface and below the ground \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn summer, warm air releases heat to buried pipes by convection, which will be dissipated to the ground by conduction. Afterward, cool air flows from the heat exchanger into the building space to create the desired thermal conditions. In winter, a heat transfer will be occurred from the surrounding ground to the pipes by conduction, and then when the cold air flows through the buried pipes, this heat will be transferred to the air by convection, increasing the supply air temperature. As the air rises, it dissipates heat into the building rooms. The difference between the outside air temperature and the ground temperature is considered as a pre-heating mechanism in winter and pre-cooling in summer \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIf the outgoing air temperature is relatively sufficient and the EAHX is well designed, it can be used directly for space heating/cooling. However, it can be further heated/cooled by either passing through conventional air conditioners or other HVAC systems \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe EAHX has many advantages, mentioned among them: long-term cost-effectiveness, high efficiency, good air quality, simple equipment required, easy control, stable capacity, low maintenance costs, noise-free, and environment friendly \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe estimation of the heat transfer rate and maximum air temperature are two essential indicators of the EAHX efficient working during the summer. The heat transfer rate and the large temperature drops improve the viability of the EAHX also. Thus, there must be a methodology to obtain the highest air temperature drop for space cooling applications.\u003c/p\u003e \u003cp\u003eDerbel and Kanoun \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e observed that the temperature difference between the inlet and outlet air of the EAHX increases by raising the pipe length, but the temperature change rate decreases. It was also observed that, by increasing the length of pipe, the heat transfer does not increase after a certain length, defined as saturation length \u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e that increases by increasing the air flow rate. Ahmed et al. defined in a parametric study that the length of the pipe is a dominating parameter among the other parameters (the diameter, the depth, the material, and the air velocity) that affect the EAHX thermal performance.\u003c/p\u003e \u003cp\u003eIt was identified in many studies that the drop/rise in air temperature increases by increasing the pipe length, but the effect of pipe length on temperature drop/rise decreases after a certain extent \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe difference between inlet and outlet air temperature decreases by increasing the airflow velocity. Moreover, the flowing air velocity significantly influences the EAHX system's performance \u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eNiu et al. \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e used the flowing flow velocities for cooling operations 0.5, 1.0, 1.5, 2, and 2.5 m/s, and they obtained that the drop rate of the air temperature was maximal at 0.5 m/s, and that's due to the high time of contact between air and pipe through the low velocity.\u003c/p\u003e \u003cp\u003eFor winter heating application, Bansal et al. \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e used these airflow velocities of 2, 3, 4, and 5 m/s and found that the temperature rise is obtained at the lowest velocity. However, 5 m/s corresponds to the maximum hourly heat gain. For a summer cooling study, Bansal et al. \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e found that the maximum air temperature drop is observed at ai velocity of 2 m/s and maximum hourly cooling at 5 m/s.\u003c/p\u003e \u003cp\u003eWu et al. \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e obtained similar results for cooling operations. The air temperature at the outlet increases by increasing the airflow velocity from 1 to 4 m/s, but the increase in the rate of mass flow guides to increasing heat transfer rate.\u003c/p\u003e \u003cp\u003eDubey et al. \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e found that the air temperature drops from 8 to 4\u0026deg;C, and COP (Coefficient Of Performance) also decreased from 6 to 3 by increasing the air velocity from 4 to 11 m/s. Bisoniya et al. \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e considered three different values of velocities (2, 3.5, and 5 m/s) for a 19.2 m length and 0.1 m diameter of an EAHX pipe.\u003c/p\u003e \u003cp\u003eThe observed minimum and maximum drops in air temperature were 11.3 and 12.9\u0026deg;C at 5 and 2 m/s airflow velocities.\u003c/p\u003e \u003cp\u003eYusof et al. \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e used different input parameters (airflow rate from 0.03 to 0.07 kg/s, ground temperature from 23 to 25\u0026deg;C, and inlet air temperature from 31 to 35\u0026deg;C) for the simulation of an EAHX exchanger under specific conditions. It was obtained that the maximal temperature drop was at the ground temperature of 23\u0026deg;C and the airflow rate of 0.03 kg/s, while at the ground temperature of 23\u0026deg;C, the air flow rate of 0.07 kg/s, the highest heat transfer rate (558.3 W) was achieved.