Pump Logic: Single Pump; Pump Logic: Lead/Standby (Auto Lead, Pump 1 Lead, Pump 2 Lead) - McQuay MicroTech II Operation Manual

Pump Logic: Single Pump

Configurations 1 and 4 use the CSM's single-pump cooling load pump logic. Single-pump logic simply starts the pump
when the system starts and stops it when the system stops. Note that the pump is identified as Cooling Load Pump #1 on the
Flow screen.
Pump Failure
After the CSM enables the pump, it continually checks the Cooling Load Pump #1 Status to verify that it is operating (true-
switch closed). If the CSM finds that the pump is not operating (Status = false-switch open), it immediately starts a timer
which is set equal to the Pump Status Check Delay Time variable (default is 30 seconds). If the status returns before the
timer expires, the timer resets and stops, and the system continues to operate normally. If the timer expires before the status
returns:
•
The No Chilled Water Flow alarm occurs and the system shuts down.
• The Cooling Load Pump #1 Fail manual reset alarm occurs. The pump will not run again until the operator clears
the CSM alarms.
• The pump 1 output is de-energized.
To set up single-pump logic
1. Set the Pump Control Option variable to "Single Pump."
2. Set the Chilled Water Loop Modulation Control Option variable to one of the following:
• "None," if there is no variable frequency drive or loop bypass valve.
• "Chilled Water Loop Bypass Valve," if there is a loop bypass valve (see "Loop Bypass Valve Control" below).
• "Pump VFD," if there is a variable frequency drive (see "Pump Speed Control" below).
3. Set the Pump Status Check Delay Time variable as required.
Note: To use single-pump cooling load pump control, connect a pump status device with dry contacts to the CSM. If pump
status is not available, a jumper can be installed, but this defeats the CSM's pump-failure alarm control. This alarm control
can fail-safe the system by shutting it down if the pump fails. Using a jumper for pump status is not recommended.

Pump Logic: Lead/Standby (Auto Lead, Pump 1 Lead, Pump 2 Lead)

Configurations 2 and 5 use the CSM's lead/standby pump logic. Lead/standby logic can be applied to a set of two pumps,
which are identified as Cooling Load Pump #1 and Cooling Load Pump #2 on the Flow screen. It allows only one pump to
operate at any one time. If the running pump fails, the other pump starts.
The "lead" pump is the pump that starts when the system starts. It can be either Pump #1 or Pump #2. You can designate
the lead pump manually or let the CSM do it automatically, according to run time. Lead/standby logic provides three
control options: Auto Lead, Pump 1 Lead, and Pump 2 Lead.
Automatic Lead Designation
When the Auto Lead option is selected, the CSM designates the lead pump as required to equalize each pump's run time.
The pump with less run time is lead, and the pump with more run time is standby. You can view each pump's run time on
the Flow screen.
Manual Lead Designation
When the Pump 1 Lead option is selected, the CSM designates Pump #1 as lead. When the Pump 2 Lead option is selected,
the CSM designates Pump #2 as lead. Once you manually designate the lead pump in this way, that pump remains lead until
you change it.
Implementing a new "Lead" pump
If the pump that is designated "lead" changes—whether manually or automatically—while the system is operating, the
CSM does not stop one pump and start the other. A new lead pump is implemented only under certain conditions.
Page 72 OM 780-2