Performance Analysis Of Solar Assisted R744 Ground Source Heat Pump In Different Climates

As the world faces serious environmental and energy crisis, ground source heat pump stands out as an efficient air conditioning system which can supply both cooling and heating load for the building. Considering the environmental influence, R744, also known as CO2 is chosen to be the working fluid.However, when the ground source heat pump operates year after year in area without moderate climate, the system and soil suffers unbalance heat transfer. The soil temperature would go up in hot summer climate due to massive heat injection to earth and it would go down in cold winter climate because of substantial heat extraction from earth. This phenomenon would affect the heat transfer characteristics of underground heat exchanger, thus deteriorate the performance of the whole ground source heat pump system. A new way to improve present situation is in need.In this thesis one possible solution was proposed. Using solar collector in cold winter climate area and air cooled gas cooler in hot summer climate area should help solve this problem. Solar collected heat remedies part of the lost heat in soil and air cooled gas cooler deliver part of the redundant heat to atmosphere.In this thesis, a prediction model of the proposed system was developed. The numerical models of components like building, heat pump, underground heat exchanger, solar collector, hot water storage tank and air cooled gas cooler were developed and validated individually. Experimental data from existing literature were used to validate the models. The solar collector and water tank model get simulated results with less than 1oC deviation. The underground heat exchanger shows reliability more than 90%. The heat pump system model agrees very well with experimental results and air cooled gas cooler data has deviation less than 10%.Based on the proposed model, this thesis studied the underground thermal balance, the investment cost and the operation cost of the system in different typical climate cities. The influence of assistant component on those issues was studied. The simulation results showed that with solar collecting assistance, the unbalance rate of soil after one year can be reduced from 95.1% to 0.1%(in Trondheim, Norway). And with air cooled gas cooler, the unbalance rate of soil after one year can be reduced from 90.6% to 0.03%(in Guangzhou, China). When compared with solo R744 ground source heat pump, annual power needed decreased 41.5%(in Trondheim, Norway) in solar assisting system. Annual power needed is lower by 23% and investment cost is lower by 20%(in Shanghai, China) in air source gas cooler system. Investment cost decreased by 88.1% compared with the solar assisted R744 GSHP without heat injection in Trondheim and by 51.7% in Harbin.