Geothermal heating for Homes
Heating and Cooling Efficiency of Geothermal Heat Pumps
The heating efficiency of ground-source and water-source heat pumps is indicated by their coefficient of performance (COP), which is the ratio of heat provided in Btu per Btu of energy input. Their cooling efficiency is indicated by the Energy Efficiency Ratio (EER), which is the ratio of the heat removed (in Btu per hour) to the electricity required (in watts) to run the unit.
Look for the ENERGY STAR® label, which indicates that the unit meets ENERGY STAR criteria. Manufacturers of high-efficiency geothermal heat pumps (GHPs) voluntarily use the EPA ENERGY STAR label on qualifying equipment and related product literature. Many GHPs carry the U.S. Department of Energy (DOE) and Environmental Protection Agency (EPA) ENERGY STAR label.
Economics of Geothermal Heat Pumps
Although the purchase and installation cost of a residential GHP system is often higher than that of other heating and cooling systems, properly sized and installed GHPs deliver more energy per unit consumed than conventional systems. For further savings, GHPs equipped with a device called a "desuperheater" can heat household water. In the summer cooling period, the heat removed from the house is used to heat the water for free. In the winter, water heating costs are reduced by about 50%.
Depending on factors such as climate, soil conditions, the system features you choose, and available financing and incentives, you may recoup your initial investment in a few years through lower utility bills. And -- when included in a mortgage -- your investment in a GHP may produce a positive cash flow from the beginning. It may also be possible to include the purchase of a GHP system in an "energy-efficient mortgage" that would cover this and other energy-saving improvements to the home. Banks and mortgage companies can provide more information on these loans.
available to help offset the cost of adding a GHP to your home. These provisions are available from federal, state, and local governments; power providers; and banks or mortgage companies that offer energy-efficient mortgage loans for energy-saving home improvements. Be sure the system you're interested in qualifies for available incentives before you make your final purchase.
Evaluating Your Site for a Geothermal Heat Pump
Shallow ground temperatures are relatively constant throughout the United States, so geothermal heat pumps (GHPs) can be effectively used almost anywhere. However, the specific geological, hydrological, and spatial characteristics of your land will help your local system supplier/installer determine the best type of ground loop for your site.
Factors such as the composition and properties of your soil and rock (which can affect heat transfer rates) require consideration when designing a ground loop. For example, soil with good heat transfer properties requires less piping to gather a certain amount of heat than soil with poor heat transfer properties. The amount of soil available contributes to system design as well -- system suppliers in areas with extensive hard rock or soil too shallow to trench may install vertical ground loops instead of horizontal loops.
Ground or surface water availability also plays a part in deciding what type of ground loop to use. Depending on factors such as depth, volume, and water quality, bodies of surface water can be used as a source of water for an open-loop system, or as a repository for coils of piping in a closed-loop system. Ground water can also be used as a source for open-loop systems, provided the water quality is suitable and all ground water discharge regulations are met.
Before you purchase an open-loop system, be sure your system supplier/installer has fully investigated your site's hydrology, so you can avoid potential problems such as aquifer depletion and groundwater contamination. Antifreeze fluids circulated through closed-loop systems generally pose little to no environmental hazard.
The amount and layout of your land, your landscaping, and the location of underground utilities or sprinkler systems also contribute to your system design. Horizontal ground loops (generally the most economical) are typically used for newly constructed buildings with sufficient land. Vertical installations or more compact horizontal "Slinky™" installations are often used for existing buildings because they minimize the disturbance to the landscape.
Installing Geothermal Heat Pumps
The ground heat exchanger in a GHP system is made up of a closed or open loop pipe system. Most common is the closed loop, in which high density polyethylene pipe is buried horizontally at 4 to 6 feet deep or vertically at 100 to 400 feet deep. These pipes are filled with an environmentally friendly antifreeze/water solution that acts as a heat exchanger. In the winter, the fluid in the pipes extracts heat from the earth and carries it into the building. In the summer, the system reverses and takes heat from the building and deposits it to the cooler ground.
