What means kWh exactly?

[askomiele]

I was 'reading' the manual of my dishwasher and found a note of the different programs with both water and energy use.

Following things I want to ask is...

The economyprogram 45° uses 1.05 kWh but runs for 165 min.
The 1.05 kWh => can I say that per hour she is running this program, she uses 1.05 kWh or is that amount of electricity for the whole cycle?

 

[dj-gabriele]

One kilowatt hour is not a measure of power but of energy, it is equivalent to 3.600.000 Joules of energy. So your dishwasher will use 3,6 MJ * 1,05 = 3,78 MJ of energy per cycle, not per hour.
The heater might be on only for say 20 minutes of the whole wash at a power of 2KW (not 2KWh) and the rest of the time only the pump is running.

 

[sudsmaster]

A watt is the amount of energy that an appliance is using at any instant in time.

If a 100 watt bulb burns for an hour, it has used 0.1 kilowatt hours. This is basically what the electric meter the utility company installs on your home. You'll note on your electric bill that you are charged per kilowatt hour or KWh.

A 1,000 watt space heater running continously for an hour would be using 1 kilowatt hour, or 1 KWh.

 

[panthera]

Askomiele,

Check out the link, I think it explains things very well.

As always when discussing electricity, there are disagreements as to the proper terminology and abbreviations.

The proper term would be "kW·h" or "kW h".

But I'm cool with KWh or kWh, even if they aren't SI or ASTM...

It helps me to think of these things compared to common appliances and uses in the house.

My tea kettle consumes 2kW h...and that is an enormous, gigantic amount of energy to my mind...and it's really cool how fast it can heat a liter of water.

The heater in my washer consumes 2.7kW h and that is tremendous! My dryer dries with 3.2kW h and that seems very wasteful.

These things are quite subjective, no?

Of course, there is a time when it is very useful and good to think of kW hours and that is your electric bill. An LED lamp which consumes 5 watts and hour would need to run for 200 hours before it had consumed 1 kW. An incandescent bulb which puts out roughly the same amount of visible light could not even run for 20 hours...

Watts, by the way have nothing to do with voltage and amperage rating of a given circuit - they are a measure of the work done. I need the same number of watts to do my drying here at 230V single phase as I do in the US at 240V split-phase.

http://en.wikipedia.org/wiki/Watt-hour

 

[askomiele]

So...

If I come again to my dishwasher...

Economy progam uses 1.05 kWh 165 min (2h 45 min):
Doing the math of 1.05kWh x 2h 45 min is the amount of electricity used for the cycle... wrong or right?
(I'm blushing because after all the answers, I'm still confused)

 

[panthera]

Askomiele

I get confused trying to decide who to vote for tomorrow...don't you worry.

To answer your question: No.

Think of kW h like bars of chocolate. Really good Rittersport chocolate.

One bar of chocolate is almost a load of dishes in your dishwasher. One bar plus one square from a second bar is exactly how much chocolate it takes.

The kW h is not time, it is quantity of energy. It doesn't matter how long your dishwasher takes, it only matters how much chocolate it eats,um how many kW h it draws.

Does that help? It is confusing!

So are the elections. I wish there was a antique machines party!

 

[dj-gabriele]

Wrong!

Also Phantera calculations might mislead you,
the kettle might have a power of 2kW (not kWh) but it won't consume 2kWh of energy but only for (say) the 3 minutes needed to boil the water so it would use only 2*3/60=0,1kWh of energy.
Also in the washer, the heater might be 2,7kW powerful but, unless doing a boilwash with a gigantic amount of water, it will use a fraction of that.
The dryer will, istead most likely use more than the 3,2kWh to dry a load, it's all a matter of how long the heating element is on during the cycle.
Your dishwasher will use 1,05kWh in total, as I said before:
here is an example of a theoric cyle

10 minutes prewash
45 minutes main wash
5 minutes cold rinse
60 minutes hot rinse and dry

the motor runs all the time for 2 hours
in the prewash the heater is off
the heater brings the temperature of main wash to 50°C in 9 minutes
in the first rinse the heater is off
in the last rinse the heater brings the water to 65°C 11 minutes
so in total the heater runs for 20 minutes

with a motor power of 200W (0,2kW) and heater power of 2000 (2kW) you have:
power x time = energy
0,2 kW x 2 hours = 0,4 kWh
2 kW x 20 minutes ( 1/3 h) = 0,66 kWh

so in total said dishwasher would use 1,06kWh of energy in the complete cycle.

