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#1 MAURITS

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Posted 20 April 2014 - 03:28 PM

What is the best "dehumidifier" for observatory domes like the Pulsar dome or the SkyShed POD? :confused:

#2 JAT Observatory

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Posted 20 April 2014 - 04:38 PM

I use an earlier version of this .

Mine has a latching power relay so it will work with remote controlled power strips and it works well in low temps without frizzing up. Since it also is an A/C unit I it to cool the OBS too.

#3 Lord Beowulf

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Posted 20 April 2014 - 05:30 PM

Whatever you can find on Craig's List! I paid $50 for the nice hefty one you can see in the corner here. I bought it to use to help dry the polyurethane when I was painting, but given how tight the warm room is, I'll likely need it in the winter if I'm spending much time in there.

Beo

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#4 MAURITS

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Posted 21 April 2014 - 03:54 PM

Is the dehumidifier permanent working in the observatory?

#5 TimN

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Posted 21 April 2014 - 05:00 PM

Maurits, if you are thinking of getting a POD, I would also post your question to their yahoo group. Wayne (the owner) and the members are usually very helpful and should be able to help with your inquiry.

#6 Lord Beowulf

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Posted 21 April 2014 - 11:34 PM

Is the dehumidifier permanent working in the observatory?


I haven't needed it recently.

Beo

#7 Scott Busby

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Posted 22 April 2014 - 08:39 AM

I use something like this. I run it constantly from Spring to Fall when I'm not in the observatory. Also has air conditioning. I vent the hot air out the bottom thru the observatory floor as well as the drain tube. My observatory is on a deck structure with a couple feet clearance underneath. In the winter when there is less humidity, I run a simple home depot oil space heater to keep the air a few degree above ambient.

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#8 TCW

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Posted 22 April 2014 - 01:47 PM

My dehumidifier only runs when the humidity is above the set point. I am sure yours must be the same.

#9 MAURITS

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Posted 22 April 2014 - 02:59 PM

Is there a specific type dehumidifier, that I need for an observatory (about 10 m³) where sometimes the temperature is to hot or to colt?

There are so many different types, that I dont know what to buy ...

#10 TCW

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Posted 22 April 2014 - 03:05 PM

A small observatory would likely call for a small dehumidifier. Some dehumidifiers are designed to work at lower temperatures. Check to see what their operating range is. You also will want one that has a hose attachment so it will drain outside otherwise it will stop working once the bucket fills up. If you have extremely high humidity a high capacity one might be your best choice.

#11 MAURITS

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Posted 22 April 2014 - 03:12 PM

I see 3 different types:

Refrigerant dehumidifier
Desiccant dehumidifier
Peltier dehumidifier

What is than best to buy? :confused:

Is a "continue working system" a better choice?

#12 TCW

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Posted 22 April 2014 - 03:46 PM

I would not use the desiccant unless your humidity levels are very low. You know your climate and conditions so match the capacity and working range of the dehumidifier to your needs.

#13 JAT Observatory

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Posted 22 April 2014 - 04:50 PM

.... . I vent the hot air out the bottom thru the observatory floor as well as the drain tube. My observatory is on a deck structure with a couple feet clearance underneath.


Scott,
I am also on a deck. I vented my water and hot air out the side as I didn't want the moisture and hot air under the observatory.

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#14 Lord Beowulf

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Posted 23 April 2014 - 11:11 PM

Yes, you definitely wouldn't want to go with a desiccant unless you plan to be changing it all the time. That uses a chemical reaction (usually reversible) to pull water out of the air. The other two options are both similar, although I would suspect that a Peltier based solution is probably the less efficient of the two, although I could be wrong. Basically a refrigerant based system is just an air conditioner without the divider between "inside" and "outside". It pulls air in through the cooling (evaporator) coils, condensing the water on the coils. It then runs that cold air through the heating (condenser) coils, bringing it back up to something above room temperature. This is generally pretty efficient since the cold air is being used to cool the hot coils that are making the refrigerant to cool the cold coils! However, the whole process takes energy and that energy ends up as heat that is exhausted as the warm air out of the unit. The result will be that all the energy used to run the unit goes into heating up your room. That's fine in the winter, but for the summer months an air conditioner has the advantage of cooling the room as well as pulling the water out of the air. It just doesn't do it as efficiently since it's using hot air (outside air) to cool the condenser coils.

Beo

#15 DeepSpacBlakHole

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Posted 24 April 2014 - 12:24 AM

Single hose AC's just suck air in from the outside (through every crack) to replace the air being blown outside.. Inside air has to be used to cool the compressor. This causes a pressure difference from inside to outside.. Very inefficient. The humidity/temp will never be that far away from the outside humidity/temp.

You need a dual hose ac that has a separate hose for intake to cool the compressor.

