What are geothermal systems?
Geothermal systems use a ground source heat pump that utilizes the earth's relatively constant temperature to provide heating, cooling, and hot water for homes and commercial buildings. Unlike other types of heating systems, which convert fuel to heat, a heat pump is designed to move heat from one place to another.
In the past, most heat pumps were the air-to-air or air source type. Air source heat pumps rely on outdoor air for their heat source. Geothermal heat pumps extract heat from the ground or from water, either below or on the surface. Because ground and ground water temperatures are a constant 7° - 13° C (45°-55° F) year-round, this type of system is much more efficient.
There are basically two ways to move energy from the ground and into your home – a closed loop or an open loop. These loops are buried either vertically or horizontally.
Vertical loops are the ideal choice when available land surface is limited. Drilling equipment is used to bore small-diameter holes from 75 to 300 feet deep.
Pond/lake loops are very economical to install when a body of water is available, because excavation costs are virtually eliminated. Coils of pipe are simply placed on the bottom of the pond or lake.
Horizontal loops are often considered when adequate land surface is available. Pipes are placed in trenches, in lengths that range from 100 to 400 feet.
Closed Loop Systems
In a closed-loop system, a loop is buried horizonatlly or drilled vertically in the earth around the home, or laid in a nearby lake or pond. A mixture of antifreeze and water is circulated continuously through the loop and heat pump, transferring heat from or to the soil respectively, as heating or air conditioning is needed. This process creates free hot water in the summer and delivers substantial hot water savings in the winter.
Virtually all loops built today use high-density polyethylene (HDPE) pipe. This type of pipe was designed to be buried in the ground; and last 50 years or more. Joints are made by fusing or melting the pipe and fittings together, which makes a nearly leak-proof connection. In a closed-loop system, the fluid never comes in contact with the soil. It is sealed inside the loop and heat pump.
Open Loop Systems
In an open-loop system, ground water is drawn up from a well and through the heat pump, then typically pumped back into a return well. New water is always being pumped through the system when it is in operation. It is called an open-loop system because the ground water is open to the environment.
What are the advantages and disadvantages of horizontal and vertical installations?
Horizontal installations are simpler, requiring lower-cost equipment. However, they require longer lengths of pipe due to seasonal variations in soil temperature and moisture content. Since a horizontal heat exchanger is laid out in trenches, a larger area is usually required than for a vertical system. Ground-based horizontal loop systems draw their heat from loops of piping buried 1.8 to 2.4 metres (six to eight feet) deep in trenches. The piping for water loop systems is installed below the winter ice level in pond or lake, or below low tide level in the ocean.
Where land is limited, vertical installations can be ideal. If regional soil conditions include extensive hard rock, a vertical installation may be the only available choice. Vertical installations tend to be more expensive due to the increased cost of drilling versus trenching, but since the heat exchanger is buried deeper than with a horizontal system, vertical systems are usually more efficient and can get by with less total pipe. Vertical loop systems use holes bored 45 to 60 metres (150-200 feet) deep with U-shaped loops of piping.
The land area needed for the vertical loop, however, depends on the depth to which the boreholes can be drilled cost-effectively. For example, if a geothermal system required 1000ft of borehole in total, four 250ft holes would use the least amount of area, however, depending on soil conditions, it may be easier and more cost effective to drill five 200ft holes, seven 143ft holes or even ten 100ft holes. There must be a minimum of 10 feet of space between each bore hole, so the more holes needed, the larger the area required.
How can I make sure the job is done right?
Use a reputable contractor. Don't be afraid to ask for and use references. Reputable dealers and loop installers will be happy to give names and phone numbers for you to call and confirm their capabilities.