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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthordhutch
    • CommentTimeNov 2nd 2012
    Its quite clear that they way we are using our house is creating high humidity levels.

    Can you get useful information from a £30 meter from Maplins et al, or are they little more than a gimmick at that level?

    What I would be interested in is to measure the current level in each room, and then work to reduce it, and take qualitative values as I go along. Obviously to a certain extent it is the the qualitative data thats important, at the moment I know there is an issue as we're getting stupid amount of condensation on the windows, frames, and the uninsulated sections of the sloping ceilings to the point its running down the walls, but curiosity would like to but a figure on it if I can for a sensible price.

    • CommentAuthorjamesingram
    • CommentTimeNov 2nd 2012 edited
    I'd have thought a basic humidity meter should do the job.
    You might be interested in this dicussion on internal CO2 levels which are closely link to humidity and ventilation rates

    Also this on Way to reduce condensation in your home http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6773&page=1
    from above :
    Thought i'd do a quick collection of the info offered.

    Key areas are the bathroom and kitchen.
    Use lids when boiling/simmering water/food
    Close doors when cooking/showering/bathing to keep the water vapour in the room
    brush of as much water as possible down before toweling
    Use a window squeegy to get excess water of shower wall/surround once finished( also help with limescale staining)
    Use extractors fans whilst cooking/showering
    or open a window in these rooms whilst doing the above
    Wipe any condensation off windows etc each morning with a cloth and dry outside
    Dont dry washing indoor unless you have to. Perhap use a dehumidifier in specific drying room
    close the toilet lid ?
    do use :
    Thermal blinds
    Pressure cookers
    MHRV/whole house HRV
    Built in wardrobes often get condensation in the back of them.
    ensure that all internal surface temperatures are above the dewpoint for the relative humidity in the house
    Average source, break down -
    45% from showers, 35% from drying clothes, 13% from cooking, 7% from breathing/sweating
    Improve/upgrade you windows
    BBC news item today re. why drying clothes indoors has health implications.
    Due to creating high humidity/moisture content
    • CommentTimeNov 2nd 2012
    <blockquote><cite>Posted By: SteamyTea</cite>Get one of these and read it once a week:
    <a href="http://www.homechip.com/catalog/product_info.php?cPath=21_31&products_id=47" rel="nofollow">http://www.homechip.com/catalog/product_info.php?cPath=21_31&products_id=47</a>

    You will need one of these as well:
    <a href="http://www.homechip.com/catalog/product_info.php?products_id=40" rel="nofollow">http://www.homechip.com/catalog/product_info.php?products_id=40</a></blockquote>

    Or go the whole hog and get a http://www.homechip.com/catalog/product_info.php?cPath=22&products_id=168 and a bunch of http://www.homechip.com/catalog/product_info.php?cPath=27&products_id=71 or http://www.homechip.com/catalog/product_info.php?cPath=27&products_id=182
    - OR (what I did) -
    Get a bunch of http://www.oregonscientific.co.uk/cat-Weather-sub-Sensors-prod-Remote-Sensor-for-WMR100---WMR200.html
    which transmit readings to a http://www.rfxcom.com/receivers.htm#80002

    Both of these allow continuous monitoring like so http:// www.ccandc.org/cgi-bin/env?START=end-3d&END=now
    -- Chris
    • CommentTimeNov 2nd 2012
    Just getting silly now :bigsmile:

    Though as the heating season is about to start I may pop my iButton in a couple of places and retrieve them in the spring.
    • CommentAuthorsavagehk
    • CommentTimeAug 21st 2014
    Apologies for bumping an old thread, but this is something we are interested in doing as well. In particular I'd like to monitor sub-floor humidity and humidity where we are getting damp / mold issues. Any newer advice for me and/or updated links to any of the homechimp links (all of which are now broken?). Ideally we'd have several sensors (at least 4?). Ideally they'd be 'set and forget' sensors sending data back so we can analyse it at our leisure.

    Thank you
    • CommentTimeAug 21st 2014 edited
    I have started to use DHT11 sensors connected to a Raspberry Pi.
    Cheap and easy to set up and seems reliable. Been running one outside under a simple cover for the last month. It logs every 6 seconds and I forget to check it for days, but seems to have always logged. The software that makes it run has built in error checking. It does seem to not read above 95%RH, I did a quick calibration it with some other sensors using a salt slurry mix and it seems to give the right reading (about 75%).

