Calculating energy usage for appliances

[Jstpssng]

I know this should be easy but I don't know how to do it. I'm sterilizing potting soil with a unit drawing 30 amps at 220 volts, and it takes about 2 1/2 hours to bring it up to 160'F. (Composted pig manure.) I can convert it to Kw, but do I then multiply by hours?


Thank you.

 

[CobyRupert]

Yes. Multiple the wattage times the amount of hours it runs to get the Energy in Watt-hour units. Power is the rate of Energy being applied. Power = Energy/time. So Energy = Power x time.

For single phase power, which is usually just 2 wires and a ground, 120V or 240V, the Power is volts x amps. The unit is Watts.

Energy, in the U.S., is measured and sold in Watt-hours, (or kilowatt-hours). A Watt-hr amount of energy is a 1 Watt load running for 1 hour. (Or .5 Watts running for 2 hours, or 2 Watts running for .5 hours, etc…)

So your heater at 30A/220V draws 6600Watts.
6600W for 2.5 hours uses 16,500 watt-hour (16.5 kilowatt-hrs).

For example: You can see that if you used a 3000Watt heater, it would take 5.5 hours to heat the same amount (i.e. transfer the same amount of energy(16.5 kW-hrs). (Time = Energy/Power)

 

[Jstpssng]

Yes. Multiple the wattage times the amount of hours it runs to get the Energy in Watt-hour units. Power is the rate of Energy being applied. Power = Energy/time. So Energy = Power x time.

For single phase power, which is usually just 2 wires and a ground, 120V or 240V, the Power is volts x amps. The unit is Watts.

Energy, in the U.S., is measured and sold in Watt-hours, (or kilowatt-hours). A Watt-hr amount of energy is a 1 Watt load running for 1 hour. (Or .5 Watts running for 2 hours, or 2 Watts running for .5 hours, etc…)

So your heater at 30A/220V draws 6600Watts.
6600W for 2.5 hours uses 16,500 watt-hour (16.5 kilowatt-hrs).

For example: You can see that if you used a 3000Watt heater, it would take 5.5 hours to heat the same amount (i.e. transfer the same amount of energy(16.5 kW-hrs).

Thank you. It will cost me about 12$/yard to sterilize the soil... better than the chance of getting trichinosis.

 

[Roadworthy]

Coby's answer was pretty thorough but I wonder about the data. Is your heater wired for thirty amps or does it actually DRAW thirty amps? If it actually draws less your actual power consumption will be somewhat lower. Of course if your line voltage is greater than 220 (and it frequently is) the consumption will be a bit higher.

 

[ponytug]

@CobyRupert has the right math.

I would use a clamp on ammeter to double check what you are drawing, or guesstimate the actual load by noting the draw at your meter, turn the sterilizer on, and measure the new draw, and the difference is what your sterilizer is actually pulling.(Works best on a digital electric meter.) I know what my house runs for baseline load, which makes it easy to subtract that usage from any load that I need to measure.

All the best,

Peter

 

[LD1]

Coby's answer was pretty thorough but I wonder about the data. Is your heater wired for thirty amps or does it actually DRAW thirty amps? If it actually draws less your actual power consumption will be somewhat lower. Of course if your line voltage is greater than 220 (and it frequently is) the consumption will be a bit higher.

Yup.

You need to actually measure your line voltage....then hang an amp clamp while its running. Multiply the two together and go from there. Meters are pretty inexpensive if you dont already have one.

On a side note....either your electric is really expensive, or you are doing a very small amount ever 2.5 hours.

My electric rates are ~14 cents per kwh. So $12 would buy me about 85kwh. Which would run your heater for about 13 hours. Are you only doing 1/4 or less yards per 2-1/2hrs??

 

[Jstpssng]

Yup.

You need to actually measure your line voltage....then hang an amp clamp while its running. Multiply the two together and go from there. Meters are pretty inexpensive if you dont already have one.

On a side note....either your electric is really expensive, or you are doing a very small amount ever 2.5 hours.

My electric rates are ~14 cents per kwh. So $12 would buy me about 85kwh. Which would run your heater for about 13 hours. Are you only doing 1/4 or less yards per 2-1/2hrs??

Yes to both. My rates are just over .18 cents per kwh. My little sterilizer probably costs about the same to run as an electric clothes dryer, although it takes longer to get to heat than to dry your clothes. It's something my father had for the greenhouse, I like to dig it out a couple of times every year so that I don't have to fight weeds in my carrots and other root crops.

 

[CobyRupert]

Coby's answer was pretty thorough but I wonder about the data. Is your heater wired for thirty amps or does it actually DRAW thirty amps? If it actually draws less your actual power consumption will be somewhat lower. Of course if your line voltage is greater than 220 (and it frequently is) the consumption will be a bit higher.

Correct.
If it draws 30 amps, it needs to run on a 40 amp breaker.
If it’s on a 30 amp breaker, it shouldn’t draw more than 24 amps.

 

[Jstpssng]

I got 30 amps from the breaker rating, for a rough estimate. Tonight I checked the manual and it's drawing 12 1/2 watts at 240 volts, the electrical rating is 3000 watts.
Thanks for the answers. Calculating loads is one of those niggling things which I should know how to do but didn't. I don't intend to do any wiring, yet it's good to know things like this.

