JOHNSON CONTROLS
121
SECTION 6 – COMMISSIONING
FORM 150.72-ICOM6
ISSUE DATE: 08/03/2022
6
A. CHECKING SUPERHEAT AND SUBCOOLING
The subcooling temperature of each system can be calcu-
lated 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 temperature is converted from a tempera-
ture/pressure chart).
Example:
Liquid line pressure =
325 psig converted to temp.
101°F
minus liquid line temp.
- 83°F
Subcooling =
18°F
The subcooling should be adjusted to 18°F (10°C) at
design conditions.
1. Record the liquid line pressure and its saturated
temperature, liquid line temperature and subcooling
below: .......................................................................
SYS 1 SYS 2
Liquid line pressure = _______ _______psig
Saturated temp. = _______ _______ °F
Liquid line temp. = _______ _______ °F
Subcooling = _______ _______ °F
After the subcooling is verifi ed, the suction superheat
must be checked. Check the superheat only after
steady state operation of the chiller has been estab-
lished, the leaving water temperature has been pulled
down to the required leaving water temperature, and
the unit is running in a fully loaded condition. The cor-
rect superheat setting for a system is 10°F to 15°F
(5.56°C to 8.33°C) 18 in. (46 cm) from the heat ex-
changer.
Set the superheat must be set for no less than 10°F
with only a single compressor running on a circuit.
The superheat is calculated as the diff erence 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.
105 psig converted to temp.
- 34°F
Superheat =
12°F
When adjusting the expansion valve (TXV only), turn
the adjusting screw no more than one turn at a time,
allowing suffi cient time, approximately 15 minutes, be-
tween adjustments for the system and the thermal ex-
pansion 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,
saturation temperature, and superheat of each sys-
tem below: ...................................................................
SYS 1
SYS 2
Suction temp. = _______ _______ °F
Suction pressure = _______ _______ psig
Saturation temp. = _______ _______ °F
Superheat = _______ _______ °F
B. LEAK CHECKING
Leak check compressors, fi ttings, and piping to ensure
no leaks. .......................................................................
If the unit is functioning satisfactorily during the initial op-
erating period with no safeties tripped and the compres-
sors cycle to control water temperature to the setpoint,
the chiller is considered ready to be placed into operation.
