Refined heat pump design and results of final testing

TRI-HP EU project aims to develop trigeneration integrated solutions that combine heating, cooling and electricity generation, based on heat pumps running with natural refrigerants and using multiple renewable energy sources. Three heat pump prototypes (propane-ice, propane-dual, CO2-ice) were already analyzed in the first testing campaign. The prototypes of the proposed heat pumps were modified for the second test campaign based on the results of the first test campaign. For the enhancement of the propane-ice heat pump, the compressor and evaporator were changed. Changing the compressor brought a 5 % increase in system efficiency (COP). One expansion valve was utilized rather than two valves for simplicity, lower cost, and higher reliability. Moreover, the extraction fan operates only in case of an emergency. Although this solution slightly reduces the safety level, it increases the COP by up to 3 %. From the comparative analysis between the first and second test campaigns, it has been observed that the propane-ice heat pump COP has increased by an average of 11.3 % compared to the first prototype, for the nominal operation temperature range for SH (30/35 °C) and DHW (52/60 °C}). Finally, the casing of the prototype was changed from a high frame to a wide frame for smooth production and a lower footprint. In terms of advancing the second prototype of the propane DSHP, a DSHX with small external tubes dimension was utilised in order to reduce the refrigerant charge amount. Only one supply port was implemented to eliminate the risk of refrigerant bypass. The exhaust distributor of the DSHX was lower than the supply distributor. It was moved to a higher position than the supply one to lower the pressure drop and increase the evaporating temperature. The frame of the second prototype was also changed to simplify the commissioning. As far as the CO2 heat pump is concerned, new and more ejectors were utilised to enlarge the application range and improve the system's performance. Evaporator control was enhanced by controlling refrigerant outlet quality along with the refrigerant pressure difference method to increase the system efficiency. The internal heat exchanger was switched with a new plate configuration. This report describes the second experimental campaign after the modification/upgrading of the heat pump prototypes. The experimental results are analysed and compared when possible with the first experimental campaign results. The main performance indica