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Effect of Insulation on seeing

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#1 Stan G

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Posted 05 July 2020 - 11:19 PM

I know that walls of an observatory should not be insulated so that the inside of the observatory can reach ambient temperature as quickly as possible. Without going into the reasons why I want to insulate the walls (with R-19 insulation for 6" thick walls), just how much of a detrimental effect would this have on observing, imaging, etc.? Does anyone know if insulating the walls would result in just a mild degradation in the image, or a big one?

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#2 OldManSky

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Posted 06 July 2020 - 07:40 AM

Personally, I'm not convinced insulation will harm the time-to-ambient much or at all for a roll-off-roof style.  As soon as you open the roof, cool air will flood the space, and insulation or not on the side walls won't make much difference.

For a dome -- sure.  Much more limited exposure to the sky.  

 

In my little ROR, it's only insulated on the roof (mainly to keep the hot roof heated by the sun from transmitting all its heat to the inside).  Once I roll off the roof, my scopes acclimate to ambient pretty quickly -- always within 30 minutes.  


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#3 mark77

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Posted 06 July 2020 - 08:00 AM

My dome observatory is insulated,

 

As I understand the issue it is about heat retention.  There was a real good thread over a year ago about this very subject, I looked but cant find it.

 

If you have a roll off roof, then the warm air can get out right away.  With a dome, this can be a big problem.  I solved it by having fans that blow out the back and therefore suck air down through the slit.  I proved that it worked by putting ribbon on the slit door to see if air was actually moving and it was.

 

There has been quite a bit of discussion and varying view points on if the fans should blow in or out.


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#4 kathyastro

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Posted 06 July 2020 - 08:10 AM

I chose not to insulate my dome.  I find that the interior temperature tends to lag the outside temperature by two degrees or so, both warming in the daytime and cooling at night.  Insulation would increase that lag.  I can set up my software to automatically open the dome shutter an hour or two before the session and slew the opening away from the Sun.

 

If you have a ROR, the effect of insulation would be minimal.  The biggest effect on interior seeing would be if you had a concrete pad as the floor: it could retain heat for hours.


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#5 mark77

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Posted 06 July 2020 - 10:50 AM

I agree with Kathy on a dome like hers.  It is just a dome, no warm room etc.

 

My setup is much more complicated.  The observatory is the 2nd story of a 24x24 foot shop. (in the words of George E. Hale, "No observatory is complete without a machine shop").

 

I have the ceiling of the downstairs very well insulated and I have the outside walls of the upstairs insulated to keep the heat OUT in the summer.  It actually does a real good job of that.

 

Last winter I was able to see a 20 degree F difference between the downstairs and the upstairs with the dome closed.  With the dome open, the inside was very near the outside temperature because of the exhaust fans.

 

I think the answer is that if you insulate, be prepared to install exhaust fans as well.

 

Mark



#6 Allan Wade

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Posted 07 July 2020 - 06:49 AM

For a ROR or Dome observatory? I’ll speak of a ROR because that’s my experience. It makes no difference at all to the seeing if you insulate the walls. As soon as you roll the roof back both sides of the walls acclimate quickly to the ambient air. 
 

My obs here in Australia is subject to very hot days in summer and full insulation was a requirement, along with climate control with the air conditioner.


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#7 speedster

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Posted 08 July 2020 - 04:52 PM

Normally no degredation at all.  When the lid comes off, either ROR or dome, cooling is a function of mass.  Think of opening the lid on a cooler.  Inside temp hits ambient in just a few minutes whether the cooler has 1" of foam or 10" of foam.  Insulation adds some mass so does slow cooling but to put it in perspective, an observatory wall with wood siding and sheet rock interior has a mass of about 3.25 pound per square foot.  R-19 batt adds 0.24 pounds.  Very little.  In comparison, 3/4" glass has a mass of ten pounds per square foot so it's pretty safe to assume your walls will reach ambient before your optics.  A lot of other factors but you get the idea.



#8 SeymoreStars

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Posted 08 July 2020 - 04:59 PM

I too have 6" walls which changed my 12'X16' into an 11'X15' observatory. The walls are not insulated, providing much needed shelf space.


