Energetic and environmental analysis of an integrated multi-source heat pump system for a school building

The concept of low energy building 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. The present works shows an example of good integration of those three elements into a real application. A new school building has been designed for Agordo town (BL) in Northern Italy. The architectural design chose high insulation thickness and smart structural features have been conceived in order to avoid coldbridge effects. Through dynamic simulation different solutions were evaluated with respect to the heating system. An integrated source absorption heat pump system has been designed to fulfil the needs of the building: the sources are ground, sun, recovery on ventilation. The heating system works at two different temperature levels: a higher one for the ventilation system and a lower one for the radiant floor space heating system. The two different systems work independently and on different time schedules. The thermal source for the ventilation heat pumps is the exhaust airflow discharged after a cross flow heat exchanger whose efficiency is limited at 50% to avoid frosting problems (the climate is there very severe). A total recovery is then produced at the absorption heat pump evaporator level. The thermal source for the space heating heat pumps can be either the ground (1300 m of vertical tube heat exchangers) or a solar section of 50 m² solar collectors that can serve directly the heating if the insolation makes it possible. In summer they can re-generate the ground.