ENGINEERING MANULA OF AUTOMATIC CONTROL
INDIVIDUAL ROOM CONTROL APPLICATIONS
410
FULL
FULL
0
0
DEDBAND
(ADJUSTABLE)
M10545
HEATING
LOAD
HEATING SETPOINT
COOLING SETPOINT
COOLING
LOAD
ZERO
MIN
AIRFLOW (CFM)
HEATING
MAX
COOLING
MAX
H
O
T D
U
C
T
AIR
FLO
W
COLD DUCT
AIRFLOW
75 75
55
78
1.4
350 943 -3.01150 925 00 77
MINIMUM
AIRFLOW
SETPOINT (CFM)
MAXIMUM
COOLING
AIRFLOW
SETPOINT (CFM)
MAXIMUM
HEATING
AIRFLOW
SETPOINT (CFM)
INCHES OF
WATER
CURRENT
AIRFLOW
(CFM)
DAMPER
PERCENT
OPEN
HEATING
DEADBAND
COOLING
SETPOINT
TEMPERATURE
WALL MODULE
HOT
DUCT
COLD
DUCT
DUAL-DUCT ATU
In a dual-duct air handling system, supply air is divided at
the central fan and hot air and cold air flow through separate
ducts throughout the building. Two of the many DDC dual-
duct control configurations are included here.
A typical original dual-duct ATU draws hot and cold air from
respective ducts, mixes the air as directed by a sensor in the
controlled space, and discharges the mixed air into the space.
This basic dual-duct mixing system is not economical because
air is cooled and heated much of the year. DDC systems are
still sometimes used with digital hot and cold duct load reset to
minimize the energy waste during mixing periods. Adapting
dual-duct systems to VAV control has resulted in significant
energy savings without discomfort.
Fig. 10. Dual-Duct Pressure Independent VAV Air Terminal Unit.
Dual Duct Pressure Independent VAV ATU
Figure 10 shows a dual-duct pressure independent ATU. The
airflow sensor in the outlet of the ATU controls the cold duct
inlet damper in the cooling mode from the cooling maximum
airflow to the minimum ventilation airflow, through the dead
band, and to the heating setpoint. As the heating load increases,
the hot duct damper modulates open to control the supply
airflow from zero to the maximum heating value. This same
sequence may be achieved with two airflow elements, one in
each primary duct
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