Geothermal Well - Open Loop System
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While the majority of geothermal
installations are closed loop
systems, a less expensive
alternative is the
l open loop system.

Instead of using a combination
water/antifreeze solution sealed
inside the buried piping, an open
loop system uses water from a
surface or underground source,
such as a pond, lake or well.

The water is pumped into the
heat pump unit where the heat is
extracted; the water is then
discharged back into the original
source or into a return well.
The well supplies both household water and water for the
heat pump. Approximately three gallons per minute of well
water are needed per ton of cooling capacity.  

A 3,000-square-foot, well-insulated home would typically
require 10 to 15 gallons per minute for a 4 ton (700 sq. ft.
per ton) unit. An open loop system is the least expensive to
install since it requires far less pipe or tubing than a closed
loop system.
Water quality is an important issue with open loop systems. Mineral deposits can build
up inside the heat exchanger, iron and other impurities can clog a return well, and
organic matter from ponds and lakes can quickly damage a geothermal system. Water
should be tested for acidity, mineral content and corrosiveness.

Open loop systems are generally avoided and even prohibited in some areas because
of environmental concerns. Aquifers can be depleted if the water is not re-injected.

Also, the risk of contamination is an increasing problem; improperly installed wells can
be a path for surface water run-off that carries pesticides, fertilizers, organic materials
and other contaminants into underlying aquifers.
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Open loop geothermal well
Open loop system
showing extraction and
return wells