Hi folks
I have a home built Stevenson screen with a fan inside, its now got to that time of year
where the sun hits the screen, it looks like its warming up the temperature inside by about
2 or 3C…
Does anyone have any ideas on how to resolve this please?
Post another photo Simon as that may give people ideas as to where improvements can be made. 
It sounds like you’re in need of a better flow-through of air though.
Hi Martin
Heres another image
On a side note, i go past a road side weather station (county owned i think) and the radiation shield
is virtually green with the rubbish off the trees near by and no doubt road dirt as well, surely this
would have a serious impact on temp readings for that station?
Do you have a double layered roof on it, or is it just a single layer?
If you only have one then it maybe worth putting a second with a 1/2" space between so that the all the heat is taken by the top layer and the top of the screen is cooled by the air gap.
Hi Martin
Yes m8, its a double layered, theres another layer below that top 1
I have a similar solution. (http://www.bartholdsson.com/wdl/info.htm - In swedish)
My thinking is that when the sun hits that part of the garden, it is that part of the garden that is getting hotter.
Anyway going from LaCrosse’s invertid coffeecup to the screen made a big (!) diffrence.
Also, if I had placed the sensor closer to the house, the temp would have been a lot higher (on the sunny side). I have more sheltered places in the garden, which is not as hot and not as cold.
Maybe you could measure the tempereture with another thermometer taking care to keep it shaded outside the box and compare the results. (I guess you’d have test the other thermometer in the screen first, so you know how it compares to your regular themometer.)
Hi
Bashy we said about it ,at another post ,you try to make it
You take PVC tube f 100 ,at top you put the fan to suck air from down sensor side , and to put out the air above ,and in the tube to put the sensor near to fun about 1-2 cm distance .
All the concept it is here .I have tried it with close to me Davis weather station and we have the same almost temps,all the year.
I wonder if it would help to have another ‘oversize’ roof, i.e. some thing that gave a bit of shade to the sides, as well as further insulating the top?
Hi guys…
After looking at my graph today, (pretty much sunny and warm’ish all day)
and the graph shows when when the sun comes up in the morning, not long after
sunrise is when the sun is on the screen, i think its on there until around 10 or 11am
(doh, not gonna be pm is it lol) but anyway, looking at it today, i aint sure if there
is really an issue any more (if there was one) I do have 2 fans in the screen, one on
the internal roof and one at the side, the side one sucks whilst the other blows (dont
say a word) but up till yesterday i only had the roof fan enabled, now there both
running…
So, looking at todays graph (below) its looking quite good, if it was the sun heating it
up 1st thing then once the sun moves away from the screen it would cool down considerably
yes? but it aint doing that, compared to the graph, its a pretty steady rise once its got
over the initial sun up 1st thing, what do you think?
Green is temp, in case ya didnt know lol and 7am is sun out time
Looks fine to me. 
Simon,
Graphs looks good gradual curve to me.
Chuck
Thanks guys, looks like the additional fan has made a difference 
Sadly, I need to sand it all down and repaint it, not quite lasted a year lol
thats my DIY for you
Wel, I just done a test this morning with a extra sensor that i had in the screen
it was showing 0.4 higher than the outdoor temp when sat next to each other
So i put the extra sensor in the shade of the house and it looks like theres a
2.0C difference between the 2, so when the sun is on the screen it is warming
it up, I aint too sure what to do now, I have 2 fans in there, its been freshly
refurbished with about 4 layers of brilliant white (external paint), what more can
i do?
It’s not clear how windy it might have been during your test or how sheltered the ‘shade of the house’ might have been. But it’s perfectly possible in reasonably calm conditions for a parcel of air in a well-sheltered position in the shade to be cooler than a comparable volume of air in continuing full sun. This is what makes it so difficult to run this sort of comparative test with any degree of accuracy and why the only official benchmark of air temperature for many years was the temperature inside a standard-pattern Stevenson screen in full sun; this was the reference reading for official air temperature irrespective of what the shade temperature might or might not have been doing and even though in sunny conditions it would have given a slight over-estimate of the true air temperature.
You could perhaps rerun your test on a fairly windy but still sunny day when the wind should help to mix up the air in different locations and see if this makes any difference.
Two things.
I’m just thinking sheilding the second thermometer close by the stevenson screen might give a different result.
Me too. e.g. The temp in the shade of the house could be influenced by the temp of the house wall, etc., especially if it’s calm.
Edit: I missed prodata’s post, where he made the same point, but with more detail.
Idea…
As a test would it be possible attach (‘dangle’?) your spare sensor just under the centre of the base of the screen - i.e. well in the ‘shade’ of the screen, but not enclosed at all?
Βashy
Do you can to show us with photos inside to screen,how and where you have the 2 fans ,and sensors ,in your Stevenson Screen ?
We will understand better ,how you have it,and to will said you the better solution.
Hi prodata, that makes sense, I will test it again during windy conditions and post the outcome
Hi PHB, no, i aint tried that, not sure what would create enough smoke, i think a car tyre is out
of the question, it wont fit in there lol
Bashy.
Here’s a Scandinavian trick for you.
Get a mushroom - the kind that sits on fallen trees which kind of looks like a roof (Amadou http://en.wikipedia.org/wiki/Amadou).
Cut it into a few peices.
Dry it.
Light in one end.
It will go on glowing for ever, generating smoke.
It is also very good agianst mosquitos.
Originally it is the raw material for the stuff (I don’t know what it is called in English) you light with a stone and steel.
