Open Loop - Ground Water Systems - Heat Controller HSS Series Installation, Operation & Maintenance Instructions Manual

H E AT C O N T R O L L E R , I N C . W AT E R - S O U R C E H E AT P U M P S
R e s i d e n t i a l S p l i t - 6 0 H z R 2 2 & R 4 1 0 A
R e v. : 5 J u n e , 2 0 0 8
Ground-Water Heat Pump Applications -
"Indoor" Compressor Section Only

Open Loop - Ground Water Systems

("Indoor" Compressor Section Only)
The "outdoor" version of the compressor section may not
be used with open loop systems due to potential freezing of
water piping. Typical open loop piping is shown in Figure 9.
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
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H e a t C o n t r o l l e r, I n c . W a t e r - S o u r c e H e a t i n g a n d C o o l i n g S y s t e m s
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.
The pump should be sized to handle the home's domestic
water load (typically 5-9 gpm [23-41 l/m]) plus the flow rate
required for the heat pump. Pump sizing and expansion
tank must be chosen as complimentary items. For example,
an expansion tank that is too small can causing premature
pump failure due to short cycling. Variable speed pumping
applications should be considered for the inherent energy
savings and smaller expansion tank requirements.
Water Control Valve
Note the placement of the water control valve in figure 9.
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 24). Note the special wiring
diagrams for slow closing valves (Figures 25 & 26).
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 11a through 11b. 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], a
minimum of 2 gpm per ton (2.6 l/m per kW) is required.