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I don't much care for going outside to find out how cold or hot it is. It's no good me calling the time-and-temperature phone number, either, as I live 30 miles from town and at a higher altitude. With that in mind I picked up a wireless remote thermometer at Big Lots for $10 or so. I then needed a good place to mount the remote sensor. Thermometers exposed to the sky will read much too high in the sun and too low when exposed to a clear night sky. Being too close to a building can affect the temperature reading as well. So I decided to build myself a small, simple version of what's known as a Stevenson screen or cotton region shelter. This is what I came up with. So far it seems to be working well.
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First a note on locating the shelter for the most accurate readings: The National Weather Service (NWS) advises that your sheltered thermometer should be
-between 4' to 6' above fairly level ground
-which is typical for your area (sand with a little grass here),
-has good cross-ventilation,
-and which is located 100' or more from concrete or asphalt paving
-and at a distance from the nearest building equal to four times the height of the building. As my house is about 12 feet high, I needed to put the post about 50' from the house. The advertised range for my thermometer is 100', but if you've got a cheap thermometer as I do, I would leave a wide margin for error (i.e. no more than 60' or so).
Now if you live on a small lot in town, you are looking at this and thinking "no way!" This is true if you want to supply data to the NWS. On the other hand, if you just want to know what the temperature is, say, out in your garden, put your shelter there and don't worry too much about it.
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The floor is (thin) aluminum also. While other materials are commonly used--i.e. wood and plastics--the aluminum is easy to work with and appears to be doing a dandy job so far. I'd be interested in seeing what other folks come up with, however.
Some web searching assures me that aluminum has been used for 'official' (as opposed to homebrew) Stevenson shelters--unshaded, at that. Whether those shelters work well is another matter.
The aluminum I'm using is very thin (little mass) and very reflective, so if I remember my physics correctly, it should reflect more heat than it will radiate.
Overall results so far show that the outdoor temperature readout, even on an absolutely clear day, is just about right (i.e. is comparable to my shaded porch). With one exception! Yesterday afternoon was both sunny and still--unusual in this season--and the temperature readout seemed a bit high. I am going to keep an eye on this for awhile longer. If necessary, I'll find a larger piece of roofing. It will, at least, be very easy to replace--make four holes for the bolts and then just swap it out for the current roof.
While I am still unsure of the necessity of more shade, one thing is certain: more shade can't hurt.
Anyways, I like what you've done, just paint the whole thing in a flat white. Believe it of not, white is more heat reflective than shiny aluminium, if you doubt that, take two pieces of shiny aluminium, paint one white, put them out in the sun and the white one will remain noticeably cooler to the touch.
After weeks of tracking the results from my shelter, I've been pleased with the results. On sunny, still days it sometimes reads a little high (1 degree or less, a figure arrived at by shading the shelter completely). I lessened that gap--believe it or not--by closing in the bottom of the shelter with more thin, reflective material (a couple pieces of a foil dog food bag taped into place, though I'll replace that soon). This works because heat is being reflected upwards from the sand. If the shelter was located over grass, I don't think that would be a problem.
I used to work in a medical research organization where they were studying the effect on firefighters of putting out airplane fires in Saudi Arabia. Firefighters wear heavy, flame protective clothing in conditions of unbearable ambient heat along with the heat of kerosene burning. A human can only perform so much hard work in those conditions. In order to do the research they had to know all they could about the heat. They used a box similar to yours but with a broader cover on top to shade the 'can' underneath. Inside they had ambient and water soaked thermometers to measure heat and humidity. They also had a thermometer mounted inside a black, brass ball (they used a painted toilet float). The reason for that was to measure cloud cover. On a cloudy day, the 'black globe' temperature was the same as the ambient temperature. That is important because on a cloudy day the firefighter would not be absorbing radiant heat from the sun. Interesting project.