Free passive obsy dehumidifier - workable?

[ollypenrice]

Noting the staggering amount of wet dripping from the (as yet) unisulated steel roof of my new observatory set me thinking.

1) insulate the underside of the roof, obviously.

2) imagine a sheet of corrugated steel roof set vertically near a wall inside the observatory with its courrugations orientated vertically. Under this you make a little gutter which vents to outside. Loads of condensation forms on the sheet, drips down the gutter and flows outside down the drain, leaving less airborne moisture on the inside.

So, ye who know, would this be worth doing?

Cheers,

Olly

[duncan.p]

Nice idea Olly but I don't think your "moisture magnet" would quite work as planned; you cannot be selective about which bit of cold metal the condensation forms on.

Have you considered a dehumidifier with it's drain routed to the outside of the obs..........

[ollypenrice]

Nice idea Olly but I don't think your "moisture magnet" would quite work as planned; you cannot be selective about which bit of cold metal the condensation forms on.

Have you considered a dehumidifier with it's drain routed to the outside of the obs..........

Yes, I have an electric one but if I tried my passive system my thinking is that there would be a net drop in humidity in the observatory. The cold surface area of my device would exceed by many times that of the more expensive cold things that live there, meaning that they ought to dry out more quickly.

I'm also looking at plant heating mats and other low heat devices. A big bag over the scope with minimal heating within should keep everything inside above the dew point. Plant mats might also protect computers left in unheated buildings?

Olly

[Merlin66]

Olly,

You either have to keep everything above the "dew point" or re-direct any condensation away from critical areas.

(If there's condensation on the roofs/ walls at least it shows that the building isn't retaining much heat and quicky reaching ambient!!)

I use a Maplin 12V doggy heating blanket - large enough to drape over the scope and mount...just enough heat to keep it above the dew point....

[steppenwolf]

I can see some advantages to your idea, Olly but there's no substitute for a moisture free environment and a desiccant - oven style dehumidifier with a pipe exiting the building is just such a sure way of managing this issue and protecting every part of the internals.

[Psychobilly]

I have run one of the Oven type dehumidifiers in the obs all year since the disaster last crimbo... Pity I have hardly used the scope but the data logger shows it's doing a cracking job... Dont know what it's done to the electricity bill though

Peter...

[steppenwolf]

Dont know what it's done to the electricity bill though

I'm too frightened to look but my precious gear stays immaculate so whatever the cost, I think it's worth it! Besides, Janie pays the electricity bill ....

[ollypenrice]

Olly,

You either have to keep everything above the "dew point" or re-direct any condensation away from critical areas.

(If there's condensation on the roofs/ walls at least it shows that the building isn't retaining much heat and quicky reaching ambient!!)

I use a Maplin 12V doggy heating blanket - large enough to drape over the scope and mount...just enough heat to keep it above the dew point....

The doggy blanket is the answer! I knew there would be something ready made to do the trick but was (ho ho, get this double pun, team...) looking at garden centre propagation heaters so I was barking up the wrong tree!!

Olly

[Psychobilly]

Now if you could cool the panel.... then....

I guess you get a good few below zero there at times... It was the long cold spell last winter and the ice that formed inside the scopes that convinced me to get the Dessicant/oven dehumidifer...

[steelfixer]

I find it facinating that people build obsys on the same model of a house.

If you seal up the scope in an air tight room you are going to get problems like this.

When I built my obsy I purposely left a 50mm gap along the sides at roof level.

This allows any ambient heat inside the obsy to escape with the net result being I do not get any condensation.

It also means my scope is always at ambient temp and I do not need to have a cooldown period before I can use it.

I think the answer to your problem Olly is ventilation or lack of it.

The more heaters you put inside the obsy the worse your problem is going to get.

[ollypenrice]

Ah no, Steelfixer, far from it; at present I have enormous gaps everywhere because quite a few minor trim panels are yet to be made and fitted. It's simply that the corrugated steel roof loses heat much faster than the other materials around it and the condensation, therefore, chooses to form on it. No amount of ventilation will alter the fact that the thin steel will cool faster than timber or breeze block.

To go back to my original idea, if I insulate the roof (today's task) but insert some cold steel panels and a gutter beneath them, any moisture that forms on them will not form elsewhere and will be exported or trapped as ice till things warm up.

