... 2.5kWhx3412/7.7lb = 1108 Btu/lb. Given the long drying time, this might
be vented indoors... 7.7/8 = 0.96 lb/h, so it would only raise the indoor
humidity ratio of an average house in Phila with 224 cfm of air leakage in
January to 0.0025+0.96/(60x224x0.075) = 0.00345, ie 22% RH at 70 F.
But is there a non-heat-pump machine that dries with less than
1000 Btu/lb of electrical energy, like an indoor clothesline?
Yeah. An indoor clothesline. It is very common in my
area to use a folding wire rack, sold expressly for
that purpose. Works especially well if you have direct
sunlight coming in your window.
I would only go back to using mechanical dryers if I
were living in an extremely small space, and/or had to
use a public laundromat, where I didn't want to haul
wet clothes back home.
Cost: One-time $15 for the rack, plus zero ongoing.
Why do people have such an attachment to those
Get Credit Where Credit Is Due
On 25 Nov 2005 11:30:10 -0500, firstname.lastname@example.org wrote:
I can't answer your question, but since we're on the topic, for
interest I just monitored one of our typical laundry loads.
Machine is a Splendide 2000, vented model. Capacity advertised at 5kg
washing, 3kg washing/drying. Set for regular wash, warm/cold, high
spin, half heat, 30 minutes drying.
Load was a mix of shirts, T-shirts, hand towels, washcloths, socks and
underwear. 5lb according to an electronic bath scale which is too
crude for the purpose. IMO the machine would be quite happy with a 50%
larger load. But since my wife disagrees and I don't need any more
Assuming I didn't miss anything (I didn't stand over it the whole
time), it filled once and spent about 45 minutes washing. In this mode
it spends about 12 seconds turning one way, rests for 5, reverses.
About 180W while turning according to a KillaWatt, on which the
display never really stabilized due to the constantly changing
After the wash cycle, the machine drains and refills for rinse, short
wash action, drains and spins for a short time. Repeats, two rinses
Next it enters spin mode, perhaps 10 minutes of various tumbling, spin
speed ramp-up and pumping. Power consumption tops out at about 400W
until it goes into scary-spin mode, about 500W steady for another 10
70 minutes to this point, .21kWh. Removed clothes and weighed, about
1.5lb gain. Too wet to hang up IMO. Clothes would probably drip, and
Replaced clothes for drying, 700W steady for 20 minutes. Vent air is
very gentle flow, barely warmer than room air. Last 10 minutes is by
design tumbling with heat off. Consumption down to about 100W when
drum is turning, about 150W with pump combined.
Total time 1:45. Total consumption .45kWh. No detectable weight loss
since spinning, but my scale was too useless to tell. Clothes were
definitely drier though, plenty dry enough to hang up. Shirts clammy
but wearable in a pinch on a summer day. Although I'm sure that any
self-respecting yuppie would leave them in at least another half hour.
On 28 Nov 2005 01:25:10 -0500, email@example.com (Nick
I didn't stand over it, so it may have rested longer at times. And I'd
expect that the other programs would include less washing, perhaps
less rinsing as well. A chart in the manual seems to confirm that. For
the "knits and delicates" program it shows "S" agitate speed, and 650
spin speed. But the energy for agitating on our machine is perhaps
60Wh per load, so there's not a lot to save regardless.
Perhaps they should be rated in Gs to account for drum diameter. :-)
Anyway, I looked it up for you - 1100 RPM max. How does it compare?
