The
Audubon Center is now heated and cooled with a system called geo-thermal
heat pumps. Why does this make more sense then air heating and
cooling? The air temperature above the earth's surface, as we
all know, is very inconsistent and we are constantly trying to
make it come out between 65 and 70 and use mass amounts of fossil
fuels to get it there. Geo-thermal heat pumps use the naturally
consist ant temperature (approximately 51 degrees F) under the
ground's surface (seven feet or more) for more efficient heating
and cooling.
This
how it works. When we use hot water systems we run the pipes into
radiators and past fans and try to take the heat in the rooms.
Geo-thermal heat pumps do something similar, but it works in both
summer and winter. Instead of generating 70 degrees of heat, we
heat the 51 degree water to 70 (19 degrees) and when we cool down
in the summer, we just let the cold water absorb the heat in the
room and return to be cooled in the ground.
There are different types of geothermal systems and we chose a
closed vertical loop. We receive water from a series of wells
that then gives us our heating or cooling. Determined by an engineering
company it would take a 60 ton chiller to gives us the cooling
for both buildings. It is then determined by different tests and
equations to figure out what is needed from the earth to equal
a 60 ton chiller. To get this we drilled 30 wells, each being
208 feet deep and 25 feet apart in any distance. The distance
apart is important as we do not want to warm the earth with our
return water. The distance was determined by engineering and is
called a conductivity test.
The piping that connects our well is filled with food grade antifreeze
to keep the water from freezing. It is pumped to the heat pumps
by a ground pump. It is then sent to the circulating pumps and
is distributed to all the individual fan coils. The heat pumps
provide us with 58 degree water for cooling and 118 degree water
of heating
Of
course the electric usage has gone up but is offset by our newly
installed photovoltaic solar arrays.
Our ground source heat pump system was funded in part from an
appropriation from HUD and individual donations and grants from
East Central Electric and Great River Energy.
