FAQ's
Open loop systems
What is an open-loop system?
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. The groundwater is pumped into the heat pump unit where heat is
extracted, and 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.
What do I do with the discharge water?
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.
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.
How much groundwater does an open-loop system need?
Geothermal heat pumps used in open-loop systems need
differing amounts of water depending on the size of the unit and the manufacturer's
specifications. The water requirement of a specific model is usually expressed
in gallons per minute (g.p.m.) and is listed in the specifications for that
unit. Your heating contractor should be able to provide this information.
Generally, the average system will use ~10 g.p.m. while operating.
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.
What problems can be caused by poor water quality?
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 or equipment manufacturer
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 high iron content you should be sure that
the discharge water is not aerated before it's injected into a return well.
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.
Does an open-loop system cause environmental damage?
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.
Some people are concerned that open-loop systems contribute
to the depletion of our ground water resources. This issue is not critical
in some parts of North America because of abundant supplies of groundwater.
Are there any laws that apply to open-loop Installations?
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.
