Free passive obsy dehumidifier - workable?

[Nillchill]

olly, why not install a false roof made out of perspex corrugated sheet, an inch or two below, it would catch the condensation and provide a barrier to the heat sink that is caused by the steel sheeting

[ollypenrice]

The problem I'm trying to solve is indeed that of the roof dripping madly onto the inside of the observatory. It doesn't happen every night but even on my other roll offs, which are just ply sided, steel framed, steel roofed affairs with loads of ventilation, I do get this as well. They are smaller so there is less of an issue. Even if left outside, though, spare steel roof panels are sometimes wringing wet in the morning so no amount of ventilation or reaching ambient will affect that.

We do get dramatic differences between night and day temperatures. In winter -5 to -10C is a kind of 'default' setting and it can go down to the minus nineteens or so. Then in the daytime, in the sun, it is much warmer - warm enough to eat outside in a light jumper. It's hard to put a temp on it because in the shade it will read cold but in the direct sun very warm. It's both a continental and a mountain climate. (We are at 900 metres/3000 feet.)

Another phenomenon is regular local temperature inversion in the morning. The valleys below us fill with damp cloud before sunrise. This often calls a halt to observing before the sunrise itself. Then the whole place goes foggy for a while as the sun lifts the moisture up into the atmosphere and leaves a lovely sunny sky. I suspect that the wet mornings are down to this effect.

I'm just going to put a heated pet blanket in a breathable bag over the mounts/scopes to keep them dry in such damp spells as we get. Ken put me onto these. They could also protect computers left in the warm room from cold damage.

Olly

[philj]

I use a passive system in my obs.

The obs is a wood roll off with good ventilation but the mount and scope at this time of year is usually dripping so I bag the scope and mount from the end of autumn to spring with one of these large patio furniture covers you can get for a couple of quid from wilcos and inside it I put one of the gell water traps that folks use in caravans.

This keeps everything nice and dry in storage and also accelerates the dry down after use.

You just got to remember to check the trap every month or so and empty the water and recharge if necessary.

Simple, effective, takes no electric and is cheap

Philj

[Merlin66]

Having spent ten years as Chief Engineer in a large paper mill - I can well understand the issues of condensation drips ( if water drips from the roof above the paper machine, it can hit the paper during forming and cause holes in the sheet - bumma another reject!)

The solutions are not easy - multiple insulation layers (to keep the bottom exposed layer above the dew point) or as has been mentioned an inclined false lower ceiling, which directs any surface condensation away from critical areas.

[Psychobilly]

I used to use the bag and chemical dehumidifier option as well... when I just had the SCT out there once the obs got filled with more kit I went for the dessicant/oven dehumidifier

[ollypenrice]

I use a passive system in my obs.

The obs is a wood roll off with good ventilation but the mount and scope at this time of year is usually dripping so I bag the scope and mount from the end of autumn to spring with one of these large patio furniture covers you can get for a couple of quid from wilcos and inside it I put one of the gell water traps that folks use in caravans.

This keeps everything nice and dry in storage and also accelerates the dry down after use.

You just got to remember to check the trap every month or so and empty the water and recharge if necessary.

Simple, effective, takes no electric and is cheap

Philj

Thanks Phil, I didn't know about these but will look them up.

Olly

[ollypenrice]

OK, just ordered two Petnap pet heater pads which look quite good. These will go under scope bags and keep mounts and scopes well above the dewpoint, I hope, at minimal running cost.

Petnap Whelping Boxes

They are intended for use in kennels and don't have to be in a dry environment, though how any environment with a puppy in it is supposed to be guranteed dry is anybody's guess!

Thanks to Ken for putting me onto these. The stuff is out there if only you can guess what it was originally intended to be used for...

Olly

[Merlin66]

Interesting....

These are 240V, rigid, and about a 1/4 the size of the 12V Maplin Blanket

[swamp thing]

I would think your principle problem is the material of the roof. Metal is a nightmare as far as a avoiding condensation. Any material that is a great conductor makes for a condensation magnet at very small changes of temp.

