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Opinions on cinder block walls?

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#1 SnowSailor

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Posted 11 August 2019 - 12:42 PM

I'm looking to build a remote observatory in Arizona sometime in the future and I'm trying to put together a list of everything I'll need and also the costs associated. One of my main concerns with a remote observatory (in a nearly endless list of concerns) is security and durability of the housing. A wooden frame with wooden walls can easily be penetrated by bullets or pretty much anyone that wants to gain access. I know a lot of lighthouses out on the west coast have been shot at since they make very nice targets when they're the only things out in the middle of an open area, so that's where a lot of my bullet concern stems from.

 

My main worry with cinder block walls is their ability to hold in heat from the sun. If they can hold enough heat and dissipate it throughout the night, that could definitely affect my seeing and make it very difficult to get quality images. However, if the heat from the walls will dissipate within an hour of the sun going down (before astrodark hits) then it shouldn't be much of a problem. What are everyone's opinions on this? Are there possible mitigations if the heat could be a problem (such as sheet metal siding to reflect/absorb most of the sun's energy)?

 

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#2 BJS

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Posted 11 August 2019 - 01:03 PM

My local club used to have two observatories...one was a dome with cinder block walls and the other was a post and aluminum sheet building.  We would go into the domed observatory to get warm during cold weather observing.  Cinder block walls will retain heat; and they are hardly bullet proof.  Tough choice when you have to balance local seeing vs security.  


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#3 Eye stein

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Posted 11 August 2019 - 01:19 PM

Hi:

been .in Fla. for many years and you are right, the block has a great deal of mass which takes

some time to cool. Filling the cores of the block with foam insulation helps, but the block has a webs where there is no foam

insulation, so then you use 1+/1/2 thick pressure treated furring strips 16" C/C on the inside of the building and staple

a double foiled product (alfol or fifoil ?) which gives R-5...or ridgid insulation which is stronger and the proper one can be left exposed ,ie.. not covered by drywall.Their are companies which fill the block after bldg. is up..Core-fil?

If you need security that's probably the way to go...

clear skies..

JL



#4 bobzeq25

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Posted 11 August 2019 - 01:19 PM

Consider your house.  On a hot summer day, mine (thin brick siding, mostly) retains heat for hours after sunset.  The less heat capacity you have in your observatory walls, the better.

 

Fans blowing on the cinder block walls would no doubt help, if that's the way you decide to go.

 

Steel siding is a possibility, that may be the best combination of security and heat capacity.  if the issue is someone gaining access, how good would you have to make the door?  Kicking those in is the usual method of breaking into an isolated building.  Thieves are usually not very sophisticated.  Picking a lock may be seen in the movies, but that's rarely the reality.

 

Would an obviously well protected door be simply an attraction?

 

My insurance agent says I'm covered for my backyard observatory.  With the possible exception of the computer, how attractive is astronomy equipment to a thief?  How would they sell it?  Thieves are usually...

 

You might want to consider renting space in Deep Sky West.  Haven't heard of any problems there.


Edited by bobzeq25, 11 August 2019 - 01:31 PM.


#5 rgsalinger

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Posted 11 August 2019 - 01:45 PM

I have an observatory in the desert about 60 miles from San Diego with a warming room in back. The observatory has concrete block walls filled with concrete with some stucco on the interior walls to seal everything up. We have one and only one steel security door to get in/out. (We keep a ladder handy in case of being locked out when the roof is open.)

 

The retained heat has never been a problem for our imaging runs. We don't start until about 90 minutes after sunset and with the roof off the obsy cools quickly. I've got a 12.5" Planewave in there and I think I'd see a problem if there was one. However, it's a big facility - 20x20 with a tiny facility things might be different.

 

Here's a link to an image taken out there (not by me) to prove the point. YMMV.

 

Rgrds-Ross


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#6 dark sky newbie

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Posted 11 August 2019 - 01:47 PM

My house is cinder blocks and the inside continues to increase in temp for hours after sunset. 6 to 7 hours in the hottest part of the summer.


