how do they calculate energy usage on dryers?

strider3700 · 03-14-10, 05:08 PM

My dryer uses 939 kwh/year during typical usage according to the energuide sticker on the top. My new clothes line uses zero.

I'm wanting to work out how much I'm saving per load dried on the line but since my watt meter doesn't handle 220 I'm hoping I can get a good estimate on the average load from the 939kwh/year.

I just can't find information on how they came up with that average. Does anyone have any ideas or other suggestions on how to work this out?

Daox · 03-16-10, 07:49 AM

According to energy star's website:

Quote:

ENERGY STAR does not label clothes dryers because most dryers use similar amounts of energy, which means there is little difference in the energy use between models.

That being said, I wonder if someone can't measure their energy usage for us and let us know how much juice they used.

WD-40 · 03-16-10, 10:04 AM

fact from http://www.energystar.gov/index.cfm?...up&pgw_code=CW
The average American family washes almost 400 loads of laundry each year, so based on strider3700 saying that his dryer uses 939 kwh/year one has to assume that you would dry the same almost 400 loads a year. Then that would work out to 2.3475 kwh/load
older dryers where rated by energystar ..my old dryer was rated at 929 kwh/year

NiHaoMike · 03-16-10, 10:37 AM

Quote:

Originally Posted by Daox

According to energy star's website:

That being said, I wonder if someone can't measure their energy usage for us and let us know how much juice they used.

But heat pump dryers clearly use less. That would be a good reason to put dryers in the Energy Star program.

strider3700 · 03-16-10, 05:54 PM

I found this late last night.

How clothes dryers are tested

even though the dryer is new it doesn't qualify for energy star since none of them do. But energuide ratings still exist on them up here and mine is 939 kwh/year

so according to that page they say the average is 416 loads/year so 2.257 kwh/load... Now we're on an annoying to calculate things tiered system here but I'm averaging 7.8 cents/kwh including all fees/taxes/... that means each load on average is costing me 17.6046 cents to dry.

Now my electric rate is going up 33% over the next 3 years putting that same load of laundry at 23.414 cents/load.

My new clothesline cost me $35 for the new stuff and $40 for what was existing. So the upgrade will pay for itself in 439.5 loads or 1 year of average use. After the rates go up it would take 320.3 loads to pay for itself. I'm apparently not the average user as I don't do 416 loads a year I do closer to 200 would be my guess. So that gives me assuming I get 1/2 the loads outside (it rains here a lot) a just over 3-4 year payback.

Either way the poles are steel and in concrete or bolted to the wall. The line is heavy duty steel wrapped in some form of plastic and the pullies are metal. I expect the thing to last me decades only needing a bit of oil to stop the pulleys from squeaking.

Now my question is how much c02 am I not producing? I know my power comes from mostly hydroelectric but if I don't use it we sell the excess to others who usually get it from coal so I have no issues ask what is 2.257 kwh work out to in C02 from a coal plant?

ICanHas · 08-31-14, 11:09 PM

Don't forget the indirect losses. Dryer is similar to a single vent portable A/C. There's been some laboratory testing done on portable ACs and many have been found to have a negative efficiency when they factored in heat gain through infiltration of outdoor air into the house for make up air.

If it's in the conditioned space and it's in the summer, you would open a nearest window and run it at night/early morning when bringing in outside air is not objectionable humidity and temperature wise so you avoid drawing a negative pressure and pulling in warm attic air into the hose.

If you run it in middle of the day, most of heat generated by the dryer goes out the vent, but the dryer is pumping out conditioned air and your A/C has to re-condition make-up air, that is drawn in as the dryer exhausts air conditioned air.

ICanHas · 09-01-14, 09:45 PM

So I hit a road block.
The dryer is not a pure 240v load. It's a three wire machine with the motor running line to neutral.

oil pan 4 · 09-03-14, 11:25 PM

I have lots of 220 volt extension cords, fluke325 amp clamp and out side sub panel with easy access to the lines.
And I have 2 clothes dryers, the inside one that never gets used during warmer months is full size, the outside one is a smaller apartment sided one.

What do you want to know?

Here is what I can tell you about electric clothes dryers with out doing any additional tests.
The minimum plug requirement for a clothes dryer is NEMA 10-30. The 10-30 has 2 lines and an L shaped neutral/ground.
Newer homes have the NEMA 14-30 cord. It has 2 lines a neutral and a dedicated non current carrying ground. I don't really see the point. NEMA 10-30 worked fine for 50 or 60 years.