As a builder we always had problems with rusting tools in the back of vans with unlined roofs in the past.

Hideous condensation would build up on the inside of the van and drip onto tools, specially during winter.

Solution. Line the roof. All modern vans have roof liners. Problem solved.

I would line the roof with an insulator.

Either that or remove the metal and replace with ply board and torch down felt.

Regards Steve

[steppenwolf]

Reading this fascinating thread is making me more and more pleased that I went for a domed observatory - 'tis true that the glass fibre walls and dome do show a temperature gradient that results in dew formation but the dehumidifier resolves this simply. I have plenty of ventilation which helps (the entire circumference of the dome is open to the elements albeit via a stepped overhang) and this along with the white finish means that the temperature difference between inside and outside remains sufficiently low that I do not have to consider cool-down time and I have never, ever suffered from dew formation on my refractors.

Downsides? Of course, both ROR and dome designs have their issues and mine are, that frustratingly small roof aperture, having to rotate the aperture every 20 minutes, not being able to enjoy the whole of the night sky from within the dome and the fact that I know that I am de-humidifying half of West Sussex at my own cost because of that all important ventilation!!!

[ollypenrice]

I would think your principle problem is the material of the roof. Metal is a nightmare as far as a avoiding condensation. Any material that is a great conductor makes for a condensation magnet at very small changes of temp.

As a builder we always had problems with rusting tools in the back of vans with unlined roofs in the past.

Hideous condensation would build up on the inside of the van and drip onto tools, specially during winter.

Solution. Line the roof. All modern vans have roof liners. Problem solved.

I would line the roof with an insulator.

Either that or remove the metal and replace with ply board and torch down felt.

Regards Steve

Very true and that's my intention, to insulate it. The other solutions are too expensive here. Ply is ludicrously expensive, for instance, and in the extremes of temp that we get steel is so durable and proven. While we don't really get the full on Mistrale here it can blow a bit, too.

Olly

[ollypenrice]

Interesting....

These are 240V, rigid, and about a 1/4 the size of the 12V Maplin Blanket

Yes, I thought that being rigid they might be more durable and being small they might use less expensive atomic French electricity!

Olly

[steelfixer]

Quote - "We do get dramatic differences between night and day temperatures. In winter -5 to -10C is a kind of 'default' setting and it can go down to the minus nineteens or so. Then in the daytime, in the sun, it is much warmer - warm enough to eat outside in a light jumper. It's hard to put a temp on it because in the shade it will read cold but in the direct sun very warm. It's both a continental and a mountain climate. (We are at 900 metres/3000 feet.)

Another phenomenon is regular local temperature inversion in the morning. The valleys below us fill with damp cloud before sunrise. This often calls a halt to observing before the sunrise itself. Then the whole place goes foggy for a while as the sun lifts the moisture up into the atmosphere and leaves a lovely sunny sky. I suspect that the wet mornings are down to this effect."

Olly with all that to contend with I am not suprised you have got problems makes me glad I live in the flat lands of rural Suffolk.

[ollypenrice]

Quote - "We do get dramatic differences between night and day temperatures. In winter -5 to -10C is a kind of 'default' setting and it can go down to the minus nineteens or so. Then in the daytime, in the sun, it is much warmer - warm enough to eat outside in a light jumper. It's hard to put a temp on it because in the shade it will read cold but in the direct sun very warm. It's both a continental and a mountain climate. (We are at 900 metres/3000 feet.)

Another phenomenon is regular local temperature inversion in the morning. The valleys below us fill with damp cloud before sunrise. This often calls a halt to observing before the sunrise itself. Then the whole place goes foggy for a while as the sun lifts the moisture up into the atmosphere and leaves a lovely sunny sky. I suspect that the wet mornings are down to this effect."

Olly with all that to contend with I am not suprised you have got problems makes me glad I live in the flat lands of rural Suffolk.

