J&E Hall JEHSD-0400-B3-M-3, Technical Manual

Page: 24 / 44

Issue: 01.08.2020 Page 24
Commissioning
Compressor Operation
The compressor(s) operate in accordance to the suction pressure setpoint which is programmed into the controller.
There is a differential pressure setting both above and below the setpoint. This allows stable operation of the
compressors without constantly switching on & off due to small variations in suction pressure. This range is known as
the Neutral Zone. When the compressor(s) are operating within this zone, there will be no change to capacity status
(i.e. no compressor switched on/off or additional loading/unloading of variable capacity compressor).
Once the suction pressure goes outside the Neutral Zone, then the controller reacts by increasing or decreasing
capacity, depending on whether the pressure is above or below the Neutral Zone. The rate at which the capacity
increases or decreases depends upon the setting of the Minimum and Maximum timers within the controller. This
means that the further away the suction pressure moves away from the Neutral Zone (either above or below), the
quicker the controller will adjust the compressor capacity.
On Digital twin compressor units, the compressor with the capacity control is always the first to start and the last to
stop.
Digital Scroll compressor motors are designed to run only in one direction.
The correct rotation of a three phase
compressor motor depends on the connection of the three incoming phases to the unit. Correct rotation can be
determined by a drop in suction pressure and a rise in discharge pressure when the compressor is energized. Running
the compressor for a short period of time in reverse direction will have no negative impact but prolonged running in
reverse direction may cause premature failure.
To reverse the rotation of a three phase digital scroll compressor,
shut off the incoming power supply to the unit, swap connection of any two of the three incoming phases at the
unit isolator, reapply power to the unit and following compressor restart, recheck operating pressures.
Digital compressor:
At initial start-up, the digital compressor will run at 50% capacity for three minutes followed by 1 minute at 100%
capacity. Following this, the compressor will modulate the capacity according to the system requirement in relation to
the suction pressure set-point.
Vacuum operation:
Do not operate scroll compressors in a vacuum condition, as this will cause the scrolls to overheat very quickly
causing premature failure.
System charge:
Ensure an adequate liquid charge has been introduced to the high side of the system before starting to ensure a
minimum operating pressure on the suction side of 0.5 bar is maintained, otherwise overheating of the scrolls and
subsequent damage may occur.