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Selk
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Join Date: Dec 2016
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HVAC - Modulating Volume Dampers

05/07/2019 12:02 PM

Typically when and where are modulating dampers are used? when is it preferred over open/close type dampers?

In the below image, Why this motorized volume damper before the Pressurization unit and after the blower fan is of modulating type? Why is it not just open or close type?
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Pathfinder Tags: Dampers HVAC
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SolarEagle
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#1

Re: HVAC - Modulating volume dampers

05/07/2019 12:46 PM

More precise temperature control....and constant airflow...

These would typically be used in commercial settings where x number of air changes per hour are required...These systems are usually constant flow of conditioned air with individual heaters installed in the ducts, this gives accurate control of temperature and humidity while providing fresh air constantly....

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SolarEagle
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#2
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Re: HVAC - Modulating volume dampers

05/07/2019 2:17 PM

https://www.flowcontrol.com/resources/System-Design-Manual.pdf

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tonyhemet
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#3
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Re: HVAC - Modulating volume dampers

05/07/2019 10:54 PM

Not exactly, " fresh air " .

More like, " cool or heated conditioned air " .

Air handlers aren't usually designed with a fresh ( outside ) inlet, to do so would be counterproductive. Adding moisture laden air would cause the compressor to run constantly, in a effort to " dry " the air in the conditioned space.
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SolarEagle
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#4
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Re: HVAC - Modulating volume dampers

05/08/2019 12:14 AM

No that is incorrect...a lot of the systems in commercial buildings can supply 100% fresh air, this usually varies according to outside temperature, but there is some fresh air being injected into the system at all times....all air conditioning systems require some fresh air intake to keep the air healthy ...ie: sick building syndrome

https://www.contractingbusiness.com/archive/how-much-fresh-air-enough

It's the law...

https://codes.iccsafe.org/content/FMC2017/chapter-4-ventilation

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khelectrical
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#5
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Re: HVAC - Modulating volume dampers

05/08/2019 7:58 AM

Yes, We use air to air heat exchanger to precondition incoming fresh air makeup. This allows fresh air injection in the system and exhaust of stale air while trying to remove as much moisture and get air to internal temperature as possible.

Modulating dampers are used as well to prevent start stop cycles on unit.
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vsar
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#6
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Re: HVAC - Modulating volume dampers

05/08/2019 9:09 AM

I agree with Mr. SolarEagle,

I had some volunteered HVAC jobs in a parish church in NYC that has the same HVAC setup as well. It is kind of an antiquated system but very functional at that time..

Where the proportional valve controlled mixing damper is actually being controlled by the thermostat settings inside the buildings..

It is a continuously tempering and mixing the hot and cold conditioned air.. Doing some kind of fine tuning the inside temperature before the final mixed conditioned air enters the ducting system going to the buildings..

There is a city code that requires about 30% fresh air that must also be mixed with the number of required air exchanges of about 8X minimum on a daily basis..

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