motorized fresh air damper

[alex1960]

Hello all,
any one can explaine the porpuse of motorized fresh air damper on roof tops since it is a code's requirement instead of manual fresh air damper.


Thanks

[passintyme]

Free cooling during colder times when there is an air conditioning load... To meet fresh air requirement in relation to occupancy and indoor air quality.

[alex1960]

My question is about fresh air not economizer.

[passintyme]

Does the unit have an economizer?? Is the f.a. damper going to the return of the unit?? Motorized v.s. manual keeps the cold or hot out when in off cycle.

[kayHVAC]

I work for a large university, and many of our dedicated fresh air dampers are motorized because they are controlled through the Building automation system off of a return CO2 sensor or CO2 sensor located in the space. If the CO2 level rises then the fresh air damper opens to bring in more fresh air and vice versa. It saves energy by only bringing in the amount of fresh air required to satisfy what is needed by the occupants and not having to condition a specific amount of outside air constantly that you would with a manual damper. I believe me try to keep the CO2 level below 800ppm.

[DDC_Dan]

I work for a large university, and many of our dedicated fresh air dampers are motorized because they are controlled through the Building automation system off of a return CO2 sensor or CO2 sensor located in the space. If the CO2 level rises then the fresh air damper opens to bring in more fresh air and vice versa. It saves energy by only bringing in the amount of fresh air required to satisfy what is needed by the occupants and not having to condition a specific amount of outside air constantly that you would with a manual damper. I believe me try to keep the CO2 level below 800ppm.

I see that a lot, and have had to program the same sequence, but have a fundamental issue with it. Essentially you are forcing the co2 level up to a point just short of making people sick. I know, gotta save energy....

Sorry, rant mode off.

Oh, and here they usually make me measure osa co2 and control 400 ppm above that rather than a fixed setpoint

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[DDC_Dan]

Motorized v.s. manual keeps the cold or hot out when in off cycle.

Bingo. Especially if the bldg. static pressure is much different than ambient you can have significant infiltration/exfiltration when the unit is not running.

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[teddy bear]

I see that a lot, and have had to program the same sequence, but have a fundamental issue with it. Essentially you are forcing the co2 level up to a point just short of making people sick. I know, gotta save energy....

Sorry, rant mode off.

Oh, and here they usually make me measure osa co2 and control 400 ppm above that rather than a fixed setpoint

Sent from my ADR6300 using Tapatalk 2

People will not get sick from CO2 levels above 1,000 ppm.
CO2 is used as marker of people occupancy indicating the need for fresh to purge the indoor pollutants. The CO2 is not a dangerous pollutant.
Regards TB

[alex1960]

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?

[ascj]

I'm no code expert......but I never heard of a code for a certain percentage for an outdoor damper. There is codes stating how much outdoor air(volume) and where ever your dampers are they are.

As far as motorized dampers......I would assume it's for smoke/fire control. They need to fail closed.

[ncboston]

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?

I think the other guy that replied about closing the damper in the 'off' cycle answered your question.

[steam638]

10% fresh air mandated in most commercial bldgs by code

[ckartson]

In our area any hvac equipment over 2000 cfm requires a duct smoke detector which will provide a safety shut down of fans and OA. Fixed position damper will not provide closure.