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.


Daniel

BBC news item today re. why drying clothes indoors has health implications.

Get one of these and read it once a week:
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

Just getting silly now

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.

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.

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.

Posted By: SteamyTeaBeen running one outside under a simple cover

Maybe all the passing cats widdle on it...

Sure - multifoil! If not kept shiny (unlikely), then prob 70% like most other building materials.

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.

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'd be pretty level, surely?

Absolute Humidity looks like this

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.

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.

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.