condensation in obsy

[spaceboy]

Think you got yoursefl a bargain there - they usually seem to be around £40 whenever I've seen them on ebay. It looks quite large in the pic - what is it's diameter?

So far I haven't noticed any condensation in my recently completed observatory - early days yet though but I've thought about employing one of those solar powered vents should a problem occur. I'd like to avoid the cost of buying and running a dehumidifier if at all possible.

Hi Mike

The actual aperture of the fan is 100mm (inside the obs) and the overall dimensions around 205mm (outside). They usually do sell for around £40 - £50 on the ebay shops but the one I got was £14 new (other) delivered which the seller sold 2 under auction for the same ending bid but I have seen used ones go for £32 so it goes to show if your patient and don't loose yourself with auction fever they do come up at good prices when not in demand. I figured for the money it's going to be a winner as the caravan vent was doing a good job by itself so the fan running from time to time was going to be a bonus. They are not a bad solution but I doubt I would have ever paid £40-50 for one given that just adding ventilation had made significant improvements to my problem.

I had always been a sceptic to the benefits of insulating what is essentially for most of us a shed to be out observing in no time while keeping the wind and prying eyes of the neighbours of us but I think this thread if anything has stressed the importance of good insulation, correct ventilation and draft proofing on new builds for anyone planning on going down the path of a de-humidifier or heater as the RH is just going to be the same as what it is outdoors otherwise and your de-humidifier is sure going to burn some of those fossil fuels trying to remove all the moisture otherwise. I know most obsy's on SGL seem to be for imagers who will no doubt have already considered insulation on the warm room anyway but it may also be a worthy consideration for those who only intend to visually gaze upon the heavens. For those of us who never gave it a thought or there was no simple way of insulating the obsy, at least with good ventilation you know the effects of condensation can be restricted to just the moisture in the air rather than it condensating all over your pride and joy.

[Baffa]

It's easy to forget the importance of having the floor properly insulated and draft proof, there is alot of moisture coming from the ground. Also it's a good idea to lead away the drain water from the roof as it will soak the ground around the obsy.

[skybadger]

So now I have moved to a larger dome - a larger 2.7m old Pulsar type, I am finding I have a significant condensation problem.

Both buildings have been erected in the same location so there's no inherent difference in humidity locally.

The question is what has changed between the two observatories ?

The first was a wood building with solid T&G floor but lots of gaps in the wall cladding for a very breezy building. The glassfibre dome was built using thin expanded polystyrene sheet inside the GFRP as well as tin foil.

This dome never had condensation ever, not on the walls or the dome.

The new dome has both walls and dome made of GFRP and while not full of holes in the walls, I consider there is a good gap around the edges for a breeze to blow. But this dome suffers massively from condensation. So much so that I went in after it had been raining hard all week and thought what I had found was rain ingress. It wasn't - it was two parallel lines of condensation drips. It drips off two low lines at the top of the dome and also runs down the dome to the interior lips, overflows them and onto the inside floor. Similarly, after a 4hr session last night, the first clear night in weeks, the walls of the building were dripping. This is with the door and shutter wide open.  

However mount, pc and telescopes were all dry..

Conclusions:

Air flow   I guess need to increase it.

Insulation - GRP hasn't got any.

Humidity -  hasn't really changed. We have all had rainy and damp winters.

Actions:

I think I am going to clad part of the walls in insulation sheet to see what the difference is. If that is good then I will do the interior of the dome. Any recommendations on sheet ? Thinking about this - why will insulation solve anything - is it because it retains heat for longer and hence stays above the dew point ?

I am not going to try to dry the universe or increase my immense electrical bill further.

Cheers

Mike

[HD-AP]

Hi mike

I have an old superscopes 3m dome walls and dome all grp .I have never had any condensation inside on the dome walls or dome itself.

I'd be interested to know if yours has a shiny finish to the internal grp or is painted .

Mine is just the dull matt grp finish and has never been damp or wet ,always in fact bone dry .

I do have active heat humidity control but this is a vain attempt to enable thermal equalization ,but as i said i used it for 10 years without anything and it's always been dry.

