Cooling Performance of an Earth to Air Heat Exchanger in Hot Semi-arid Climate : Parametric study

The objective of this work is to perform a parametric study in order to investigate the thermal performance of an earth to air heat exchanger (EAHX) for buildings' air cooling in a hot semi-arid climate. The effect of the EAHX pipes' length and diameter as well as the burying depth, the air velocity, the number of pipes and pipes spacing, identified as the main influential parameters for a given location, were numerically investigated. The cooling performance of the EAHX was assessed using an indicator called the “maximum daily cooling efficiency” which expresses the ratio of the maximum outdoor air temperature drop, after its passage through the EAHX buried pipes, to the potential of this drop. The latter is the temperature difference between the outdoor air and the soil at the maximum depth considered in this study. Continuous operation mode during the cooling season is considered. Simulations of all combinations of the EAHX main influential parameters are performed using TYPE 460 of TRNSYS. The results are presented in terms of the “daily maximum cooling efficiency” charts for combinations of two parameters while the others are maintained at their reference values. The results show that the effect of the EAHX burying depth and pipes' spacing are not significant beyond 4m and 4D respectively. Some guidelines for the design of the EAHX are drawn.