Ductwork in the home distributes the heated or cooled air through the house, just like conventional systems. The box that contains the indoor coil and fan is sometimes called the air handler because it moves house air through the heat pump for heating or cooling. The air handler contains a large blower and a filter just like conventional air conditioners.
Contact your insurance provider to ensure that the geothermal heat pump is covered. Even if your provider will cover your system, it is best to inform them in writing that you own a new system.
Benefits of Geothermal Heat Pump Systems
The biggest benefit of GHPs is that they use 25% to 50% less electricity than conventional heating or cooling systems. This translates into a GHP using one unit of electricity to move three units of heat from the earth. According to the EPA, geothermal heat pumps can reduce energy consumption -- and corresponding emissions -- up to 44% compared with air-source heat pumps and up to 72% compared with electric resistance heating with standard air-conditioning equipment. GHPs also improve humidity control by maintaining about 50% relative indoor humidity, making GHPs very effective in humid areas.
Geothermal heat pump systems allow for design flexibility and can be installed in both new and retrofit situations. In addition, the hardware may require less space than a conventional HVAC system, thus possibly freeing up space for other uses. GHP systems also provide excellent "zone" space conditioning, allowing different parts of your home to be heated or cooled to different temperatures.
The underground piping associated with GHP systems often carry warranties of 25 to 50 years, and the heat pumps often last 20 years or more. In addition, the components in the living space are easily accessible, which increases the convenience factor and helps ensure that the upkeep is done on a timely basis.
GHPs have no outside condensing units like air conditioners, so there's no concern about noise outside the home. A two-speed GHP system is so quiet inside a house that users usually do not know it is operating.
Geothermal is an excellent renewable heat source but there are many variables in calculating whether it's cost effective
Geothermal Heating Systems for Homes
Domestic Geothermal heating systems can be a great way to heat a home, replace a furnace, and are labeled as money savers. Question is, are they worth the hype? Here's a quick view first of how they operate.
Starting at depths of between 6 and 10 metres, the temperature of the earth is no longer influenced by variations in surface temperature, and stays relatively constant at around 8 to 10 C. So the underlying principle of geothermal heating and cooling is to use that consistent interior earth temperature to balance our wildly varying North American & Canadian surface temperatures.
With the use of heat pumps, geothermal heating and cooling systems extract heat energy and transfer it into buildings, saving approximately 50 to 60% on heating and cooling costs, depending on the fuel being compared to.
In summer months, geothermal cooling functions in a similar way to standard air conditioning, only heat is not simply ejected into the outside air, but rather deposited deep in the ground for future use. The result is guilt-free air conditioning because the heat extracted in summer months is actually used to warm the earth deep below, heat which will increase the efficiency of the ground source heat pump in winter months.
Geothermal home heating systems:
Vertical closed-loop geothermal systems have a sealed U-shaped pipe of high density polyethylene that carries a heat transfer fluid (usually a water / methanol mix) in a continuously circulating loop allowing an exchange of heat by conduction. As the liquid returns to the surface, either heated or cooled depending on the season, the additional or reduced amount of heat in the water is used to condition the home. The required depth for this system is generally 300 feet or more, and the cost is calculated by the foot. Through the nose, but by the foot.
Horizontal closed-loop geothermal systems function in the same manner as vertical systems, except that pipes are run back and forth 6 to 10 feet underground. Installation involves excavating trenches (at least 300 feet of them), rather than digging a well.
Horizontal ground source heat pump systems can be cheaper to install but require a significant amount of space, and it does some pretty intense damage to any ecosystems that lay in its intended path. For a given length of pipe, horizontal loop systems are a bit less efficient than vertical loop systems, as they can be more easily affected by surface temperatures. The other downside is that if or when there's a leak in the circuit, with a horizontal mat or grid style system the whole garden area has to be dug up again in search of a tiny leak that is losing the system pressure.
Open-loop geothermal systems use ground water pumped directly from a supply well (75 to 100 feet deep) in order to draw and inject heat. Water is pumped out of the first well, and after the heat exchange is carried out, it gets injected into the second well.
