Imagine an HVAC and water
heating system that can save 20%
to 50% on a building's energy
costs while minimizing CO2 and
carbon emissions. Imagine a
system that is more reliable, is
2.5 to 4 times more efficient,
provides the lowest life cycle
cost, and a high degree of
design flexibility.
Where can you find such a
system? You need look no further
than right under your feet. The
earth is a huge energy storage
device that absorbs 47% of the
sun’s energy. When combined with
the constant upward flow of heat
from the earth’s red hot
interior, the result is
geothermal energy. Geo = earth,
Thermal = heat. This clean,
renewable energy is stored in
masses of rock in the upper six
miles of the earth’s crust. In
nearly every state of the Union,
there is sufficient geothermal
energy to heat, cool and provide
hot water for all types and
sizes of buildings.
Temperatures near the earth’s
surface remain relatively
constant all year round – warmer
than outside air in the winter,
and cooler than outside air in
the summer. Geoexchange systems
(or ground coupled heat pumps)
extract the earth's heat during
the winter and release it to the
building interior. In the summer
the process is reversed, drawing
the hot air from inside the
building and transferring to the
earth. Nearly all geoexchange
systems on the market can also
provide low cost hot water -
further increasing their
operational efficiency
According to the EPA and DOE,
geoexhange systems are the most
energy efficient,
environmentally clean and
cost-effective space
conditioning systems available.
They rate the systems 40% more
efficient than air source heat
pumps 48% greater than gas
furnaces and 75% greater than
oil furnaces. Though geoexchange
units do require a power source,
they have a much greater energy
efficiency ratio. In heating
mode, the system will move at
least three units of solar
energy from the ground for each
unit of electricity used.
There are three principal
components in a geoexchange
system: The ground loop, the
heat pump unit and the heat
distribution channel
Ground Loop
For most buildings, the
connection to the geothermal
heat source is made via a
‘closed’ loop configuration. A
series of flexible, high-density
polyethylene pipes are installed
beneath the ground in horizontal
trenches or vertical holes. A
fluid (water or a mixture of
water and environmentally benign
antifreeze) is circulated
through the loops, absorbing the
earth’s heat as it passes
through the pipes and
transporting it to the
geoexchange unit inside the
building. In cooling mode, the
building’s interior hot air is
absorbed by the unit,
transported back through the
loops and absorbed into the
surrounding earth.
Post-installation the holes or
trenches are backfilled, then
covered with native landscaping,
grass or even parking lots.
Horizontal trenching is
usually the most cost effective
configuration when adequate
space is available and trenches
are easy to dig Vertical
drilling is used when the land
area is limited, or where the
soil is too shallow for
horizontal trenching. The loops
should be installed by
professionals who follow
procedures established by the
International Ground Source Heat
Pump Association (IGSHPA), and
are either certified by IGSHPA
or can prove equivalent training
by manufacturers or other
recognized authorities.
Geoexchange Heat Pump
The most commonly used unit is
the single package water-to-air
heat pump, which combines heat
exchanger, refrigerant piping,
control valve, compressor, air
coil, and fan, in one single
enclosure about the size of a
small gas furnace. The single
package design is a major
advantage over the "split"
system used for air- source heat
pumps. There are numerous
manufacturers, brands and models
of heat pumps available. They
are rated by the Air
Conditioning and Refrigerant
Institute according to their
respective Coefficient of
Performance (heating) and Energy
Efficiency Ratio (cooling).
ENERGY STAR qualified
geoexchange pumps consume 40-60
percent less energy than a
standard heat pump.
Heat Distribution Channel
Conventional ductwork is
generally used to distribute
heated or cooled air from the
geothermal heat pump throughout
the building. A well-designed
geoexchange system allows
building occupants precise
temperature control by room or
by zone, with ideal humidity
levels. The system requires no
flue or chimney. There is no
rooftop equipment or chilling
towers that add weight to the
structure or limit alternative
roof styles such as vegetated
roofing. Their compact size
requires significantly less
interior storage space. The
heated water coursing through
the system can be utilized for
additional building uses, such
as heating swimming pools and
spas, melting sidewalk and
parking lot ice and snow- even
providing water for a car wash!
The largest commercial
geoexchange system in the world
is the Waterfront Office and
Galt East Hotel complex in
Louisville, Kentucky. This 1.7
million plus square foot complex
is fitted with a 2,700 ton
capacity geoexchange system, at
a cost of $1,500 per ton. The
project manager estimates that a
conventional HVAC system with
centrifugal chillers, cooling
towers and insulated pipes would
have cost from $2,000 to $3,000
per ton. Using Geoexchange
technology freed up about 25,000
square feet of additional
commercial space that would
otherwise have been used for
conventional equipment rooms.
Energy savings are estimated at
$25,000 per month while allowing
individual temperature control
to each room or suite. Annual
maintenance costs are about 5
cents per square foot versus
much higher average costs with
standard HVAC systems.
Best of all, complaints about
heating and cooling “have been
virtually non-existent, whereas
before we had frequent comments
about lack of adequate comfort"
Daniele
Loffreda is Managing Principal
of Plateau Enviro Associates, a
consulting firm specializing in
green building, sustainable
communities and marketing
communications. He serves on the
Board of Directors of the U.S.
Greenbuilding Council Colorado
Chapter, and is a Leadership in
Energy and Environmental Design
(LEED) Accredited Professional
