Geothermal Heating and Cooling Systems
What is a geothermal heating and cooling system?
A geothermal heat pump system
is an electrically powered device that uses the natural heat storage ability of the earth and/or the earth's ground water to heat and cool your home.
Geothermal heat pumps provide the most efficient method of heating or cooling your home or business by using the constant temperature of the earth as the exchange medium instead of the outside air temperature. The operating costs can be as much as 70% cheaper to operate than a basic heating and cooling system.
Specifically, a water antifreeze solution is piped through polyethylene loops to collect the earth’s natural heat, which is circulated to a heat exchanger that reacts with a refrigerant to create more heat (like your refrigerator in reverse). The loops can be inserted in vertical boreholes, laid in horizontal trenches or sunk in a pond or lake. This heat is distributed to your home through existing ductwork.
How does a geothermal heating and cooling system work?
Outdoor temperatures fluctuate with the changing seasons but underground temperatures don’t. Four to six feet below the earth’s surface, temperatures remain relatively constant year-round, ranging from 45°F or so in northern latitudes to about 70°F in the southern states. A geothermal system takes advantage of this constant temperature to provide extremely efficient heating and cooling.
In winter, a water antifreeze solution circulating through pipes buried in the ground absorbs heat from the earth and carries it into the home. The geothermal system inside the home uses a heat pump to concentrate the earth's thermal energy and then to transfer it to the air circulating through your ductwork to fill your home with warmth.
In the summer, the process is reversed: heat is extracted from the warm air in your house and it is then transferred through the heat pump to the ground loop piping. The water antifreeze solution in the ground loop then carries this excess heat back to the earth. The only external energy needed for the geothermal system is the small amount of electricity needed to operate the ground loop pump, fan, and compressor.
What is the science behind geothermal heat pump system?
Anyone with a refrigerator or an air conditioner has witnessed the operation of a heat pump, even though the term heat pump may be unfamiliar. All of these machines, rather than making heat, take existing heat and move it from a lower temperature location to a higher temperature location. Refrigerators and air conditioners are heat pumps that remove heat from colder interior spaces to warmer exterior spaces for cooling purposes. Heat pumps also move heat from a low temperature source to a high temperature space for heating.
An air source heat pump, for example, extracts heat from outdoor air and pumps it indoors. A geothermal heat pump works the same way, except that its heat source is the warmth of the earth. The process of elevating low temperature heat to over 100°F and transferring it indoors involves a cycle of evaporation, compression, condensation and expansion. A refrigerant is used as the heat transfer medium which circulates within the heat pump. The cycle starts as the cold, liquid refrigerant passes through a heat exchanger (evaporator) and absorbs heat from the low temperature source (fluid from the ground loop). The refrigerant evaporates into a gas as heat is absorbed.
The gaseous refrigerant then passes through a compressor where the refrigerant is pressurized, raising its temperature to more than 180°F. The hot gas then circulates through a refrigerant to an air heat exchanger where heat is removed and pumped into the building at about 100°F. When the refrigerant loses the heat, it changes back to a liquid. The liquid is cooled as it passes through an expansion valve and begins the process again. To work as an air conditioner, the system’s flow is reversed.
What are the components of a geothermal system?
The three main parts consist of the heat-pump unit, the liquid heat-exchange medium (open or closed loop), and the air-delivery system (ductwork).
What are the different types of geothermal 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.
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 100–400 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.
Open Loop System
This type of system uses well or surface body water as the heat exchange fluid that circulates directly through the geothermal 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.
Do I need separate earth loops for heating and cooling?
No. The same loop works for both. To switch heating to cooling, or vice versa, the flow of heat is simply reversed.
Does the underground pipe system really work?
The buried pipe, or "ground loop", is the most recent technical advancement in geothermal technology. The idea to bury pipe in the ground to gather heat energy began in the 1940s. But it's only been in the last few years that new designs and improved pipe material have been combined to make geothermal units the most efficient heating and cooling systems available.
How much groundwater does an open-loop system need?
A geothermal system using an open-loop system needs a different amount of water depending on the size of the unit and the manufacturer's specifications. The water requirement of a specific model is usually expressed in gallons per minute (GPM) and is listed in the specifications for that unit. Generally, the average system will use 4 to 10 GPM while operating.
Does an open-loop system cause environmental damage?
