Zehnder Rittling VS Series Installation, Operation And Maintenance Manual page 19

Ground water
applications
Open loop ground
Shut off valves should be included
for ease of servicing. Boiler drains
or other valves should be "tee'd"
into the lines to allow acid flushing
of the heat exchanger. Shut off
valves should be positioned to
allow flow through the coax via the
boiler drains without allowing flow
into the piping system.
P/T plugs should be used so that
pressure drop and temperature
can be measured. Piping materials
should be limited to copper or
PVC SCH80.
Water quantity should be plentiful
and of good quality. Consult
Table 5 for water quality
guidelines. In ground water
situations where scaling could
be heavy or where biological
growth such as iron bacteria
will be present, an open loop
system is not recommended.
Heat exchanger coils may lose
heat exchange capabilities, over
time, due to build up of mineral
deposits. Heat exchangers must
only be serviced by a qualified
technician, as acid and special
pumping equipment is required. In
areas with extremely hard water,
the owner should be informed that
the heat exchanger may require
occasional acid flushing.
Water quality standards
Table 5 should be consulted
for water quality requirements.
Scaling potential should be
assessed using the pH/calcium
hardness method. If the pH <7.5
and the calcium hardness is less
than 100 ppm, scaling potential is
low. If this method yields numbers
out of range of those listed, the
Ryznar Stability and Langelier
Saturation indicies should be
calculated.
Use the appropriate scaling
surface temperature for the
application, 150 °F (66 °C) for
direct use (well water/open loop);
90 °F (32 °F) for indirect use.
A monitoring plan should be
implemented in these probable
scaling situations. Other water
quality issues such as iron
fouling, corrosion prevention and
erosion and clogging should be
referenced in Table 5.
Water control valve
Always maintain water pressure
in the heat exchanger by placing
the water control valve(s) on
the discharge line to prevent
mineral precipitation during the
off-cycle. Slow closing valves
are recommended to reduce
water hammer. If water hammer
persists, a mini-expansion tank
can be mounted on the piping to
help absorb the excess hammer
shock. Ensure that the total 'VA'
draw of the valve can be supplied
by the unit transformer.
Applications 17