McQuay WDC

20 Product Manual PM WSC/WDC
By constantly monitoring chiller status, MicroTech will automatically take proactive measures to relieve
abnormal conditions or shut the unit down should a fault occur. For example, should a problem occur in the
cooling tower and discharge pressure start to rise, MicroTech will automatically hold the load point and activate
an alarm signal. A further rise in pressure will initiate compressor unloading to maintain the setpoint pressure.
Should the pressure continue to rise, the unit will shut off at the cutout pressure setting.
MicroTech’s memory retains a snapshot of any fault, all the operating conditions at the time of the shutdown,
and the time/date stamp. The MicroTech memory (no batteries required) can retain and display the cause of the
current fault and the last eight fault conditions. This method for retaining the fault, and operating conditions at
the time of the fault, is extremely useful for trouble shooting and maintaining an accurate record of unit
performance and history.
To complete the local interface, MicroTech features a two level password security system to provide protection
against unauthorized use.
MicroTech increases chiller operating economy
Many standard features have been incorporated into MicroTech in order to improve the operating economy of
McQuay centrifugal chillers. In addition to replacing normal relay logic circuits, we’ve enhanced MicroTech’s
energy saving capabilities with the following features:
• Direct control of water pumps. Optically isolated digital output relays provide automatic lead-lag of the
evaporator and condenser pumps, permitting pump operation only when required.
• User-programmable compressor soft loading. Prevents excessive power draw during pull down from high
chilled water temperature conditions.
• Chilled water reset. Can be accomplished directly on the unit by controlling from return water temperature
or from a remote 4-20ma or 1-5 VDC EMS signal.
• Demand limit control. Maximum motor current draw can be set on the panel or can be adjusted from a
remote 4-20ma or 1-5 VDC EMS signal. This feature controls maximum demand charges during high usage
periods.