Cooling the observatory

[I.C.D]

G'Day All,
Well I have finally finish the observatory (will post some pic)and have sort of move in, still finishing off the inside .Though I have insulated the inside it still get's very hot inside .What can we I do to keep the temperature down any ideas
Ian C :help::question:

[sheeny]

Passive stuff would be things like double skin the roof, so there's an air gap between the top skin and the roof you have now. What sort of obs do you have? Roll off roof or dome?

If you want to be a little less passive, what about a solar exhaust fan? I was considering one for my POD but I see the links to the solar fans are gone from the POD website, so I guess the opinion is the dome covers they sell are more effective. Google for 12V solar exhaust fan. There are some good options in the range of $90 to $170 for fully self contained solar panel and fan extractors.

Of course, there's always the brute force method of installing air con...

Al.

[kinetic]

I'm in a semi unique situation to most Roll Off Roof type Obs
and Fibreglass shell type Obs.

Mine is made of foam, so unfortunately it works just like an
esky. It takes a while to cool down. I help it along
with a few brute force fans as Sheeny suggests.
Usually, if the night is looking good the doors will be off the Obs
several hours before the session anyway.

In summer it's usually a double edged sword...insulates well from
the heat of the day but takes longer to cool if the temp drops
after sunset.
I have only really noticed any dome temp probs when imaging in all
seriousness during high F.L. imaging of planets. And that has
only ever been during winter months anyway for Mars apparitions.
2003-Jul-Sept, 2005 Sept-Oct etc.
I found having a coffee or monitor on in the dome while doing that
actually affected the scope performance more than any dome type
temp differential.

Without fully understanding the theory myself, I'd guess that probably
the worst thing you may want to do is in fact insulate an observatory.
Keep the ambient cool down time to a minimum?

FWIW.

Steve

[Ian Robinson]

Based on my many years of engineering I'll only insulate the roof when I build my observatory , will use insulated roof sheets , I think insulating the walls of an observatory is a big mistake .... you want the walls to have minimal thermal mass and minimal thermal inertia and to not retard cooling of the interior in anyway.
Insulated roof sheets will stop a lot of the heat from radiating into the interior.



A small window mounted 1/2 horsepower a/cond mounted through a wall will do the trick .... when I build my ROR shed , that'll be my plan .... I've an old Kelvinator 1/2 horse that used to cool our main bedroom before I bought the big Fugitsu 2.4kW split unit and retired it.

Was more than adequate for our big bedroom , so will work a treat in a 4m x 3.2m shed.

You can also get portable a/con units on wheels , they be OK too.

[astro_nutt]

What about a whirly-vent? they do a good job extracting hot air and cost nothing to run.

[leon]

Put a fly, no, not a real fly but a canvas or blue tarp a few inches above the existing roof for air flow, it makes hell of a difference, I have one on mine all year round.

leon

[alan meehan]

I have a whirlybird on top of my observatory and it works a treat ,then i think leons idea of a 2nd skin is a good idea as well

[PeterM]

My observatory is a 3x3m Metal shed, so had to do something or would have fried in there.
On the western wall I changed the facade to look like a western red cedar shed with silver foil in between the timber and metal wall.
On the north facing wall I have heavy duty shade cloth that can be rolled up like a blind when not needed. I also lined the inside of the shed with batts inbetween the north & west walls.
For the tin roof I bought a can (app $60) of Silver Ormonoid bitumen paint from Bunnings - this stuff is great, some of the guys use it at Leyburn and it gets very hot out there. I put 2 coats of the stuff on the sliding roof and I also used some 1 inch thick freezer (white foam) on the underside of the roof - I tried gluing this but it kept coming off so ended up screwing from below into the metal roof with large washers stopping the foam from pulling through. I also sealed the top of the screws that slightly poked through the top of the roof.
I also put a small ceiling vent into the sliding roof - they can be bought from caravan spare parts places. I have a locally purchased solar powered vent but haven't got around to installing that yet.


Has made a huge difference to the temperature inside.

PeterM.

