Technical solution for malfunction of air coolers and condensers in hot climates: thermal design of a Geothermal Air-Cooler

Abstract

ABSTRACT The purpose of this study is to present a technical solution to avoid the malfunction of air coolers and condensers when the ambient temperature exceeds the operating limits of these systems. These critical climatic conditions are obtained especially during scorching temperatures in hot climates. First, this article describes this technical solution called Geothermal Air-Cooler (GAC). Second, to design the GAC components, a simple calculation methodology is presented and validated. A real dry cooling tower, available in the literature with its technical characteristics, was considered as a case study applied to the region of Biskra (Algeria). The GAC principle is to use an air mixer to couple a finned tubes heat exchanger (air condenser or dry cooling tower) with an Earth-Air Heat Exchanger, EAHE. The proposed calculation methodology uses an original model to estimate the soil radius surrounding the pipes, required to the EAHE design. Thermal design of the EAHE is validated using experimental data obtained in a previous research by the authors’ team and good agreements were found (average relative error, ±0.99%). Results relating to the case study showed that the GAC can improve the operating limits of the conventional air conditioning systems to 57°C. Besides, for 0.75, 1.75 and 3.00 kg/s of fresh air mass flow rates, the GAC can increase the operating limit temperature of solar adsorption chiller to 42°C, 50°C, and 57°C, respectively. It has been shown that when a large heat transfer area of finned tubes is required, several EAHEs can be used together. Abbreviations EAHE: Earth-air heat exchanger; EWHE: Earth-Water heat exchanger; GAC: Geothermal air-cooler