Sciencemadness Discussion Board

drying large amounts of air

chief3 - 5-12-2014 at 00:33

I wonder how to get a certain old house dry ; it is not really heated in winter, and to preserve it the moisture must be taken out of it ...

Now it also has _volume_ , and the average electric dryer will never work well enough, electricity is also expensive in germany ...

So I think about using a hygroskopic salt, which I could recycle by burning it in a furnace ...

Now handling of liquids is always way more complicated than handling of solids ...

Since its about removing _masses_ of water from the air ... the recycling should not really contain any complicated boiling/crystallization ... , better would be to just burn some solid, to some temperature ... , and expose it in the room, ever again ...


Also all the salts act quite differently ... ; each has its specifics, about how it takes water from air of a given moisture, ant how dry it can make the air ...

Also: It would be nice to use some stuff that is readily available in the hardware-store ... ; Ideas are: CaO, CaSO4, NaCl, mortar , fertilizers , ... , ...

What do you think ?

[Edited on 5-12-2014 by chief3]

[Edited on 5-12-2014 by chief3]

forgottenpassword - 5-12-2014 at 00:42

I think you'll be a lot better off with a commercial dehumidifier. They can remove several litres per hour. If electricity is expensive maybe a petrol-burning generator would be cheaper; especially if no one is living in the house. Making a fire in the fireplace wouldn't harm things either.

[Edited on 5-12-2014 by forgottenpassword]

chief3 - 5-12-2014 at 05:16

Well, I'm thinking about the dehumidifyer-option ; but I would need several ones, and the cheap ones don't work too well ... ...

On the other hand: a dehumidifyer is a refrigerator with a ventilator ; refrigerators are cheap , and I have several ... ; maybe I give it a try to blow 100 m^3 of air per hour through one of those ...
==> gotta work out the thermodynamics ... ... :cool:

forgottenpassword - 5-12-2014 at 06:20

Surely you could rent one? I have a little (second-hand) experience of this from a washing-machine that leaked. My friends rented one and it made short-work of drying out the carpet and floorboards. Sometimes it's easier and cheaper to use the proper equipment for the job. ;)

chief3 - 5-12-2014 at 06:25

Yes, I know ... ; but its for ever-again: No short-term thing ...

forgottenpassword - 5-12-2014 at 06:35

Okay. Well, I'd suggest getting the bulk of the water out with a dehumidifier, then keeping it dry long-term with calcium chloride placed in open containers around the house in different rooms. Maybe a commercial product such a 'damprid' or whatever you have in Germany would be best, as it has an indicator to show you when it needs replenishing. You can reactivate it by drying it in your oven at 110C, or over a barbecue outside, or something, if you don't want the water being transferred to your own home! They will probably recommend NOT to regenerate it, but to buy some fresh stuff, for obvious reasons of wanting to sell more! If you heat it evenly and slowly, and avoid charring anything (if that's even possible), there's no reason why you can't re-use it over the coming years.

[Edited on 5-12-2014 by forgottenpassword]

WGTR - 5-12-2014 at 09:15

I use a dehumidifier in my house, and empty about a gallon a day when it's humid outside. It doesn't matter if I keep the house closed up; the humidity quickly permeates everything. I remember hearing that the average house has the equivalent of a large hole in the side of it, due to all of the various air leaks throughout the house.

Anyway, I keep the humidity down around 45-50%. This inhibits mold growth, and keeps down odors.

macckone - 5-12-2014 at 10:18

Calcium chloride snow melt pelts are relatively cheap.
They are great for bulk drying but you need to engineer
A container, a fan and a liquid catch.
None of this is beyond the average handyman
you also need a minimal heat source to keep
Things above freezing. Heating the exit air not
The container or liquid catch or entering air.

jock88 - 5-12-2014 at 10:32

and you could (perhaps) sell/use the now 'liquid' calcium chloride for it's original intended use. Two birds with the one stone.............

Bert - 5-12-2014 at 10:56

The Calcium chloride may be re-cycled with heat, depending on relative cost of energy to do so vs. cost of purchasing new dry chemicals.

You must make sure their is an overflow basin to catch any liquid calcium chloride/water solution that escapes from the setup, it will happily keep sucking in more moisture and diluting itself, increasing volume and overflowing long after the salt is completely dissolved. We have used such arrangements to dehumidify large unheated explosives magazines.

aga - 5-12-2014 at 12:21

Just to mention, for practical purposes:-

CaCl2 boils at 1935 C, so you can happily put it in a metal pan and set a wood fire under it to dry it for re-use.

markx - 6-12-2014 at 04:12

Truly, there is no reasonable way to prevent the humidity from permeating a house. Trying to remove the actual water from air is a futile fight with an overwhelming enemy. If your house is not perfectly airtight (I have not seen one so far) then forget about the salt type's just cheating yourself. Once the desiccant lowers the relative humidity inside the house, the process of diffusion from outside starts to replenish it in an everlasting cycle no matter how hard you try to stop it. Hence the only rational approach is to raise the temperature and with it also the relative humidity drops, even though the actual amount of water in the air remains the same. In result also all the harmful effects of high relative humidity are supressed (mold and bacteria growth, odours, deterioration of biodegradable materials etc.)

Nowadays the automated heat pump units have become really affordable and show a very reasonable efficacy. I see no reason why you could not install one of those in the house and program it to keep the temperature lets say at +10C. There are also units that can be controlled remotely via GSM or internet. So if you wish to switch it off or on you can do it without actually going to the house. In case it is far away...
You can also install an electrical dryer unit, but these are more specific than the heat pump units and hence more expensive (even though they operate on the same principle and consume about the same amount of energy). Therefore I would really suggest to opt for a heat pump unit with suitable parameters and forget about the hygroscopic salts. They work well for keeping moisture out of hermetically sealed glass jars on the laboratory table, but a whole house is something else.