Differences in Calculations of Annual Heating and Cooling Energy Need Carried out by Modified Simple Hourly Method and Dynamic Simulations

This paper presents differences in calculations of annual heating and cooling energy need performed by numerical dynamic simulations software IDA ICE and those carried out by the modification of simple hourly method from EN ISO 13790 EN ISO 13790, widely used for determining building energy need. A simple model of a nearly-zero energy building was created and all heat gains and set-points that could lead to a mismatch in initial or boundary conditions were analysed. The impact of those on the annual heating and cooling energy need was examined by adding and/or removing every single one of them. Boundary conditions in numerical dynamic simulations were set up to match those in simple hourly method. Such an approach enables evaluation of differences in results and definition of their origin. The comparison of results has shown that in most cases, annual energy need for heating and cooling calculated using numerical dynamic simulations software differs from that calculated using EN ISO 13790. Among the others, more detailed heat accumulation model of heat gains in building’s envelope in IDA ICE software was marked as the main reason. Fact that solar heat gains seem to be underestimated by EN ISO 13790 and differences in heat transfer towards ground contribute to the differences in results as well.