This module generates the appropriate temperature control state for a Unit Ventilator ASHRAE Cycle 1 zone control application. This module accepts the temperature and setpoint inputs as well as the heating, cooling, and damper control statuses. The module outputs the current state as calculated by the ZN-T Sequencing Finite State Machine. For information on how the FSM determines the state, see FSM (Occupied Zone Sequencing [UV Cycle 1] v51).
ASHRAE Cycle 1 supplies 100% outside air at all times, except during the warmup state. As the zone temperature rises into the range of the heating setpoint, the outside air damper is fully opened. The heating valve is modulated in response to the zone temperature to maintain setpoint. Low discharge air temperature can override zone heating control to maintain a minimum discharge air temperature into the space. Low limit control logic can also override the damper position if opening the heating valve is unable to maintain either the zone or discharge setpoints.
This module also provides a quick transition from heating to cooling mode during major changes to space load conditions or setpoints (for example, a large group of people enter a space, or a schedule changes from unoccupied to occupied mode).