Geothermal heating and cooling systems use the natural constant ambient temperature of the earth to heat in the winter and cool in the summer. This is accomplished with a compressor or heat pump unit, the liquid heat exchanger medium, and the air delivery system. Quite simply, geothermal systems in heating take heat from the earth, transfer that heat to a refrigerant, then distribute the heat into the structure with a forced-air or hydronic system. In cooling, geothermal systems take heat from the structure, transfer the heat to the refrigerant, then transfer the heat back to the water or loop fluid. This works the same as a standard air conditioner, except a geothermal system uses water or loop fluid at a constant temperature (average 50 degrees) instead of varying outdoor temperature.
In other words, it’s
like heating and cooling your home when it’s 50 degrees outside – all year!
“Coaxial” heat exchanger cutaway view. Water or loop fluid flows in the center
rifled tube, and refrigerant flows around the outside of the copper tube. This is where the exchange takes place
between water or loop fluid and refrigerant.
In heating, heat from the water, in the center of the tube, exchanges to
the refrigerant in the outer area inside this coaxial coil.
GeoExcelÒ
products use a CopelandÒ Scroll compressor to pump refrigerant through the
refrigeration circuit. In heating, high
pressure, high temperature refrigerant leaves the compressor and travels to the
air coil. At the air coil, similar to a
radiator on a car; return air passes across the coil, cooling the refrigerant
to low temperature and pressure, ultimately causing the refrigerant to turn
from a gas to a liquid (condensed).
After the refrigerant is metered, with a Thermostatic Expansion Valve,
or TXV, it is then on to the Coaxial Heat Exchanger. At the Coaxial Heat Exchanger, or Coax for short, the very cold
refrigerant is heated by the flow of “warm” water, and “evaporated” back to a
gas. The refrigerant then is pumped
back to the compressor, where the cycle begins again. In cooling, the same process happens in reverse. High temperature, high pressure gas is
pumped by the compressor to the Coax.
At the Coax this refrigerant is cooled to a liquid or “condensed”. The very cold refrigerant then enters the
air coil where warm air from the structure heats the refrigerant to a gas
(evaporates). The refrigerant then
returns to the compressor and the cycle begins again. As you can see, the constant temperature of the ground water or
loop fluid in the earth causes this compressor to work much less hard than it
would if it were exposed to outdoor air temperature.
For more information on scroll compressors, see http://www.emersonhometechnologies.com/copeland.html.
Another
feature on most geothermal systems is a Hot Water Generator. Hot Water Generators, or HWG’s, take refrigerant from the compressor, where
it is very hot, and directs it to another small coaxial heat exchanger. In this HWG heat exchanger, water from a
standard domestic hot water tank flows through, picking up heat from the hot
refrigerant. This heat exchanger is
double-walled, and vented so that there would be no contamination from the
refrigerant if a leak occurred.
The HWG accomplishes three functions. First, it typically heats 60% to 80% of a home’s hot water – for FREE utilizing waste heat from the refrigeration process. Second, it increases the efficiency of the compressor by removing some of the heat from the compressor. Third, it increases the life expectancy of the compressor by allowing it to operate at a cooler temperature.
There are many different configurations for the “source” of a geothermal system. Here are a few:
1. Open Loop: Open loop systems use water from a well. Well water is pumped to the geothermal unit, where heat is either taken from it (heating) or put into it (cooling). There is no change to the water, or contamination, other than a slight change in temperature. Generally speaking, geothermal systems require 1.5gpm per ton of air conditioning. Most homes would use between 4 and 6 gallons per minute while the system is running. This is the least expensive source for a geothermal system, and works quite well when there is sufficient water quality and quantity, and there is a place to “discharge” the water such as a drain, ditch, stream, or pond.
2. Closed Loop: Closed loop systems are the second most common type of geothermal source. Closed loops utilize polyethylene piping buried or drilled into the ground, filled with a water/anti-freeze solution. The loop fluid circulating in this closed piping system absorbs heat or rejects heat into the surrounding earth. Typically, in the Midwest, loop systems are installed in a “horizontal” configuration as pictured above. In other parts of the country, where digging is more difficult or expensive, “vertical” loops are used. Vertical loops are placed in vertical holes usually drilled in the ground with a machine similar to a drill rig used to install water wells. Vertical loops are also commonly used in commercial applications or applications where there is not enough room for a horizontal loop. Closed loops are virtually maintenance free, and since they re-circulate the same fluid, have no need for a well or a place to discharge the water. However, closed loops, due to the excavation costs, are generally more expensive than open loop systems.
3. Pond/Lake Loop: Pond or lake loops may indeed be the best system available. Pond loops use coils of polyethylene piping submerged into a pond or lake. They have the benefit of low installation costs in addition to the benefits of a closed loop. Also, pond and lake loops typically have more mild operating temperatures. Pond loops are also in widespread use in the commercial market due to the compact size and low initial cost compared to horizontal and vertical loops.
There
are many ways to design a geothermal system; open
or closed, vertical or horizontal, and we will be glad to honestly explain the
advantages and options of every possible approach.
The important thing to remember: Geothermal systems heat and cool more efficiently than any system available. That saves you money now, and saves our environment for the future.
For
more information on loops, see http://www.igshpa.okstate.edu/