No. They are pollution free. The geothermal unit merely removes heat from or adds heat to the water. No pollutants are added whatsoever. The only change in the water returned to the environment is a slight increase or decrease in the temperature. However, before an open loop system is considered, both the quantity and quality of the groundwater should be determined. An acceptable point of water discharge must be determined.
Will an earth loop affect my lawn or landscape?
Digging a trench can get messy. But experience has shown that loops have no adverse effect on grass, trees or shrubs. Most horizontal loop installations use trenches about two feet wide. This of course, will leave temporary bare areas that can be restored with grass seed or sod. Vertical loops require little space and result in minimal disruption.
If I have a pond near my home can I put a loop in it?
If it is at least eight feet deep, a pond is a perfect heat exchanger.
Can you really get heat out of a cold water pond, or out of the frozen ground?
The earth is a wonderful source of heat. Just ask the burrowing animals that depend on it for warmth in the winter. In fact, the earth stores 47 percent of the solar energy that reaches us, making it a natural source of heat for our homes. Geothermal heating and cooling systems, also called earth loop, or ground-coupled heat pumps, move the heat from the ground into your home using the same technology your refrigerator uses to remove heat from food. When a cat curls up at the bottom vent of a refrigerator it simply is enjoying the warm result of the refrigeration process.
Is geothermal new?
Not really. The basic technology has been around for more than 50 years, and many homeowners and businesses have been enjoying the benefits of geothermal for over 20 years.
In recent years many improvements have been made in the materials used, the installation methods, and the efficiencies of the compressors, pumps and other equipment.
Why is geothermal considered so environmentally friendly?
Geothermal systems work with nature, not against it. They emit no greenhouse gases, which have been linked to global warming, acid rain and other environmental hazards. Geothermal provides an earth loop antifreeze which will not harm the environment in the unlikely event of a leak and also utilizes R-410A performance enhancing refrigerant which will not harm earth’s ozone layer.
Can you be more specific about the environmental advantages?
According to data supplied by the U.S. Department of Energy and U.S. Environmental Protection Agency, a typical 3-ton residential geothermal system produces an average of about one pound less CO2 per hour of use than a conventional system. To put that in perspective, if just 100,000 homes were converted to geothermal, the country could reduce its CO2 emissions by 880,000,000 lbs.
That would be the equivalent of converting about 58,700 cars to zero-emission vehicles, or planting more than 120,000 acres of trees.
The waste heat removed from the home's interior during the cooling season may be used to provide virtually free hot water-resulting in a total savings in hot water costs of about 30% to 50% annually, and lowering emissions even further.
What are the major benefits to the homeowner?
Homeowners enjoy lower utility bills (40% to 80% lower than with conventional systems), lower maintenance, and higher levels of comfort, year-round. Even more than that, though, they have the peace of mind of knowing they're being environmentally responsible.
Since a geothermal system burns no fossil fuel to produce heat, it generates far fewer greenhouse gas emissions than a conventional furnace, and completely eliminates a potential source of poisonous carbon monoxide within the home. Even factoring in its share of the emissions from the power plant that produces electricity to operate the geothermal system, total emissions are far lower than for conventional systems.
Are there other advantages to residential geothermal?
There are no noisy “on” cycles with blasts of hot or cold air, and no fluctuations in temperature. There are no flues or chimneys and no carbon monoxide concerns and no potentially noisy outdoor units. Household costs may also be reduced by partially heating your hot water supply. Above all else, geothermal systems are the most environmentally friendly available on the market today!
What does a residential geothermal system cost to operate?
The incredible efficiency of geothermal energy makes the systems highly cost-effective. Energy is coming from the ground and your only costs are for the electricity to run the heat pump, compressor and fan. Homes converting to a geothermal system from oil or electric resistance may cut about 70% off its yearly heating and cooling costs and as much as 80% when switching from propane.
Does a geothermal system use a lot of electricity?
In a word, geothermal units use less electricity than conventional heating and cooling systems. Actually, utilities like geothermal systems because they use electricity in a way that benefits them and the customer. Because of the way they operate, geothermal systems provide a steady base load for utilities, pretty much avoiding the sharp peaks of electricity usage that require expensive reserve power sources. Those savings may be passed on to the customers in the form of special rates.
Geothermal systems do use electricity, but because they only use it to move heat already available in the ground, they use a lot less than other electric heating systems. Geothermal systems operate at efficiencies 3 to 4 times higher than electric resistance heat.
