Dehumidifying Tumble Dryer

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Mr Sandman

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Jun 22, 2008, 10:41:50 AM6/22/08
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Has any one considered using a dehumidifier with a condensing tumble dryer?
I am keen on the room dryer solution, but the wife (surprise surprise)
isn't...she likes her tumble dryer! So was thinking if one could sit an
innocent looking dehumidifier next to the tumble and pump the air from the
tumble to and from it......

Steve

Ian Stirling

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Jun 22, 2008, 11:18:49 AM6/22/08
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Sure.
Now compute the size of the dehumidifier needed.
It's really quite large.
Venting the exhaust may be the easiest solution.

Harry Bloomfield

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Jun 22, 2008, 12:08:05 PM6/22/08
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It happens that Ian Stirling formulated :

If the exhaust it plumbed straight to the dehumidifier and the output
of that returned to the drier, it would work as well as saving juice.
Basically that is how a modern condensing drier works, but using cold
water to provide the cooling effect. Trouble is adapting what was never
designed for this purpose - both the drier and the dehumidifier.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk


stevelup

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Jun 22, 2008, 12:33:35 PM6/22/08
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Surely you mean a non-condensing dryer? A condensing dryer does not
exhaust any moisture laden air.

Steve

Ian Stirling

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Jun 22, 2008, 12:40:02 PM6/22/08
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Yeah - the problem is that you need a truly massive dehumidifier to do this,
consider how large a dehumidifier you need to extract 60l/day.

Also - the dehumidifier will not be designed for air input temperatures
of around 100C.

You can of course let the temperature drop, and use the heat output
from the dehumidifier to evaporate the water from the clothing - but
this will take a _lot_ longer as it'll only be 50C or so, and will be
beating the hell out of the clothing all the time.

As a completely random comment - a vacuum clothes drier that had the
ability to warm the clothes to 50C, pull a hard vacuum on them, wait till
the water stops boiling off, and repeat a couple of times could be quite
efficient.
Unfortunately, the design of the pump is challenging.

Andrew Gabriel

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Jun 22, 2008, 2:08:29 PM6/22/08
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In article <ucWdnXLlLeX_HcPVnZ2dneKdnZynnZ2d@plusnet>,

ro...@mauve.plus.com (Ian Stirling) writes:
>
> Yeah - the problem is that you need a truly massive dehumidifier to do this,
> consider how large a dehumidifier you need to extract 60l/day.

I'm not convinced -- I dry a washing machine load with my 400W
dehumidifier-in-a-cupboard in about 1 hour (large towels and
jeans take longer).

So how long does it take to dry a washing machine load in a
domestic tomble drier (say, one built in to a washing machine),
given you have to split the washing machine load into multiple
drier loads to run consecutively?

> Also - the dehumidifier will not be designed for air input temperatures
> of around 100C.
>
> You can of course let the temperature drop, and use the heat output
> from the dehumidifier to evaporate the water from the clothing - but
> this will take a _lot_ longer as it'll only be 50C or so, and will be
> beating the hell out of the clothing all the time.

Not convinced the lower temp will matter much, given the air will
be near 0% RH, but still quite warm.

> As a completely random comment - a vacuum clothes drier that had the
> ability to warm the clothes to 50C, pull a hard vacuum on them, wait till
> the water stops boiling off, and repeat a couple of times could be quite
> efficient.
> Unfortunately, the design of the pump is challenging.

What about microwaving them?
I dried out a soaked breadboard that way once (and amazingly
in hindsight, it didn't crack/split in spite of the hissing).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andy Champ

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Jun 22, 2008, 4:57:14 PM6/22/08
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http://www.greenandeasy.co.uk/Product/Product.aspx?productkey=1427

Also available with a John Lewis badge on it - or something that looks
very like it.

Andy

meow...@care2.com

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Jun 22, 2008, 5:18:46 PM6/22/08
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On Jun 22, 7:08 pm, and...@cucumber.demon.co.uk (Andrew Gabriel)
wrote:


> What about microwaving them?
> I dried out a soaked breadboard that way once (and amazingly
> in hindsight, it didn't crack/split in spite of the hissing).

I did that years ago, and its extremely fast. The item dries in a few
minutes max. 2 issues though: first not all clothes are happy to be
dried at 100C, though jeans tolerate it. Second if you set the time
too long burning occurs - a simple solution is to put a cup of water
in with them, but this can add an extra minute to dry times.

So yes it works well enough, but only for a subset of typical domestic
clothing.


