Re: GBlist: Humidity/CO2/IAQ -Reply

Loren Abraham (loren@cstone.net)
Sat, 8 Mar 1997 02:51:47 -0500

You wrote:
----------
>From: Tommy V WILLIAMS <Tommy.Williams@EWEB.Eugene.OR.US>
>
>Not a bad idea but are we talking about the level of CO 2 put out
by
>people or waiting for some back-drafting before bring fresh air
in? Why
>not just say no to backdrafting?
-SNIP-
>From:
> SLGHVAC@aol.com
> To:
> hysave@fta.com
>
>CO2 level is the most accurate means of controlling the need for
outside
>air.
>
> This is called demand controlled ventilation DCM, and is used
primarily
>with direct digital control DDC systems that are able to
accurately
>control dampers based on sensor signgals.
>
>Energy can be saved by only bringing in the amount of outdoor air
>necessary at any particular time.
>
>Thanks for the question.
>Scott

Hal Levin and I have had this discussion before. I am very much
in favor of the concept of demand controlled ventilation DCM,
however the means of determining the demand must be somewhat
instantaneous. E.g., take the case where the building is at
minimum ventilation overnight and an assembly room fills to
capacity with 800 people at 8:00 AM. How long will the response
time of a CO2 sensor be before the air makeup shifts into maximum
fresh air mode? For this reason I suggest that another means of
measuring demand be utilized, perhaps by "counting" occupants
(trip beam) or determining occupant density PSF (infra-red
sensor).
_____________________________________
Loren E. Abraham, AIA, IDSA
Charlottesville, VA
Vc: 804 296 4197 Pg: 804 963 1511 Fax: 804 971 3729
© 1997 Daybreak Technologies Inc. / Environmental Research Group
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