Supply air temperature setpoint determination - Johnson Controls - LIT-12011950 - Building automation software - Smart Equipment Controller - 5.0

Smart Equipment Controls Sequence of Operation Technical Bulletin

Brand
Johnson Controls
Product name
Smart Equipment Controller
Document type
Technical Bulletin
Document number
LIT-12011950
Version
5.0
Revision date
2024-06-06
Product status
Active
Language
English

If the operational space temperature rises + 2°F or more above the VAV cooling supply air temperature reset setpoint, the VAV cooling supply air temp lower setpoint is used for the operational VAV cooling setpoint.

If the operational space temperature falls below the supply air temperature reset setpoint the supply air temperature upper setpoint is used for the operational VAV cooling setpoint.

If the temperature/humidity control enable is turned on, the temperature/humidity control function also affects the supply air temperature setpoint. The control lowers the current operational VAV cooling setpoint in one degree increments when the return humidity increases above the temperature/humidity setpoint.

For example, with an operational VAV cooling setpoint of 55°F a temperature/humidity setpoint of 50% and the temperature/humidity value per 1°F offset at 5%, the following sequences can occur:

  • If the return humidity rises to 55%, the operational VAV cooling setpoint is lowered to 54°F. If the return humidity decreases below 55%, the operational VAV cooling setpoint returns to 55°F.
  • If the return humidity rises to 60%, the operational VAV cooling setpoint is lowered to 53°F. If the return humidity decreases below 60%, the operational VAV cooling setpoint returns to 54°F.

Operation

Operation without a thermostat input

For this sequence the thermostat only control enable (Tstat-Only) must be No.

The supply air temperature is controlled to the operational VAV cooling setpoint. A stage percent command for cooling determines how many stages of cooling are running. The stage percent command increases or decreases based on relationship of the operational VAV cooling setpoint and supply air temperature, see Table 1 for additional information.

The rate of change is determined by the deviation from setpoint and length of time away from setpoint. View the staged cooling command (StgClgCmd) on the UCB local display.

If the SAT is above the setpoint by more than 1.8°F, the staged percent command for cooling increases and stages compressors ON based on staging switch points.

If the SAT is below the setpoint by more than 1.8°F, the staged percent command for cooling decreases and stages compressors OFF based on staging switch points.

Operation with thermostat input

For this sequence the thermostat only control enable (Tstat-Only) must be Yes.

Y1, Y2, Y3, and Y4 provide independent compressor control. See Constant volume sequences for additional operational information.