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R e s i d e n t i a l S p l i t

R e v. : 1 3 M a r c h , 2 0 1 5

Ground-Water Heat Pump Applications -
“Indoor” Compressor Section Only

Open Loop - Ground Water Systems

Typical open loop piping is shown in Figure 6. Shut o

ﬀ

valves

should be included for ease of servicing. Boiler drains or other
valves should be “tee’d” into the lines to allow acid

ushing

of the heat exchanger. Shut o

ﬀ

valves should be positioned

to allow

ow through the coax via the boiler drains without

allowing

ow into the piping system. P/T plugs should be

used so that pressure drop and temperature can be measured.
Supply and return water piping should be limited to copper,
HPDE, or other acceptable high temperature material. Note
that PVC or CPVC material is not recommended as they are
not compatible with the polyolester oil used in HFC-410A
products.

Water quantity should be plentiful and of good quality.
Consult Table 4 for water quality guidelines. The unit can
be ordered with either a copper or cupro-nickel water
heat exchanger. Consult Table 4 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
quali

ed 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

ushing. In some cases, the

desuperheater option should not be recommended due to
hard water conditions and additional maintenance required.

Water Quality Standards

Table 4 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 4.

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

eld, 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

ow 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
6. 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 o

ﬀ

-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 23). Note the special
wiring diagrams for slow closing valves (Figures 24 & 25).

Flow Regulation

Flow regulation can be accomplished by two methods. One
method of

ow 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

ow rate from Table 12. Adjust the valve until the

desired

ow of 1.5 to 2 gpm per ton [2.0 to 2.6 l/m per kW]

is achieved. A second method of

ow control requires a

control device mounted on the outlet of the water control
valve. The device is typically a brass

tting with an ori

ce of

rubber or plastic material that is designed to allow a speci

ow rate. On occasion,

ow 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.

CAUTION!

To avoid equipment damage, DO NOT allow

system water pressure to exceed 100 psi. when using the
RPVE Outdoor Compressor Section. The expansion tank
in the RPVE has a maximum working water pressure of
100 psi. Any pressure in excess of 100 psi may damage
the expansion tank.