McQuay MicroTech III RAH Operation And Maintenance Manual page 109

Operator's Guide
Sump Pump Control
The pump output is turned on whenever the unit is in the Cooling state and the Sump Pump
Fail condition described below is false. The Sump Pump is turned on before any compressor
or condenser fan is turned on.
A Sump Pump Fail condition exists if the Sump Pump status is open after the Sump Pump
Output has been turned on for more than the Sump Pump Delay time (Default equals 30
seconds). The Sump Pump Fail condition remains for one cooling stage time. The Sump Pump
is turned off and the maximum Cooling Stage is set to zero when the Sump Pump Fail
condition exists. A Sump Pump Fail Problem that disables cooling becomes active if Cooling
has been limited to Stage Zero due to Sump Pump Fail conditions three times between 2:00
AM of one day and 2:00 AM of the next day.
If the unit is equipped with a Dolphin system, the sump pump is run every three days to reduce
scaling. The Pump output is turned on for one hour if all of the following are true:
• Dolphin System= Yes
• Sump Pump has been off for more than 72 hours but less than 120 hours
• The OAT is greater than 35°F
• The Freeze Protection Valve is Closed
Sump Temperature Control
All condenser fans are off when all compressors are off. Whenever any compressor is turned
on, Condenser Fan # 1 (the lead condenser fan) on both circuits is turned by sending a signal
to the VFD via the ModBus network internal to the unit. Condenser fan # 1 for both
compressor circuits are on even if no compressors are operating on one of the circuits.
Condenser Fan # 1 on both circuits are turned off when all compressors are off, and they are
turned off as described in paragraphs that follow when the sump temperature gets low.
The VFD is controlled and monitored by the main controller via ModBus network internal to
the unit. Whenever any condenser fan is on, signals are sent to the VFD to control connected
fans to a calculated setpoint. The speed varies from a minimum value (25% default) to 100%
as the sump temperature varies from the Min Sump Temp to the Max Sump Temp setting.
In addition to the fans controlled by the VFD there are up to three staged condenser fan output
that are controlled based on sump temperature. The condenser fan outputs controlled by these
outputs are mechanically prevented from operating when no compressors on that circuit are
operating. When compressors are operating on both circuits, the number of fans operating on
the two circuits is the same since these output are wired to turn on the same fans on each
circuit.
The number of staged condenser fan outputs operating will increase if the time since the last
change in the number of operating fans exceeds the Evap Condensing Stage Time and the
Sump Temperature exceeds the Max Sump T. The number of fans operating per circuit will
decrease if the time since the last change in the number of operating fans exceeds the Evap
Condensing Stage Time, and the Sump Temperature drops below the Min Sump T.
After the two lead condenser fans are turned off via the VFD, they are turned back on as soon
as the Sump Temperature rises above the Maximum Sump Temperature. This transition from
Stage zero to stage one is the only transition that does not require the Stage Timer to expire.
All of the condenser fans need to be run periodically when evaporative condensing is used to
prevent damage to the motors due to their high humidity environment. As indicated above, the
condensing fans controlled by the VFD always run when evaporative operation is in effect so
no special control of these fans is required. The fan motors controlled directly through the
staged condenser fan outputs are turned on and off based on time on and time off. When a
condenser fan output must be turned on for normal operation, the output that has been off for
the longest period of time is started. When condenser fan must be turned off for normal
operation, the output that has been on for the longest period of time is turned off.
McQuay OM 920-1 109