Performance analysis of water-to-water CO2 heat pump in different compressor rotational speed

Abstract

Ozone layer depletion can be weakened when carbon dioxide (CO2) replaces hydrochlorofluorocarbons and chlorofluorocarbons as the refrigerant in heat pumps. Performance investigations on water-to-water CO2 heat pumps are still insufficient, especially in real life and experimental conditions. Seldom studies have reported that the compressor frequency may affect the performance of CO2 heat pumps in some degree. However, the influence of compressor frequency on the performance of the water-to-water CO2 heat pumps is still unknown. Hence, this study presented the experimental investigations on the water-towater CO2 heat pumps in different compressor frequency. The investigated CO2 heat pump is located in the Energy and Indoor Environment Laboratory in the Department of Energy and Process Engineering at Norwegian University of Science and Technology. It is mainly composed of evaporator, compressor, gas cooler, liquid separator, internal heat exchanger, and expansion valve. The compressor was produced by the Officine Mario Dorin Spa. The plate heat exchangers were applied as evaporator, gas cooler, and internal heat exchanger. The PI controller controlled the discharge pressure by adjusting the expansion valve opening. Experimental cases in which the compressor rotational speed of 1,100 rev/min and 1,300 rev/min were conducted. The coefficient of performance (COP) was calculated by measuring the compressor power and heating capacity in the gas cooler. The analysis on the water to-water CO2 heat pump COP in different measured cases was depicted. This study therefore fills the research gap on the performance of the water-to-water CO2 heat pump in different compressor rotational speed.