The promise and problem
A geothermal
heat pump can
save you so much money
in energy costs (while helping
the environment) that you will
be tempted to install one immediately.
However, a geothermal system costs so much
to install that you will be tempted to
forget the whole thing.
Fact 1: It works like your fridge
Your fridge removes heat from its interior and transfers it to
your kitchen. A geothermal heat pump uses the same principle,
but it transfers heat from the ground to your house (or
vice versa). It does this through long loops of underground
pipes filled with liquid (water or an antifreeze solution).
The loops are hooked up to a geothermal heat pump in your
home, which acts as both a furnace and an air conditioner.
During the heating season, the liquid pulls heat from the
ground and delivers it to the geothermal unit and
then to refrigerant coils, where the heat is distributed
through a forced-air or hydronic system. During
the cooling season, the process runs in reverse. The
pump removes heat from your house and transfers
it to the earth. Many units can provide domestic hot
water as well.
A geothermal heat pump
is vastly more efficient than
conventional heating systems
because it doesn’t burn fuel to
create warmth; it simply moves
existing heat from one place
to another. And because temperatures
underground remain a
relatively constant 50 degrees F
year round, the system requires
a lot less energy to cool your
home than conventional AC systems
or air-source heat pumps,
which use outside air as a transfer
medium.
Geothermal heat pump system
Figure A: Geothermal Heat Pump
A geothermal heat pump draws heat from the ground and releases it in your home.
Fact 2: The upfront costs are scary
Let’s not sugarcoat it—installing
a geothermal system is expensive.
It costs $10,000 to $30,000
depending on your soil conditions,
plot size, system configuration,
site accessibility and
the amount of digging and drilling required. For a typical
2,000-sq.-ft. home, a geothermal retrofit ranges from $10,000
to $20,000. The system may require ductwork modifications
along with extensive excavation. In a new home, installation
costs would be on the lower end. Even so, a geothermal
system will cost about 40 percent more than a traditional
HVAC system.
Recouping these costs through energy savings could take
as little as four years or as long as 15 years depending on
utility rates and the cost of installation. It takes some homework
and professional estimates to figure out whether a
geothermal system makes financial sense in your situation.
Fact 3: Geothermal has real benefits
Much lower operating costs than other systems. A
geothermal heat pump will immediately save you 30
to 60 percent on your heating and 20 to 50 percent on
your cooling costs over conventional heating and cooling
systems.
Uses clean, renewable energy (the sun). With a geothermal
heat pump, there’s no onsite combustion
and therefore no emissions of carbon dioxide, carbon
monoxide or other greenhouse gases. Nor are there any
combustion-related safety or air quality issues inside
the house. (However, the pump unit uses electricity,
which may be generated using fossil fuels.)
Can be installed in both new construction and retrofit
situations. However, it’s a lot more expensive in retrofits
requiring ductwork modifications.
Much quieter than other cooling systems. There’s no
noisy outdoor compressor or fan. The indoor unit is
generally as loud as a refrigerator.
Low maintenance and long-lived. The indoor components
typically last about 25 years (compared with 15
years or less for a furnace or conventional AC unit) and
more than 50 years for the ground loop. The system has
fewer moving parts and is protected from outdoor elements, so it requires minimal maintenance.
Fact 4: There are downsides, besides the cost
Not a DIY project. Sizing, design and installation
require pro expertise for the most efficient system.
Still relatively new, so there are fewer installers
and less competition (which is why prices remain
high).
Installation is highly disruptive to the landscape
and may not be possible on some lots. Heavy drilling
or digging equipment will definitely crush your
prize petunias.
Fact 5: Type of loop affects the cost
The three closed-loop systems shown below are the
most common. There is also a less common open-loop
system that circulates surface water or water
from a well through the system and returns it to the
ground through a discharge pipe.
The best system, loop length and design for a
particular home depend on a variety of factors such
as climate, soil conditions, available land, required
heating and cooling load, and local installation costs
at the site.
Figure B: Horizontal System
Layered coils or straight runs
of polyethylene pipe
are placed in 6-ft.-deep trenches.
This is the cheapest underground
option, but it requires a lot of open
space. A 2,000-sq.-ft. house requires
400 ft. of 2-ft.-wide trenches.
Figure C: Vertical System
A vertical system
is used when
space is limited.
Four-inch-diameter
holes are drilled about 15 ft. apart
and 100 to 400 ft. deep. Two pipes are
inserted and connect at the bottom.
Figure D: Pond/Lake System
This system draws heat
from water rather than
from the soil. If there's a
body of water nearby, this is
the lowest cost option. A blanket
of water covers coils anchored
on racks about 10 ft. deep.
Is Geothermal Right for You?
About 100,000 geothermal heat
pumps are installed in the United
States each year, and according
to Bob Donley, customer support
manager at GeoSystems LLC in
Minnesota, interest in geothermal is
really on the rise. “In 2008 alone, the
industry saw a 40 percent increase
in homeowner interest.” Donley says
you’re a good candidate for a geothermal
system if you:
• Can stomach the upfront costs
and plan to stay in your house for
at least four to seven years (new
construction) or 10 to 12 years
(retrofit) to recoup initial costs
through energy/cost savings.
• Live on a large lot with a pond or
a well. This would allow you to
use a less expensive loop system
(see Figure D).
• Are building a new house and can
roll the upfront costs right into the
mortgage. You’ll be saving on heating
and cooling costs on day one.
• Have an existing house with very
high energy bills. This most likely
means you currently use propane, oil or electricity for heating and cooling.
