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INDIVIDUAL ROOM CONTROL APPLICATIONS
kPa
0.35
13
0.165
MINIMUM
MAXIMUM
AIRFLOW SETPOINTS (m
OPEN
MAX
PRIMARY
AIRFLOW
POSITION
INDUCTION
DAMPER
ZERO
CLOSED
The induction VAV ATU maintains mor e air motion in the
space a t lower loads than a thr ottling VAV ATU. The r ehea t
coil is optional, and ma y be in the induced air or suppl y air.
Parallel F an ATU
The par allel fan ATU (F ig. 8) replaces the induction VAV
ATU damper s with a small centr ifugal fan to r ecirculate r etur n
air a t a constant v olume after pr imar y air decr eases. The fan
acts as the f irst sta ge of reheat after pr imar y flow is at minim um
or can be s witched on a t a lo w pr imar y flow thr eshold w hile
pr imar y flow goes to zero. The r eheat coil is optional.
PLENUM AIR
PRIMARY
VAV BOX
AIR
0.575
0.465
CURRENT
AIRFLOW
3
3
/s)
(m
/s)
MIN
FULL
HEATING
LOAD
HEATING SETPOINT
Fig. 7. Induction VAV Air Terminal Unit.
RHC
24
00
58
PERCENT OPEN
0
0
DEADBAND
(ADJUSTABLE)
The oper ation c ycle in F igur e 8 shows tha t when space
temper atur e is below the hea ting setpoint, the pr imar y air f low
is at a minim um, and the f an is on. As the hea ting load g oes to
zero, the r eheat valve closes, then the f an stops. After the space
temperature rises through a deadband, as the cooling load
incr eases, the pr imar y air f low incr eases to maxim um.
Ser ies F an ATU
The ser ies fan ATU (F ig. 9) deliver s a constant v olume of
dischar ge air with a v ar iable volume of AHU suppl y air. In this
ATU, the fan is on contin uously dur ing occupied hour s. Pr imar y
air is modula ted to meet space demand f or cooling . As pr imar y
air damper modula tes closed, mor e plen um air is dr awn in to
maintain a constant disc har ge volume. Optional r eheat can be
sequenced as required.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
404
WALL MODULE
TEMPERATURE
COOLING
SETPOINT
24
24
-1.5
HEATING
DEADBAND
FULL
COOLING
LOAD
COOLING SETPOINT
M15308
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