"Carbon dioxide
Carbon dioxide (CO2) is a surrogate for indoor pollutants emitted by humans and correlates with human metabolic activity. Carbon dioxide at levels that are unusually high indoors may cause occupants to grow drowsy, get headaches, or function at lower activity levels. Humans are the main indoor source of carbon dioxide. Indoor levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity. To eliminate most Indoor Air Quality complaints, total indoor carbon dioxide should be reduced a difference of less than 600 ppm above outdoor levels. NIOSH considers that indoor air concentrations of carbon dioxide that exceed 1,000 ppm are a marker suggesting inadequate ventilation. ASHRAE recommends that carbon dioxide levels not exceed 700 ppm above outdoor ambient levels.[15] The UK standards for schools say that carbon dioxide in all teaching and learning spaces, when measured at seated head height and averaged over the whole day should not exceed 1,500 ppm. The whole day refers to normal school hours (i.e. 9.00am to 3.30pm) and includes unoccupied periods such as lunch breaks. European standards limit carbon dioxide to 3500 ppm. OSHA limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes."
from http://en.wikipedia.org/wiki/Indoor_air_quality#Carbon_dioxide

Aprrox. reading for 21:00-21:30 (bedroom windows open slightly through out day till just before sunset) no central heating on
Lounge/kitchen/diner: 1800ppm (no ventilation)
Bed 1 , small double room, 2 occupant 2200ppm (window open on first latch)
Bed 2, box room, 1 occupant 2100ppm (no ventilation)
Bed 3 , main bedroom, unoccupied 1910ppm (no ventilation)
Bathroom, 1850ppm (window open on first latch)

all looking a bit high, any thoughts, other than open some more windows and stick the heating on
cheers

Hi James, Those figures do look very high, it would feel uncomfortably stuffy at about 2000ppm. Also a good idea to look at CO2 over time so you see what's happening - CO2 levels change readily in response to internal and external conditions... for example our attic room fills up with CO2 overnight despite no-one sleeping up there but on a windy night much less so. I use one of the units below hooked up to a PC or Arduino to data log over time so as to get a picture of what is happening. Also, I would expect a reading of low 400's for external CO2? Looking at CO2, especially when refurbishing older properties is very valuable as it is quite easy to reduce the air change rate to below where it should be for building and occupant health without compensating with vents or MVHR.

http://www.airsensor.co.uk/index.php?page=shop.product_details&category_id=1&flypage=flypage.tpl&product_id=10&vmcchk=1&option=com_virtuemart&Itemid=2

Thanks for the info , I'll monitor over a week or so doing what we normally do re. venting and see what levels are .
Got a small HRV I've been meaning to fit to upstairs, so be interesting to see before and after values
06:30-07:00
Outside : 508
Lounge/kitchen/diner: 1780ppm (no ventilation)
Bed 1 , small double room, 2 occupant 2750ppm (window open on first latch)
Bed 2, box room, 1 occupant 2200ppm (no ventilation)
Bed 3 , main bedroom, 2 large occupant 2250ppm (no ventilation) went to 2930 overnight on window sill near bed
Bathroom, 1790ppm (window open on first latch)

Posted By: jamesingramCarbon dioxide (CO2) is a surrogate for indoor pollutants emitted by humans and correlates with human metabolic activity

Hopng not to hijack the thread, but I'd had humidity in mt mind as the best surrogate for all the other pollutants?

May be splitting hairs, but cd help to be clear - why does CO2 have to rely on bulk air movement to disperse?

The prime vehicle for vapour dispersal is not bulk air movement, but dispersal of each vapour present through still air, driven by ea vapour's PVP (partial vapour pressure).

A local concentration of a vapour creates a local vapour pressure that's 'visible' to that vapour alone, and that pressure tails off outward, in other words a PVP (partial vapour pressure) gradient exists, within still air, and molecules of that vapour move outward through the still air, driven by their private vapour pressure gradient. That could be the PVP gradient established between indoors and outdoors, as soon as a window is opened a crack.

Volatility is the measure of how strong the PVP is, at given concentration, for ea vapour substance. Perfume has very high volatility - you can smell it (molecules of it reach your nose) as soon as she walks into the room (or even he - yuk), even without any bulk air movement to carry them.

