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Water in obo

Jack Martin

By Jack Martin
in DIY Observatories

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Jack Martin

Jack Martin

Posted
Posted

The obo runs all night sometimes in the morning the walls are wet from condensation so the water runs down to the floor and gets trapped between the wooden floor and the floor matts. I have taken the matts up to allow the floor to dry out does anyone know how to avoid this from recurring?

Jack

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nmoushon

nmoushon

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You can use a fan to keep the air moving which helps a bit. Or a dehumitifier. Or A/C or heater on a timer to keep the air from going past the dew point. Can put it on a timer so you dont have to have it on all night. Not sure if they are very effective in an obsy or not (with all the nice equipement) but thats the typical  ways to deal with it else where.

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nightvision

nightvision

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You could install a low wattage underfloor heating wire in/on the walls (cheap as you wont be needing the sensor or thermostat).  With the right set up you could ensure the walls are just warm enough to keep away the dew but not so warm that they effect the view.  I will need to do this when I get my obsy finished as I live near the sea, may put it on a dimmer.  So many ideas... just need the time to build it! :smiley:

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JamesF

JamesF

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James,

What diameter vent holes do you recommend?

I would probably have a look around a local DIY shed or something to see what vent covers are available to keep birds and large insects out, but I'd have thought something like a 6" diameter or 6"x4" vent at either end would help.

I'm assuming that warm air gets trapped inside the obsy at some point and the temperature outside subsequently drops, cooling the walls.  Condensation then forms on the walls just as it can on the inside of a window on a cold day.  Allowing the warm air to escape outside should hopefully reduce the condensation in that situation.

Does that sound like a plausible cause though?  If the moisture isn't condensing out of the air onto the walls, or if it's happening when the obsy is open then perhaps a different approach is required.

James

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BlueAstra

BlueAstra

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I notice the original post it says the obs is used all night, and therefore I suppose open to the sky all night. I think most of the solutions offered will work well in a closed obs, but not so sure when it's open. I lined the walls and roof of my obs with Jablite insulation from B&Q. This insulated the cold wall surfaces and limited the condensation forming in the cold atmosphere when open.

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nightvision

nightvision

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IMHO ventilation is better than underfloor heating as preventing damp is better than warming it up and allowing the rot to set in.

It's the low surface temperature of the walls that allows condensation to form, if the obsy has been open all night it's likely the walls will often be much colder than the daytime air temperature.

The proposal was to gently warm the walls and prevent condensation forming not heat the wet floor!   :rolleyes::laugh:

It's just the same principle as well proven dew-heaters but on a slghtly larger scale, combing this approach during a long session with good (post session) daytime ventilation (and wall heating) would ensure that any remaining moisture exits the obsy.

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MadAlbert

MadAlbert

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It's the low surface temperature of the walls that allows condensation to form, if the obsy has been open all night it's likely the walls will often be much colder than the daytime air temperature.

The proposal was to gently warm the walls and prevent condensation forming not heat the wet floor!   :rolleyes::laugh:

It's just the same principle as well proven dew-heaters but on a slghtly larger scale, combing this approach during a long session with good (post session) daytime ventilation (and wall heating) would ensure that any remaining moisture exits the obsy.

What would the power requirement be for such a venture? (Assuming the temp of the wall(s) will need to be raised above the dew point.)

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nightvision

nightvision

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The power requirements depend on how much you spread the wire out and how long the wire, the dual wire kits (see below) use about 10 watts per linear metre.  A little trial and error would soon give the density per square metre to raise the wall temperature just enough (the wire could be temporarily attached to a test board).  The important consideration is that the wire should be able to radiate and not be insulated all round or it ill overheat and fail.  The heating wire can not be cut, the supplied sensor might still be useful if the supplied thermostat was mounted in the warm room.  

All this obsy design talk has got me wanting to get on with my build.

http://www.thefloorheatingwarehouse.co.uk/acatalog/Ecoflex_Cable_Kits.html

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Macavity

Macavity

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I never noticed any damp patches UNTIL I covered the floor with those (otherwise splendid) tiles.

I sense the (almost inevitable) minor leaks at corners etc., just evaporated before. I might leave

a gap around the edge. Add a few 1" air holes, drilled through, the floor at the offending points?

Close-fitting tiles like these tend to expand under the sun, rise up into annoying "hill ranges"... :p

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