Clothes dryers do have 120 volt requirements. I know this because I have resurrected a few over the years. You have 3 things in there that use 120 volt power:
Buzzer
Timer
Drum motor

The drum motor ends up using up to around 400 watts.

The small apartment sized dryer uses about 17 amps of line to line power when the heater elements are on. Then one leg of line power has about another 4 amps on it.
The full size dryer uses closer to 21 to 22 amps of line to line power plus another 400 to 500 watts on the line to neutral that power the little stuff.

When you adjust the temperature of the dryer you aren't reducing peak power consumption at all. The cooler setting just uses a different set of thermostats to cut power to the heater coils at different temperatures. Most dryers have 2 settings, I think I have seen up to 4 heat settings.

I don't use much power with my dryer, I line dry the clothes, weather permitting (dust storms here) and then put the dryer on about the 15 minute setting, gives about 5 minutes of heat and just air tumbles the rest of the time. That's a huge savings compared to 30 or 40 minutes of heat. I do that to make cloths less stiff and gets the white shepherd mix dog hair off blue and black hospital uniforms.

I do this because it saves power and keeps hours of run time off the machine. I don't like fixing dryers or buying dryers so I like it when they last a real long time.

You should be able to run your dryer off purely line to neutral power.
My dad talked about doing this when I was a kid and understood nothing about electricity because "that house didn't have any 220 volt plugs" and said "that the dryer takes for ever to dry clothes only running off 120 volt power". I don't think it was a 120v dryer, originally.
Then I figure if you use hot attic air you could run the heaters with 120 volt power to slightly further warm the prewarmed attic air and not have it take forever to dry clothes.
A heavy duty "SPCO" switch could be used to enable or disable 220 power as opposed to rewiring the back of the machine every time you want 220v or 120v power. I have only thought about doing this, have not tried it yet and pretty sure I know how to wire it up.

A standard full size clothes dryer heater element is rated for 5100 watts at 230v. Ohms law tells us that a 5100 watt heater is going to draw about 22 amps and offer about 10 Ohms of resistance. This resistance is due in part to electron mobility decreasing with increased temperature.
So we will assume at the heater element operated on 120 volts and at lower temperature will offer a little less than 10 Ohms of resistance.
So we will figure the 5100 watt 230 volt heater element running off 120 volts will consume only up to about 1400 watts.
That reduces heater power down to about 1/4 of what it originally was.

The Ideal setup:
Have one clothes dryer set up inside. Have it draw attic air during warmer months and use Line to Neutral power for the heater elements during the summer. When its winter flip the switch and run full power to the heater element and have the dryer draw air from inside the house and discharge it into your house. I figure if you run your dryer like a normal person that's at least 15,000BTUs of free heat.
If you blow 15,000BTUs of fully usable heat out of your house during the cold winter you are just another wasteful person who hates the earth. I don't care if you drive a prius.

How much CO2 does it produce? Who cares. Worry about how much of your hard earned money its burned up.
Its safe to assume if you are saving money through saving energy you are producing less plant food.

oil pan 4 · 09-04-14, 02:54 PM

Yep you can run a dryer and its heater element off 120 volt power. All you have to do is disconnect one of the lines and put a jumper to connect that line terminal to nertral.
All the 120v stuff like the drum motor, timer and buzzer work like normal since they are 120v powered already and when you connect the heater element to line to neutral power you half its voltage and it works, but it just doesn't get as hot.

I just tried it on my apartment sized one. Heater element power is much lower than extected, around 5 amps. The air coming out the discharge was warmed up some but not hot.

Now the dryer draws 10 amps of 120 volt power as opposed to 17 amps of 220v power on one line and 21 on the other line (for an average of about 19 amps at 220). That's 1,200 watts versus 4,300 watts.
And remember, full size dryers use more power. This is my 220 volt compact apartment sized machine I am talking about. 220v machines this size are kind of rare.

mejunkhound · 09-04-14, 07:39 PM

We have 2 electric dryers and only use them in the winter.

One wash day per week. The poco records show that laundry days art 15 to 17 kW-Hr higher than other days, some of that is the washer, and will say that is only 1 kW-hr.

So 15*(52-14) = 570 kW-hrs for the 2 of us and some grandkids clothes.

The - 14 weeks is parts of year DW can hang outside.

Maybe one of these days I'll cobble together a heat pump dryer if I come across a cheap or free compressor. Would save us all of about $40 per year, sure would not pay to buy one of the high priced things.

