Outdoor temperatures fluctuate with the changing seasons but underground temperatures don't. Four to six feet below the earth's surface, temperatures remain relatively constant year-round. A geothermal system, which typically consists of an indoor unit and a buried earth loop, capitalizes on these constant temperatures to provide "free" energy. In winter, fluid circulating through the system's earth loop absorbs stored heat and carries it indoors. The indoor unit compresses the heat to a higher temperature and distributes it throughout the building. In summer, the system reverses, pulling heat from the building, carrying it through the earth loop and depositing it in the cooler earth.
Permalink Unlike ordinary systems, geothermal systems do not burn fossil fuel to generate heat; they simply transfer heat to and from the earth to provide a more efficient, affordable and environmentally friendly method of heating and cooling. Typically, electric power is used only to operate the unit's fan, compressor and pump.
PermalinkThe three main parts consist of the heat-pump unit, the liquid heat-exchange medium (open or closed loop), and the air-delivery system (ductwork).
PermalinkAll heating and cooling
systems have a rated efficiency from a U.S. government agency. Fossil fuel
furnaces use AFUE. Air conditioners use SEER while heat pumps use HSPF and
SEER.
Geothermal heat pumps rate
heating efficiencies according to their coefficient of performance or COP. It’s
a scientific way of determining how much energy the system produces versus how
much it uses. Most geothermal heat pump systems have COPs of 3-4.5. The
WaterFurnace Envision holds the highest recorded certified performance of 5.4
COP in an open loop. That means for every dollar of energy used to power the
system, $5.40 of energy are supplied as heat. Where a fossil fuel furnace may
be 78-98% efficient, a geothermal heat pump is about 500% efficient.
For cooling, geothermal units
are rated by Energy Efficiency Ratio (EER). EER is a measure of efficiency in
the cooling mode when measured at a constant temperature (95 degrees F). The
higher the EER, the more efficient the unit. The WaterFurnace Envision holds
the highest recorded certified performance of 30EER for closed loop and 32.1EER
for open loop.
PermalinkA geothermal system is over
five times more efficient in heating and more than twice as efficient in
cooling as the most efficient ordinary system. Because geothermal systems move
existing heat rather than creating it through combustion, they provide four to
five units of energy for every one unit used to power the system.
PermalinkNo. Geothermal systems are
practically maintenance free. The buried loop will last for generations. The
unit’s fan, compressor and pump is housed indoors, protected from the weather
and contamination. Usually, periodic checks and filter changes are the only
required maintenance.
While WaterFurnace does offer
an outdoor geothermal unit for jobs where space is limited, its rugged housing
is sealed so that no components are exposed to the elements.
PermalinkGeothermal systems work with
nature, not against it. They emit no greenhouse gases – which have been linked
to pollution, acid rain, and other environmental hazards. WaterFurnace’s
earth-loop antifreeze will not harm the environment in the unlikely event of a
leak. And all of the current WaterFurnace product lines use R-410A, a
performance-enhancing refrigerant that will not harm the earth’s ozone layer.
PermalinkNo. There are different kinds
of geothermal heat pumps designed for specific applications. Many geothermal
heat pumps, for example, are intended for use only with higher temperature
ground water encountered in open-loop systems. Others will operate at entering
water temperatures as low as 25°F, which are possible in
closed-loop systems. Most geothermal heat pumps provide summer air
conditioning, but a few brands are designed only for winter heating. Geothermal
heat pumps also can differ in the way they are designed. Self-contained units
combine the blower, compressor, heat exchanger and coil in a single cabinet.
Split systems (such as the WaterFurnace Envision Series Split) allow the coil
to be added to a forced-air furnace and utilize the existing blower.
PermalinkHeat pumps don’t create heat. They take existing
heat and move it. Anyone with a refrigerator has witnessed the operation of a
heat pump. Refrigerators collect heat from the unit’s interior and move it to
the exterior for cooling purposes. Unlike a refrigerator, a heat pump can
reverse itself. An air-source heat pump, for example, can extract heat from
outdoor air and pump it indoors for heating purposes.
