The cooling effect of a tin shed observatory

[rogerg]

Well, today I actually measured it and hence proved what I've always suspected: My tin observatory significantly cools the air inside when the sun leaves it.

When I came in to the closed observatory it was 34.2 degrees outside and 32.4 degrees inside. After opening up the roof the temperature equalised to the then temperature of 33.6.

It's interesting to actually have measured that the cooling effect is 1.8 degrees in this case.

Does anyone fully understand why this occurs? why does the corrugated Colourbond tin suck the heat out of the shed when the sun leaves it? :shrug:

Obviously the heat is conducted by the tin out, but I'm not sure why that would occur.

Roger.

[Shawn]

Roger, just be careful here, rapid cooling causes moisture, the bane of my life..

[rogerg]

Yeap, at the wrong time of the year it can cause dew on the inside of the walls before the sun has set below the horizon :)

[[1ponders]]

From memory bird (?) did a bit of a spiel on IR irradiance of various metals and coatings quite a while ago (long time ago). If you do a search you might come up with something. I could be wrong with who started the thread but I'm sure bird had some valuable input. It was to do with materials used for scopes and the various degrees of dewing from IR loss.

[ChrisM]

I suspect that thin "tin" walls cool quickly after the sun goes off them because of two factors. The first and most obvious, is because they don't have much thermal mass. The second factor has to do with the sky temperature and radiation cooling.

I bought an IR temperature "gun" from Bunnings when on special for $50-something recently. It's been invaluable in the observatory (still in late construction phase) to measure the temperature of the ground, the concrete floor, the concrete and steel pier, the dome and the "tin" walls. I've also pointed it at the sky numerous times, and have been fascinated by how sensitive the reading is to just whereabouts in the sky I point it. Even small patches of clouds change the reading significantly. During the day, the sky temp is quite positive, but as the sun sets, it plummets, especially if there are no clouds, in which case it has gone as low as -33 degrees C. (on a clear night late last year). Tonight, after a stinking hot day of 45 deg C, the sky temp is -7 deg C, and the ground temp is +24.

I wasn't originally going to insulate and line the observatory walls, but now have. I figure that if I can stop it heating up during the day (with it closed up), there won't be so much cooling to be done after it gets dark. Those parts that are insulated (it's a two-storey job) would, arguably, take longer to cool, but they shouldn't give off their heat very quickly. I plan on having a good flow-through system to aid cooling.

I think that your tin shed interior would cool even quicker if you could circulate the internal air to make use of the tin as a radiator.

Cheers,
Chris

[omnivorr]

" After opening up the roof the temperature equalised... "

says it all , really :P

[astro_nutt]

Hi all!
Having considered what to do with the tin roof of my roll-away ob..I deceided to coat the inside with a few coats of bitumin paint, ( to prevent condensation)...followed by lining the roof with polystyrene sheeting..(check with the local schools if they've received any new whiteboards as the packing foam is perfect!) and glued on with a water-based construction adheisive..
The outside was given a few coats of gloss white acrylic..I must mention that the gable capping has been extended 200mm at both ends to allow any heat build up to escape and to allow better air flow-through...
Cheers!