A comparative study of CO2 heat pump performance for combined space and hot water heating

Abstract

Heat pumps used for combined space and hot water heating are often used in modern energy-efficient buildings. Performance depends on both system design (exchanger sizes, compressor efficiency, etc.) and operating conditions (inlet water temperature, ratio between space and water heating, etc.). Designs using both CO2 and HFCs, such as R410A, are available, but the relative performance of these is not extensively studied.<p><p> This article presents performance results based on a system model developed in MATLAB where exchangers are modelled using fixed temperature pinches and pressure drops. Ejectors and compressors are modelled using defined efficiencies. Operating parameters are optimized using the Genetic Algorithm for a set of sensitivity studies. The results show that CO2 can outperform R410A when the ratio of space to water heating is below 0.6 – 1.0, feedwater is below 20°C (as in norther Europe) and heat exchangers are designed with temperature pinches below 10 K.