Comfort-Aire HBH Series 6-10 Tons - Manual (Page 16)

IOM Manual HBH SERIES Heat Controller, Inc.
15
Open Loop - Ground Water Systems - Typical open loop
piping is shown in Figure 10. 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. Note: Due to the pressure and temperature
extremes, PVC SCH40 is not recommended.
Water quantity should be plentiful and of good quality.
Consult table 3 for water quality guidelines. The unit can
be ordered with either a copper or cupro-nickel water
heat exchanger. Consult Table 3 for recommendations.
Copper is recommended for closed loop systems and open
loop ground water systems that are not high in mineral
content or corrosiveness. In conditions anticipating heavy
scale formation or in brackish water, a cupro-nickel heat
exchanger is recommended. 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 over time
lose heat exchange capabilities 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. Desuperheater coils can likewise become scaled
and possibly plugged. In areas with extremely hard water,
the owner should be informed that the heat exchanger
may require occasional acid flushing. In some cases, the
desuperheater option should not be recommended due to
hard water conditions and additional maintenance required.
Water Quality Standards - Table 3 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
indecies should be calculated. Use the appropriate scaling
surface temperature for the application, 150°F [66°C] for
direct use (well water/open loop) and DHW (desuperheater);
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 3.
Expansion Tank and Pump - Use a closed, bladder-type
expansion tank to minimize mineral formation due to air
exposure. The expansion tank should be sized to provide
at least one minute continuous run time of the pump using
its drawdown capacity rating to prevent pump short cycling.
Discharge water from the unit is not contaminated in any
manner and can be disposed of in various ways, depending
on local building codes (e.g. recharge well, storm sewer,
drain field, adjacent stream or pond, etc.). Most local codes
forbid the use of sanitary sewer for disposal. Consult your
local building and zoning department to assure compliance
in your area.
Water Control Valve - Note the placement of the water
control valve in Figure 10. 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. Pilot operated 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. Insure that
the total ‘VA’ draw of the valve can be supplied by the unit
transformer. For instance, a slow closing valve can draw up
to 35VA. This can overload smaller 40 or 50 VA transformers
depending on the other controls in the circuit. A typical pilot
operated solenoid valve draws approximately 15VA (see
Figure 14). Note the special wiring diagrams for slow closing
valves (Figures 15 & 16).
Flow Regulation - Flow regulation can be accomplished
by two methods. One method of flow regulation involves
simply adjusting the ball valve or water control valve on
the discharge line. Measure the pressure drop through the
unit heat exchanger, and determine flow rate from Tables
8a through 8e. Since the pressure is constantly varying,
two pressure gauges may be needed. Adjust the valve
until the desired flow of 1.5 to 2 gpm per ton [2.0 to 2.6
l/m per kW] is achieved. A second method of flow control
requires a flow control device mounted on the outlet of the
water control valve. The device is typically a brass fitting
with an orifice of rubber or plastic material that is designed
to allow a specified flow rate. On occasion, flow control
devices may produce velocity noise that can be reduced by
applying some back pressure from the ball valve located
on the discharge line. Slightly closing the valve will spread
the pressure drop over both devices, lessening the velocity
noise. NOTE: When EWT is below 50°F [10°C], 2 gpm
per ton (2.6 l/m per kW) is required.
Ground-Water Heat Pump Applications