Engineering Design Guide HBH SERIES Heat Controller, Inc.
7
For operation in the shaded area when water is used in lieu of
an antifreeze solution, the LWT (Leaving Water Temperature)
must be calculated. Flow must be maintained to a level such
that the LWT is maintained above 42°F [5.6°C] when the
JW3 jumper is not clipped (see example below). Otherwise,
appropriate levels of a proper antifreeze solution should be
used in systems with leaving water temperatures of 42ºF [5.6°C]
or below and the JW3 jumper should be clipped. This is due
to the potential of the refrigerant temperature being as low as
32°F [0°C] with 40°F [4.4°C] LWT, which may lead to a nuisance
cutout due to the activation of the Low Temperature Protection.
JW3 should never be clipped for standard range equipment or
systems without antifreeze.
Example:
At 50°F EWT (Entering Water Temperature) and 1.5 gpm/ton, a
8 ton unit has a HE of 72,200 Btuh.
To calculate LWT, rearrange the formula for HE as follows:
HE = TD x GPM x 500, where HE = Heat of Extraction (Btuh);
TD = temperature difference (EWT - LWT) and GPM = U.S.
Gallons per Minute.
TD = HE / (GPM x 500)
TD = 72,200 / (12 x 500)
TD = 12°F
LWT = EWT - TD
LWT = 50 - 12 = 38°F - antifreeze must be used
In this example, a higher fl ow rate will be required for EWTs at or below 50°F without antifreeze.
WATER/BRINE
EWT
°F
FLOW
gpm
PD
psi
PD
ft.
50
12.0 1.7 4.0
18.0 4.5 10.3
24.0 7.9 18.2
HBH096
Heating - EAT 70°F
HC kW HE LAT COP
96.7 7.17 72.2 95.9 4.0
101.9 7.27 77.1 97.4 4.1
104.7 7.32 79.8 98.2 4.2
Performance Data
Selection Notes
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