Energy performance evaluation of a nearly Zero Energy Building and the reasons for the performance gap between expected and actual building operation

Abstract

As energy standards focus on reducing energy use in new buildings, attention is drawn to the gap between the expected and actual building operation and energy performance. This performance gap can be associated with the building construction, its systems, its unbalanced operation, the assumptions on occupancy profiles during the design phase, or the users’ interaction with the systems’ operation and control. This work focuses on a nearly zero-energy (nZEB) single-family house located in central Denmark. The analysis of indoor environment and energy use is based on year-long data monitoring. The reasons for the deviation between the expected and actual energy use are suggested. The indoor environmental quality is analyzed to verify the compliance with the standards. The European recommendation for the yearly primary energy use of new single-family houses is 50 – 65 kWh/m2. For the current case, the simulation tool Be18 gives a result of 30.8 kWh/m2 for the design phase. However, the actual energy use is measured to be 58.2 kWh/m2. The sensibility of nZEBs to such imbalances can lead to houses that do not function as intended. It is thus crucial to investigate further the causes of these disparities in order to bridge the gap between expected and final energy use in dwellings.

The Role of Occupants in Buildings’ Energy Performance Gap: Myth or Reality?

“…The characteristics reported are generally inconsistent across the studies due to differences in research foci and data availability issues. The most reported characteristics are the number of people [9,10,15,26,33,49,59,60,[79][80][81], age [9,10,15,17,21,26,33,59,77,80,81], household composition [6,7,12,14,17,30,59,77,80,82,83], and income [9,10,21,26,29,33,79,80]. Additional characteristics reported were ownership status [9,10,26,79,80,84] and education levels [17,21,…”

“…The most common sources of energy data were bills (electricity, gas consumption) and data from principal meters and submeters. There were very few studies (7%) that had dedicated energy use metering [15,37,66,83,87].…”

“…Most of the publications (76%) used aggregated annual data on energy use, while 10% of studies used monthly data. The rest of the studies (14%) included high-resolution data, involving 5 min intervals [15,83], 15 min intervals [38,58,74], 30 min intervals [35], and daily measurements [22,48,89]. In terms of spatial granularity, studies on non-residential buildings focused on reporting energy use mostly per building and rarely per floor [51].…”

“…Indoor conditions were monitored in 20% of the selected studies to evaluate discrepancies between assumed and actual indoor conditions. Air temperature was the most commonly monitored indoor parameter to investigate the performance gap, followed by the relative humidity [7,10,12,[14][15][16]49,72] and the CO 2 concentration levels [10,[14][15][16]27,35,53,54,83,91], which were often used as a proxy for occupancy. Indoor environmental conditions were usually monitored via sensors placed in dwellings, but rarely in non-residential buildings.…”

“…Indoor environmental conditions were usually monitored via sensors placed in dwellings, but rarely in non-residential buildings. Only two studies monitored operative temperature [83,91] and only one TVOCs [27]. In a third of the studies, the deviation of the actual measured indoor temperatures from the assumed set-points was used to explain the performance gap.…”