R e s i d e n t i a l P a c k a g e d U n i t s - 6 0 H z P u r o n
®
R e v. : 4 J a n . , 2 0 1 2
12
Ground-Loop Heat Pump Applications
antifreeze solution is used in most areas to prevent freezing.
All air and debris must be removed from the earth loop piping
before operation. Flush the loop with a high volume of water
at a minimum velocity of 2 fps (0.6 m/s) in all piping. The
steps below must be followed for proper fl ushing.
1. Fill loop with water from a garden hose through the fl ush
cart before using the fl ush cart pump to insure an even fi ll.
2. Once full, the fl ushing process can begin. Do not allow
the water level in the fl ush cart tank to drop below the
pump inlet line to avoid air being pumped back out to
the earth loop.
3. Try to maintain a fl uid level in the tank above the return
tee so that air cannot be continuously mixed back into
the fl uid. Surges of 50 psi (345 kPa) can be used to help
purge air pockets by simply shutting off the return valve
going into the fl ush cart reservoir. This “dead heads” the
pump to 50 psi (345 kPa). To purge, dead head the pump
until maximum pumping pressure is reached. Open the
return valve and a pressure surge will be sent through the
loop to help purge air pockets from the piping system.
4. Notice the drop in fl uid level in the fl ush cart tank when
the return valve is shut off. If air is adequately purged from
the system, the level will drop only 1-2 inches (2.5 - 5 cm)
in a 10” (25 cm) diameter PVC fl ush tank (about a half
gallon [2.3 liters]), since liquids are incompressible. If the
level drops more than this, fl ushing should continue since
air is still being compressed in the loop fl uid. Perform the
“dead head” procedure a number of times.
Note: This
fl uid level drop is your only indication of air in the loop.
5. Consult Whole House Dehumidifi cation AOM
for fl ushing instructions for units equipped with
Whole House Dehumidifi cation Whole House
Dehumidifi cation option.
Antifreeze may be added before, during or after the fl ushing
procedure. However, depending upon which time is chosen,
antifreeze could be wasted when emptying the fl ush cart
tank. See antifreeze section for more details.
Loop static pressure will fl uctuate with the seasons.
Pressures will be higher in the winter months than during
the cooling season. This fl uctuation is normal and should
be considered when charging the system initially. Run the
unit in either heating or cooling for a number of minutes to
condition the loop to a homogenous temperature. This is
a good time for tool cleanup, piping insulation, etc. Then,
perform fi nal fl ush and pressurize the loop to a static
pressure of 50-75 psi [345-517 kPa] (winter) or 35-40 psi
[241-276 kPa] (summer). After pressurization, be sure to
loosen the plug at the end of the Grundfos loop pump
motor(s) to allow trapped air to be discharged and to insure
the motor housing has been fl ooded. This is not required
for Taco circulators. Insure that the Flow Controller provides
adequate fl ow through the unit by checking pressure drop
across the heat exchanger and compare to the pressure
drop tables at the back of the manual.
Antifreeze
In areas where minimum entering loop temperatures drop
below 40°F [5°C] or where piping will be routed through
areas subject to freezing, antifreeze is required. Alcohols
and glycols are commonly used as antifreeze; however your
local sales manager should be consulted for the antifreeze
best suited to your area. Low temperature protection should
be maintained to 15°F [9°C] below the lowest expected
entering loop temperature. For example, if 30°F [-1°C] is
the minimum expected entering loop temperature, the
leaving loop temperature would be 25 to 22°F [-4 to -6°C]
and low temperature protection should be at 15°F [-10°C].
Calculation is as follows:
30°F - 15°F = 15°F [-1°C - 9°C = -10°C].
All alcohols should be premixed and pumped from a
reservoir outside of the building when possible or introduced
under the water level to prevent fumes. Calculate the
total volume of fl uid in the piping system. Then use the
percentage by volume shown in Table 2 for the amount
of antifreeze needed. Antifreeze concentration should be
checked from a well mixed sample using a hydrometer to
measure specifi c gravity.
Table 1: Approximate Fluid Volume (gal.) per 100' of Pipe
Fluid Volume (gal [liters] per 100’ [30 meters) Pipe)
Pipe
Size
Volume (gal) [liters]
Copper
1”
4.1 [15.3]
1.25”
6.4 [23.8]
2.5”
9.2 [34.3]
Rubber Hose
1”
3.9 [14.6]
Polyethylene
3/4” IPS SDR11
2.8 [10.4]
1” iPS SDR11
4.5 [16.7]
1.25” IPS SDR11
8.0 [29.8]
1.5” IPS SDR11
10.9 [40.7]
2” IPS SDR11
18.0 [67.0]
1.25” IPS SCH40
8.3 [30.9]
1.5” IPS SCH40
10.9 [40.7]
2” IPS SCH40
17.0 [63.4]
Unit Heat Exchanger
Typical
1.0 [3.8]
Flush Cart Tank
10” Dia x 3ft tall
[254mm x 91.4cm tall]
10 [37.9]
Low Water Temperature Cutout Setting
- CXM Control
When antifreeze is selected, the FP1 jumper (JW3) should
be clipped to select the low temperature (antifreeze 10°F
[-12.2°C]) set point and avoid nuisance faults (see “Low
Water Temperature Cutout Selection” in this manual). Note:
Low water temperature operation requires extended range
equipment.
