Ground or solar source for space heating: which is better? Energetic assessment based on a case history

High efficiency heating systems can be considered as those having a primary energy ratio PER greater than that of traditional boilers, so basically heat pumps. Heat pumps performances are very sensitive to both evaporator and condenser temperature; outdoor air is a common heat source, whose limits are well known, therefore it is possible to take advantage of better sources than air, as for instance the ground and the solar heat. However the use of different sources requires additional investment cost. It is then interesting, starting from a given additional investment, on one side to evaluate different compositions for a set of sources and on the other to choose the most favourable source from time to time, according to the building energy demand and the thermal level of each available source. This paper presents a study conducted in the design phase of a new well-insulated school building in northern Italy, equipped with a heating system based on multi-source absorption heat pumps. By means of dynamic simulation in TRNSYS environment, several scenarios were assessed with respect to primary energy consumption.