It must be (I don't know) that CO2 has such low volatility that it's insufficient to drive adequate CO2 dispersal by PVP alone, hence Plan B has to come in - moving the whole array of CO2 molecules bodily within bulk air movement.

Lecture over.

Posted By: Viking House: “Hi James, can you calibrate it for 380ppm outside?”

Trouble is, outside tends to be pretty variable on short time scales and distances. See for example some measurements in Paris:

http://www.realclimate.org/index.php/archives/2007/05/beck-to-the-future/

That's why Keeling's measurements were made on the top of Mauna Loa, not at more convenient locations like his lab in California.

Robur , measurements taken after meter in area for a least 10 minute and straight away, before I get time to pervert reading with breath . Yes i did breath on it to see what would happened, when I first got it , It just said "HI" :) (>5000ppm)

So outdoor still reading 505ppm ( 19:30 )
took it to job today just to check it wasn't misreading
outside was reading 480 ( slight more rural ( Chalfont ))
Internal was reading 550-800ppm , though house was empty all day
Please to say bathroom with single room mhrv I fitted was reading 650-700 first thing , after client had just left.
as was kitchen.

I'm slightly concerned its mis-reading
It's been pretty damp, overcast , all most misty and still , I live next to a moderately busy road .
, perhap it's just because I live in Slough
I haven't noticed stuffyness or poor air , though my wife does/has
As for negative symptom, i always wake up knacker and aching , but then I'm a builder .

I'll monitor for the next few days , see if I can get a better outside reading in fine windy weather
before I worry to much about my indoor readings, might well be misreading.

most rooms at home are currently around 1400ppm

this is the property for those interested ( half done refurb of a 1960s poured concrete council house )
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6234&page=1#Item_29

> @ Sprocket, the COZIR sensor looks interesting, is it expensive?

Hi Rob

I bought three (wanted five but the price put me off)
A bit pricey. £118 each (and add another 20% for vat).
That was for the 5000ppm version including the optional temp and humidity sensor.

They are neat though. Pretty low power (just a few ma every 0.5s to run the LED). The output is plain 9600 baud serial ascii at 3.3V TTL levels; which is not so convenient for me (would have preferred SPI or I2C so I can use the normal serial port on my controller for modbus).

To experiment with it on a PC for now I just plugged it into one of these cables (available pretty cheaply from RS or Farnell).

http://www.ftdichip.com/Products/Cables/USBTTLSerial.htm

Sprocket and others , fancy seeing what your meters give for CO2 ppm outside .
cheers

374 ppm was recorded indoors via 4 calibrated sensors on one morning last week at a visitor centre in Co Antrim which I monitor. This is a rural coastal location about 2 miles ftom the nearest town.

The sensors are used to control ventilation on occupancy. The internal levels have not exceeded 900 ppm, occupancy rates have been at design + 25%. Design ventilation rate is 12 l/s per person.

Ventilation is held off until 450 ppm is reached, then operates at 33%. The next ventilation stages are 600 ppm = 66%, 800 ppm = 100%.

Sent CO2 ppm meter for recalibration as noticed temperature was out and am unsure about CO2 ppm readings, so we'll see what reading i get on it's return.
I've fitted a small single room MHRV unit to bathroom and split incoming air vent to two north facing bedrooms that were not vented at night due to traffic noise and suffered from condensation and mold last winter.
I'll monitor with system on an off once I get the meter back. Already room air quality has noticably improved first thing regarding odours etc. but be interesting to see CO2 concerntration relative to the high reading I was getting 3 weeks ago with no/low night ventilation.

http://gse.cat.org.uk/cpd/pluginfile.php/21/mod_resource/content/1/Airtightness%20and%20ventilation.PDF
http://www.engineeringtoolbox.com/air-change-rate-room-d_867.html

Couple of links re. air changes per hour / ventilation

Energy efficient ventilation in dwellings: A guide for specifiers (Energy Saving Trust CE124)

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&ved=0CDEQFjAA&url=http%3A%2F%2Fwww.beama.org.uk%2Fdownload.cfm%2Fdocid%2F87794827-edc1-410d-a88932d132e89ddf&ei=Usb-UOa3E6iZ0QW9oYDYDA&usg=AFQjCNG5BBh6F1nPfPTFxYTQVLeo1f-EwA&sig2=KLUIlAX5C2ZvYRoa4O5bfQ&bvm=bv.41248874,d.d2k