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TRG-TRC014-EN 51
period three
System Configurations
notes
The morning warm-up/cool-down mode typically occurs as a transition from
the unoccupied mode to the occupied mode. It establishes the occupied
comfort conditions for the building as rapidly as possible, because they were
allowed to drift from occupied set point during the unoccupied mode, usually
to save energy.
In this mode, the building does not initially require ventilation because it is not
occupied, but it may eventually be provided for a preoccupancy purge (diluting
the contaminants that accumulated during the unoccupied mode).
During the morning warm-up/cool-down mode, the system is controlled as
follows:
n The AHU fan operates continuously to provide primary air to the spaces for
cooling or heating. If separate perimeter heat is installed and heat is
demanded, the perimeter heat source operates and the AHU fan remains off.
n The supply fan is controlled to maintain the static-pressure set point for the
system.
n The outdoor air damper is closed unless ventilation is needed for
preoccupancy purge.
n The terminal units may be fully open, allowing “wild” (uncontrolled) warm-
up or cool-down, or they may modulate to achieve the occupied
temperature set points for a “controlled” warm-up or cool-down.
Morning warm-up or cool-down mode is ended when the perimeter zone
thermostats or a single, representative thermostat reaches its occupied set
point. Then the system switches to the occupied mode.
Morning Warm-up/Cool-down Mode
▲ Main supply fan operates continuously
▲ Main supply fan controlled to maintain the
system static-pressure set point
▲ Outdoor air damper is closed, unless required
for preoccupancy purge
▲ Terminal units are either fully open or
modulated to maintain their respective
“occupied” space thermostat set points
Figure 70