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Comments
You might be interested in this dicussion on internal CO2 levels which are closely link to humidity and ventilation rates
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9740&page=1#Item_25
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 :
Ventilation
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
http://www.bbc.co.uk/news/uk-scotland-20176376
http://www.homechip.com/catalog/product_info.php?cPath=21_31&products_id=47
You will need one of these as well:
http://www.homechip.com/catalog/product_info.php?products_id=40
http://www.homechip.com/catalog/product_info.php?cPath=21_31&products_id=47
You will need one of these as well:
http://www.homechip.com/catalog/product_info.php?products_id=40
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
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.
Thank you
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.
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?
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.
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.
(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.)
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.
alanbetts.com/workspace/uploads/ec-sem01_betts-1274648223.pdf
Richard
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.
Tom
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,
Date/Time,Temp,RH
21/08/2014 21:13:22,12.0,83.0
It seems absolute humidity is not recorded as a matter of course. Relative humidity is. This site :-
http://nw3weather.co.uk/wx10.php
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.
Richard
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.
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.
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.
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.