More correctly, the load weighed that much after spinning. My scale
wasn't accurate enough to detect the weight loss after drying so I
described it as best I could. We have one of those chintzy baby scales
as well, so I may try using that on another load for interest. Since
the thinner items were relatively dry, I expect that most of the
moisture still remaining was in the towels and washcloths. I don't
generally pay this much attention to the washing, but in my new role
as Iaundry critic, I noticed this morning that those towels are
definitely crispy to the touch. I suppose for maximum efficiency one
could remove the lighter items after a half-hour and leave the heavy
ones in longer. But I will *not* be making any recommendations. :-)
It wasn't an experiment, merely some quick and dirty observations to
give an idea of how one machine works and how we use it. Perhaps I'll
post similar notes on the dishwasher as well since these per-use
energy consumption figures with setting details seem to be hard to
ditto. I was a very obvious joke. (LOL may indicate
That's a pretty fast spin cycle. It's a good thing they
are only off balance when they first start up. Mine has
danced across the rom a few times before the pinball
tilt switch picks up on it and shuts it down.
... of electrical energy, vs 0 Btu/lb for an indoor clothesline.
I wonder how often the drum moves and how much of that energy
comes from the motor.
They are, on some sites.
I'm not sure. One US DOE site lists "Remaining Moisture Content" standards
warm spin cold spin
15 min 4 min 15 min 4 min
100 Gs ~45% ... 50%
500 Gs 24% ... 30%
Digital scales are getting cheaper...
If we can tumble-dry a load of clothes containing 5 pounds of water in
0.5 hours at 130 F with Ps = 4.53" Hg and Pd = 0.374 (?) (70 F at 50% RH
with wd = 0.00788, approximately) and 0.1A(Ps-Pd)0.5 = 5, using an ASHRAE
swimming pool formula, we might say their equivalent area A = 24 ft^2.
Let's arbitrarily reduce this to 10 ft^2, with no tumbling, which makes
the numbers easy: drying time = 5/(Ps-Pd).
So an indoor clothesline in free air at 70 F and 50% RH might dry in 5/0.374
= 13.3 h at an approximate Twb = 9621/(22.47-ln(460+70+37.4-Twb). Plugging in
510 R (50 F) on the right makes Twb = 522 on the right, then 516, 519, 517.3,
518.5, 517.8, 518.2, and 518.0 R (58.0 F)
If we dry clothes in 20 hours in a closet with C cfm of airflow at 0.25 lb/h,
Pd = 29.921/(1+0.62198/(0.00788+0.25/(4.5C)) = (4.2441C+29.921)/(11.338C+1)
and Ps = e^(17.863-9621/(460+T)) = Pd + 0.25 = (7.0583C+30.171)/(11.338C+1).
If the only heat comes from room air, (70-T)C = 1000P = 250, so T = 70-250/C
= 9621/(17.863-ln(Ps))-460, ie C = 250/(530-9621/(17.863-ln(Ps))). Plugging
in C = 100 on the right makes C = 60 cfm on the left, then 74, 67, 70, 68.5,
69.0, and 68.8, which makes T = 70-250/68.9 = 66.4 F, approximately.
If we speed this up with closet insulation and heat, 10 hours at 100 F makes
Ps = 1.979 "Hg, Pd = Ps - 0.5 = 1.479, wd = 0.62198/(29.921/Pd-1) = 0.03234
= 0.00788 + 0.5/(4.5C), and C = 4.54 cfm (not much), with 10h(100-70)4.54
= 1363 Btu of heat, about 0.4 kWh, only 27% of the water's latent heat :-)
With good insulation, longer drying times and higher temps and less airflow
minimize the electrical energy needed for drying: 5 hours at 120 F make Ps
= 3.579 "Hg, Pd = Ps - 1 = 2.579, wd = 0.62198/(29.921/Pd-1)) = 0.05867, and
C = 4.38, with 5h(120-70)4.38 = 1094 Btu, ie 0.32 kWh... 10 hours makes Pd
= Ps - 0.5 = 3.079, wd = 0.62198/(29.921/Pd-1)) = 0.07134, and C = 1.75 cfm,
with 10h(120-70)1.75 = 875 Btu, ie 0.26 kWh. This might come from a Holmes
HFH111 1500 W fan space heater ($12.88 at Wal-Mart) with its thermostat set
to 130 F (if that's below the upper temp limit) running 100x260Wh/(1500Wx10h)
= 1.7% of the time.
