York YLAA0180 - D. CHECKING SUPERHEAT AND SUBCOOLING; E. LEAK CHECKING

JOHNSON CONTROLS
104
FORM 150.72-ICOM7
ISSUE DATE: 10/22/2020
SECTION 6 – COMMISSIONING
JOHNSON CONTROLS
3
FORM 150.72-CL1 (120)
ISSUE DATE: 03/06/2020
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 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
Liq Line Press = _______ _______psig
Saturated Temp = _______ _______ °F
Liq Line Temp = _______ _______ °F
Subcooling = _______ _______ °F
Afterthesubcoolingisveried,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 tempera-
ture, 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 in. (46 cm) from the heat ex-
changer.
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di󰀨erence
between the actual temperature of the returned re-
frigerant gas in the suction line entering the compres-
sor and the temperature corresponding to the suction
pressure as shown in a standard pressure/tempera-
ture 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
adjusting screw should be turned not more than one
turn at a time, allowing su󰀩cient 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,
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ensure
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.