Paper No 625 – Transcritical CO2 heat pump for tap water heating: experimental validation of an auto adaptive algorithm for high pressure optimization – 14th IEA Heat Pump Conference, Chicago, USA
Recent developments pushed by F-gas regulations and European guidelines for the renovation of domestic heating systems have led the HVAC market to use new alternatives to propane (R-290) and fluorinated refrigerants. CO2 (R-744) heat pumps are a consolidated solution for domestic hot water (DHW) applications, with the advantages resulting from using an environmentally friendly, not toxic and not flammable refrigerant. Another benefit of CO2, when used in DHW applications, is that high-temperature hot water (up to 70°C) can be obtained without the use of a supplementary heating system. In this case, heat rejection pressure has a strong influence on the efficiency of the unit, and there’s an optimal value that makes the system reach the maximum coefficient of performance (COP). In this work, the performance of a real transcritical air/water CO2 heat pump for tap water heating has been investigated and compared at different heat rejection pressure values. Considering that the optimal pressure value is strictly affected by the variability of the operating conditions (such as water inlet temperature, water outlet temperature or evaporating pressure), an auto adaptive algorithm has been adopted and the consequent results are reported. The algorithm is based on the CO2 thermodynamic properties calculated via Artificial Neural Network by the controller; one of its main advantages is that it does not require the system modeling and it is not dependent on the use of a specific unit or component.