Application

Application Notes
Dual Duct Sequence Configurations
19
Siemens Industry, Inc.
Application Note
A6V11692053
Smart Infrastructure – Building Products
2019-04-01
If the last active duct = hot duct, then when the system exits the temperature deadband the behavior is as
follows:
• Exiting deadband on a call for heat when last duct is the hot duct and CtlStrgy = Snap acting;
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. (Hot duct remains the active duct.)
• Exiting deadband on a call for cool when last duct is the hot duct and CtlStrgy = Snap acting;
On an increase in cooling load, the hot duct closes (snap action) and the cooling loop becomes the active
loop / duct. As the cooling flow demand on the cold duct modulates from cooling flow min to cooling flow
max, the cold duct air flow will be the greater of vent demand and cooling demand.
Use Case 4: VAV DD - Dedicated duct for ventilation from DOAS
(dedicated outside air system)
In use case 4 configurations, the mechanical equipment consists of a multiple fan AHU with DOAS,
and separate elements (if present) for heating / cooling air distribution. When the thermal load is in
deadband, air flow in the duct used for temperature control can be zero (Duct 1 in graphic).
Duct 1
Duct 2
Parameter configuration for use case 4:
• VavSuChovrCnd1 = Cooling
• VavSuChovrCnd2 = Neither
• VntDuctSprt = Duct 2
• CtlStrgy = n/a
1)
• VntSprtDdband = n/a
1)
1)
CtlStrgy and VntSprtDdband are ignored when VntDuctSprt does not equal "Both ducts".