Slower heating = lower consumption?

[askomiele]

Hi guys
I have a technical question for you, kind of theory I would like to discuss. True or false?

In older days the energyconsumption of a heatingelement in a washer was high, also the amount of water that needed to be heaten was quit big.

conclusion: the higher the waterlevel, the more energy a washer need to heat up water.

Between 1980 and 2000, manufactures lowered the waterlevel, designed a new way of washing to use the water and detergent more effective.

conclusion: the waterlevel dropped (to a reasonable level), so did the energyconsumption.

First theory is confirmed.

Pay attention to this one because that's where the theory is going down (at least that where I stumble acrosse something I don't really understand).

Today, certain manufactures claim that using more time to heat up the water and spreading the time to heat up the water also lowers the energyconsumption. That, I find hard to believe. Because you heat up the same amount of water, but only over a longer period of time. The maths will prove me wrong because the electricity consumption is counted in kilowatt's per hour. So if we lengten the time we can heat up water, we need less power to do per hour. Still at the end of the cycle, we heated up the same amount of water then we did in a older cyclesequence... so our energyinput should be the same.

Or am I so wrong and tampering with the laws of energy?

In addition to this question...

What about clothesdryers... can we conclude that drying on a low setting is more energyefficient? Or is the energyimput the same as drying on a high setting but do we stretch the dryingtime and thus using less kilowatt's per hour?

 

[splittub]

Perhaps it requires more energy to heat up the water quickly *and maintain the heated temperature* for the duration of the wash, than to allow the water to reach the desired temperature *during* the wash.

 

[logixx]

According to the instruction manual of my Bosch/Siemens dryer, setting it on low heat consumes the same amount of power as high heat - just takes longer to dry.

Drying time and energy consumption on 10 amps (low heat) and high heat (16 amps).

 

[launderess]

One Assumed The Low/Gentle Heat Option

Merely disconnected or otherwise reduced the heating power for the dryer. However after reading various service manuals and such now believe low/gentle heat option simply lowers the temperature reached in the drum during cycle, but uses the same amount of electric power as things will take longer to dry.

I mean if one *bakes* laundry dry at a high heat setting it will be done sooner, but consume "X" amount of electric power. However if one goes to simmer or medium heat things take longer but the same amount moisture still must be removed so the same amount of heat is going to be used regardless.

 

[julianweber]

For the dryer, the same amount of energy will be required to vaporize the water in the clothes weather it is done over a longer period of time or a shorter period of time. However, the drum is being spun by a motor that is drawing energy at a constant rate. So if we allow the motor to spin twice as long then the motor will draw twice as many kilowatt hours of electricity. In other words, there should be a power consumption difference simply because the drum is spinning longer on the low setting. I suspect this difference is minimal though. Has anyone hooked a clamp meter on the drum motor to see what its power draw is?

 

[chestermikeuk]

"so the same amount of heat is going to be used regardle

Not necessarily, all depends on the airflow, high airflow with a lower heat will dry clothes using less energy, rather like a blowy windy day with a little sun,
the clothes will dry much quicker in the wind!!

 

[DADoES]

 
One must consider this question from the P.O.V. of the power company.  A higher input wattage = higher instantaneous demand on them.  Demand costs extra.  The cost is included/averaged in the rate even if they don't bill a residential account directly for it.

As a somewhat extreme example, consider why power companies don't like electric tankless water heating.  A full-size, whole-house unit can pull 28,000 watts or more.  The power company has no way to know in advance when a consumer may suddenly "demand" that much instantaneous power, even if for only a couple minutes, so they must have enough reserve capacity on the system to feed it any moment.  As compared to a traditional tank unit that may pull maximum of 4,500 to 5,600 watts.  Even if it takes 20 to 30 minutes to heat a 50-gallon tank, that's much less instantaneous demand that the power company much purchase from the generating station.

 

[launderess]

Using A Miele Condenser Dryer

As an example we can see from the schematic that the *Heizung* (heat) circut that the dryer has two setting on it's thermostat, 58C and 73C. One assumes these are from switching the temperature dail between high and low but unless is reading the thing incorrectly(could be with such a bad copy) both legs of the heater are being fed regardless.

http://elektrotanya.com/PREVIEWS/13293261/23432455/mosogep-szaritogep/miele/miele_t369_c_2.pdf_1.png

 

[mrb627]

Fuel Consumption

Driving your car at a lower speed saves energy, doesn't it?  I would assume clothes drying would follow the same logic.

 

Malcolm

 

[tomturbomatic]

Lower heat and longer time can actually cost you if the dryer is vented to the outdoors and is in a heated or air conditioned space because the dryer pulls 150 cu. ft. of air per minute through itself and squirts it outside the building. The building draws that replacement air in from the outside and it must be heated or cooled once inside. There are many factors that enter into the equation and they vary enough that a one size fits all pronouncement cannot be made. This is why I use gas dryers outside during the summer and unvented electric dryers with heavily filtered exhaust inside during the winter to recapture the heat and humidity and direct it into the room with the tropical plants.

 

[sudsmaster]

Theoretically, the amount of energy required to heat a body of water to a final temperature is the same regardless of the rate of heating.

However it's possible that a slower heating rate could result in a smoother temperature curve, especially when the final temp has been reached and is being maintained. Smoothing out the peaks could save a small amount of energy. A slower heating rate could also result in less heating of the non-water mass and surrounding air in the washer, resulting in further small savings.

BTW, cars use more fuel per mile to travel at faster speeds due to wind resistance. An analogy to a dryer might be with air flow, but I don't think that heating rates have the same sort of effect.

