Condensation

[CDKPhil]

Originally Posted by Marke

Phil if its well sealed you could get yourself a cheap de-humidifier and put it on a timer if its really bad. I thought of this option if it was needed but so far I have had no condensation at all - touch wood.

Ten points to this man.

Today was wet, and the temperature got to a cosy 8.5C. I checked the humidity in the dome at midday and it was 87%. The inside temp was 9.5C and the mount temp was 8.7C. Much to my disgust there was a lot of condensation on the mount. A phone call from another IIS member jolted my memory about dehumidifiers.

I was looking at the exhausting option but it would have meant cutting a 150mm dia hole in the side of the dome. Not a great option.

I went out looking for dehumidifiers and found some seconds stock at Harvey Norman. They had a Delonghi model that would do 20L of water per day. The price had been reduced from over $400 to $220. So I bought it.

When I got home the mount was still covered in condensation. I plugged the dehumidifier in and waited to see what happened.

After about ten minutes the condensation evaporated.
Over the space of two hours the humidity dropped about 13% down to 74%.

I think if I cover the floor I will get a better result. but if I don't have to I won't.

The down side to this machine, it draws 400W.
If I use a timer to turn the machine on and off. It will not turn back on, the on button needs to be pressed.
The operating temp is from 2C to 38C

The dehumidifier has some auto settings. 50%, 60% and 70% relative humidity. If I choose one of these settings the machine will come on if the humidity goes above these levels.

I will monitor how it goes and let you all know after another bout of minus weather.


Thanks heaps guys for all you suggestions

Fingers crossed it is going to solve my problem.

Cheers

[Marke (Mark)]

Thats great hope it works out , I had heard of others using these in high humidity climates in the obs to try and keep mould and such down.

[rat156]

Good to see it worked out Phil, of course that's the same system in use in most cars these days. Mine automatically turns on the AC if it detects fog on the windscreen, fog gone in a couple of seconds.

Where does the condensate go?

I like the RH setting, I assume that there's a RH where you don't get the problem.

Cheers
Stuart

[ChrisM]

Phil,

To my surprise, I've had a heap of condensation on the mount twice in the last month or so when it's been cold. I keep a cover over the scope and mount http://www.iceinspace.com.au/forum/a...e.php?a=102717
with a few silica gel canisters around the mount, but what I think has happened is that some moist air has been trapped inside the cover when I've put the scope to bed, and the moisture in the air has condensed when the temperature has dropped. Unfortunately, once it's in the air-space inside the cover, it's trapped there and the small canisters are obviously no match for that quantity. I'm now considering how I might pipe some dry air up through the pier.

I also have a Delonghi dehumidifier, but it's more for drying out the observatory and other contents eg. books / papers etc. Having said that though, the other night I operated the dehumidifier for about 20 minutes around the telescope and mount before slipping on the cover. I'll see whether that worked next time I uncover it in the cold.

I have noted that the dehumidifier's heat exchanger tends to ice up if the ambient air temp inside the obs is much less than about 5 - 7 deg C. The Delonghi also needs a button pressed to start it (so a timer in the GPO won't do it); I intend to investigate its inner workings one day to get around this.

And finally, just to add to the radiative cooling discussion - on a clear night an infrared thermometer aimed at the zenith will typically indicate -30 to -38 deg C here. No wonder stuff cools quickly. In summer it is not quite so cold - at about -20 deg C.

Chris

[CDKPhil]

So far so good, at the moment the inside temperature of the dome is 14˚C the mount temp is 11.7˚C, no condensation has formed. The humidity inside the dome is 64%.

Originally Posted by rat156

Where does the condensate go?

Hi Stuart, there are two options for the condensate. The dehumidifier has a catchment tank which will fill up over time and then has to be emptied, or a hose can be attached to the outlet pipe and directed outside. The latter option is what I will be doing. I will attach a hose and run it down through the floor and out from under the dome.

Originally Posted by ChrisM

Phil,

To my surprise, I've had a heap of condensation on the mount twice in the last month or so when it's been cold. I keep a cover over the scope and mount

Delonghi also needs a button pressed to start it.

Great setup Chris, I would be doing what you said, trying to duct the dehumidified air up through the pier or up under the cover. I guess you could run the dehumidifier next the the telescope an see if that makes a difference.

I was playing around with the button just now, if you keep the button depressed the unit will come back on when it is disconnected and then reconnected to the mains. I don't know if it will cause problems if the button is depressed for a long period of time.

Cheers

[cohiba (Robert)]

I had a similar problem, I have a Sirius Dome mounted on raised open decking. I overcame it by laying down some rubber backed marine carpet (Clarke Rubber) and using a couple of containers of deccidant (Bunnings) I also keep a sheet over the Scope and Mount, simple and works a treat

[CDKPhil]

Hi Robert, thanks for sharing your experience.
It is good to hear that you solved your problem.

The Sirius Domes are fibreglass, do you get much condensation on the inside surface of the dome?

Does it cost a lot for the desiccant and can you dry it out and reuse it?

cheers

[CDKPhil]

Originally Posted by ChrisM

The Delonghi also needs a button pressed to start it (so a timer in the GPO won't do it); I intend to investigate its inner workings one day to get around this.

Chris

I opened up my Delonghi today, to investigate the push button switch dilemma.
It was not very hard to work out, all I had to do was solder a bridge across the on/off switch on the PCB. If I want I could replace the micro switch with one that doesn't turn off when it is disconnected from the mains.

Now it is ready for a timer.

Cheers