INDIVIDUAL ROOM CONTROL APPLICATIONS
ENGINEERING MANUAL OF AUTOMATIC CONTROL
415
Zone day/night control requires one zone night thermostat
for two or mor e unit v entilator s that mak e up a z one. Dur ing
night oper ation, the coil valve opens, the outdoor air damper
closes, and the night ther mosta t cycles the fans to maintain the
setpoint of the z one night ther mosta t. For da ytime oper ation, a
centr al switch deacti vates the zone night ther mosta t and
pr ovides contin uous fan oper ation.
Unit Ventilator Digital Control
Digital contr ol offers several enhancements to unit v entila tor
control, including PID control, enhanced digital control, and
graphic displa y.
Figure 27 is of a DDC ASHRAE Cyc le III basic system.
Unless the space temper atur e is below set point the f an disc har ge
temper atur e is constant a t 13°C. The space sensor modula tes
the HW valve for comfort control. Other than PI control and
friendly displa y of values and setpoints, this figur e is the
standar d cycle III.
Figur e 28 utilizes the dig ital system ca pabilities to pr ovide
enhanced Cycle II operation.
Fig. 27. Cycle III Digital Control
M15314
RA
OA
ON
CONTROL
PROGRAM
22.5
22.5
13
77
77
WALL MODULE
TEMPERATURE
COOLING
SETPOINT
13
13
PERCENT OPEN
TO OUTSIDE AIR
OPEN
CLOSED
VALVE OR
FACE DAMPER
OUTDOOR
AIR DAMPER
COOL
WARM
ROOM TEMPERATURE
1/2
NORMAL
OA AT 10°C
OA AT -1°C
OA AT -7°C
OA AT -18°C
PERCENT
OPEN
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