Observatory cooling...

In the current hot weather my roll-off observatory has reached new
record high temps. Today everything was very warm to the touch and
there was a distinct odour of hot rubber. It's been a huge bonus to
leave everything set up or stored in the observatory but now I'm
worried that the temperature is too variable after all. Could it damage
my scope or CCD accessories?

What range of temperatures is your equipment (happily) coping with in
your observatory?

Or is active cooling recommended? How? Vented fans or something?

Thanks
A slightly worried Beats

justbeats wrote:
In the current hot weather my roll-off observatory has reached new
record high temps. Today everything was very warm to the touch and
there was a distinct odour of hot rubber. It's been a huge bonus to
leave everything set up or stored in the observatory but now I'm
worried that the temperature is too variable after all. Could it damage
my scope or CCD accessories?

Mainly by plasticiser vapour pressure being higher at elevated
temperatures and plating out on cooler surfaces. Like the inside of car
windscreen gunge effect.

What range of temperatures is your equipment (happily) coping with in
your observatory?

I am still agonising about it. Front garage door currently is above 60C
facing into the sun and my LCD thermometer strips (from RS) max out at
that!

Or is active cooling recommended? How? Vented fans or something?

Not until you have used up all the tricks for passive cooling first.
The one I found most effective was to use the foil backed polystyrene
on the inside surfaces of sun facing parts of the structure S & W and
roof. This slows down ingress of heat significantly.

Some mechanism to let the hottest air out of the top without letting
dust or rain in might be worth considering too. I don't have this.

Ideally you want the outside painted brilliant white with the highest
loading of white pigment you can find. After that shading strategies to
cast shadows onto the structure are worth considering. Desert plants
use this method.

Effectively putting a Stephenson screen on the S side to shade the
structure.

Or a thin outer second skin with an air gap and free air movement
behind it. Really only needed in mid summer in the UK. Problems arise
if you live in a windy place like I do. Greenhouses blow down regularly
in winter storms up here.

Regards,
Martin Brown

Martin Brown wrote:

The one I found most effective was to use the foil backed polystyrene
on the inside surfaces of sun facing parts of the structure S & W and
roof. This slows down ingress of heat significantly.

"Celotex" very expensive in B+Q, but similar from Travis Perkins.
Polystyrene is horrible, it might not burn these days, but it would drip
molten plastic in a fire. Celotex doesn't.



Some mechanism to let the hottest air out of the top without letting
dust or rain in might be worth considering too. I don't have this.

Greenhouse vent ? The wax powered piston jobs.

Steve

Thanks for the responses guys...

I considered using insulation when building the Zerba Tree but decided
against it in the end. It would delay warming for sure, but would also
slow the cooling process, removing a key benefit of having the scope
permanently set up in "near ambient" conditions.

I like the greenhouse vent idea - nice and simple. I'll install a
couple this weekend. Be warned; if it works then the remainder of the
summer will be unseasonably cool :-)

Cheers
Beats

Steve Taylor wrote:
Martin Brown wrote:

The one I found most effective was to use the foil backed polystyrene
on the inside surfaces of sun facing parts of the structure S & W and
roof. This slows down ingress of heat significantly.

"Celotex" very expensive in B+Q, but similar from Travis Perkins.
Polystyrene is horrible, it might not burn these days, but it would drip
molten plastic in a fire. Celotex doesn't.



Some mechanism to let the hottest air out of the top without letting
dust or rain in might be worth considering too. I don't have this.

Greenhouse vent ? The wax powered piston jobs.

Steve

justbeats wrote:
Thanks for the responses guys...

I considered using insulation when building the Zerba Tree but decided
against it in the end. It would delay warming for sure, but would also
slow the cooling process, removing a key benefit of having the scope
permanently set up in "near ambient" conditions.

No, you are isolating it FROM daytime ambients, for as long as possible.

Insulate heavily, like the big boys seem to do, then put a big fan in
shed wall to pull ambient air in, when internal external temp.

Steve

Steve Taylor wrote:
No, you are isolating it FROM daytime ambients, for as long as possible.

Insulate heavily, like the big boys seem to do, then put a big fan in
shed wall to pull ambient air in, when internal external temp.

Hmm, good point.

You're maximising the thermal inertia of the system (scope plus
observatory) while I'm minimising it (on the premise that I only use it
at night after it's had time to track falling ambient temperatures and
cool sufficiently anyway).

Worth noting that I've had no problems with SCT cooldown. The scope is
always ready for immediate use with no tube currents apparent. The real
issue (potential new problem I need to solve) is the temperature on
very hot days MAY be rising too high.

