Additional Information and Considerations
This chapter explains some special tips and considerations that apply to the Trane Communicating Thermostats. These tips and considerations are grouped in the following categories:
•MS/TP network integration
•Objects and parameters
•Tracer SC network configuration
MS/TP Network Integration
Before doing any BACnet integration, make sure to have Trane PICS (Protocol Implementation Conformance Statement). This PICS document lists all the BACnet Services and Object types supported by a device and can be found on the Trane portal.
The Trane Communicating Thermostats do not support the Change of Value (COV) service. COV reporting allows an object to send out notices when its
Site Graphics
For example, some site graphics might poll every data item linked to the graphic page on a COV basis. If the third party device does not support COV, the graphic interface then relies on a pre- configured polling interval, which is usually in hundredths of milliseconds. Any device containing a monitored object could be subject to network traffic congestion if such a polling interval is used. Trane strongly recommends a polling interval of 5 seconds or more for any graphic interface. This becomes even more critical in area graphics where a single representation might poll many devices. If proper poll rate is not respected, devices may be reported offline by certain front ends by saturating the traffic handling capacity of BACnet MS/TP without COV subscription.
Free Programmed Objects or Loops (Supervisory Controllers Other Than Tracer SC)
As for the application program, you might want to read and write any MS/TP data on an “If Once” basis or a “Do Every” loop basis instead of reading or writing to a third party device’s object directly in the program. Otherwise, any read or write request will occur at the Supervisory Controller’s program scan rate, which might be in hundredths of milliseconds. This can easily bog down a network as single commands can be sent to all ASC devices down the MS/TP trunks every hundredth of a millisecond.
Fan Coils
Programs writing to the devices should have a structure similar to the following:
If Once Schedule = On then |
| Do Every 5min |
MV13 = Occupied |
| If Schedule = On Then |
End If |
| MV13= Occupied |
If Once Schedule = Off | OR | Else |
Then |
| MV13 = Unoccupied |
MV13 = Unoccupied |
| End If |
End If |
| End Do |
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