Operating instructions

8
zone. Small Grundfos pumps (230 Vac) should be used as
circulator pumps. These pumps are impedance protected
and do not require additional fusing if powered directly
from the heat pump.
CAUTION – Never operate with hydronic flow rates less
than specified. Low flow rates, or no flow, may cause the
unit to shut down on a pressure lockout or may cause a
freeze rupture of the heat exchanger.
Circulator pumps must be sized to provide the required
flow to a heat pump heat exchanger at its corresponding
system pressure drop calculated from the pressure drop
through the piping, plus the pressure drop of the water
storage tank, and plus the pressure drop through the heat
pump heat exchanger. Table 4 shows the hydronic water-
flow requirements and pressure drop (dP), and Table 3
shows the dP multiplier for various levels of freeze
protection. Use these tables for sizing the circulating pump
between the hydronic side of the heat pump and a storage
tank.
Table 4 – Storage Tank Circulators
Hyd. Loop
Grundfos
Series
Flow
(gpm)
dP
(psig)
Circulator
GW240
40
3.4
*
GW360
54
3.3
*
*Size circulators for specific installations.
Note: See Table 3, Heat Exchanger Pressure Differential (dP)
Correction Factors for Freeze Protection.
Table 4 represents the minimum pump size to supply the
heat pump’s required hydronic side flow to a storage tank at
the pressure drop of the heat pump and 30 feet of ¾” type K
copper tubing (or a combination of approximately 20 feet
with typical elbows and fittings) (2” pipe on 240 and 360
series).
A common problem with circulator pumps is trapped air in
the system. This air accumulates in the suction port of the
circulator causing cavitation in the pump, which leads to
premature pump failure and noisy operation. The air can be
eliminated by completely purging the system or by placing
an air separator in the plumbing lines. The entire system
must be purged of air during initial installation and
pressurized to a 10-25 psig static pressure to avoid air
entering the system. This static pressure may fluctuate
when going from the heating to cooling modes but should
always remain above zero. If a leak in the system causes the
static pressure to drop, the leak must be repaired to assure
proper system operation.
The hydronic side circulator supplying the heat pump
should be controlled to run only when the compressor runs.
If the pump is allowed to circulate cold water through the
system during off cycles, the refrigerant in the heat pump
will migrate to the hydronic side heat exchanger. This can
cause heat pump starting problems (especially when this
refrigerant migrates into the condenser).
C. Circulation Fluid
The fluid circulating through the hydronic side of the
geothermal heat pump system is the transfer medium for the
heating and cooling being supplied to the conditioned
space. Selection of this fluid is very important. Water is the
most readily available fluid but has the drawback of
expansion during freezing which can damage the system.
System operation in the cooling mode, extended power
interruption to a structure, or disabling of an outside zone
(such as a garage floor) provides the opportunity for
freezing the circulating fluid.
CAUTION – the hydronic side of the system must be
freeze protected to reduce the risk of a freeze rupture of the
unit. A propylene glycol based antifreeze (readily available
through HVAC wholesalers) and water solution is
recommended. A non-flammable antifreeze solution is
recommended for use on any hydronic system where heat is
being added to the system for structural heating purposes.
Freeze protection for the hydronic side fluid down to 18
o
F
(20% propylene glycol by volume in water) is
recommended for most indoor applications. Forty percent
propylene glycol in water (-5
o
F freeze protection) is
recommended by radiant tube manufactures for snow melt
applications to protect the tubing from expansion in outdoor
applications. Using over 40% in hydronic side applications
can cause pumping problems due to high viscosity.
The water being added to the system should have 100-PPM
grain hardness or less. If poor water conditions exist on the
site, softened water is recommended, or acceptable water
should be brought in. Bacteria or algae growth in the water
is a possibility at the temperatures produced in the heating
system and can cause buildup on hydronic side heat
exchanger surfaces, reducing the efficiency of the system or
causing the heat pump to run at higher head pressures and
possibly lock out. A gallon of bleach or boiler system
conditioner can reduce the possibility of growth and can
clean up other components in the system.
D. Expansion Tanks
Expansion tanks must be used in the hydronic side of the
water-to-water system to absorb the change in pressure of
the closed system due to the change in temperature when
heat is supplied to the system. Diaphragm-type expansion
tanks should be used. EPDM diaphragm tanks are
compatible with glycol-based antifreeze fluids (butyl rubber
diaphragms will slowly dissolve with glycol-based
antifreezes).
Expansion tanks from 1 to 10 gallons are generally used
with heat pump systems in residential and light commercial
applications. Expansion tanks should be installed in the
system near the suction of the circulator pump to maintain
positive pressure at the circulator pump and reduce the
highest working pressure of the system. A pressure gauge
near the inlet of the expansion tank gives a good indication
of how the system is operating.