I'm sure your suggestion will fix that - but with costs for insulation
and fan.

Greenhouse vents could fix it too - probably lower cost - certainly
less effort.

Being a lazy sod, I'll still try the vents first :-)

Cheers
Beats

Originally Posted by justbeats

In the current hot weather my roll-off observatory has reached new
record high temps. Today everything was very warm to the touch and
there was a distinct odour of hot rubber. It's been a huge bonus to
leave everything set up or stored in the observatory but now I'm
worried that the temperature is too variable after all. Could it damage
my scope or CCD accessories?

What range of temperatures is your equipment (happily) coping with in
your observatory?

Or is active cooling recommended? How? Vented fans or something?

Thanks
A slightly worried Beats

Could you install a small fan to move the air around ? This should help cool it if air can escape.

BTW - temp @ 4PM BST this afternoon in cloudless blue sky in my closed ali dome http://home.freeuk.com/m.gavin/mydome.htm
= 37C eg a few degrees warmer that outside in shade essentially identical to July 28 2002 - phew!

Nytecam 51N 0.1W

justbeats wrote:

Hmm, good point.

You're maximising the thermal inertia of the system (scope plus
observatory) while I'm minimising it (on the premise that I only use it
at night after it's had time to track falling ambient temperatures and
cool sufficiently anyway).

No, We're not changing the inertia at all, just the time response !
Changing the inertia would require more mass.

Worth noting that I've had no problems with SCT cooldown. The scope is
always ready for immediate use with no tube currents apparent. The real
issue (potential new problem I need to solve) is the temperature on
very hot days MAY be rising too high.


I'm sure your suggestion will fix that - but with costs for insulation
and fan.

Greenhouse vents could fix it too - probably lower cost - certainly
less effort.

Being a lazy sod, I'll still try the vents first :-)

Aluminium foil on the roof then you idle cheapskate
;-)

Steve

justbeats wrote:
Steve Taylor wrote:
No, you are isolating it FROM daytime ambients, for as long as possible.
Insulate heavily, like the big boys seem to do, then put a big fan in
shed wall to pull ambient air in, when internal external temp.

Hmm, good point.

There are some solar powered fans that are just about up to this duty
too.
(for most other tasks in the UK solar power is a waste of space)

You're maximising the thermal inertia of the system (scope plus
observatory) while I'm minimising it (on the premise that I only use it
at night after it's had time to track falling ambient temperatures and
cool sufficiently anyway).

No the inertia is about the same. What the objective of insulating the
inside and putting a mirror aluminium finish on it is to limit the
coupling between the hot observatory outer wall and the interior space.
I have known it good for a 10-20C improvement in air temperature
provided there is a small amout of air exchange with the exterior.

And as soon as you open the shed or remove the lid you are back to
where you were. The aim is to stop as much heat as possible from
entering the protected space.

Steve is right that polystyrene would be a real menace if it caught
fire, but then if my observatory went up in smoke the wood would burn
well enough to wreck things anyway.

Worth noting that I've had no problems with SCT cooldown. The scope is
always ready for immediate use with no tube currents apparent. The real
issue (potential new problem I need to solve) is the temperature on
very hot days MAY be rising too high.

A temporary second skin of canvas is as cheap a way as any.

BTW Greenhouse thermostatic vents can and do fail in winter storms.
They do not like frosts and you really need a good waether seal for a
scope midsummer thunder storms can be pretty ferocious. PS The some
roads in N Yorks completely melted today.

Regards,
Martin Brown

"Martin Brown" wrote in message
oups.com...

justbeats wrote:
Steve Taylor wrote:
No, you are isolating it FROM daytime ambients, for as long as
possible.
Insulate heavily, like the big boys seem to do, then put a big fan in
shed wall to pull ambient air in, when internal external temp.

Hmm, good point.

So......and back to a much more basic question:

I have my LX200GPS set up on it's tripod right now and it has been for the
last week or so. During the day, I cover it with a plain and simple white
sheet. I presume it's OK like this as it must have been designed with
daytime as well as night time observing in mind.

It's great just to be able to walk out when it gets dark, turn it on and
observe - or even not turn it on and just observe (of course, it needs some
time to cool down, but it gets dark so late right now that I figure by the
time it's totally dark, the heat has already all beld out)

Are the current hot UK daytime temperatures and the associated thermal
stresses likely to cause any damage ? My heart says "No", but my head says
"let's see what uk.s.a. thinks....

Metcheck say it may rain Thursday afternoon, so I might need to either get
my big plastic bag out, or tear it down and pack it away.

I'm seeing the attraction of building a real observatory though///