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TamarackSkies Observatory build pics

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#76 JJK

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Posted 08 December 2013 - 03:49 PM

I like the green also :).

My concern is that stone cladding so close to the end of the OTA will cause worse issues (convection currents) than the other stone/brick/asphalt shingle and driveway that is part of the project - but farther away from the equipment.

I have researched this but can't come up with anything definitive. What I find are discussions about elevating an obs to overcome the "ground effect" of warm earth surrounding an obs. I have elevated this obs above the asphalt driveway and above the stone cladding near the ground and hope this will be helpful. So I worry that I might now "elevate the ground" up to the obs by installing the stone cladding at the obs level.

And I remind myself that I'm not just building an obs where I can give priority to astronomy in every decision. The project is a family vacation home that needs to make everybody happy. I just don't want to do something (else?) crazy dumb at the final stage of the project. This is literally the last exterior decision.


You can look up the specific heats of all the materials near the observatory, and roughly calculate how long it'd take for the daytime heat to be shed from the roof and nearby stone facing. My guess is that the small additional thermal mass of the small amount of stone would be a drop in the bucket compared to the massive roof.

#77 rlandsboro

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Posted 08 December 2013 - 04:29 PM

Thanks for the tip on Specific Heat. Its helping me wrap my head around this, and hopefully its helpful for others. Asphalt and stone have pretty similar values - and asphalt has the higher value. (O.22 btu's per pound for asphalt and 0.20 btu's per pound for stone.) And there are a great deal more pounds of asphalt on the roof than there will be from a little more stone cladding. I think I get the idea that the materials will radiate their stored heat at a rate based on their mass, and not on their thickness.

My concern has been for the air space immediately in front of the OTA. But I'm starting to understand that the issue is not so locally contained.

#78 TCW

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Posted 12 December 2013 - 12:37 AM

As a builder I was wondering what size foundation your engineer specified. A concrete pier that tall would need a massive foundation to be stable enough for a telescope.

#79 stmguy

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Posted 12 December 2013 - 05:52 AM

I'd be concerned that the stone roof would act like a massive heat sink, they make high end wood stoves out of soapstone for a reason.
An aluminum shingle type roof might be a good compromise, it looks a bit like a slate roof and although the metal will heat up it will radiate that heat off very rapidly as the night cools down .
Norm

#80 rlandsboro

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Posted 12 December 2013 - 07:05 AM

As a builder I was wondering what size foundation your engineer specified. A concrete pier that tall would need a massive foundation to be stable enough for a telescope.


The pier foundation directly under the pier is a thickened part of the basement wall. So it its unusual in its shape ( not a traditional cylinder or cube) - but also really big, and serves a dual purpose. The rebar was huge, too. And it did take some extra work during framing to prevent sway at the top of the pier. The pier would not move on its own, but could be made to deflect by pushing horizontally at the top. Happily it appears to be rock-solid now. (Non-scientifically tested by having two 250+ lb workers jump up and down on the floor next to the pier - with no detectable vibration on the pier).

It's hard to answer your question with a specific number since in essence the entire basement wall concrete is the foundation for the pier. I thought the structural engineer did a great job with my unusual site and needs - and she is now reviewing the proposed plan for the final framed transition and anchoring of the dome to the structure.

#81 rlandsboro

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Posted 12 December 2013 - 07:22 AM

I'd be concerned that the stone roof would act like a massive heat sink, they make high end wood stoves out of soapstone for a reason.
An aluminum shingle type roof might be a good compromise, it looks a bit like a slate roof and although the metal will heat up it will radiate that heat off very rapidly as the night cools down .
Norm


I had the same concern. But this project is in a resort community with tight parameters for exterior design and materials - so I could not always pick optimal materials to promote my hobby. I got over it :).

The roof and stone cladding will be a heat sink. So I may need to develop some roof temperature profiles over time to help determine optimal times for imaging. Part of the fun :).

#82 rlandsboro

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Posted 12 December 2013 - 07:25 AM

Just my 2 cents , but it seems like between the roof, the stone cladding on the rest of the house, the stone patio, and the driveway (not sure what material?) you'll have heat radiating out all around you. A little extra stone around the observatory itself won't make much difference. On the other hand, keeping the wife happy will make a BIG difference!

-Dan


Dan, you are a very smart man!

#83 TCW

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Posted 13 December 2013 - 08:20 PM

You will likely needs several hours if not until after midnight until things calm down. My best option is a roof top observatory but I have not done anything due to the heat sink issue. :bawling:

#84 rlandsboro

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Posted 14 December 2013 - 01:06 AM

You will likely needs several hours if not until after midnight until things calm down. My best option is a roof top observatory but I have not done anything due to the heat sink issue. :bawling:


I think you are right about the timing - and I'm OK with whatever it turns out to be. A lot of people do some pretty nice astronomy and imaging from some pretty challenging sites. I started this project with the belief that if you match your expectations, equipment, and targets to the conditions you have - then you can still get good results within the various windows of opportunity and time those conditions give you. But that's another thread :)

If you can determine the windows of time you have when your own conditions stabilize, and what you have when they do - you can make good decisions about committing your time, energy, and funds to a rooftop obs. There are jewels of wisdom in these forums for ingenious and no-cost ways to do this.

#85 Mary B

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Posted 14 December 2013 - 01:47 PM

run a zigzag line of tubing under the stone roof, couple hours before dusk start running cold water through the line to cool the roof.

#86 rlandsboro

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Posted 14 December 2013 - 07:13 PM

run a zigzag line of tubing under the stone roof, couple hours before dusk start running cold water through the line to cool the roof.


That's an interesting thought, thanks.

#87 HunterofPhotons

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Posted 15 December 2013 - 12:17 PM

run a zigzag line of tubing under the stone roof, couple hours before dusk start running cold water through the line to cool the roof.


Really?
Besides being a waste of a resource, what happens if (when) the water freezes in the line?
Are people in Minnesota not familiar with burst pipes? <g>

dan k.

#88 Mary B

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Posted 15 December 2013 - 04:22 PM

:grin:Antifreeze closed system

#89 rlandsboro

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Posted 04 January 2014 - 08:12 PM

Finally getting the dome's base ring installed now. Here is a pic from the ground showing a bit of the rollers and guides

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#90 rlandsboro

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Posted 04 January 2014 - 08:14 PM

Here is another pic showing the framed transition and observatory interior.

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#91 rlandsboro

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Posted 04 January 2014 - 08:16 PM

Here is a pic showing a close up of the rollers and guides. The silver metal is part of the snow melt system. The colored wire will heat the silver metal and prevent snow build up.

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#92 MHamburg

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Posted 05 January 2014 - 06:00 PM

That is a very impressive system. Let us know how it does with the snow which we have too much of already here in the Northeast.
Michael






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