You get a lot of choices these days when it comes to HVAC systems. One of the more efficient options takes advantage of the earth’s constant underground temperature around 30 feet below the surface.
Geothermal heat pumps (GHPs), also known as ground-source heat pumps, can heat, cool, and even supply hot water to a home. It does this by transferring heat to or from the ground. This technology has been providing comfort to consumers for more then 50 years and has the potential to cut energy bills by up to 65% compared to a traditional HVAC system. Below are 5 things you need to know about geothermal heat pump systems.
GEOTHERMAL HEAT PUMPS CAN BE USED IN ANY CLIMATE
Geothermal heat pumps can operate in any climate—hot or cold—because of the earth’s constant underground temperature (from 45° to 75° F depending on location). In fact, millions of GHP systems are already heating and cooling homes and businesses worldwide, and that includes all 50 U.S. states.
According to a U.S. Department of Energy report, more than half of GHP shipments in 2009 went to 10 states: Florida, Illinois, Indiana, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, and Texas. The map below also shows a higher concentration of GHP applications in states that have cold climates and high population densities.
Open and Closed-Loop Systems
Consumers have several options to consider when it comes to selecting a GHP system, including closed- or open-loop designs. The majority (85%) of GHPs in the United States use ground heat exchangers to circulate fluid through a closed-loop design. The pipes are typically made of plastic tubing and are buried horizontally (up to 6 feet deep) or vertically (up to 600 feet deep). The design of a ground heat exchange system can vary and depends on the climate, soil conditions, land availability, accessibility to groundwater or surface water bodies, and local installation costs at the site.
Geothermal Heat Pumps Last a Long Time
Think of GHPs as a long-term investment. They’re built to last and have extremely long life spans. Expect to get around 25 years out of GHP indoor components (i.e. the heat pump) and 50-plus years for ground loops.
Although installation costs can be up to several times more expensive, GHPs are up to 65% more efficient than traditional HVAC units and pay themselves back over time in energy savings—typically within 10 years.
Geothermal Heat Pumps Reduce Peak Electricity Demands and Carbon Emissions
As mentioned above, GHPs are more energy efficient than traditional HVAC systems and can help lighten the load on the electric grid, especially during summer peak demand. In addition, they can help reduce carbon emissions thanks to their high efficiency.
Geothermal Heat Pumps Create U.S. Jobs
GHP systems also help grow the U.S. energy economy. Virtually all of the parts (ground heat exchangers, heat pumps, etc.) are made in the United States and the installation of GHPs can never be outsourced. This helps stimulate local economies by hiring area contractors to dig holes and install each GHP system.
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Geothermal heat pumps (GHPs), sometimes referred to as GeoExchange, Geothermal systems or earth-coupled, ground-source, or water-source heat pumps, have been in use since the late 1940s. They use the constant temperature of the earth as the exchange medium instead of the outside air temperature.
As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water. Some models of geothermal systems are available with two-speed compressors and variable fans for more comfort and energy savings. Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.
A dual-source heat pump combines an air-source heat pump with a geothermal heat pump. These appliances combine the best of both systems. Dual-source heat pumps have higher efficiency ratings than air-source units, but are not as efficient as geothermal systems. The main advantage of dual-source systems is that they cost much less to install than a single geothermal unit, and work almost as well.
Even though the installation price of a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, the additional costs are returned to you in energy savings in 5 to 10 years. System life is estimated at 12-15 years for the inside components and 50+ years for the ground loop. There are approximately 50,000 geothermal heat pumps installed in the United States each year. For more information, visit the International Ground Source Heat Pump Association.
Types of Geothermal Heat Pump Systems
There are four basic types of ground loop systems. Three of these — horizontal, vertical, and pond/lake — are closed-loop systems. The fourth type of system is the open-loop option. Which one of these is best depends on the climate, soil conditions, available land, and local installation costs at the site. All of these approaches can be used for residential and commercial building applications.
Most closed-loop geothermal heat pumps circulate an antifreeze solution through a closed loop — usually made of plastic tubing — that is buried in the ground or submerged in water. A heat exchanger transfers heat between the refrigerant in the heat pump and the antifreeze solution in the closed loop. The loop can be in a horizontal, vertical, or pond/lake configuration.
One variant of this approach, called direct exchange, does not use a heat exchanger and instead pumps the refrigerant through copper tubing that is buried in the ground in a horizontal or vertical configuration. Direct exchange systems require a larger compressor and work best in moist soils (sometimes requiring additional irrigation to keep the soil moist), but you should avoid installing in soils corrosive to the copper tubing. Because these systems circulate refrigerant through the ground, local environmental regulations may prohibit their use in some locations.
This type of installation is generally most cost-effective for residential installations, particularly for new construction where sufficient land is available. It requires trenches at least four feet deep. The most common layouts either use two pipes, one buried at six feet, and the other at four feet, or two pipes placed side-by-side at five feet in the ground in a two-foot wide trench. The Slinky™ method of looping pipe allows more pipe in a shorter trench, which cuts down on installation costs and makes horizontal installation possible in areas it would not be with conventional horizontal applications.
Large commercial buildings and schools often use vertical systems because the land area required for horizontal loops would be prohibitive. Vertical loops are also used where the soil is too shallow for trenching, and they minimize the disturbance to existing landscaping. For a vertical system, holes (approximately four inches in diameter) are drilled about 20 feet apart and 100 to 400 feet deep. Into these holes go two pipes that are connected at the bottom with a U-bend to form a loop. The vertical loops are connected with horizontal pipe (i.e., manifold), placed in trenches, and connected to the heat pump in the building.
If the site has an adequate water body, this may be the lowest cost option. A supply line pipe is run underground from the building to the water and coiled into circles at least eight feet under the surface to prevent freezing. The coils should only be placed in a water source that meets minimum volume, depth, and quality criteria.
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. This option is obviously practical only where there is an adequate supply of relatively clean water, and all local codes and regulations regarding groundwater discharge are met.
Hybrid systems using several different geothermal resources, or a combination of a geothermal resource with outdoor air (i.e., a cooling tower), are another technology option. Hybrid approaches are particularly effective where cooling needs are significantly larger than heating needs. Where local geology permits, the “standing column well” is another option. In this variation of an open-loop system, one or more deep vertical wells is drilled. Water is drawn from the bottom of a standing column and returned to the top. During periods of peak heating and cooling, the system can bleed a portion of the return water rather than reinjecting it all, causing water inflow to the column from the surrounding aquifer. The bleed cycle cools the column during heat rejection, heats it during heat extraction, and reduces the required bore depth.
- Information for this post comes from www.energy.gov
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