observatory walls

[cristian abarca]

Hi everyone I'm building a 4 x 4 metre observatory on a concrete slab with a concrete pier (seperate from the slab). It will be timber framed to support a geodesic dome. I'm looking at the type of cladding to use and whether or not to use insulation or line the walls. Is the idea to keep the inside temperature the same as the outside and/or will the temperature difference affect the telescope. The observatory will be used primarily for photography. Any advise would be appreciated.

Cristian

[Terry B]

I just used second hand colourbond sheeting with the corrugations horizontal. This is suppose to create a little shadowing when the sun is high reducing the heating slightly. I haven't lined the walls. It cools off very quickly. Insulation might slow down the cooling off. Professional observatories refrigerate the inside during the day to beat the cooling off. This is a bit over the top for a little observatory.

[Ian Robinson]

Air refrigerating the observatory during the hot days of summer is an idea.

Wouldn't be hard to do , all you need is 240VAC to the observatory and one of those small window mounted refrigerative airconditioners (0.5 HP), cut a hole in a convenient wall install a power point with a timer (to turn it on during the daylight hours) , direct the airflow at the slab , and hey presto .... one nice cool (or cooler) observatory slab at night.

Something I might do if I settle on a concrete slab , I happen to have an old window mounted airconditioner that used to live in a hole in the main bedroom wall (until I upgraded to a 2.4 HP split reverse cycle to cool / heat the entire house and insulated my walls when recladding, and insulated the ceilings).
It still works too despite being 30 years old, I recently powered it up and was pleased it still works (pays to hold onto these kind of things when they become redundant), was considering partitioning and lining and insulating part of the double garage for use as a study and cooling it.
Since changed my mind - I desire a permanent home for my telescopss more.:D

corrugations horizontal idea , more likely the corrugations orientated horizontally enhances turbulent air flow rather than the laminar airflow you'd get if the corrugations were orientated vertically (or you had a non-corrugated sheet of metal, I'm a bit rusty on convection cooling under laminar and turbulent flow conditions) , a higher Stanton number due to turbulent air flow (the air has to rise boyantly over a longer length of metal (higher velocity wrt the metal) results in a higher rate of heat transfer).

I am not sure if sufficent shadowing of the metal surface by the corrugations on a vertical sheet whith corrugations oriented horizontally will really have that much effect, the radiant heating by the sun would see essentially a vertical sheet of metal (though the view angles would vary some being very close to parallel with the sun's rays, some not.
Also as the surface of the metal warms , thermal conduction will even out the lit side of the shed's wall's surfaces temperature considerably too.

[cristian abarca]

Thanks guys you've answered my questions. Colourbond cladding with no insulation or lining it is.

Cristian

[Michael Clark]

Cristian,
Remember to let your concrete dry and you shoulds really seal it as well to keep the dust down and also to stop moisture coming through and condensing on the inside of the dome and dripping onto your equipment, yuk!

cheers
Michael

[Ian Robinson]

Hadn't thought of that .... :thumbsup:

The same stuff as you paint on to sealing concrete floors prior to tiling them ?

[rogerg]

That's what I'd go with. I insultated half my colourbond observatory (the enclosed half) and can say quite definitely that if you want good cool down time colourbond without insullation is the way to go, acts like a fridge once the sun leaves it in the afternoon :thumbsup: ... insullation messes that up, doesn't cool down all night... good in winter or me, bad in summer for me and the scope.

[GrampianStars]

I went with just the foil
under the west and north walls and the roof :thumbsup:
you won't regret it
radiant heat :mad2: is considerably reduced & does not get into the obs as much

[Terry B]

I have foil sarking under the roof iron but none on the walls. There is lots of airflow around the roof for me and it doesn't get wet. The only problem is that it let those anoying mudwasps in and I have to wrap the scope in a sheet to stop them building nests.

[rmcpb]

My scope storage shed has an insulated roof with large eves to shade the walls, as well as shrubs to protect them. Cools really quickly in the evening but doesn't get the spike in the day time so the cooling time is reduced.

[Terry B]

I'm sure it can be done but I think the cost of running an aircon to keep a little shed cold all day long to save ~30mins of cooling time with a small mirror is a bit extravagant on green house gases and the electricity bill. OK if you have a 1 tonne mirror that would never cool doen otherwise.

[Ian Robinson]

It's the concrete slab that would be the heat sink that would need help .

But you are right, a tad extravagant , but an option , and you'd have a nice cool astronomer.

[cristian abarca]

Thanks again guys

Cristian