Ground-Source Heat Pump System Information

Geothermal Heat Pump 

Distribution Subsystem 

Water Heating 

Types of Systems

Closed and Open Loops
There are two basic types of loops: closed and open.
Open loop systems are the simplest. Used successfully for decades, ground water is drawn from an aquifer through one well, passes through the heat pump's heat exchanger, and is discharged to the same aquifer through a second well at a distance from the first. Generally, two to three gallons per minute per ton of capacity are necessary for effective heat exchange. Since the temperature of ground water is nearly constant throughout the year, open loops are a popular option in areas where they are permitted. Open loop systems do have some associated challenges:

1. Some local ground water chemical conditions can lead to fouling the heat pump's heat exchanger. Such situations may require precautions to keep carbon dioxide and other gases in solution in the water. Other options include the use of cupronickel heat exchangers and heat exchangers that can be cleaned without introducing chemicals into the ground water.
2. Increasing environmental concerns mean that local officials must be consulted to assure compliance with regulations concerning water use and acceptable water discharge methods. For example, discharge to a sanitary sewer system is rarely acceptable. 

Horizontal Loops
Horizontal closed loop installations are generally most cost-effective for small installations, particularly for new construction where sufficient land area is available. These installations involve burying pipe in trenches dug with back-hoes or chain trenchers. Up to six pipes, usually in parallel connections, are buried in each trench, with minimum separations of a foot between pipes and ten to fifteen feet between trenches.

Vertical Loops
Vertical closed loops are preferred in many situations. For example, most large commercial buildings and schools use vertical loops because the land area required for horizontal loops would be prohibitive. Vertical loops are also used where the soil is too shallow for trenching. Vertical loops also minimize the disturbance to existing landscaping. 
For vertical closed loop systems, a U-tube (more rarely, two U-tubes) is installed in a well drilled 100 to 400 feet deep. Because conditions in the ground may vary greatly, loop lengths can range from 130 to 300 feet per ton of heat exchange. Multiple drill holes are required for most installations, where the pipes are generally joined in parallel or series-parallel configurations. 

Slinky Loops
Increasingly, coils -- overlapping coils of polyethylene pipe -- are used to increase the heat exchange per foot of trench, but require more pipe per ton of capacity. Two-pipe systems may require 200 to 300 feet of trench per ton of nominal heat exchange capacity. The trench length decreases as the number of pipes in the trench increases -- or as Slinky coil overlap increases. (Illustration below shows a slinky coil in a pond)

Pond Loops
Pond closed loops are a special kind of closed loop system. Where there is a pond or stream that is deep enough and with enough flow, closed loop coils can be placed on the pond bottom. Fluid is pumped just as for a conventional closed loop ground system where conditions are suitable, the economics are very attractive, and no aquatic system impacts have been shown.

Conclusion 
Geothermal heating and cooling systems can be connected to the earth in a variety of ways -- all thoroughly field proven. However, high performance requires the use of experienced professionals who understand local conditions. Contact Groundwater Services today to discuss the best system for you.

Details and Diagrams

Geothermal Heating and Cooling Systems (see our Geothermal Simulator)
In a geothermal heating and cooling systems, the heat pump is connected to the building by a distribution system -- most commonly air ducts. And the heat pump is connected to the earth through a series of pipes called a "loop" (see Types Of Systems above). The system exchanges heat with the earth, meaning that no noisy or unsightly outdoor unit is needed. 

Vapor Compression Cycle
All heat pumps use a vapor compression cycle to transport heat from one location to another. In heating mode, the cycle starts as the cold liquid refrigerant within the heat pump passes through a heat exchanger (evaporator) and absorbs heat from the low-temperature source (fluid circulated through the earth connection). The refrigerant evaporates into a gas as heat is absorbed. The gaseous refrigerant then passes through a compressor where it is pressurized, raising its temperature to over 180 degrees F. The hot gas then circulates through a refrigerant-to-air heat exchanger where the heat is removed and sent through the air ducts. When the refrigerant loses the heat, it changes back to a liquid. The liquid refrigerant cools as it passes through an expansion valve, and the process begins again. 
Although heat pumps are complex internally, they are marvels of compact design for reliability. Some include features such as additional heat exchangers for water heating, and microprocessor-based automatic controls and protection devices. 

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Geothermal Advantages

The Benefits Speak for Themselves
Tens of thousands of homes are being built or retrofitted with geothermal heating and cooling systems every year, because of the advantages these systems offer: economical operation, noise reduction, and product quality. Initially reserved for the most expensive homes, now these systems have become affordable options for thousands of low and moderate income housing units because of the system's low life cycle costs compared to all other alternatives in almost every region of the country.

Geothermal Heating and Cooling Makes Sense
Geothermal systems are efficient, environmentally-sensitive, comfortable, and economical. Operating savings often provide paybacks of considerably less than five years -- sometimes less than two years. In addition, electric utilities such as BGE are so convinced of the value of this technology for their customers that they offer design assistance, referrals, or financial incentives to defray the first cost increment of geothermal systems. 
The key is that geothermal heat pumps use electricity to move heat, not to generate it by the burning fuel or using electric resistance elements. Indeed, the U.S. EPA has found that no other technology with more favorable operating efficiencies and economics than emerging geothermal heat and cooling systems.

An Important Renewable Energy Technology
The U.S. Environmental Protection Agency has concluded that well-designed and properly installed high efficiency geothermal heat pump systems produce less environmental harm than any other alternative space conditioning technology currently available. On a full fuel cycle basis, emerging geothermal systems are the most efficient technology available, with the lowest CO2 emissions for minimum greenhouse warming impact. Overall, the EPA found emerging geothermal heating and cooling systems to have the lowest environmental cost of all technologies analyzed -- including air-source heat pumps and natural gas furnaces.

Geothermal Heat Pump Systems Work!
No existing space conditioning technology offers greater comfort, economy, or environmental benefits than the geothermal heat and cooling systems now available for residential and commercial installations. Hundreds of thousands of installations are in place in the United States today, and the number is rapidly increasing. More than 97 percent of all geothermal heat and cooling customers are completely satisfied with their systems. 

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