If i was going to insulate i would use the thin polystyrene sheet that's used to line walls under wall paper it's very thin but a good insulator ,i'd avoid the foil backed type as i think condesation may form on it .

My conclusion is that shiney gellcoat surfaces or painted surfaces seem to form condensation matt grp unpainted dosen't ,hope some of this rambling is of some use.

cheers  

[skybadger]

Hi HD-AP

Hmm, bit of both to tell the truth .. The internal side is not gel coated and has been painted to make the GRP less translucent.

I noted from Cloudy nights that some people recommended a layer of felt in the inside of a the dome to provide insulation. No-one has really suggested expanded polystyrene sheet, although an obvious candidate.

The primary places the condensation is dripping from is on the shutter  - there are channels across the width in two places acting as stiffeners and the water drips from the edges in two parallel lines. I might just fill them in with body filler to get a smooth surface so the water runs down the shutter and out in both directions. The other place is the gutters - it runs down the walls and fills them and then drips onto the floor.

So I have two options to consider - ventilation to improve transpiration and insulation to remove the cold surfaces where condensation takes place.

The materials I have as candidates for insulators include:

expanded polystyrene wall paper roll.

felt

lino (cheap closed cell foam type  - 2mm or so but heavy...)

I saw purpose-sold insulation with sticky backing on ebay but it was £15 for 3m by 0.6 mm so expensive.

radiator wall insulation - glue the foil side to the dome.. Keeps out the IR.

Anyone have any others ?

Spaceboy - where did you fit your solar vents ? floor and roof , floor line only ?

Cheers

Mike

[Davey-T]

Ventilation is good to balance the external and internal temps, I think it's good to try and reduce condensation as much as possible before spending a fortune running a dehumidifier, read somewhere about painting the exterior black and the interior white (I think it was that way round but could be visa versa) to balance the inside and outside.

Dave

[Tinker1947]

Has anybody used Bubble wrap in a Dome Obby, it comes in different size, its very light weight, not sure what would hold it in place, maybe a coat of unibond on the structure then when its dry another on the bubble wrap.....???

http://www.globepackaging.co.uk/500mm-x-100m-roll-of-small-bubble-wrap-promotion-price.html?source=googlebase&kw=&fl=1000&ci=43316314543&network=pla

[daaveyboy]

Just came across this thread about condensation in a observatory,as I am nearing my self build observatory (photos & description to follow when I get time) I would like to know if I will need a dehumidifier in my observing area and a heater in the warm room.

[Davey-T]

Depends what you constructing it out of, metal and GRP suffer more than wood, mines made of plastic and gets very little condensation, dehumidifiers are expensive to run.

Defo need a heater in warm room else it'll be a cold room

Dave

[daaveyboy]

It is a brick built one about 4.3 mt,s x 2.6 mt,s with a 6'.0" x 6'.0" sliding roof opening .

[tteedd]

I have an old Pulsar obsy that I bought 2 years ago. The first few months of winter last year it was OK but then suddenly I had masses of condensation on the inside of the GRP dome and condensation on the telescope. After reading online reports from owners of similar observatories I put a dehumidifier in which appeared to solve the problem. This winter I have not been able to use the obsy much due to poor weather and my wife needing my attendance after an operation.

When I went to check I found everything in order except for a white growth/mildew on my main mirror. This was alarming but easily removed whit a little isopropyl. I suspect that the main reflector is remaining cold on days (which we have had a few) where it has been very frosty at night but sunlight has rapidly increased the temperature in the dome once the sun was up.

Looking at other reports here I already have a cover over the scope and a dehumidifier (which probably does not work if the temperature inside  the dome ever falls below zero).

I have sent for a cheap temperature and humidity controller and will be using this and a low wattage heater below the scope when the heater arrives. I shall also be getting a better cover and insulating the inside of the dome.

[michaelmorris]

On 12/12/2012 at 10:23, fwm891 said:

My RoR is of ali sheeting and where its not insulated inside I get quite a bit of condensation. Its far from well sealed, having quite a gap around the tracks and to the sides where the roof rolls past the main structure. At present there is no dehumidifier in the obsy but I will probably install a dessicant type at some stage.

