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Old 24-11-2021, 02:36 PM
jasperskies (Alan)
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Dehudifier use in observatory

Hi,
I have a roll-off roof observatory in sub-tropical northern NSW and the observatory is not air tight at all (unlike a domed observatory). I run a dehumidifier and it takes 10L of water out each day (its maximum limit).
I suspect it is a self-defeating exercise as I have never been able to confirm that the humidity levels actually drop as a result.
Do others with similar observatories run dehudifiers? Do they have better success?
Thanks, Al
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Old 24-11-2021, 03:31 PM
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h0ughy (David)
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Mine runs most of the time to 50 percent and no domes are not sealed, they have outdoor air flow all the time. Worth their weight in all the liquid gold the take out of the enclosed space. If you measure the humidity in there and outside you will see how effective it is
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Old 25-11-2021, 12:24 PM
jasperskies (Alan)
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My roll off roof is quite big and the air gap between roof and walls is considerable. I've never been able to bring the inside humidity down to 50% when its been raining like lately for days and days. The humidifier is always full (10L) when I check it each day so plan to run it continuously with a drain tube through the wall.
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Old 25-11-2021, 12:50 PM
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h0ughy (David)
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Always operated with a drain outlet
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Old 25-11-2021, 01:29 PM
glend (Glen)
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Alan, I tried to dehumidify my roll off roof observatory for a couple of years after I built it. After burning out two dehumidifiers I gave up and adopted a different approach. I simply do not leave equipment inside the observatory (with the exception of the CGX mount which is on a pier). In this recent sort of weather you cannot do any astronomy anyway, so why leave gear in there to potentially deteriorate. Scopes are easy to store inside your house, unless maybe you have a +16" Dob.
My mount lives inside an insulated shroud in the observatory, the shroud which is aluminised foil insulation, is constructed as a chimney to provide air flow upward through the shroud, exiting through the top. At the bottom of the shroud is a 25w decorative light bulb, which provides just enough heat to provide a chimney effect, and this rising warm air prevents any condensation on the mount itself. It takes just two minutes to remove the shroud when I want to use the mount. Usually I have a 24 hr timer running the bulb, and this prevents any cold weather condensation.

Of course if your one of those people who want everything setup perfectly, scopes, camera, etc, then a few minutes of prep time when you want to use it, then this approach might annoy you.
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Old 26-11-2021, 09:07 AM
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xthestreams (Paul)
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Not sure that 50% is required or even desirable, I would imagine that once it’s below 70-80% the main risk has been addressed.

I also have mine plumed into the dome, draining as it goes, no need to service it. It’s setup on a timed circuit to only run for a few hours after daylight, always does the trick.

If you’ve got an Ultimate Power Box V2 Yiu can measure the impact it’s having and even setup scripts to automate the dehumidifier if Yiu be fancy like that.
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Old 27-11-2021, 05:09 PM
jasperskies (Alan)
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Interesting alternative, Glen. I guess I'm one of those people that do want a permanent set-up. Constant air flow into the observatory while trying to control the humidity still seems like a losing battle in a sub-tropical environment. I have also begun running an exhaust fan but don't have any hard evidence it helps.
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Old 30-11-2021, 06:22 AM
appiice (Ed)
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Heat Source

I have tried a similar solution to Glen, the changes are I tried a 20ish watt bulb but at some stage it blew, I replaced that with a heating element that was / are designed to apply small amounts of heat to outdoors machinery, it from memory is around the 30 watt mark and was sold by an electrical wholesaler per made with a standard 240volt plug.
The second change was my cover was made from wall sarking and is not vented, my reasoning ( which maybe flawed ) was to not provide a continuous change of air but to provide a blanket of low heat around the scope and mount to prevent condensation.
The mount and scope do not feel hot but are warmer than everything else in the dome, I don't have the means to measure the humidity but it does make me feel better.
I idea of moving a 11" scope, camera, Hyperstar and smaller scope off the mount isn't appealing doing it by myself I use a small block and tackle hung off the dome but it is a task, if I was younger and fitter maybe but the heating element works.
Ed
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Old 12-12-2021, 08:47 AM
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mura_gadi (Steve)
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The only effective way would be to take enough of the outside air to create a mostly positive air pressure in the shed/obs.

Heating the air doesn't remove it, you need to pump in dehumidified air with enough force to create a mostly positive air pressure inside the obs to keep the moist air out.

Try and minimize the roof gaps using a longish brush trim or similar around the roof gaps maybe.
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Old 19-12-2021, 11:49 AM
Boozlefoot
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Alan, I've gone through the mill with trying to decrease the gap on roll-off's and domes, roof to wall. The best way I could determine, and I'm confident, was to employ a flexible "brush" type seal. Whilst not completely airtight, it would be dense enough to prevent ambient air blowing through the gap, and getting rid of the worst of the wasp/spider ingress.

https://www.truckandtrailerpartsonli...ush-100mm~1146

This type of brush is ideal for forming around uneven or non parallel surfaces.

I've since opted for an insulated and dehumidified warm room, adjacent to my "pier garden", as I have several scopes.
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Old 07-02-2022, 06:52 AM
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mura_gadi (Steve)
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Hello,


Just had a thought about a possible alternative option.

You could encase the scope and the mount head in a plastic bag, attach the dehumidifier to one end and pump air through the bag with an outlet up the top. Means the unit can be mobile in the obs for no plumbing (or a hose to take water outside)and it will recycle slightly less humid air as well from within the obs.

It won't do the whole obs for PC's and other equipment etc, but a small unit would keep the bag fairly well regulated humidity wise.

Fridge shipping bags are huge and you might find them around the recycling centres or try white good stores who deliver. Or if your good with wood, a simple hinged T box. Might be possible to enclose the loop with just a tiny air hole for pressure, that might reduce the need to empty the water chamber as often.

Last edited by mura_gadi; 07-02-2022 at 09:49 AM.
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