Winter Mode - Metasys - LIT-12012070 - Field Device - VAV: Variable Air Volume Controller

Air Handling Unit Reset Application Note

Brand
Metasys
Product name
VAV: Variable Air Volume Controller
Document type
Application Note
Document number
LIT-12012070
Revision date
2018-03-01
Language
English

The purpose of the winter mode is to maintain the temperature request setpoint, which allows the VAV reheat to operate efficiently.

In the winter mode, the discharge air pressure setpoint is adjusted to the fixed pressure setpoint (default 1.0 in. W.C.) Only the discharge air temperature setpoint adjusts.

  1. When the supply fan starts, the discharge air temperature setpoint is equal to the fan start temperature setpoint (default 65°F).
  2. After a time interval (default 5 minutes), the logic totalizes all of the temperature requests from the VAV boxes.
  3. If the occupancy status equals Occupied and the warmup/cooldown status does not equal Warmup, the logic continues to the next step. If the occupancy status does not equal Occupied or the warmup/cooldown command equals Warmup, the logic holds the discharge air temperature setpoint at its current value and returns to the previous step.
  4. If the total number of temperature requests is greater than the temperature requests setpoint, the logic decreases the discharge air temperature setpoint by the trim temperature setpoint (default 2.0°F).
  5. If the total number of temperature requests is equal to the temperature requests setpoint, the logic holds the discharge air temperature setpoint at its current value.
  6. If the total number of temperature requests is less than the temperature requests setpoint, the logic increases the discharge temperature setpoint by the respond temperature setpoint (default 4.0°F).
  7. The discharge air temperature setpoint does not adjust higher than the maximum temperature setpoint (defualt 65°F) or lower than the minimum temperature setpoint (default 55°F).
  8. When the supply fan stops, the logic adjusts the discharge air temperature setpoint equal to the fan off temperature setpoint (default 80.0°F).