A 3-ton earth-coupled heat pump system designed specifically for easy installation in modular classrooms, mobile office buildings, and mobile homes is being tested in a modular classroom in Johnston County, North Carolina. Approximately 2,000 gallons of saltwater is stored in plastic bladders underneath the building. The saltwater is circulated through the heat pump at a temperature that is conducive to efficient operation in both cooling and heating modes. The earth underneath the bladders exchanges heat with the water and provides long-term thermal storage. Heat is also exchanged between the storage water and the ambient air. A computer model predicted annual energy usage of approximately one-half that of a traditional air-source heat pump for a typical meteorological year. Data collected during the past year show that this prediction is being met for the heating mode. In the cooling mode, the earth-coupled heat pump used about 80% as much electricity as the air-source heat pump. However, the earthcoupled heat pump maintained the classroom at a lower temperature during the summer and was more heavily loaded. When differences in the building loads are taken into account, the measured performance is close to the model prediction.

Units: I-P