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Ground source heat pumps


Although we may not know it heat pumps are very familiar to us - fridges and air conditioners are two examples. Ground source heat pumps (GSHP) transfer heat from the ground into a building to provide space heating and, in some cases, to pre-heat domestic hot water.

For every unit of electricity used to pump the heat, 3-4 units of heat are produced. As well as ground source heat pumps, air source and water source heat pumps are also available.

How does it work?

There are three important elements to a GSHP:
1) The ground loop. This is comprised of lengths of pipe buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe absorbing heat from the ground.
2) A heat pump. This has three main parts:
the evaporator - (e.g. the squiggly thing in the cold part of your fridge) takes the heat from the water in the ground loop;

the compressor - (this is what makes the noise in a fridge) moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit;

the condenser - (the hot part at the back of your fridge) gives up heat to a hot water tank which feeds the distribution system.
3) Heat distribution system. Consisting of under floor heating or radiators for space heating and in some cases water storage for hot water supply.

Ground Source Heat Pump
Also called an earth-coupled heat pump, or a geothermal heat pump, a ground-source heat pump operates much like the common air-source heat pump by transferring heat, rather than creating it. Unlike air-source, a ground-source heat pump transfers heat to and from the earth to provide cooling and heating for your home.

Below the frost line, the temperature of the earth in Nebraska stays fairly constant at 55°F. In summer, the soil temperature is cooler than the outside air. In winter, it's warmer. A ground-source heat pump uses this constant temperature to heat and cool your home very efficiently.

At home with the environment
Geothermal is the most earth-friendly home heating and cooling system available today. When you install a geothermal system, you're investing in a home that uses less energy, consumes fewer natural resources and keeps the air clean and fresh. There's no flame, no flue, no odor and no pollutants.

Cost-Effective Heating
In the heating season, a ground-source heat pump supplies three to four units of heat to your home for every unit of electrical energy required to operate the system. So you get two to three kilowatt hours (kWh) of free energy for every one kWh of electrical energy you pay for. In other words, a ground-source heat pump is 300% to 400% efficient.

Vertical Closed-Loop
In a vertical closed-loop ground heat exchanger, a water/antifreeze mixture is circulated through sealed pipe loops buried in vertical bore holes. the bore holes are typically 150 to 200 feet deep. As with a horizontal closed-loop system, heat is transferred by the heat pump system, from the ground during the winter and to the ground during the summer. A vertical heat exchanger can be installed on smaller lots rather than a horizontal system.
Horizontal Closed-Loop
In a horizontal closed-loop ground heat exchanger, a water/antifreeze mixture is circulated through sealed pipe loops buried horizontally, about six feet underground. During cold weather, the pipe loops absorb heat from the earth and deliver it to the heat pump located in the house. The heat pump transfers heat from the loop to warm the air that is circulated throughout the house by ductwork. The special, nontoxic antifreeze ensures that the system willnot freeze during severe winter weather. In the summer, the process is reversed for air conditioning, and the heat pump system transfers heat from the house to the ground.

Well water system
As its name suggests, this system utilizes two wells and underground water. Water from one well is pumped through the heat pump, then returned to a second well or discharged into a pond. This system requires three to five gallons of water per minute, per ton, to operate.

Because water is returned to the earth, the underground water supply is not depleted by the heat pump's operation.

What are my next steps?

Pick a heating contractor that has experience with installing geothermal heat pumps.
Ask your heating contractor to accurately evaluate your home for the installation of a heat pump system. This evaluation could consist of a computer generated heating analysis showing the amount of heating and cooling needed to condition your home for winter and summer.
Request bids for a Standard efficient, Middle efficient, and a High efficient geothermal heat pump.
Once you receive the bids, have your contractor explain the EFFICIENCY of the heat pump he or she sells. The efficiency rating for the heat pump air conditioning cycle is called the Energy Efficiency Ratio or EER. The EER rating can range from 10 EER to 24 EER. The efficiency rating for the heat pump heating cycle is called the Coefficient of Performance or COP. The COP rating can range from 3 COP to 4.5 COP.
Find out the size of your heating system. This includes the tonnage of the heat pump and the BTU output of the heating system.
The important thing to remember is: the larger the EER and COP rating, the more efficient your heat pump will be . It is recommended that you purchase the most efficient system that you can afford. As time goes on, the more efficient heating system that you buy today will save you money tomorrow.

Geothermal heat pumps offer high efficiency and low operating cost. According to the EPA, GHPs can save homeowners 30 to 70 percent on heating and 20 to 50 percent on cooling costs over conventional systems. GHPs provide a high level of occupant comfort. There is a potential for utility bill savings, and many local utility companies provide incentives for investing in GHPs.

The initial cost of a GHP system varies greatly according to local labor rates, geological profile, type of system installed, and equipment selected. The initial cost of GHP systems does come at a premium when compared to air source heat pump systems. For either system, the cost of installed ducts should be identical. Equipment costs can be 50-100% more expensive for a GHP system when the circulating pump, indoor tubing, and water source heat pump are considered. This 50-100% premium translates to $1000 - $2000 for a 3-ton system.

The ground loop is generally the most expensive component of a GHP system and is highly dependent on local labor rates and drilling conditions. An installed ground loop stubbed out in a home can run betwee $1000 and $3000 per installed ton. Overall, one could expect to pay between $4000 and $11000 more for a turnkey 3 ton GHP system than for an air source heat pump system. Many consumers justify this initial investment with the savings they expect to realize on their heating and cooling bills over time.


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