Post in 'The Green Room' started by Badfish740, Feb 28, 2011.
I need a leaf blower...now I have an excuse. I mean, reason
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I'm really curious just exactly how much electricity a dryer uses per load. I'm sure it varies (lots of factors) but I wish I could get an average. I have one of those "kill-a-watt" devices but of course it is only useful for standard plugs (not the mega-high watt plug types on the dryer).
In any case - having now put up clothes lines in the house near the stove we have saved a lot of electricity (only used the dryer during a 2 day period so far this year when the kids were sick - vomiting overloaded our drying capacity..) and as a bonus it has added a lot of humidity to the air. Have to plan a bit better - we do 4-5 loads a week (4 kids - lots of laundry) so we have only 2-3 days a week that a load doesn't get washed/hung to dry.
I'm not sure that we'll be able to keep it up all year though - getting to be too warm to burn at night (drying time) and not warm enough to hang clothes outside and expect them to dry. Guess we'll just have to burn the electrons again until it warms up enough to hang outside.
Older dryers drew 5800 watts. Newer ones draw 5000 watts.
Of course the heating element does not run continuously
And it doesn't have to run on high. We almost always run it on low.
Electric dryers have several thermal cut-off switches that would shut the dryer down when temps get excessive from a clogged vent or internal passage. There are usually two on the upper rim of the heater coil and a few by the blower assembly.
Another good thing to do is remove the lint screen every month or so and run it under hot water to remove any built up fabric softener that can clog it. You really have to look close at it to see that it is blocked.
If correct, most of us should typically use between 2 and 6 kWh of electric energy per dryer load.
Depending upon one's electric power rates, this would then cost us anywhere between 0.1 and 1.0 US $.
Now comes the kicker, though. Unless I found the wrong numbers it looks as if the typical dryer blower has a 500-1500 cfm capacity. So, let's assume we may blow as much as 50,000 cubic feet of warm house air into the outside world per (big) dryer load. This equals about 1,350 cubic meter, or roughly 1,350 kilograms of air.
On a cold day, we may have to heat the replacement air by 40F or so. It takes about 1 kiloJoule to heat 1 kg of air by 1 degree Kelvin.
Unless I screwed up the math, I am finding that reheating all that air by 40 deg F will cost about 8 kWh (~ 27,000 BTU) , or so.....
Please Lord, let me be wrong...... (I am in a bit of a hurry and don't have time to carefully check my calcs). However, if I am not, we may be paying more (on a cold day) to reheat all the air we blew off through that dryer than we are paying to run the dryer in the first place
In case you were thinking: "well we need to ventilate the house anyhow.....", let me point out that a 1,000 cfm dryer-type "home ventilator" blows at least 10 times more air than the recommended ventilation ("room air turnover") rates for your average 20,000 cubic feet home.
Moreover, few if any homes are wired in such a way that the forced home ventilation via the dryer is somehow subtracted from what the "whole house fan" is programmed to do every day......
That sounds about right. 28k btu in oil for me with a 86% efficient furnace would be 1/3 gallon of oil. That's about $1.25 right now per load of laundry in heating oil, plus the electricity. For us with the low heat dryer setting and the $0.14 kwh rate that means we use about $0.36 in electricity. A total of $1.61 per load. Luckily we hardly ever run the dryer winter or summer unless it's raining. In the winter we hang our clothes inside and the super dry Maine winter air dries our clothes within a day or two. In the summer they are hung outside. I suppose this is how we manage a sub $50 per month electric bill.
Sort of makes me wonder why they don't have OAKs for the dryer... in winter it would then pull in cold (and very dry) air to dry the clothes. Even if the air wasn't heated to a particularly high temperature as a result, it would in theory dry just as fast (perhaps even faster) than using air from inside the house that is likely of a higher relative (and absolute?) moisture content.
I'm sure there are reasons...
Thanks for that number - 2-6Kwh per load... so if I'm avoiding 5 loads per week then I'm saving between 10-30Kwh of electric a week (40-120Kwh/mo). That's quite a bit to me - I average 514Kwh/mo so that is something like 8-23% in savings. I expect given that I have a front loading washer that spins very well I'm likely much closer to the lower end of that spectrum, but that is still significant.
Nah. Thanks for the moral support! However, my calculations have to be wrong somewhere. After all, if it would cost 8 kWh to reheat all the outside air by 40 F, then it should be double that for heating that same amount of air by 80 F or so inside the dryer.... And this is not even counting the power needed to run the fan/drum motor, as well as to evaporate and heat all that water.
I think what's happening is that a typical dryer fan never reaches its maximum cfm rating because of the resistance in the vent pipe/hose. My guess is that the 50,000 or so cu.ft. of air blown through the dryer for 1 heavy load that I estimated (i.e. almost 3,000 pounds worth!) is probably more like 10,000 to 20,000 cu ft. Still more air than any of us can lift, but more in line with the inside heating requirement side of the equation.
edit: also, I should have corrected for the ~15 % lower density of the hot air inside the dryer!