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#9 Jeff B

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Posted 08 July 2020 - 05:41 PM

With my uninsulated observatories, the interior temperatures were always a good 10 degress warmer than ambient, if not more, due to the solar thermal radiation load.  I could literally feel the heat radiate from the interior surfaces.  This was a thermal disaster for all of my instruments.  Modifying one of them with extensive wall and ceiling insulation resulted in the interior temperatures lagging high sun ambient by a good 5-6 degrees, sometimes even more.  This made a huge difference at sunset when the roof was opened, with the scope at or a couple of degress below ambient, even in the winter.  This resulted in no optical/thermal issues, making the scope immediately useful, and giving it a head start with falling ambient temps.   

 

Since then, all of my observatories have been super insulated, including one with a dome. 

 

That's my direct experience.  

 

Jeff


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#10 KLWalsh

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Posted 08 July 2020 - 10:26 PM

I insulated the South, East, and West- facing walls plus the South-facing half of the ROR because the solar load was making the interior so hot in the Summer it was taking a long time for the interior to reach outside ambient.
I left the North side un-insulated.
Overall the insulation was a huge improvement.
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#11 tedbnh

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Posted 29 July 2020 - 05:36 PM

With my uninsulated observatories, the interior temperatures were always a good 10 degress warmer than ambient, if not more, due to the solar thermal radiation load.  I could literally feel the heat radiate from the interior surfaces.  This was a thermal disaster for all of my instruments.  Modifying one of them with extensive wall and ceiling insulation resulted in the interior temperatures lagging high sun ambient by a good 5-6 degrees, sometimes even more.  This made a huge difference at sunset when the roof was opened, with the scope at or a couple of degress below ambient, even in the winter.  This resulted in no optical/thermal issues, making the scope immediately useful, and giving it a head start with falling ambient temps.   

 

Since then, all of my observatories have been super insulated, including one with a dome. 

 

That's my direct experience.  

 

Jeff

Jeff, how did you insulate your dome?  I have an 8' Explora-Dome here in Arizona, and I'd love to insulate under it to keep the daytime temps down.

Ted



#12 Scott Horstman

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Posted 29 July 2020 - 06:55 PM

 

 

If you have a ROR, the effect of insulation would be minimal.  The biggest effect on interior seeing would be if you had a concrete pad as the floor: it could retain heat for hours.

Insulation such as "Reflectix" radiant barrier in the roof of a roll off has proven effective to reduce heat build up. The above post is a little misleading as concrete floors tend to hold the ground temp beneath and are cooler overall than a wood deck. It's not like your driveway out in the sun all day building up heat. In cold weather it is a good practice to have a fan blowing on the scope and mount to deter condensation. Personally I run a heater fan set to the lowest heat setting aimed at the mount when the dew point in a concern. I haven't seen a need to insulate but ymmv.



#13 Stevegeo

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Posted 29 July 2020 - 07:18 PM

My dome observatory is uninsulated as well , and I have two thermostatic fans  one in, one out when it gets to hot inside .  Opening  up the shutters during sessions an hour or so before equalizes the inside outside temp, and my C11 .

This summer with outside temps in high 90s the scope  the fans mitigated a lot of the temp swing . 

 

I am considering another 4 in fan to circulate air across the dome, pointed up at my C11 base for additional cooling .  But that's another day ...

 

Stevegeo,  

 


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#14 Galaxyhunter

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Posted 29 July 2020 - 07:49 PM

Insulation such as "Reflectix" radiant barrier in the roof of a roll off has proven effective to reduce heat build up. The above post is a little misleading as concrete floors tend to hold the ground temp beneath and are cooler overall than a wood deck. It's not like your driveway out in the sun all day building up heat. In cold weather it is a good practice to have a fan blowing on the scope and mount to deter condensation. Personally I run a heater fan set to the lowest heat setting aimed at the mount when the dew point in a concern. I haven't seen a need to insulate but ymmv.

Absolutely on the money.    I have "Reflectix" under my steel roof with a 3.5" vented air gap.  My Observatory temp is normally 5-10° cooler then the ambient temp.  My concrete pad is the coolest part of my Observatory.

 

The less heat you allow into your Observatory, The less you need to bleed off at night.


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