Oh, I don't have much to contend with sky-wise! 250 to 300 clear nights a year, Mag 7 zenith, 21.6 on the Sky Quality Meter. It's one of the best sites in mainland Europe. A bit of dripping from a tin roof isn't much of a hardship!

Olly

[steelfixer]

Well if you put it like that i guess not.

You wouldn't consider sending a few of those clear nights over this way would you?

The Suffolk skies are pretty good, the only drawback is being pretty much at sea leavel and very close to the north sea.

[steelfixer]

Olly I have just come across this.- Grafo Therm

If it is any good to you these people are only 20 miles down the road from me.

graham

[m.tweedy]

Olly I have just come across this.- Grafo Therm

If it is any good to you these people are only 20 miles down the road from me.

graham

That looks good my solution in my shed was to insulate the walls with jablite which keeps the shed "just" above the dew point.

Olly have you considered this

Profiled Roof | Profiled Roof Insulation | Jablite, UK

[George]

Either clad the roof with ply or polystyrene or maybe those loft lagging space blankets, either of them should be fairly cheap given your roof area.

[Gina]

You could suspend a sheet of vapour barrier under the roof and tilt it towards a corner.

[ollypenrice]

Graham, that Grafo Therm link is excellent and would have done the trick nicely. However, I'm just fixing polystyrene sheets under the roof. It's cheap and simple.

Thanks anyway and I'll remember it next timùe I make myself another camper van, if I ever do. Thanks also to Michael for another good link.

In truth there is no problem here, just putting the insulation sheet under the steel will, I'm sure, do the trick. Because of the internal construction the work involved is minimal.

Olly

[Catanonia]

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.

Totally agree here.

My observatory is built from fence panels so wood all around. The roof is bitumen corrugated roofing and I have "air" gaps all around.

The roof leaks a little down the sides, but the scpe and electrics are always covered with an old motorcycle cover so are protected.

Never once had condensation issues and my whole scope is always at ambient temperature.

As said, the objective is to keep the scope dry, but still outside !!!!

As said the roof of metal is the problem. Try sourcing other forms of corrugated roofing.

Linky for what I used

http://www.wickes.co.uk/bitumen-corrugated-sheet/invt/240039/?source=123_74

[ollypenrice]

I have solved the problem now by lining the roof. I know the bitumen-on-ply would have avoided the issue but the trouble is the cost of ply here. It would have cost me about 250 quid plus the bitumen. The steel is really attracive here because it handles the extremes of temperature -very high and very low - extremely well. The intensity of the sunlight tends to kill most plastic type corrugated sheeting, or make it go droopy (I had that on another obsy) and it also has no trouble with the wind. Finally the whole roll off roof is quite a size - nearly 2.5 metres on a side - so weight is an issue. It is the roof and upper sides whch roll so I can get to low targets. We can shoot down to the horizon in extremis here because of the minimal LP, altitude and low humidity. Ah yes, another issue with roof felts is dragging them off when you pull the snow off them. We do get big snowfalls here and once it starts to freeze-thaw it clings to whatever it is sitting on.

I think steel was the right decision. There has been no sign of humidity since I lined it.

Just finished the concrete floor inside today. There was a bit of it that wasn't already concreted but it is going to spend the night under a tarp with a radiator for company inside the scope area!

And then Yves will soon be down here armed with The Beast, the mount and the camera - plus a Mac, which will confuse me... Uh Oh.

Olly

[Catanonia]

Glad you got it sorted mate

[Balder]

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.

Won't work IMHO as your "cold" steel will be as warm as everything else in there. It has no temperature differential to the moist air/anything else in the room.

[ollypenrice]

Won't work IMHO as your "cold" steel will be as warm as everything else in there. It has no temperature differential to the moist air/anything else in the room.

Ah, but I think it does have a differential because it cools quicker. That's why the uninsulated roof was running with water when the block and woodwork was bone dry. Similarly your car windsreen may be soaking wet inside in the morning but you seats aren't soggy. The steel is a good conductor and has an enormous surface-area-to-volume ratio being very thin with both sides exposed to the air.

Olly