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ABSTRACT The current report describes testing work of a Sanyo made CO2 heat pump. The heat pump has been modified by Sanyo based on the Swedish end users’ habit in order to fit the Swedish market. In the current study, the heat pump’s COP, its tank performance and the control scheme of defrosting are studied and reported. Based on the testing results, comments on the heat pump’s performance as well as on European heat pump testing standard (EN 14511-1) are given. Furthermore, suggestions on the methods to improve the heat pump performance and on further work are stated in the end. The general test results show that the CO2 heat pump’s performance is highly dependant on the application and the surround systems. For applications, where there is a huge demand of hot water (hospitals, sport facilities etc.) or where there is a relative large ratio between the demand of hot tap water and space heating (i.e. newly built low energy buildings with floor heating), the CO2 heat pump will be competitive with traditional heat pumps. For typical Swedish houses, where the energy demand for space heating is much larger than for hot tap water, the CO2 heat pump will show a poorer performance, due to the typically relatively high return water temperatures to the heat pump and the relatively small temperature lift needed from the heat pump. The heat pump performance test results (i.e. the heat pump performance, without water tank) show that the tested CO2 heat pump, under the same testing conditions, achieved similar performances as presented in the manufactures technical manual. Furthermore, the tests also show that the European heat pump test standard (EN 14511-1) is not suitable for evaluating the performance of CO2 heat pumps. This is mainly due to the reason that the standard states testing conditions with relative high return water temperature (the most critical parameter that influences the CO2 heat pump performance) to the heat pump, which is very unfavorable to a CO2 heat pump. Therefore, if the same test standard is adopted to compare the CO2 heat pumps with traditional heat pumps, the performance of CO2 heat pump will be underestimated compared to cases with low inlet water temperature. One way would be to extend the test procedure with additional operating conditions allowing for a lower water flow, thus enabling a larger temperature glide for the heat sink. When performing the system tests (e.g. testing with the water tank and the radiator load), the CO2 heat pump achieves a lower COP than conventional heat pumps. The main reason for the poor system performance of the tested CO2 heat pump system is due to the influence of water tank. The performance of the CO2 heat pump is very sensitive to the water inlet temperature to the gas cooler. A high water inlet temperature will introduce large thermodynamic losses due to the characteristics of the working fluid, and thus greatly lower the heat pump performance. The typical water tank design for conventional heat pumps does not fit a CO2 heat pump since it delivers water to the CO2 heat pump at an unfavorable high temperature. Furthermore, it has been noticed that the important tank stratification is destroyed every time the heat pump delivers new hot water to the tank. This can be improved by changing the design of 6PDF Image | CO2 heat pumps for the Swedish market
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