The gap between plan and practice: Actual energy performance of the zero-energy refurbishment of a terraced house

Pret-a-Loger, TU Delft’s entry to the Solar Decathlon Europe 2014 (SDE2014), demonstrated the conversion of a common terraced house to energy neutrality, whilst adding value to its living quality. The house was retrofitted according to principles of smart & bioclimatic design, using local circumstances intelligently in the sustainable redesign. Basis of the Pret-a-Loger concept is a new skin around the house: thermal insulation in the facade and roof, a greenhouse structure to the south-east, and phase change materials in the crawlspace. The project received a lot of acclaim and was awarded five prizes at SDE2014. During SDE2014, under the circumstances of Versailles, France, the Pret-a-Loger house proved to be energy producing, and simulations indicated that over a year’s period it would be net zero energy. In spite of these promising results, there are several ways in which a zero-energy (re)design may perform differently than predicted, also in the case of Pret-a-Loger. Firstly, there may be a difference between design and realisation. Secondly, simulation models may not predict the actual performance correctly. Thirdly, user behaviour can be a decisive factor. With Pret-a-Loger, the first category could be monitored by the team itself. The fact that the house was constructed three times could however cause small construction deviations from the ideal situation. The second category is the main topic of the research project presented in this paper. Realtime measurements in the house (reconstructed at the TU Delft campus) are executed to validate simulations. Different user behaviour is applied to test differences in actual energy performance, providing useful insight for millions of homes. The results show, for building envelope characteristics, there is no significant difference between the simulations and reality.. A higher variation in the predicted energy can be accounted to user behaviour, specifically to experienced comfort and specific user actions.