Open-loop systems have a very high thermal efficiency and installation can be up to 50% less expensive than vertical closed loop systems. However, conditions necessary for the proper function of these systems are rarely found in urban areas, as they require an abundant source of ground water and a high water table.
Will geothermal heating save me money?
That truly depends on the size of the project to heat. No geothermal system is cheap to install, and because it offers only a reduction in consumption, the return on investment is really only viable for larger buildings. For this reason geothermal is more suited to commercial or multi-unit residential projects of substantial size.
A home would have to be quite large, and somewhat poorly-insulated to actually make it pay for itself in a reasonable time frame. In many cases, particularly with moderately-sized new homes being built, that large of a financial investment towards energy efficiency could offer much greater returns if put towards heat retention instead - better windows, additional home insulation in new build, insulating existing walls from the outside during a house renovation, or better tapes and membranes for air sealing, etc.
Ball park pricing for a geothermal system: For an averaged size home (2000 sq. ft.) a GSHP will easily cost $30,000 to have installed, and that is in exchange for a monthly saving of about 50% on the heating bill. So payback for the average single family home is simply too far away to make this a financially competitive option with all but the highest consuming homes - and even then only when the boiler or furnace has failed and needs replacement.
That same investment of $25,000 (or perhaps less) in a better thermal envelope would likely reduce heating bills easily by 70 or 80%, perhaps more. Geothermal energy is an excellent global technology, but poorly insulated single family homes will get far more bang for the buck if the money is put into insulation instead, or balanced between energy saving renovations and high efficiency heat pumps
All You Need to Know About Home Geothermal Heating & Cooling
Have you heard of home geothermal heating and cooling? It’s an HVAC system that can save homeowners serious money on utility bills.
Unfortunately, many people have never heard of home geothermal, or they don’t understand it. A lot of people think it has something to do with capturing heat from volcanoes or geysers.
That would be pretty tricky to pull off for most homeowners, and it would seriously limit the number of people who could take advantage of geothermal energy.
Thankfully, you don’t have to live anywhere near an active volcano to have an effective, money-saving home geothermal system installed.
Home geothermal heating and cooling is actually fairly simple. Here’s how it works.
How does home geothermal energy work?
The temperature of the earth 10 feet below surface level is a constant 55 degrees Fahrenheit year-round.
When the air outside your home is below freezing, just 10 feet below the snow-covered ground it’s still 55 degrees. Or when summer brings 96-degree weather, the earth beneath your house keeps steady at 55 degrees.
You have probably experienced this phenomenon at home without even realizing it. When you go into your basement on a hot day, it’s nice and cool down there because the earth on the other side of your foundation is, you guessed it, 55 degrees.
In the winter, even an unheated basement stays relatively warm because of that consistent 55-degree insulation from the surrounding earth.
Geothermal systems, such as the Dandelion Energy system, take advantage of this naturally occurring constant. They harness the steady temperature surrounding any home to heat or cool it as needed.
Although it’s referred to as geothermal energy, geothermal and other home geothermal systems don’t make electricity. They use the sustained temperature of the ground to heat or cool your home.
Differences between geothermal systems
Though many geothermal systems are similar, there are differences between them. Some used a closed or open loop system, pond loops, or slinky coil ground loops.
There are pros and cons to the various loop configurations for geothermal home heating. Dandelion engineers use closed-loop systems. They see them as the most efficient and safest option for homeowners.
When a Dandelion system is installed, closed-loop pipes with a water solution are buried in the ground beneath your home. “Closed loop” means the pipes are contained only to your house. They aren’t connected to a larger infrastructure, and won’t interact with any fluid outside your system.
As this water circulates through Dandelion’s pipes, the water solution within the pipes changes temperature. In the wintertime, this 55-degree solution is warmer than the outside air.
Dandelion’s system pulls this warm solution through the pipes and uses a heat pump to warm the air from your home. This allows you to adjust the air in your home to whatever temperature you desire.
The same principle works in reverse in the summertime when Dandelion’s system uses the temperature of the ground to cool the air in your house.