Even if your math is not perfect it is still enlightening. Definitely makes a case for outside air.
I posted this years ago here, but it bears repeating; I replaced my dryer vent with 4" PVC pipe. The smooth inside surface helps maintain air velocity as well as keeping clear of lint readily. The drying time was noticably shorter versus the old dented corro-aluminum vent. Note that I have an electric dryer.
It's still really interesting.
I have noticed that when we run the dryer, the rooms between it and the stove are warmer -- because it's pulling air through the house. Same thing with the bathroom exhaust fan. If they both run for a while, you can actually feel a path of warmer air.
I for one have never heard of a dryer that has a moisture sensor. But then again, my dryer is a good 10 years old and it was the $300 model. TImer, couple heat settings and not much else. Does the cost of moving up to a moisture sensor dryer cover the energy savings over its lifetime thoguh?
I don't think you can buy a new dryer without -- even the cheapest model ($224) at HD has one.
Very interesting thread...
I wonder if it should be titled "How much energy is my clothes line saving?"
Sure, it's not really the weather for it but we got a new, front loading dryer in the fall and have found that when the weather is nice, we hang the clothes out on a line on our balcony. Some of the clothes we'll throw in the dryer on the "steam refresh" cycle for 10-15 minutes before folding or wearing. Sure, takes a little more time and effort but i think it saves a fair amount of energy. Don't really have a good "control" to look at this scientifically.
Btw, on a side note, anybody have any experience with one of those heat diverters like this one at amazon? We had a mold issue in our attic and the washer/dryer is on the 2nd floor so i'm a little hesitant to expose the household to excess moisture but always looking for a way to save $$ on heating the house.
My folks who live in CO (VERY dry area) use on and believe it is a very good thing for them. They believe it has added quite a bit of humidity to the house but not excessive amounts in the area where it vents - i.e. they have no mold concerns. Then again, it is just the two of them and I think the average relative humidity is less than 40% most of the time anyway (year round).
If you have issues in your attic, you may be well advised to investigate air leaks into the attic from the house - that is where the moisture is most likely coming from. Seal up those air leaks and the whole house will be more efficient as well as solving the attic problems. Win-win situation if there ever was one. Of course I'm assuming you aren't venting anything into the attic (big mistake there naturally).
In the winter I use an indoor lint trap for my dryer vent and run it directly into the basement air. The basement is by far the coolest and dryest room in the house, so adding heat and moisture for 40 minutes at a time a few times a week is a good thing. Beware that anything that goes inline in a dryer vent is a potential lint trap and needs to be checked regularly, cleaned if necessary.
Cool, learn something new every day. My 10 year old dryer definitely does not have one...or if it does its not advertised on the unit, nor is there an auto dry setting available on it...you can run the thing for as long as you want and it oesn't matter how dry your clothes are...it'll keep running.
Same here. We haven't used our dryer in over a year. In the winter we have a clothesline in the basement (where the stove is) and it dries clothes quickly. In the spring summer they go outside.
In addition to electricity costs, it is much easier on your clothes and they last longer.
I have wondered as well. My house is sealed up well enough that if the dryer is running and anything else that draws air from teh house (bath fan, kitchen stove fan, etc) I have to crack a window open or it backdrafts the woodstove.
Seriously Nate, you are in AK and not using an OAK on your BK? Your house must not be as tight as you think. Seems like the farther north you are the more you would benefit from an OAK since every bit of air that your stove blows up the chimney is cold and DRY outside air leaking into your home. Humidity control is a big benefit of OAK.
I wonder why they haven't put an intake duct on dryers yet. Perhaps this will be the next big thing like when they started adding intake systems for water heaters and furnaces. Has anybody looked on their dryer to see if it is possible to add a duct to the intake?
We figured out the mold issue- at some point ~ 2 yrs ago (probably when the roofers were up there the previous owners surmise) the dryer vent was disconnected and spent 1-2 yrs venting moist air into the attic which caused the mold. It was professionally mitigated prior to our purchase (and the dryer exhaust repaired) but we're still a little wary about it.
I've wondered this too. I've also wondered if driers could be built with a heat exchanger, extracting heat from exiting air and adding it to incoming air, in function like a a Heat Recovery Ventilator.
Seems I need to tear my drier apart to clean per someone else's advice here so I may have a look then.
I'm surprised they sell dryer's without the moisture sensor option. I've noticed on the two that we've had that they have a metal looking sensor that makes contact with the clothes as they tumble. I'll bet that's the moisture sensor.
Trouble with overcooling the dryer exhaust is the same as with overcooling chimney flue exhaust. The liquids will condense, you'll get gallons of water in the duct which will weigh it down or leak out onto the floor.
Man, I need to clean my dryer vent. I also have a extra foot of pipe coiled around the floor that I need to get shorten. Tonight!
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