 

[julianweber]

There are a lot of variables that go into the drying equation. Here are some of the ones I am aware of...

Relative Humidity of the air entering the dryer
Temperature of the air entering the dryer
Amount of energy added to the air column entering the dryer (Kilowatt or BTU)
Volume of air flow through the dryer
Amount of surface contact between the heated air and the clothes being dried
Amount of time the hot air is interacting with the clothes in the dryer drum before it makes its way out the vent.

Here are some questions I have relating to the energy consumption of the clothes drying system...

1. What percentage of the energy used to heat the incoming air actually vaporizes water in the clothes?

2. Does that percentage go up or down and by how much as the drying air temperature is raised?

3. If the airflow through the dryer is increased, is a larger percentage of energy exhausted as hot air instead of vaporizing the water in the clothes?

4. If we could heat the clothes instead of the air, would the efficiency go up?

Now, I believe that #2 & #3 are actually a curve not a simple ratio. So if we could find out what temperature and what airflow extract the most percent of water for the energy used we could find the answer to our question. The problem is that I suspect these curves will be dependent on the temperature of the wet clothes as well as the temperature and relative humidity of the incoming air. I have linked to a web site which gives a pretty good explanation of how energy input affects relative humidity and dew point, all of which are important factors in this equation. One point I noticed is that if we were to heat the incoming air to a temperature that is below the dew point, 100% of the energy we add to the incoming air will be exhausted as no water will be extracted from the clothes. So there are at least some points on the curves where the energy used to dry the clothes would be infinite since the clothes would never dry.

Does anyone have some experience or data to fill in the blanks with?

Julian

http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html

 

[tomturbomatic]

Manys the time I have dried clothes in an outside dryer while it is raining. I am always amazed that even in the rain, the heat of the burner can increase the air's capacity to hold moisture sufficient to remove it from the tumbling load of laundry.

 

[arbilab]

Fun question. Let's stick to heating wash water. Drying adds several other sets of variables.

In a lossless system--perfectly insulated--it always takes exactly the same kWh to heat the same amount of water from the same start temperature to the same operating temperature, no matter how fast or how slow you do it.

In a lossy system--imperfectly or poorly insulated--the longer the water is above ambient the more heat is lost by radiation. In that case, faster is CHEAPER. But not by much, because the hotter it gets the greater the loss, so more time at full temp = greater loss.

Industrial electric customers are billed by demand. Above is correct, that though demand isn't measured for domestic customers (in the US--Europe may differ) it's figured into the rate. Demand billing favors slower consumption. So even though the loss may be higher, the cost may be lower.

At the rates Europe pays for electric, I can't for my life explain their obsession with boiling laundry. In 3 generations nobody in my family has washed above 140F and nobody has experienced a laundry-borne disease. I wash at 120F and I haven't had more than a 24-hour sniffle in 5 years. Oh, and I'm genetically European, specifically, UK. The only extraordinary step I take is, anytime I leave the house I do NOT touch my face with my hands, and wash them immediately when I get home. Wouldn't matter if I boiled clothes or went nekkid.

Know what the most contaminated surface in everyday life is? The handle of a shopping cart. Can't boil those now, can we?

 

[mikeklondon]

Try it out

All I know is that if you use the low heat setting on a Miele it uses a low less power and only takes a few more minutes to dry the load + it does the job a lot better. Its all about the air flow.

 

[mikeklondon]

Care labels

Most care labels recommend low heat, in the uk one dot is low 2 dots high

 

[Iowegian]

Washers make clothes wet by necessity, obviously.

If you want your clothes to get dry, you need to decide now much energy you're going to use in the washer to spin the clothes dry, and how much energy you're going to use in the dryer by blowing heated air into the clothes. The sum of the energy consumption of the 2 machines tells you your total cost.

It's not rocket surgery.

But a lot of people a couple of generations before me only had washing machines and used clotheslines to dry their laundry - outside mostly, but they even dried clothes in the basement on clotheslines too in the winter.

Go figure.

I wonder if CVS sells clothespins? I'll have to check the next time I go there.

 

[sudsmaster]

Shopping cart handles...

Yes, I could see those as being highly contaminated. However, I recently read that the highest bacteria count (E. coli) can be found on... drum roll... gas pump handles...

It makes me wonder what these people do inside their cars...

In any case, I keep a small bottle of sanitizer gel in my car cup holder, and I TRY to wash my hands every time I return from a trip outside the home. Sometimes I forget and often I seem to come down with a cold as a result.

Washing hands is great for controlling colds... but influenza virus is also spread by sneezing and coughing... I get a bit annoyed when I'm in a checkout line or on public transport and another customer is coughing or sneezing, esp if they don't bother even the gesture of covering their mouth and nose. Even worse when the checker is the one who's ill. I wonder how many other people he or she has infected that day.

My last workplace was definitely not on the clean side. In addition to the mess created by the open machinery, my supervisor would spit on the shop floor, smoke, not cover his mouth when coughing, and not wash his hands after using the restroom. I'm so glad I'm out of there.

 

[sudsmaster]

It seems to me that boil washes date back to the days when fat based soaps were used, and high water temps really were needed both for maximum cleaning and rinsing. The high temps also help to remove stains from whites - just as high temps will fade most colors. I suppose that in the days when energy was cheap, boiling was cheaper than soap or those newfangled detergents. There's also something to be said for high temps killing most bacterial spores, but of course only even higher temps and pressure than are possible with home washers is really needed for sterilization (as I recall, it's 250F under 15 lbs pressure - something a home pressure cooker could do, in a pinch, if one needs to sterilize towels or knives for emergencies).