NT

meow...@care2.com

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Jun 22, 2008, 5:30:01 PM6/22/08
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On Jun 22, 5:40 pm, r...@mauve.plus.com (Ian Stirling) wrote:

> Harry Bloomfield <harry.m1...@nospam.tiscali.co.uk> wrote:
> > It happens that Ian Stirling formulated :
> >> Mr Sandman <sadvsz...@dcvs.com> wrote:

> >>> Has any one considered using a dehumidifier with a condensing tumble dryer?
> >>> I am keen on the room dryer solution, but the wife (surprise surprise)
> >>> isn't...she likes her tumble dryer!  So was thinking if one could sit an
> >>> innocent looking dehumidifier next to the tumble and pump the air from the
> >>> tumble to and from it......
>
> >> Sure.
> >> Now compute the size of the dehumidifier needed.
> >> It's really quite large.
> >> Venting the exhaust may be the easiest solution.

Dehumidifier based TDs are available ready built. More energy
efficient, but more cost too.

If you want to keep the TD and like the drying closet, why not do
both. Convert a big wardrobe to dh use, and over time I reckon she'll
decide the dryer stage is a waste of time & effort. And if not, each
of you can do whichever you want. Or perhaps borrow a dh for an
overnight demo in the bathroom. Add the fan if you want to impress, it
makes a big difference to dry times.


> > If the exhaust it plumbed straight to the dehumidifier and the output
> > of that returned to the drier, it would work as well as saving juice.
> > Basically that is how a modern condensing drier works, but using cold
> > water to provide the cooling effect. Trouble is adapting what was never
> > designed for this purpose - both the drier and the dehumidifier.
>

> Yeah - the problem is that you need a truly massive dehumidifier to do this,
> consider how large a dehumidifier you need to extract 60l/day.
>

> Also - the dehumidifier will not be designed for air input temperatures
> of around 100C.
>
> You can of course let the temperature drop, and use the heat output
> from the dehumidifier to evaporate the water from the clothing - but
> this will take a _lot_ longer as it'll only be 50C or so, and will be
> beating the hell out of the clothing all the time.

When youre not drying them hot there's no longer any reason to tumble.
Its hot drying that causes stiffness.

> As a completely random comment - a vacuum clothes drier that had the
> ability to warm the clothes to 50C, pull a hard vacuum on them, wait till
> the water stops boiling off, and repeat a couple of times could be quite
> efficient.
> Unfortunately, the design of the pump is challenging.

Well, there are ways to stop the pump seeing the damp. How long would
it take to reach sufficient vacuum? How hard would it need to be?


NT

Bob Mannix

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Jun 23, 2008, 3:14:21 AM6/23/08
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"stevelup" <stev...@gmail.com> wrote in message
news:cd4558bd-9421-452e...@34g2000hsf.googlegroups.com...

That would be clever! It exhausts air with considerable less water in than
it started with, which may be enough to be cleared naturally from the room -
still has plenty of water in though. The only way to get rid of all the
moisture is to the outside but a condensing tumbler may be a good solution.

(Which the OP meant though, taking your general point, I'm not sure!)


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not


Andy Champ

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Jun 23, 2008, 5:51:42 AM6/23/08
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Bob Mannix wrote:
>
> That would be clever! It exhausts air with considerable less water in than
> it started with, which may be enough to be cleared naturally from the room -
> still has plenty of water in though. The only way to get rid of all the
> moisture is to the outside but a condensing tumbler may be a good solution.
>
> (Which the OP meant though, taking your general point, I'm not sure!)
>
>

This is true of some designs, but not others.

Some recycle the same air through the clothes over and over again,
drying the air on each pass.

Some take in fresh air, and dry it on the way out.

On the latter type there is probably going to be some moisture in the
outgoing air; with the former, there is no contact between the exhaust
air and the clothes, so no chance of any moisture getting into the room.

Andy

Ian Stirling

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Jun 23, 2008, 8:49:41 AM6/23/08
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meow...@care2.com wrote:

> On Jun 22, 5:40?pm, r...@mauve.plus.com (Ian Stirling) wrote:
>> Harry Bloomfield <harry.m1...@nospam.tiscali.co.uk> wrote:
>> > It happens that Ian Stirling formulated :
>> >> Mr Sandman <sadvsz...@dcvs.com> wrote:
>
>> >>> Has any one considered using a dehumidifier with a condensing tumble dryer?
>> >>> I am keen on the room dryer solution, but the wife (surprise surprise)
>> >>> isn't...she likes her tumble dryer! ?So was thinking if one could sit an

>> >>> innocent looking dehumidifier next to the tumble and pump the air from the
>> >>> tumble to and from it......
>>
>> >> Sure.
>> >> Now compute the size of the dehumidifier needed.
>> >> It's really quite large.
>> >> Venting the exhaust may be the easiest solution.
>
> Dehumidifier based TDs are available ready built. More energy
> efficient, but more cost too.

