LB-17-C029 -- Residential Hybrid-Ground Source Heat Pump -- Phase I PDF

A ground source heat pump (GSHP) is a central heating and cooling system that transfers heat to the ground during cooling mode and removes heat from the ground during heating mode. The concept behind this technology is the use the approximately constant temperature of the deep ground to make possible a vapor compression system to work more efficiently. As the system operates along the year, the ground temperature changes due to the heat transferred because the ground needs some time to dissipate the heat to ground farthest from the ground heat exchanger. So, the GSHP system efficiency decreases with the advance of winter and summer. To avoid the negative impact on the ground temperature from removing heat during winter and adding heat during summer, hybrid-GSHP systems are considered as an option. For example, in commercial systems, the use of a cooling tower reduces the amount of heat added to the ground and consequently the temperature of the ground does not rise as much as without the use of the cooling tower. However, for houses the use of a cooling tower is not justified. In this sense, the hybrid-GSHP project being developed in a research house located in Tyler TX, will be investigating the economic and technical feasibility of a system using a water-to-air heat exchanger as an ancillary heat exchanger. The overall idea is that the two heat exchangers, connected in parallel, can be used depending in which one offers the higher entering water temperature during operation in heating mode or the lower entering water temperature during operation in cooling mode. The project has been planned to be developed in three phases, in order to have one year data for each phase. In Phase I, which is presented in this paper, the system will be operating only with the ground heat exchanger. In Phase II the system will operate with the two heat exchangers without the option or regeneration of the ground. Finally, in Phase III the system will operate with the two heat exchangers in parallel but at the same time, the air-to-water heat exchanger will be used to regenerate the ground when the system is not working to satisfy the house demand for thermal energy. This paper describes the research facility, the concept of the hybrid-GSHP to be developed in three phases, and energy performance of the system in Phase I for the data being collected.