Are you adhering to the "Honeywell" indications, or Aprilaire, dial numbers of say 25% and less in thw 0-15 deg days, generally ?

What would I tell the customer of retro 1700 to additions getting to now 3700 sq ft ,
all 1/2" Poly sprayed, then fiberglassed original studs true 4", 6" on new walls; and 20" blown FG in attic and flats and vaulted has 2" air gap over shoved-in batts he did on his own...?  Same 30-35% avg 25-45-deg days?

JP

Posted By Dana1 on 17 Apr 2012 10:45 AM
...snip...

Lee: If your house is as small and as tight as Apollo 13 you have a real CO2 risk.  In most houses it would take days-WEEKS even to run into SERIOUS CO2 issues, even it were hermetically sealed, assuming the door was open for at least 30 seconds per day.  CO2 is never an indoor air quality risk the way CO or VOCs can be.

Like Todd, I was curious about where the ventilation rate specification came from, and I listed all the possbile reasons that I could think of.  I have seen references to people using a CO2 sensor to operate their ventilation system, so I added that to the list.  I have never worried about CO2 buildup in a house, until I just went through the numbers.  You have computed that it will take days or WEEKS to run into serious CO2 issues in a hermetically sealed house.  I get a different result, so please point out the source of error in my calculations.

From Note 3 in http://www.inive.org/members_area/medias/pdf/Inive%5CPalencAIVC2007%5CVolume2%5CPalencAIVC2007_V2_112.pdf humans give off CO2 at the rate of about 11.2 liters CO2/hr/person.  Converting into cubic meters, we get 11.2 x 10-3 m^3 CO2/hr/person.  For a family of four persons, this would be 4.48 x 10-2 m^3 CO2/hr.  For strategery's house, the volume is 174 m^3.  Having hermetically sealed strategery's house, how long would it take to build up to 1000 ppm where adverse health effects might first begin?  So 174 m^3 / 4.48 x 10-2 m^3 CO2/hr / 1000 = 3.88 hours!  

I could hardly believe these results, but notice that the measured CO2 values in the above reference built up to 700 ppm in about an hour after starting their testing.  They were adding ventilation to reduce it after that, I think.  

Being surprised by these results, I looked for an alternative reference for human expiration rates of CO2, and found http://users.rcn.com/jkimball.ma.ul...onary.html which gives concentrations of CO2 expired from humans at 3.6% (we'll assume volume%), and they say at rest, humans breath 15-18 times per minute at 0.5 liters per breath.  Assuming 16 breaths per minute, and 60 minutes per hour, this works out to 3.6% x 16/min x 60 min/hr x 0.5 liters = 17.3 liters CO2/hr/person, so higher than the first reference.  (The first reference was by Japanese investigators, and perhaps their subjects were also lower than Western mass subjects.) 

So let us compare these numbers with your results that show that it will take WEEKS for CO2 levels to build up in a hermetically sealed house with the door opened for 30 second per day.  The numbers that I provided were for resting adults.  What happens if they're having SEX?    

The solution is to never have sex indoors, of course. ;-)

OK, I was exaggerating for effect rather than making a rigorous case, but 1000ppm isn't a serious CO2 problem- it's a NORMAL level (if the high-end of normal.) Set the "SERIOUS" threshold at 2x that and you're good for the overnight, even packing 4 non-copulating people into that pretty-tight space. Most homes have a much higher volume/human ratio, and most aren't hermetically sealed.

In tight but not hermetically sealed houses with 2-3x the per-person volume as 4 people in strategery's would have, and occupancy rates less than 70% (most people DO go to work or school, spending more than 2/3 of the day elsewhere), the natural ventilation will usually keep up with the CO2, but not necessarily the humidity or VOCs, or the CO & particulates from cooking, etc. Active exhaust-venting during cooking & showing, and ventilating enough to purge human-exhaled humidity there won't be anything like a CO2 issue.

You could also invest in some house plants, that do more for the indoor air quality than mere CO2 reduction.

What indoor plants would be good for improving my house' air quality?

interesting L-
thanks D-
I have seen such discussion in inner school room auditorium concerns...
People falling into daydreaming with high CO2.  Very interesting again.

