Influence of the hydronic loop configuration on the energy performance of a CO2 heat pump for domestic hot water production in a multi-family building

In this work, a numerical analysis of the influence of the hydronic loop on the energy performance of a CO2 heat pump dedicated to DHW production for an apartment block located in Bologna (Italy) is presented. The energy model of the whole heating system, implemented in TRNSYS17, has been validated by means of a monitoring campaign performed during the winter season of 2017- 2018. The experimental results highlighted a poor and unexpected energy performance of the heat pump. The comparison between experimental and numerical results showed a significant penalty of the heat pump performance due to an erroneous use of the hot stratified thermal storage system. Outcomes of this paper confirm that CO2 heat pumps are very sensible to the temperature of the fresh water at the inlet of the gas cooler. This value can be strongly reduced thanks to the presence of the stratified tank in the hydronic loop.