Abstract
In recent years, due to many reasons, such as environmental and economic problems, the use of shallow geothermal as a clean energy source has been of great interest inside the scientific community. However, the main targeted application is air cooling and heating in buildings by using a buried pipe in the ground known as Earth to Air Heat Exchanger (EAHE). This system (EAHE) alone cannot fulfill the comfort conditions in countries characterized by hot and cold climates, and an auxiliary system is required. The present work proposes a new hybrid system consisting of coupling the EAHE (primary system) with a concentric two pipes heat exchanger (secondary system). The inner pipe has multiple longitudinal fins filled with frozen water or a mixture of ethylene glycol and water as a phase change material (PCM). The air is cooled when exchanging heat with a frozen PCM in the secondary heat exchanger (Water/PCM HEX). A theoretical investigation of the proposed hybrid system has been carried out. However, transient models have been developed for both heat exchangers, and the nonlinear equations obtained have been solved using numerical methods. The simulation of the behavior of this hybrid system located in Madinah city (Kingdom of Saudi Arabia), presenting a hot climate, has been carried out. The effect of geometrical parameters and operation conditions on the outlet air temperature and the operation period has been investigated. The study results show that the convective heat transfer coefficient is significant in the Water/PCM HEX. As long as its value is low, the cooling is not significant; as shown by decreasing the freezing temperature from 0 degrees C to -10.71 degrees C, the gain in the outlet air temperature dropping is <1 C. When the external pipe diameter has been reduced from 8 to 6 in., the air is cooled down by almost 5 degrees C. The proposed system presents an attractive cooling solution during peak periods, especially for hot climates less severe than Madinah.