It doesn’t matter if it’s a crisp 65 degrees or a toasty 88 degrees outside. Your geothermal system makes it easy to get comfortable at home.
Is geothermal really worth it?
Installation of a Dandelion system can save homeowners up to 50% on their heating and cooling bills every month. It’s a smart investment that leads to long-term savings, all while keeping your home comfortable all year round.
In the US, heating and cooling residential and commercial buildings contribute about 11 percent of the nation’s total carbon dioxide emissions.
Home geothermal systems create zero carbon emissions. Over the course of a year, using one Dandelion Energy system reduces enough carbon emissions to equal removing two cars from the road.
These wonders of engineering are also safer for your home than traditional heating and cooling systems. With Dandelion geothermal, there’s no risk of explosion or carbon monoxide leaks to endanger your family.
Geothermal heating and cooling cost
While the price of electricity, oil, or natural gas fluctuates, the cost of operating a geothermal system will stay pretty much the same. The electricity costs of a geothermal system are low and seldom vary from month to month.
Despite their many advantages, installing a conventional geothermal system for a typical home used to cost up to $50,000 or more.
However, the engineers at Dandelion, a spinoff from a Google X project, set out to drive those costs down. Thanks to their ingenuity, geothermal systems are now affordable to more homeowners.
Instead of using large drill rigs like those used to bore artesian wells, Dandelion began experimenting with smaller, more efficient drills that make one or two deep holes just a few inches wide.
The company then installs U-shaped pipes into these holes. This innovation takes up less space and creates less of a disturbance in the back yards of Dandelion customers.
Using the new equipment, installation of the ground loop pipes can be completed in days instead of a weeks, saving customers time and money.
A complete Dandelion Home Geothermal System typically costs $18,000 to $25,000. Dandelion has a no-money-down financing plan allowing homeowners to install a geothermal system with no upfront cost, and with payments starting at $150 per month.
That’s a significant decrease from current utility bills.
Geothermal Heating and Cooling
How does geothermal heating and cooling work?
Geothermal energy utilizes the relatively stable temperature of the earth that is buried and stored a few feet under its surface. Geothermal energy can potentially be harnessed in the front or back yard of your home.
Geothermal energy is harnessed from the earth.
One of the three main aspects of a geothermal system, is the series of pipes that are buried in the ground. These pipes store and transfer the relatively constant temperature the lies under the surface of the ground.
Regardless of the season or the degree of the outside temperature, the temperature of the earth a few feet underground remains constant. Where I live in Western Colorado, this temperature is 56 degrees Fahrenheit. This can differ depending on the latitude and climate of your specific location.
Over time, a substantial energy saving can be gained by using geothermal energy to heat and cool a building. This is because energy is not used or burned to produce heat, instead, energy is used to move heat through a system.
When compared to the cost of heating and cooling a residence with propane, using geothermal heating and cooling can cut up to 2/3rds of the cost.
Both large institutions as well as smaller private residences can benefit from the utilization of geothermal energy as a heating and cooling energy source.
(Side note: Geothermal energy is an extended beneficiary of the passive solar element of the Earth’s ability to store and absorb the sun’s heat in its large planetary mass. Thus, theoretically it can be debated as an extension of passive solar heating and cooling.)
There are the 3 main components of a geothermal system:
1. The Loop
The loop is located outside the building, typically buried in the ground. The loop houses a liquid that absorbs the energy of the stable temperature that exists underground. A liquid, usually water or water blended with a refrigerant (glycol antifreeze solution) runs continuously through the entire length of the loop. The geothermal loop can be installed in a vertical or horizontal orientation (see below). It is usually composed of a type of high density polyethylene pipe.
2. Geothermal Heat Pump
Also referred to as a ground source heat pump (GSHP) it is located within the building and transfers or utilizes the heat energy from the warmer or cooler temperature of the liquid solution coming from the loop to heat or cool the house. Because it is transferring energy from a stable temperature (58 degrees) in the winter, when the air outside the house is cold, the heat pump pulls the warmer temperature that is gained from the ground and uses it to heat the building. (This is possible because all temperatures above -200 degrees Fahrenheit carry heat. While -200 degrees Fahrenheit sounds very cold to me, heat can still be extracted from temperatures above that amount. Luckily, the temperature of the ground being utilized for geothermal is well above that threshold.)