What makes a geothermal system different from ordinary systems?
Unlike ordinary systems, geothermal systems do not burn fossil fuel to generate heat. They simply transfer heat to and from the earth to provide a more efficient, affordable and environmentally friendly method of heating and cooling. Typically, electric power is used only to operate the unit’s fan, compressor and pump.
How efficient is a residential geothermal system?
A residential geothermal system is three to four times more efficient than the most efficient ordinary system. Because geothermal systems do not burn fossil fuels to make heat, they provide three to four units of energy for every one unit used to power the system.
Is the efficiency rating actual or just a manufacturer’s average?
All heating and cooling systems have a rated efficiency from a U.S. governmental agency. Fossil fuel furnaces have a percentage efficiency rating. Natural gas, propane and fuel oil furnaces have efficiency ratings based on laboratory conditions.
Geothermal heat pumps, as well as all other types of heat pumps, have efficiencies rated according to their coefficient of performance (COP). It’s a scientific way of determining how much energy the system produces versus how much it uses. Most geothermal heat pump systems have a COP that ranges from 3.0 to 4.0. That means for every one unit of energy used to power the system, three to four units are supplied as heat. Where a fossil fuel furnace may be 80% to 96% efficient, a geothermal heat pump is about 400% efficient.
Do geothermal systems require much maintenance?
No. Geothermal systems are practically maintenance free. When installed properly, the buried loop will last for generations. And the other half of the operation – the unit’s fan, compressor and pump – is housed indoors, protected from the harsh weather conditions. Usually, periodic checks and filter changes are the only required maintenance.
Are all geothermal heat pumps alike?
No. There are different kinds of geothermal heat pumps designed for specific applications. Many geothermal heat pumps, for example, are intended for use only with higher temperature ground water encountered in open-loop systems. Others will operate at entering water temperatures as low as 25°F, which are possible in closed-loop systems. Most geothermal heat pumps provide summer air conditioning, but a few brands are designed only for winter heating. Geothermal heat pumps also can differ in the way they are designed. Self-contained units combine the blower, compressor, heat exchanger and coil in a single cabinet. Split systems allow the coil to be added to a forced-air furnace and utilize the existing blower.
Does a geothermal system heat and cool too?
One thing that makes a geothermal heat pump so versatile is its ability to be a heating and cooling system in one. With a simple flick of a switch on your indoor thermostat, you can change from one mode to another. In the cooling mode, a geothermal heat pump takes heat from indoors and transfers it to the cooler earth through either groundwater or an underground earth loop system. In the heating mode, the process is reversed.
Can a geothermal system also provide household hot water?
Besides heating and cooling, a geothermal system may also be adaptable to supply warmed water to your existing hot water tank, thus greatly reducing the energy your hot water would typically utilize to get cold water up to hot water temperatures. In the process, the system may be able to provide practically free hot water. A geothermal option called a desuperheater may be able to be added to the system to create hot water assistance. Some units may be capable to supply all of your hot water, making your hot water tank obsolete.
Can a geothermal heat pump be added to my fossil fuel furnace?
Split systems can easily be added to existing furnaces for those wishing to have a dual fuel heating system. Dual fuel systems use the heat pump as the main heating source and a fossil fuel furnace as a supplement in extremely cold weather if additional heat is needed.
Is a geothermal heat pump difficult to install?
Most units are easy to install, particularly when they replace another forced-air system. They can be installed in areas unsuitable for fossil fuel furnaces because there is no combustion, thus no need to vent exhaust gases.
I have ductwork, but will it work with this system?
In all probability, the answer is yes. Your qualified heating and cooling contractor will be able to determine ductwork requirements and any minor modifications if needed.
Do I need to increase the size of my electric service?
Geothermal heat pumps don’t use large amounts of resistance heat so your existing service is likely adequate. Generally, a 200-amp service will have enough capacity and smaller amp services may be large enough in some cases. Your electric utility or contractor can determine your service needs.
What is the BTU size of the furnace that’s being proposed?
Furnaces are designed to provide specific amounts of heat energy per hour. The term “BTUH” refers to how much heat can be produced by the unit in an hour. Before you can determine what size furnace you’ll need, you must have a heat loss/heat gain calculation done on you home. From that, an accurate determination can be made of the size of the system you’ll need. Most fossil fuel furnaces are substantially oversized for heating requirements, resulting in increased operating cost and unpleasant temperature swings.
