Multisource heat pump system from design to operation: the case study of a new school building

The concept of a low energy building in the temperate climate (according to the Koppen climate classification) is based on the reduction of heat losses through a better insulation, the heat recovery on mechanical ventilation and the use of high efficiency heating/cooling systems integrated with renewables. It is very difficult to achieve good results in terms of global energy efficiency if one of these elements is missing. In 2009 a new school building, integrating those three elements, started its operation in Agordo town, northern Italy. Its main features concern a well insulated envelope and a space heating and ventilation system driven by an innovative multisource heat pump system concept. Outdoor air is a common heat source, whose limits are well known. Heat pump features can take advantage of better sources than air, as for instance the ground heat, solar heat, and heat recovery. These sources are those used by the analyzed system. A multisource system aims to enhance the performances of the heat pump, both in terms of heating capacity and of efficiency. The present work shows data monitoring and analysis for a real working application, for a period of about two heating seasons, during which the behavior of the system can be analysed and the eventual malfunctioning of the plant can be identified. 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, thus leading to a lower stress on the ground and to a higher utilization of the solar system. The results are then compared to those could have been obtained with the use of a single source system, i.e. the ground, taking no advantage from the heat recovery and the solar system.