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#7 ShaulaB

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Posted 11 August 2019 - 02:43 PM

We found a bullet hole at the outhouse on some land of ours. The height of the hole was where an average person's head might be while sitting on the throne. There are too many stupid guys with guns. Fires set by vandals destroyed valuable items on our property.

 

After the state troopers busted the folks running a meth lab a mile away from our site, the serious vandalism stopped. Now beer cans and remains of fireworks are what we find after the local kids have had their fun.

 

Perhaps building a concrete block wall, or even a surrounding enclosure, 20 feet away from a plywood-walled observatory would absorb bullets. Heaven help us.


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#8 kathyastro

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Posted 11 August 2019 - 03:05 PM

Masonry of any kind retains heat for a long time.  Our house has a concrete slab floor with in-floor heat.  It takes an hour of furnace time to warm the slab up one degree, and then the heat lasts for 10-12 hours.

 

Cinder blocks won't retain the heat quite as long, but heat retention will still be a problem.


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#9 fcathell

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Posted 11 August 2019 - 03:22 PM

Placing a sign that reads, "DANGER! Toxic and radioactive waste dump" on the outside may help prevent break ins.

 

FC 



#10 SnowSailor

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Posted 11 August 2019 - 05:43 PM

Placing a sign that reads, "DANGER! Toxic and radioactive waste dump" on the outside may help prevent break ins.

 

FC 

Haha I actually considered something like that but I wasn't sure of the legality. It would be on my own land so it probably wouldn't be a problem. Might put up something more tame (and boring) like "US Government Weather Monitoring Station" to hopefully have would-be thieves dismiss it as some boring equipment they wouldn't be able to sell or scrap.



#11 SnowSailor

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Posted 11 August 2019 - 05:52 PM

Consider your house.  On a hot summer day, mine (thin brick siding, mostly) retains heat for hours after sunset.  The less heat capacity you have in your observatory walls, the better.

 

Fans blowing on the cinder block walls would no doubt help, if that's the way you decide to go.

 

Steel siding is a possibility, that may be the best combination of security and heat capacity.  if the issue is someone gaining access, how good would you have to make the door?  Kicking those in is the usual method of breaking into an isolated building.  Thieves are usually not very sophisticated.  Picking a lock may be seen in the movies, but that's rarely the reality.

 

Would an obviously well protected door be simply an attraction?

 

My insurance agent says I'm covered for my backyard observatory.  With the possible exception of the computer, how attractive is astronomy equipment to a thief?  How would they sell it?  Thieves are usually...

 

You might want to consider renting space in Deep Sky West.  Haven't heard of any problems there.

While DSW would be the best choice, I prefer to do things on my own. It feels much more rewarding in the end when you're the one that has to solve the problems and smooth out all the kinks.

 

As for security, yes I was thinking something like a metal/steel door with a good lock. It could possibly make it more attractive, but I would have monitoring cameras/software running to alert me of anyone on the property. It would take someone much longer to break down a more heavily secured door than a wooden one. That, as well as signs mentioning that the place is monitored, should act as enough of a deterrent that it shouldn't be too much of a concern. I would make sure to have it all insured (since it would be $40k in the astro equipment alone and I wouldn't want to risk losing that somehow).

 

I would like to do some tests at home since this observatory is still several years in the future. I can pick up some cinder blocks from a hardware store and build a small wall (without mortar, which shouldn't affect the end result too much) and use a thermal camera to check the temperature after the sun goes down. I can also test the effect of a piece of metal siding placed a few inches away from the wall to provide shade (not touching it to avoid heat transfer as much as possible). If the blocks cool to several degrees above ambient before astrodark hits, I think that should be fine.



#12 SnowSailor

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Posted 11 August 2019 - 05:58 PM

I also am curious about concrete foundations. While the foundation inside the housing would not be exposed to the sunlight, it can still be heated just by the ambient temperature inside the observatory rising throughout the day as the sun beats down on the roof. Perhaps I would want some sort of venting system to allow the hot air to escape so it doesn't end up heating the concrete? I would also assume the ground beneath the concrete can act as a sort of natural heat sink as well. I've done a little research into concrete foundations and the general consensus seems to be that it's fine, but I wanted to get as many opinions as possible.



