Performance Study Of Carbon Dioxide Ground Source Heat Pump For Driving Constant Temperature And Humidity Air Handling Unit

The constant temperature and humidity air handling unit has high control precision for temperature and humidity,long running time,and high energy consumption.Faced with a serious energy shortage,the concept of green low-carbon development has put forward,and a series of policies to promote it have been introduced all over the country.While the ground source heat pump technology conforms to the trend of low-carbon,energy-saving era,and is called " Green Cavity Technology" in the 21 st century.Based on this,two new types of transcritical carbon dioxide ground source heat pump systems for driving constant temperature and humidity air handling unit were proposed,and the operation process of single-stage and two-stage cycles in winter was introduced respectively.The systems were modeled,programmed,and calculated with MATLAB and REFPROP9.0.Through the calculated results from the temperature of fresh air,fresh air ratio,inlet water temperature of buried pipes,condensation pressure,middle pressure and flow coefficient,the energy performance of two systems were compared and analyzed.The results show that:For both systems,the energy performance decreases with the increase of outdoor fresh air temperature,and the downward trend of COP changes when outdoor fresh air does not need preheating.In this case,the fresh air ratio has the greatest influence on the trend of the energy performance of systems,followed by the exhaust pressure of the compressor and the inlet water temperature of the buried pipes.While,it approximately increases linearly with the fresh air ratio.In this case,the outdoor fresh air temperaturehas the greatest impact on the trend of system performance,followed by the water temperature of the buried pipe inlet and the compressor discharge pressure.Also,it increases with the water temperature at the entrance of buried pipes,and the higher the inlet water temperature of buried pipes,the faster the system performance increases.In this case,the compressor discharge pressure has a greater impact on the change trend of the system performance,followed by the fresh air ratio and the outdoor fresh air temperature.However,the energy performance decreases with the compressor exhaust pressure.In this case,the water temperature at the entrance of the buried pipes has a greater impact on the performance of the system,followed by the fresh air ratio and the outdoor fresh air temperature.For transcritical carbon dioxide two-stage ground source heat pump system,the energy performance of it decreases with the flow coefficient,and the larger the flow coefficient,the slower the performance of the system decreases.While the system performance increases first and then decreases with the intermediate pressure.In most cases,there is an optimal pressure between 5.9MPa and 6.2MPa.The energy performance of two-stage system is always higher than that of single-stage system.The energy performance growth rate between the two-stage system and the single-stage system first keeps approximately 42.83% unchanged with the outdoor fresh air temperature,and then decreases in a straight line when the outdoor fresh air does not need preheating.It increases with the fresh air ratio and compressor discharge pressure,while decreases approximately linearly with the water temperature at the entrance of the buried pipes.