Field measurements evaluation and modeling of CO2 heat pump for residential building (Gamen 12)

Abstract: Carbon dioxide, as a natural refrigerant, is safe and environment-friendly. It is also an economic refrigerant which can be utilized in residential heat pumps. Analysis has been done to evaluate the performance of the CO2 heat pump in Gamen 12 (Skrapan) in the Sodermalm area, owned by Vasakronan; which is a real estate company. The building satisfies its heating needs through connecting to the district heating network. Furthermore, the CO2 heat pump was installed to recover the available high- potential- waste energy from the building. The evaluation starts with one year of field measurements of an existing system (May 2017 to May 2018). Additionally, quality control and a revision of the data are essential to have the most accurate values. The use of necessary equations is then followed to estimate and establish the critical parameters to the heat pump's performance. For instance, some of the essential parameters include temperature and pressure. In this study, a numerical model was used to present four different scenarios which handle the parameters that impact the performance of the heat pump. These scenarios also aim to improve the system for future installations. The results show that the performance of the heat pump can be improved by 16% and 14% respectively when the outlet gas-cooler temperature and the evaporation temperature are optimized. The best performance of the system is achieved when the outlet gas-cooler temperature decreased, and the evaporation temperature increased simultaneously. This change yielded to the best optimal value, which is up to 30% higher than the previous performance. Another scenario was created for future installations. In this scenario, it was assumed that the heat pump consists of three gas coolers, two of which were utilized for heating domestic water while the third one was used for space heating. Results showed that the new installed scenarios were economically promising and yielded in better performance of the system. Finally, an economic assessment was adopted in this study which showed cost-saving effect at a specific running capacity of the system; 8% of the total cost which equal to 168 000 SEK was saved annually when the heat pump runs at average capacity 54%. After applying the suggested improvements, the savings will be higher and would reach 218 000 SEK annually and the capacity of the heat pump reaches 70%, which is equal to 11% of the total cost of providing heating to the building.