\u003c/p\u003e \u003cp\u003eThe inlet air temperature plays an important role because the heat transfer rate between air and soil is governed by the temperature difference between ground and air. Kumar et al. \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e observed that the increase of the ambient air temperature leads to the rise of the outlet air temperature, but the amplitude significantly decreases. The outlet temperature varied from 23.8 to 27.9\u0026deg;C, while the inlet temperature varied from 27 to 45.9\u0026deg;C for an 80 m pipe length. Elminshawy et al. \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e used a laboratory-scale EAHX experimental setup under controlled operating parameters such as air flow rate, induced air temperature, and soil bulk temperature at three different compaction levels. It was observed that the cooling capacity of the EAHX system increases by 227% when the inlet air temperature is increased from 40 to 55\u0026deg;C.\u003c/p\u003e \u003cp\u003eNiu et al. \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e studied the impact of the inlet air temperature on the EAHX performance through a control volume model of 1-D steady-state. It was observed that the air temperature decline rate in EAHX was higher when the inlet air temperature was high. For the inlet air temperature 26, 28, 30, 32, and 34\u0026deg;C the lowest and highest air temperature decline rate was found for respectively 26 and 34\u0026deg;C.\u003c/p\u003e \u003cp\u003eVidhi et al. \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e presented an EAHX application condenser cooling of a supercritical Rankine cycle (SRC) power generation. A 2-D model was developed to analyze the effect of different parameters on air cooling in EAHX and the thermodynamic cycle efficiency. The diameter, the length and the installation depth were kept as respectively 25\u0026ndash;50 cm, 25-75m, and 1\u0026ndash;4 m.\u003c/p\u003e \u003cp\u003eIt was found that the SRC efficiency increases by increasing the length and depth of the pipe. However, the improvement rate in SRC efficiency is very low after a certain limit.\u003c/p\u003e \u003cp\u003eThe constructal design has been used widely to search for the optimal geometries that lead to the best performances. Rodrigues et al. \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e presented a numerical investigation based on the constructal design of various geometrical configurations of an EAHX to achieve the highest thermal potential. The results showed that the thermal potential improved up to 73% and 115% respectively, for cooling and heating by increasing the number of pipes for the same mass flow rate of air and the same occupied area.\u003c/p\u003e \u003cp\u003eThis paper provides a parametric study of an EAHX implemented in the near Zero Energy Building LUCIA situated in the city of Valladolid, Spain. Four main parameters were chosen, which are the depth in the soil, the pipe length, the pipe diameter, and the air velocity, in order to analyses their effects on the daily average cooling/heating potential over the whole year and the mean efficiency of the EAHX. The final aim is to find the maximal energy savings that can be reached using this exchanger in function of these parameters.\u003c/p\u003e"},{"header":"Case Study","content":"\u003cp\u003eThe studied Earth-Air Heat Exchanger (EAHX) is integrated in LUCIA building as one of the energy-efficient renewable energy systems that makes the LUCIA building considered as a nZEB. It has a useful space of 7500 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({m}^{2}\\)\u003c/span\u003e\u003c/span\u003e that is committed to research and development through laboratories, spaces for spin-offs and research areas.\u003c/p\u003e\n\u003cp\u003eThe LUCIA building of the University of Valladolid (UVA) has obtained certifications that endorse it as the most sustainable building in Europe, the entire Northern Hemisphere, and the second in the world.\u003c/p\u003e\n\u003cp\u003eThe sustainability of the building began with its own design, with a reduction in energy demand of up to 41 percent, to which have been added efficient systems to consume only the necessary energy. It also has \"clean energy\" generation systems such as geothermal, through Canadian wells that treat air, photovoltaic, or biomass cogeneration system.\u003c/p\u003e\n\u003cp\u003eThe building (see Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) is at the forefront of energy technologies, with many systems that provide this characteristic, allowing it to be used as a model to achieve the objectives using only renewable sources. It can be said that the building has a zero CO2 balance.\u003c/p\u003e\n\u003cp\u003eThe objective of the building is validated with a reduction of energy demand by more than 50% because of its bioclimatic design, increased insulation, passive ventilation, and other strategies. Compared to a standard building with similar characteristics, the savings produced in demand for electricity and gas reach 60%. In addition, it is important to highlight the transferring surplus energy possibility to neighboring buildings that facilitates the savings of these buildings that benefit from this energy input.\u003c/p\u003e\n\u003cp\u003eEnergy generation is based on a tri-generation system with biomass, through four rectified motors to work with poor gas, plus one that is in reserve, each with 112 kW of power, to which additionally, photovoltaic panels exist for the complete production of electricity using different technologies.