Energy, in the U.S., is measured and sold in Watt-hours, (or kilowatt-hours). A Watt-hr amount of energy is a 1 Watt load running for 1 hour. (Or .5 Watts running for 2 hours, or 2 Watts running for .5 hours, etc…)

^^^^
This is what I thought, but wasn't completely certain.

 

[ponytug]

So, about $0.54/ hour to run it, assuming it runs on high the whole time. (Heat to temperature and quit, rather than heat to temp and hold for awhile)

All the best,

Peter

 

[CobyRupert]

I got 30 amps from the breaker rating, for a rough estimate. Tonight I checked the manual and it's drawing 12 1/2 watts at 240 volts, the electrical rating is 3000 watts.
Thanks for the answers. Calculating loads is one of those niggling things which I should know how to do but didn't. I don't intend to do any wiring, yet it's good to know things like this.



^^^^
This is what I thought, but wasn't completely certain.

I think you mean it draws 12.5 amps. At 240V, 12.5 amps would be expected for a 3000W rated heater. (240v x 12.5A = 3000W)
Running this heater for 2.5 hours consumes 7500watt-hrs (7.5kW-hrs)

Watt-hours is a rather weird unit to use for Energy. The System International (SI) (metric) unit for Energy is the Joule (similar to a BTU).
Remembering that Power is the rate of energy (Power = Energy/time); 1 Watt = 1 Joule/second.
So it’s weird to express Energy as a Watt-hr (1 Watt x 1 hour) because that’s the same as saying it’s:
1 Joule/sec x 3600 seconds, this gives you 3600 Joules/sec-seconds; or what we would just call 3600 Joules.

Using the term “watt-hours” is sort of like saying a distance of 100 miles is a distance of “100mph-hours”. It’s kind of silly. (It doesn’t matter if it’s 50mph for 2 hours, or 200mph for a .5 hours, etc..JUST SAY 100 MILES! ..or Joules!)

…of course in the U.S. we say “How far is it? Oh, about 2 hours.”

 

[ponytug]

...Using the term “watt-hours” is sort of like saying a distance of 100 miles is a distance of “100mph-hours”. It’s kind of silly. (It doesn’t matter if it’s 50mph for 2 hours, or 200mph for a .5 hours, etc..JUST SAY 100 MILES! ..or Joules!)

…of course in the U.S. we say “How far is it? Oh, about 2 hours.”

Yes, units are messed up, but it doesn't seem likely to change anytime soon. Quick, how big is a barn-mega parsec" https://en.wikipedia.org/wiki/List_of_humorous_units_of_measurement

Well, I don't think it is just the US that answers distance with time, and personally I think "about two hours" is way more useful than "oh, it is 32 miles", that omits there are 372 hairpins on the thirty two miles...Of course, you always have to factor in local wisdom, about the road and knowing that you have to dog leg through aunt Susie's sister's yard to actually stay on the road.

The one that always strikes fear into my heart in a new area is "oh, you can't miss it!"

All the best,

Peter

 

[LD1]

I think you mean it draws 12.5 amps. At 240V, 12.5 amps would be expected for a 3000W rated heater. (240v x 12.5A = 3000W)
Running this heater for 2.5 hours consumes 7500watt-hrs (7.5kW-hrs)

Watt-hours is a rather weird unit to use for Energy. The System International (SI) (metric) unit for Energy is the Joule (similar to a BTU).
Remembering that Power is the rate of energy (Power = Energy/time); 1 Watt = 1 Joule/second.
So it’s weird to express Energy as a Watt-hr (1 Watt x 1 hour) because that’s the same as saying it’s:
1 Joule/sec x 3600 seconds, this gives you 3600 Joules/sec-seconds; or what we would just call 3600 Joules.

Using the term “watt-hours” is sort of like saying a distance of 100 miles is a distance of “100mph-hours”. It’s kind of silly. (It doesn’t matter if it’s 50mph for 2 hours, or 200mph for a .5 hours, etc..JUST SAY 100 MILES! ..or Joules!)

…of course in the U.S. we say “How far is it? Oh, about 2 hours.”

I see the point.

IF anything its backwards actually.

HAving a heater rated for 3000w and using it for 2 hours and sayting you used 6kwh of electric...

Should it not be that the heater is rated at 3000w/hrs and that if you run it you simply just use 6kw of electric?

 

[Jstpssng]

I see the point.

IF anything its backwards actually.

HAving a heater rated for 3000w and using it for 2 hours and sayting you used 6kwh of electric...

Should it not be that the heater is rated at 3000w/hrs and that if you run it you simply just use 6kw of electric?

You just hit on the source of confusion which caused me to start this thread.

 

[Drewintoledo]

Get yourself a kill-a-watt meter or knock off. Not only will it measure amperage and wattage used, but you can track kWh too for under 30 bucks. If it’s 220v you can install a Sense unit or something similar but it’s more expensive.
for the curious, would you mind posting a photo of your sterilizer?
here’s how the sense unit works

 

[CobyRupert]

You just hit on the source of confusion which caused me to start this thread.

