Multi-criteria optimization of a geothermal system used for indoor refreshment during summer in a hot region.

In this paper, earth–air heat exchanger is examined to achieve better system operation to cool a building in the arid climate of Ouargla city (Algeria). A higher cooling power requires a big pipe size which increases the pressure losses. Based on fluid dynamics, a new approach is carried out to evaluate the air flow pressure losses that contribute to the determination of the required blower power. The mathematical model of governing equations set is presented, and its numerical solution is calculated using a Matlab program. The multi-objectives optimization between two opposite targets is adopted for achieving the compromise solutions between maximal efficiency and minimal system size. For a given cooling power, the resolution of the earth–air heat exchanger model is carried out using the weighting method to perform the bi-objective optimization. At each cooling power, Pareto curves are generated for plotting the optimal points of efficiency and lateral pipe area. Obtained results show that for a chosen cooling power range, the system operation must reach at least an efficiency of 35% but less than 90% to cover all the size-efficiency compromises. Also, the lateral pipe area must be at least 6.025 m²/kW to start with acceptable efficiency. On the hottest summer day, for 3.5 kW as cooling power, the pipe outlet temperature reaches about 26 °C at a relatively high pipe length of about 95 m. [ABSTRACT FROM AUTHOR]