If we dislike stiff clothes and don't mind extra labor, we might put
a dryer inside the closet with a sequencer that only turns it on for
1 out of every 10 minutes and a humidistat and fan that circulates
room air through the closet when the RH reaches 80%.
... of electrical energy, about 10% more than the latent heat, vs 0 Btu/lb
for an indoor clothesline. How often does the drum move and how much of
that energy comes from the motor? US dryers have no yellow energy labels,
but they probably use a lot more, on the order of 5kW x 1 hour.
If we can tumble-dry a load of clothes containing 5 pounds of water in
0.5 hours at 130 F with vapor pressure Ps = 4.53" Hg near the clothes and
Pd = 0.374 "Hg(?) in dryer air (70 F at 50% with wd = 0.00788, approximately)
and 0.1A(Ps-Pd)0.5 = 5, using an ASHRAE swimming pool formula, we might say
their equivalent area A = 24 ft^2. Let's arbitrarily reduce this to 10 ft^2,
with no tumbling, which makes the numbers easy: drying time = 5/(Ps-Pd).
An indoor clothesline with lots of 70 F airflow might dry clothes in 5/0.374
= 13.6 hours.
Drying in 20 hours in a T (F) closet with C cfm of airflow at 0.25 lb/h
makes wd = 0.00788+0.25/(60x0.075C) and Pd = 29.921/(1+0.62198/wd)
= (4.2441C+29.921)/(11.338C+1) and Ps = Pd+0.25 = (7.0583C+30.171)/(11.338C+1).
If heat only comes from room air, (70-T)C = 1000P = 250 Btu/h, approximately,
T = 70-250/C = 9621/(17.863-ln(Ps))-460, ie C = 250/(530-9621/(17.863-ln(Ps))),
using a Clausius-Clapeyron approximation. Plugging in C = 100 on the right
makes C = 60 cfm on the left, then 74, 67, 70, 68.5, 69.0, and 68.8, which
makes T = 66.4 F, approximately.
Drying in 8 hours in a 130 F closet makes Pd = 4.53-0.625 = 4.47 "Hg, and
T = 9621/(17.863-ln(Pd))-460 = 128 F at 100% RH, so we might condense 5 lb of
water on a 128 F or cooler surface. If P pounds of water starts at 70 F and
warms to 128, (128-70)P = 5000 Btu makes P = 86 pounds, eg 20 2-liter 4"x12"
soda bottles in a 16"x20"x12" tall box, adding no water vapor to house air,
with 5000 Btu of drying energy from a heater, with perfect closet insulation.
Now suppose we have 2 86 pound heat batteries, A at 70 F and B charged up to
about 130 F with condensation from drying a load of clothes, and we remove
the clothes and put in another load and use B to heat closet air until A
reaches 100 F, then use the heater to warm closet air until A reaches 130
and the clothes are dry, with half the usual energy. Then we cool B to 70 F
with room air and repeat the cycle. What can we do with 3 batteries?
Is there a continuous- vs discrete-battery process that can dry clothes with
a small fraction of their latent heat? An efficient condensing clothes dryer
might use very little energy to move liquid water from one place to another.
800 rpm spin is basic, 1000 so so, top end ones do 1400 now. At 800
clothes come out saturated, at 1300 they come out no more than damp.
Theres really no need for a dryer if youve got a fast spin washer, but
for some reason driers have become common anyway.
(The old twintubs used to do around 2000-2500 rpm, but that was with a
much smaller drum.)
Machine design is an ongoing issue, getting them to do high spin speeds
without jumping about, pummelling other nearby appliances or dancing
across the floor. This is a common fault mode. Modern machines need to
have off balance load sensors so they dont try to spin up when not
distributed correctly, If they did, the drum housing would break. As
you can guess, heavy vibration is normal.
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