#13 JMKarian

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Posted 11 August 2019 - 06:04 PM

Best luck I’ve had is with domed fiberglass. So much of the heat gets radiated away due to the intense white gloss.

#14 bobzeq25

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Posted 11 August 2019 - 06:10 PM

I also am curious about concrete foundations. While the foundation inside the housing would not be exposed to the sunlight, it can still be heated just by the ambient temperature inside the observatory rising throughout the day as the sun beats down on the roof. Perhaps I would want some sort of venting system to allow the hot air to escape so it doesn't end up heating the concrete? I would also assume the ground beneath the concrete can act as a sort of natural heat sink as well. I've done a little research into concrete foundations and the general consensus seems to be that it's fine, but I wanted to get as many opinions as possible.

My observatory sits on about 2 inches of crushed rock.  Haven't noticed an issue.  It's shaded and well vented.

 

I took a bit of leftover ridge vent from a recent house reroof, and ridge vented the full length of the roof.  There's plenty of intake, I have no soffit at all.  The most noticeable thing is that the interior is not noticeably hotter than the outside air, in daytime.


Edited by bobzeq25, 11 August 2019 - 06:12 PM.

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#15 kathyastro

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Posted 11 August 2019 - 06:30 PM

I also am curious about concrete foundations. While the foundation inside the housing would not be exposed to the sunlight, it can still be heated just by the ambient temperature inside the observatory rising throughout the day as the sun beats down on the roof. Perhaps I would want some sort of venting system to allow the hot air to escape so it doesn't end up heating the concrete? I would also assume the ground beneath the concrete can act as a sort of natural heat sink as well. I've done a little research into concrete foundations and the general consensus seems to be that it's fine, but I wanted to get as many opinions as possible.

One good thing about concrete is that it warms up as reluctantly as it cools off.

 

If you find that the interior temperature is higher than the outside temperature, ventilation would be a good idea.  If you have a white roof, you will likely find that the inside temperature is lower than outdoors during the day.  Venting would be a bad idea in that case.

 

The temperature inside my dome is usually about half a degree or a degree cooler than outdoors until sunset.


Edited by kathyastro, 11 August 2019 - 06:30 PM.


#16 speedster

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Posted 12 August 2019 - 12:18 AM

Insulation only affects the rate of heat flow.  The amount of heat you have to lose is determined by specific heat and mass.  Low mass has less heat to lose and has faster response.  High mass has much slower response - some times days - to reach equilibrium.  Several variables involved but simplified, 8" block has about a 6 hour thermal lag.  The sun goes down and it's about 6 hours before the wall reaches ambient.  Insulation slows it down to longer than 6 hours.  Fans (convective loss) will speed it up.  Filling block cores with insulation does not speed up equilibrium.  It actually slows it down a tiny bit.  Filling cores with grout (to make it bulletproof) significantly increases lag time.

 

The slab is thermally coupled to the earth below.  There are temperature swings on the edges but the center is pretty immune to diurnal swings.  If sun hits the slab, it's a different story and you're back into lag times similar to block walls. 


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#17 Tom K

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Posted 12 August 2019 - 01:33 AM

In the 80's I did an infrared study on the observatory at SDSU's Mt. Laguna Observatory.  These were block wall buildings with domes and they glowed like mad at night.   It is hard to say exactly whether the thermal currents that had to be coming off of those walls affected seeing (perhaps a thermodynamicist could calculate it), but it is a variable you can control.   How about putting a wood exterior surface on the outside furred out with rigid insulation between the wood and the exterior walls? That should cut down a bit on the heat loading.  You could leave the north side uncovered I would imagine.

 

Block walls are probably the most stable you could get for a ROR for sure.


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#18 SnowSailor

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Posted 12 August 2019 - 02:03 AM

In the 80's I did an infrared study on the observatory at SDSU's Mt. Laguna Observatory.  These were block wall buildings with domes and they glowed like mad at night.   It is hard to say exactly whether the thermal currents that had to be coming off of those walls affected seeing (perhaps a thermodynamicist could calculate it), but it is a variable you can control.   How about putting a wood exterior surface on the outside furred out with rigid insulation between the wood and the exterior walls? That should cut down a bit on the heat loading.  You could leave the north side uncovered I would imagine.

