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P.P. Housez, U. Pont, A. Mahdavi:
"A comparison of projected and actual energy performance of buildings after thermal retrofit measures";
Talk: CESBP - 2nd Central European Symposium on Building Physics, Wien, Österreich; 2013-09-09 - 2013-09-11; in: "Proceedings of the 2nd Central European Symposium on Building Physics 9-11 September 2013, Vienna, Austria", A. Mahdavi, B. Martens (ed.); ÖKK-Editions, 1 (2013), ISBN: 978-3-85437-321-6; 229 - 236.

This paper addresses the discrepancies between projected and actual energy performance of thermally retrofitted buildings. It is based on the detailed observation of seven recently thermally retrofitted
residential buildings in Austria. These include five multifamily residences in Vorarlberg, the upper level of a duplex in Lower-Austria, and a residential complex for the elderly in Styria. During the heating season 2009/2010 (1st October - 30th April), indoor temperature and relative humidity were measured and logged in
these buildings. For each building, the actual energy use during this period was derived based on bills for gas and electrical power. Additionally, existing energy calculations (energy certificates) were examined. In six of seven cases, a large discrepancy between projected and actual space heating demand was noted. To explore
the reason for this discrepancy, for each of the buildings an energy certificate was generated and a detailed thermal simulation was conducted. Thereby, the main input parameters for energy calculations (air change rate, indoor air temperature, outside air temperature, internal gains) were taken into consideration. If all of
these parameters are set to the standard (default) values as suggested by Austrian standards, the above mentioned
discrepancy cannot be explained. Measurements in the buildings, as well as interviews with the building´s inhabitants implied that standard-based input data assumptions were not reliable. A subsequent multifactor study suggested that specifically the assumptions regarding air change rates might be responsible for the large deviations of the calculated values from the actual heating demand.

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