Geothermal
Geothermal heat-pump systems are the fastest growing segment in the energy efficiency field. The technology, which uses the earth's underground heat to produce heating and cooling for homes, has been around since the early 1980s, but it was too costly for most homeowner until energy prices soared in recent years. Now, the monthly savings from geothermal units pay for the installation costs in a relatively short period, while reducing energy usage and greenhouse gas emissions.
Geothermal Heating and Cooling - An Introduction
Geothermal heating and cooling is in step with the times-and with the future. "Green" technologies-which work with the environment instead of against it-continue to gain momentum amid concerns over pollution and energy conservation.
Geothermal technology is proven, reliable and safe. It significantly reduces energy usage and utility bills for homeowners. Hundreds of thousands of geothermal systems are saving money and protecting the environment across North America, Europe, Asia and Australia.
Geothermal Basics
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. A geothermal system, which typically consists of an indoor unit and a buried earth loop, capitalizes on these constant temperatures to provide "free" energy. In winter, fluid circulating through the system’s earth loop absorbs stored heat and carries it indoors. The indoor unit compresses the heat to a higher temperature and distributes
it throughout the building. In summer the system reverses, pulling heat from the building, carrying it through the earth loop and depositing it in the cooler earth.
What makes a Geothermal system different from ordinary systems?
Unlike ordinary systems, Geothermal systems do not bum fossil fuel heat 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.
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).
How efficient is a Geothermal system?
A Geothermal system is three to five 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 rating based on laboratory conditions. To get an accurate installed efficiency rating factors such as flue gas heat losses and cycling losses caused by over sizing, blower fan electrical usage, etc., must be included.
Geothermal heat pumps as well as all other types of heat pumps, have efficiencies rated according to their performance or COP (Coefficient of Performance). It's a scientific way of determining how much energy the system produces versus how much it uses. Most geothermal heat pump systems have COPs of 3-4.5 (Water Furnace's Envision Series is rated up to 5). That means for every one unit of energy used to power the system, 3-5 units are supplied as heat. Where a fossil fuel furnace may be 78-95 percent efficient, a geothermal heat pump is about 400 percent efficient. Some geothermal heat pump manufacturers and electric utilities use computers to accurately determine the operating efficiency of a system for your home or building.
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 condition. Usually, periodic checks and filter changes are the only required maintenance.
What does Geothermal mean for the environment?
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. We provide an earth-loop antifreeze which will not harm the environment in the unlikely event of a leak. And much of the WaterFurnace product line uses R-410A, a performance-enhancing refrigerant that will not harm the earth’s ozone layer.
Geothermal Heat Pumps
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 degrees 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. There are also water-to-water heat pumps that create hot water and chilled water.
How does a Geothermal heat pump work?
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 removed 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 degrees 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 stars 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 108 degrees F. The hot gas then circulates through a refrigerant-to-air heat exchanger where heat is removed and pumped into the building at about 100 degrees F. When it loses the heat, the refrigerant changes back in 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.
Does a Geothermal system heat and cool?
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.
Will the minimum entering water temperature affect which Geothermal heat pump I buy?
Yes. If you have an open loop system, your entering water temperatures (EWTs) may range from 47 to 50°F. All heat pumps can handle temperatures in the moderate-to-warm range. A closed loop system, on the other hand, may encounter EWTs below freezing. Not all geothermal heat pumps will operate efficiently at those temperatures. It’s important to know what EWTs at which your heat pump will operate most efficiently.
Can a Geothermal system also heat domestic water?
Yes. Some geothermal heat pumps can provide all of your domestic hot water needs on demand at the same high efficiencies as the heating/cooling cycles. An option called a desuperheater can be added to most heat pumps. It will provide significant savings by heating water before it enters your hot water tank.
In The Loop
Do I need separate earth loops for heating and cooling?
No. The same loops 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 earth loop, was an important technical advancement in heat pump technology. The idea of burying pipe in the ground to gather heat energy originated in the 1940s. New heat pump designs and more durable pipe materials have been combined to make geothermal heat pumps the most efficient heating and cooling systems available.
What types of loops are available?
There are two main types: open and closed.
What is an open loop system?
An open loop system uses groundwater from an ordinary well as a heat source. The groundwater is pumped into the heat pump unit where heat is extracted and the water is disposed of in an environmentally safe manner. Because groundwater is a relatively constant temperature year-round, wells are an excellent heat source.
How much groundwater does an open loop system require?
The water requirement of a specific model is usually expressed in gallons per minute (g.p.m.) and is listed in the unit’s specifications. Generally, the average system will use 1.5 g.p.m. per ton of capacity while operating, but the amount of water required depends on the size of the unit and the manufacturer’s specifications. Temp Right Service will provide this information. Your well and pump combination should be large enough to supply the water needed by the heat pump in addition to your domestic water requirements. You probably will need to enlarge your pressure tank or modify your plumbing to supply adequate water to the heat pump.
What do I do with the discharge water?
