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Frequently Asked Questions
About Geothermal Heating and Cooling Systems
What is a Geothermal Heat Pump?
A heat pump is a mechanical device used for heating and cooling which operates on the principle that heat can be moved from a warmer temperature to a cooler temperature. A geothermal heat pump uses the earth to warm us in the winter and cool us in the summer. You already have a heat pump in your home – your refrigerator. If you put your hand behind it you’ll feel the heat that has been removed from the food inside the refrigerator. This is the same principle that a geothermal heat pump uses to move heat to and from the home and earth.
The Technical View of the Heat Pump Process.
Remember that the heat pump moves heat from a low temperature source to a high temperature source. 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 (liquid 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 over 160º F. The hot gas then circulates through a refrigerant-to-air heat exchanger where heat is removed and pumped into the home at about 100º 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 air condition, the flow is reversed.
We know a geothermal heat pump can heat, but can it also cool my home?
Yes, one of the reasons a heat pump is so versatile and efficient is its ability to heat and cool as one system. With a flick of a switch on your indoor thermostat the geothermal heat pump changes from heating to cooling.
How do I get the heat from the ground into my home?
There are several types of systems that gather the heat from the ground. The most commonly used are open-loop and closed-loop systems.
What is an open-loop system?
An open-loop system is used less frequently, but may be employed cost-effectively if ground water is plentiful. Open-loop systems in fact, are the simplest to install and have been used successfully for decades in areas where local codes permit. This type of system uses ground water from an aquifer and is piped directly from the well to the building, where it transfers its heat to a heat pump. After it leaves the building, the water is disposed of by one of three methods.
- Surface drainage – to a low area such as a pond, river, lake or stream, etc.
- Sub surface – to a dedicated drainfield sized to the required volume of water of the heat pump.
- Re-injection or discharge well - water is pumped back into the same aquifer through a separate discharge well.
Local environmental officials should be consulted whenever an open-loop system is being considered.
How much groundwater does an open-loop system need?
Geothermal heat pumps used in open-loop systems need differing amounts 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 (g.p.m.) and is listed in the specifications for that unit. Your water well and heat pump combination should be large enough to supply the water needed by the heat pump in addition to your domestic water requirements.
What problems can be caused by poor water quality?
Poor water quality will cause serious problems in open-loop applications. Your water should be tested for hardness, acidity and iron content before the heat pump is installed. Poor water quality can cause mineral deposits to build up inside the heat pump heat exchanger and periodic cleaning will be required. Water from flowing springs, ponds, lakes or river sources are not recommended for heat pump use, unless proven to be free of excessive particulate and organic matter. These sediments will contaminate the heat exchanger heat pump system and make it inoperable.
Does an open-loop system cause environmental damage?
No, the heat pump only moves heat from one source to another, therefore no pollution is generated. The only change in the water after it's used by the heat pump is a slight increase or decrease in temperature.
Are there any laws that apply to open-loop installation?
In some localities, all or parts 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.
What is a closed-loop system?
Closed-loop systems are becoming most common. There are 5 types of closed loop systems. All types use a continuous loop where the heat transfer fluid is circulated. A horizontal loop is usually the most cost effective when adequate yard space is available and trenches are easy to dig. Using trenchers or backhoes digging trenches three to six feet below the ground, you then lay a series of parallel plastic pipes. The trench is then back filled, taking care not to allow sharp rocks or debris to damage the pipe. A typical horizontal loop will have 400-600 feet of pipe per ton of heating and cooling capacity.
Vertical loops are preferred in many installations where yard space is insufficient and where preservation of existing landscaping is desirable. Contractors bore vertical holes in the ground 150-450 feet deep. Each hole contains a single loop of pipe with a U-bend at the bottom. The hole is then backfilled or grouted to improve the thermal conductivity. Each vertical pipe is then connected to a horizontal pipe underground to and from the heat pump. Vertical loops are generally more expensive to install, but require less piping than horizontal loops.
Slinky loops are used to reduce the heat exchanger per foot trench requirements but require more pipe per ton of capacity. This pipe is coiled like a slinky, overlapped and laid in a trench. Two-pipe systems may require 200-300 feet of more pipe per ton of nominal heat exchange capacity. The trench length decreases as the number of pipes in the trench increases or as slinky overlap increases.
