Water Corrosion; Remedies Of Water Problems - Bard Q-TEC Series Literature Assembly

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 your 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) of
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.
Manual 2100-738A
Page 56 of 71
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
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 the "Cleaning
Water Coil", Figure 34. 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.
WARNING
Thin ice may result in the vicinity of the
discharge line.
For complete information on water well systems and
lake and pond applications, refer to manual from dis-
tributor.
), the carbonate of calcium
2