    Here are a couple of quick charts with the readings averaged out to every half hour but charted at the 3 hour interval.
    • CommentTimeAug 21st 2014 edited
    You get enormous swings. A lot of 96%RH every night? What does that feel like?
    Has it been the hot, moisture laden outside air, saturating when going cold indoors at night?
    But recently, cooler outside air holding less moisture, so not saturating when going to same indoors cold at night?
    • CommentTimeAug 21st 2014
    Most nights it is fine, I open a window, get under duvet and sleep.
    But that is the outside RH, eventually I shall set up so around the house, I bought the cable, it is sitting on my bench.
    • CommentTimeAug 21st 2014 edited
    Posted By: SteamyTeathat is the outside RH
    I wonder if it's the general outside air RH, or just the RH of the film of air touching a surface (e.g. your sensor) that's exposed to cloudless sky?

    Because of unbalanced radiation exchange with gas (air) (because of discontinous/spectral emission by gasses) compared with the balanced exchange with liquid (clouds) (full spectrum emission), any surface that 'sees' a clear night sky is over-cooled compared with surrounding air, so forms a condensing surface, hence dew, ground frost even when general air is above freezing, and soggy caravans (they start dying from day 1, as ever due not to leaks, but to copious condensation on their roof undersurface, which can never dry out because of the vinyl wallpaper).

    So your sensor needs a radiation shield (or even multifoil!) between it and the sky - if lacking that, you've been getting over-high RH readings (i.e. always 95%) on clear nights. Actually on clear days too, because the over-cooling still happens even when the sun's shining. But then direct sun's over-heating of your sensor may outweigh the over-cooling, so then you'll get too-low RH readings from the over-hot film of air next to it.
    • CommentAuthorGotanewlife
    • CommentTimeAug 21st 2014 edited
    Posted By: SteamyTeaBeen running one outside under a simple cover
    • CommentTimeAug 21st 2014
    Well, each layer halves radiation - maybe he needs more layers, hence multifoil. I find it hard to believe 95% RH (saturated) for most of every night in summer. His sensor is unnaturally cold, I bet.
    Maybe all the passing cats widdle on it...
    • CommentAuthorEd Davies
    • CommentTimeAug 21st 2014 edited
    Posted By: fostertomWell, each layer halves radiation…
    Or more if the emissivity is low. A shiny metal cover would reduce the sky radiation effect much more than a piece of painted ply, for example.

    (PS, also even if they're black-body layers the ones after the first don't halve, it's more of a 1/n thing.)
    • CommentTimeAug 21st 2014
    Sure - multifoil! If not kept shiny (unlikely), then prob 70% like most other building materials.
    This is an American paper. But the diurnal RH at 2 meters above ground seems to follow steamy's results for medium/wet soils. Graph is on bottom right of page 209. But is an effect of this just the dew we get on grass at this time of year ? I have chickens and most mornings there is some moisture on the grass at 7 AM at this time of year.


    • CommentTimeAug 21st 2014
    I was just testing out the hardware really, was not trying to get accurate readings.
    I should really build a Stevenson Screen (or see if the local Met Office has an old one).

    The point is that it seem to be reliable, the DHT11 are pre calibrated (I think I read this in the data sheet).
    I do think they really need a decent airflow around them when sampling every few seconds, though I could take them out the plastic cover.

    You should buy some, and an RPi, would only cost you a few quid, then you can start collecting your own data. I made a light meter really easily.

    Right it is chucking it down with rain as I type this,
    21/08/2014 21:13:22,12.0,83.0
    • CommentTimeAug 22nd 2014
    Posted By: SteamyTeaHere are a couple of quick charts with the readings averaged out to every half hour but charted at the 3 hour interval.

    It would be interesting to see the chart of absolute humidity. i.e. use the temp readings to convert the RH to a more useful number.
    • CommentTimeAug 22nd 2014
    It'd be pretty level, surely?
    It seems absolute humidity is not recorded as a matter of course. Relative humidity is. This site :-


    gives historical data and daily information. The daily one seems to match what steamy has recorded. I would say absolute humidity varies quite a bit from day to day and over the year. Think of a dry sunny day as opposed to a hot rainy day. It only takes 10's of grams of water per cubic meter of air to give 100% RH.

