noobing out working out average electrical power used!

tigerstyle · 28 Jun 2012 at 17:28

So I've been staring at excel trying to work this out, and think I have it all wrong!

I'm measuring a pump with a usb meter that records the data every 3 minutes. To work out the total power used per day I've been multiplying the average power of the pump recorded over the 24 hour period by the amount of time the pump is on (got that figure by looking at the highs+lows in the data)

My flash of stupidness is that all I need to do is multiply the daily average power by 24 to get it's total daily use. But have gone around in circles so now need that sane 3rd party to say yes, that's obvious, why were you wasting hours before?

Hope that makes sense!
So the higher value here is correct.

Zefan · 28 Jun 2012 at 17:31

If it uses 0.8 per hour, then a day's worth of use is simply 24 of that amount. Yes!

paradisiac · 28 Jun 2012 at 17:33

Zefan said:
If it uses 0.8 per hour, then a day's worth of use is simply 24 of that amount. Yes!

but if its only on 12hours a day, will that not mean even in a 24 hour period it would still be 0.8*12 as the other 12 hours it would be off, meaning 0*12? or did I miss something.

tigerstyle · 28 Jun 2012 at 17:33

Zefan said:
If it uses 0.8 per hour, then a day's worth of use is simply 24 of that amount. Yes!

I was thinking because what I initially thought was correct was all complicated then it must've been right.

Ahhhhh clarity~! Nice feeling, thanks!

That was my trap paradisiac!!!!! But as the initial 0.8kW is an average over a whole 24 hours data, including off course periods of OFF and ON that 'thing/factor' is already taken care of. I think. He said...

Zefan · 28 Jun 2012 at 20:55

0.8kwh is one hour average use so 12 hours use will be 12 * 0.8. If that's how much you use per day then that's your daily useage.

Seems like you're reeeeally making it far more complicated than it needs to be

ChilledLJ · 28 Jun 2012 at 21:49

so if it's only on for 12 hours, thats 9.6kwh. Power draw in kilowatts multiplied by time in hours used equals kwh of electricity used

tigerstyle · 29 Jun 2012 at 03:57

Ok, so you've just got be bactracking again here.

0.8kW isn't the power the pump uses when it's on, it's the average over the whole 24 hour period. Minimum is 0kW maximum is 2kW. So the daily total would be daily average (0.8) * 24? I want to avoid singling out the periods it's on in excel as this leads to innacuracy when the pump is on or off or just working slowly for example.

Zefan said:
0.8kwh is one hour average use so 12 hours use will be 12 * 0.8. If that's how much you use per day then that's your daily useage.

I think this would be right if I only MANUALLY turned the pump on for 12 hours per day. I don't it's self controlling over a 24 hour period. So I have to take the daily average * daily hours, 0.8 * 24

Ok just read that last bit through again, I am being dense over this I know, just falling into all the commom kW and kWH mistakes! What you've said makes sense Zefan (of course!) average hourly use * how long I used it for. 0.8 * 24 it is!

Richie · 29 Jun 2012 at 07:00

If 0.8 is the average per hour over a 24 hour period then it is 0.8*24

Averages take into account "off" periods as well (in this example) i.e. if it actually used 1.6 units in one hour but was only on for 30 mins (half of the total period), then the average is shown as 0.8 (1.6/2)

Basically, the pump is using 1.6 units per hour for 12 hours. The other 12 hours of it being off brings the average down to 1/2 of that due to 12 being exactly half of 24 i.e. 0.8

Zefan · 29 Jun 2012 at 11:24

Oh god. I didn't realise it was auto-controlled. Not sure how I missed that

If it's on for 12 hours then it's the total power divided by the units of time, so X/12. If you leave it on for 24 hours then it's X/24. There's absolutely no reason to be taking the power used over 12 hours, dividing it by 24 to find half the average power used, and then confusing yourself over whether to double it to find the 12hr usage! Is there not any way you can find out how long it was actually on for?

:edit: How is this managing to confuse me :confused:

Feels like it's much harder than it should be.

tigerstyle · 29 Jun 2012 at 12:04

Zefan said:
:edit: How is this managing to confuse me Feels like it's much harder than it should be.

The assistance and perseverance is appreciated! It's one of those things that unless you totally understand, even a small thought/error can spiral, and you know the simplest solution is the best but then second guess your own thinking. Bah, it's done now, so feeling good.

It really is basic stuff, just has got lost in my brain over the years (I'm not even 30

...)

But my knowledge is now refreshed!