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INDIVIDUAL ROOM CONTROL APPLICATIONS
DUAL-DUCT ATU
In a dual-duct air handling system,
the centr al fan and hot air and cold air f low thr ough separ ate
ducts thr oughout the b uilding . Two of the man y DDC dual-
duct contr ol configur ations ar e included her e.
A typical or iginal dual-duct ATU dr aws hot and cold air fr om
respecti ve ducts, mixes the air as dir ected b y a sensor in the
contr olled space , and disc har ges the mix ed air into the space .
This basic dual-duct mixing system is not economical because
air is cooled and hea ted m uch of the y ear. DDC systems ar e
still sometimes used with digital hot and cold duct load reset to
minimiz e the ener gy waste dur ing mixing per iods. Adapting
dual-duct systems to VAV contr ol has r esulted in signif icant
ener gy savings without discomf ort.
25.5
kPa
0.35
13
0.165
MINIMUM
AIRFLOW
SETPOINT
3
(m
/s)
COOLING
MAX
HEATING
MAX
AIRFLOW
MIN
ZERO
suppl y air is di vided a t
HOT
DUCT
COLD
DUCT
0.543
0.443
MAXIMUM
MAXIMUM
COOLING
HEATING
AIRFLOW
AIRFLOW
SETPOINT
SETPOINT
3
3
(m
/s)
(m
/s)
0
FULL
HEATING
LOAD
HEATING SETPOINT
Fig. 10. Dual-Duct Pressure Independent VAV Air Terminal Unit.
Dual Duct Pr essur e Inde pendent 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.
0.445
24
00
77
DAMPER
CURRENT
3
PERCENT
(m
/s)
OPEN
0
COOLING
DEDBAND
LOAD
(ADJUSTABLE)
COOLING SETPOINT
ENGINEERING MANUAL OF AUTOMATIC CONTROL
406
WALL MODULE
TEMPERATURE
COOLING
SETPOINT
24
-1.75
HEATING
DEADBAND
FULL
M15311
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