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Chella
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Join Date: Jan 2010
Location: Chennai India
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Relative Humidity Controls - HVAC

01/17/2010 4:50 AM

Hi,

Could you please explain me the Rh control working mechanism using Bypass damper without reheat coil, also any other strategy to control Rh other than dedicated outdoor system.(DAOS)

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 Chellapillai Srinivasan
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t-stat
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Location: Canada, East Coast
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#1

Re: Relative Humidity Controls - HVAC

01/17/2010 6:03 AM

are you asking how a humidistat/de-humidistat controls a bypass damper, or how a bypass damper controls humidity??

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#2
In reply to #1

Re: Relative Humidity Controls - HVAC

01/18/2010 12:04 PM

Actually i want know the feasibility of Rh control without reheat coils, my intention behind is not to waste energy by heating the cooled air..........
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cwarner7_11
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#3
In reply to #2

Re: Relative Humidity Controls - HVAC

01/19/2010 2:38 AM

Relative humidity is a function of air temperature. If you want to decrease relative humidity without changing the water content of the air, increase the temperature (heat it or mix with un-cooled air). If you want to increase relative humidity, cool the air. If you cool the air to less than the dew point, you will decrease the absolute moisture content of the air due to condensation. There are, of course, chemical means of reducing moisture content of air, but these are generally considerably more expensive (and less environmentally friendly) than just applying the appropriate temperature changes. To increase moisture content of the air, blow it over a body of water.

These are the basics...
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toughguy1
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Location: Charleston, SC
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#4

Re: Relative Humidity Controls - HVAC

01/25/2010 11:54 AM

This concept basically provides "reheat" without a heating coil in order to provide a "poor man's" humidity control. What you are doing is bypassing some warm 75 degree return air around the cooling coil and partially waming the cooling supply air. This effect will trick the thermostat into thinking it not satisfying the temperature, and therefore the cooling coil will continue to cool/dehumidify the air and remove condensate. This bypass has a maximum flow. You can't bypass too much air or the coil will freeze. This solution is not super effective. It will work marginally, but real re-heat (electic, hydronic, etc.) is really required to provide effective humidity control.

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Anonymous Poster
#5
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Re: Relative Humidity Controls - HVAC

01/27/2010 3:53 AM

Thanks Mr.Turner
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Chella
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Location: Chennai India
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#6
In reply to #4

Re: Relative Humidity Controls - HVAC

01/27/2010 4:06 AM

Thanks Mr.Turner

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 Chellapillai Srinivasan
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Chella
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#7
In reply to #4

Re: Relative Humidity Controls - HVAC

05/16/2010 4:28 AM

Dear Mr.Turner, I have got some paper on bypass damper control, i will send you for your persual,, could you please send your email ID?

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 Chellapillai Srinivasan
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toughguy1
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#8
In reply to #7

Re: Relative Humidity Controls - HVAC

05/16/2010 8:43 PM

I didn't understand what you said. Could you clarify what you are meaning to say?

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