#16 ManicSponge

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Posted 24 April 2014 - 10:25 AM

Be aware that any of the compressor based units (which are the only ones that work well) have a large starting load. They can give a pretty good voltage drop to the circuit they are on, at start up.
If you have sensitive equipment plugged into the same circuit, it might be a factor worth considering.
The compressor models also add significant heat to a small area, sometimes requiring AC to offset it.
I would skip the Peltier units.
http://secretscotlan...of-the-pelti...
We bought one to try in our travel trailer. I was skeptical, so I left the bathroom vent fan off when I took my shower, and set the unit in the room when I was done. I came back 3 hours later, and there was not a drop of water in the bucket.
Regards, Kyle

#17 Midnight Dan

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Posted 24 April 2014 - 10:48 AM

I see 3 different types:

Refrigerant dehumidifier
Desiccant dehumidifier
Peltier dehumidifier


There's a 4th type - basically a low power heater/fan.

Keep in mind that condensation only occurs when the combination of air temperature and relative humidity puts it below the dew point. There's 2 ways to avoid that: 1) keep the air dry with a dehumidifier, or 2) keep the air temperature warmer than the dew point. Warming the air a small amount and circulating it with a fan will keep it, and the surfaces in your small observatory, above the dew point and dry, without the power consumption and drainage issues that go along with a dehumidifier.

I know of a couple of people who have had good success with these units from West Marine in their PODS.
http://www.westmarin...ifier--P0078...
They produce a nice low 100 watts of warm air, and are designed to run continuously to keep a boat cabin dry for long periods of time while the boat is at dock.

I purchased one but can't use it because my solar power setup doesn't provide enough power to run it for very long. I may run 120v ac out to my POD at some point and then I will begin using it.

-Dan

#18 DeepSpacBlakHole

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Posted 24 April 2014 - 12:31 PM

Wouldn't increasing the dew point still leave you vulnerable to mold on your optics? Or Mold in general? I don't think mold cares about the temp as long as theres enough moisture in the air? Thoughts?

#19 Midnight Dan

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Posted 24 April 2014 - 02:13 PM

As far as I'm aware, mold needs moisture to grow. As long as things are dry it shouldn't be a problem. Humidity in the air is just that - in the air - not on surfaces or available to organisms, unless it condenses. Could be wrong, but I thought that's the way it works.

-Dan

#20 MAURITS

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Posted 25 April 2014 - 03:38 AM

I see 3 different types:

Refrigerant dehumidifier
Desiccant dehumidifier
Peltier dehumidifier


There's a 4th type - basically a low power heater/fan.


-Dan


I think this is the way that I go, with the low power heater/fan! :)

It's the ideal solution for the small observatory ...

#21 Scott Busby

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Posted 25 April 2014 - 06:55 AM

Although this is a minor depature from the topic, I wanted to add in my experience with a wireless data logger. My concern was with tempature and humidity inside my observatory. I purchased a simple wireless data logger from a company called Dataq. The DL monitors temp and %RH and is accessible via the cloud over the internet. It is parameter settable and will send automatic emails anytime a parameter is exceeded. I have mine setup to notify me any time the observatory exceeds 80F and 60%RH. I can change settings anytime over the internet to suit my needs. I live in N.VA and RH can get pretty high during the warmer months. I run a portable dehumidifier and it was important to me to see just how efficient it was in keeping the humidity down inside the observatory. Plus it should help me in determining what timer settings I should use for the dehumidifier. It works pretty cool and it provides nice to know info. My goal is to use it to identify optimum dehumidifier settings to around 70F and >50%RH.

Before I got the DL, I used a wireless security camera to watch a simple battery powered temp and humidity indicator, but found it to be not as accurate as the DL.

#22 MAURITS

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Posted 25 April 2014 - 01:21 PM

Well I ordered the "Stor-Dry" warm air dehumidifier with fan here in Europe (made in Canada), model 9406. :)

It's the same type as this from west-marine in the USA.

Thanks all for the great posts in this thread ... :waytogo:

#23 TCW

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Posted 25 April 2014 - 07:24 PM

Moisture is absorbed by materials such as drywall and wood. Mold grows when the moisture level is above a certain level. One source I found says 55% relative humidity. Heating the air allows it to hold more moisture which in turn causes materials to absorb even more. ;)

#24 Midnight Dan

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Posted 25 April 2014 - 09:31 PM

>> Heating the air allows it to hold more moisture which in turn causes materials to absorb even more.

Yes it can indeed hold more. But more water doesn't just appear out of nowhere. If you have air that's at say 50% relative humidity, it means it is holding 50% of what it is capable of at that temperature.

If you heat this air up, it is now capable of holding more water. But since the actual amount of water in the air has not changed, it is now only holding say 30% of what it is capable of at that higher temperature. So the relative humidity is now 30%. This means moisture in surrounding material, such as drywall and wood, will be more likely to evaporate into the air, and these materials will become drier.

This is why many northern climate homes need whole house humidifiers in the winter time. The cold outdoor air comes into the house and is heated up, which drops its relative humidity. Sometimes it can become so low, like 10% or less, that it contributes to furniture and musical instruments becoming too dry and cracking.

-Dan






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