\u003c/p\u003e\n\u003cp\u003eThe building's air conditioning system is covered by an Air Treatment Unit (ATU) that provides heating and cooling, along with the ventilation of the building. The dissipation system is made of 4-pipes fan coils that supply heating or cooling to each space of the building. There is the ability to use free-cooling in the ATU when demand is cold, and the ambient temperature is lower than that of the interior air of the building, increasing the systems thermal efficiency and reducing consumption through the geothermal exchanger EAHX. Additionally, free cooling can be provided by the night ventilation of the building. Therefore, the air conditioning of the building can be with or without free-cooling, and the same also for the EAHX.\u003c/p\u003e\n\u003cp\u003eThe EAHX system (see photos in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) consists of 52 tubes of 200 mm diameter, in \"staggered\" disposition, equivalent to a total area of 0,031 m2 with a length of 16 meters, providing a total passage section for all tubes of 1,63 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({m}^{2}\\)\u003c/span\u003e\u003c/span\u003e and a total exchange length of 832 m, circulating an average airflow of 15 000 m3/h. They are buried at a depth of 2.02, 2,72 and 3,42 m. The EAHX is designed to provide an estimated input in summer of 62 000 kWh/year and winter of 50 740 kWh/year. This will reduce emissions estimated at 21 000 kg CO2 during the 6264 hours of the building operation per year.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eThermo-physical properties of the air, soil, and pipe used in the simulation\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMaterial\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDensity\u003c/p\u003e\n\u003cp\u003e(\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({K}{g}/{{m}}^{3})\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eHeat capacity\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({J}/{K}{g}.{C}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eThermal conductivity\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(({W}/{m}.{C})\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAir\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1,225\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1006,43\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0,0242\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSoil\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3200\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e840\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e8,7\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ePipe\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e950\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1900\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0,5\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eThe ground where the EAHX tubes are positioned has a sufficient extension to provide the necessary heat recovery energy to facilitate energy reduction and project toward an efficiency improvement. This system allows for acclimating the outdoor air naturally before introducing it in the Air Treatment Unit. It is considered a bioclimatic device for renewable energy production. Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e represents the thermos-physical proprieties that are the density, the heat capacity and the thermal conductivity of the ambient air, the soil in the region where the study was carried out, and the pipe materiel.\u003c/p\u003e\n\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003eA. Modeling of the earth air heat exchanger EAHX\u003c/h2\u003e\n\u003cp\u003eThe soil temperature mathematical model is based on the theory of the heat conduction applied to a homogenous semi-infinite solid. The following differential equation gives the heat conduction in the ground:\u003c/p\u003e\n\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ1\" class=\"mathdisplay\"\u003e$$\\frac{{\\partial }^{2}T}{\\partial {Z}^{2}}-\\frac{1}{\\alpha }\\times \\frac{\\partial T}{\\partial t}=0$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\alpha\\)\u003c/span\u003e\u003c/span\u003e is the thermal diffusivity of the soil in \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({m}^{2}{s}^{-1}\\)\u003c/span\u003e\u003c/span\u003e which is given by:\u003c/p\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equa\" class=\"mathdisplay\"\u003e$$\\alpha = \\frac{{\\lambda }_{soil}}{{\\rho }_{soil}\\times {C}_{p soil}}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({\\lambda }_{soil}\\)\u003c/span\u003e \u003c/span\u003e is the thermal conductivity of the soil in \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(W{m}^{-1}{^\\circ C}^{-1}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({C}_{p soil}\\)\u003c/span\u003e\u003c/span\u003eis the soil specific heat in \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(J{Kg}^{-1}{^\\circ C}^{-1}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\rho }_{soil}\\)\u003c/span\u003e\u003c/span\u003e is the density of the soil in \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(Kg{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e, and z is the depth below the ground surface.