There are basically four types of GHPs (click on the thumbnails to view larger):

• Horizontal
• Vertical
• Pond/lake (these three are closed-loop systems)
• and open-loop systems

Horizontal: This is generally most effective for new-construction, residential installations. The most common layouts use either two pipes with one buried at six feet and one at four feet or two pipes buried side-by-side at five feet

Vertical: This is often used by comercial buildings when the land area that is required for horizontal GHPs isn’t feasible, and when the soil is too shallow for trenching. Four inch holes are drilled twenty feet apart and one hundred to four hundred feet deep; pipes that are connected to horizontal pipes are dropped into these holes. The horizontal pipes are connected to the heat pump in the building. This type of GHP minimizes disturbance on existing landscaping.

Pond or Lake: Of course this type of GHP is used only when there is an adequate body of water nearby. If that is the case, this can be the cheapest option. The pipes are coiled at least eight feet under the surface of the water to prevent them from freezing. The volume, depth, and quality of the body of water are all factors you have to consider when looking at this type of heat pump.

Open-loop System: This uses a well or surface body water as the heat exchange fluid that circulates through the pump system. After it has circulated the water is returned to the ground through another well. This option is only possible when there is relatively clean water in the area and local regulations are met.

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Geothermal heat pumps (GHPs), also know as GeoExchange, ground-source, earth-coupled, or water-source heat pumps, have been used since the late 1940’s. This kind of heat pump uses the constant temperature of the earth as the exchange medium. GHPs are more efficient in colder climates than air-source heat pumps. They have a much higher efficiency than air-source heat pumps too, and can, if properly equipped, supply the house’s hot water. Because they are underground they are not susceptible to vandalism, and they are extremely quiet. GHPs control indoor humidity making them very effective in humid climates.

The main reason GHPs are not more widely used than other heat pumps is the high cost. They are quite expensive, but mainly because they are so difficult to install. The average cost is about $2500 per ton. However, GHPs are gaining popularity; approximately 40,000 GHPs are installed in the US every year. Typical anual energy savings are 30-60% which means that it is possible to recoup the initial investment in 2-10 years just through lower utility bills!

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Energy Star funded a research that shows more than 50% of all heat pumps have problems with leaky ducts,

Low air-flow: There should be 400 to 500 cubic feet per minute (cfm) air-flow for ever ton of the pump’s air conditioning capacity. the pump’s efficiency deteriorates if the air-flow is much less than 350 cfm. Cleaning the evaporator coil and increasing the fan speed can sometimes help here, but modifications to the duct-work is often needed.

Incorrect refrigerant charges: This usually doesn’t occur in the packaged systems because they got charged in the factory, but the split-systems get charged in the field, which often results in too much or too little charge. The system should be checked for leaks every time it is serviced. The air-flow needs to be measured before the system is charged because that changes the amount of refrigerant the system needs. Too much or too little refrigerant reduces the heat pump’s performance and efficiency.

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This is a type of heat pump which utilizes outside air to heat or cool an interior space. They are more efficient than many heat pumps, but less efficient than ground-source heat pumps. However, they are cheaper to install than ground-source heat pumps, and have become widespread in recent years.

Air-source heat pumps work best in more moderate climates. Extended periods of below-freezing temperatures make the pump work too hard for it to be very efficient.

Most air-source heat pumps are split-systems: they have one copper coil indoors and one outdoors. The supply and return ducts are connected to a central fan also located indoors. Some air-source heat pumps are packaged systems. These usually have both coils and the fan outside with the air delivered through duct-work in the wall or roof.

Air-source heat pump efficiency is indicated by the HSPF (Heating System Performance Factor) and the SEER (Seasonal Energy Efficiency Ratio).

• HSPF is the rating for the system’s heating efficiency. The most efficient systems have an HSPF rating between 8 and 10.
• The SEER rates the pumps cooling efficiency. Usually the higher the SEER the more expensive the system. The most efficient pumps have a SEER between 14 and 18. This rating is more important than the HSPF in warmer climates.

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