ENGINEERING MANULA OF AUTOMATIC CONTROL
INDIVIDUAL ROOM CONTROL APPLICATIONS
408
0024 75 75
551.4
350 986 -2.51200 58
MINIMUM MAXIMUM
INCHES OF
WATER
CURRENT
AIRFLOW
(CFM)
PERCENT OPEN
AIRFLOW SETPOINTS (CFM)
HEATING
DEADBAND
COOLING
SETPOINT
TEMPERATURE
WALL MODULE
PLENUM AIR
RHC
VAV BOX
MAX
PRIMARY
AIRFLOW
POSITION
REHEAT
MIN
ZERO
FULL FULL00
DEADBAND
(ADJUSTABLE)
M10541
HEATING
LOAD
HEATING SETPOINT
COOLING SETPOINT
COOLING
LOAD
PRIMARY
DAMPER AIRFLOW
INDUCTION
DAMPER
POSITION
OPEN
CLOSED
INDUCTION
DAMPER
PRIMARY
AIR
Fig. 7. Induction VAV Air Terminal Unit.
The induction VAV ATU maintains more air motion in the
space at lower loads than a throttling VAV ATU. The reheat
coil is optional, and may be in the induced air or supply air.
Parallel Fan ATU
The parallel fan ATU (Fig. 8) replaces the induction VAV
ATU dampers with a small centrifugal fan to recirculate return
air at a constant volume after primary air decreases. The fan
acts as the first stage of reheat after primary flow is at minimum
or can be switched on at a low primary flow threshold while
primary flow goes to zero. The reheat coil is optional.
The operation cycle in Figure 8 shows that when space
temperature is below the heating setpoint, the primary air flow
is at a minimum, and the fan is on. As the heating load goes to
zero, the reheat valve closes, then the fan stops. After the space
temperature rises through a deadband, as the cooling load
increases, the primary air flow increases to maximum.
Series Fan ATU
The series fan ATU (Fig. 9) delivers a constant volume of
discharge air with a variable volume of AHU supply air. In this
AT U, the fan is on continuously during occupied hours. Primary
air is modulated to meet space demand for cooling. As primary
air damper modulates closed, more plenum air is drawn in to
maintain a constant discharge volume. Optional reheat can be
sequenced as required.
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