Should I buy a geothermal heat pump large enough to heat with no supplemental heat?
Your qualified heating and cooling contractor should provide a heating and cooling load calculation (heat loss, heat gain) to guide your equipment selection. Geothermal heat pumps typically are sized to meet your cooling requirements. Depending on your heating needs, a geothermal heat pump will supply 80-100 percent of your design heating load. Sizing the heat pump to handle your entire heating needs may result in slightly lower heating costs, but the savings may not offset the added cost of the larger heat pump unit and larger loop installation. Also, an oversized unit can cause dehumidification problems in the cooling mode, resulting in a loss of summer comfort.
How long is the payback period for a residential geothermal system?
To figure this accurately, you must know how much you’ll save each year in energy costs with a geothermal system as well as the price difference between it and an ordinary heating system and central air conditioner.
As an example: If you’ll save $1,500 per year with a geothermal system and the price difference is $12,000, your payback will be approximately eight years.
Are incentives available from the state or federal government?
Yes. Home and commercial building owners who install geothermal heating and cooling systems are now eligible for federal tax incentives under the American Recovery and Reinvestment Act of 2009 (H.R. 1: Div. B, Sec. 1122, p. 46), which removed the maximum credit amount for all eligible technologies (except fuel cells) placed in service after 2008 and installed up through the end of 2010. The legislation offers a one time tax credit of 30 percent of the total investment for residential ground loop or ground water geothermal heat pump installations, with no limit on the maximum credit.
To qualify for the tax credit, residential systems must meet Energy Star requirements. The contractor who sold and installed the product should list the purchase as a “geothermal heat pump” on the invoice and note that the unit “exceeds requirements of the Energy Star program currently in effect.” The home served by the system does not have to be the taxpayer’s principal residence. The act also provides incentives for residential wind and solar systems, biomass, and efficient appliances and vehicles. Some states offer tax incentives, and some utilities offer rebates or special electric rates.
Are we going to be comfortable and will the air be clean?
You will probably be more comfortable and the air cleaner than ever. A geothermal system moves warm air throughout your home via a standard duct network. Because the system moves a larger volume of air, heat is more even throughout the home and the initial cold air blast common with fossil fuel furnaces is eliminated. It's also a great comfort to know that you've reduced your energy consumption while using a renewable source - the earth. Geothermal means a cleaner house because there is no soot from combustion, and increased air flow means increased filtration.
How do geothermal owners feel about them?
State and national surveys show that over 90 percent of owners are very satisfied with their geothermal units. More than 95 percent said they would choose the system again and recommended it to others.
How much does a geothermal system cost?
That depends on how you measure cost. While they do cost more to install in homes than conventional systems, because of the ground loop piping, geothermal systems typically have the lowest life-cycle cost of any heating and cooling system. Heating and cooling for a typical 2,000-sq.-ft. home can run as low as $1.00 a day.
Total installation cost depends on so many variables: unit size, type and style of loop, modifications to existing ductwork, among others. The initial cost is more than offset by operating cost savings, which could be way more than half your current heating bill if you use propane or fuel oil.
Altogether, geothermal systems are a sound investment. The amount they save the homeowner every month in energy costs is typically more than enough to offset their higher installation cost, resulting in a positive monthly cash flow.
Remember, too, that geothermal means extra savings on repair, maintenance, and potentially, hot water bills. And the energy efficiency of geothermal adds value to the home.
Is geothermal energy used primarily in homes?
Not really. While many homes have been fitted with geothermal systems, commercial enterprises, including factories, retail stores, office building and schools also use geothermal to save energy and protect the environment. In fact, there were already more than half a million installations in the United States in 2008.
According to the United States EPA, schools are a particularly attractive place for the use of this technology. Across the country, schools using geothermal right now are saving an estimated $25,000,000 in energy costs-which can be used instead for better educational equipment and more teachers. These schools also save a half-billion pounds of CO2 emission per year.
Should all of the nation's schools convert to geothermal, the EPA has estimated that we could reduce oil imports by 61 million barrels annually, and provide the same environmental benefits of planting 8 million acres of trees or converting nearly 4 million cars to zero-emission vehicles.
If the same comparison were made across all commercial and residential segments, the potential for environmental benefit would be staggering.