In the summer, when the outside air is hot, the loop provides a place for the warmer temperature to be discharged. By the time the solution has run through the extent of the loop, it has been cooled and returns to cool the inside temperature of the house.
The geothermal heat pump functions similar to how a furnace functions, for example, it transfers the heated or cooled air from the loop to the duct work of the building. Its filter also needs to be periodically replaced.
3. Distribution System
This is the duct work within the building that distributes the heated or cooled air throughout the building. In contrast to a forced air system that periodically disseminates blasts of air, a geothermal heating or cooling system is constantly pumping air.
Option to add to the system – Hot Water Heater
A “desuperheater” can be added into a geothermal system to heat domestic hot water. In the summer when heat is being drawn from the house, the heat can first be discharged in the domestic hot water heater before it otherwise would be dispelled in the ground loop.
While geothermal heating and cooling is more energy efficient than a traditional forced air system, the cost of installing a geothermal system can cost significantly more. The extra cost spent up front, however, can be returned in the years that follow.
“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 5–10 years. System life is estimated at 25 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.”
– Energy Efficiency and Renewable Energy, U.S. Department of Energy, energysavers.gov
“In 1997, Choptank Elementary School in Cambridge, Maryland began using a GeoExchange system to efficiently heat and cool 45,000 square-feet.
It expects to save $400,000 in energy and maintenance costs over the next 20 years. Choptank Elementary School was the first school in Maryland to use a GeoExchange system.
The school is supplied by 41 ceiling-mounted GeoExchange units located above the classrooms and hallway ceilings. Three other units supply the gymnasium, cafeteria, and small conference rooms. The ground loop is buried beneath the school’s playground. It consists of 1-inch diameter pipes sunk in 100 vertical boreholes, each 275 feet deep. The system’s heating/cooling capacity is 157 tons.”
– Courtesy DOE – NREL, Lingo supplied by the Geothermal Heat Pump Consortium
The geothermal loop system is often installed vertically or horizontally. The decision to use a vertical or horizontal loop lies in the area of land that is available to encase the loop. In order to install a horizontal loop, it is said that there should be at least 1 acre of land available. Less land area is needed to install a vertical loop. The vertical loop can have pipes run at 3, 4 and 5 feet under the ground.
Most of the geothermal loop systems installed are closed loops. T
his means that the water – antifreeze solution is within the closed system of the loop.
A closed loop system can also be installed within or near water, because a large body of water will also have a constant and stable temperature.
Open loop geothermal systems can incorporate water from an outside source. These types of systems must also have an additional layer of filters installed and are not recommended for residences. If water is used, it must be in an area where the bottom layer of liquid does not freeze.
After a geothermal system is installed, the residence usually disconnects propane or other type of heating.
Electricity is still needed to operate the heat pump. The overall electricity usage and hence cost associated with electricity will typically rise, but will tend to be a lower amount than the original cost paid to the previous utility.
Here is another example of a geothermal heating and cooling application at the Oregon Institute of Technology campus
“The Oregon Institute of Technology has been using a geothermal district heating system since 1964, making it the first modern system. Today, the system heats 11 buildings (600,000 square feet), provides domestic hot water, melts snow on 2300 square feet of sidewalk, and even cools five buildings (277,3000 square feet) during the summer. The district heating system saves around $225,000 each year in heating costs, as compared to the previous fuel oil boiler system.”
– Courtesy DOE-NREL
Other Notable Snippets on Geothermal Energy
The terminology of geothermal can be confusing because it has been used to refer to any type of energy obtained from under the surface of Earth, thus geothermal can refer to hot springs, which are located intermittently throughout the world, or can refer to the harnessing and utilization of the constant relative temperature of the ground to heat and cool buildings. The information in this article dealt with harnessing the stable temperature of the ground for geothermal energy.
