Experimental characterization and numerical modelling of an air to water CO2 heat pump under different outdoor and operating conditions for domestic hot water generation

Abstract

Abstract This work assesses the influence of different outdoor and operating conditions on the performance of an air-to-water CO2 heat pump for domestic hot water (DHW) generation. For that purpose, an air to water CO2 heat pump with internal heat exchanger (IHX) was developed and characterized in an experimental campaign under well-controlled lab conditions. The system includes an in-house control system implemented to operate at the optimal gas cooler pressure. The heat pump and the control system are tested for DHW generation. The heat pump uses a finned-tubes heat exchanger as evaporator and plate heat exchangers as gas cooler and internal heat exchanger. The numerical model used a 1dimensional, cell by cell discretization method to characterize the performance of both, the gas-cooler and the evaporator under a wide range of values of their key variables. The IHX is also modelled with the same strategy. ARHI equations are considered to describe the compressor performance. The experimental data obtained are used to validate a numerical model of the heat pump under different air velocities, air temperatures and air humidity at the evaporator. The effectiveness of the control system proposed is experimentally confirmed during the experimental tests. Results show a good agreement between the numerical simulations and the experimental data what permits to validate the model and to assess the performance of the transcritical heat pump under different climate conditions.