Manual 2100-738C
Page
58 of 73
Water Corrosion
Two concerns will immediately come to light when
considering a water source heat pump, whether for
ground water or for a closed loop application: Will there
be enough water? And, how will the water quality affect
the system?
Water quantity is an important consideration and
one which is easily determined. The well driller must
perform a pump down test on the well according
to methods described by the Nation Well Water
Association. This test, if performed correctly, will
provide information on the rate of flow and on the
capacity of the well. It is important to consider the
overall capacity of the well when thinking about a water
source heat pump because the heat pump may be
required to run for extended periods of time.
The second concern, about water quality, is equally
important. Generally speaking, if the water is intended
for drinking purposes, it should pose no problem for
the heat pump. The well driller or local water softening
company can perform tests which will determine the
chemical properties of the well water.
Water quality problems will show up in the heat pump
in one of more of the following ways:
1. Decrease in water flow through the unit.
2. Decreased heat transfer of the water coil (entering
to leaving water temperature difference is less).
There are four main water quality problems associated
with ground water. These are:
1.
Biological Growth
This is the growth of microscopic organisms in
the water and will show up as a slimy deposit
throughout the water system. Shock treatment of
the well is usually required and this is best left
up to the well driller. The treatment consists of
injecting chlorine into the well casing and flushing
the system until all growth is removed.
2.
Suspended Particles in the Water
Filtering will usually remove most suspended
particles (fine sand, small gravel) from the water.
The problem with suspended particles in the
water is that it will erode metal parts, pumps, heat
transfer coils, etc. So long as the filter is cleaned
and periodically maintained, suspended particles
should pose no serious problem. Consult with the
well driller.
3.
Corrosion of Metal
Corrosion of metal parts results from either
highly corrosive water (acid water, generally not
the case with ground water) or galvanic reaction
between dissimilar metals in the presence of
water. By using plastic plumbing or dielectric
unions, galvanic reaction is eliminated. The use
of corrosion resistant materials (such as the
Cupronickel coil) through the water system will
reduce corrosion problems significantly.
4.
Scale Formation
Of all the water problems, the formation of scale by
ground water is by far the most common. Usually
this scale is due to the formation of calcium
carbonate, but magnesium carbonate or calcium
sulfate may also be present. Carbon dioxide gas
(CO
2
), the carbonate of calcium and magnesium
carbonate, is very soluble in water. It will remain
dissolved in the water until some outside factor
upsets the balance. This outside influence may be
a large change in water temperature or pressure.
When this happens, enough carbon dioxide gas
combines with dissolved calcium or magnesium
in the water and falls out of solution until a new
balance is reached. The change in temperature
that this heat pump produces is usually not high
enough to cause the dissolved gas to fall out of
solution. Likewise, if pressure drops are kept to a
reasonable level, no precipitation of carbon dioxide
should occur.
Remedies of Water Problems
Water Treatment
Water treatment can usually be economically justified
for close loop systems. However, because of the large
amounts of water involved with a ground water heat
pump, water treatment is generally too expensive.
Acid Cleaning the Water Coil or Heat Pump Recovery
Unit
If scaling of the coil is strongly suspected, the coil can
be cleaned up with a solution of phosphoric acid (food
grade acid). Follow the manufacturer’s directions for
mixing, use, etc. Refer to Figure 37. The acid solution
can be introduced into the heat pump coil through the
hose bib A. Be sure the isolation valves are closed to
prevent contamination of the rest of the system by the
coil. The acid should be pumped from a bucket into
the hose bib and returned to the bucket through the
other hose bib B. Follow the manufacturer’s directions
for the product used as to how long the solution is to
be circulated, but it is usually circulated for a period of
several hours.
For complete information on water well systems and
lake and pond applications, refer to manual from
distributor.
WARNING
Thin ice may result in the vicinity of the
discharge line.
