Q: What is a geothermal heat pump?
A: A geothermal or
“ground-source” heat pump is an electrically-powered device that uses
the natural heat storage ability of the earth and/or the earth’s
groundwater to heat and cool your home
or business.
Q: How does it work?
A:
Like any type of heat pump, it simply moves heat energy form one place
to another. Your refrigerator works using the same scientific
principle. By using refrigeration, the geothermal heat pump removes
heat energy stored in the earth and/or the earth’s groundwater and
transfers it to the home.
Q: How is heat transferred between the earth and the home?
A:
The earth has the ability to absorb and store heat energy. To use that
stored energy, heat is extracted from the earth through a liquid medium
(water or an anti-freeze solution) and is pumped to the heat pump heat
exchanger. There, the heat is used to heat your home. In summer the
process is reversed and indoor heat is extracted from your home and
transferred to the earth through the liquid.
Q: You mentioned heating and cooling. Does it do both?
A:
One of the things that makes a heat pump so versatile is its ability to
be a heating and cooling system in one. You can change from one mode to
another with a simple flick of a switch on your indoor thermostat.
Plus, a geothermal heat pump can assist in heating hot water year-round.
Q: Do I need separate ground loops for heating and cooling?
A:
No. The same loop works for both. All that happens when changing from
heating to cooling, or vise versa, is that the flow of heat is reversed
inside the unit.
Q: What types of loops are available?
A: There are two main types: open and closed. See below.
Q: Does the underground pipe system really work?
A:
The buried pipe, or “ground loop”, is the biggest technical advancement
in heat pump technology to date. The idea to bury pipe in the ground to
gather heat energy began in the 1940s. But it’s only been in the last
twenty-five years that new heat pump designs and improved pipe
materials have been combined to make geothermal heat pumps the most
efficient heating and cooling systems available.
Geothermal Heat Pumps: Closed-Loop Systems
Q: What is a closed-loop system?
A:
The term “closed-loop” is used to describe a geothermal heat pump
system that uses a continuous loop of special buried plastic pipe as a
heat exchanger. The pipe is connected to the indoor heat pump to form a
sealed, underground loop through which water or an anti-freeze solution
- depending on where you live - is circulated. Unlike an open-loop
system that consumes water from a well, a closed-loop system
recirculates its heat transferring solution in pressurized pipe.
Q: Where can this loop be located?
A:
That depends on land availability and terrain. Closed-loops are
trenched horizontally in yards adjacent to the home if the yard is
large enough. Or, for smaller yards, the loops can be installed
vertically using a drill rig, much like a water well installation.
 Vertical Loop Installation
Q: How deep and long will my horizontal trenches be?
A:
Trenches are normally four to six feet deep [1.2 -1.8 meters]. One of
the advantages of a horizontal loop system is being able to lay the
trenches according to the shape of the land. As a rule of thumb, 125 -
300 feet of trench are required per ton of heat pump capacity [11 - 27
meters per kW of capacity].
 Horizontal Loop Installation
Q: How many pipes are in a trench?
A:
Anywhere from 1 to 6 pipes per trench may be used, depending upon the
optimal design for the yard. More pipe per trench shortens the total
amount of trench required.
Q: What if I don’t have enough room for a horizontal loop?
A:
Closed-loop systems can also be vertical. Holes are bored to about 150
- 300 feet per ton of heat pump capacity [13 - 27 meters per kW of
capacity]. U-shaped loops of pipe are inserted in the holes. The holes
are then back-fi lled with a sealing solution (grouting material).
Q: How long will the loop pipe last?
A:
Closed-loop systems should only be installed using the appropriate
high-density polyethylene pipe. Properly installed, these pipes will
last over 50 years. They are inert to chemicals normally found in soil
and have good heat conducting properties. PVC pipe should not be used
under any circumstances.
Q: How are the buried pipe sections of the loop joined?
A:
The only acceptable method to connect pipe sections is by thermal
fusion. Pipe connections are heated and fused together to form a joint
stronger than the original pipe. Mechanical joining of pipe for an
earth loop is never an accepted practice. The use of barbed fi ttings,
clamps and glued joints is certain to result in loop failure due to
leaks.
Q: Will an earth loop affect my lawn or landscape?
A:
No. Research has proven that loops have no adverse effect on grass,
trees or shrubs. Most horizontal loop installations use trenches about
3 feet [1 meter] or less wide. This, of course, will leave temporary
bare areas that can be restored with grass seed or sod. Vertical loops
require little space and result in minimal lawn damage.
Q: Can I reclaim heat from my septic system disposal field?
A:
No. Depending upon your geographic location, an earth loop will reach
temperatures below freezing during extreme conditions and may freeze
your septic system. Such usage is banned in many areas.
Q: If the loop falls below freezing, will it hurt the system?
A: No. The antifreeze solution used in loops that operate at low temperatures will keep it from
freezing down to about 15°F [-9°C] fluid temperature. In the U.S. and Canada, three types of
antifreeze
solution are acceptable: propylene glycol, methyl alcohol, and ethyl
alcohol. Some states/provinces may require one type over another.
