9
Application
Considerations
Closed Loop System
Closed loop systems (both ground source
and surface water) provide heat rejection
and heat addition to maintain proper water
source temperatures.
Operating and maintenace cost are low
because an auxillary fossil fuel boiler and
cooling tower are not required to maintain
the loop temperature. The technology has
advanced to the point where many electric
utilities and rural electric cooperatives are
offering incentives for the installation of
geothermal systems. These incentives are
offered because of savings to the utilities
due to reduced peak loads that flatten out
the system demand curve over time.
For ground source geothermal systems,
(See Figure 5), when building cooling
requirements cause loop water
temperatures to rise, heat is dissapated into
the cooler earth through buried polyethylene
pipe heat exchangers. If reversed, heating
demands cause the loop temperature to fall,
enabling the earth to add heat to meet load
requirements.
Where local building codes require water
retention ponds for short term storage of
surface run-off, a ground source surface
water system, (See Figure 6), can be very
cost effective. This system has all the
advantages as the geothermal system in
cooling dominated structures.
Another benefit of the ground source system
is that it is environmentally friendly. The loop
is made of chemically inert, non-polluting
polyethylene pipe. The heat pumps use
HCFC-22 refrigerant, which has a lower
ozone depletion potential than CFC-12.
Because the closed loop system does not
require a heat adder, there are no CO
2
emissions. Less electric power consumed
reduces secondary emissions from the
power plant. Therefore, the system offers
advantages not seen by other central
furnace or heat pump systems.
Figure 5: Ground source geothermal system
Figure 6: Ground source surface water system