Optimization of heat transfer performance of earth-air heat transfer system based on orthogonal test

In order to improve the heat transfer performance of the earth-air heat transfer system, a theoretical model of heat transfer of the earth-air heat transfer system is established and validated. Using the orthogonal test method, taking heat transfer efficiency, heat transfer quantity and coefficient of performance as evaluation indexes, the effects of ventilation time, air velocity, tunnel equivalent diameter, tunnel length, soil type and tunnel buried depth on the heat transfer performance of the earth-air heat transfer system are studied. The results show that the tunnel equivalent diameter has significant influence on different indexes and is the most key factor affecting the heat transfer performance.The optimal level combination of heat transfer performance of the system under the test conditions is air velocity 3 m/s, tunnel equivalent diameter 0.3 m, tunnel length 90 m, and soil type of sandstone. Under this combination, the heat transfer efficiency of the system is 70%, the heat transfer quantity is 2 550 W, and the coefficient of performance is 8.94.