FAQ's
Geothermal Heat Pumps: Closed loop systems
What is a closed loop system?
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 an antifreeze solution
is circulated. Unlike an open-loop system that consumes water from a well,
a closed-loop system re-circulates its heat transferring solution within
a pressurized piping system.
Where can this loop be located?
That depends on land availability and terrain. Most closed
loops are trenched horizontally in yards adjacent to the home. But any area
near a home or business with appropriate soil conditions and adequate square
footage will work.
How deep and long will my trenches be?
Trenches are normally four to six feet deep and up to
400 feet long, depending on how many pipes are in a trench. 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, 500-600 feet of pipe is required
per ton of system capacity. A well insulated, 2,000 square foot home would
need about a three-ton system with 1,500-1,800 feet of pipe.
How many pipes are in a trench?
Normally, a run of pipe is laid at five feet then looped
back over itself at three feet once the bottom pipe is covered with soil.
This allows more length of pipe to be put in one trench and has no adverse
affect on system efficiency. Other loop designs use four or six pipes and
allow for shorter trenches if land area is limited.
What if I don't have enough room for a horizontal loop?
Closed-loop systems can also be vertical. Holes are bored
to about 120 - 150 feet per ton of heat pump capacity. U-shaped loops of
pipe are inserted in the holes. The holes are then backfilled with a sealing
solution.
How long will the loop pipe last?
Closed-loop systems should only be installed using high
density polyethylene or polybutylene pipe. Properly installed, these pipes
will last 50-75 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.
How are the pipe sections of the loop joined?
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 fittings,
clamps and glued joints is certain to result in loop failure due to leaks.
Will an earth loop affect my lawn or landscape?
No. Research has proven that loops have no adverse effect
on grass, trees or shrubs. Most horizontal loop installations use trenches
about six inches 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.
Can I reclaim heat from my septic system disposal field?
No. An earth loop will reach temperatures below freezing
during extreme conditions and may freeze your septic system. Such usage
is banned in many areas.
If the loop falls below freezing, will it hurt the system?
No. The antifreeze solution in the loop will keep it
from freezing down to about 10 degrees F. Three types of antifreeze solution
are acceptable: propylene glycol, calcium chloride and methyl alcohol.
Can I install an earth loop myself?
It's not recommended. In addition to thermal fusion of
the pipe, good earth coil contact is very important for successful loop
operation. Non-professional installations may result in less than optimum
system performance.
I have a pond near my home. Can I put a loop in it?
Yes, if it's deep enough and large enough. A minimum
of six feet in depth at its lowest level during the year is needed for a
pond to be considered. In pond loops, copper, polyethylene or polybutylene
pipe can be used.
