Quantech QTC3040T, Installation Operation & Maintenance

Page: 109 / 190

109
QUANTECH
FORM QTC3-NM1
ISSUE DATE 08/03/2022
SECTION 6 – COMMISSIONING
6
G. 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 temperature is converted from a
temperature/pressure chart).
Example:
Liquid line pressure = 101°F
325 psig converted to temp.
minus liquid line temp. - 83°F
Subcooling = 18°F
The subcooling should be adjusted to 18 °F (-8 °C) at
design conditions.
1. Record the liquid line pressure and its saturated
temperature, liquid line temperature, and sub-
cooling below: .......................................................
SYS 1 SYS 2
Liquid line pressure = _______ _______ psig
Saturated temperature = _______ _______ °F
Liquid line temperature = _______ _______ °F
Subcooling = _______ _______ °F
After the subcooling is verified, check the suction
superheat. Check the superheat 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. The correct
superheat setting for a system is 10°F to 15°F (-12°C
to -9°C) 18 in. (46 cm) from the heat exchanger.
Set the superheat for no less than 10°F (-12°C)
with only a single compressor running on a
circuit. The superheat is calculated as the difference
between the actual temperature of the returned refrig-
erant gas in the suction line entering the compressor
and the temperature corresponding to the suction
pressure as shown in a standard pressure/tempera-
ture chart.
Example:
Suction temperature = 46°F
minus suction pressure
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. Allow 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
(-12.2°C) with a single compressor running on each
circuit.
2. Record the suction temperature, suction pressure,
saturation temperature, and superheat of each
system below: ...........................................................
SYS 1 SYS 2
Suction Temp = _______ _______ °F
Suction Pressure = _______ _______ psig
Saturation Temp = _______ _______ °F
Superheat = _______ _______ °F
H. LEAK CHECKING
Leak check compressors, fittings, and piping to en -
sure no leaks ...................................................................
If the unit is functioning satisfactorily during the initial
operating period with no safety trip and the compres-
sors cycle to control water temperature to the setpoint,
the chiller is considered ready to be placed into opera-
tion.