 

Block walls are probably the most stable you could get for a ROR for sure.

I just ordered an infrared thermometer on Amazon and I contacted my local hardware store to see if I could experiment. They said I could buy some cinder blocks for a wall, do some tests, and then return them as long as they didn't have mortar on them and they were still usable. I will test both sheet metal siding as well as wood siding to see what works best (and if either of them prevent the accumulation of heat within the wall enough). I'd imaging wood is cheaper, but also a little more prone to warping and general decay even when treated.


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#19 Galaxyhunter

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Posted 12 August 2019 - 06:31 AM

Steel w/ an air gap would be your best bet on the outside of your block walls.  I have checked my steel roof just before Sundown and it was basically the same as the ambient temp.  If you build the observatory  with steel walls, you MUST use some type of radiant barrier with a air gap plus vents.  Just think of a steel building as an oven heating up your observatory contents. My observatory is wood framed, steel roof w/ a radiant barrier and concrete flood, & it's almost always 8 -10° cooler then the ambient temp.


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#20 dark sky newbie

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Posted 13 August 2019 - 10:38 AM

  Filling block cores with insulation does not speed up equilibrium.  It actually slows it down a tiny bit.  Filling cores with grout (to make it bulletproof) significantly increases lag time.

This makes me think...

Since the holes in the block overlap, perhaps vents along the bottom and a fan in the roof would greatly increase the cooling if you leave the tops of the walls open as much as possible. Pulling the air through the center of the walls might drop the temp fairly quick.


Edited by dark sky newbie, 13 August 2019 - 10:42 AM.


#21 Galaxyhunter

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Posted 13 August 2019 - 12:18 PM

This makes me think...

Since the holes in the block overlap, perhaps vents along the bottom and a fan in the roof would greatly increase the cooling if you leave the tops of the walls open as much as possible. Pulling the air through the center of the walls might drop the temp fairly quick.

That would help, although it would take quite a few vents. The down side to leaving the top of the wall open is it provides  bees - wasps & other undesirable critters a condo.

The best & most efficient  way to cool an observatory it to minimize the heating effect in the first place. It really doesn't take a Rocket Scientist to figure out that the less something heats up - the less that is needed to cool off.   If you do use block for your wall, do some research to find paint that will reflect as much of the Suns energy as possible. 



#22 kathyastro

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Posted 13 August 2019 - 01:54 PM

This makes me think...

Since the holes in the block overlap, perhaps vents along the bottom and a fan in the roof would greatly increase the cooling if you leave the tops of the walls open as much as possible. Pulling the air through the center of the walls might drop the temp fairly quick.

"Fairly quick" is a relative term.  It would certainly speed it up considerably.  I wouldn't hold my breath waiting for the walls to cool down, though. ;)



#23 dark sky newbie

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Posted 13 August 2019 - 04:40 PM

"Fairly quick" is a relative term.  It would certainly speed it up considerably.  I wouldn't hold my breath waiting for the walls to cool down, though. wink.gif

Well, I view through a Mak Cas, so I'm used to waiting.


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#24 rgsalinger

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Posted 13 August 2019 - 04:57 PM

Well, I still have a concrete observatory that sits right now in 98 degree heat as usual in the summer. We have no trouble getting great images from there. There are two other similar observatories in the same row and they seem to work just fine as well. You don't have to have your observatory walls cooled to ambient in order to image. I can understand that there "could" be some issue but my experience is that there really isn't. I imaged for a while in an even smaller one (again cinder block filled with concrete) in Benson Az. in the summer. No issues. 

Rgrds-Ross



#25 Galaxyhunter

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Posted 13 August 2019 - 08:18 PM

I would imagine that location has a great part of the effect. I had this discussion with one of our moderators & he told me that even a 2° difference between the ambient temp & the temp of your concrete slab will make a difference. Maybe if you are on top of  Mauna Kea in premo conditions that might be true.  For me in the Mid West at an elevation of 762', where 75' behind my Observatory starts miles & miles of farm fields, a couple of degrees don't mean squat.  A few people with rooftop observatories never seem to report a problem.




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