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Dehumidifier – which type should I get?


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I hear there are different types of dehumidifier.

Which type should I get for a small wooden roll off roof observatory?

Also if left switched on all the time, how much would one cost to run continuously.

Links would be helpful.

Many thanks for any replies,

Lee

(please move to appropriate topic area)

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+1 for dry-it-out.com. The important thing is to get the desiccant adsorption type. They are effective down to 0C, unlike the refrigerant type which don't work at low temps.

Adrian

I don't have an observatory but got a desiccant type when the old one broke. I use it for the house but it is great for the scope and eyepieces when I come in after a  dew fest. 

The desiccant types turn on far less too, saves on the bills because they are efficient at all temperatures :smiley: . The time you'd probably want it on most is in winter and autumn and when it gets cold, the conventional ones just suck up very little water when it is cold. They work great in a hot summer when you don't need them, but their quoted capacity is seldom reached, since that only happens at a specific reference temperature. The reference temperature vendors use to quote sales figures is quite high and will not be reached in the colder weather, of even close to it.

Worth reading a couple of reviews, whilst I've had no issue with mine, there is a tendency for some of the cheaper models to break down quite often after 6 months.

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Based on experience refridgerant dryers are not effective below +2 or +3 C dew point. Depending on ambient conditions that could still be 40% or less, but if the DP drops below ) C then they become ineffective.

(The company I work for sells hygrometers...and driers for calibration)

Dessicant is better and has a wider range, but make sure you can re-charge it. Some dessicants allows baking around 150C for a couple of hours to regenerate, some just have to be replaced.

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.... Dessicant is better and has a wider range, but make sure you can re-charge it. Some dessicants allows baking around 150C for a couple of hours to regenerate, some just have to be replaced.

I think what you're referring to are static containers of desiccant material that absorbs moisture and has to be replaced or removed and regenerated regularly. The dehumidifiers we're talking about are active, powered dehumidifiers that have a (non-removable) rotating desiccant disk that is constantly being regenerated by a built-in heater. Moisture is extracted and drains from an outlet hose.

Adrian

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Interesting ... that type gets rid of the water just by blowing out the moisture-laden air. The commercial types I've seen work on the same heated rotating disk principle, but they collect the moisture as a liquid condensate that goes to a tank or drain hose.

Adrian

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How much does it actually cost to run?  I know Steve Richards has a dehumidifier in his Pulsar observatory and maybe if he reads this he can give his views on both the cost, how to install and maybe any comments about the additional heating that may occur.

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Most models seem to consume something around 350 Watts on Low and 600 Watts on High setting.  But modern units go into a very low power 'air sampling' mode, or cut off altogether, when the preset target humidity is reached, so it's hard to predict what actual running costs would be.  It would depend on weather conditions and how well the structure is insulated and sealed from external conditions ..... i.e. how hard it has to work and how often it cuts in.   The spec of mine says that the heater will raise the temperature of the incoming air by 10 -12 degrees C.

I switched mine off recently.  Two days later, my camera (which I leave attached to the scope) was dripping with condensation :eek:.  Worth thinking about when considering running costs!

Adrian  

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Thanks Helen.  Didn't pick up on the 46P per day.  But he didn't say where he lives - see re Adrian's comments above.  I live in a very wet area - around 70ins a year or more and 1 - 2ins in a day is not unusual and the Pulsar isn't exactly well insulated.  I have my scope covered by a Telegizmos cover with silica gel packs inside.

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Thanks Supernova. Looks like dehumidifiers only really work if the rainfall isn't too excessive.  I had exactly 1 inch of driving rain yesterday.  Observatory dry except for a puddle near the door where I hadn't sealed it.  But scope nice and dry inside the cover.

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The dehumidifier will reduce the RH of the air inside the obs even in the "wettest" conditions... The only reason I took them out of the obs was because the gear was getting so little use I couldnt really justify the cost of running them...So the obs was stipped of scopes and other gear - who knows one day we might get an imp[rovement in the weather and it may go back in again...

We now use them in the house and for laundry drying where they dry a room full of clothes  at a fraction of the cost of a tumble dryer....

Peter...

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I built one to my own design...

It started out as a rotating dome with zenith hole but as I prefered widefield i added a slide off roof to it... When I fire up the pc later I will dig out a post...

Obs_Sideview.jpg

I scrimped on the dome ring and it's come back to haunt me... rectifying the problem may be difficult :(

I'm setup for mobile these days anyway to get darker skies and better horizons... So the obs is being used as a garden shed... It's usually a garden shed that gets converted into an obs trust me to be different...

Peter..

Sent from my GT-P7300 using Tapatalk 4

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