\u003c/p\u003e\n\u003cp\u003eThe corresponding boundary conditions at z\u0026thinsp;=\u0026thinsp;0 is the following:\u003c/p\u003e\n\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ2\" class=\"mathdisplay\"\u003e$$T\\left(0,t\\right)= {T}_{mean}+ {A}_{s}\\times \\text{c}\\text{o}\\text{s}\\left(\\omega \\left(t -{t}_{0}\\right)\\right)$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\omega\\)\u003c/span\u003e\u003c/span\u003e is the frequency of the annual temperature wave and for the infinite depth z \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\to \\infty\\)\u003c/span\u003e\u003c/span\u003e, we obtain:\u003c/p\u003e\n\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ3\" class=\"mathdisplay\"\u003e$${T\\left(\\infty ,t\\right)= T}_{mean}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ4\" class=\"mathdisplay\"\u003e$$\\text{T}(\\text{z},\\text{t})={\\text{T}}_{\\text{mean }}+{\\text{A}}_{\\text{s}}\\times \\text{E}\\text{x}\\text{p}\\left(-\\left(\\text{z}\\right)\\sqrt{\\frac{\\pi }{365\\alpha }}\\right)\\times \\text{c}\\text{o}\\text{s}\\left(\\frac{2\\pi }{365}\\times \\left(\\text{t}-{\\text{t}}_{0}\\right)-\\left(\\frac{\\text{z}}{2}\\right)\\times \\sqrt{\\frac{365}{\\frac{\\text{T}}{\\alpha }}}\\right)$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({T}_{mean}\\)\u003c/span\u003e \u003c/span\u003e is the mean annual soil temperature, which can be calculated approximately from well water at a specific location, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({A}_{s}\\)\u003c/span\u003e\u003c/span\u003e is the temperature wave amplitude of the temperature at the soil surface (z\u0026thinsp;=\u0026thinsp;0), t is the day of the year and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({t}_{0}\\)\u003c/span\u003e\u003c/span\u003e is the day of the maximum temperature at the soil surface.\u003c/p\u003e\n\u003cp\u003eThe coefficient of the convective heat transfer in a pipe is defined by:\u003c/p\u003e\n\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ5\" class=\"mathdisplay\"\u003e$${\\text{h}}_{\\text{c}\\text{o}\\text{n}\\text{v}}=\\frac{\\text{N}\\text{u}\\times \\lambda }{\\text{D}}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe following equation calculates the Nusselt number:\u003c/p\u003e\n\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ6\" class=\"mathdisplay\"\u003e$$\\text{N}\\text{u}=\\text{0,0214}\\times \\left({\\text{R}\\text{e}}^{\\text{0,8}}-100\\right)\\times {\\text{P}\\text{r}}^{\\text{0,4}}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe Reynolds number and Prandtl number of the air inside the pipe are calculated by:\u003c/p\u003e\n\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ7\" class=\"mathdisplay\"\u003e$$\\text{R}\\text{e}=\\frac{{\\text{V}}_{\\text{a}\\text{i}\\text{r}}\\times {\\text{D}}_{\\text{i}}}{v}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equ8\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ8\" class=\"mathdisplay\"\u003e$$Pr=\\frac{v\\times \\rho \\times \\text{C}\\text{p}}{\\lambda }$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe following correlation gives the transferred heat:\u003c/p\u003e\n\u003cdiv id=\"Equ9\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ9\" class=\"mathdisplay\"\u003e$$\\varphi =\\dot{\\text{m}}\\times {\\text{C}\\text{p}}_{\\text{f}}\\times \\text{d}\\text{T}\\left(\\text{x}\\right)=\\frac{\\text{d}\\text{x}}{{\\text{R}}_{\\text{conv }}+{\\text{R}}_{\\text{pipe }}+{\\text{R}}_{\\text{soil }}}\\times \\left(\\text{T}\\right(\\text{z},\\text{t})-\\text{T}(\\text{x}\\left)\\right)$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e9\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe soil and pipe thermal resistance are expressed respectively as:\u003c/p\u003e\n\u003cdiv id=\"Equ10\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ10\" class=\"mathdisplay\"\u003e$${\\text{R}}_{\\text{soil }}=\\frac{1}{{\\lambda }_{\\text{soil }}\\times 2\\times \\pi }\\times \\text{l}\\text{n}\\left({\\text{R}}_{(\\text{z},\\text{t})}/{\\text{r}}_{\\text{e}}\\right)$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e10\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equ11\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ11\" class=\"mathdisplay\"\u003e$${\\text{R}}_{\\text{pipe }}=\\frac{1}{{\\lambda }_{\\text{pipe }}\\times 2\\times \\pi }\\times \\text{l}\\text{n}\\left({\\text{r}}_{\\text{e}}/{\\text{r}}_{\\text{i}}\\right)$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e11\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhile the convective thermal resistance between the air in the pipe and the internal surface of the pipe is expressed as:\u003c/p\u003e\n\u003cdiv id=\"Equ12\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ12\" class=\"mathdisplay\"\u003e$${\\text{R}}_{\\text{c}\\text{o}\\text{n}\\text{v}}=\\frac{1}{{r}_{i}\\times {\\text{h}}_{\\text{c}\\text{o}\\text{n}\\text{v}}\\times 2\\times \\pi }$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e12\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe EAHX total thermal conductance is then defined by:\u003c/p\u003e\n\u003cdiv id=\"Equ13\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ13\" class=\"mathdisplay\"\u003e$${G}_{Tot}= \\frac{1}{{R}_{conv}+{R}_{pipe}+{R}_{soil}}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e13\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe energy balance is obtained by combining the two equations (\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e) and (\u003cspan class=\"InternalRef\"\u003e13\u003c/span\u003e):\u003c/p\u003e\n\u003cdiv id=\"Equ14\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ14\" class=\"mathdisplay\"\u003e$$\\frac{dT\\left(x\\right)}{T(z,t)-T\\left(x\\right)}=\\frac{{G}_{Tot}}{\\dot{m}\\times {C}_{pf}}\\times dx$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e14\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eBy making the integral of the Eq.