Technical and economic feasibility of horizontal, multiple shallow-well, and deep-well ground coupling for residential heat pump applications

An analytical assessment of ground-coupled heat pump systems in ten representative cities of the United States showed that simple payback relative to air-source heat pumps is shortest for deep-well ground-coil systems and ranged from 8 to 10 years in three cities, 12 to 15 years in two cities, and above 30 years in Seattle which has low electrical rates and space conditioning loads. Simple payback with any of three types of ground-coil systems is non-existent in Phoenix and Houston, which have highest cooling loads and low water table. Simple payback with horizontal ground-coil systems was only slightly longer than with deep-well systems. Deep-well ground-coil systems had shorter simple payback than multiple shallow-well systems, particularly in areas where deep wells can be drilled into rock layers. Life-cycle costs with a real discount rate of 2.0 percent for horizontal and deep-well ground-coil systems were shorter than that for air-source systems in all cities except for Phoenix, Houston, and Seattle. Seasonal heating coefficient of performance for the ground-coupled systems varied between 2.0 to 3.1 compared to 1.7 to 2.0 for air-source systems. Values of seasonal cooling coefficient of performance for ground-coupled systems were highest with the single deep-well coil. Cooling COP values with a horizontal coil were generally equal to or lower than values for air-source systems. Cooling COP values for air-source systems were higher than values for ground-coupled systems in southern climates with higher cooling loads.