I hope this explains it nicely

 

[panthera]

Gabriele

Right;-)))
I didn't say they were running for one hour at that rate!

That is the energy they would consume if they were to run for one hour. They don't, of course.

Your times are right.

What I did say is that that seems, to me, to be a tremendous amount of energy. When you consider that a really fit, really strong, really built and seriously well-trained man like Lance Armstrong just barely manages to burn 1,000 Calories/hour - and 1kW h is: 859845.22785899 calories!!!!

And the human body only needs 2000 calories to run perfectly well for 24 hours, then it is a lot of power.

Sorry if it was confusing.

 

[twintubdexter]

once a friend, now practically an enemy

old enough to remember Ready Kilowatt?

 

[sudsmaster]

Askomiele,

To answer your second question, your dishwasher is using a TOTAL of 1.05 KWh of energy to do a load at that setting. That is on average what you'll be billed for each load it does on that setting, regardless of how long it takes to do the load.

(More or less, as these things are obviously estimates and dishwashers that adjust their cycles according to how much dirt there is may take longer or shorter to do the load and MAY use more or less energy as a result. But you still would not need to multiply the number of hours it takes times 1.05... instead the energy consumption differences adjusted for load would be slight and just a fraction of 1.05 KWh.)

Panthera,

I've seen it written every which way. PG&E lists it as "Kwh" on my latest bill. I think that looks ugly so I prefer "KWh" which graphically I think scans much nicer. And it's just as easy to type ;-).

And if we can't drop the subject of proper capitalization of electrical energy unit abbreviations, I'll start referring to electric power in terms of Ergs, where one KWh=3.6 x10^13 Ergs.

So there. ;-)

 

[sudsmaster]

LOL, I remember my Dad once had a cool Ready Kilowatt lapel pin. He promised to get me one but apparently that was easier said than done. Never did get one. Still, I always got a kick out of seeing one on his jacket.

 

[sudsmaster]

PS-How could those services be "priceless" if they cost "pennies a day"???

 

[panthera]

Rich,

I'll see you one erg and raise you 10,000,001.

Hah!

It does get crazy, doesn't it?

Last semester, my students were required to define 10 SI units or derivatives on their finals. I saw the section more as a case of giving them easy points. Silly me.
One student stopped at seven and maintained that all others were "made up" - by me - as they are all derived.

Because I'm teaching so many at one time this semester, I'm in a classroom with fairly sophisticated technology. It makes life easier - I've got a computer to project the proper terminology and even my gawd-awful scrawl isn't a problem because I can place a perfect circle, sphere, whatever on the Intelloboard.

It does fascinate me, tho', how a committee can take the simplest concept and make it difficult.

Coulomb, joules, ergs, kW H, sweaty horses, hot, heavy breathing men pulling together on a rope...it's all force and mass in the end.

 

[favorit]

Asko...Miele G1000/2000 !! )

Miele DW use more water to wash better.
So to get the AAA rating the miele-ecocycle is :

- no prewash
- 45°C neverending wash
- cold rinse
- 60°C rinse
- neverending fan drying

B/S/H and Zanussi/Aeg/Electrolux ecocycle formula is :

- cold prewash
- 50°C neverending wash
- cold rinse
- 65°C rinse
- neverending "nothing happens"(or fan drying if a fan exists)

so there's a bath more than the miele with the same 12/14 litres of consumption.

 

[panthera]

the never ending

is right!
My Miele washes perfectly clean at 45°C...but four hours until the sensor is happy?

 

[favorit]

Variospeed .... for our sake

BSH have "Variospeed" and mieles have "Turbo".
Wonder why ZanussAeg'o'lux haven't yet a similar "aredhotchilipepperinthebriefs" option

 

[sudsmaster]

Panthera,

When I took physics a long long time ago, I soon learned that the single equation one had to remember was F=MA. All else could be derived from that. Of course one had to know one's units to be able to various derivations. The equivalent basic equation in electronics is P=VA (power=volts*amps) - for which inductance and capacitance must be taken into account for non-purely resistive loads.