Outside Air Damper Unoccupied Mode

[John_187]

Hello,

For the 2009 IECC, does an outdoor air damper need to close in unoccupied mode? At face value, I thought yes, however there are exceptions and conditions.

This unit is partially being used as a makeup air unit as well (one of the rooms is not being returned due to 24/7 continuous exhaust requirements). Therefore, there is an argument that the OA damper should always be open even when unoccupied for that (even though that room exhaust could also be made up through intake louver).

The air handler would have a motorized damper, which would be at a minimum position, except for when economizing.

An air handler rep stated that their unit did not come packaged with the controls to close the outside air damper in unoccupied mode, and they've obviously been selling and using this unit. 2009 IECC is the most lenient. Also, in the past roof top units have been installed with manual dampers - those have obviously not been able to close the outside air damper in unoccupied mode.

Thanks for any feedback

 

[GT-EGR]

How much exhaust makeup is it? For the whole unit to really have to run it should be a large demand and also something critical that needs 24/7 exhaust.

I’m assuming your unit is off when unoccupied? In which case the damper should go to its failsafe position, which for outside air should be normally closed unless that really is some hazardous/critical exhaust you are making up. Even then though, the exhaust isn’t going to pull any airflow through that whole unit, it will find some other easier path to the outdoors.

One of the main points of that damper is it should be closed to stop outside air from migrating in on its own when not in use. An AHU manufacturer should understand that and if they have an integral damper should provide that without asking.

 

[willard3]

A control for the OA damper can be installed independent of the AHU controls.