Tumble drying using heat pump?

[rogermunns]

Is this feasible?

[knighty]

I'm not sure how hot a tumble dryer has to be to work ?

but.... if you sucked air on over the heat pumps condenser (hot bit, like the back of a fridge) and then blew it back out over the evaporator (cold bit) if could be a pretty efficient system ?

[beelbeebub]

Yes a heat pump tumble dryer is feasible and in fact AEG made some about 10 years ago.  They were very expensive (around £1000) and only available in Germany, but were beautifully built.

I actually did quite a lot of development work on one about 10 years ago, when I was working for a large appliance manufacturer.

The heat pump dryer would work like a condenser dryer i.e. a closed loop.  The air from the drum is passed over the cold coil at about 10C.  This condenses out the water in the air stream. This cool air, which is pretty damp like cold foggy day, is then passed over the hot coil at about 50C, picking up the heat it gave up earlier plus any heat from the pumping energy.  The air is now warm (about 45C) and very dry, like a hot desert breeze.  This is passed over the clothes where it picks up more moisture and cools.  The cycle then repeats.  The water that is condensed out is collected and then drained away, but the air is in a sealed system, so no external vent pipe is required. Any heat leaking from the system simply contributes to the house heating.

Research showed that, excluding heating, a standard tumble dryer accounts for about 15% of the electricity usage of an "average" household.  So a reduction in the energy usage would have been really beneficial.

Unfortunately the prototype were were tasked with developing was focused on outright speed.  It's energy consumption per kg was about 5 times standard.  However, because of the way it operated (in essence, it stored energy up and used it on one big burst to dry quickly) the extra energy consumption wasn't taken into account in the energy rating system so it appeared as an "A" grade.

I was told to stop development of the heat pump concept as it wasn't novel (as AEG had one, thought the patents were lapsed) ad speed was the way forward.  

My counter argument was that all we needed to do was develop a cheaper, mass market, one rather than the expensive AEG, after all Ford didn't invent the motor car, he just produced the first affordable ones.

Alas my pleas fell on deaf ears and the tumble dryer project was refocused on gas (hummm, really novel) then quietly taken out the back and put out of it's misery.

 

[myozone]

You can still get them here ...

http://www.kitchenappliances123.co.uk/shop/pc/AEG-T59850-7KG-Free-Standing-Condenser-Heat-Pump-Tumble-Dryer-White-p6234.htm

http://www.google.co.uk/products/catalog?hl=en&safe=off&q=AEG+T59850&cid=13453001825180482012&ei=8aEtTdCvHJfS2ASXyrDWCg&sa=title&ved=0CAcQ8wIwADgA#p


cheap on Economy 7

[Nicedad]

I hate to admit that I have one.

After several years of trying to ween my wife off a tumble drier, I gave up and brought the most efficient unit (save the ultra expensive Miele unit) available. Its an AEG 59840 and uses heat pump technology and from what I understand uses the principle beelbeebub has detailed. It was about £540. The power draw is variable, but is certainly less overall that the 2.2kW unit I had before.  

Nicely made and quiet in operation, had it about 9 months.  

[beelbeebub]

wow, didn't know they still made them, the cost has come down quite a lot (over £1000 10 years ago to less than £600 now, esp with the euro stronger now).

My only worry is that even at ~£500 you still have to be going a bit to save enough electricity to be financially and secondly, good luck getting a repair man to fix a heat pump dryer!

That being said, if the build quality is the same as the original then they should last, but a simple vented electric dryer is pretty hard to beat for reliability our (rarely used) one is over 25 years old and still clanks along.

[martin]

we use one of these - 

[rogermunns]

Thought we would make a fortune on a novel idea!!

We have a split air con unit and my wife arranges clothes on her drier stand in front of it while we have it on heating mode. THis helps a bit I suppose.

From what I remember it is the final bit of drying - actually driving off the last of the water - that is the arduous bit. Latent Heat of Vapourisation?

[qeipl]

I use the same as Martin.
It hangs in the utility room which has two big Velux windows for solar gain.
My ASHP cylinder is in an adjacent cupboard, with its main intake from the utility room.
The heat loss from the cylinder adds to the solar gain.
Works even better than I'd hoped.

[guydewdney]

i have both - the rack is heated by the generator.... we have found that a desk fan halves the drying time....

[rogeriko]

Anyone want to become a millionaire then invent a vacuum operated tumble drier. A small vacuum pump will remove all the moisture in no time maybe freeze the clothes but im sure something could be made to work.

[wyleu]

They dry sand like that.

[beelbeebub]

we tried vacuum and freeze drying too.... from memory none of them were economical, either in energy or (in the case of the vacuum) in capital equipment cost.

I think microwaves were tried at one point, they weren't afraid of "novel"

Looking back their biggest failing wasn't lack of innovation, enthusiasm or even brains, it was that they were always trying to be different, and assuming that different would be better, rather than always trying to be better, even if it meant being different.

[Eleanor]

We've recently bought a twin tub so we can feed in warm water and have found that the spinner is so good that the clothes are virtually dry when they come out. I think I'd rather invest in a decent spin drier 

[Baz]

Dehumidifier. House is damp enough without letting more water just evaporate.