Not sure this quite answers your question but our solution is

Sheila maid from ceiling in the Utility room. http://nutscene.com/product-category/sheila-maid-airers/
We actually bought a sleek looking stainless steel version but it's not as good as the traditional design. Doesn't take up floor space, can hang big stuff like sheets.

For exterior use we've got a Brabantia rotary airer. No idea what size as we've had it well over 10 years and it's still going strong. Holds a lot of washing in a small space, easy to hang, won't blow over in the wind.
http://www.philipmorrisdirect.co.uk/hardware/rotary/brabantia-airers/dept/

We've also got a couple of these things http://www.argos.co.uk/product/3896871 from living in flats while building.

Posted By: fostertomBear in mind that drying things indoors is not 'free' of energy requirement - may not be better than tumble drier.

Hmm, I think the only guarantee is that it is definitely not worse than using a tumble drier. I'd be amazed if any tumble driers come close to the same efficiency. Having said that, I agree that it's better to dry things outdoors when possible.

Posted By: djhI think the only guarantee is that it is definitely not worse than using a tumble drier

Because the energy that goes into evaporation will be the same, but if it's the exhaust-to-outside variety it extracts indoor air plus heats it on the way out? What about condensing tumble driers, which exhaust to indoors? I suppose they dump the heat of re-condensation into mains water running to waste?

Heat pump drier vs ambient.

Even if Drier is 100% efficient do you not need to compare source of ambient heat? If energy to the drier is provided by grid and heating by gas are you not still better of ambient by a factor of 3? ( that's the COP at which air source/ground source are better than gas isn't it?)

Posted By: Ed Davies22p at 15p/kWh would be a little less than 1.5 kWh or roughly 5.3 megajoules.

Water takes roughly 2.45 MJ/kg to evaporate at room temperature [¹]. So that amount of energy would evaporate 2.16 kg of water. You should have a lot less than that in a washing load after the spin

I seem to remember working on about the same cost figure but I think it was from manufacturers figures. In reality the drying time seems to vary quite widely - ours has a 'perfect dry' function where it runs for 30 seconds or so and then adjusts the drying time (and I think adjusts as it goes along). Duvet covers and sheets often wrap themselves into a ball and need disentangling and restarting. Towels take two cycles (so even with the auto drying time function there must be a max cycle time).

I'm pretty sure that our (8kg) fast spin washing machine does leave more than 2kg water in some stuff.

What it really needs it so weight the washing in and out and run a power meter on the drier (not so easy with the socket directly behind it)

The socket for ours is next to it under the counter.. I simply need to pop the top draw out thats next to it and I could plug in a kill-a-watt meter for a reading or too.
The dryer has a number of settings, we usually opt for cupboard dry.. it sits there gently spinning and turning it over for about a minute before popping up the estimated time. this adjusts as it goes, but tends to be about right (generally takes less time that it initially thinks, by about 5-10 minutes)

We use a "Sheila Maid" airer/dryer, with a dehumidifier in the same (utility) room. That seems to me a good compromise as all the electrical energy used for drying stays in the house - and as the dehumidifier is basically a heat pump, it only uses about 30% of the nominal drying energy that a Tumble dryer uses.

Following on from Eds data in the 'damp, condensation and mould' thread, some data from a test I have just done.

Did a similar experiment and was also interested in how much difference the dehumidifier makes. Feeling is that it helps drying quite a lot (whilst also stopping too much water floating around). In winter we dry washing in a spare room usually using a dehumidifier which is a standard compressor type and was set to keep levels at around 60 RH. Both tests were similar temperature ranges 17.5 to 20. Humidity was monitored by a cheapo temp/ humidity meter and was a lowish background of around 55. Used 2 normal family wash loads. Washing machine 1400 spin. All weights in grams.

Test 1 – with dehumidifier. Pre-wash weight 6518, post-wash weight 8936 so 2418 water weight. After 9 hrs, weight down to 6753 (so minus 2183 from post wash, 235 above pre-wash). 1445 water collected from dehumidifier and 1.4kwh electricity used. After 21hrs, weight down to 6342 (176 less than pre-wash weight). Additional 525 water from dehumidifier and additional .7kwh used. So total water collected was 1970 versus 2594 differences in weight between immediately post-wash and final dry weight.

Test 2 – no dehumidifier. Pre-wash weight 5953, post-wash weight 8590 so 2637 water weight. After 9 hrs, weight down to 6880 (minus 1710 water, 927 above pre-wash weight). After 21hrs weight down to 5959 (6 above pre-wash weight). Some clothes a little damp still so would have gone under pre-wash weight if continued.

Graph below shows data as proportion of initial pre-wash dry weight (to correct for differences in load weights). I think it shows the dehumidifier does speed up drying, but maybe not as much as I would have expected. Maybe due to relatively low background RH due to cold weather? Obviously main reason for using dehumidifier is capturing water so that it doesn’t cause additional problems. Hope this is interesting to someone!