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Geothermal Heat Pumps for Cell Tower Equipment Shelter Cooling

Researcher: Brandon LaBrozzi
Principal Investigator: Professor Jefferson Tester

Equipment shelters located at cellular tower sites house an array of radios and electronic equipment necessary to the operation of the wireless network. Inherently, this equipment generates a large amount of heat, peaking at 18 kW and averaging 10 kW. This heat must be constantly removed in order to prevent damage to the equipment. Current systems employ conventional window mounted air conditioning units to cool the shelter. With rising energy prices and an ever-growing focus in green technologies, finding sustainable alternatives is essential. Closed loop geothermal heat pumps have the ability to effectively cool the shelters while reducing the consumption of electricity.

Due to the limited area at most cell tower locations, vertical boreholes present the best option concerning well field configuration. Since this application only requires cooling and runs continuously, there exists the possibility of heat build up in the ground. This constant heat rejection scenario requires a complete transient heat transfer analysis of the geothermal well field to address the sustainability of the well field over the lifetime of the site. Several base cases will be examined using differing values for ground temperature, thermal conductivity and ground permeability to calculate proper borehole length. The effect of enhanced grouts and several borehole flow arrangements (single/double pass U-tube and co-axial) were examined.

Additionally, a hybrid, GHP/air economizer cooling system was analyzed that takes advantage of cool air to provide cooling at night and during non-summer months. Using the lower temperature ambient air allows for the run time and the overall size of the GHP system to be reduced, saving a considerable amount of money in terms of both operating and capital expenses. In certain cases, there are months of the year in which the air is cold enough to provide enough cooling to satisfy the demand and the GHP system is not needed.