[Ian Robinson]

Can make a big difference to how heat is absorbed by the roof and walls by :

- painting them white (make sure it reflects well in IR range too)
- buying galvanised metal sheets and installing them as is. (not terribly good)
- shading the east , north and west walls (put the shed close to north fence, or grow some greenery along the walls .... plenty of fast growing natives that'll do the trick.
- insulated roofing sheets (like are used for patios) with integrated foam insulation are a great choice too , most your heat will come in via the metal roofing sheets , is reradiated to the interior of the shed (my double garage is a hot box in summer when closed up because the roof , though galvanised) is not insulated.

Eric's double skin roof idea is also worth trying (especially if you have an existing shed which would be expensive to modify).

[Quark]

Hi All,

A very interesting thread.

I note the original subject was "Cooling the observatory", interesting.
However this does raise a few points that, I think, are not that well understood.

In the first instance, I believe, it is imperative to construct amateur observatories that very readily conduct heat. It is vitally important that the observatory structure, as best as is possible, follow the ambient temp. I think Kinetic "Steve" makes this point very well.

The more insulation that is used the greater the lag in the reaction of the structure to the rise and fall of ambient temp.

Obviously, during the day in hot weather, if direct sunlight can be shielded in some way, then it would be of some benefit. Also if there is abundant vegetation, garden, surrounding the observatory rather than concrete or other man made structures having varying thermal properties, then this would also help, especially early in the night.

In my opinion one of the best design features is maximizing the airflow through the observatory, but in a way that is adjustable. The whole idea of having an observatory is to provide shielding from the wind and extraneous light sources. Having the ability to have forced air circulation for a couple of hours prior to observing or especially very high res planetary imaging is a good thing.

I think thin metal cladding provides far and away the best thermal properties for an observatory, it may be hot during the day but as the ambient drops through the early hours of the morning, it will result in far less of a temperature differential between the ambient air and the structure.

Regards
Trevor

[mozzie]

al ive the solar fan in mine there a great idea and possibly do keep the temp down but i think the amount of hot air that acculiminates in the pod is to great for the little fan 48deg in it today and its a stinker outside haveing all the trees around me lets me have dark skies but the breeze strugles ive opened the door and put the fan on inside blowing the air out the door drops the temp quickly im considering some type of cover over as mentioned in this thread that air gap is needed im a little concerned that the temps may get a little high for the gear
mozzie

[PeterM]

If it is hot outside it will be hot inside (unless you air condition the observatory) the trick is not to let the observatory get hotter than outside and just insulating the internal walls will not be enough. My observatory is always 5-8C below the outside temperature from the methods I employ.
In a roll off roof observatory or the like, it will take very little time for the telescope to reach ambient temperature once the roof is rolled back. The idea of using shade cloth drop downs on the north, west (and probably east) works wonders - try it you will be amazed. A thought comes to mind that this could also be done over the roof with little cost and certainly more appealing than a tarp stretched over it. Also especially makes sense to roll the roof back just after sunset so by the time you are ready to observe you should have no issues whatsoever. I never have any issues with mine. A dome slit on the other hand acts like a chimney and takes a long time to release trapped heat (probably retains much heat regardless of what you do) and you will be observing through this, making it vital to look at every other possible means of cooling. Shrubs and gardens around the structure certainly help.
At Leyburn some of the caravans have "tropical roofs" a second skin (as noted in a prior post) that allows the air gap and again works wonders, but on a roll off roof adds lots of weight - try the dark green shade cloth, I will bet it does exactly the same.

PeterM.

[bloodhound31]

I just open up the dome and put a pedestal fan on for an hour or so before imaging. That brings all the hot stuff on the inside back down to ambient very effectively.

Keep it simple.

Baz.

[pmrid]

Mine is a roll-off so what I do is roll the roof back a couple of feet for a couple of hours before dark to let the breezes tunnel their way through the obs. It acts as a sort of funnel, almost a big venture, and sucks the hot air out. Also, I have glued a heap of double-sided aluminium insulating bats to the inside of the ceiling and on north and west-facing walls. That also breaks quite a bit of the heat down.
Peter