Quote:
Originally Posted by stevehull
...Let's think of an really airtight house...
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Steve, I don’t need to 'think' of a really airtight house because I live in one right now.
Quote:
Originally Posted by stevehull
...CO2 at the end of one week... is 0.03% ....an almost vanishing small number to trigger with.
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Vanishing to your arithmetic perhaps, but not disappearing. This is probably why CO2 sensors have been so expensive for so long.
Here are ASHRE & OSHA specs:
- normal outdoor level: 350 - 450 ppm
- acceptable levels: < 600 ppm
- complaints of stiffness and odors: 600 - 1000 ppm
- ASHRAE and OSHA standards: 1000 ppm
- general drowsiness: 1000 - 2500 ppm
- adverse health effects expected: 2500 - 5000 ppm
- maximum allowed concentration within a 8 hour working period: 5000 ppm
I also previously came across some studies of German shool children that indicated a much elevated level of performance when levels of CO2 were reduced well below ASHRE standards. I just did a search for that information I had found previously, and am not able to locate it... However,
I did find this:
Quote:
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Elevated carbon dioxide may impair reasoning
Insufficient ventilation allows exhaled gas to build up indoors, diminishing decision-making abilities
By Janet Raloff
Web edition: October 16, 2012
Carbon dioxide has been vilified for decades as a driver of global warming. A new study finds signs that CO2, exhaled in every breath, can exert an equally worrisome threat — impaired cognition — in nearly every energy-efficient classroom, meeting hall or office space.
The work assessed decision-making in 22 healthy young adults. Their performance on six of nine tests dropped notably when researchers raised indoor carbon dioxide levels to 1,000 parts per million from a baseline of 600 ppm. On seven tests, performance fell substantially more when the room’s CO2 was boosted to 2,500 ppm, scientists report in a paper to be published in Environmental Health Perspectives.
These data are surprising, says Roger Hedrick of Architectural Energy Corp. in Boulder, Colo., because “1,000 ppm of CO2 used to be considered a benchmark of good ventilation.” Hedrick, an environmental engineer, chairs the committee that drafts commercial ventilation standards through the American Society of Heating, Refrigerating, & Air-Conditioning Engineers.
Carbon dioxide levels are often substantially higher in buildings than the 350 to 400 ppm typically found outdoors. Indoor values of 600 ppm are considered very good. But depending on how many people inhabit a room and how many times per hour its air is exchanged with outdoor air through ventilation, “there are plenty of buildings where you could easily see 2,500 ppm of CO2 — or close to it — even with ventilation designs that are fully compliant with current standards,” Hedrick says.
“We’ve seen higher CO2 levels associated with increased student absences and poorer performances on school-type tasks,” says study coauthor William Fisk of Lawrence Berkeley National Laboratory in California. “But we never thought CO2 was actually responsible. We assumed it was a proxy for other [pollutants].”
His group recruited college students to spend much of a day in a room with computers. Individuals could read or do what they wanted for much of the time. But for part of each 2.5-hour period, participants completed role-playing tests on a computer that required them to manage an organization as it underwent a series of problems or crises. Throughout each of three test segments, conducted in random order, room ventilation was kept very high. Only carbon dioxide levels varied by segment: 600 ppm, 1,000 ppm or 2,500 ppm.
The role-playing tests are more complicated than most used to measure cognitive abilities, notes epidemiologist and coauthor Mark Mendell of Lawrence Berkeley. But they offer a gauge of important real-world skills, he says. “And the magnitude of effects measured at 2,500 ppm was astonishing — so astonishing that it was almost hard to believe,” he says.
If these trends are confirmed in follow-up studies, Hedrick says, “it would be very strong evidence that ventilation rates need to be increased.” Carbon dioxide standards were developed largely with the aim of controlling body odor, he notes. High levels of CO2 were viewed as suggesting occupancy levels were climbing to where “a place may begin smelling bad.”
Classrooms are fairly densely occupied, he notes, so their carbon dioxide frequently exceeds 1,000 ppm. With an increasing push to reduce heating and cooling costs, “there are plenty of school districts using lesser amounts of ventilation,” he says. “So I would not be at all surprised to find 2,500 ppm in a lot of school districts.”
In fact, “CO2 levels are not that hard to control,” says Jack Driscoll of PID Analyzers in Sandwich, Mass. Building managers just need to measure them on a regular basis, he notes. At the American Chemical Society’s fall national meeting in Philadelphia, he described a new rapid, hand-held CO2sensor designed for classrooms and office buildings.
Citations
J.N. Driscoll et al. Wireless indoor environmental quality (IEQ) monitoring in classrooms and laboratories (VOC's, CO, CO2, and T). American Chemical Society meeting, Philadelphia, Aug. 22, 2012. [Go to]
U. Satish et al. Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance. Environmental Health Perspectives. doi: 10.1289/ehp.1104789. [Go to]
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Here are relevant specs for the Telaire 6004:
- Measurement Range = 0 to 2000 ppm
- Accuracy = @ 72°F (22°C) when compared against a certified factory reference ± 40 ppm + 3% of reading
My design parameters are:
- FANS_ON @ 1000 ppm (0.1%)
- FANS_OFF @ 300 ppm (0.03%)
I'm sure I'll be tinkering with that.
Quote:
Originally Posted by stevehull
A FAR better option... bathrooms... winter humidities... No steam covered windows... no mildew in walls.
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No steam covered windows, no mildewed walls? Maybe your standards are a bit low?
The CO2 monitor is the first part of the project, after I get that going I will integrate a
DH22 (AKA:
RHT03) into the controller to monitor humidity.
Quote:
Originally Posted by stevehull
I looked at CO2... People "believe" CO2 will build up... the use of CO2 as a trigger doesn't cut it.
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People "believe"?
Doesn’t cut it?
Steve, right now I live in a house that I am radically insulating & sealing. I actually have first hand experience with what it is like to not have sufficient fresh air. I don’t need to imagine what it would be like... I am there right now. It is unpleasant, I am not just dreaming up a new project.
Steve, your research would be more interesting if it actually had a bearing on what I am now experiencing.
Do you have any experience with circuit design or software?
-AC