Green Building Bible, Fourth Edition |
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Posted By: PeterStarckThey are for space heating followed by total energy use.
Posted By: tonyIs that 20C 1251? Or 12.51?So that's 12 kWh/m²/a for space heating and 51 kWh/m²/s for total energy use (so 39 kWh/m²/a for non-space-heating energy use).
Posted By: djhSorry, but kW per hour doesn't make much sense as a unit. It makes my brain hurt even thinking about it.I've seen it used properly.
Posted By: Jeff BSo if a wood pellet boiler (or any kind of boiler for that matter) is rated at 20 kW what does that mean in reality? If burning 1 kg of wood pellets produces approx 5kWh of energy, do I take it then that a 20kW boiler is capable of burning a maximum of 4 kg of pellets per hour when going flat out?
Posted By: Jeff BExamples of electrical appliances are easy: 1 kWh is equivalent to running a 100W light bulb for 10 hours, a 10kW shower for six minutes or a 2kW kettle for half an hour.Yes. You multiply the power by the time to get the energy.
Posted By: Jeff B1 kW per hour = 1 kWh doesn't it?NO!
Posted By: Ed DaviesPosted By: Jeff BExamples of electrical appliances are easy: 1 kWh is equivalent to running a 100W light bulb for 10 hours, a 10kW shower for six minutes or a 2kW kettle for half an hour.Yes. You multiply the power by the time to get the energy.Posted By: Jeff B1 kW per hour = 1 kWh doesn't it?NO!
A watt is like a knot [¹] in that it's already a rate. Talking about 1 watt (or kilowatt) per hour doesn't make any more sense than talking about 1 knot per hour (other than odd cases like a rate of change of power or rate of change of speed of a supertanker respectively).
To put it another way “1 kW per hour” is doing division, “1 kWh” is doing multiplication.
1 kWh = 1000 W x 1 hour = 1000 J/s x 3600 seconds = 3'600'000 J = 3.6 MJ.
1 kW per hour, if anybody was to use it properly, would be: 1 kW/h = 1000 J/s / 3600 s = 0.2777… J/s². Sort of like the acceleration due to gravity on the Earth's surface being roughly 9.81 m/s².
[¹] 1 knot = 1 nautical mile per hour. 1 watt = 1 joule per second.
Posted By: WillInAberdeenI gave up on being a units pedant after that, it was no fun with folk like that around.It's not just pedantry, there's real confusion on significant matters. See further up this thread.
Posted By: Peter_in_HungarySo is 1 kWh 1 kW in 1 hour whereasYes, it's something else.
1 kW / hr is something else