Trane Understanding BACnet Thermostats and Tracer SC Integration

Additional Information and Considerations

Rooftop and Heat Pump Units

Programs writing to the devices should have a structure similar to the following:

If Once Schedule = On then		Do Every 5min
MV11 = Occupied		If Schedule = On Then
End If		MV11= Occupied
If Once Schedule = Off	OR	Else
Then		MV11 = Unoccupied
MV11 = Unoccupied		End If
End If		End Do

Retries and Timeouts (Supervisory Controllers Other Than Tracer SC)

Another thing to look for in a BACnet integration is the Device object of the Supervisory Controller (and the Operator’s Workstation). This object contains the 2 following required properties:

•Retry Timeout

The Retry Timeout property specifies the time between re-transmissions if the acknowledgement has not been received. When you are experiencing problems with controllers dropping off-line, increasing this value may help.

•Number of APDU Retries;

The Number of APDU Retries property specifies the number of times unsuccessful transmissions will be repeated. If the receiving controller has not received the transmission successfully after this many attempts, no further attempts will be made.

For example, if one of the thermostats does not reply to a Supervisory Controller (Tracer SC) request, and the Retry Timeout is set to 2000 msec and the Number of APDU Retries is set to 1 (still at the Tracer SC level), then the Tracer SC will send one other request, 2 seconds later. If the MS/ TP device does not reply, it will be considered Off-line by the workstation.

So having a Retry Timeout value of 10000 msec and a Number of APDU Retries property set to 3 at the SC level may prevent device from dropping Off-line. These properties should also be changed at the Workstation level since the workstation will likely issue requests to any MS/TP devices when the graphics are used.

Objects and Parameters

The following items apply to all equipment types.

•Each thermostat is delivered from the factory with the default MAC address set at 254. At this value, the BACnet communication is NOT active and the device will not participate in the token pass either. The local LED status (located on the backside of the board) is one short flash only. To enable the BACnet communication, set the local MAC address configuration property of the thermostat to any valid value from 0 to 127 using the Installer Configuration Parameter menuon the Thermostat. (Refer to the Trane Communicating Thermostats for Heat Pump Control User Guide (BAS-SVU10A-EN), Trane Communicating Thermostats for Rooftop Control User Guide (BAS-SVU11A-EN), or the Trane Communicating Thermostats for Fan Coil Control User Guide (BAS-SVU12A-EN) for details.)

•All configuration objects are available and can be edited locally from the device itself using the local configuration routine. (See the Communicating Thermostat User Guides mentioned previously in this section or in “Related Documents,” p. 6.)

•In its default mode of operation, the device will automatically match its baud rate to the baud rate of the network. Automatic baud rate detection will occur when the MS/TP communication port is initialized (on power up). If the network speed is changed, the device will keep listening at the previously detected speed for 10 minutes before resuming automatic baud rate detection. Re-powering the devices will force immediate auto-detection.

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