There are a number of ways to dispose of water after it has passed through the heat pump. The open discharge method is the easiest and least expensive. Open discharge simply involves releasing the water into a stream, river, lake, pond, ditch or drainage tile. Obviously, one of these alternatives must be readily available and have the capacity to accept the amount of water used by the heat pump before open discharge is feasible. This type of discharge can only be used for a cooling only system in Western Montana.
A second means of water discharge is the return well. A return well is a second well bore that returns the water to the ground aquifer. A return well must have enough capacity to dispose of the water passed through the heat pump. A new return well should be installed by a qualified will driller. Likewise, a professional should test the capacity of an existing well before it is used as a return.
Are there any laws that apply to open loop installations?
All or part of the installation may be subject to local ordinances, codes, covenants or licensing requirements. Check with local authorities to determine if any restrictions apply in your area.
Does an open loop system cause environmental damage?
No. They are pollution free. The heat pump merely removes or adds heat to the water. No pollutants are added. The only change in the water returned to the environment is a slight increase or decrease in temperature.
Can I reclaim heat from my septic system disposal field?
No. An earth loop will reach temperatures below freezing during extreme conditions and may freeze your septic system.
What problems can be caused by poor water quality?
Poor water quality can cause serious problems in open loop systems. Your water should be tested for hardness, acidity and iron content before a heat pump is installed. Your contractor or equipment manufacturer can tell you what level of water is acceptable. Mineral deposits can build up inside the heat pump’s heat exchanger. Sometimes a periodic cleaning with a mild acid solution is all that’s needed to remove the build-up.
Impurities, particularly iron, can eventually clog a return well. If you water has high iron content, make sure that the discharge water is not aerated before it’s injected into a return well.
What is a closed loop system?
A closed loop system uses a continuous loop of buried polyethylene pipe. The pipe is connected to the indoor heat pump to form a sealed, underground loop through which an environmentally friendly antifreeze-and-water solution is circulated. A closed loop system re-circulates its heat-transferring solution in pressurized pipe, unlike an open loop system that consumes water from a well. Most closed loops are trenched horizontally in areas adjacent to the home. However, where adequate land is not available, loops are vertically bored. Any area near a home with appropriate soil conditions and adequate square footage will work.
What if I don’t have room for a horizontal loop?
Closed loop systems also can be vertical. Holes are bored up to 250 feet per ton of heat pump capacity, depending on where you live. U-shaped loops of pipe are inserted in the holes. The holes are then backfilled with a sealing solution.
How long will the loop pipe last?
Closed loop systems should be installed using only high-density polyethylene pipe. Properly installed, these pipes will last for many decades. They are inert to chemicals normally found in soil and have good heat conducting properties. PVC pipe should never be used.
How deep and long will my trenches be?
Trenches are normally four to six feet deep and up to 400 feet long, depending on the number of pipes in a trench. One advantage of a horizontal loop system is being able to lay the trenches according to the shape of the land. As a rule of thumb, 500-800 feet of pipe is required per ton of system capacity. A well-insulated 2,000 square foot home would need about a three-ton system with 1,500-2,400 feet of pipe.
How are the pipe sections of the loop joined?
Pipe sections are joined by thermal fusion. Thermal fusion involves heating the pipe connections and then fusing them together to form a joint that’s stronger than the original pipe. This technique creates a secure connection to protect from leakage and contamination.
Will an earth loop affect my lawn or landscape?
No. Research has proven that loops have no adverse effect on grass, trees, or shrubs. Most horizontal loop installations use trenches about 24 inches wide. This, of course, will initially leave temporary bare area, but they can easily be restored with grass seed or sod. Vertical loops require little space and result in minimal lawn damage.
I have a pond nearby. Can I put a loop in it?
Yes. If it’s deep enough and large enough. A minimum of 10 feet in depth at its lowest level during the year is needed for a pond to be considered. The amount of surface area required depends on the heating and cooling load of the structure. You should opt against using water for an open loop from a spring, pond, lake or river as a source for your heat pump system unless it’s proven to be free of excessive particles and organic matter. They can clog a heat pump system and make it inoperable in a short time.
What Every Home Owner Should Know
How do I know if the dealer and loop installers are qualified?
A loop installer should be an IGSHPA certified installer and factory trained as a fusion technician. Temp Right Service has this certification and training.
Can a Geothermal heat pump be added to my fossil fuel furnace?
Split systems easily can 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 area unsuitable for fossil fuel furnaces because there is no combustion, thus no need to vent exhaust gases. Ductwork must be installed in homes that don’t have an existing air distribution system. The difficulty of installing ductwork will vary and should be assessed by a contractor. Another popular way to use geothermal technology is with in-floor radiant heating, in which hot water circulating through pipes under the floor heats the room.
I have ductwork, but will it work with this system?
In all probability, yes. Your installing contractor should 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 may be adequate. Generally, a 200-amp service will have enough capacity and small 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 the structure. 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 a Geothermal heat pump be sized large enough to heat with no supplemental heat?
Your contractor should provide a heating and cooling load calculation (heat loss, heat gain) to guide your equipment selection. 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.
How long is the payback period for a 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. Temp Right Service can provide energy cost calculations, price difference between systems, and a return on investment or simple payback calculations.