03-14-10, 05:08 PM	#1
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	how do they calculate energy usage on dryers? My dryer uses 939 kwh/year during typical usage according to the energuide sticker on the top. My new clothes line uses zero. I'm wanting to work out how much I'm saving per load dried on the line but since my watt meter doesn't handle 220 I'm hoping I can get a good estimate on the average load from the 939kwh/year. I just can't find information on how they came up with that average. Does anyone have any ideas or other suggestions on how to work this out?

03-16-10, 10:04 AM	#3
WD-40 Lurking Renovator Join Date: Nov 2009 Posts: 24 Thanks: 3 Thanked 2 Times in 2 Posts	fact from http://www.energystar.gov/index.cfm?...up&pgw_code=CW The average American family washes almost 400 loads of laundry each year, so based on strider3700 saying that his dryer uses 939 kwh/year one has to assume that you would dry the same almost 400 loads a year. Then that would work out to 2.3475 kwh/load older dryers where rated by energystar ..my old dryer was rated at 929 kwh/year Last edited by WD-40; 03-16-10 at 10:17 AM.. Reason: add info

08-31-14, 11:09 PM	#6
ICanHas Banned Join Date: Aug 2014 Location: US Posts: 150 Thanks: 7 Thanked 5 Times in 5 Posts	Don't forget the indirect losses. Dryer is similar to a single vent portable A/C. There's been some laboratory testing done on portable ACs and many have been found to have a negative efficiency when they factored in heat gain through infiltration of outdoor air into the house for make up air. If it's in the conditioned space and it's in the summer, you would open a nearest window and run it at night/early morning when bringing in outside air is not objectionable humidity and temperature wise so you avoid drawing a negative pressure and pulling in warm attic air into the hose. If you run it in middle of the day, most of heat generated by the dryer goes out the vent, but the dryer is pumping out conditioned air and your A/C has to re-condition make-up air, that is drawn in as the dryer exhausts air conditioned air. Last edited by ICanHas; 08-31-14 at 11:11 PM..

09-03-14, 11:25 PM	#8
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	I have lots of 220 volt extension cords, fluke325 amp clamp and out side sub panel with easy access to the lines. And I have 2 clothes dryers, the inside one that never gets used during warmer months is full size, the outside one is a smaller apartment sided one. What do you want to know? Here is what I can tell you about electric clothes dryers with out doing any additional tests. The minimum plug requirement for a clothes dryer is NEMA 10-30. The 10-30 has 2 lines and an L shaped neutral/ground. Newer homes have the NEMA 14-30 cord. It has 2 lines a neutral and a dedicated non current carrying ground. I don't really see the point. NEMA 10-30 worked fine for 50 or 60 years. Clothes dryers do have 120 volt requirements. I know this because I have resurrected a few over the years. You have 3 things in there that use 120 volt power: Buzzer Timer Drum motor The drum motor ends up using up to around 400 watts. The small apartment sized dryer uses about 17 amps of line to line power when the heater elements are on. Then one leg of line power has about another 4 amps on it. The full size dryer uses closer to 21 to 22 amps of line to line power plus another 400 to 500 watts on the line to neutral that power the little stuff. When you adjust the temperature of the dryer you aren't reducing peak power consumption at all. The cooler setting just uses a different set of thermostats to cut power to the heater coils at different temperatures. Most dryers have 2 settings, I think I have seen up to 4 heat settings. I don't use much power with my dryer, I line dry the clothes, weather permitting (dust storms here) and then put the dryer on about the 15 minute setting, gives about 5 minutes of heat and just air tumbles the rest of the time. That's a huge savings compared to 30 or 40 minutes of heat. I do that to make cloths less stiff and gets the white shepherd mix dog hair off blue and black hospital uniforms. I do this because it saves power and keeps hours of run time off the machine. I don't like fixing dryers or buying dryers so I like it when they last a real long time. You should be able to run your dryer off purely line to neutral power. My dad talked about doing this when I was a kid and understood nothing about electricity because "that house didn't have any 220 volt plugs" and said "that the dryer takes for ever to dry clothes only running off 120 volt power". I don't think it was a 120v dryer, originally. Then I figure if you use hot attic air you could run the heaters with 120 volt power to slightly further warm the prewarmed attic air and not have it take forever to dry clothes. A heavy duty "SPCO" switch could be used to enable or disable 220 power as opposed to rewiring the back of the machine every time you want 220v or 120v power. I have only thought about doing this, have not tried it yet and pretty sure I know how to wire it up. A standard full size clothes dryer heater element is rated for 5100 watts at 230v. Ohms law tells us that a 5100 watt heater is going to draw about 22 amps and offer about 10 Ohms of resistance. This resistance is due in part to electron mobility decreasing with increased temperature. So we will assume at the heater element operated on 120 volts and at lower temperature will offer a little less than 10 Ohms of resistance. So we will figure the 5100 watt 230 volt heater element running off 120 volts will consume only up to about 1400 watts. That reduces heater power down to about 1/4 of what it originally was. The Ideal setup: Have one clothes dryer set up inside. Have it draw attic air during warmer months and use Line to Neutral power for the heater elements during the summer. When its winter flip the switch and run full power to the heater element and have the dryer draw air from inside the house and discharge it into your house. I figure if you run your dryer like a normal person that's at least 15,000BTUs of free heat. If you blow 15,000BTUs of fully usable heat out of your house during the cold winter you are just another wasteful person who hates the earth. I don't care if you drive a prius. How much CO2 does it produce? Who cares. Worry about how much of your hard earned money its burned up. Its safe to assume if you are saving money through saving energy you are producing less plant food. Last edited by oil pan 4; 09-04-14 at 12:12 AM..

