Application

Sequence of Operation
Hot Water Reheat
11
Siemens Industry, Inc.
Application Note, App 6663
140-1109
2014-10-27
FLOW is the input value for the flow loop. It is calculated as a percentage based on
where AIR VOLUME is between 0 cfm (LPS) and OCC FLOW. In the following text,
this percentage is referred to as % flow.
 If AIR VOLUME equals 0 cfm (LPS), then FLOW is 0% flow.
 If AIR VOLUME equals OCC FLOW, then FLOW is 100% flow.
The FLOW STPT percentage that corresponds to UNOCC FLOW is calculated as:
(UNOCC FLOW ÷ OCC FLOW) × 100% flow.
Example
If UNOCC FLOW = 250 cfm, and if OCC FLOW = 1000 cfm
then, in unoccupied mode the FLOW STPT
= (250 cfm ÷ 1000 cfm) × 100% flow
= 0.25 × 100% flow
= 25% flow
Since 25% of 1000 cfm equals 250 cfm, the flow setpoint in unoccupied mode will be
25%.
UNOCC FLOW can be set less than or equal to, but not greater than OCC FLOW.
Temperature Loop – The temperature loop will modulate HTG LOOPOUT and control
the heating elements in order to maintain the room temperature in both heating and
cooling modes.
Hot Water Reheat
The temperature loop modulates the heating valve in order to maintain the room
temperature setpoint. The reheat valve will be modulated whenever necessary to
maintain the room temperature regardless of the status of HEAT.COOL.
Calibration
Calibration of the controller’s internal air velocity sensor(s) is periodically required to
maintain accurate air velocity readings. CAL SETUP is set with the desired calibration
option during controller startup.
Depending on the value of CAL SETUP, calibration may be set to take place
automatically or manually. If CAL AIR = YES, calibration is in progress.
CAUTION
On long board controllers, the Autozero Module is connected to DO 8.
NOTE:
The first time after startup or initialization, the controller will calibrate the dampers as
if not using Autozero Modules, although the Autozero Modules will be activated. All
subsequent calibrations will use the Autozero Modules only.
At the end of a calibration sequence, CAL AIR automatically returns to NO. A status of
NO indicates that the controller is not in a calibration sequence.
The Autozero Module is enabled when it is wired to DO 8 and CAL MODULE is set to
YES.