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Can convection be used to drive a passive dehumidifier?

Ok, I have a couple of radiators and a greenhouse that is too humid. In winterr can convection drive fluid from a radiator mounted low in the warm greenhouse to a second radiator mounted outside in the cold and then back to create a chilled metal radiator that will have water condense on it and drip into the soil.

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NachoMahma6 years ago
.  If you are using natural gas and/or LPG heaters, switch to electric. Gas heat produces water (and CO2).
drewgrey (author)  NachoMahma6 years ago
I just have a small electric heater as the greenhouse is only 120 sq ft. I think I will double glaze the door as suggested. I have also cosidered adding a trunk line from my house forced air system to the greenhouse with a filtered return. this would also solve the humidity problem and add some humidity in the house. the greenhouse is only a few feet from the house and the lines could be well insulated. The prospect of having lemon blossom wafting through the house is intriguiing. But then what do I do with the radiators? Solar something?
.  I like the idea of using the moisture to help humidify the house.
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.  Filled with antifreeze (in case the heat fails), they could make good heat storage units to help regulate the temp inside the greenhouse.
I like the way your thinking but a problem I see is if you get someting set up like what you want there are so many variabules (outside temp per day, clouds, weather in general) that you would be constantly fiddling with it. Would be a lot more work than it first appears.
drewgrey (author) 6 years ago
The reason I thought of this was that I have a glass door that in the winter has an amazing amount of water on it if I dont run a dehumidifier. I have worn out 2 dehumidifiers and would like to find a passive solution rather than buying yet another one . The greenhouse is small - less than 120 sq. ft. but has a koi pond in it. My lemon trees like it and so do my Epiphyllums .Also I have the radiators and can arrange the inlets and outlets to encourage flow . I would mount this on a north wall with one radiator inside and one radiator outside. Having a third radiator in direct sunlight to heat the fluid while the outside radiator cools the fluid and the working radiator sits shaded in path of air flow. What I dont know is How powerful is convection. Is it just a very slow process or if encouraged by clever arrangement of these components could it be dynamic enough to move the fluid fast enough to make this work at least as well as the glass door.
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Is the solution just to get an insulated door with double pane sealed windows? Maybe build a small double door entranceway so you have an "airlock".
Yes probably, maybe. ;-)

You will probably need to install a heater in one of the lines to setup the convection, otherwise, if both lines cool equally, they will probably stagnate.

However, this is going to increase the heating cost of your greenhouse. a traditional dehumidifier, while expensive to run, would offset the need for heating.

I'd suggest you also learn to read psychrometric charts to see it the delta t is sufficient to condense the water at a sufficient rate.
caitlinsdad6 years ago
Seems you are trying to create a giant air conditioner. This may get complicated since you have to sense the environment and drive it to the dew point. There should be methods out there on controlling greenhouse temp and humidity if you search for it. Setting up a system may not be cost effective for what you have rather than just opening and closing the windows. Good luck.