Q: Can I install an earth loop myself?
A:
It’s not recommended. In addition to thermal fusion of the pipe, good
pipe-to-soil contact is very important for successful loop operation.
Nonprofessional installations may result in less than optimum heat pump
performance.
Q: I have a pond near my home. Can I put a loop in it?
A:
Yes, if it’s deep enough and large enough. A minimum of 8 - 10 feet
[2.5 - 3 meters] in depth at its lowest level during the year is needed
for a pond to be considered. In pond loops, polyethylene pipe must be
used. Generally, a minimum of ½ acre [0.2 hectare] pond is required to
provide adequate surface area for heat transfer.
Pond Loop Installation
Geothermal Heat Pumps: Open-Loop SystemsQ: What is an open-loop system?
A:
The term “Open-Loop” is commonly used to describe a geothermal heat
pump system that uses groundwater from a conventional well as a heat
source in winter and a heat sink in summer. The groundwater is pumped
through the heat pump where heat is extracted (in winter) or rejected
(in summer), then the water is disposed of in an appropriate manner.
Since groundwater is a relatively constant temperature year-round, it
is an excellent heat source/heat sink. 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.
Q: How much groundwater does an open-loop system need?
A:
Geothermal heat pumps used in open-loop systems need differing amounts
of water depending on the size of the unit. The water requirement of a
specific model is usually expressed in gallons
per minute (l/s) and
is listed in the specifications for that unit. Your heating and cooling
contractor should be able to provide this information. Generally, the
average system will use 6-10 G.P.M. [0.4 - 0.6 l/s] while operating. An
extremely cold day might result in a usage of 6,000-10,000 gallons
[23,000
- 38,000 liters] of water. Your well and pump combination should be
large enough to supply the water needed by the heat pump in addition to
your domestic water requirements. You will probably need to enlarge
your pressure tank or modify your plumbing to supply adequate water to
the heat pump.
Q: What problems can be caused by poor water quality?
A:
Poor 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 can tell you what
level of water quality 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 a high iron content you should be sure that the
discharge water is not aerated before it’s injected into a return well.
 Groundwater Installation
Q: What do I do with the discharge water?
A:
There are a number of ways to dispose of water after it has passed
through the heat pump. The open discharge method is the 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 must possess
the capacity to accept the amount of water used by the heat pump before
open discharge is feasible. Finally, you should opt against using water
from a spring, pond, lake or river as a source for your heat pump
system unless it’s proven to be free of excessive particles and organic
matter. They can clog a heat pump system and make it inoperable in a
short time. If water quality is a concern, a closed-loop system should
be used.
Q: Does an open-loop system cause environmental damage?
A:
No. They are pollution free. The heat pump merely removes heat from or
adds heat to the water. No pollutants are added whatsoever. The only
change in the water returned to the environment is a slight increase or
decrease in temperature.
Q: Are there any laws that apply to open-loop installations?
A:
In some localities, all or parts of the installation may be subject to
local ordinances, codes, covenants or licensing requirements. Check
with local authorities to determine if any restrictions apply in your
area.
Geothermal Heat Pumps: Parts of the System
Q: What are the components of a geothermal heat pump system?
A:
The three main parts are the heat pump unit, the liquid heat exchange
medium (open or closed loop), and the air delivery system (duct work).
Q: Are all geothermal heat pumps alike?
A:
No. 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 20°F [-7°C] which is required for closed loop
systems. Geothermal heat pumps can also differ in the way they are
designed. Self-contained units combine the blower, compressor, water
heat exchanger and air coil in a single cabinet. Split systems allow
the coil
to be added to a forced-air furnace and utilize the existing blower.
Q: Will I have to add insulation to my home if I install one of these systems?
A:
Geothermal heat pumps will reduce your heating and cooling costs
regardless of how well your home is insulated. However, insulating and
weatherizing are key factors in realizing the most savings from any
type of heating and cooling system.
Q: Can a geothermal heat pump also heat water for my home?
A:
Yes. Using what’s called a Hot Water Generator (HWG), some types of
geothermal heat pumps can save you up to 50 percent on your water
heating bill by pre-heating tank water. The HWG is
a factory-installed option.
Q: Is a geothermal heat pump difficult to install?
A:
Most units are easy to install, especially when they are replacing
another forced-air system. They can be installed in areas unsuitable
for fossil fuel furnaces because there is no combustion, thus, no need
to vent exhaust gases. Ductwork must be installed in homes that don’t
have an existing air distribution system. The difficulty of installing
ductwork will vary and should
be assessed by a contractor.
Q: Can a geothermal heat pump be added to my fossil fuel (Gas, oil, propane) furnace?
A:
Split systems can easily be added to existing furnaces for those
wishing to have a dual-fuel system. Use the heat pump as the main
heating source and a furnace as a supplement in extremely cold weather
if additional heat is needed
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Geothermal Heating & Cooling
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