We
tend to think of the climate in terms of hot and cold,
but a more scientifically accurate way of thinking about
it is in terms of hot and less hot. What we perceive as
cold is really an uncomfortable drop in the amount of
heat in the air. The complete absence of heat is a
theoretical concept called absolute zero, which is
calculated as being less than minus 450 degrees on the
Fahrenheit scale.
Using the “hot” and “less hot” line of thought, an air
conditioner or a heater can be described as a heat
mover. In the summer months, the air conditioning system
moves heat from inside to outside; in the winter, it
does one of two things: either it generates heat using
fossil fuels or electricity, or it takes the heat from
outside and moves it inside.
This may seem counterintuitive — bringing in winter air
to heat the house — but remember that our winters are
nowhere close to absolute zero. There is still a great
deal of heat out there that can be harnessed, and when
it is condensed it can keep a home comfortable in the
winter.
GROUND
HEAT
However, it does require a great deal of energy to
gather this heat during the months when weather is most
extreme. This is where the thermal properties of the
Earth come in handy. Just below the surface of the
Earth, as close as four feet below the ground, the
temperature hovers around 55 degrees. This is heat
emanating outward from the planet’s molten core.
Instead of drawing winter heat from the outside air
(which can feel like absolute zero even if it’s nowhere
close), a geothermal heat pump draws heat from the
ground. It requires much less energy to gather heat from
a 55-degree environment than a minus-20-degree
environment.
PIPES,
FANS AND ANTIFREEZE
Antifreeze is a heat-sensitive chemical that evaporates
at low temperatures, absorbing the heat around it like a
sponge as it expands into its gaseous state. In a
geothermal heat pump, cold liquid antifreeze is run into
the ground in pipes. When the antifreeze comes into
contact with the 55-degree ground temperature, it heats
up and evaporates, soaking up the ground’s heat and
carrying it along the pipeline.
Fifty-five degrees isn’t warm enough by most people’s
standards of winter comfort, so a compressor squeezes
the warmed-up antifreeze gas, concentrating its heat
into a smaller area. This concentrated hot gas snakes
through a serpentine pipe pattern as a fan blows air
across it. As the air rushes past, it absorbs the pipes’
heat. This air is then transported through air ducts and
blown into the house.
The antifreeze, meanwhile, begins to condense back into
a liquid, having given up its heat to the passing air.
It then comes to an expansion valve. The effort of
expanding causes it to lose more of its heat, and it
turns completely back into a liquid. It’s ready to start
the loop over again.
One advantage of the geothermal system is that it is a
type of heat pump. A heat pump is versatile, serving as
both heater in the winter and air conditioner in the
summer. With the flip of a switch, the antifreeze can
flow in the opposite direction and the heat-moving cycle
is reversed: in the summer, instead of bringing in heat
from the outside, it moves the heat out of the inside.
ADVANTAGES
While
the geothermal heat pump does use electricity to run,
it’s more environmentally friendly than a traditional
heating/air conditioning unit because it moves heat
instead of generating it. It doesn’t rely on fossil
fuels or electricity-generated heat, which means a
geothermal user is pouring fewer greenhouse gases into
the atmosphere. It also means the person paying the
utility bills is paying for fewer resources every month.
These savings mean that a geothermal system can pay for
itself in as few as five to 10 years.
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