One of the many important parts of a good geothermal heat pump systems is the method used to gather and disperse heat. This heat transfer is called geoexchange. In the summer months when we want to cool our homes, we use the heat pump to attract the heat from the house and transfer it to the geoexchange system and place the heat in the earth. In the winter months, we gather heat from the earth using the heat pump and transfer it to the interior of the home.
There are two types of geoexchange that are typically used in Minnesota. Open loop geoexchange and closed loop geoexchange. An open loop exchange system is when water from a well, lake or river is pumped through a geothermal heat pump. The heat pump adds heat to or removes heat from the water. The water is then pumped and lost into a lake or river . This is commonly referred to as a "pump and dump" geo-exchange system. If you want to consider this application, you will need permission from government agencies to do so. This option is simple and may be the least expensive way to gather and lose heat. However, permission (permits) are hard to obtain and will consume a lot of your time, making it a less desirable option.
In a closed loop system, a series of high quality plastic loops are installed,filled with water and food grade anti-freeze . The solution is then circulated to gather or lose heat in the earth through the geothermal heat pump. There are three types of closed loop systems
1. Using a private lake or pond of sufficient depth and size, a series of loops are filled with antifreeze solution and sunk to the bottom. The loops are connected to a manifold and connected to the geothermal heat pump inside the home.This is a very good option if you own the lake and do not need permission from government agencies to install this loop system. Permits from the DNR or U S Army Corp of Engineers, if needed, are very hard to obtain and in most cases you will want to use option #2 or option #3.
2. Horizontal loop fields consist of excavating an 8' deep a trench and installing a loop field. The width and length of the trench and loop field will vary with the size of the geothermal heat pump.The sizing of the Geothermal heat pump is a function of house size and the thermal efficiency of the home. The loops are connected to a manifold that enters the house and connects to the geothermal heat pump inside. This is a good option if you have new construction on an open acreage lot with wet sand.
3. Vertical loop field consist of a series of 4" holes that are drilled with well drilling equipment to a depth of 180-200'. The 4-3/4" holes containing the vertical loops are installed 10'-12' apart and are sealed with bentonite to prevent contamination of the ground water. The number of vertical loops is a function of the size of the Geothermal heat pump and the thermal efficiency of the home. A back hoe then connects the vertical loops to a manifold. This loop field is used most often for retro fits and remodeling, or where there is a lack of soil moisture. In most remodeling situations, this the only choice for the loop field since there is a minimal disruption of the landscape and will work on a city lot.
Here is a good video on geoexchange systems.
click here http://www.youtube.com/watch?v=nWCNEoUTte4
Thanks,
Builder Bob http://www.bmichels-const.com/
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