An evaluation for spiral coil type earth-air heat exchanger at different climate conditions

Abstract

ABSTRACT The experiments have proven that the temperature level of subsoils in the summer and winter is, respectively, lower and higher than the ambient air temperature. The buried tubes in the soil can use this potential to cool or heat the ambient air. The spiral tube heat exchanger is a good choice for earth-air heat exchangers as they are buried in a fixed buried depth, and they serve higher heat transfer coefficient due to the existence of secondary flow in the cross section of tube. In this research, the spiral tube, in an earth-air heat exchanger, has been analyzed, and the performance has been evaluated in different eras and areas of use. Cities have been selected under different climatic conditions in Iran and thus the system had been simulated in both heating and cooling modes. Furthermore, the effects of various factors, such as the depth level of buried heat exchanger in soil, the velocity and the temperature of inlet air on the exhaust air temperature, as well as the thermal load absorbed by the heat exchanger, are all being investigated. Higher buried depth of the heat exchanger increases the transferred heat, while the increase in the inlet air velocity reduces the heat exchange between the soil and the air. Tabriz which is a city located in a semi-arid climate in Iran, serves the best heating and cooling loads; whereas Babolsar another city in Iran which has a humid subtropical climate, indicates the poorest performance of all in comparison to other cities and climate levels in Iran.