Damp and damage

[rfdesigner]

Hi

I'm not posting much at the moment as I'm trying to build the obsy in between everything else..  a VERY long list...

Anyway my obsy is now 1foot off the ground (brickwork) and I'm starting work on the wooden frame.

So I'm starting to look ahead in fine detail at how to keep the scope and everything else in the obsy bone dry (and mould free), googling around I found the following link for museums, where a lot of effort has been expended on how to keep valuable artifacts dry and various problems identified and appropriate solutions proposed.

I just thought the link might be handy.

http://www.cci-icc.gc.ca/caringfor-prendresoindes/articles/10agents/chap10-eng.aspx

Derek

[r3i]

Interesting article - thanks.

The weather station in my obs had been showing my humidity at typicallly 60-70% but recently, with the onset of the damp autumnal conditions, it has crept up and has hit 80% on occassions.  Pehaps I need to put in some countermeasures.

[oly2b]

I  too are experience my first winter with a completed ROR observatory.

I thought mine was well ventilated (obs built on raised decking with 1/2" gaps between decking boards) but the other week with 99% outside RH and peaking 85% RH inside the obs and my mount feeling damp to the touch, I am now reviewing what other measures to use. Considered natural forced air systems but not easy on a pent roof. May install a kitchen type mains extractor fan with built in humstat and timer.

[AndrewG]

My advice would be get a descant dehumidifier (DRY IT OUT do them - search the web); mine is on a timer with 6 hours on and 6 hours off set to 40% RH (during the six hours it only comes on when needed to keep 40%).

After 2 years I have never had an issue and all my kit is kept dry, I even got a second one for the house!!!

There is another thread on this if you search for it..

Hope the above helps.

[rfdesigner]

My advice would be get a descant dehumidifier (DRY IT OUT do them - search the web); mine is on a timer with 6 hours on and 6 hours off set to 40% RH (during the six hours it only comes on when needed to keep 40%).

After 2 years I have never had an issue and all my kit is kept dry, I even got a second one for the house!!!

There is another thread on this if you search for it..

Hope the above helps.

Essentially we have two problems, scope room and warm room.  The warm room needs some way of removing any moisture that gets in (fan + heater to drop RH), the scope ought to be at atmospheric temperature, so I don't know about that, but have assumed that lots of free air movement around it was good.

Am I wrong?

[AndrewG]

Essentially we have two problems, scope room and warm room.  The warm room needs some way of removing any moisture that gets in (fan + heater to drop RH), the scope ought to be at atmospheric temperature, so I don't know about that, but have assumed that lots of free air movement around it was good.

Am I wrong?

The problem is that using a heater will reduce the RH expressed as a percentage of humidity but it does not actually remove any moisture meaning that although the RH% is lower (because the temperature is higher) the dew point is unchanged.   Given we all breathe out moisture the only way to control the dew point within the observatory is to dehumidify or increase ventilation using outside air; the problem with outside air is that it is not controlled, this can provide issues at certain times of the year I.e. If you have a wet day the air will be humid and the dew point would be high, if you then have a cold night and the observatory or the scope falls below dew point condensation will form.

If it was mine I would probably just use a dehumidifier in the observatory and stick an extract fan in the warm room .     

The problem is that only a small amount of condensation in a telescope will cause damage   !

[rfdesigner]

Yes this is pretty much what I thought...  but for me, my obsy room was going to be pretty open, (looking closed, but lots of room to allow air movement).

I was thinking about running a dehumidifier right into the scope to keep the optics dry, but allow the rest of the obsy room to remain at atmospheric temperature, the warm room was to have an extractor fan on a humidistat & a radiator on a thermostat

[Bizibilder]

i have gone for an observatory with good ventilation. The roof overhangs the walls to keep water out but allows air to circulate.  Some folk use all sorts of seals to close all the gaps but, in my opinion, this is a mistake.  Three years with my metal shed and i have never had problems with damp or mould etc.  The new wooden observatory is also well ventilated and we shall see if this is OK too - it should be!

As for dehumidifiers - I'm not convinced.  They must cost quite a bit to run and will remove water vapour from the air.  However any "new" air that gets in will, quite likely, be of higher humidity and will need the water vapour removing.  By opening the roof and/or doors you simply create a vicious circle of introducing moist air and having to treat it.

Humidity itself is a "moving target" - dew forms at lower relative humidities for cool air than for warm air.

[AndrewG]

i have gone for an observatory with good ventilation. The roof overhangs the walls to keep water out but allows air to circulate.  Some folk use all sorts of seals to close all the gaps but, in my opinion, this is a mistake.  Three years with my metal shed and i have never had problems with damp or mould etc.  The new wooden observatory is also well ventilated and we shall see if this is OK too - it should be!

As for dehumidifiers - I'm not convinced.  They must cost quite a bit to run and will remove water vapour from the air.  However any "new" air that gets in will, quite likely, be of higher humidity and will need the water vapour removing.  By opening the roof and/or doors you simply create a vicious circle of introducing moist air and having to treat it.

Humidity itself is a "moving target" - dew forms at lower relative humidities for cool air than for warm air.

Obviously if you have a wooden roof then maybe the condensation (dripping of the roof) has not been too much of an issue; maybe I am a bit "belt and braces" (being a Mechanical Engineer) . 

One of the reasons I control the humidity in the observatory (I used a data logging RH / temp sensor to determine that using 6 hours on and 6 hours off the RH never exceeds 60% even with infiltration) is that if you get the humid air inside the optics when it cools down at night the condensation can form inside the OTA which will eventually (it may take years though) cause mould.  

I think Dave Richards book every photon counts mentioned this as he had to pay serious money to get his OTA's fixed; although I ain't 100% sure.

Given the cost of my equipment  (don't tell the wife) , the cost to run the dehumidifier to have "piece of mind" does not come into it  !

[rfdesigner]

Ah..   just realised, I think you use refractors..  I have Newts..   big difference.

Derek

[pete_l]

As for dehumidifiers - I'm not convinced.  They must cost quite a bit to run and will remove water vapour from the air.  However any "new" air that gets in will, quite likely, be of higher humidity and will need the water vapour removing.  By opening the roof and/or doors you simply create a vicious circle of introducing moist air and having to treat it.

A dehumidifier will also heat the air around it, which will drop the R.H. in the obsy as a side effect. If you're lucky it might even keep it frost-free.

Typically reckon on about 250 Watts while running, maybe 3 - 4p per hour of use.

I do get the feeling that using a dehumidifier in a typical observatory is a bit like trying to dehumidify the world, as there will always be draughts and new, moist air getting in.

Maybe the best course is to keep all the delicate bits covered with an anti-frost fleece covering (yes, really) that gardeners use and if your scope is going to be unused for weeks or months, to bring it indoors.

[Digz]

Good ventilation and the correct application of breather membranes and vapour control layers will help in preventing moisture buildup. And a dehumidifier won't hurt either :-)

[redfox1971]

I always have to leave my dew band switched on through the winter as I found the inside of the correcter would dew up from the centre.its not been problem since.