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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%

12%

11%

* Must not be denatured with any petroleum based product