What is it?
A geothermal heating system that exchanges heat with the renewable energy stored in the earth. This system uses conductive heat transfer to heat or cool an area. When the system is cooling, it extracts the heat out of the air in the building. This air leaves through the return ducts and can do two things: be rejected back outside or used to preheat water in a hot water tank. When the system is heating, heat is absorbed from the ground from fluid in underground wells. The heat load is transferred into a geothermal heat pump system and is distributed into the building as warm air. Basically the process in the Winter is the opposite of the process in the Summer. You can see the process of geothermal heating and cooling in the figures and animation to the right.
Components
Geothermal heating systems contain three main parts. The primary component is the geothermal heat pump. The two secondary components are the underground loop and the air delivery system. You can visualize the components and the more specific pieces of equipment used, like the evaporator and compressor, in the figures to the right.
The Geothermal Heat Pump
The heat pump moves the heat from one location to another. This process follows the natural flow of air when it comes to temperature: moving from an area of high temperature to an area of low temperature.
The Underground Wells
The loop is a system of pipes buried underground by the building. A fluid, refrigerant or water, flows through the pipes to release or extract heat to or from the earth. These underground wells can be vertical or horizontal. Horizontal wells are usually buried around 4 to 6 feet underground while vertical wells can be reach 500 feet in depth. Because of their verticality, vertical wells usually require less square feet of land.
The Air Delivery System
The air delivery system is very typical for an HVAC system and consists usually of ducts and pipes to distribute the air throughout the building. Vents are placed in specific areas to release the air into the building to make it comfortable. Filters are added to the system to filter the air being removed from the building. This allows the air to be recycled with a decrease in air contaminants.
Figure 1
Figure 2
Animation 1
Materials
The ductwork typically is made out of sheet metal formed into square or tubular ducts. Usually, insulation is added to the ductwork because sheet metal is not very thermally insulated.
The fluid in the underground wells can be water or a type of refrigerant. There are many different options for types of refrigerant. Refrigerant is great for transporting thermal loads, but could possibly cause groundwater contamination if the system were to burst for some reason.
The pipes in the underground wells can be made out of a variety of different materials. Metal pipes, like copper, are the best because they are thermally conductive but they can become very costly. Poly-pipes can also be used at a lower cost, but aren't as effective.