\u0026nbsp;(\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003e), we obtain:\u003c/p\u003e\n\u003cdiv id=\"Equ15\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ15\" class=\"mathdisplay\"\u003e$$-\\text{l}\\text{n}\\left(\\text{T}\\right(\\text{z},\\text{t})-\\text{T}(\\text{x}\\left)\\right)=\\frac{{\\text{G}}_{\\text{T}\\text{o}\\text{t}}}{\\text{m}\\times {\\text{C}\\text{p}}_{\\text{f}}}\\times \\text{x}+\\text{ Cte}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e15\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eFor the boundary condition at the surface of the ground, the temperature is given by:\u003c/p\u003e\n\u003cdiv id=\"Equ16\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ16\" class=\"mathdisplay\"\u003e$$T\\left(0\\right)= {T}_{amb}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e16\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWe obtain by replacing \"Cte\" by its expression found from the boundary equation in Eq.\u0026nbsp;(\u003cspan class=\"InternalRef\"\u003e15\u003c/span\u003e):\u003c/p\u003e\n\u003cdiv id=\"Equ17\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ17\" class=\"mathdisplay\"\u003e$$\\text{l}\\text{n}\\left(\\text{T}\\left(\\text{x}\\right)-\\text{T}(\\text{z},\\text{t})/\\left({\\text{T}}_{\\text{a}\\text{m}\\text{b}}-\\text{T}(\\text{z},\\text{t})\\right)\\right)=\\frac{-{\\text{G}}_{\\text{T}\\text{o}\\text{t}}}{\\dot{\\text{m}}\\times {\\text{C}\\text{p}}_{\\text{f}}}\\times \\text{x}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e17\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eAt the outlet of the pipe, the air temperature is given by the following expression:\u003c/p\u003e\n\u003cdiv id=\"Equ18\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ18\" class=\"mathdisplay\"\u003e$${\\text{T}}_{\\text{s}}={\\text{T}}_{\\text{a}\\text{m}\\text{b}}+\\left(\\text{T}(\\text{z},\\text{t})-{\\text{T}}_{\\text{a}\\text{m}\\text{b}}\\right)\\times \\left(1-Exp(\\frac{-{\\text{G}}_{\\text{T}\\text{o}\\text{t}}\\times \\text{m}\\times \\text{f}}{\\text{m}}\\times \\text{x})\\right)$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e18\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe mass flow rate of the air is expressed as follows:\u003c/p\u003e\n\u003cdiv id=\"Equ19\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ19\" class=\"mathdisplay\"\u003e$$\\dot{m}= {\\rho }_{a}{V}_{a}\\pi {D}_{i}^{2}/4$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e19\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eBy using the Fourier series, the ambient temperature daily variation is as follows:\u003c/p\u003e\n\u003cdiv id=\"Equ20\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ20\" class=\"mathdisplay\"\u003e$${\\text{T}}_{\\text{a}\\text{m}\\text{b}}\\left(\\text{t}\\right)=\\frac{{\\text{T}}_{max}+{\\text{T}}_{min}}{2}+\\frac{{\\text{T}}_{max}-{\\text{T}}_{min}}{2}\\text{cos}\\left(\\frac{\\pi }{12}\\left(t-14\\right)\\right)$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e20\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe following equation gives the mean daily thermal efficiency of the EAHX:\u003c/p\u003e\n\u003cdiv id=\"Equ21\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ21\" class=\"mathdisplay\"\u003e$${\\eta }_{\\text{mean }}=\\frac{\\sum _{\\text{i}=1}^{24} \\left({\\text{T}}_{\\text{a}\\text{m}\\text{b}}\\left(\\text{i}\\right)-{\\text{T}}_{\\text{out }}\\left(\\text{i}\\right)\\right)}{\\sum _{\\text{i}=1}^{24} \\left({\\text{T}}_{\\text{a}\\text{m}\\text{b}}\\left(\\text{i}\\right)-{\\text{T}}_{\\text{soil }}\\right)}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e21\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe average daily cooling potential is calculated according to the following equation:\u003c/p\u003e\n\u003cdiv id=\"Equ22\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ22\" class=\"mathdisplay\"\u003e$${\\text{Q}}_{\\text{c}\\text{o}\\text{o}\\text{l}}=\\sum _{\\text{i}=1}^{24} \\dot{\\text{m}}\\text{C}\\text{p}\\left({\\text{T}}_{\\text{a}\\text{m}\\text{b}}\\left(\\text{i}\\right)-{\\text{T}}_{\\text{out }}\\left(\\text{i}\\right)\\right)$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e22\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe pipe is divided into 45 sections along the length, and all the previous equations are solved sequentially through sections from the inlet to the outlet of the EAHX.\u003c/p\u003e\n\u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\n\u003ch2\u003eB. MODEL VALIDATION\u003c/h2\u003e\n\u003cp\u003eThe model was validated using experimental data before carrying out the parametric study. The LUCIA building is equipped with measuring probes of energy variables such temperature, humidity, enthalpy, radiation, energy consumption, etc... The monitoring system allows a data recording with a frequency of taking measurements between 5 and 10 minutes, which provides a wide database for further analysis. Thanks to this dynamic monitoring management system, it is possible to determine the monthly, daily, or even hourly energy savings provided by the different energy systems installed, positioning the LUCIA building as a benchmark for avant-garde energy technology.