Summer Heat Problem

[centroid]

With the summer now starting to 'kick in', and more and more people building a 'backgarden observatory', I thought it might be useful to highlight an often overlooked problem, and describe what I did to help.

My permanently mounted scopes, are quite tolerant of living in an observatory, where in winter, the internal temperature equals that outside.

In summer however, it can be a different story, and on hot sunny days, the internal temperature of my obs (when closed up), and the attached 'control room', can reach well in excess of 40C.

I considered that this could not be a good environment for the equipment within. Therefore, I looked into what I could do to reduce the internal temperature on hot days.

My solution was to install two domestic extractor fans, one in the 'gable end' of the 'roll-off-roof', and another at high level, in the wall of the control room.

Ventilation 'grills' were also installed at low level, in the wall of both the obs and the cont-room.

The fans are controlled by a wall-mounted (in the obs area) thermostat, which switches the fans on, when the internal temperature reaches 25C.

The principle of operation being, that the hot-air is sucked out at high level, while pulling the cooler outside air in at low level, through the ventilation grills.

On hot sunny days, the system struggles to keep the internal temperature down to the outside temperature, but it does now prevent the internal temperature rising to worrying levels.

The only problem that I often encounter, is forgetting to unplug the fan, before rolling the roof off

So, if you are in the process of building an observatory, or thinking about building one, this is something you might want to consider.

The picture below, shows the 6" fan, fitted into one of the 'roll off roof's' gable ends, the 'plugging point' and Thermostat.

Dave

[geppetto]

Good sollution Dave

Thanks for sharing 8)

[Akyra]

Maybe instead of 'plugging in' you could fit solar panels to the roof, with the sun out and all, and wire the fans straight in.

So when you pull the roof off, the solar panels, cables and fan move with it.

Just an idea...

[centroid]

Maybe instead of 'plugging in' you could fit solar panels to the roof, with the sun out and all, and wire the fans straight in.

So when you pull the roof off, the solar panels, cables and fan move with it.

Just an idea...

Hmm!!, just a little bit more involved (and expensive). than what I had in-mind

Dave

[Akyra]

£12.50 on eBay - Output Power 1.5W @ 17.5v

Would that power the fan though?

EDIT : Another that can power a fluroscent!

[MartinB]

Having an airflow through the observatory must be good for the seeing as well Dave.

[George]

Only problem Im having with heat buildup is my piggybacked ST80 and finders go out of line everyday :x I guess this due to the different materials expanding and contracting in the heat.

Pain in the Bottom realigning everything

As regards ventilation i just roll the roof back a few inches and lock it off.

[Astroman]

Heat? Do I know heat?! My dome is painted with an elastomeric roofing compound called Kool Seal. It's white and kinda rubbery and reflects more heat than I can imagine or describe. Even on days in AZ where the temp reaches >46ºC, the metal dome feels cool to the touch, and the inside temp is the same as ambient. The rolloff roof would heat up, much as described before I did the same with it-painted the Kool Seal on it and Poof! ashes Nope, ambient temperature inside. Airflow is great, but can cause turbulence in the slit of the dome and thus bad extremely local seeing, but it's worth the trade-off.

[centroid]

As regards ventilation i just roll the roof back a few inches and lock it off.

That's fine when you are at home, but it doesn't help when you are away on holiday etc.

I like the 'sound of 'Kool Seal', as suggested by Astroman, and I guess the black felt roof of my obs, could be given a 'coat' of that. I'll have to see if it, or an equivalent, is avaibale in UK.

Thanks guys

Dave

[robindurant]

The Shed I keep my Celestron 8i in is approx. 8'x4'6" and the temperature on a hot day reached 40c so I installed a Toilet fan ( e.bay under £10.00) and a Cooling/ heating changeover SPC02/ T360B1069 thermostat from RS Components, stock No. 2001314. This reduces the heat to 30c. If your room is air tight you will need to install a grille at low level for air inlet, this is important. I checked with Celestron and Hinds re. heat tolerance but both were un decisive. They said that the circuit boards could be effected. I checked on a USA forum and the general thought is that scopes are sometimes kept in car boots with no adverse effect. I do know that if you have a ETX Mead you need to be careful as the mirror is GLUED on and this could be damaged with excess heat. When I had a Meade I also could not find out the temperature limit. Everone is understandably reluctant to give figures. I hope this info. helps.

[MartinB]

Airflow is great, but can cause turbulence in the slit of the dome and thus bad extremely local seeing, but it's worth the trade-off.

I read an interesting article by Ron Wodaski about poor seeing and observatories. Apparently the large observatories built a few years ago suffered very poor seeing because of their enclosed design. With no through air flow there were just lots of convection currents. Observatories are now made with lots of ventilation in an attempt to encourage a steady air flow. Apparently different rates of cooling of the objects within the observatory also have an influence. Ron recomends wrapping anything likely to be warmer than ambient in silver foil. Studies of seeing have shown that the biggest influence on seeing isn't things like the jet stream but very local factors immediately in front of the scope.

The jist is - hot observatories will crucify seeing.

[centroid]

With my obs, being a 'roll-off-roof' design, convection currents aren't really an issue, as unlike the 'dome' and it's 'slot', the whole obs area is open to the sky, as as such rapidly achieves equilibrium with ambient.

I know that concrete base slabs, can retain quite a lot of daytime heat, which is released as convection currents for several hours after 'sundown'.

To combat this problem, my obs does not stand on a concrete base, but has a wooden floor, supported on 'blocks', which provides a 4" air gap between the gound (soil) and the underside of the obs floor. The Pier is attached to a 'cube' of concrete, cast in the ground.

Having the obs well ventilated, not counting the extractor fans for the heat issue, keep it very free of condensation during the winter months.

Robin referenced ventilation inlets at low level, but I did say:

"Ventilation 'grills' were also installed at low level, in the wall of both the obs and the cont-room".

In my inititial 'post'.

The 'bottom line', is that installing the fans to remove the heat from the obs when its closed up, has been very worthwhile. As has been said, there is no dinfinitive answer as whether 40C+ is actually detrimental to the equipment, but I always reckon that prevention is better that cure.

[MartinB]

Sounds spot on Dave you jammy devil

[CELESCOPE]

Thankfully , i wont be imaging in the summer much at,all , i did read about this and the possible problems with Domes, but keeping to the winter and Autumn, hopefully wont cause me a problem, have to think of so many advantages , like stray , light , and most of all , its always darn windy here ,so that will be a big help, and if its a prob , i can always rent it out , holiday home or something like that ehehehhehehe .

[centroid]

Thankfully , i wont be imaging in the summer much at,all

I don't do very much in the summer either, too light!!.

The gear however, lives in the observatory all year round.

If you're thinking about building an observatory, you'll not regret doing so. IMO, it the biggest asset to the enjoyment of this hobby you can have.

Dave

[MartinB]

Thankfully , i wont be imaging in the summer much at,all

IMO, it the biggest asset to the enjoyment of this hobby you can have.

Dave

:envy:Yes I know!

[CELESCOPE]

:)