How does a geothermal heating and cooling system work?
What makes a geothermal system different from ordinary systems?
What are the components of a geothermal system?
How is efficiency rated for geothermal?
Heating and cooling systems carry an efficiency rating which is certified by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI). Fossil fuel furnaces use AFUE. Air conditioners use SEER while heat pumps use HSPF and SEER.
Geothermal heat pumps rate heating efficiencies according to their coefficient of performance, or 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 COPs of 3-4.5. The WaterFurnace 7 Series holds the highest recorded certified performance of 5.3 COP in a closed loop and 5.9 in an open loop. That means for every dollar of energy used to power the system, up to $5.90 of energy are supplied as heat. Where a fossil fuel furnace may be 78-98% efficient, a geothermal heat pump is over 500% efficient.
For cooling, geothermal units are rated in Energy Efficiency Ratio (EER). This is a measure of the instantaneous energy efficiency of cooling equipment. The higher the EER, the more efficient the unit. The WaterFurnace 7 Series carries a certified rating of 41 EER for closed loop and 53.2 EER for open loop. This is more than twice as efficient as any traditional heat pump or air conditioner and a third higher than any other two-stage geothermal heat pump.
How efficient is a geothermal system?
A geothermal system is over five times more efficient in heating and more than twice as efficient in cooling as the most efficient ordinary system. Because geothermal systems move existing heat rather than creating it through combustion, they provide four to five units of energy for every one unit used to power the system.
Do geothermal systems require much maintenance?
No. Geothermal systems are practically maintenance free. The buried loop will last for generations. The unit’s fan, compressor and pump is housed indoors, protected from the weather and contamination. Usually, periodic checks and filter changes are the only required maintenance.
While WaterFurnace does offer an outdoor geothermal unit for jobs where space is limited, its rugged housing is sealed so that no components are exposed to the elements.
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 pollution, acid rain, and other environmental hazards. WaterFurnace’s earth-loop antifreeze will not harm the environment in the unlikely event of a leak. And all of the current WaterFurnace product lines use R-410A, a performance-enhancing refrigerant that will not harm the earth’s ozone layer.
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 (such as the WaterFurnace Envision Series Split) allow the coil to be added to a forced-air furnace and utilize the existing blower.
How does a geothermal heat pump work?
Heat pumps don’t create heat. They take existing heat and move it. Anyone with a refrigerator has witnessed the operation of a heat pump. Refrigerators collect heat from the unit’s interior and move it to the exterior for cooling purposes. Unlike a refrigerator, a heat pump can reverse itself. An air-source heat pump, for example, can extract heat from outdoor air and pump it indoors for heating purposes.
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-air heat exchanger where heat is removed and pumped into the building at about 100°F. When it loses the heat, the refrigerant 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.
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.
Can a geothermal system also heat water?
Yes. Some geothermal heat pumps can provide all of your hot water needs 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.
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 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 1940’s. 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 water flow does an open loop system require?
The water requirement of a specific model is usually expressed in gallons per minute (gpm) and is listed in the unit’s specifications. Generally, the average system will use 1.5 gmp per ton of capacity while operating, but the amount of water required depends on the size of the unit and the manufacturer’s specifications. Your contractor should be able to 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’ll probably 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 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.
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 well 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.
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 your 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 constantly recirculates 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 building. However, where adequate land is not available, loops are vertically bored. Any area near a home or business with appropriate soil conditions and adequate square footage will work.
How long will the loop pipe last?
Closed loop systems should be installed using only high-density polyethylene pipe. Properly installed, these pipes can outlast the house. They are inert to chemicals normally found in soil and have good heat conducting properties. PVC pipe should never be used.
How deep or 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, 500-600 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 1,500-1,800 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.
I have a pond nearby. Can I put a loop in it?
Yes, if it’s deep enough and large enough. A minimum of six 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 loads of the structure. You should opt against using water from a spring, pond, lake or river as a source for an open loop 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.
Can I install an earth loop myself?
It’s not recommended. Good earth-to-coil contact is very important for successful loop operation. Nonprofessional installations may result in inefficient system performance.
What if I don’t have enough 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 back-filled with a sealing solution.
How do I know if the dealer and loop installers are qualified?
Don’t be afraid to ask for references from dealers. A reputable dealer or loop installer won’t hesitate to give you names and numbers to call to confirm his capabilities.
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. Duct-work must be installed in homes that don’t have an existing air distribution system. The difficulty of installing duct-work 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 duct-work, but will it work with this system?
In all probability, yes. Your installing contractor should be able to determine duct-work requirements and any minor modifications if needed.
If a home has ceiling cable heat or baseboard heat, do air ducts need to be installed?
Not always. It may be desirable to install geothermal heat pump room units. For some small homes, a one-room unit would handle the heating and cooling needs. Ceiling cable or baseboard units could be used for supplemental heat if desired.
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 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 thats 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 over-sized 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 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 over-sized unit can cause dehumidification problems in the cooling mode, resulting in a loss of summer comfort.
How long is the payback period for a geothermal system?
Geothermal systems are so energy-efficient that the payback period is remarkably brief. A study by the Air Force Institute of Technology calculated that it takes on average just seven to eight years to recoup costs.
Your specific payback point depends on factors like local utility rates, excavation/drilling costs, how well your house is insulated, the efficiency of the model you choose, and what incentives your state or utilities provide.
One of the best aspects about geothermal is cash flow. If you install a geothermal system, the monthly savings in operating costs generally offset the additional monthly financing cost, resulting in an immediate positive cash flow – especially in a new home. Again, your specific situation may vary.