\u003c/p\u003e\n\u003cp\u003eBefore carrying out the parametric analysis, the model is validated using the experimental data reported from some data logger installed at the inlet and the outlet of the EAHX. Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e represents the relative error and the outlet temperature for the experimental and the numerical results. As it can be observed that the relative error is below 4.3%.\u003c/p\u003e\n\u003cp\u003eIt was calculated through the following equation:\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({\\epsilon }\\)\u003c/span\u003e \u003c/span\u003e \u003cstrong\u003e=\u003c/strong\u003e \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{\\left|{{T}{o}{u}{t}}_{{e}{x}{p}}-{{T}{o}{u}{t}}_{{s}{i}{m}}\\right|}{{{T}{o}{u}{t}}_{{e}{x}{p}}} \\times 100\\)\u003c/span\u003e\u003c/span\u003e (23)\u003c/p\u003e\n\u003cp\u003eThus, we can conclude that the thermal performance of the EAHX can be predicted by our model.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eModel validation with the obtained experimental results\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{T}{i}{n}}_{ }\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{T}{o}{u}{t}}_{{e}{x}{p}}\\)\u003c/span\u003e\u003c/span\u003e (\u0026deg;C)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{T}{o}{u}{t}}_{{s}{i}{m}}\\)\u003c/span\u003e\u003c/span\u003e (\u0026deg;C)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eRelative error \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }\\)\u003c/span\u003e\u003c/span\u003e (%)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e11.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e11.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.63\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e12.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e12.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.6\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e13.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e13.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.64\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e14.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e14.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.06\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e25\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e16.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e16.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.34\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e18.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e18.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.09\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"Results And Discussion","content":"\u003cp\u003eIn this section, a deep discussion about the performance of the proposed exchanger is detailed.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e shows the soil's temperature in the Valladolid region at different depths. We observed that the soil temperature sine wave decreases by rising the underground depth until the temperature becomes relatively constant at a depth of 8 m, allowing us to use the ground as a heat source.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e shows the air temperature variation along the length of the pipe at different depths. In the beginning, the air temperature decreases until it becomes equal to the temperature of the soil. It is noted at a depth of 8 m (Z\u0026thinsp;=\u0026thinsp;8) that the temperature of air drops from the maximum ambient air temperature corresponding to July, which is around 29 \u0026deg; C to reach the temperature of the soil, which is about 13\u0026deg;C in the region of Valladolid. Moreover, the air temperature at the outlet becomes lower as the depth is increased. At a depth of 1 m, the difference of the air temperature between the EAHX inlet and outlet is about 3\u0026deg;C that is not sufficient for the cooling of the building. It is also noticed that the air temperature inside the pipe is constant at a certain length (L\u0026thinsp;=\u0026thinsp;20 m).\u003c/p\u003e\n\u003cp\u003eAs we can see in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the difference in the air temperature between the outlet and inlet of the EAHX as a function of heat exchanger tube length at a maximum ambient air temperature of 29\u0026deg;C in July. As can be seen in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, the difference in the air temperature between the entrance and exit of the EAHX increases significantly over the entire pipe length. Still, starting from a length of around 20 m, the increase in the temperature difference is no longer significant, and it becomes almost constant (16\u0026deg;C).\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e shows the variation of the outlet air temperature along the pipe length for different pipe diameters at a depth of 8 m. As can be seen in this figure, the diameter has an important impact on the outlet temperature. We deduced that the smaller diameter corresponds to the longer pipe length needed to reach the soil temperature at the outlet of the EAHX and vice versa.