03-16-10, 05:54 PM	#5
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	I found this late last night. How clothes dryers are tested even though the dryer is new it doesn't qualify for energy star since none of them do. But energuide ratings still exist on them up here and mine is 939 kwh/year so according to that page they say the average is 416 loads/year so 2.257 kwh/load... Now we're on an annoying to calculate things tiered system here but I'm averaging 7.8 cents/kwh including all fees/taxes/... that means each load on average is costing me 17.6046 cents to dry. Now my electric rate is going up 33% over the next 3 years putting that same load of laundry at 23.414 cents/load. My new clothesline cost me $35 for the new stuff and $40 for what was existing. So the upgrade will pay for itself in 439.5 loads or 1 year of average use. After the rates go up it would take 320.3 loads to pay for itself. I'm apparently not the average user as I don't do 416 loads a year I do closer to 200 would be my guess. So that gives me assuming I get 1/2 the loads outside (it rains here a lot) a just over 3-4 year payback. Either way the poles are steel and in concrete or bolted to the wall. The line is heavy duty steel wrapped in some form of plastic and the pullies are metal. I expect the thing to last me decades only needing a bit of oil to stop the pulleys from squeaking. Now my question is how much c02 am I not producing? I know my power comes from mostly hydroelectric but if I don't use it we sell the excess to others who usually get it from coal so I have no issues ask what is 2.257 kwh work out to in C02 from a coal plant?

09-01-14, 09:45 PM	#7
ICanHas Banned Join Date: Aug 2014 Location: US Posts: 150 Thanks: 7 Thanked 5 Times in 5 Posts	So I hit a road block. The dryer is not a pure 240v load. It's a three wire machine with the motor running line to neutral.

09-04-14, 02:54 PM	#9
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	Yep you can run a dryer and its heater element off 120 volt power. All you have to do is disconnect one of the lines and put a jumper to connect that line terminal to nertral. All the 120v stuff like the drum motor, timer and buzzer work like normal since they are 120v powered already and when you connect the heater element to line to neutral power you half its voltage and it works, but it just doesn't get as hot. I just tried it on my apartment sized one. Heater element power is much lower than extected, around 5 amps. The air coming out the discharge was warmed up some but not hot. Now the dryer draws 10 amps of 120 volt power as opposed to 17 amps of 220v power on one line and 21 on the other line (for an average of about 19 amps at 220). That's 1,200 watts versus 4,300 watts. And remember, full size dryers use more power. This is my 220 volt compact apartment sized machine I am talking about. 220v machines this size are kind of rare.

09-04-14, 07:39 PM	#10
mejunkhound Apprentice EcoRenovator Join Date: Apr 2011 Location: PNW Posts: 197 Thanks: 0 Thanked 47 Times in 31 Posts	We have 2 electric dryers and only use them in the winter. One wash day per week. The poco records show that laundry days art 15 to 17 kW-Hr higher than other days, some of that is the washer, and will say that is only 1 kW-hr. So 15*(52-14) = 570 kW-hrs for the 2 of us and some grandkids clothes. The - 14 weeks is parts of year DW can hang outside. Maybe one of these days I'll cobble together a heat pump dryer if I come across a cheap or free compressor. Would save us all of about $40 per year, sure would not pay to buy one of the high priced things.