new idea for heat pump clothes dryers

As many know, most heat pump (ventless) clothes dryers use R22, a HCFC that is about to be phased out. Once that happens, they will most likely have to switch to a HFC. However, it turns out that a HFC suitable for use in a clothes dryer is hard to find. R22 already has operating pressures in excess of 500PSI in a clothes dryer, so anything with a higher operating pressure will be impractical. That is, unless you use a new idea that can reduce operating temperatures without increasing drying time too much.
Why not pull a partial vacuum (25" Hg or so should be easy to achieve with a very simple vacuum pump) on the chamber before drying so water boils at a lower temperature? That corresponds to lower refrigerant pressures.

that makes sense, standerd home vacuum style fan assembly on a idler box with a gear up of say 1:10 ie one drum rev equals 10fan revs.

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Originally Posted by star882

That is, unless you use a new idea that can reduce operating temperatures without increasing drying time too much.

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Or, select a different refrigerant.

The vacuum pump idea is interesting...sort of like freeze drying your clothes.:D However, depending on the required power input of the vacuum pump you might loose the Energy Star rating.:o

I have a zerro Kw/h washer and drier! though hanging the line can be a pain in wind storms, and the soap is a bit hard on the hands!

At that level of vacuum, it shouldn't take very long to evacuate the drum, should it? The vacuum pump I have in mind for this would be something like a small air compressor, except running in reverse and built to endure moisture. It shouldn't need more than 200w and it should take only a few minutes to pull down.
And if someone can provide a P/T chart for water, maybe an even more modest vacuum can decrease temperatures enough to make some refrigerants practical.

would i still get both socks back as a pair, our current machine is a TARDIS and socks vanish.
LRAC

So you think thats clever? My machine makes my red socks dissappear and makes my white shirts turn pink :p

Whats a washing machine??????

Ian

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Originally Posted by Pooh

Whats a washing machine??????

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It's the person who does your laundry.:D

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Originally Posted by star882

At that level of vacuum, it shouldn't take very long to evacuate the drum, should it? The vacuum pump I have in mind for this would be something like a small air compressor, except running in reverse and built to endure moisture. It shouldn't need more than 200w and it should take only a few minutes to pull down.
And if someone can provide a P/T chart for water, maybe an even more modest vacuum can decrease temperatures enough to make some refrigerants practical.

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Search "saturated steam table", law of partial pressures, pyschrometrics. Maybe look at how the latent heat of vapourization increases as the temperature decreases.

With enough vacuum, would you need heat?

If the vacuum was low enough would you need heat?

Be a saturated state, it needs the Btus to evaporate.

I believe other ventless ones just use heat and an HX to dump the heat to room air, uses the room air temp as the dewpoint to condense the moisture out.

Condensate drains away, be a deep trap with a vaccuum.

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Originally Posted by SIGNSTU

If the vacuum was low enough would you need heat?

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With a low vacuum the water vapour would indeed boil off the clothes, but unless you have some method of extracting it from the drying chamber the clothes would not dry.

still needs heat to change state. Biggest heat loss from a swimming pool is evaporation. Evaporating water absorbs sensible heat from the water it leaves behind

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I believe other ventless ones just use heat and an HX to dump the heat to room air, uses the room air temp as the dewpoint to condense the moisture out.

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Some do work like that (those mostly intended for use in cold climates?), but most new ones (at least the ones sold in my area) actually use heat pumps. You can recognize that type as it will put only a little heat into the room. The LG I have puts about maybe 500w of heat into the room (just guessing). A good amount of heat actually goes into the condensate that appears to be used to subcool the refrigerant. The compressor is about 1HP based on amperage draw. It can take about 2 hours to dry a load, but the heat conservation feature of the heat pump more than makes up for it when counting the total energy used. (Then consider the fact that it doesn't exhaust any conditioned air - more savings!) Warmup takes a while as the only significant heat source is the compressor itself.
It's some pretty awesome technology, but only time will tell how it works out. And I'm not sure what the R22 ban would do...

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Originally Posted by star882

As many know, most heat pump (ventless) clothes dryers use R22, ...

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F:confused: :o
First time I hear of a HP clothes dryer.

I thought europe was crawling with ventless clothes dryers

I know that pure steam (not with air) takes up 1,600 more space than water at sea-level boiling point. But, I think that when water vapor is mixed with air, it is different... I've never studied that, so I can't say how different. If that 1,600 X volume still is true, you have a lot of volume to pump.

I also wonder if heat has an additional function besides drying. It may also help get rid of wrinkles, as the clothes are tumble dried. I am not sure. If you just use unheated air in a standard dryer, do the clothes come out more wrinkled?

Joe Dunfee

perhaps you could post a photo of your LG, you must of have the back off of it some time, be interesting to see

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Originally Posted by Abby Normal

I thought europe was crawling with ventless clothes dryers

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I've never seen a heat pump dryer either. I bought a machine recently, tried a few shops and they all had the same range of condensing machines - as someone mentioned these use an aluminium air-air heat exchanger which uses the room air temperature to condense the recirculating air from the drum. It works, and there's surprisingly little heat coming from the vent - much more seems to be lost off the back of the machine.

Anyway, I need all the heat I can get here, so I put clothes on to dry in the evening and it warms a room up :cool: