Solar heating of common materials.

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Rusted
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Solar heating of common materials.

Post by Rusted »

I'm not sure where to post this. I didn't want to hijack another thread.

Somebody may find the following useful:
Solar temperature gain and insulation has interested me for many decades.
In my youth it was the fear of global cooling. Now it has swung the other way. :lol:
Our observatories and observing spots are subject to local, solar heating.
Which can spoil the view of the sun due to rising heat tremors. Convection currents.
The local seeing is considered as poor to bad.

There is a very simple and inexpensive test:
Prop some sheets or objects of different metals and materials out in the sunshine.
Size doesn't matter much. This test will shock you at the difference in temperature achieved.
You can use a "pistol" remote reading thermometer. These now cost as little as £10/$10/10€.
One of these handy tools [toys] may save you a trip to the ER or A&E!

I wanted to see which material would be most suitable for covering a dome/observatory walls for solar work.
Note that I am not allowed traditional white. My rural situation would make it far too visible from a distance.
I prefer the anonymity and invisibility of green. Despite the very obvious, thermal drawbacks.
There are temporary measures planned for excluding solar heating.

Objects and sheets of brass, mild steel, stainless steel and copper are easily found and placed out in the sun.
Several will soon be far too hot for human touch.
All my own test samples were "shiny." Shiny [green] fibreglass soon soars well over 100F.
As does [green] painted, birch plywood. Only the plywood cooled rapidly when clouds passed over the sun.

Even the open slit of a cool, white dome can act as a solar collector.
Early solar heating experiments employed simple, open boxes.
If the sunlight falls on black painted walls inside an observatory they will heat up.
They won't even enjoy the cooling effect of a breeze inside a dome.

Beware aluminium, foil-faced insulation!
I bought some after seeing people use it on their mounts. It is anything but cool!

White, lightweight tarpaulins do remain cool. As does white, woven "big bag" material.
This would be a dirt cheap way of temporarily shading hot ground surfaces around your solar telescope.
Or draped on the south facing walls of your roll off roof observatory?

Most of the world's roofs are covered in materials which soar in temperature in summer sunshine.
Which is why those who can afford it will choose a trendy black roof and air conditioning. :lol:
Replacing all the dark, south-facing roofs with white materials could "save the planet!" :shock:
Ask your architect why they insist on a red hot roof surface when you are having bedrooms fitted into the attic.

I have regularly toured builders merchants', open air, roofing displays.
Just testing which material is coolest for a southerly exposure.
We have had attic bedrooms for decades in several different homes and know about unwanted solar heating.

Only pure white, fibre reinforced, corrugated cement sheeting remains cool so far.
After the "Great Danish Storm" of 1999 most damaged roofs were replaced with black.
The misery this must have caused homeowners should be properly investigated as homeowners are bribed to fit heat pumps.
These can be used in summer as very inefficient, air conditioning. This is unlikely to reduce their CO2 burden.


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Re: Solar heating of common materials.

Post by AndiesHandyHandies »

Hi

Just bought some of this. Not tried it yet.

https://www.ebay.co.uk/itm/154277688540

Cement sheet would make a heavy observatory.

Cheers. Andrew.


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Re: Solar heating of common materials.

Post by Rusted »

AndiesHandyHandies wrote: Fri Aug 20, 2021 7:40 am Hi

Just bought some of this. Not tried it yet.

https://www.ebay.co.uk/itm/154277688540

Cement sheet would make a heavy observatory.

Cheers. Andrew.
Good luck with that.
A major paint manufacturer was told to stop advertising its "insulating" paint.
Because it simply didn't work as claimed.

White corrugated cement could be used on a south facing facade or roll-off roof.
It is strong, so needs only a simple, wooden, support structure.
It is considered one of the lightest roofing materials.
It regularly replaces thatch without needing roof reinforcement.

There are also thinner, flat sheets of this material available for wall cladding.
This would need much greater care when fixing to avoid damage.
Being fairly brittle it could crack between screw fixings on corners.


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Re: Solar heating of common materials.

Post by AndiesHandyHandies »

Hi

Oh dear.

Ah cement is not heavy then.

Cheers. Andrew.


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Re: Solar heating of common materials.

Post by Bob Yoesle »

What you're apparently looking for is high emissivity materials - meaning these materials release heat more effectively than low-emissivity materials.

Cool-roof materials and paints are the best for solar work, and are used on most all professional solar telescope protective buildings and telescope structures. I found this quite effective in dealing with poor daytime seeing coming from a standard green metal roll-off-roof: Henry Co. 687 Enviro-White elastometric roof coating rated nearly as good as the DKI Solar Telescope's ACS Acu-Shield paint, way less expensive, and much more readily available at the local Home Depot. It can be thinned with water to a paint consistency and applied in multiple coatings. If I had to do it over again I would skip the meatal roofing altogether and just cool-roof paint the plywood underlayment.