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e shows the average efficiency of the geothermal heat exchanger as a function of the length of the underground piping at a depth of 8 m. In this figure, it is observed that at the beginning, the two parameters rise in length significantly, but after 20 m, the increase is no more significant almost.\u003c/p\u003e\n\u003cp\u003eWe observe also that, more the pipe diameter is higher, more than the mean efficiency reaches its maximum at a shorter pipe length.\u003c/p\u003e\n\u003cp\u003eWe can deduce that the EAHX performance that is considered a device for the air conditioning is principally influenced by the temperature of the soil and the temperature of the air ambient since these two values of temperature change from month to month. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e shows the monthly variation of the ambient air temperature over a year, the air at the outlet, and the difference between both. It can be deduced also that the maximal difference of the air temperature between the inlet and outlet air is around 8.2\u0026deg;C and 7.3\u0026deg;C for respectively July and August, while the minimal difference is around 0.6\u0026deg;C and 0.8\u0026deg;C for respectively November and March. We can conclude from these results that the EAHX is efficient in the summer and winter, while it is not for the spring and autumn.\u003c/p\u003e\n\u003cp\u003eIt can be seen from Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e that the temperature difference between the outlet and the inlet decreases with the increasing of the air velocity inside the pipes. This drop is due to the diminution of the thermal transfer time between the pipe surface and the air passed through it.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e presents the monthly temperature of the ambient air and cooling/heating performance potential for EAHX over a year. It can be observed that the daily cooling capacity potential peaks at 1.75 kWh, corresponding to July when the ambient air temperature is at its highest. In October, the cooling performance potential for EAHX was a minimum of 0.16 kWh. The negative values for cooling potential shown in the figure represent the potential for daily heating when the ambient air temperature is lower than the soil temperature. The maximum daily heating potential values are 1.4 and 1.5 kWh, respectively, corresponding to December and January, when the ambient air temperature is the lowest. In addition, the corresponding thermal potential minimums in October and May are 0.25 and 0.3 kWh, respectively.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn the Valladolid region in Spain, the optimum depth for the EAHX used in the air conditioning applications is 8 m, which was determined using a special MATLAB program based meanly on the criteria of a constant ground temperature per year. The EAHX is then simulated using Valladolid climate conditions. The developed model was firstly validated by using the experimental results taken by the monitoring system installed in the Air Treatment Unit. Then, a parametric analysis was carried out to study and evaluate the effect of the buried pipe length and diameter on the outlet air temperature. We can summarize the main conclusions here:\u003c/p\u003e \u003cp\u003eIn the beginning, the air temperature in the pipe dropped and decreased significantly along the pipe until it became equal to the ground temperature at about 20 m. At 8 m depth, the air temperature drops from a maximal ambient air temperature value 29\u0026deg;C, corresponding to July, until it reaches a constant temperature of around 12\u0026deg;C.\u003c/p\u003e \u003cp\u003eIn August, the maximum difference between ambient air temperature and the outlet air temperature of the EAHX reached approximately 12\u0026deg;C. The EAHX used in this analysis had a maximal value of the daily cooling potential of about 1.75 kWh in July.\u003c/p\u003e \u003cp\u003eThanks to the EAHX, the cooling/heating energy savings for one year is approximately 152 MWh. It complements the energy sustainability of the building and directly implies a significant reduction in CO2 emissions to the atmosphere and contribute to a significant reduction in environmental pollution.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eACKNOWLEDGMENTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors extend their appreciation to the Deputyship for Research and Innovation, Ministry of Education in Saudi Arabia for funding this research work through the project number \u0026ldquo;IF_2022_nbu_4093. The authors gratefully thank the Prince Faisal bin Khalid bin Sultan Research Chair in Renewable Energy Studies and Applications (PFCRE) at Northern Border University for their support and assistance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAVAILABILITY OF DATA AND MATERIALS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eEurostat T. Final energy consumption by sector. \u003cem\u003eDostupno na https//www\u003c/em\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003eecondb com/dataset/TSDPC320/\u003c/span\u003e\u003cspan address=\"http://econdb com/dataset/TSDPC320/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003cem\u003e[Pristupljeno 26-lip-2018]\u003c/em\u003e. Published online 2014.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eD\u0026rsquo;Agostino D. Assessment of the progress towards the establishment of definitions of Nearly Zero Energy Buildings (nZEBs) in European Member States. J Build Eng. 2015;1:20\u0026ndash;32.