Rapid Restart; Low Ambient Lockout - McQuay MicroTech II Operation Manual

Automatic
To allow other methods to schedule the CSM, this variable must be commanded to Automatic. After the Automatic
command is issued, this variable will read Occupied or Unoccupied @ various priority (see Scheduling on page 80 for each
scheduling method's priority). This means that the CSM's occupancy is now determined according to its internal
scheduling, timed override, external time clock, network scheduling, or optimal start features.
Manual Occupied (ON)
A Manual Occupied command places the CSM into the On: Manual state. After the Manual Occupied command is issued,
this variable reads Occupied @ 8, where priority "8" indicates a manual input from the user interface. When the CSM is in
the On: Manual state, it acts as though it were in the Automatic mode with a permanently occupied schedule. This means
that the CSM enables and disables chillers according to its low ambient lockout and sequencing control features and also
controls auxiliary equipment such as cooling load pumps and cooling tower fans.

Rapid Restart

The rapid restart feature allows you to specify how the CSM will perform after a temporary loss of power.
Power-Loss Period Is Shorter than Rapid Restart Time
If the power-loss period is less than the Rapid Restart Time setting, the CSM returns to normal operation without changing
the current chiller stage. Any chillers that are enabled when the CSM comes back on-line continue to be enabled.
Power-Loss Period Is Longer than Rapid Restart Time
If the power-loss period is greater than the Rapid Restart Time setting, the CSM acts as though it has just entered the
Occupied mode when its power is restored:
• Any operational chillers are DISABLED by the CSM when communication is re-established.
• The CSM's chiller stage-up sequencing starts from the beginning.
If the Rapid Restart Time is set to 00:00:00 (zero seconds), the function is disabled which means it reacts as described for
"Power-Loss Period Is Longer than Rapid Restart Time".
Note: The CSM has a battery backup that keeps the controller functioning normally for a time after power is lost while a
software backup takes place. Until the backup is completed, the CSM continues to operate the chiller system normally on
battery power. The Rapid Restart feature does not function unless the backup has been completed and the CSM shuts
down. The CSM will not detect power failures of less than two seconds. Power failures of over two seconds are
detected by the CSM and result in the CSM performing a power-down sequence and then a rapid restart when power
returns.
If the CSM loses power and shuts down, but the chillers remain on, the chillers operate on the last commands received from
the CSM unless the chiller's Comm Loss configuration variables have been set. Configuration variables allow the operator
to define the Chiller's operating state (Chiller Enable, Cooling Setpoint) if communication is lost. See "Setting up the
CSM's Chiller Data" for information on setting the Comm Loss configuration variables. For more on what happens when
the CSM loses communications with its chillers, see the "Alarm Monitoring and Control" section of this manual.

Low Ambient Lockout

The CSM's low ambient lockout feature can disable the entire chiller system whenever the outdoor air temperature is less
than the Low Ambient Lockout Setpoint. If this occurs, the operating state changes to Off: Ambient. As a result, the CSM
disables all of its associated chillers and shuts down all auxiliary system equipment. This occurs regardless of the CSM
Control Mode setting.
When the outdoor air temperature rises to equal the Low Ambient Lockout Setpoint plus its differential, which is fixed at
2°F (1.1°C), the CSM enables normal chiller system operation again.
For the low ambient lockout feature to function, the Outdoor Air Temperature Source variable (I/O Config screen) must be
set to provide a valid OAT input and this input must not be in an alarm condition.
Note: If communications are lost with a BAS that is supplying the outdoor air temperature to the CSM, it retains and uses
the last temperature it received until communications are restored.
OM 780-2 Page 33