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Model SCM Air to Water Heat Pump — Installation, Operation & Maintenance Manual
Section 7: Glycol/Water System
Figure 12 SCM Glycol Concentrations (10% Minimum, 50% Maximum)
Glycol/Water System Design
Each SCM Heat Pump has a recommended ow that should be
maintained during all times of operation. For the SCM-036, the
recommended ow is 10 GPM, at which the head loss through the
heat exchanger is 15.8 ft. WC, 6.8 PSI or 47 kPa. For the SCM-
060, the recommended ow is 12 GPM, at which the head loss
is 24.2 ft. WC, 10.4 PSI or 72 kPa. These head loss values are
based upon pure water, see Figure 12 for multipliers to correct for
various concentrations of anti-freeze solution.
Note: these are the recommended ow values. Should the ow
drop signicantly below this value, the heat pump will shut down
and display the code FL on the display. This is not an indication
of a fault in the heat pump, but rather points to insufcient pump
or plumbing capacity, or air trapped within the system.
System Volume and Expansion Volume
To ensure smooth temperature control and minimize cycling of
refrigeration system, all installations must have total circulating
volumes equal to or greater than 7-1/2 gallons per nominal ton
of the unit performance (The greater of either heating or cooling
produced). In other words, in the case of a four ton heat pump the
minimum total system volume is 4x7-1/2=30 gallons. Multiple heat
pump installations that are operating in a staged conguration follow
the same rule, so that only a single heat pump tonnage needs to be
considered. Additionally, the system requires an expansion volume
(air) to compensate for the change in volume of the glycol mixture
as it heats and cools, see Figure 12 for expansion volume.
Ethylene Glycol % 10 20 30 40 50
Min. Ambient Temp for Operation 23°F/-5°C 14°F/-10°C 2°F/-17°C -13°F/-25°C -36°F/-38°C
SpacePak Capacity Multiplier 0.98 0.96 0.93 0.91 0.89
Pressure Drop Multiplier (Cooling) 1.06 1.12 1.16 1.25 1.36
Pressure Drop Multiplier (Heating) 1.06 1.12 1.16 1.22 1.28
Minimum Expansion Volume / System Volume
Heating and Cooling (Gallons) 1 gallon expansion per 15 gallons system volume
Heating only, HP only (Gallons) 1 gallon expansion per 20 gallons system volume
Heating Only, with Boiler (Gallons) 1 gallon expansion per 15 gallons system volume
Propylene Glycol % 10 20 30 40 50
Min. Ambient Temp for Operation 26°F/-3°C 18°F/-8°C 8°F/-13°C -7°F/-22°C -29°F/-34°C
SpacePak Capacity Multiplier 0.99 0.98 0.96 0.93 0.88
Pressure Drop Multiplier (Cooling) 1.10 1.20 1.34 1.5 1.65
Pressure Drop Multiplier (Heating) 1.10 1.20 1.34 1.46 1.5
Minimum Expansion Volume / System Volume
Heating and Cooling 1 gallon expansion per 15 gallons system volume
Heating only, HP only 1 gallon expansion per 20 gallons system volume
Heating only, with Boiler 1 gallon expansion per 15 gallons system volume
A typical multiple heat pump installation may actually have a
volume far greater than the minimum required, and it is this entire
volume that must be considered when sizing the expansion tank.
Note that the nominal expansion tank volume is not the same as
the expansion volume. If the actual air volume is not published,
consider it to be no more than half the nominal volume.
As an example, a four ton nominal heat pump, used for both
heating and cooling, requires a minimum of thirty gallons of
circulated system volume. A 40 gallon buffer tank is selected for
best operation. When the system installation is complete, the
total liquid volume of plumbing, air handlers, and heat pump is
45 gallons. (Note the expansion tank, no matter how large, is
not considered circulated volume) This requires an acceptance
volume of 3 gallons. If the acceptance volume is not specied,
assume it is 50% of the total volume. Therefore, this system
would require an expansion tank of 3 gallons acceptance
volume, or six gallons nominal full volume.
Air Separator
Locate at least one high efciency air separator as shown in the
piping to remove any air from the system.
Glycol / Water Mixture
The water system must contain a mixture of
inhibited glycol and water with thermal protection
sufcient for the coldest expected temperature for
the installation. The inhibitor level can degrade over
time, and may need to be adjusted periodically.
The inhibitor is essential to prevent the glycol from
accelerating corrosion of metal components in the
system. The glycol and inhibitor levels must be
checked regularly (no less than once annually).
The minimum allowable concentration of glycol is
10% by volume in all installations.
Automotive glycol is not suitable for use in the LAHP
system. Over time it may leave deposits which will
degrade the performance and damage pumps or
other devices in the system. Use only ethylene
glycol or propylene glycol mixtures specically
labeled for boiler or HVAC use.
Figure 13
Piping Pressure Losses*
Pressure Drop, Ft water/100Ft
Flow rate GPM 1" 1-1/4" 1-1/2" 2"
Pex Pipe
10 13.4 5.2 2.4 0.6
11 15.9 6.2 2.8 0.7
12 18.5 7.2 3.2 0.9
14 24.4 9.4 4.2 1.2
Copper Pipe (Type L)
10 7.1 2.6 1.1 0.3
11 8.4 3.1 1.3 0.3
12 9.9 3.6 1.5 0.4
14 13.2 4.8 2 0.5
*Remember to check the CV rating of your ttings and valves to make
sure your getting the correct ow through the equipment.
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