This block outputs VAV system operating mode. It is implemented according to ASHRAE guideline G36, section 5.4.3, section 5.4.4, section 5.4.5 and section 5.4.6.
Note that, from the user's point of view, schedules can be a set for individual zones, or they can be set for an entire zone group, depending on how the user interface is implemented. From the point of view of the BAS, individual zone schedules are superimposed to create a zone-group schedule, which then drives system behavior.
Each zone group shall have the operating modes shown below.
A zone group is in the occupied mode when
occupancy input uOcc
is true. This input shall be retrieved from
other sequences that specifies occupancy variation and time remaining to the
next occupied period tNexOcc
. A zone group could be in the occupied
mode when any of the following is true:
Warm-up mode shall start based on the zone with the longest calculated warm-up
time maxWarUpTim
requirement, but no earlier than 3 hours
(preWarCooTim
) before the start of the scheduled occupied period,
and shall end at the scheduled occupied start time. Zones where the window switch
indicates that a window is open shall be ignored. Note that for each zone,
the optimal warm-up time shall be obtained from an Optimal Start sequences,
computed in a separate block. The figure below shows the sequence.
Cooldown mode shall start based on the zone with the longest calculated
cooldown time maxCooDowTim
requirement, but no earlier than 3 hours
(preWarCooTim
) before the start of the scheduled occupied period,
and shall end at the scheduled occupied start time. Zones where the window switch
indicates that a window is open shall be ignored. Note that for each zone,
the optimal cooldown time shall be obtained from an Optimal Start sequences,
computed in a separate block.
During unoccupied mode, if any 5 zones (or all zones, if fewer than 5)
in the zone group fall below their unoccupied heating setpoints, or if the average
zone temperature of the zone group falls below the average unoccupied heating setpoint
(uSetBac
becomes true), the zone group shall enter setback mode until
all spaces in the zone group are 1 °C (2 °F) above their
unoccupied setpoints (uEndSetBac
becomes true).
During unoccupied Mode, if any single zone falls below 4 °C (40 °F), the zone group shall enter setback mode until all zones are above 7 °C (45 °F), and a Level 3 alarm shall be set.
During unoccupied mode, if any 5 zones (or all zones, if fewer than 5)
in the zone group rise above their unoccupied cooling setpoints, or if the average
zone temperature of the zone group rises above the average unoccupied cooling setpoint
(uSetUp
becomes true), the zone group shall enter setup mode until
all spaces in the zone group are 1 °C (2 °F) below their
unoccupied setpoints. Zones where the window switch indicates that a window is
open shall be ignored.
Unoccupied mode shall be active if the zone group is not in any other mode.
0
to 0.0
.