Dehumidifier speculation

[David]

A dehumidifier works (I am assuming) by drawing air at the ambient temperature over a cooling area where the air temperature drops past the dew point and water condenses out.

The higher the ambient temperature the more moisture the air can contain and so running increasingly warmer air over a roughly 0C matrix will extract more moisture.

Alternatively the dehumidifier may be able to maintain say a 10C temperature drop over ambient and so perform much the same from about 10C upwards.

The issue this time of year is with outbuildings where the ambient temperature is just a few degrees C )if you are lucky).

As most of the moisture has already condensed out, potentially there is little more a dehumidifier can do.

O.K. - so warm the air up first and then dehumidify? Although once warmed the air will probably have taken up the water and then there is no more humidity problem.

Alternatively, warm the air up and then pump it outside (with the humidity condensing at the outlet in a nice cloud of vapour) and replace it with external air at about 4C which will have relatively little moisture.

This could be an extractor fan at one end and a fan heater and inlet vent at the other.

Given that as far as I can see you have to warm the air up anyway before the dehumidifier can work, would this venting warm moist air and replacing with cold dry air be a cost effective method for the winter? Given also that dehumidifiers seem to cost around the £200 mark for good ones.

This also applies to camper vans and caravans (cars too, I suppose). In the winter they are prone to condensation because of the inability of the air to hold much moisture, so condensation settles out everywhere unless the interior is warmed up. So, again, dehumidifier or just bung in a fan heater and open a roof vent so the air warms up, picks up moisture, rises and takes the moisture outside? Downside is that you end up with a warm room containing moisture which will just condense out again unless you are very sure that you have replaced all the moist air with dry cold air before turning off the heating.

Cheers

Daver

[harryagain]

Once air is cooled to around 5 deg C, there is negligable water in it. So some dehumidifiers work by condensing out the airborne moisture on a cold surface.

Others have a dessicant wheel which absorbs water on part of the cycle and is dried out by heating on another part.

[David]

So using a dehumidifier in a room at 5C or below is pretty pointless?

Cheers

Dave R

[meow2222]

yes, for refrigerant types

if it contains more, yes

that's what keeps houses dry, despite us dumping water vapour into the air from breathing, cooking, showering

dumping heated air is rather more expensive, and less effective

This is why I sometimes suggest replacing an extractor fan with a dehumidif ier.

You might improve your proposition by using HRV to reuse the heat.

NT

[Brian Gaff]

Hmm, or why not go for broke and use some huge ones and dehumidify the whole world. I mean... Surely, you need a heater and a de humidifier, end of story. Who wants to dehumidify the freezer, well you may say, that is exactly what frost free freezers in fact are, so there you have it, a big frost free freezer is what you need... thud. Brian

[harryagain]

[stuart noble]

+1