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<DIV><FONT size=2 face=Arial>JStraub's response to earlier message off
list. He approved posting message. I think it is of interest.
</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV>RH is not a measure of IAQ. It is a measure of human comfort, and too
high levels can damage buildings. </DIV>
<DIV>ASHRAE 55 covers the comfort side and suggests RH levels of 20 to 60.</DIV>
<DIV>ASHRAE 62.2 is a standard. Of course the number of people is not
equal to bedrooms + 1. But what guess would you make? The
ventilation rates have been calibrated against this assumption. There is no good
science to tell you what cfm/sf or cu ft will provide good IAQ. All we do
is set a value that by consensus solves most problems most of the time.</DIV>
<DIV>You cant make a sensor for IAQ, because we dont know what to measure: which
of the thousands of chemical compounds in the, say, cleaning and building
products should you focus on? Does that mean you should ignore the smell
of burnt meat? Foul body odors? Wintertime RH?</DIV>
<DIV>The answer has been we ventilate a certain amount, one rate for people (it
varies from 3 to 20 cfm per person depending on which standard and when) and one
rate to deal with building emissions (varies from zero to 0.06 cfm/sf or 0.2
ACH). </DIV>
<DIV>We have experience with hundreds of thousands of homes with mechanical
ventilation systems and thousands of commercial buildings (offices use 5
cfm/person +0.06 cfm/sf for example). If ventilate at about half this rate,
problems begin to crop up at an increasing rate. If you are good about
avoiding polluting materials, and have some tolerance for odors, you can
decreases the rate further with no problems. Rates of twice this much dont
seem to have any noticeable effect on peoples perception or even most pollution
levels measured.</DIV>
<DIV>CO2 is a reasonably good measure of human occupancy and activity as well as
background ventilation. Hence it is explicity allowed in ASHRAE 62.1
(commercial code) and widely used. Even when you use CO2 measurement,
background ventilation to remove buildng generate odors and emissions is
recommended. CO2 only measures the human side of the equation.</DIV>
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<DIV>
<DIV>On 2011-08-13, at 2:35 PM, elitalking wrote:</DIV><BR
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<BLOCKQUOTE type="cite"><SPAN
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<DIV>
<DIV><FONT size=4><EM>John Straube wrote:</EM></FONT></DIV>
<DIV>
<DIV><FONT size=4><EM></EM></FONT> </DIV>
<DIV><FONT size=4><EM>The problem with RH is that it varies wildly with with
outdoor conditions. You can have all the windows open in the summer and
the RH will be high, and have too little ventilation and the RH be very low in
cold weather in Denver. Hence RH is a horrible measure of ventilation
need unless you add a lot of other non measured info like outdoor conditions,
floor area, etc.<BR>CO2 is a good measure of occupancy and intensity, which
correlate fairly well with the need for ventilation.<BR><BR>On 2011-07-26, at
9:29 AM, Corwyn wrote:<BR><BR>> On 7/24/2011 10:50 AM, Peter Kidd
wrote:<BR>>> dioxide for ventilation control<BR>>><SPAN
class=Apple-converted-space> </SPAN><BR>>>> On Sun, 24 Jul 2011
09:21:36 -0400, elitalking<BR>>>> <</EM></FONT><A href=""><FONT
size=4><EM>elitalking@rockbridge.net</EM></FONT></A><FONT size=4><EM>>
wrote:<BR>>>><SPAN
class=Apple-converted-space> </SPAN><BR>>>>><SPAN
class=Apple-converted-space> </SPAN><BR>>>>> Does anybody
have a good inexpensive CO2 monitor recomendation? What<BR>>>>>
levels of CO2 are tolerable for good indoor air quality?<BR>><SPAN
class=Apple-converted-space> </SPAN><BR>> Greetings,<BR>><SPAN
class=Apple-converted-space> </SPAN><BR>> I find it hard to believe
that the first warning sign of drastically low ventilation levels is going to
be elevated CO2 levels.<BR>><SPAN
class=Apple-converted-space> </SPAN><BR>> Why not use humidity?
