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McQuay OM 751 15
Description of Operation
Night Purge Mode (State 8)
Night Purge mode is provided as a means to more easily and quickly ventilate a space. Night
purge can be useful in helping to remove odor build up at the end of each day, or after
cleaning, painting, or other odor generating operations occur within the space. Night Purge
mode consists of a single UVC state: Night Purge [8].
Night Purge is a full ventilation with exhaust mode, during which room comfort is likely to be
compromised. Therefore, McQuay strongly recommends using Night Purge only when the
space is unoccupied.
When Night Purge mode becomes active, the UVC stops all normal heating and cooling. Since
any new energy used to treat the incoming air would be wasted in the purge process. In the
Night Purge mode, the space fan is set to high speed, the OA damper is set to 100% open, and
the Exhaust Fan binary output (see “External Binary Outputs” on page 38) is set to ON. If the
UVC is not set to another mode within 1 hour (fixed), the UVC automatically switches to the
Fan Only mode (see “Fan Only Mode (State A)” on page 15).
While in Purge mode, the UVC does not maintain DA temperatures. If the space temperature
drops below the EHS, the UVC is forced into the Emergency Heat mode (see “Emergency
Heat Mode (Super State)” on page 16).
Figure 8: Night purge state diagram
Fan Only Mode (State A)
The Fan Only mode is provided so that the UVC can be forced into a Fan Only operation via a
keypad/display or a network connection. Fan Only mode consists of a single UVC state: Fan
Only [A].
When Fan Only mode becomes active, the UVC stops all normal heating and cooling.
While in Fan Only mode, the UVC does not maintain DA temperatures. If the space
temperature drops below the EHS, the UVC is forced into the Emergency Heat mode (see
“Emergency Heat Mode (Super State)”).
Figure 9: Fan only state diagram
Night Purge
8
UVC Mode
≠
Night purge
UVC Mode
=
Night purge
Transition
point
Fan Only
A
UVC Mode
≠
Fan Only
UVC Mode
=
Fan Only
Transition
point