3 8 |
Bosch Geothermal Heat Pumps
Bosch Thermotechnology Corp.
Data subject to change
Applications Manual
6.2 Open-Loop Geothermal Heat Pump
System Water Quality
Poor water quality can cause serious problems in Bosch
open-loop geothermal heat pump system applications.
Supply water should be tested for hardness, acidity and
iron content before the Bosch geothermal heat pump is
installed. Poor water quality can cause mineral deposits to
build up inside the Bosch geothermal heat pump water-to-
refrigerant coaxial heat exchanger and periodic cleaning
will be required. Water from owing springs, ponds,
lakes or river sources are not recommended for Bosch
geothermal heat pump use, unless proven to be free of
excessive particulate and organic matter. These sediments
will contaminate the water-to-refrigerant coaxial heat
exchanger in the Bosch geothermal heat pump system and
could make it inoperable.
Copper is adequate for groundwater that is not high in
mineral content. If the well driller expresses concern
regarding the groundwater quality available, or knows of
any hazards in the area, it is recommended that proper
testing be performed to assure the groundwater quality
is suitable for use with the Bosch geothermal heat pump.
In conditions anticipating moderate scale formation or in
brackish water a cupro-nickel water-to-refrigerant coaxial
heat exchanger is recommended.
The principal concerns with an open-loop geothermal heat
pump system are corrosion, scaling, encrustation and
erosion.
Galvanic corrosion occurs when dissimilar metals are
used together. For example, using iron or galvanized pipe
together with copper pipe will cause problems. Acceptable
materials are copper, PVC, polyethylene, polybutylene and
rubber.
Scaling is the process where minerals precipitate out
of the groundwater and build up or scale on the inside
surfaces of the pipes and water-to-refrigerant coaxial heat
exchanger in the geothermal heat pump (Fig. 22).
Fig. 22 Scaling
Courtesy
of International Ground Source Heat Pump Association/Oklahoma State
University
Scaling reduces heat transfer and increases pumping
costs. The minerals that combine to form scale are
normally present to some degree in groundwater. If
the water temperature rises suddenly and/or the water
pressure drops suddenly, the suspended minerals will be
released and form a carbonate scale.
The rst step to prevent scaling is to keep all water lines
under pressure. The second step is to limit the water
temperature rise to approximately 20 degrees in the
cooling mode. Most residential geothermal heat pumps
don't raise the water more than 10 to 12 degrees when
cooling. If a larger rise is noted, the water ow rate should
be adjusted. Scaling typically does not occur during the
heating mode.
Encrustation is a build-up of a slimy orange-brown deposit
caused by iron bacteria that can occur primarily in return
wells (Fig. 23). This can clog the system as easily as scales.
Keeping the water lines pressurized and free of contact
with air inhibits the growth of these bacteria. If it is found,
it can be removed with periodic cleaning using a chlorine
bleach solution.
Fig. 23 Encrustation
Courtesy of International Ground Source Heat Pump Association/Oklahoma
State University
Erosion occurs when sand or other particulates
prematurely erode the tubing inside the geothermal heat
pump. Proper screening or ltering can reduce the number
of particles that pass through the geothermal heat pump,
and thus minimize erosion (Fig. 24).
Fig. 24 Erosion
Courtesy of International Ground Source Heat Pump Association/Oklahoma
State University
A well screen with a ne enough mesh to lter out known
sand-sized particles found during drilling is necessary. A
lter should also be placed between any pressure tank
and a geothermal heat pump intake to trap any possible
particles. A replaceable cartridge, with the cartridge
replaced by a screen, is recommended.
Cupro-nickel has a higher resistance to abrasion than
copper.
