Simulation study on the performance of direct expansion geothermal refrigeration system using carbon dioxide transcritical cycle

In the direct expansion geothermal refrigeration system using carbon dioxide transcritical cycle, the refrigerant loops are buried underground, and directly exchange heat with the soil. It can avoid polluting the underground water and soil even if the loops have the danger of corrosion and leakage, since carbon dioxide is a kind of safe natural substances. In this paper, the performance of this system is studied through simulation. The mathematic models of each component are established using the Static Distribution Parameter Method and the Lumped Parameter Method according to the characteristic of each thermodynamic process. Then, the simulation model of the direct expansion geothermal refrigeration system using carbon dioxide transcritical cycle is established. Based on the models, the performance of the transcritical refrigeration system is simulated. The simulation results manifest that the optimum high side pressure is 14.6 MPa and the maximum COP is 0.966 under the simulating conditions. The increases of gas cooler pressure, flow rate and inlet temperature of the chilled water all lead to a certain increase of the refrigeration capacity, the power consumption and COP. However, with the initial soil temperature rising, both the refrigeration capacity and COP tend to descend, but the power consumption rises on the contrary. (C) 2019 The Authors. Published by Elsevier Ltd.