Possible explanations for the gap between calculated and measured energy consumption of new houses

The overall aim to reduce CO2 emissions has brought the energy requirements for new houses into focus. The question is whether the stepwise tightening of the energy requirements for new houses has had the expected impact on the actual realized energy consumption. In the news media, headlines at regular intervals state that new houses do not perform as expected with regard to energy consumption based on a simple comparison to the building class (energy frame). The gap is sometimes explained by a higher indoor temperature than used in the standard calculation or more generally by resident's “careless” energy behavior. However, this may not be the full explanation and there may be other reasons for the difference. Or more specifically: Does the theoretical calculated energy demand, based on standard assumptions and without taking into account the effect of variations in e.g. hot water consumption, internal heat gains or construction faults, underestimate the actual energy consumption in general? As an example, the registered measured energy consumption for heating and hot water of approximately 800 new houses was compared to the calculated energy demand. The analyzed energy consumption data show that a significant share of the houses consumes more energy in a simple comparison with the theoretical energy frame based on standard assumptions. The objective of the study was to find and evaluate possible explanations/reasons for this gap between the theoretical calculated energy demand based on standard assumptions and the real-life registered measured energy consumption for new houses. It includes an evaluation of the possible impact on the energy demand caused by deviations from the standard assumptions for a series of parameters like indoor temperature, hot water consumption, internal heat gains, U-values, thermal bridges and ventilation rates.