Yup.
_much_ more costly.
<snip>


>> Also - the dehumidifier will not be designed for air input temperatures
>> of around 100C.
>>
>> You can of course let the temperature drop, and use the heat output
>> from the dehumidifier to evaporate the water from the clothing - but
>> this will take a _lot_ longer as it'll only be 50C or so, and will be
>> beating the hell out of the clothing all the time.
>
> When youre not drying them hot there's no longer any reason to tumble.
> Its hot drying that causes stiffness.

If you blow dry air at 50C past a ball of stationary clothes in the
middle of the dryer, they aren't really going to dry especially fast.

>> As a completely random comment - a vacuum clothes drier that had the
>> ability to warm the clothes to 50C, pull a hard vacuum on them, wait till
>> the water stops boiling off, and repeat a couple of times could be quite
>> efficient.
>> Unfortunately, the design of the pump is challenging.
>
> Well, there are ways to stop the pump seeing the damp. How long would
> it take to reach sufficient vacuum? How hard would it need to be?

Unfortunately not - well - there are, but it involves a cryotrap, which is
a place for the water vapour to condense due to extreme cold - held at -50C
or so.

Quite hard - 30Pa or so, .3% of the atmospheric pressure, at the end
of the cycle, 500Pa (5%) at the start.

The idea would be - you start off with the water in the clothes at 50C.
You then pump it down to 30Pa, when it's ice at -20C, and has evaporated
about half its volume due to the heat stored in the water and clothes,
then repeat again a couple of times.

Andy Champ

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Jun 23, 2008, 4:06:52 PM6/23/08
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Ian Stirling wrote:
>
> Unfortunately not - well - there are, but it involves a cryotrap, which is
> a place for the water vapour to condense due to extreme cold - held at -50C
> or so.
>
> Quite hard - 30Pa or so, .3% of the atmospheric pressure, at the end
> of the cycle, 500Pa (5%) at the start.
>
> The idea would be - you start off with the water in the clothes at 50C.
> You then pump it down to 30Pa, when it's ice at -20C, and has evaporated
> about half its volume due to the heat stored in the water and clothes,
> then repeat again a couple of times.
>

Well if you're going to go for the incredibly complex - why not zap them
with microwaves to keep them warm while pumping down?

Andy

meow...@care2.com

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Jun 23, 2008, 9:01:01 PM6/23/08
to
On Jun 23, 1:49 pm, r...@mauve.plus.com (Ian Stirling) wrote:

Why would you arrange them in a ball? :)


> >> As a completely random comment - a vacuum clothes drier that had the
> >> ability to warm the clothes to 50C, pull a hard vacuum on them, wait till
> >> the water stops boiling off, and repeat a couple of times could be quite
> >> efficient.
> >> Unfortunately, the design of the pump is challenging.
>
> > Well, there are ways to stop the pump seeing the damp. How long would
> > it take to reach sufficient vacuum? How hard would it need to be?
>
> Unfortunately not - well - there are, but it involves a cryotrap, which is
> a place for the water vapour to condense due to extreme cold - held at -50C
> or so.

One could adapt the desiccant wheel dehumidifier principle using 2
tubes of desiccant and valves to change over the air flow. Of course
it doesnt compare to a cold trap, so wont help create a great vacuum,
but good enough for preventing condensation in the pump.


NT

Ian Stirling

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Jun 24, 2008, 7:52:22 AM6/24/08
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meow...@care2.com wrote:

> On Jun 23, 1:49?pm, r...@mauve.plus.com (Ian Stirling) wrote:
>> meow2...@care2.com wrote:
<snip>

>> > When youre not drying them hot there's no longer any reason to tumble.
>> > Its hot drying that causes stiffness.
>>
>> If you blow dry air at 50C past a ball of stationary clothes in the
>> middle of the dryer, they aren't really going to dry especially fast.
>
> Why would you arrange them in a ball? :)

I was assuming the original thread topic - 'tumble drier'.


>
>
>> >> As a completely random comment - a vacuum clothes drier that had the
>> >> ability to warm the clothes to 50C, pull a hard vacuum on them, wait till
>> >> the water stops boiling off, and repeat a couple of times could be quite
>> >> efficient.
>> >> Unfortunately, the design of the pump is challenging.
>>
>> > Well, there are ways to stop the pump seeing the damp. How long would
>> > it take to reach sufficient vacuum? How hard would it need to be?
>>
>> Unfortunately not - well - there are, but it involves a cryotrap, which is
>> a place for the water vapour to condense due to extreme cold - held at -50C
>> or so.
>
> One could adapt the desiccant wheel dehumidifier principle using 2
> tubes of desiccant and valves to change over the air flow. Of course
> it doesnt compare to a cold trap, so wont help create a great vacuum,
> but good enough for preventing condensation in the pump.

Not really.
Through the pump - when it's working as designed - is going 100% water
vapour.

And dessicant does not hold onto water vapour that aggressively - unless
you're talking of really aggressive stuff like 95% sulphuric acid.

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