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUnion E. Directive 2002/91/EC of the European Parliament and of the Council of 16 December 2002 on the energy performance of buildings. Off J. Published online 2002.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlnaser NW. Building integrated renewable energy to achieve zero emission in Bahrain. Energy Build. 2015;93:32\u0026ndash;39.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDumont O, Quoilin S, Lemort V. Experimental investigation of a reversible heat pump/organic Rankine cycle unit designed to be coupled with a passive house to get a Net Zero Energy Building. 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Geothermics. 2019;77:12\u0026ndash;23.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMihalakakou G, Souliotis M, Papadaki M, et al. Applications of earth-to-air heat exchangers: A holistic review. Renew Sustain Energy Rev. Published online 2021:111921.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCongedo PM, Baglivo C, Bonuso S, D\u0026rsquo;Agostino D. Numerical and experimental analysis of the energy performance of an air-source heat pump (ASHP) coupled with a horizontal earth-to-air heat exchanger (EAHX) in different climates. Geothermics. 2020;87:101845.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJakhar S, Misra R, Soni MS, Gakkhar N. Parametric simulation and experimental analysis of earth air heat exchanger with solar air heating duct. Eng Sci Technol an Int J. 2016;19(2):1059\u0026ndash;1066.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBenhammou M, Draoui B. 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Int J Eng Trends Technol. 2013;4(6):2463\u0026ndash;2467.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBisoniya TS, Kumar A, Baredar P. Cooling potential evaluation of earth-air heat exchanger system for summer season. Int J Eng Tech Res. 2014;2(4):309\u0026ndash;316.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYusof TM, Ibrahim H, Azmi WH, Rejab MRM. Thermal analysis of earth-to-air heat exchanger using laboratory simulator. Appl Therm Eng. 2018;134:130\u0026ndash;140.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar R, Kaushik SC, Garg SN. Heating and cooling potential of an earth-to-air heat exchanger using artificial neural network. Renew Energy. 2006;31(8):1139\u0026ndash;1155.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eElminshawy NAS, Siddiqui FR, Farooq QU, Addas MF. Experimental investigation on the performance of earth-air pipe heat exchanger for different soil compaction levels. Appl Therm Eng. 2017;124:1319\u0026ndash;1327.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVidhi R, Goswami DY, Stefanakos E. Supercritical Rankine cycle coupled with ground cooling for low temperature power generation. Energy Procedia. 2014;57:524\u0026ndash;532.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRodrigues MK, da Silva Brum R, Vaz J, Rocha LAO, dos Santos ED, Isoldi LA. Numerical investigation about the improvement of the thermal potential of an Earth-Air Heat Exchanger (EAHE) employing the Constructal Design method. Renew Energy. 2015;80:538\u0026ndash;551.\u003c/span\u003e\u003c/li\u003e\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":"","lastPublishedDoi":"10.21203/rs.3.rs-1925622/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1925622/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIntroducing near Zero Energy Buildings (nZEBs) in the European Union involves integrating new renewable energy technologies into buildings. Geothermal energy is one of them that can be exploited through the application of the Earth-Air Heat Exchanger (EAHX). It is basically constituted of a series of pipes buried underground at a particular depth. It utilizes the soil as a heat source or sinks to supply cooling or heating to the building. This type of exchanger can offer many advantages in terms of energy savings for the air-conditioning requirements and for assuring the indoor thermal comfort. This paper presents a performance analysis of an EAHX applied to the ventilation of a near Zero Energy Building situated in Spain. The proposed considered the thermo-physical proprieties of the soil in the region under investigation. The purpose is to study the effect of changing the depth in the ground, the pipe length, the pipe diameter, and the air velocity on the outlet air temperature. The mean efficiency of the EAHX is detailed then. The numerical model is implemented using Matlab environment. Results showed that, for specific parameters, the daily average cooling capacity can reach 1.7 KWh, and the EAHX can provide an energy saving of approximately 152 MWh for one year.\u003c/p\u003e","manuscriptTitle":"Performance analysis of an Earth-Air Heat Exchanger applied to the ventilation of a near Zero Energy Building","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-08-29 14:26:12","doi":"10.21203/rs.3.rs-1925622/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":"1ac8bcf6-3c6a-47d7-8bdd-ac485e7dde62","owner":[],"postedDate":"August 29th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2022-09-22T06:59:34+00:00","versionOfRecord":[],"versionCreatedAt":"2022-08-29 14:26:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-1925622","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1925622","identity":"rs-1925622","version":["v1"]},"buildId":"FbvkV6FR0MCFSLy54lSbu","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}