Understand, simulate, anticipate and correct performance gap in NZEB refurbishment of residential buildings

The gap between expected and real energy performance of new or newly refurbished residential buildings was an unexpected mine in the way towards a 2000 W society in Switzerland. Previous research has contributed to understand and quantify this gap by providing knowledge for the extent and amplitude of the problem. Now it is necessary to go into detail understanding of this phenomenon, in order to anticipate and correct the problem. This article analyses statistical findings of heating energy consumption in a whole Swiss canton - Geneva - and shows that results of specific research works on limited apartment residential building samples can be generalised. We show that the performance gap may be simulated with simple common tools, used for compliance energy calculations by applying the right conditions of use. We introduce the notion of "standard", "realistic" and "out of control" conditions of use. We simulate energy performance of the most common refurbishment actions on a standard existing residential building using these values and we compare the results with observed values on case studies or statistical samples. We show that simulations with the "out of control" conditions predict the performance gap of refurbished buildings. We may also observe that there are combinations of refurbishment works subject to higher or lower risk of performance gap. Simulating the performance deviation, we show which conditions of use must be better controlled to anticipate and limit the problem.