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