At 10:57 AM 3/10/97 -0500, Loren Abraham wrote:
>
>Hal:
>
>Why not post this? I think your comment about CO2 detector is a
>valid point:
>
Hal wrote:
>>I have a bigger problem with the
>>accuracy of CO2 monitoring devices since some of them tend to
>drift and lose
>>their calibration over time.
>
>...and I find your suggestion about the "sudden increment
>approach" is intriguing.
>
>Loren
>
>----------
>>From: Hal Levin <hlevin@cruzio.com>
>>To: Loren Abraham <loren@cstone.net>
>>Subject: Re: GBlist: Humidity/CO2/IAQ -Reply
>>Date: Sat, 08 Mar 1997 08:24:07 -0800
>>
>>Loren:
>>
>>I stand by my previous position. Motion detectors, or people
>counters or
>>whatever seem to have fewer potential problems. I also wonder if
>thermal
>>changes couldn't be used - RA temp, for example?
>>
>>I don't want to confuse people with this, so I won't post it to
>the list.
>>.....But, CO2 might work if connected to a microprocessor with an
>algorithm
>>to detect sudden changes in concentration. Perhaps a ten %
>increment over
>>two or three or five minutes would work. I have a bigger problem
>with the
>>accuracy of CO2 monitoring devices since some of them tend to
>drift and lose
>>their calibration over time. The sudden increment approach
>addresses that,
>>although it may not adequately do so. I don't know. I think there
>is a need
>>for some good research to evaluate the method. In the case of an
>auditorium,
>>though, there may be too long a lag time when air exchange rate
>is low and
>>the space volume is large. If the CO2 sensor is in the return
>air, the
>>question is, how long will it take for the concentration in the
>space to
>>rise significantly?
>>
>>In any case, why do it if motion sensors or light beam people
>counters at
>>doorways are more reliable than CO2 sensors?
>>
>>Hal
>>
>>
>>At 02:51 AM 3/8/97 -0500, you wrote:
>>>
>>>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
>>>________________________________________________________________
>__
>>>This greenbuilding dialogue is sponsored by Oikos
>(www.oikos.com)
>>>and Environmental Building News (www.ebuild.com). For
>instructions
>>>send e-mail to greenbuilding-request@crest.org.
>>>________________________________________________________________
>__
>>>.-
>>>
>>>
>>
>>Hal Levin <hlevin@cruzio.com>
>>
>
>.-
>
>
Hal Levin <hlevin@cruzio.com>
__________________________________________________________________
This greenbuilding dialogue is sponsored by Oikos (www.oikos.com)
and Environmental Building News (www.ebuild.com). For instructions
send e-mail to greenbuilding-request@crest.org.
__________________________________________________________________