JOHNSON CONTROLS
105
SECTION 6 – COMMISSIONING
FORM 150.72-ICOM6
ISSUE DATE: 12/29/2017
6
JOHNSON CONTROLS
3
FORM 150.72-CL1
ISSUE DATE: 12/29/2017
D. 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 temperature/
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 (-8 °C) at de-
sign conditions.
Record the liquid line pressure and its saturated
temperature, liquid line temperature and subcooling
below: ..........................................................................
SYS 1 SYS 2
Liq Line Press = _______ _______PSIG
Saturated Temp = _______ _______ °F
Liq Line Temp = _______ _______ °F
Subcooling = _______ _______ °F
After the subcooling is veried, 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 to 15 °F (5.56 °C to
8.33 °C) 18” (46 cm) from the heat exchanger.
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 stan-
dard 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), the ad-
justing screw should be turned not more than one turn
at a time, allowing sufcient time (approximately 15 min-
utes) between adjustments for the system and the ther-
mal expansion valve to respond and stabilize.
Assure that superheat is set at a minimum of 10 °F (5.56
°C) with a single compressor running on each circuit.
12. 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
E. LEAK CHECKING
Leak check compressors, ttings, and piping to en-
sure no leaks. ...............................................................
If the unit is functioning satisfactorily during the initial
operating period with no safeties trip and the compres-
sors cycle to control water temperature to the setpoint,
the chiller is considered ready to be placed into operation.
To Next Page
Loading...