NUMERICAL COMPARISON OF SEVERAL CONTROL STRATEGIES FOR DOMESTIC HOT WATER GENERATION IN A CO2 HEAT PUMP WATER HEATER

Resumen

This paper presents a numerical comparison of several control strategies of a CO2 heat pump water heater that improves its energy efficiency by recovering the energy contained in the greywater used as secondary fluid in the evaporator. Based on the correlations provided by the compressor manufacturer for the mass flow rate and the power consumption, and later adjusted to experimental data collected in our experimental facility, the paper compares the COP of the system during domestic hot water generation at 60 °C. Two different control strategies will be analyzed for the water loop: constant water flow rate with variable inlet and outlet water temperature and constant water outlet temperature with variable water flow rate and water inlet temperature. Each water control strategy will be analyzed under two different control strategy for the refrigerant loop: constant gas cooler pressure and variable (optimal) gas cooler pressure. The paper begins with the description of the experimental facility developed for the tests used to adjust compressor’s model. Then the adjustment of the experimentally measured values ofcompressor power consumption and mass flow rate to typical AHRI correlations is presented. This adjustment will be used in a simplified numerical model to assess the influence of the control strategy in the system’s performance. Finally, in order to validate the model, it will be compared to some experimental results.