– 14 –
Model
LAHP48
Air to Water Heat Pump — Installation, Operation & Maintenance Manual
Section 7: Glycol/Water System
Figure 13
LAHP Glycol Concentrations (30% Minimum, 50% Maximum)
Glycol/Water System Design
Size the Piping and Select the System Pump
Each LAHP48 has a recommended flow of 11 GPM. The pressure
drop at 11 GPM is 8 PSI or 17 ft/head (based on pure water, see
Figure 13 for pressure drop correction for glycol mix), size the
system piping (see Figure 14 for piping pressure losses) and size
pump accordingly. Adjust the pressure drop through piping and
heat pump using the glycol correction multipliers in Figure 13.
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 configuration 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 13 for expansion 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.
Ethylene Glycol %
30
40
50
Min. Ambient Temp for Operation
2°F/-17°C
-13°F/-25°C
-36°F/-38°C
SpacePak Capacity Multiplier
0.93
0.91
0.89
Pressure Drop Multiplier (Cooling)
1.16
1.25
1.36
Pressure Drop Multiplier (Heating)
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 %
30
40
50
Min. Ambient Temp for Operation
8°F/-13°C
-7°F/-22°C
-29°F/-34°C
SpacePak Capacity Multiplier
0.96
0.93
0.88
Pressure Drop Multiplier (Cooling)
1.34
1.5
1.65
Pressure Drop Multiplier (Heating)
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
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 specified,
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 efficiency 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
sufficient 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
30% 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 specifically
labeled for boiler or HVAC use.
Figure 14
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 fittings and valves to make
sure your getting the correct flow through the equipment.
