Buildings and construction sectors together account for around 36\% of final energy use and 39\% of energy-related carbon dioxide emissions annually according to global status report, with space heating, space cooling and domestic hot water being the key contributors. It is possible to achieve both economical and environmental benefits by implementing an energy system that uses natural working fluid to meet all thermal demands of the building. The purpose of this research is to show the energy potential of a combined heat pump and refrigeration system for a hotel located in hot climate. The energy system includes features such as thermal storage, tri-partite gas coolers for better heat transfer in different operating conditions.
To estimate annual demands for space heating and space cooling, the building simulation software IESVE (Integrated Environment Solutions - Virtual Environment) was used to generate a model of the hotel. The curves for domestic hot water demand, refrigeration and freezing room loads were created additionally as they could not be obtained in IESVE due to the software constraints. A simulation model of the CO2 heat pump system was created in EES (Engineering Equation Solver) to study the potential of the energy system. Several modes of the heat pump operation were simulated for the performance investigation.
The outcome from the EES simulations demonstrated that the proposed energy system for the hotel is capable of meeting all of the seasonal thermal demands. The system has higher heating COP in winter than the cooling COP in summer, spring and autumn seasons. The average heating COP during winter was found to be 3.9 where as the summer, spring and autumn scenarios have cooling COP of 3.2, 2.8 and 3 respectively. The CO2 system has yearly average system efficiency of 7.1.
The influence of multi-ejector was also investigated which proved to be beneficial for the system. The energy system showed improvements in the heating and cooling COP during the winter and summer modes of operation respectively. The heat rejected to the ambient in summer mode was found be extremely high and this needs to be improved in order to make this system design more efficient and economical.
KEYWORDS: Transcritical heat pump, carbon dioxide (CO2), COP, energy system, refrigeration system