Re: Energy demand is the problem - CO2
From: Norman Gauss (
Date: Sat, 16 Jul 2011 10:55:43 -0700 (PDT)

Here is an excerpt from the Wikipedia website on carbon dioxide:

"In indoor spaces occupied by people the carbon dioxide concentration will
reach higher levels than in pure outdoor air. Concentrations higher than
1,000 ppm will cause discomfort in more than 20% of occupants, and the
discomfort will increase with increasing CO2 concentration. The discomfort
will be caused by various gases coming from human respiration and
perspiration, and not by CO2 itself. At 2,000 ppm the majority of occupants
will feel a significant degree of discomfort, and many will develop nausea
and headaches. The CO2 concentration between 300 and 2,500 ppm is used as an
indicator of indoor air quality."

Your community's goal to minimize heating fresh air before it enters the
building's circulation means that a compromise must be reached between
maintaining indoor air quality and keeping the temperature within the range
of human comfort.  In the process of pumping in fresh air, there also must
be a consideration of getting rid of stale air.  Buildings situated in areas
with extremely cold winters frequently have special devices known as heat
exchangers.  In some tight buildings it is necessary to pump indoor air to
the outdoors because it is stale.  Before this happens, the stale air is
routed to heat exchangers so that the heat of the stale air can be used to
heat the incoming fresh air.  For very tight buildings this is essential
because of the back pressure that stale air can present when fresh air is
trying to enter the building.

In our common house, we have continuously running exhaust fans in our
restrooms and shower which also pump air out of the rest of the building so
that there tends to be a partial vacuum.  We have vents that supply makeup
air for these exhaust fans.  Since our climate has mild winters, we have no
need for heat exchangers.

It is important not to confuse the concept of exhaustion of combustion gases
with air quality in the occupied spaces.  Upon installation, furnaces and
water heaters have efficient ways to avoid mixing combustion gases with
indoor air.

Norm Gauss

-----Original Message-----
From: Sharon Villines [mailto:sharon [at]] 
Sent: Friday, July 15, 2011 1:47 PM
To: Cohousing-L
Subject: Re: [C-L]_ Energy demand is the problem

On 15 Jul 2011, at 1:22 PM, ehrbar [at] wrote:

> The heat which a CO2 molecule prevents from escaping from the earth 
> through the greenhouse effect is tens of thousands times more than the 
> combustion heat generating this molecule.
> One can say carbon combustion is a gift that keeps giving.

Well, it isn't directly off topic since we all make energy consumption
decisions and redesign plans for our communities. 

I have a related question related to CO2. We have two fresh air ducts on our
HVAC system for the large dining room and kitchen of our commonhouse. The
dampers were always open but we only needed that much fresh air when the
room was fully occupied. We asked the HVAC engineer to wire the dampers and
put a switch upstairs so we could open the dampers when we were expecting a
large crowd but otherwise not be heating and cooling outdoor air.

He said that was against code and instead put a CO2 sensor on the vent that
is supposed to open the damper when the CO2 is above 1000 (we think). The
other night, with no one in the CH and no cooking going on, it was 954.

Some of the numbers I've found say that outdoor air is 300-400 and that
people start complaining at 600-800. CO2 itself isn't highly toxic but is
used as indicator of other toxins that might be present. On TED there is one
lecture from a man in Delhi who lowered the levels in his building and saw a
dramatic reduction in sick days and productivity. He used plants to improve
the air quality.

What levels do you consider optimal? Not compared with "this won't kill you"
but with healthy air.

Anyone out there can answer, I just noticed that Hans raised CO2 and thought
he might know.

Sharon Villines
Takoma Village Cohousing, Washington DC

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