Application

Application Notes
Dual Duct Sequence Configurations
10
Siemens Industry, Inc.
Application Note
A6V11692053
Smart Infrastructure – Building Products
2019-04-01
Use case 1: VAV DD - Ventilation source in one duct
In use case 1 configurations, the mechanical equipment consists of a multiple fan AHU with separate elements
for heating and cooling air distribution. The hot and cold air streams are drawn from different sources and driv-
en by separate fans. Outside air ventilation is provided in either the hot duct or the cold duct, not both.
Use Case 1a – VAV DD with ventilation in cold duct only (Duct 1):
Cold duct does not close if ventilation re-
quirement remains constant.
Cold duct may close if ventilation require-
ment goes to zero.
Parameter configuration for use case 1a:
• VavSuChovrCnd1 = Cooling
• VavSuChovrCnd2 = Heating
• VntDuctSprt = Duct 1
• CtlStrgy = n/a
1)
• VntSprtDdband = n/a
1)
1)
CtlStrgy and VntSprtDdband are ignored when VntDuctSprt does not equal "Both ducts".
In use case 1a, when the thermal load is in deadband the cold duct air flow will equal the current value of the
ventilation flow demand (may vary per room operating mode or DCV); the hot 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. Cold duct air flow will be the greater of vent demand and cooling demand. Hot 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. Cold duct air flow will be the current value of ventilation flow demand. The total air flow dur-
ing heating will be the sum of the ventilation air (from the cold duct) and the modulating heating flow.