Energy Performance Gaps in Office Buildings: Long-Term Monitoring of Ventilation Systems Operation

Improving energy efficiency in the buildings sector is one of the key elements in achieving the decarbonisation targets. Despite the fact that much is being done at policy level, practice shows, that buildings, which are designed and built as energy-efficient, often fail to achieve the desired efficiency goals. This is particularly acute in non-residential buildings, e.g. offices. A common issue in existing office buildings is the level of systems’ automation, which is often too low and/or management strategies are inefficient leading to waste of energy.The aim of this study is to demonstrate, based on long-term monitoring of 4 offices, to what extent mechanical ventilation leads to energy performance gaps in office buildings and to estimate the resulting environmental impact over the life cycle of the building. The monitored buildings may be considered as relatively new. The monitored parameters were: occupancy and indoor parameters, mainly concentrating on the relation between real occupancy and CO2 concentration, as parameter representing ventilation system performance. Monitoring results showed, that most of the time buildings were over ventilated - ventilation rates were not corresponding to real demand, causing energy waste. The actual occupancy in the monitored buildings was much lower than the design, for two buildings it has never reached 50% of the design value. The simulation results demonstrated, that the primary energy demand after simply applying the reduction of ventilation air flow rate based on more realistic occupancy decreased by 30%. This gave an effect of 12.5% of annual CO2 emission reductions of the building.The results contribute to closing the knowledge gap on why the building sector is struggling to move towards decarbonisation. The results of this work are of great practical value as they show investors, designers and managers the importance of a properly automated and managed building. The practical value of the results is added by the fact that the analysis covers data from the pre-pandemic to the post-pandemic period of Covid-19, which makes it possible to assess the peculiarities of the management of the systems in the light of the new realities of a changed work culture and office occupancy.