Heat pumps in refurbishment of existing buildings

This paper presents an analysis on the opportunities for heat pumps application in the refurbishment of existing buildings. After a short introduction on the heat pump technology, the work focuses on the main aspects of heating systems in the refurbishment. The first problem analyzed is that of the heating devices supply temperature. The high original design temperature for the radiator system, mostly incompatible with the heat pump operations, is mainly due to poorly insulated buildings. The improvement in the building envelope insulation during the refurbishment allows for a decrease in radiators supply temperature. This requires a thorough analysis. The second problem is that of DHW production. While the boiler selection can be driven by the need of instantaneous production of tap water, thus to higher heating capacity than that required for space heating, the heat pump selection – given the higher capacity cost, since the higher technology level of the product – should be conducted more carefully. First of all the heat pump requires a hot water storage with an adequate sizing of the heat exchanger area and of the DHW set point. The risk is that the heat pump cannot exchange its heating capacity toward the storage, particularly when in summer its capacity is higher due to the favorable source temperature: the heat pump would then be heavily modulated, requiring a long time to satisfy the DHW demand. The paper finally illustrates some evaluations, in terms of primary energy consumption, of air to water heat pump applications in three different European climates (Athens, Milan, Helsinki), compared to that of a boiler unit in the refurbishment of a detached house and of an apartment building considering the annual operation of the plant.