motorized fresh air damper

[dlove]

It apears that I did not explain my question properly. Let me clear it up.
With manual dampers, you can adjust the percentage of fresh air (outdoor Air) from zero and up., normaly 15% ( code Requires ??) for unit over 5 tons is recomended to presurize the building. Equipment brings the outdoor air regardless of low or high OA. there is no sensor. you get warm air in the summer, cold air in winter as long as the blower fan runs. There is some aluminum filters to prevent insects and rain to get in the retun side.
Now they changed the code and want motorized damper to open blades to let OA get into the retun air. Also there is minimum setting from 15% and up. as soon as blower fan starts, actuator opens the blade to preset position. The damper motor opens the blades as long as blower fan motor runs. And it spring closes the blade when there are no power to damper motor. There is no sensor no thermostat, nothing, no control but blower fan motor low voltage. Now my question is that what is the purpose of this Motorized damper which is inspector asking for it? I just Like to know what's the logic behind it. The manual damper wouldn't do the same?

That is your OAT intake, your economizer and the dampers are set to maintain MIN of proper fresh air intake per code.. I assume this is a new install the inspector is checking only what is required...Like you said some years ago all units over 5tons need to have auto dampers no fixed. I will assume you will have all this balanced. Once everyone is gone and if you have a control system you should be able to set the min to what you want...In deep summer, high temps-high Humidity i shut mine to 0%. and depending on the size you may need spill dampers to maintain static. This is basic HVAC


Just a note about CO2...so many people worry about indoor CO2 but very few have sensors outside... I have seen where the CO levels outside are worse than inside and the dampers still open because many forget to measure outdoor and indoor CO2. If your going to install CO2 sensors do it right.

[ZeroCool]

I've seen some codes that wanted a motorized damper for smoke/fire shut down instead a RTU mounted chimney with barometric relief and fixed % intake.

[glennac]

10% fresh air mandated in most commercial bldgs by code

Steam that was the "standard" or "rule of thumb" before we had 62.1. and the code requirement for ventilation. There is no "10%" standard anymore. The IMC 2006 calls for different ventilation rates based on the type of building and rooms such as restrooms, classrooms, office areas, etc.

Typically you are talking about 15% or more in most cases. LEED points for air quality requires a lot more. The 2012 code does require motorized dampers for outside air. We don't have that code yet in GA but will have it Jan 1, 2014. Don't know to much about that yet other that in some cases you are allowed to have less OA than in the IMC 2006. Thank you very much