How does a geothermal pump work to heat and cool homes? Janalee Coyle
Audience & Scope: The purpose of this document is to provide homeowners and people interested in building their own homes with information on geothermal heating and cooling systems. The document assumes readers have a basic knowledge of heating and cooling systems used in homes. This documents provides readers with advantages, components, the heating/cooling process, maintenance, and costs of geothermal systems.
Introduction: The ground makes for an optimum source of heat. In the United States, shallow ground remains at a constant temperature throughout the year. For these reasons, geothermal heat pumps are used to heat and cool homes throughout the country. Geothermal temperature controls are heating and cooling systems used to heat and cool homes through a set of pipe loops containing water to gain or transfer heat to and from the ground. This type of heating and cooling system is different from traditional systems because it does not convert the outside air to warm or cool temperatures. Geothermal systems are becoming increasingly popular; about 50,000 systems are installed each year in the United States.
Advantages: Table 1: Geothermal System Consume less energy No outside units Reduce air pollution Less noise 400%-600% efficient Inside unit lasts 25 years Outside components last 50 years Less fossil fuel use Lower utility bills No weather damage to outside units
Traditional System Consume more energy Air conditioning unit outside More air pollution Noisy Gas furnaces are 98% efficient Air conditioners last 8 to 15 years Gas furnaces last 15 years Use fossil fuels to heat homes Higher Utility bills Weather can damage outside units
Components/Parts Geothermal heat pump systems consist of three parts: the heat-pump unit, the liquid heat-exchange medium (open or closed loop), and the air-delivery system (ductwork). Heat-Pump Unit: The pump unitâ€™s main purpose is to deliver air to the air ducts. The pump works differently according to the season. In the winter, the pump will remove heat from the heat exchanger. In the summer, the process is reversed; the pump moves heat from the indoor air into heat exchanger. Sometimes the heat from the indoor air is used to heat water. Heat-Exchange Medium: There are two types of heat exchangers, closed loop and open loop. Both systems use pipes to transfer fluid, water or antifreeze, to and from the home. In an open loop system, water is pumped out of a well or aquifer and sent into the home to exchange its heat. It is then pumped back out and discharged into the well in which it was originally pumped. This option is only practical where there is an adequate supply of relatively clean water and all local codes allow it. The figure below shows a schematic of a typical open loop system.
In a closed loop system, all the fluid leaves the home to go through the heat exchanger and is delivered back to the home after it finishes its loop. Closed loop systems are typically buried 5 to 8 feet underground. At a depth of 5 to 8 feet, the ground temperature is around 55 degrees Fahrenheit and is not affected my climate or weather conditions. The piping is installed in long, horizontal rows so the water is able to gain enough heat. Many times pipes are in the shape of slinkys to save space. The image below shows a schematic of a typical closed loop system.
Figure 2 Air-Delivery System/Ductwork: After the heat exchanger converts the air, it delivers it to ducts, which delivers warm or cool air throughout the home.
Heating/Cooling Process: Geothermal heating and cooling systems have two different functions depending on the time of the year. Heat likes to move to cooler areas to transfer energy and provide warmth to the area. Geothermal heating and cooling systems apply this concept when using the ground to heat the water within the pipe loops. When water runs through the heat exchanger loops, the heat from the ground moves to the pipe to heat the water or heat moves from the heat exchanger to the ground. The system only needs a few materials to function and can provide comfortable temperatures to homes with very little effort. Heat:
During the winter, geothermal heating and cooling systems absorb heat stored in the ground through the water circulating in its underground loop. The heat is carried through the in ground pipes to the heat pump where it is concentrated and then sent as warm air throughout the home. The cool air from the home is sent back out of the home through the heat pump and then into the in ground pipes. This cool air is reheated and sent back into the home. Air continually recycled to preserve energy and keep heat within the home. The same concept is applied to homes using the geothermal system to provide heat to the water heater. The figure below displays how the air is circulated in and out of the heat pump unit and water heater.