Before installing geothermal, it is recommended to make sure that the building is properly insulated.
The overall size of the loop depends upon the average kilo watt hour (Kwh) energy usage of the building.
Geothermal does not create any surplus of energy for a grid-tie in situation, whereas active solar can generate surplus energy.
Geothermal energy relies on electricity to power the heat pump. If there is an electrical power failure, unless a type of back up electricity is installed, the geothermal heating and cooling system will stop working.
The costs for installing geothermal are significant because of the amount of piping for the loop that must be installed in the ground. Costs for upkeep of a geothermal system are minimal, however, it is a possibility that a leak could occur within the loop. Geothermal, however, is a renewable and sustainable energy source that relies on the constant temperature of the earth.
Thank you to the Delta-Montrose Electric Cooperative for answering my questions about geothermal. DMEA has a program called GeoExchange that helps with the installation of geothermal heat and cooling pump systems for their members.
Geothermal, along with passive and active solar, wind, ocean – wave, hydro and biomass are different types of potential energy sources that can be harnessed as a more sustainable and renewable energy sources.
Geothermal Heating and Cooling Technologies
Geothermal technology harnesses the Earth’s heat. Just a few feet below the surface, the Earth maintains a near-constant temperature, in contrast to the summer and winter extremes of the ambient air above ground. Farther below the surface, the temperature increases at an average rate of approximately 1°F for every 70 feet in depth. In some regions, tectonic and volcanic activity can bring higher temperatures and pockets of superheated water and steam much closer to the surface.
Three main types of technologies take advantage of Earth as a heat source:
Geothermal energy is considered a renewable resource. Ground source heat pumps and direct use geothermal technologies serve heating and cooling applications, while deep and enhanced geothermal technologies generally take advantage of a much deeper, higher temperature geothermal resource to generate electricity.
Ground Source Heat Pumps
A ground source heat pump takes advantage of the naturally occurring difference between the above-ground air temperature and the subsurface soil temperature to move heat in support of end uses such as space heating, space cooling (air conditioning), and even water heating. A ground source or geoexchange system consists of a heat pump connected to a series of buried pipes. One can install the pipes either in horizontal trenches just below the ground surface or in vertical boreholes that go several hundred feet below ground. The heat pump circulates a heat-conveying fluid, sometimes water, through the pipes to move heat from point to point.A commercial-scale ground source heat pump system. This example is a demonstration project at a university.If the ground temperature is warmer than the ambient air temperature, the heat pump can move heat from the ground to the building. The heat pump can also operate in reverse, moving heat from the ambient air in a building into the ground, in effect cooling the building. Ground source heat pumps require a small amount of electricity to drive the heating/cooling process. For every unit of electricity used in operating the system, the heat pump can deliver as much as five times the energy from the ground, resulting in a net energy benefit. Geothermal heat pump users should be aware that in the absence of using renewable generated electricity to drive the heating/cooling process (e.g., modes) that geothermal heat pump systems may not be fully fossil-fuel free (e.g., renewable-based).
How It Works
The steps below describe how a heat pump works in “heating mode”—taking heat from the ground and delivering it to a building—and “cooling mode,” which removes heat from the building and transfers it to the ground.
- Circulation: The above-ground heat pump moves water or another fluid through a series of buried pipes or ground loops.
- Heat absorption: As the fluid passes through the ground loop, it absorbs heat from the warmer soil, rock, or ground water around it.
- Heat exchange and use: The heated fluid returns to the building where it used for useful purposes, such as space or water heating. The system uses a heat exchanger to transfer heat into the building’s existing air handling, distribution, and ventilation system, or with the addition of a desuperheater it can also heat domestic water.
- Recirculation: Once the fluid transfers its heat to the building, it returns at a lower temperature to the ground loop to be heated again. This process is repeated, moving heat from one point to another for the user’s benefit and comfort.
- Heat exchange and absorption: Water or another fluid absorbs heat from the air inside the building through a heat exchanger, which is the way a typical air conditioner works.
