Applications Guide Tracer Graphical Programming - Trane

®
Chapter 6 VAV AHU example
In this case, the space temperature setpoint originates at the operator
display. Obtain the effective cooling and heating setpoints using the following
relationships.
CSP Effective = STS + Offset
where,
CSP Effective = Effective cooling setpoint
HSP Effective = Effective heating setpoint
STS = Space temperature setpoint
Increasing or decreasing the space temperature setpoint affects the effective
occupied and unoccupied setpoints. However, the default setpoints
remain constant and are unaffected by changes to the space temperature
setpoint. Remember the following about the setpoints calculation:
• For occupied and occupied standby modes, the default setpoints determine
the offset between effective cooling and heating setpoints.
• For unoccupied mode, the default and effective setpoints are the
same.
• Changes to the space temperature setpoint increase or decrease effective
occupied and occupied standby setpoints in a coordinated manner.
Effective setpoint calculation examples
The following tables show an example of effective setpoint calculation. In
this example, the setpoints have been assigned the values in Table 16.
Table 16: Default and adjustable setpoint values
Setpoints
HSP Effective = STS – Offset
Default setpoints
Space temperature setpoint
Unoccupied cooling
Occupied standby cooling
Occupied cooling
Occupied heating
Occupied standby heating
Unoccupied heating
72.0°F
85.0°F
78.0°F
74.0°F
71.0°F
67.0°F
60.0°F
First, calculate the occupied and occupied standby offset values.
( 74.0 + 71.0)
Offset Occ = 74.0 – ------------------------------- = 1.5
2
( 78.0 + 67.0)
Offset OccStby = 78.0 – ------------------------------- = 5.5
2
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