Application

Application Notes
Dual Duct Sequence Configurations
11
Siemens Industry, Inc.
Application Note
A6V11692053
Smart Infrastructure – Building Products
2019-04-01
Use Case 1b – VAV DD with ventilation in hot duct only (Duct 2):
Hot duct does not close if ventilation re-
quirement remains constant.
Hot duct may close if ventilation require-
ment goes to zero.
Parameter configuration for use case 1b:
• VavSuChovrCnd1 = Cooling
• VavSuChovrCnd2 = Heating
• VntDuctSprt = Duct 2
• CtlStrgy = n/a
1)
• VntSprtDdband = n/a
1)
1)
CtlStrgy and VntSprtDdband are ignored when VntDuctSprt does not equal "Both ducts".
In use case 1b, when the thermal load is in deadband the hot duct air flow will equal the current value of the
ventilation flow demand (may vary per room operating mode or DCV); the cold duct air flow will be zero.
On an increase in heating load, the heating flow demand on the hot duct modulates from heating flow min to
heating flow max. Hot duct air flow will be the greater of vent demand and heating demand. Cold duct air flow
will be zero.
On an increase in cooling load, the cooling flow demand on the cold duct modulates from cooling flow min to
cooling flow max. Hot duct air flow will be the current value of ventilation flow demand. The total air flow dur-
ing cooling will be the sum of the ventilation air (from the hot duct) and the modulating cooling flow.
Use case 2: VAV DD - Ventilation in both ducts, with mixing control
In use case 2 configurations, the mechanical equipment consists typically of a single fan AHU with separate
elements for heating and cooling air distribution. The hot and cold air streams are drawn from the same
source(s) and driven by the same fan. Outside air ventilation is provided using both ducts.
Ventilation in deadband – When ventilation is provided in both ducts, different possibilities exist for ventila-
tion in deadband: cold duct (Duct 1), hot duct (Duct 2), and "Last duct". The dual duct can be configured ac-