FORM 150.66-NM2
ISSUE DATE: 09/25/2020
43
JOHNSON CONTROLS
SECTION 5 - COMMISSIONING
55
CHECKING SUPERHEAT AND SUBCOOLING
The subcooling temperature of each system can be
calculated by recording the temperature of the liquid
line at the outlet of the condenser and subtracting it from
the liquid line saturation temperature at the liquid stop
valve (liquid line saturation temp. is converted from a
temperature/pressure chart).
Example:
liquid line pressure =
328 psig converted to temp. 102°F
minus liquid line temp. - 87°F
Subcooling = 15°F
The subcooling should be adjusted to 15°F at design
conditions.
1.
Record the liquid line pressure and its corre-
sponding temperature, liquid line temperature and
subcooling below:
SYS 1
liq line Press = _______ PSIG
Saturated Temp = _______ °F
liq line Temp = _______ °F
Subcooling = _______ °F
After the subcooling is verified, the suction superheat
should be checked. The superheat should be checked
only after steady state operation of the chiller has been
established, the leaving water temperature has been pulled
down to the required leaving water temperature, and the
unit is running in a fully loaded condition. Correct superheat
setting for a system is 10°F - 15°F (5.56°C - 8.33°C) 18 in.
(46 cm) from the cooler.
Superheat should typically be set for no less than 10°F
with only a single compressor running on a circuit.
The superheat is calculated as the difference between the
actual temperature of the returned refrigerant gas in the
suction line entering the compressor and the temperature
corresponding to the suction pressure as shown in a
standard pressure/temperature chart.
Example:
Suction Temp =
46°F
minus Suction Press
106 psig converted to Temp - 34°F
Superheat = 12°F
When adjusting the expansion valve (TXV only), the
adjusting screw should be turned not more than one
turn at a time, allowing sufficient time (approximately
15 minutes) between adjustments for the system and the
thermal expansion valve to respond and stabilize.
Ensure that superheat is set at a minimum of 10°F (5.56°C)
with a single compressor running on each circuit.
2.
Record the suction temperature, suction pressure,
suction saturation temperature, and superheat of
each system below:
SYS 1
Suction Temp = _______ °F
Suction Pressure = _______ PSIG
Saturation Temp = _______ °F
Superheat = _______ °F
LEAK CHECKING
1.
Leak check compressors, fittings, and piping to
ensure no leaks.
If the unit is functioning satisfactorily during the initial
operating period, no safeties trip and the compressors
cycle to control water temperature to setpoint, the chiller
is ready to be placed into operation.
Summary of Contents for YCAL0012EC
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