A geothermal well heat pump system simply transfers thermal energy (heat) from the ground or groundwater into the space being conditioned during the winter months and transfers excess heat from the structure back into the ground or groundwater in the summer months. Because the temperature of the ground or groundwater remains fairly constant throughout the year, ranging from about 45-50 degrees F in northern latitudes to 70-80 degrees F in the deep south, operating efficiencies are high year-round.
The typical geothermal heat pump system consists of three main parts:
- The air handling system (fan and ductwork) that distributes air within the spaces being heated or cooled.
- The ground or groundwater heat exchanger that absorbs heat from the earth or discharges heat to the earth.
- A reversible refrigerant loop that transfers heat between the air handling system and the ground or groundwater heat exchanger.
The air handling system is typical of any forced-air heating or cooling system. A fan moves heated or cooled air through ducts to the individual rooms in a building, and returns air to the geothermal heat pump system.
The ground-coupled heat exchanger can take a number of forms. In an open-loop system, two wells are typically used. These are similar to conventional water wells, with one acting as a source well, and the other acting as a sink. Water is pumped from the source well, through a water-to-refrigerant heat exchanger on the GeoExchange system, and returned to the second well. Alternately, the water from the source well can be returned to a lake, pond, or stream, if there is one in proximity to the site, and local regulations permit. The water remains unaffected by the system, except that its temperature is raised in summer and lowered in winter.
In a closed-loop system, the ground-coupled heat exchanger takes the form of sealed high-density polyethylene piping buried vertically or horizontally in the ground. In the case of vertical systems, a series of 4-in. to 6-in. diameter bore-holes are made (typically using water well drilling equipment to attain depths of 150 to 300 feet), a loop of piping is inserted into each hole, the various loops are tied together by a manifold and then the holes are grouted and backfilled. For horizontal systems, similar piping loops are buried in horizontal trenches dug 4 to 6 feet deep, the piping is connected by headers, and the trenches backfilled. In both vertical and horizontal closed-loop systems, the water or water/nontoxic antifreeze mixture in these pipes remains within the pipes for the life of the system.