- Circulation: The above-ground heat pump moves the heated fluid through a series of buried pipes or ground loops.
- Heat discharge: As the heated fluid passes through the ground loop, it gives off heat to the relatively colder soil, rock, or ground water around it.
- Recirculation: Once the fluid transfers its heat to the ground, the fluid returns at a lower temperature to the building, where it absorbs heat again. This process is repeated, moving heat from one point to another for the user’s benefit and comfort.
The above-ground heat pump is relatively inexpensive, with underground installation of ground loops (piping) accounting for most of the system’s cost. Heat pumps can support space heating and cooling needs in almost any part of the country, and they can also be used for domestic hot water applications. Increasing the capacity of the piping loops can scale this technology for larger buildings or locations where space heating and cooling, as well as water heating, may be needed for most of the year.
Direct Use Geothermal
Direct use geothermal systems use groundwater that is heated by natural geological processes below the Earth’s surface. This water can be as hot as 200°F or more. Bodies of hot groundwater can be found in many areas with volcanic or tectonic activity. In locations such as Yellowstone National Park and Iceland, these groundwater reservoirs can reach the surface, creating geysers and hot springs. One can pump hot water from the surface or from underground for a wide range of useful applications.
How It Works
- Pumping: To tap into hot ground water, a well is drilled. A pumping system may be installed, although in some cases, hot water or steam may rise up through the well without active pumping.
- Delivery: Hot water or steam can be used directly in a variety of applications, or it can be cycled through a heat exchanger.
- Refilling: Depending on the use requirements of the system and the conditions of the site, the ground water aquifer may need to be replenished with water from the surface. In some cases, the movement of ground water might refill the aquifer naturally.
The water from direct geothermal systems is hot enough for many applications, including large-scale pool heating; space heating, cooling, and on-demand hot water for buildings of most sizes; district heating (i.e., heat for multiple buildings in a city); heating roads and sidewalks to melt snow; and some industrial and agricultural processes. Direct use takes advantage of hot water that may be just a few feet below the surface, and usually less than a mile deep. The shallow depth means that capital costs are relatively small compared with deeper geothermal systems, but this technology is limited to regions with natural sources of hot groundwater at or near the surface.
Deep and Enhanced Geothermal Systems
Deep geothermal systems use steam from far below the Earth’s surface for applications that require temperatures of several hundred degrees Fahrenheit. These systems typically inject water into the ground through one well and bring water or steam to the surface through another. Other variations can capture steam directly from underground (“dry steam”). Unlike ground source heat pumps or direct use geothermal systems, deep geothermal projects can involve drilling a mile or more below the Earth’s surface. At these depths, high pressure keeps the water in a liquid state even at temperatures of several hundred degrees Fahrenheit.
How It Works
- Pumping: Hot water or steam is pumped up through a deep well. As the water rises to the surface, the pressure drops and the water vaporizes into superheated steam that can be used for high-temperature processes.
- Delivery: The heat from the hot water or steam can be used to heat a secondary fluid (a “binary” process), or the hot water or steam can be used directly.
- Recirculation: Once the heat is transferred to the delivery system, the now-cooler water is pumped back underground.
- Dispersal: Unlike ground source heat pumps, used ground water in this case is simply injected and allowed to disperse back into the ground, rather than being pumped through a closed loop of pipes.
Deep geothermal sources provide efficient, clean heat for industrial processes and some large-scale commercial and agricultural uses. In addition, steam can be used to spin a turbine and generate electricity. Although geothermal steam requires no fuel and low operational costs, the initial capital costs—especially drilling test wells and production wells—can be financially challenging. Steam resources that are economical to tap into are currently limited to regions with high geothermal activity, but research is underway to develop enhanced geothermal systems with much deeper wells that take advantage of the Earth’s natural temperature gradient and can potentially be constructed anywhere. Enhanced systems can use hydraulic fracturing techniques to engineer subsurface reservoirs that allow water to be pumped into and through otherwise dry or impermeable rock.