A geothermal heat pump works the same way, except
that its heat source is the warmth of the earth. 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 (fluid from the
ground loop). The refrigerant evaporates into a gas as heat is absorbed.
The gasseous refrigerant then passes through a
compressor where the refrigerant is pressurized, raising its temperature to
more than 180°F. The hot gas then circulates through a refrigerant-to-air heat
exchanger where heat is removed and pumped into the building at about 100°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
work as an air conditioner, the system’s flow is reversed.
PermalinkOne thing that makes a geothermal heat pump so
versatile is its ability to be a heating and cooling system in one. With a
simple flick of a switch on your indoor thermostat, you can change from one
mode to another. In the cooling mode, a geothermal heat pump takes heat from
indoors and transfers it to the cooler earth through either groundwater or an
underground earth loop system. In the heating mode, the process is reversed.
PermalinkYes. Some geothermal heat pumps can provide all
of your hot water needs at the same high efficiencies as the heating/cooling
cycles. An option called a desuperheater can be added to most heat pumps. It
will provide significant savings by heating water before it enters your hot
water tank.
PermalinkNo. The same loop works for both. To switch
heating to cooling or vice versa, the flow of heat is simply reversed.
PermalinkThe buried pipe, or earth loop, was an important
technical advancement in heat pump technology. The idea of burying pipe in the
ground to gather heat energy originated in the 1940’s. New heat pump designs
and more durable pipe materials have been combined to make geothermal heat
pumps the most efficient heating and cooling systems available.
PermalinkThere are two main types: open and closed.
PermalinkAn open loop system uses groundwater from an
ordinary well as a heat source. The groundwater is pumped into the heat pump
unit where heat is extracted and the water is disposed of in an environmentally
safe manner. Because groundwater is a relatively constant temperature
year-round, wells are an excellent heat source.
PermalinkThe water requirement of a specific model is
usually expressed in gallons per minute (gpm) and is listed in the unit’s
specifications. Generally, the average system will use 1.5 gmp per ton of
capacity while operating, but the amount of water required depends on the size
of the unit and the manufacturer’s specifications. Your contractor should be
able to provide this information. Your well and pump combination should be
large enough to supply the water needed by the heat pump in addition to your
domesting water requirements. You’ll probably need to enlarge your pressure
tank or modify your plumbing to supply adequate water to the heat pump.
PermalinkThere are a number of ways to
dispose of water after it has passed through the heat pump. The open discharge
method is easiest and least expensive. Open discharge simply involves releasing
the water into a stream, river, lake, pond, ditch, or drainage tile. Obviously,
one of these alternatives must be readily available and have the capacity to
accept the amount of water used by the heat pump before open discharge is
feasible.
A second means of water
discharge is the return well. A return well is a second well bore that returns
the water to the ground aquifer. A return well must have enough capacity to
dispose of the water passed through the heat pump. A new return well should be
installed by a qualified well driller. Likewise, a professional should test the
capacity of an existing well before it is used as a return.
PermalinkNo. They are pollution free.
The heat pump merely removes or adds heat to the water. No pollutants are
added. The only change in the water returned to the environment is a slight
increase or decrease in temperature.
PermalinkPoor water quality can cause
serious problems in open loop systems. Your water should be tested for
hardness, acidity and iron content before a heat pump is installed. Your
contractor or equipment manufacturer can tell ynou what level of water is
acceptable. Mineral deposits can build up inside the heat pump’s heat
exchanger. Sometimes a periodic cleaning with a mild acid solution is all
that’s needed to remove the build-up.
Impurities, particularly
iron, can eventually clog a return well. If your water has high iron content,
make sure that the discharge water is not aerated before it’s injected into a
return well.
PermalinkA closed loop system uses a
continuous loop of buried polyethylene pipe. The pipe is connected to the
indoor heat pump to form a sealed underground loop through which an
environmentally friendly antifreeze-and-water solution is circulated. A closed
loop system constantly recirculates its heat-transferring solution in
pressurized pipe, unlike an open loop system that consumes water from a well.
Most closed loops are trenched horizontally in areas adjacent to the building.
However, where adequate land is not available, loops are vertically bored. Any
area near a home or business with appropriate soil conditions and adequate
square footage will work.
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