Air-Conditioning: During the summer, the ground is cooler than the air. For this reason, the system is able to absorb warm air from the home and reject it to into the underground loop as it is absorbed into the ground. The cool air is returned to geothermal pump and delivered through vents throughout the home. The warm air from the home is also transferred into the hot water heater to provided hot water to the home. This process is more efficient in the summer because the heat is directly moved from the home into the hot water heater. The figure below displays how the air is circulated in and out of the heat pump unit and water heater.
Maintenance: Geothermal heating and cooling systems require minimal maintenance. They have fewer components than other systems, and most of these components are protected from weather. Most of the underground piping systems are guaranteed to last 50 years or more. The inside components are easily accessible. The only required maintenance is periodic checks for filter changes and annual coil cleaning.
Costs: Geothermal systems have a higher up front cost than traditional heating and cooling units but can greatly reduce the month-by-month utility costs. Systems can reduce heating, cooling, and hot water costs by about 80%. The following factors will affect the cost of the installation of a typical geothermal heating and cooling system:
The type of group loop o Horizontal loops near the surface are less expensive than vertical loops deeper within the ground o Drilling can greatly increase the costs of the system The type of landscaping needed after excavation o After excavating the system a great amount of landscaping is usually required The size of the home o The greater the size of the home the greater the cost of the system The cost of the contactor The installation of duct work The option for water heating o Water heating is an additional option most contractors supply The soil density o Dense soils are best for installation o Also rough terrain will increase costs
Geothermal systems typically pay for themselves within 5 to 10 years of installation due to lower energy costs. In addition, energy star certified systems come with a tax rebate including 30% of installation costs. The following chart displays a cost comparison between a geothermal heating and cooling system and a conventional heating and cooling system.
Table 2: Geothermal System (2,000 sq. ft. home) $2,500 per ton capacity 3 ton unit $7,500 30% tax rebate $2,250 Initial cost with rebate $5,250 $35-$70 energy savings per month 12 months $840 How many years does it takes for savings to cover installation costs? 6.25 years Conventional Systems (average prices) Air Conditioning Unit 1 unit $2,600 Furnace 1 unit $1,500 Initial Cost $4,100 Electricity $30-$100 12 months $1,200 Gas $40-$150 12 months $1,800 Utility Costs per year $3,000 *Please note maximum utility prices were used
Conclusion: Geothermal heating and cooling systems are efficient home appliances which help to reduce energy consumption and costs. They help improve the environment and only use a few components. Although installation costs are extremely high, the long lifespan of systems and lower utility bill costs make this a great option for homeowners and homebuilders.
References: Content: "Geothermal Energy." Renewable Energy World. National Renewable Energy Laboratory and the Department of Energy., 2014. Web. 01 Mar. 2014. <http://www.renewableenergyworld.com/rea/tech/geothermal-energy>. "Geothermal Heat Pumps." Energy.gov. US Department of Energy, 2012. Web. 02 Mar. 2014. <http://energy.gov/energysaver/articles/geothermal-heat-pumps>. Egg, Jay. "Ten Myths About Geothermal Heating and Cooling." National Geographic. National Geographic, 17 Sept. 2013. Web. 03 Mar. 2014. <http://energyblog.nationalgeographic.com/2013/09/17/10-myths-aboutgeothermal-heating-and-cooling/>. Klar, Robert. "Principles and Components of Geothermal Heat Pump Systems." Buildipedia. N.p., 2 Dec. 2009. Web. 03 Mar. 2014. <http://buildipedia.com/aec-pros/construction-materials-and-methods/principlesand-components-of-geothermal-heat-pump-systems>. Figures: Figures 1 & 2: "Geothermal Heat Pumps." Energy.gov. US Department of Energy, 2012. Web. 02 Mar. 2014. <http://energy.gov/energysaver/articles/geothermal-heat-pumps>. Figures 3 & 4: "How It Works: Geothermal Heating and Cooling." Water Furnace. N.p., n.d. Web. 03 Mar. 2014. <http://www.waterfurnace.com/how-it-works.aspx>. Cover Photo: "Geothermal Energy Illustrated." Alternate Energy Geek. N.p., n.d. Web. 03 Mar. 2014. <http://www.alternative-energy-geek.com/diagram-of-geothermal-energy.shtml>. Note: I created Tables 1 & 2