That can be done easily, cheaply, and many systems are already configured for
it. Unless you have a CO2 generating source which is NOT putting out
vastly more H20 than CO2<BR></EM></FONT></DIV>
<DIV>
<DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT size=4>My
Comment:</FONT></SPAN></DIV>
<P style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT
size=4></FONT></SPAN> </P>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT
size=4>John Straub and Corwyn correctly surmised my interest in CO2 monitoring
for evaluating the air quality and the need for ventilation.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>It is interesting that these
two smart and generous contributors of their knowledge to this list disagree
on the implications of relative humidity in evaluating air
quality.<SPAN> </SPAN><?XML:NAMESPACE PREFIX = O
/><O:P></O:P></FONT></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><O:P><FONT
size=4> </FONT></O:P></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT size=4>I
am wondering if their might be developments in a combination of sensors to
evaluate objectively the need for ventilation air.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>It strikes me that the ASHRAE
guidelines for Required ventilation/min = (.01cfm/sf x Area(sf)) +
(7.5cfm/occupant x #occupants) is incomplete.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>Using bedrooms as an indicator
, Occupants =#Bedrooms +1, makes an assumption that the master bedroom is
double occupied with a couple.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>This strikes me as a rule of
thumb.<SPAN> <SPAN class=Apple-converted-space> </SPAN></SPAN>It
seems odd to give a volume ventilation rate based on an area.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>Also, the # of bedrooms does
not recognize the great variations of occupancy.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>If the bodies are away at
work, they are not consuming O2.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>If we have a party, there are
a lot more bodies breathing and exhaling
moisture.<SPAN> </SPAN><O:P></O:P></FONT></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><O:P><FONT
size=4> </FONT></O:P></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT
size=4>Hence, my interest is in objective sensors for regulating ventilation
to reduce energy cost for conditioning air when it is not
needed.<SPAN> </SPAN><O:P></O:P></FONT></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><O:P><FONT
size=4> </FONT></O:P></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT size=4>I
know that assembly functions such as a courtroom have CO2 sensors to evaluate
when ventilation is needed.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>I suppose CO2 is an indication
of O2 consumption.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>Is it a true indication of O2
available?<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>Would an O2 reading be more
direct to determine if there is enough air?<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>Does high CO2 mean low
O2?<O:P></O:P></FONT></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><O:P><FONT
size=4> </FONT></O:P></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT
size=4>Can humidity be used to evaluate when you need air?<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>It can be used to evaluate
when drying is needed.<SPAN> <SPAN
class=Apple-converted-space> </SPAN></SPAN>However, as John points out,
ventilating because of indoor high relative humidity is counterproductive if
the exterior air has higher humidity such as a rainy
day.<SPAN> </SPAN><O:P></O:P></FONT></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><O:P><FONT
size=4> </FONT></O:P></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT
size=4>Can there be sensors for other pollutants in indoor air that are
problematic (Dust, CO, VOC)? </FONT></SPAN></DIV>
<P style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT
size=4></FONT></SPAN> </P>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT
size=4>Perhaps this is too complex and a genral flushing of the air specified
by ASRAE formula is the appropriate method. </FONT></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><O:P><FONT
size=4> </FONT></O:P></SPAN></DIV>
<DIV style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt"><SPAN
style="FONT-FAMILY: 'Times New Roman', serif; FONT-SIZE: 16pt"><FONT
size=4>Eli<O:P></O:P></FONT></SPAN></DIV></DIV></DIV></DIV></DIV></SPAN></BLOCKQUOTE></DIV><BR>
<DIV><SPAN
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<DIV>John Straube</DIV>
<DIV><A href="">www.BuildingScience.com</A></DIV>
<DIV><BR></DIV></SPAN><BR
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