Geothermal energy is heat that comes from the subsurface of the earth — a region of the mantel where temperatures range from 45 to 75 degrees Fahrenheit at all times. Geothermal power plants tap into this thermal heat to generate electricity. We can also use this energy to heat or cool homes directly through a residential geothermal energy system.
Residential geothermal systems use a heat pump to exchange heat with the earth to heat a home in the winter and cool it in the summer. These systems have significant environmental advantages. First, geothermal energy is a clean source of energy and the system requires only a small amount of electricity to operate. Also, geothermal energy is accessible 24 hours a day, making it a reliable energy source with an extremely low carbon footprint.
Selecting the best geothermal system for your home depends on your local climate, how much land you have available, and soil conditions. If you’re interested in using geothermal energy in your home, it’s essential to understand the different options available, including closed-loop, open-loop, and hybrid systems.
This type of geothermal energy system is the most common, and it typically includes two different loops made of plastic tubing. The first is the refrigerant loop, which is installed inside your home. The second is the water loop, which is typically buried underground.
As the fluid circulates in the outside tubing, the ground heats it. Then, the fluid goes into the home where it exchanges heat with the refrigerant loop. Of the closed-loop systems, there are three varieties to know:
1. Vertical Loop System
In this geothermal system, you install the tubing vertically in the ground. If your property has limited land available — or you want to minimize the impact on your landscaping — this option may be ideal. However, if you live in an area with rocky ground, digging holes between 100 and 500 feet deep may prove too difficult.
Of all the closed-loop systems, vertical systems are considered the most expensive to install. However, the total cost will depend on multiple factors, including environmental factors, regulations, and square footage. Consult with a professional to receive an accurate cost estimate.
2. Horizontal Loop System
For this type of geothermal system, you install the tubing horizontally, which tends to be more effective than vertical installations. However, this requires more land than a vertical system. Plus, with the tubing closer to the surface of the ground — around 3.5 to 6.5 feet — it’s more likely to be affected by weather conditions. Therefore, it’s usually not recommended for homeowners who see long or cold winters.
This closed-loop geothermal system is typically cheaper than its vertical counterpart, making the initial installation more affordable. Contact a professional to learn more about specific land requirements and pricing.
3. Pond/Lake Loop System
Do you have a body of water on your land? If so, you can choose this geothermal energy system, where you install the tubing at the bottom of a pond or lake. The tubing is laid in a coil, also called a “slinky” closed-loop at least eight feet under the water’s surface to prevent winter freezing.
This geothermal system is ideal when it is a viable option because it tends to be less expensive than other installations. The price varies depending on how close the water body is to your home.
Similar to a pond/lake loop system, an open-loop system requires water via a well or a surface body of water. The liquid gets directed into the tubing and to the heat pump, where the heat is exchanged with the refrigerant loop. Then the water returns to the ground through the well or surface discharge. This option is best for homeowners who have an adequate supply of clean water and can meet all local codes and regulations.
On average, open-loop systems are cheaper to install than closed-loop ones, allowing you to save up to 60 percent on the costs. Keep in mind, however, that these systems also require more maintenance than other geothermal systems, including filter changes, water softening, and well testing.
Hybrid systems aren’t as conventional as closed- or open-loop systems, but they’re still available.
They take advantage of a combination of geothermal resources, such as standing column wells and cooling towers. These geothermal systems are primarily used for cooling, rather than heating, making them a viable option for homeowners in warmer regions.
Choosing the Right Geothermal System
If you plan to make the switch to geothermal energy, you can realize many benefits. Geothermal heat pumps typically use 25 percent to 50 percent less electricity than conventional heating and cooling systems. They are also generally quieter, last longer, and need less maintenance than conventional systems. You can save up to 60 percent on heating costs and up to 50 percent on cooling costs each year. Plus, you can take advantage of federal tax credits to bring down the costs of installation.
Before you make the switch, do your research and decide which type of system is right for you. Closed-loop, open-loop, and hybrid options all come with pros and cons, but each one delivers key benefits for homeowners. Determining which type of system fits your living situation will lead to long-term contentment.
See how a residential geothermal system works in this video from the U.S. Department of Energy:
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