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50 TRG-TRC014-EN
notes
period three
System Configurations
In a typical commercial facility, the unoccupied mode occurs at night. The
building does not require ventilation because it is not occupied, and the
temperature in the perimeter spaces must be prevented from getting too cold
(perhaps 60°F [15.6°C]) or too hot (perhaps 85°F [29.4°C]). Temperature control
of the interior spaces is typically ignored because proper control of the
perimeter spaces normally adequately limits the interior space temperatures.
The top floor of the building may require temperature limiting for all spaces.
During the unoccupied mode, the following occurs:
n The main supply fan cycles on whenever any perimeter space or a centrally
located nighttime thermostat demands heating or cooling. If separate
perimeter heat is installed and heat is demanded, it will operate and the
main supply fan remains off.
n The supply fan is controlled to maintain the static-pressure set point of the
system.
n The outdoor air damper is closed.
n All terminal units with demand for central heating or cooling maintain their
respective unoccupied temperature set points. All other terminal units
remain off.
Unoccupied Mode
▲ Main supply fan operates only as needed to
maintain thermostat set points
▲ Main supply fan controlled to maintain the
system static-pressure set point
▲ Outdoor air damper is closed
▲ Terminal units maintain respective
“unoccupied” space thermostat set points
Figure 69