“Should it be 3000W/hrs?”
I don’t think so.
Power (Watts), like speed (mph), is a RATE. The rate of something else. Power is the rate of Energy used and Speed is the rate of distance traveled, based on Time.

The term “Watt” already has the “per second” or (“per time”) built into it. (It’s a Joule/sec) It’s already a RATE, so making it into another rate like Watt/hr (the rate of a rate) doesn’t really make sense (for anything related to this discussion).

It’s also nicely designed that if we know the Power (rate of energy), we can easily calculate the rate of electrons (current /Amps) the circuit requires to achieve that power.

(Example: Say it takes 1 kW-hrs (3600kJoules) of energy to boil a pot of water. That doesn’t tell us if it takes 2 hours or 2 days. Only knowing the power can we calculate the time (and current). Same with distance. Destination is 100 miles away, only knowing the speed rate can we calculate time.)

Another way to think of the same thing is to say we can calculate the total Energy applied and the total Distance traveled by knowing the rate applied, and for how long (time). [Energy= Power x time, Distance = speed x time)

You can only label a heater with its Power (it’s Rate of Energy usage) because you don’t know how long it will be turned on for, so there’s no way to know it’s total ENERGY usage.

Watt/hr is like saying MPH/hr.
…but a Watt-hour is like saying MPH-hour. In both cases you’re canceling out the Time component, no longer talking about a rate, but are expressing a cumulative total of Energy and Miles.

Clear as mud?

 

[sea2summit]

Get yourself a kill-a-watt meter or knock off. Not only will it measure amperage and wattage used, but you can track kWh too for under 30 bucks. If it’s 220v you can install a Sense unit or something similar but it’s more expensive.
for the curious, would you mind posting a photo of your sterilizer?
here’s how the sense unit works

Beat me by that much.

 

[DarkBlack]

I think you mean it draws 12.5 amps. At 240V, 12.5 amps would be expected for a 3000W rated heater. (240v x 12.5A = 3000W)
Running this heater for 2.5 hours consumes 7500watt-hrs (7.5kW-hrs)

Watt-hours is a rather weird unit to use for Energy. The System International (SI) (metric) unit for Energy is the Joule (similar to a BTU).
Remembering that Power is the rate of energy (Power = Energy/time); 1 Watt = 1 Joule/second.
So it’s weird to express Energy as a Watt-hr (1 Watt x 1 hour) because that’s the same as saying it’s:
1 Joule/sec x 3600 seconds, this gives you 3600 Joules/sec-seconds; or what we would just call 3600 Joules.

Using the term “watt-hours” is sort of like saying a distance of 100 miles is a distance of “100mph-hours”. It’s kind of silly. (It doesn’t matter if it’s 50mph for 2 hours, or 200mph for a .5 hours, etc..JUST SAY 100 MILES! ..or Joules!)

…of course in the U.S. we say “How far is it? Oh, about 2 hours.”

Like you said- watt is a rate of energy- the same as MPH.
You’re making it confusing by confusing that with time duration. Watt/hours or kwh is rate * time duration to give you work done. Just like saying something was 50 mph, is the rate, but “50 mph for 10 minutes “ tells the rate and time duration which tells the work done

 

[CobyRupert]

Like you said- watt is a rate of energy- the same as MPH.
You’re making it confusing by confusing that with time duration. Watt/hours or kwh is rate * time duration to give you work done. Just like saying something was 50 mph, is the rate, but “50 mph for 10 minutes “ tells the rate and time duration which tells the work done

Watt/hours is very different than watt x hours (watt-hours). Watt-hours are just Joules (energy).
While mph x hours = miles traveled (distance), mph/hr would be a measure of acceleration ( often measured in ft/sec^2, or meters/sec^2) .
Not sure where Watt/hr would ever be used as a measurement or rating. I guess it would be if you were describing how the wattage varies over time.
Example: if something’s power input (or output) changed from 6000 Watts to 8000 Watts over 2 hours, you could say this thing has a Watt/hour rating of 1000 W/hr; but that does nothing to tell you what power it operates at or how much energy it used. This wouldn’t be used to describe the output of a heater with a fixed resistance and constant wattage, as its Watts/hr rating will always be zero. Just like a car at a fixed mph speed is experiencing an acceleration of zero.

 

[DarkBlack]

Watt/hours is very different than watt x hours (watt-hours). Watt-hours are just Joules (energy).
While mph x hours = miles traveled (distance), mph/hr would be a measure of acceleration ( often measured in ft/sec^2, or meters/sec^2) .
Not sure where Watt/hr would ever be used as a measurement or rating. I guess it would be if you were describing how the wattage varies over time.
Example: if something’s power input (or output) changed from 6000 Watts to 8000 Watts over 2 hours, you could say this thing has a Watt/hour rating of 1000 W/hr; but that does nothing to tell you what power it operates at or how much energy it used. This wouldn’t be used to describe the output of a heater with a fixed resistance and constant wattage, as its Watts/hr rating will always be zero. Just like a car at a fixed mph speed is experiencing an acceleration of zero.

I meant watt-hours. Pretty sure you know that