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Ground Source Heat Pumps

The Basics

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Ground Source Heat Pumps

Definition:

•A central heating/cooling system that pumps heat to or from the ground utilizing the constant temperature of the earth rather than outside air temperature.

•Uses the earth as a heat source in the winter or a heat sink in the summer.

•Even in geographic areas that experience air temperature extremes from winter to summer, ground temperature remains relatively constant and therefore can be used to create a very efficient heating/cooling system.

•http://energy.gov/energysaver/articles/geothermal-heat-pumps

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Ground Source Heat Pumps

Types of Ground Source Heat Pumps:

• Horizontal Closed Loop

• Vertical Closed Loop

• Pond/Lake Closed Loop

• Open Loop

• Direct Exchange

• Hybrid systems utilizing a combination of the different types or heat pumps and/or in addition to another technology such as an air cooled system are also possible.• Effective where cooling needs are larger than heating needs

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Ground Source Heat Pumps

Horizontal Closed Loop Systems

• Generally the most cost effective approach for residential installations or for new construction projects where sufficient land is available.

• 4 foot deep minimum trenches with two pipes placed side by side in a 2 foot wide trench.

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Ground Source Heat Pumps

Vertical Closed Loop System• Most commonly used for commercial

installations where total amount of available land is limited or for areas where soil is too shallow for trenching.

• Holes approximately 4 inches in diameter are drilled about 20 feet apart.

• Depth ranges from 100 to 400 feet depending on system design criteria and demand.

• Pipes are fed into the holes and are connected at the bottom with a U-bend to form a loop. The loops are then connected to a manifold or directly to the heat pump system location inside the building.

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Ground Source Heat Pumps

Pond/Lake Closed Loop System

• Lowest cost option if a site has adequate water body

• Water must reach a minimum volume, depth and quality criteria

• A supply line pipe is run underground from the building to the pond/lake and coiled at least 8 feet under the surface to prevent freezing.

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Ground Source Heat Pumps

Open Loop System

• This type of system uses well or surface body water as the heat exchange fluid that circulates directly through the GHP system. Once it has circulated through the system, the water returns to the ground through the well, a recharge well, or surface discharge.

• Only practical where there is an adequate supply of relatively clean water and where local codes and regulations regarding groundwater discharge allow.

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Ground Source Heat Pumps

Direct Exchange System

• Ground coupling is achieved through a single loop circulating refrigerant in direct thermal contact with the ground (as opposed to a combination of refrigerant loop and water loop)

• There is no direct interaction between the fluid and the earth, only heat transfer through the pipe wall

• Higher efficiency is related to the elimination of a water pump and water-to-refrigerant heat exchanger and the latent heat phase change of the refrigerant in the ground itself.

• While contained the refrigerant is harmless, however leaks and improper disposal cause the refrigerant to be an ozone depleting substance. This refrigerant is slowly being phased out and replaced with ozone-friendly R410A.

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Ground Source Heat PumpsAdvantages Disadvantages

• Extremely efficient operation• Can be used for both heating and

cooling• Renewable energy• Clean operation. No combustion on

site.• Long life (25 years for indoor

equipment and 50+ for ground loop)• Very low maintenance for ground loop• Elimination of noise caused by outdoor

air cooled units• Installation cost payback through

energy savings in as little as 5 to 10 years

• Costly installation• Not a good solution for retrofits, which

typically require high output temperatures, ultimately lowering the efficiency of the system.

• Majority of energy use is electricity to operate indoor equipment

• Low output temperatures are required for high efficiency

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Ground Source Heat Pumps

Economic Impact

• The US Environmental Protection Agency (EPA) has called ground source heat pumps the most energy-efficient, environmentally clean, and cost-effective space conditioning systems available.

• Ground source heat pumps can be designed for a 100% renewable energy system if it includes components that use only renewable energy.

• Produce less greenhouse gases than air conditioners, oil furnaces, and electric heating.

• For areas not served by natural gas, no better alternative currently exists.

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Ground Source Heat PumpsCONCLUSION . . .

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