R e s i d e n t i a l H & V - 6 0 H z H F C - 4 1 0 A :
R e v : O c t o b e r 5 , 2 0 2 1
16
G e o t h e r m a l H e a t i n g a n d Co o l i n g
Table 2: Antifreeze Percentages by Volume
Ground-Loop Heat Pump Applications
GROUND-WATER HEAT PUMP APPLICATIONS
Open Loop - Ground Water Systems
Typical open loop piping is shown in Figure 13. 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.
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 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.
Pressure Tank and Pump
Use a closed, bladder-type pressure tank to minimize
mineral formation due to air exposure. The pressure 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.
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 pressure tank requirements.
Water Control Valve
Note the placement of the water control valve in figure 13.
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 22).
Type
Minimum Temperature
for Low Temperature Protection
10°F
[-12.2°C]
15°F
[-9.4°C]
20°F
[-6.7°C]
25°F
[-3.9°C]
Methanol
Propylene Glycol
Ethanol*
21%
29%
23%
17%
24%
20%
13%
18%
16%
8%
12%
11%
* Must not be denatured with any petroleum based product
