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Geothermal Heat Pumps What are they? Our Experience How do they work?
The water loop consists of an open or closed loop piping system that is buried in the ground. Open loop systems require a nearby stream or well; therefore, closed loop systems are more common. In a closed loop system, plastic pipe is buried either horizontally at 4-6 feet deep, or vertically at 100-400 feet deep.
Other pipe layout designs exist such as burying the pipe under a pond or lake, but the horizontal and vertical layouts are most common. (See Figures 1 and 2.) The pipes are filled with an antifreeze/water solution that acts as a heat exchanger. The fluid running through the pipes extracts heat from the ground during the winter and deposit heat during the summer. A pump located at the point where the pipe enters the house pushes the water solution through the loop. The refrigerant loop is a pipe system with refrigerants such as HCFC-22 or R-22 running through it. These refrigerants are the same ones that are used in conventional air conditioning units. The refrigerant loop passes through the compressor, the reversing valve, the indoor coil, the heat exchanger, and the expansion device. (See Figure 3.)
During operation of the system, the refrigerant performs a phase change in which it changes from a liquid to a gas, or vice versa, depending on whether the system is in heating or cooling mode. When the refrigerant changes from a liquid to a gas it is essentially absorbing heat, and when it condenses from a gas to a liquid it is releasing heat. The compressor is used to pump the refrigerant through the loop at a high pressure. This high pressure is needed in order to help initiate the phase changes. From the compressor the refrigerant travels into the reversing valve, which in turn directs the flow to either the heat exchanger or the indoor coil. The reversing valve does just what its name suggests; it reverses the flow depending on whether the system is in heating or cooling mode. The heat exchanger transfers the heat back and forth between the refrigerant and the antifreeze/water mixture. The heat exchanger contains a tightly wound coil that brings the two fluids near to each other so that the heat can be transferred. Likewise, the indoor coil is used to transfer heat back and forth between the air that is being circulated around the house. As air passes over the coil it becomes either warm or cool depending on the phase of the refrigerant flowing through the coil. Located between the indoor coil and the heat exchanger is an expansion device. The expansion device insures that the phase changes occur in the heat exchange and the indoor coil. The air loop consists of a fan and an air delivery ductwork system. The fan is situated near the indoor coil in order to push the newly transformed air into the air delivery ductwork to be distributed throughout the house or building. Just like in conventional heating and air-conditioning systems, the air delivery ductwork provides a means for the cooled or heated air to travel throughout the house or building. The desuperheater loop is an optional part of the system that provides hot water for the house or building in which the geothermal heat pump is installed. This loop transfers water from the building's water heater to another heat exchanger inside the heat pump. In the exchanger, the water in the loop picks up the excess heat from the refrigerant loop and travels back to the water heater. Summary The antifreeze/water mixture exits the house or building and is cool. The water is pushed through the water loop and the Earth surrounding the pipe warms it. Once it is warmed, the water is pushed into the building by a pump. The warm water enters the heat exchanger where it acts as a heat source. In the heat exchanger, the water loop passes near the refrigerant loop and causes the refrigerant (which is in liquid phase) to undergo a phase change. The water is now cool again and leaves the heat exchanger to make another trip outside. The refrigerant, now holding the heat, travels through the expansion device and into the indoor coil. While the heated refrigerant is in the coil, air passes over the coil and gets warmed. The refrigerant changes phase back into a liquid as the air picks up the heat. The refrigerant then travels through the reversing valve into the compressor. Once it has been through the compressor the liquid travels back around through the reversing valve and back into the heat exchanger for another round. Meanwhile, the air that was warmed over the coil gets picked up by the fan and from there it travels out into the air delivery ductwork. The air delivery ductwork distributes the warm air throughout the house. The reason that geothermal heat systems work is because beginning at five feet below the surface of the Earth the ground stays a constant temperature of about 55 degrees. Since the Earth is such a large mass, adding or extracting heat from it doesn't fluctuate the overall temperature. This constant temperature is the key to a steady workload for the unit and a much smaller chance of backup heat being needed. Conventional air source heat pumps use the air outside as a heat source/sink which makes for a more variable workload and backup heat being utilized more because the temperature of the air outside can fluctuate so dramatically. How do they improve your
home? In addition, the life expectancy of a geothermal system is longer than conventional systems because of a lower workload and because half of the system is buried under the ground where it isn't exposed to the elements. Also, geothermal systems are quieter than conventional systems because the unit doesn't have an outdoor fan. At the Avalon Village project the houses are designed so that there could be four units in the same 20 square foot area. If these systems were conventional air source heat pumps, the noise level would be much higher. Finally, to relieve some of the cost of the initial investment, the State of Oregon and most local electricity companies offer rebates for installing geothermal heating systems. Websites and Brochures
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