Thermal design of Earth-to-air heat exchanger. Part II a new transient semi-analytical model and experimental validation for estimating air temperature

Abstract

Abstract This paper is the second in a series of thermal design of Earth-to-Air Heat Exchanger (EAHE). The first part explains a transient semi-analytical model ‘named RBM model’ to estimate the disturbed soil thermal resistance of EAHE pipe as a function of duration of operation. In this part, a new semi-analytical model, called Generalized RBM model (GRBM model), is developed to predict the thermal performance of EAHE operating under transient conditions for cooling mode. Therefore, an experimental investigation was carried out in the region of Biskra (Algeria) to validate the developed model. The GRBM model development is based on the subdivision of the soil and the pipe into many layers and the use of RBM model, presented in the first part, to estimate the temperature of disturbed soil surrounding the inspected layer. Furthermore, the experimental horizontal EAHE setup, installed in the University of Biskra, is described. The experimental tests were performed in May 2013 for 6 h of continuous operation mode of the EAHE setup. To validate the GRBM model, a comparison between the calculation and the experimental results at various sections along the pipe is conducted. The results of the GRBM model are in a good agreement with the measured temperatures with an average relative error of 2.8%. Furthermore, both analytical aspect and the simplicity of the GRBM model will make the thermal design of EAHE more accurate with significantly reduced calculation time.