Application

Room Segment Functions
Device Control Functions HVAC
62
Siemens Industry, Inc.
Application Note
A6V11692042
Smart Infrastructure – Building Products
2019-04-01
If supply air temperature sensor (TSu) fails, the heating coil request (HclHReq) will
modulate the heating coil valve position (HclVlvPos).
NOTE:
Both the room control function for heating and room segment HVAC device MUST
support supply air temperature cascade control.
Basic function: Accept request signal from associated room supply air
temperature cascade control PID controller and map it to appropriate control
setpoint; Compare setpoint to present value of supply air temperature sensor; Pass
result through a device mode logic switch prior to outputting as a command to the
object that controls the device.
Hot water valve modulation: In response to heating request from the room, the
heating valve is modulated to control the room temperature at setpoint. It can also
be 2-positioned in response to external trigger(s) for special modes such as
warmup or cool down, or safety conditions.
Interlocks
Interlocks are (typically) binary signals that ensure equipment protection.
Additional signals help coordinate the interaction sequences between HVAC
devices.
A signal's direction In / Out (and function, to some degree) depend on the HVAC
device. For example, an airflow status (AirFlSta) interlock signal can be output from
a supply damper or a fan, and sent as input to a coil or an OA damper. In the table
that follows, descriptions of a signal's functionality reflect its usage by the electric
heating coil, two binary output.
NOTE:
Signals in table are internal signals, not BACnet objects. For this reason they are
not visible in the tool, but the parameters associated with them are. See
Comments column for hints on parameters that affect interlock functionality.
Signal
Type
Description
Comment
AirFlSta
Boolean
Air flow status → Interlock signal, from a fan or a supply
damper, that keeps the coil locked unless that same fan or
supply damper provides airflow.
No related parameters in
electric coils. AirFlSta is hard-
coded.
AirFlHReq
Boolean
Air flow heating request → Initiates airflow (fan turns on or
VAV supply damper provides airflow) to satisfy airflow
support request for heating. Signal is sent to fan or VAV
supply damper depending on application.
See Configuration section for
parameters named
"...AirFlHReq".
AirFlHldH
Boolean
Air flow hold for heating → Interlock signal to fan or supply
damper requesting equipment protection airflow support for
a period of time, such as when the electric heating coil has
just turned off.
See Configuration section for
parameters named
"...AirFlHldH".