OPlly

[Psychobilly]

To go back to my original idea, if I insulate the roof (today's task) but insert some cold steel panels and a gutter beneath them, any moisture that forms on them will not form elsewhere and will be exported or trapped as ice till things warm up.

OPlly

Thats along the lines of how the cheaper "fridge" type de-humidifiers work...

Good luck with your DIY solution..

Peter...

[Gina]

If you warm the scope etc. above dew point then take the cover off and let it cool down to ambient for observing or imaging, the dew will start forming again on it. IMO the only way is to keep the moisture level down so dew doesn't form.

[Merlin66]

Unfortunately, when you open the lid to use the scope you're subjected to the whole night sky...the ambient moisture content in the atmosphere and the local dew point will determine the amount of dew that drops out.

I thought the issue was the build up of dew/ drips etc inside the closed observatory between sessions....

[steelfixer]

Olly in one way you have just proved my argument about building an obs like a house.

Breeze block walls ect = Permenant self built storage heaters.

Whilst I understand peoples desire to build these structures like this and to be quite honest some of the obs I seen posted on here are built better than my house it still seems to me that it defeats the object.

People build these things fit them up with heaters and dehumidifiers and the like to protect the scope and its electrics but as as soon as they open the roof and the cold moist air hits thier perfectly protected 'warm' equipment instant moisture overload occurs.

Surely the basic aim is to keep the equipment dry and as near to the outside temp as possible.

If all things are the same tempreature you will not get condensation.

It would be an interesting poll to find out how many people get problems with scopes stored in 'garden sheds' as opposed to people who have fully insulated heated obs.

Mind being that you live in the South of France I dare say your day time to night time temps vary by a marked difference compared to mine which will exasperate the problems even more.

[Merlin66]

If all things are the same tempreature you will not get condensation.

Hmmm, not the case...

See my previous message about the dew point....

If everything, exposed to the cool night air, is above the dew point temperature, then no dew will form....

[steelfixer]

Merlin I think we have a missunderstanding between 'dew' and 'condensation'

What Olly is discribing is I take to be condensation caused by the difference in tempreature of the steel roof to the inside temp of the obs.

If the temp inside the obs is the same as the temp outside then condensation will not form on the inside of the closed roof panels as there will be no temp difference.

[Merlin66]

Probably yes, but the temperature still has to be above the dew point temperature.

Dew point - Wikipedia, the free encyclopedia

[Earl]

I just stuck soem camping mat on the roof it has helped loads but its not 100%.

Good enough though.

[chiltonstar]

For what it's worth, I'll pass on the solution I'm going to try for a very similar problem....

The key issue for me is the early morning; as the walls warm in the sun, the coldest thing around is the large chunk of glass/metal sitting in the centre of the observatory - it will act as a condensation magnet. The evening is less of a problem; here, the walls are cooled by the night air and will attract most humidity.

The solution I'm going to try is to use a low powered Peltier type dehumidifier (about 50 watt, 0.5 l of water capacity per day, powered by a small solar panel and battery with a mains inverter (Maplin) on a timer so that the charge accumulated during the day is used to power the dehumidifier for a couple of sessions.

CHRIS

[steelfixer]

Merlin I agree that increasing local temp eg dew heaters removes the dew problem but surely by increasing the obs temp you will incite more general condensation?

Interesting thread this.

[steelfixer]

Chris - I like your thinking. I would be interested to know if it works out.

[steelfixer]

As a general point I built my obs with a 40mm x 40mm steel box section frame clad with 10mm marine ply with the view of trying to not allow condensation problems.

The floor of my obs is a 6 inch thick concrete slab so day or night it is always the coldest thing inside the obs.

[theodore]

Hi,

my scope shed is well ventilated, but my scope (12" newt), of course, is closed when not in use. I find that I have to have a dew heater inside the tube next to the primary so that after use it is warmed slightly again (on a timer from midnight till 6 am, but off obviously when in use). The reason for this is simple. The temperature of the mirror lags the ambient by a long way, so after a cold night as the day warms up, the mirror will dew very badly. By warming it after use before the day time no dew (or condensation) forms. Note that its only a very slight, dew heater type warmth. Electronics etc. at the moment I keep in the house, when not in use but if I had them outside I would keep them closed in boxes with a good amount of silica gel.

Theo

[steelfixer]

Fair point Theo and a good idea, mind you that is a serious lump of glass.

Am I jealous ????? ok so I am.

:D:D:D