Hybrid geothermal heat pumps for cooling telecommunications data centers

Abstract

The technical and economic performance of hybrid geothermal heat pump (GHP) systems supplying year-round cooling to small data centers were analyzed and compared to air-source heat pump (ASHP) cooling systems. Numerical TRNSYS models were used to simulate the operation of five configurations that included GHPs, ASHPs, air-cooled heat exchangers – dry coolers (DCs), and/or waterside economizers (WSEs). The models were validated against data measured from an experimental GHP cooling system in Ithaca, NY, USA. The average coefficient of performance (COP) and the total cost of ownership (TCO) of the optimized systems were evaluated and compared to a base case ASHP cooling system. The results showed that the GHP systems had higher lifetime average COPs than the ASHP system, while the TCOs of the GHP systems were slightly higher than the ASHP system. The reductions in cooling capacity and performance of the geothermal systems due to subsurface temperature increases were calculated and showed that the addition of a DC or WSE mitigated capacity reductions and improved lifetime performance. The economic performance of the GHP systems relative to ASHP systems were analyzed using weather data from several locations across the U.S., with sensitivities to soil conductivity, price of electricity, and cost of drilling the geothermal wells quantified. GHP systems performed best in colder climates with greater temperature variability both seasonally and diurnally.