User Manual

Sequence of Operation
Occupancy Notification
20
Siemens Industry, Inc.
Application Note, App 14900
140-1231
2020-02-11
● An optional occupancy sensor can be used in conjunction with the schedule. The
thermostat will follow the assumptions above, but an input from the occupancy
sensor during a scheduled unoccupied period will put the thermostat into Occupied
mode for the duration of the timer set in Parameter P404 (OCC MRT) Occupancy
Min run Timer (OccMinRun). If the optional occupancy sensor is used, Parameter
P404 can be used to set a minimum run timer for any actions that are activated by
occupancy, such as Economizer Enable, Control to occupied temperature
setpoints, and so on. Note that many occupancy sensors also have onboard proof
timers.
● If the unit does not have an active schedule, or if it has an active schedule set
locally with the effective setpoint being overridden by BMS, the thermostat
assumes that the space is always occupied.
Economizer Enable
The Economizer Enable relay energizes whenever a cooling relay is energized or the
space is occupied. The space is assumed to be occupied when the schedule mode is
set to Comfort. An optional occupancy sensor can also be used for definitive proof of
occupancy.
An output configured for Occupancy Notification can also be used for Economizer
Enabling, for example, while working with Siemens POL 220 Series Economizer
Controller.
Economizer Enable relay (if configured) functions as follows:
● Occupied = Relay energized
● Unoccupied and no call for cooling = Relay not energized
● Unoccupied and call for cooling = Relay energized
● Fresh Air icon is activated
Pre-Purge
To enable the economizer and energize the fan relay prior to scheduled occupancy,
set Parameter P403 (PRE OC PRG) PreOcpyPrg to the number of hours before
scheduled occupancy for pre-purge to begin. This function requires a schedule to be
configured.
Three conditions enable this functionality:
● Unit must have an active onboard scheduler.
● One of the outputs must be set to ECONOMIZER ENABLE.
● PRE-OCCUPANCY PURGE parameter must be greater than 0.
The Economizer Enable and fan relays energize at X number of hours before the first
scheduled occupancy period. (where X is the value entered for PRE-OCCUPANCY
PURGE parameter). The Fresh Air and Fan icons are activated. Other
icons are activated or deactivated per standard operation.
The pre-purge period stops when the first scheduled occupancy period starts. At that
time, everything reverts to normal operation.
Semi-Continuous Fan
If Parameter P405 (CONT FAN) is selected in the set-up menu, the fan relay energizes
any time the space is occupied as determined by the Scheduler, or input from the
occupancy sensor.