I have a metal roof on my roll off roof design.  Gluing polystyrene wallpaper veneer

http://www.wickes.co.uk/Wickes-Polystyrene-Veneer-Lining-Paper-White-10m/p/105968

to the inside of the roof with No More Nails has very successfully stopped any condensation forming on the inside of the roof.

 

[iapa]

On 01/01/2013 at 11:47, andyboy1970 said:

My OBSY is nice and dry but was only built in the summer 2012, the walls are insulated with 25mm polystyrene and damp proof membrane, the roof and door are not insulated but I may do them in the summer.

The inner skin on the walls is recycled laminate flooring. The floor also has a damp proof membrane under laminate flooring.

I suspect I will install two vents also to circulate the air.

During construction.

Almost completed.

What did you use for hinges along the roof edges?

 

[patm]

It really boils down to air inside the obs getting heated up during the day (which allows the air to carry more moisture) then cooling down at night past the dew point (a temp too low for the air to carry the amount of moisture it already has).

A house doesn't have condensation problems because it is heated all the time. So one solution would be to keep the obs heated but beyond the price of insulating/heating is the issue of hot air currents once you open up to observe.

An attic doesn't have condensation problems because it is well ventilated. During the day the air gets hot (and carries lot of water) but as the outdoors cools down the hot air escapes through vents and keeps the attic humidity pretty close to the outdoor humidity. This happens fairly quickly because of natural ventilation. Since hot air rises we put vents at the top and bottom of the space. Hot air rises and leaves through the top vents (usually in gables) causing a low pressure which draws cooler air in through the bottom (soffit vents etc).

Mechanical dehumidification would work but then you'll need to a lot of sealing to see any benefit and prevent drying the great outdoors.

Complicating matters is the choice of materials. metal and glass tend to cool faster than wood and other organic matter, as do thin plastics. Even worse is when they are exposed to the sky (which is -270C ish) which we're all quite familiar with due to scopes fogging up. An uninsulated metal or plastic/fiberglass roof can cause rain showers under the right conditions.

So the simplest humidity control is to add venting. Both near the floor to let cold dry air in and near the roof to let warm wet air out. A solar powered fan would be a plus not just for humidity but also for faster cool down when observing. Also add insulation to any thin (non wood) panels to slow down the cooling of the inside surface and create a thermal break so its inner temperature doesn't get as low as the outer. Insulation doesn't really add a lot of thermal mass so it won't hurt cool down time all that much.

My own preference is to add natural ventilation - one time low cost and usually pretty effective. I'd add a solar powered fan or two later if natural proves insufficient. That said, I also live in the northern latitudes so i rarely get those really hot muggy days (I've been to the tropics many times - believe me there's a huge difference). I think if I was somewhere down south I might go with sealing everything and adding powered dehumidification.

 

P.S. my background is as a power engineer at recreation centers. One of my responsibilities was for dehumidification of ice rinks and swimming pools and I've lots of experience with mechanical and desiccant dehumidification. At one pool, after all the mechanical engineers were done, I added sensors, rewired and reprogrammed the system, and saved an additional 30% on natural gas (around $20,000CAD that year). Natural venting is not an option in either case because of strict temperature control requirements.

 

 

[mhard26339]

On 09/12/2012 at 23:49, opticalpath said:

I use a dessicant-type dehumidifier (dry-it-out.com model DD122FW) that is very effective. My shed is certainly not airtight, but leaving this device on at LOW setting keeps humidity around 50%. It's pretty efficient.

Adrian

That is what in my dome Adrian, run it on low for 8 hours thro the night (and 9 to 5 on Saturday, free electricity) with no problems with condensation; if it's cats and dogs will leave it on for a bit longer but not normally necessary.

regards

Mike

[sloz1664]

I also use the dessicant-type dehumidifier (model DD122FW). I use a humidity stat that keeps humidity constant to 60%. No issues so far.

Steve