    • CommentTimeAug 22nd 2014
    Absolute Humidity looks like this
    • CommentAuthorbella
    • CommentTimeAug 22nd 2014
    Perhaps I am missing something important and getting this wrong but - wouldn't one expect RH of the air to rise as the temperatures falls at night? As air is warmed during the day it will be loaded up with moisture in our climate. The cooler night air will have a much higher RH so is 100% humidity that surprising? It looks as though there is a reversal of the graph showing the absolute moisture load of the air in g/cu m i.e.falling overnight as it would do with water vapour condensing when RH is 1oo%.
    • CommentTimeAug 23rd 2014 edited
    One thing that has to be taken into account is the frequency, or how often things happen.
    If the RH and AH is averaged by temperature class, or in English, what is the RH or AH between 0 and 1°C, 1 and 2°C and so forth, then a different picture emerges.
    Because the times of very low and very high RH and AH account for a tiny fraction of the time, are these extremes a problem.
    The chart below may help show what I mean a bit more clearly.
    Also, my data is not really meant to be for accurate weather measurement, I was just testing the hardware and software.
    I may make a 'moving air' sensor, this is just a tube with the sensor in it connected to a fan. This way it can be placed in a position that is totally shaded but still sucks in the surrounding air.
    It also has to be remembered that this is sensing the 'local weather', I would probably get different readings if I moved it to the front of the house. Also, and I am not sure about this at all (but something I would like to investigate one day), I am a couple of miles from the coast, a coast with very large tides, and relatively warm water, so this may be affecting my local weather. Also the topology around here is odd, with hills to the South of me, and the prevailing wind from the SW, a couple of degrees different in wind direction can make a difference to rainfall (I look at wind direction to decide which coast to go to to sunbath).
    The chart.
    • CommentAuthorbella
    • CommentTimeAug 23rd 2014
    ST, can see that the frequency distribution for temperature accords with the temperature graph above so assume this the same data set. But where do the figures for RH and absolute moisture content come from for temperatures below 10 degrees C?
    • CommentTimeAug 23rd 2014 edited
    Posted By: bellaBut where do the figures for RH and absolute moisture content come from for temperatures below 10 degrees C?
    There are a few times that the temperature falls below 10°C, 277 instances out of 167,284.
    This is a problem when using a simple mean as it 'weights' all values equally. That is why I put the the count in.
    If you look at the green line below the RH or AD values you are interested in, you will see that they are virtually at zero.
    The normal way to get around this problem is to add in the Standard Error of the Mean. Or if you hate statistics, just disregard the values you don't trust, politicians and social scientists do it all the time.
    It is also possible that some of these figures came about when I was setting it up, or they were just bad readings, but at 0.1656% of all readings, and for what I am trying to test (if the hardware and software works), I am not concerned.

    The main thrust of this was to see if I could cheaply monitor temperature and humidity, with a reliable system (more reliable than my wireless network as that keeps loosing the connection to the RPi in my shed which is about 10 m away).
    I do intend to wire up some sensors in my house sometime, just finding a way to do it without the wires showing (wiring and hiding 8 or 9 sensors is not easy), but I will probably sample at a much lower rate, probably every minute, so that I can catch showering and kettle boiling.
    • CommentAuthorbella
    • CommentTimeAug 23rd 2014
    OK I'll do what politicians do and ignore temperatures below 10 and above 25 degrees. Broadly, then, for now, one can say that in the temperature range of a South West England summer at the seaside atmospheric RH rose and fell in the opposite direction to diurnal atmospheric temperature changes whereas absolute humidity moved mostly in the same direction but with a tendancy towards lower average values at both lower and upper ends of the frequency curve for temperature.

    Statistics are OK - but electronics (and politicians of course) are something else so hope you arrive at a nice, simple system for monitoring moisture and temperature together.
    • CommentTimeAug 23rd 2014
    Posted By: bellaBroadly, then, for now, one can say that in the temperature range of a South West England summer at the seaside atmospheric RH rose and fell in the opposite direction to diurnal atmospheric temperature changes whereas absolute humidity moved mostly in the same direction but with a tendancy towards lower average values at both lower and upper ends of the frequency curve for temperature.
    Not really.
    All that can be said is that for the duration of this test, with this equipment, at this location and with that post processing, those are the results.

    But yes, I have a simple, reliable and cheap set up. Less than £50 for up to 10 sensors.

    What you can do, without serious calibration, is monitor change. And most people want to know what is changing rather than absolute values.
    This is especially true when dealing with 'one point' data collection.
    So I can see from my data that the temperature goes up and down, the RH goes up and down. This implies that the AH changes too, but not as much as I thought (and probably others thought).
    From this sort of data it is possible to deduce the risk of condensation, if that is your aim, as you are not bothered about condensation at a different location.
    • CommentAuthorbella
    • CommentTimeAug 23rd 2014
    Well, using your averaged data the absolute moisture content of the air as much as doubled with temperature changes of some 6-7degrees. Would it help if the scale used for absolute humidty shown in the last graph (showing the frequency distribution for temperatures) was the same as the one used in the previous graph showing AH - even if this is a "try out" the results are interesting.
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