xkcd #3038: Uncanceled Units
xkcd #3038: Uncanceled Units
Edit: Alt Text: Speed limit c arcminutes^2 per steradian.
For something that doesn't run continuously, like eg. a refrigerator, then an average daily usage is more useful, no? "This product draws 1.5 kW with a duty cycle of 0.08" doesn't really help when comparing efficiencies of potential purchases, you'd need to convert it to electricity consumed in a set period anyway.
No, it's because watts are joules per second, so kWh are (energy / time) * time. Cancelling the units would be expressing the energy directly in joules.
Exactly, it's a unit of convenience, not a unit of abstract precision.
Even a unit of "gallons/sqft" could be handy in the right context. If you were trying to design a storage solution for discretely packaged product for example, it could be a figure of merit despite literally factoring out to a unit of length.
I could imagine a scenario where gal/ft² is useful. Like with grocery store shelving figuring shelving and product stacking. If liquid storage containers are stackable then you have have more gallons per square footage of shelf space. Or of they're not stackable, then taller containers would hold more liquid in the same shelf space than shorter containers with the same footprint.
Yeah it seems odd to represent something as a volume/area, but that is the relevant information you're comparing and it's intuitive how that number changes based on changes to volume as projected onto an area. Bigger number points toward a more efficient use of shelving.
Yeah a chest freezer is a good example of a situation where both are useful things to put on the tag
You could also list some long term average power draw instead of the peak.
kWh is already an uncanceled unit, drives me nuts even without adding per day
(Energy / time) * time? fuck you
It's because the times aren't the same. Maybe same unit but different context so they can't be canceled.
It's like saying you work 8 Hours/day (Eight hours per day). Both are units of time, but their context is different and their combination forms a new meaning beyond the units.
1 KWh is using 1KW for one hour. Because of demand pricing the time you use that KW is important. Like in terms of energy grid using a whole ton of power for one minute vs same total over a long time is different and important dispite being the same amount of energy.
Edit: some phrasing
Good point, and agreed that thinking in kWh is very intuitive and convenient in some contexts like household appliances, but it's being used as a more general unit for energy while Joules are just so much better at, well, representing energy and being able to transition from electric to thermal etc.
I know why but it's stupid and arbitrary and the arbitraryness is what's forcing it.
It's the time. It's always the time.
SI units are all derived from seconds but instead of working with kiloseconds we have minutes and hours and days with a bunch of idiotic conversions.
The "second" you invite time into your measure, you invite some real bullshit ad-hoc pseudo-unit convenience units and fuck them. May as well just go imperial and have 14 rods to the fucking hogshead.
Because nobody's used to seeing Joules, you could swap in kJ for kW-seconds but then you probably need to switch base (MJh) to keep it practical, and now people need to do extra math to tell what will be on their power bill
But go ahead and call your power company to get them to list Joules
My power company provides me electricity in kWh, and heating (in the form of hot water) in GJ. And my cold water gets charged in m3.
So they DO know. For a few years, they'd even "helpfully" translate the GJ into kWh, untill it started to piss off people who bought electric heaters and found that those two numbers weren't actually the same in the real world.
It's also due to social inertia.
Power companies charge by the kWh because their generators are measured in total output wattage and consumers consume at different wattages at different times.
Sure, it would be easier to measure in total joules consumed per period time but it would also be easier to measure with world standard metric units. The pain of changing is harder than staying the same, so muh freedum units.
It gets even better when you read about annual or even daily energy production of a specific power plant.
For example, the annual production of Aswan dam in Egypt is about 10 042 GWh, which translates to an average power output of about 1.1 GW. Now that you have this number, you can compare that with the maximum theoretical power output which is 2.1 GW. Therefore, they should have plenty of capacity left, but you can't tell that just by looking at the published numbers. They just have to use convoluted units, because that's the tradition in a bunch of industries.
There's nothing wrong with kilowatts, it's an SI unit. The problem is hour, which is 3600 seconds, and we have ancient Egyptians to blame for this, who divided the day into 24 hours despite having already developed base-10 numerical system.
Kilowatt per kilosecond, which is 1 megajoule, would work better.
I really don't get the issue with kWh. Things are rated in W and we mostly care about the hours they're powered on. If I wanna figure out how many kWh a PC that needs 300W used in 4 hours, I multiply 300*4. If I wanna know how many joules it used, I have to do 300*4*3600. Only one of those can be done in your head in 3 seconds.
You gotta use an escape character, specifically a backslash ( \ ), when dealing with *s on lemmy.
Otherwise you end up with "stufflike this!"
When it could have been "stuff*like this*!"
ETA: Damn, you're good. Fixed it before I even finished this post!
One pet peeve of mine is the usage of watts and kilowatts though. Chargers are often labelled like 1 second lasting batteries :/
That's 203.7cm for anyone wondering
Damn, would've been an added joke to make the ceiling 150 gallons / ft2
Assuming US Gallons. With Imperial Gallons, it's 2.447 m
My car needs 0.07 square millimeters of fuel on the highway.
Isn't that crazy efficient? I seem to remember about 0.3mm²?
Way back of you asked Google "38 mpg in mm^-2" it would tell you.
I love that it's the size of the thread of fuel you would consume as you drive down the road.
Edit: oh no, that's about right. It's a diameter of about 0.25 mm. I think that's what I was thinking of.
Not sure. I asked my cat Jeepity.
square? Damn it uses no volume of fuel at all!
I need the alt text!
Sorry! I added it now.
First of all, thanks for posting new threads here, it was getting somewhat dull that I was in recent weeks always the first one, sometimes after several days.
You might want to post comics the same way I did: https://discuss.tchncs.de/post/28278776 i.e. not just with the alt text, but also with a link to explainxkcd. You can easily copy the alt text if you switch to m.xkcd.com.
6’8” in Murica units.
Ssh, adults are talking
Going from Watts to BTU's while researching for a solid state multi-power-state TEC cooling solution. I feel this.
And they're cursed for a region, you don't define a distance as volume! As I'm typing that, I realise this also defines a distance as a bodypart, ah well
But what temperature is that at? And what is the ambient temperature? And what if the power is not at exactly 120V? And what about if I put a fresh dead hooker in it every day?
Ahh, daylight saving saves on Kwh!