Applications Guide Tracer Graphical Programming - Trane

®
Chapter 6 VAV AHU example
charge air. Use the effective heating and cooling setpoints to
determine heat or cool mode.
To calculate the effective setpoints:
1. Calculate the average of the cooling and heating setpoints.
2. Subtract the average from the cooling setpoint to determine the offset.
3. Add the calculated offset to the space temperature setpoint to determine
the effective cooling setpoint.
4. Subtract the calculated offset from the space temperature setpoint to
determine the effective heating setpoint.
These are the basic steps in calculating the effective setpoints. See the following
sections for more details and instructions.
Calculating the offset values
Some familiarity with how Comm5 devices determine effective setpoints
may be helpful here. Use the following six default setpoints to determine
offset values:
• Unoccupied cooling
• Occupied standby cooling
• Occupied cooling
• Occupied heating
• Occupied standby heating
• Unoccupied heating
These default setpoints are included in the DAC profile as a network configuration
input, nciSetpoints. Determine the offset values using the following
relationships.
For occupied mode,
( CSP
Offset Occ CSP Occ + HSP Occ )
= Occ – ------------------------------------------------
2
where,
CSP Occ = Occupied cooling default setpoint
HSP Occ = Occupied heating default setpoint
And for occupied standby mode,
( CSP
Offset OccStby CSP OccStby + HSP OccStby )
= OccStby – -----------------------------------------------------------------
2
where,
CSP OccStby = Occupied standby cooling default setpoint
HSP OccStby = Occupied standby heating default setpoint
In unoccupied mode, no offset calculation is required. Instead, set the
effective cooling and heating setpoints to the default unoccupied cooling
and heating setpoints, respectively.
What does this look like in graphical programming? Use the module in
Figure 125 on page 137 to complete the first part of the program that cal-
136 CNT-APG001-EN