Applications Guide Tracer Graphical Programming - Trane

®
Chapter 8 Constant-volume AHU with warm-up, pre-cool, and communications
Writing the communications program
The only new program in this chapter is concerned solely with communications.
The sequence of operation requires that the following items be
communicated to the air handler:
• Occupancy
• Space temperature setpoint
• Outdoor air temperature
• Space relative humidity
• Economizer enable
If communication with the BAS is lost, the air handler should use its predetermined
default setpoints and operate in the occupied mode. The following
information is communicated to the air handler in the programs
you modified so far in this chapter.
• The occupancy mode, whether it is communicated or based on the
local schedule, is accounted for by using the Occupancy block in both
the mode and setpoints and the fan control programs. The outdoor air
temperature and economizer enable are received in the mixed air control
program.
• The space relative humidity is communicated as part of the SCC profile
using the nviSpaceRH network variable input in the discharge air
control program.
• The space temperature setpoint is communicated as part of the SCC
profile using the nviSetpoint network variable input in the mode and
setpoints program.
Send some information building automation system (BAS). The air handler
must communicate the following items to the building automation
system:
• Space temperature
• Discharge air temperature
• Mixed air temperature
• Effective setpoint
• Effective occupancy
• Supply fan status
• Cooling valve status
• Heating valve status
• Outdoor air damper status
• Alarm status
• Application mode
Theseitemsarecommunicatedsothatthebuildingoperatorcanviewthe
status of the air-handling unit. Because communications to the building
automation system are not critical to air-handler operation, this program
executes once per minute. Create a new program and set its properties as
shown in Figure 178 on page 219.
218 CNT-APG001-EN