Solar boys "ventilation rate specs" said :
Surface area walls and roof x 3.5 BtuH per sqft is LOOSE,
1.5 x surface are is TIGHT for average older homes/windows (not as your new)
 losses 80-deg dT design...peaks observed:
how does 1.5 x  800 + 1.5 x 900
2540 BtuH loss at -10 to -15 below sound due to air infiltration
(this guessing is pretty effective too, as they were sizing Space-Heating solar with only 30-405 in mind)

 If you do not have a conditioned basement , is the floor sealed to it?
Is any air moving around in the basement?
Recommend a little ducted 25w ceiling fan 8 ft from walls for
 Vertical Air Stabilization Distribution  - VASD
which does 'wonders' reducing mold build up, as well as a little desk fan on the floor moving air about in a basement.
NOT GOOD IF RADON IS PRESENT

did you seal the return airs at least?
Does a blower cabinet leak and need some quick vinyl taping on the panels?
Door on the filter rack actually work?

At your conditions , if in sub zero winters, ` 30% glass to wall...
the 1/4 basement and 1/2 sqft for heat pump cfm works well:
450 (no basement HVAC) 550-600 cfm for corner-corner comfort
with 7ft high more central Return air of somekind in main
3/4 rated-size a/c would never run 24 hours on 98 degree days ,
and 300 cfm better for humidity


D's ventilation agreed:
As desired-  some central Effectual air control:
A simple basement 3" (like dryer flex venting) Al-tube
S- 'trap' from an opening (bug-screened inlet)
straight-way going down to floor and back up about 30"
near any basement wall
having a small  1" opening at top of 90-bend
just before it turns down from that outside penetration
for reasons I have not calculated- 
sufficiently stops most cold air in -10 deg days
and breathes as needed for several applications...
and can be simply removed / dampened if not desired

other designs are out there short of just putting 2" dampered-insulated
ducting to return air/ not really concerned with erv in your wonderfully tighter home
- but doable.

**************************

PLANTS:
-think you will find that CO2
not O2
is emitted by plant life not exposed to what causes 02 production:
Daylight equivalent.

 Been told repeatedly
It is cosmic bombardment of our atmosphere that produces much of Earth's 02
according to the late HS Prof of Physics David Laird
This was agreed by physics teacher at Univ Cinti, 4 years later,
 and BioChem major, assist Prof,  in 1980
When things go bump in the night: Starting at Sundown
CO2
 is from the plants

What happens if they're having SEX?

For what duration?

daylight hours only,  plenty of plant O2.

When things go bump in the night: Starting at Sundown
CO2
is from the plants

In the interest of the general educational level, photosynthesis is the reaction in which plants fix carbon by ABSORBING carbon dioxide (CO2) and EMITTING oxygen (O2). That is where the majority of the O2 in the atmosphere comes from. Generation of O2 through photolysis of H2O (cosmic bombardment) is tiny by comparison.

Plants don't give off CO2 except when they break down their cellular structure - death and decay.

this is contrary (without sunlight) to what I thought I have been taught at night reactions

and

O2 in atmosphere from space is WHAT % of the Earth's life usable/breathable content.
I have a number that BOTH Pof's gave the classes. -including oceanic-

Thanks for all IC

this is contrary (without sunlight) to what I thought I have been taught at night reactions

and

The light reactions (daytime) require high energy photons to convert CO2 to intermediate high energy compounds and then to sugars and, of course, O2. The dark reactions are simply steps that can occur without additional photon energy input (dark reaction, nighttime). This doesn't mean that plants only take in CO2 during the day and then release O2 at night. We just compartmentalize the reactions as a thought process.

O2 in atmosphere from space is WHAT % of the Earth's life usable/breathable content.

Planetary sciences have come a long way in only 30 years. The ultimate source of O on earth is another question, but in terms of the rich atmospheric content of O2 that enables animal life as we know it; that is nearly all due to biological processes.

If only lovell had brought a ficus with him to space....

FWIW

I am unable to find any reports of CO2 poisoning from a tight house in the National Library of Medicine database http://www.ncbi.nlm.nih.gov/pubmed

There are of course reports in grain silos ship hulls and other small sealed areas.

Todd:

at 1,1 ach  the 945 looks more like 94 .5 CFper minute, 
having then  .01477 x 60 air changes per hour ~ = .9 ai changes per hour  closer to the 1.1 you mentioned.

hoping A/C bills go down~
 but not if no run cycle is long enough to dehumidify, then I guess a dehumidifier helps.

Is the a/c fixed speed? can you baffle/block closing registers (simple) some air and go to low blower without icing?
or bypass air (vent before a/c coil) to a working point above freezing the coil? (-from supply-piped ~ 6" or 5" rd with a damper to the return, if that is better)

Shoot to Dana1 a thought

JP


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