The Cool roof Rating Council figures comparing the two products shows them to be essentially identical in reflectance, emittance, and SRI at 1 and 3 years:

ACS v 687 SRI.jpg
ACS v 687 SRI.jpg (25.02 KiB) Viewed 3064 times

* The Solar Reflectance Index (SRI.) is a measure of the ability to reject solar heat, as shown by a small temperature rise. It is defined so that a standard black (reflectance 0.05 [5%], thermal emittance 0.90 [90%]) is 0 and a standard white (reflectance 0.80 [80%], emittance 0.90 [90%]) is 100. Materials with the highest SRI values are the coolest. Due to the way SRI is defined, especially hot materials can take slightly negative values, and particularly cool materials can exceed 100.
Last edited by Bob Yoesle on Sun Aug 22, 2021 7:34 pm, edited 2 times in total.


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Re: Solar heating of common materials.

Post by Rusted »

Thanks Bob.

Very useful information.

Flexible materials, which show no solar gain, are most useful to the amateur observatory builder like myself. Those who must adhere to local norms [partners and neighbours] for appearance, may be denied permanent finishes. However desirable they may be from a theoretical viewpoint.

Temporarily draping an offending surface or building, to avoid thermal issues, can have great value IMHO. A temporary tarpaulin, as a sun screen, can be rapidly folded and stored in a corner. Or, the back of a dome could be finished in green and parked, to face that way when not in use. While the active shutter side may be a more desirable white. Drop down, white blinds could cover green shutters only when required for observation and imaging.

It is also an incredibly easy way to asses the visual impact of any planned observatory. A mock-up of posts and battens, or even bent, PVC plumbing pipe to simulate a dome, can be draped with a lightweight tarpaulin. Green and white are commonly available at low cost. Each colour will provide an instant valuation of social acceptability in any situation. Preferably before typically large sums are invested in such a structure. Only to become a cause of local hostility.

An alternative might be tall shrubs or conifers in pots. To be easily moved about on inexpensive trolleys. Or even a sack truck. To provide solar shade. Or visual shielding from neighbours' glares.


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Re: Solar heating of common materials.

Post by marktownley »

Rusted wrote: Sun Aug 22, 2021 9:13 am Those who must adhere to local norms [partners and neighbours] for appearance, may be denied permanent finishes.
Totally agree. In a 'deprived inner city area' - where I live, it also must not be something that jumps out at the local 'hoodlums' and 'thieves' as the potential next spot for a burglary so they can raise a few quid selling 'scrap' to get the next fix to shoot up their arm...
Rusted wrote: Sun Aug 22, 2021 9:13 am Temporarily draping an offending surface or building, to avoid thermal issues, can have great value IMHO. A temporary tarpaulin, as a sun screen, can be rapidly folded and stored in a corner.
This is what 've done around and over the pier that's permanently installed in my garden, they form a roof with an eye over it. I'll get some pics up when i'm back home again...
Rusted wrote: Sun Aug 22, 2021 9:13 am An alternative might be tall shrubs or conifers in pots. To be easily moved about on inexpensive trolleys. Or even a sack truck. To provide solar shade. Or visual shielding from neighbours' glares.
In addition to the sun screens careful 'shrubbage' surrounding the perimeter of the pier hides from prying eyes. The pier and mount head (no scopes are left mounted outside) are covered with a tarpaulin bbq style cover held on with bungee cords which to the untrained eye makes it look like a rotary washing line folded down and covered up.


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Re: Solar heating of common materials.

Post by marktownley »

Ok, back home now, and some sun, so the scopes were out. Here's some pics to illustrate the use of 'sails' for screening the scope and surrounding area both thermally and visually.

Pier sits behind sails infront of the greenhouse:

ImageP1010482 by Mark Townley, on Flickr

Gates from the front of the garden - 'nothing to see here...'

ImageP1010493 by Mark Townley, on Flickr

Internally the scope peeps through the gap. Gap position easily adjusted by moving sail anchor points.

ImageP1010483 by Mark Townley, on Flickr

ImageP1010485 by Mark Townley, on Flickr

View from above, shrubs also provide screening...

ImageP1010489 by Mark Townley, on Flickr

Peeping out...

ImageP1010492 by Mark Townley, on Flickr

I'm pleased with the results and 2 sails cost a few tens of pounds... Easy to put up, easy to take down.


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Re: Solar heating of common materials.

Post by Bob Yoesle »

Very nice implementation of screening Mark! And I love the urban green-scaping. :D


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Re: Solar heating of common materials.

Post by marktownley »

Thanks Bob! It's all a balance. In the perfect world I wouldn't have greenhouses anywhere near where I observe from, but it's all a balance, not just my better half, but also neighbours of which I have no control of...


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Re: Solar heating of common materials.

Post by Rusted »

Excellent screening Mark! :bow

The sun can't heat where the sun don't shine. :D


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Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Solar heating of common materials.

Post by Sandrogoewey »

Due to global warming, we are faced with excessive heating of the roof of our houses. This was a problem because, on sunny days, the temperature in the house rose to critical levels. My friend contacted one company, saying that this is the top Indianapolis roof company for you and the roofers offered me a cheap and simple solution to the problem. For these purposes, mineral or glass wool is installed immediately under the roofing material, after the vapor barrier. Thanks to its presence, it can restrain the penetration of heat inside.
Last edited by Sandrogoewey on Wed Sep 07, 2022 6:59 am, edited 1 time in total.


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Re: Solar heating of common materials.

Post by solarchat »

reminder
this is a solar astronomy forum. :)


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