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Installation, Operation & Maintenance HTV/HTD/HTH SERIES Heat Controller, Inc.
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 fl ushing of the
heat exchanger. Shut off valves should be positioned to allow fl ow
through the coax via the boiler drains without allowing fl ow 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 qualifi 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 fl ushing. 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 fi 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 fl 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 pressure
tank requirements.
Water Control Valve
Note the placement of the water control valve in fi gure 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). Note the special wiring
diagrams for slow closing valves (Figures 23 & 24).
Flow Regulation
Flow regulation can be accomplished by two methods. One method
of fl 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 fl ow rate from
tables 9a through 9c. Since the pressure is constantly varying, two
pressure gauges may be needed. Adjust the valve until the desired
fl ow of 1.5 to 2 gpm per ton [2.0 to 2.6 l/m per kW] is achieved.
A second method of fl ow control requires a fl ow control device
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