Pond loops are a special kind of closed loop system. Where there is a pond or stream that is deep enough and with enough flow, closed loop coils can be placed on the bottom. Geothermal transfer fluid is pumped just as a closed loop ground system. First cost economics are very attractive and there is no aquatic environmental impact.
How long will the pipe last?
A high-density polyethylene pipe is used in a closed loop system and has a 50-year warranty. Independent tests show a useful life span of over 200 years.
How are the pipe sections of the loop joined?
Thermal fusion and stab fittings are the only acceptable method used to connect pipe sections. Thermal fusion connections are either socket or butt fused together to form a joint stronger than the original pipe. Stab fittings are fairly new but are proving themselves to be reliable. Using barbed fittings, clamps and glued joints are unacceptable and will eventually cause the loop to leak and fail.
What is the fluid in the loops?
There are two types of antifreeze solutions that are used: propylene glycol and methyl alcohol. These heat transferring solutions are mixed with water to form a solution for your specific climate and ground conditions.
Can a heat pump provide 100% of my heating and cooling needs?
Heat pumps can provide 100% of your heating and cooling requirements. All heat pumps will show significantly improved energy efficiency; however some are designed for higher heating loads while others are biased towards higher cooling loads, still others provide a more balanced approach. These factors combined with your geographical region can have a large impact on the economics.
Can a geothermal heat pump heat my hot water for my home?
Domestic hot water is available with the use of a heat pump for pennies a day or even free. A hot water desuperheater is a heat exchanger built into the heat pump and is designed to remove high temperature heat from the refrigerant gases. A typical hot water desuperheater will generally provide 120° F water and can supply most of the domestic water needs depending on the amount of consumption.
Do I need to increase the size of my electric service?
Most homes already have adequate electrical service.
How efficient is a geothermal heat pump?
If I said up to 500% efficient, would you believe me? Yes that’s right. Depending on individual circumstances savings can be that high. On average, the operating costs of heat pumps are about 75% less than electric heating devices and 50% less than air source heat pumps. Cooling costs are 25% - 50% lower when compared to conventional air conditioners. In addition, when hot water is supplied by the heat pump at these efficiencies and higher, your overall savings are increased even more.
What does a system like this cost? How long is the payback period for your geothermal heat pump system?
This, of course will vary greatly depending on individual circumstances, but on average a typical home of 2000 square feet will cost between $14,000 - $18,000. This represents somewhere around double the costs of a conventional heating, cooling and hot water system. When it comes to payback, we often see a 3 – 5 year payback of these additional costs. Then it’s money in the bank from that point on.
Can geothermal do snow melting?
Yes. Snow melting on sidewalks and driveways is becoming more fashionable and can be incorporated into the overall geothermal system design.
Can I heat my pool?
Yes. Indoor and outdoor pools are easily heated inexpensively with heat pumps.
I have a very large house, can your unit heat my home?
Yes. Heat Pump systems have been designed for homes of all sizes. Your HVAC contractor will size your heat pump according to your needs.
What kind of maintenance can I expect?
A properly installed closed-loop heat pump requires very little maintenance aside from regularly maintaining the air filter and air blower assembly. Water coil maintenance is recommended on open-loop installations as water quality can greatly affect the heat exchanger efficiency.
Is there improved indoor air quality with this system?
Yes. An all-electric heat pump system produces no products of combustion and therefore no indoor air pollutants are possible. Conventional gas and propane systems require chimneys to vent away harmful carbon monoxide and other dangerous gases.
How is a heat pump sized?
Capital Electric will work with your HVAC contractor to size your heat pump based on an accurate heating and cooling analysis of the home or building. Factors like the type of windows and insulation R. values are taken into account and a BTU per hour heat loss and heat gain will result. The heat pump is then sized and will keep you warm during the coldest winter night and cool on the hottest summer day.
How do geothermal heat pumps compare to conventional systems?
Although heat pumps normally cost more to install over conventional systems, the increased comfort, lower energy and maintenance costs result in customer satisfaction.
Will this system add value to my home?
Yes. More and more Home Appraisers and Real-estate Agents are educated and acknowledge a geothermal system as a renewable energy source with greater value.
Is it true that geothermal heat pump systems have the lowest impact on the environment?
Yes. Heat pumps only move the heat from one place to another. Because only a fraction of the energy generated is consumed by the heat pump, it therefore has a very low impact on the environment.
What is the life of a system?
Experts believe 18-23 years of serviceable life is expected from ground source heat pumps. This is nearly double that of conventional systems.