Performance improvement of integrated CO2 systems with HVAC and hot water for hotels

Abstract

Carbon dioxide (R744) systems have emerged as a sustainable and viable alternative to hydrofluorocarbon (HFC) applications within refrigeration. During the past decade, advancements in R744 technology and system architecture have paved the way for new areas of application. Integrated R744 systems for heating and cooling in hotels have demonstrated promising results within a sector characterized by high thermal demands and a large carbon footprint. However, further research is necessary to establish integrated R744 systems as a competitive alternative to traditional HFC systems in hotels. This paper presents the numerical model of an R744 heating and cooling unit installed in Northern Europe. The system is integrated with HVAC and a 6 m3 thermal storage for domestic hot water. A dynamic model of the hotel’s thermal system was created and validated for three seasonal representative weeks using recorded ambient temperatures, heating, and cooling loads. A low load charging strategy, which exploits the thermal storage flexibility, was evaluated as an approach to improve the overall system performance. Simulations demonstrated that charging the thermal storage for longer periods at low compressor loads enhanced the overall efficiency of the system. Energy savings in the range of 5.8–13.2% were achieved based on the different seasonal scenarios. Additionally, peak power usage, operational fluctuations, and ON/OFF cycles were considerably reduced with the low load charging strategy. The proposed strategy can be implemented in similar applications to enhance overall system performance.