City of Alexandria, VA
Page updated Jul 27, 2012 9:28 AM
Ground-Source Heating and Cooling
Ground-source heat pumps have earned generous amounts of praise and attention recently, but what sets it apart from other heating and cooling systems?
Also known as geothermal, geoexchange, or water-source heat pumps, ground-source heat pumps utilize the earth's relatively constant temperature of 50 - 60°F to heat and cool buildings. Unlike other heating systems, ground-source heat pumps do not convert heat from an energy source but simply move the earth’s natural heat to and from a building. As a result, geothermal systems are 50 - 70% more efficient than other heating systems and 20 - 40% more efficient than most air conditioners. Geothermal heat pumps even achieve greater efficiency than traditional air-to-air heat pumps which rely on extremely variable outdoor air temperatures.
The two categories of geothermal heat pumps, closed-loop and open-loop systems, differentiate in ground connection and can be adapted to a variety of building scenarios. Typically areas near rivers, lakes, and streams benefit most from the very cost-effective open-loop systems, which draw water to use as a heat source or heat sink. Open-loop water-source systems are generally slightly more efficient than closed-loop designs, depending on factors such as water quality and source. It is important to note that open-loop systems, though widely regarded as environmentally friendly, are subject to local and state regulations in environmentally sensitive areas where water should not be redistributed into the ground supply.
Closed-loop, or earth-coupled, systems circulate a solution of water and non-toxic antifreeze (propylene-glycol) via ground loop piping to extract the earth's heat. Depending on the available space and design, the polyethylene ground loops can be installed horizontally or vertically with drilling equipment. In northern Virginia where space is limited, a vertical closed-loop system would effectively meet the heating and cooling needs of home and business owners. For buildings with high energy needs and limited ground availability, a hybrid design supplementing a ground-source heat pump with a boiler or chiller can meet the necessary heating and cooling demands. Although closed-loop systems are associated with larger upfront costs than open-loop systems, they are virtually maintenance-free after installation.
Users of ground-source heat pumps discover significant savings in operation and maintenance costs, when compared to conventional heating systems. Since all necessary equipment remains housed indoors or underground, ground-source heat pumps boast an average lifespan of 25 years compared to a lifespan of 10-15 years for standard heat pumps. Additionally ground-source heating systems can provide up to 40 to 50% of a building's hot water needs and at no additional cost to the owner. Electric utilities also frequently offer special incentives and rebates for owners of geothermal systems, as geothermal heat pumps assist in reducing expensive peak loads.
Furthermore, ground-source heat pumps provide numerous environmental benefits, including decreased dependence on costly fossil fuels, reduced greenhouse gas emissions, and increased energy conservation. Homeowners undergoing new construction and renovations are increasingly demanding more eco-friendly, high-efficiency equipment, like ground-source heat pumps, from builders and contractors.
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