Deciding to go with a geothermal system over the gas fired boiler was an education process. I really had to understand how it worked. I struggled at first with the concept of heating a home from a constant lower temperature and cooling a home by removing hot air as opposed to adding cold air. There were so many new terms and lots of new vernacular for me to grasp, so I started a list of FAQs that helped me understand each of the parts of the system. We’ve included our own photo display to accompany this blog so it helps put it into perspective.
This is part of our effort to lower our home’s operating costs over its lifecycle.
Q: What is a geothermal heat pump?
A: A geothermal or “ground-source” heat pump is an electrically-powered device that uses the natural heat storage ability of the earth and/or the earth’s groundwater to heat and cool your home.
Q: How does it work?
A: Like any type of heat pump, it simply moves heat energy from one place to another. Your refrigerator works using the same principle. By using refrigeration, the geothermal heat pump removes heat energy stored in the earth and/or the earth’s groundwater and transfers it to the home.
Q: How is heat transferred between the earth and the home?
A: The earth has the ability to absorb and store heat energy. To use that stored energy, heat is extracted from the earth through a liquid medium (in our case, water) and is pumped to the heat pump heat exchanger. There, the heat is used to heat your home. In summer the process is reversed and indoor heat is extracted from your home and transferred to the earth through the liquid.
Q: You mentioned heating and cooling. Does it do both?
A: One of the things that makes a heat pump so versatile is its ability to be a heating and cooling system in one. You can change from one mode to another with a simple flick of a switch on your indoor thermostat. Plus, a geothermal heat pump can assist in heating hot water year-round.
Q: Do I need separate ground loops for heating and cooling?
A: No. The same loop works for both. All that happens when changing from heating to cooling, or vice versa, is that the flow of heat is reversed inside the unit.
Q: What types of loops are available?
A: There are two main types: open and closed. We’re installing a closed loop system
Q: Does the underground pipe system really work?
A: The buried pipe, or “ground loop”, is the biggest technical advancement in heat pump technology to date. The idea to bury pipe in the ground to gather heat energy began in the 1940s. But it’s only been in the last twenty-five years that new heat pump designs and improved pipe materials have been combined to make geothermal heat pumps the most efficient heating and cooling systems available.
Q: What is a closed-loop system?
A: The term “closed-loop” is used to describe a geothermal heat pump system that uses a continuous loop of special buried plastic pipe as a heat exchanger. The pipe is connected to the indoor heat pump to form a sealed, underground loop through which water or an anti-freeze solution – depending on where you live – is circulated. Unlike an open-loop system that consumes water from a well, a closed-loop system continuously circulates its heat transferring solution in pressurized pipe.
Q: Where can this loop be located?
A: That depends on land availability and terrain. Closed-loops are trended horizontally in yards adjacent to the home if the yard is large enough. Or, for smaller yards, the loops can be installed vertically using a drill rig, much like a water well installation. We are installing vertically and expect our well to go as far as 800 feet deep to reach water.
Q: How deep and long will my horizontal trenches be?
A: Trenches are normally four to six feet deep [1/2 – 1.8 meters]. One of the advantages of a horizontal loop system is being able to lay the trenches according to the shape of the land. As a rule of thumb, 125-300 feet of trench are required per ton of heat pump capacity [11-27 meters per kW of capacity].
Q: How many pipes are in a trench?
A: Anywhere from 1 to 6 pipes pre trench may be used, depending upon the optimal design for the yard. More pipe per trench shortens the total amount of trench required.
Q: What if I don’t have enough room for a horizontal loop?
A: Closed loop systems can also be vertical. Holes are bored to about 150 – 300 feet per ton of heat pump capacity [13 – 27 meters per kW of capacity]. U-shaped loops of pipe are inserted in the holes. The holes are then back-filled with a sealing solution (grouting material).
Q: How long will the loop pipe last?
A: Closed-loop systems should only be installed using the appropriate high-density polyethylene pipe. Properly installed these pipes will last over 50 years. They are inert to chemicals normally found in soil and have good heat conducting properties. PVC pipe should not be used under any circumstances.
Q: How are the buried pipe sections of the loop joined?
A: The only acceptable method to connect pipe sections is by thermal fusion. Pipe connections are heated and fused together to form a joint stronger than the original pipe. Mechanical joining of underground pipe for an earth loop is never an accepted practice. The use of barbed fittings, clamps and glued joints is certain to result in loop failure due to leaks.
Q: Will an earth loop affect my lawn or landscape?
A: No. Research has proven that loops have no adverse effect on grass, trees or shrubs. Most horizontal loop installations use trenches about 3 feet [1 meter] or less 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 lawn damage.
Q: Can I reclaim heat from my septic system disposal field?
A: No. Depending upon your geographic location, an earth loop will reach temperatures below freezing during extreme conditions and may freeze your septic system. Such usage is banned in many areas.
Q: Can I use water from my geothermal well for other applications?
A: It depends. You cannot in most states, including RI, use the same well for heating and for your drinking supply. You can however, divert water externally to fill a rainwater harvesting tank, as we are doing in our home. When the float in our tank gets too low, it will call to the well for a refill. This will allow us to use only our well water and our rainwater supply for irrigation, not municipal water will be used at all.
Q: If the loop falls below freezing, will it hurt my system?
A: No. The antifreeze solution used in loops that operate at low temperatures will keep it from freezing down to about 15F [-9C] fluid temperature. In the U.S. and Canada, three types of antifreeze solution are acceptable: propylene glycol, methyl alcohol, and ethyl alcohol. Some states/provinces may require one type over another.
Q: I have a pond near my home. Can I put a loop in it?
A: Yes, if it’s deep enough and large enough. A minimum of 8 – 10 feet [2.5 0 3 meters] in depth at its lowest level during the year is needed for a pond to be considered. In pond loops, polyethylene pipe must be used. Generally, a minimum of ½ acre [0.2 hectare] pond is required to provide adequate surface area for heat transfer.
Q: Can a geothermal heat pump also heat water for my home?
A: Yes. Using what’s called a Hot Water Generator (HWG), some types of geothermal heat pumps can save you up to 50% on your water heating bill by pre-heating tank water. We installed the Geothermal Superheater for a mere $400.
Q: Is a geothermal heat pump difficult to install?
A: Most units are easy to install, especially when they are replacing 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.
Q: Do I need to increase the size of my electric service?
A: 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.
Q: How efficient is a geothermal heat pump?
A: Geothermal heat pumps are 3.5 – 5 times as efficient as the most efficient fossil fuel furnace. Instead of burning a combustible fuel to make heat, they simply move heat that already exists. By doing so, they provide 3.5 – 5 units of energy for every unit used to power the heat-pump system.
Q: What about comfort?
A: In winter, a geothermal heat pump system moves warm air (90 – 105F) throughout your home via a standard duct network. Typically, a very even comfort level is found throughout the home. This is because the warm air is moved in slightly higher volumes and, therefore, saturates the home with warmth more evenly. This even helps out hot or cold spots and eliminates the hot air blasts common with fossil fuel furnaces.
In summer, cool, dehumidified air is dispersed through the same duct network.
Q: Can I get a tax credit for installing this system?
A: It depends on where you live. Some states do have tax credits for installing geothermal systems. There are federal tax credits for 2009 and 2010.
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