Abstract The concept of a low energy building in a temperate climate (according to the Koppen climate classification) is based upon the following principles: reduction of heat losses through enhanced insulation; the inclusion of heat recovery on mechanical ventilation; and the use of high efficiency heating/cooling systems integrated with renewable technologies. It is almost impossible to achieve optimum results in terms of global energy efficiency if one of these elements is omitted from the design. In 2009, a new school building, integrating these three key elements, was opened in Agordo town, located in northern Italy. The main design features of the building incorporate a well insulated envelope and a space heating and ventilation system driven by an innovative multisource heat pump system. Outdoor air is a common heat source, although it does have widely documented limitations. Heat pump systems can utilise more efficient sources than air, including those of ground heat, solar heat, and heat recovery. The installed system within the school building incorporates these three sources. A multisource system aims to enhance the performance of the heat pump, both in terms of heating capacity and overall efficiency. The present work includes evaluation and analysis of data obtained through real time monitoring of the working system in operation, for a period of approximately two heating seasons. During this time, the behaviour of the system was assessed and the incorrect settings of the plant were identified and subsequently adjusted as required. The energy balance indicates that the integration of different sources not only increases the thermal performance of the system as a whole, but also optimizes the use of each source. Further savings can be obtained through correct adjustment of the set point of the indoor temperature. During the final stage of the study, the total energy consumption of the new building is calculated and compared to that of the former building that housed the same school, which had similar dimensions.
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