EcoRenovator - View Single Post - Heat loss in watts, stored heat in joules

briligg · 03-21-12, 02:24 AM

MN Renovator - i edited my previous reply to be clearer and more complete just after you replied, so some things maybe don't match up anymore.
But i think the bulk of the confusion comes from the fact that we are in no way discussing anything electrical here, this purely deals with heat.
1 kWh is equal to 3412 Btu. But 1 kW is not. If it was 1 kW for 1 hr, it would be. Sure, there could be something wrong with my calculation, but it isn't so straightforward as that i need to tack on an h to the result. I tried to explain the method as clearly as i could, and how i've done my best to reproduce in metric the calculation as done in Imperial. The trip up comes when the metric unit doesn't mention a time-scale. Think about my point that a 21 MW power plant is actually one rated for 21 MW per hour. Or, i guess it's 21 MWh per hour. Watts are pinned to seconds - joules per second. 21 MJ per second. If it was pumping out 21 MJ in a tenth of a second, it would be a 210 MW power plant. Sometimes time-scales aren't stated, just implied. The 5.678 Btu/ hr x ft2 x deg F = 1 W/ m2 x K conversion rate works, if i assume that the rate is for one hour. I can illustrate the point with an example.... Tomorrow. G'night.

03-21-12, 02:24 AM	#12
briligg Lurking Renovator Join Date: Feb 2012 Location: Mexico Posts: 14 Thanks: 2 Thanked 0 Times in 0 Posts	MN Renovator - i edited my previous reply to be clearer and more complete just after you replied, so some things maybe don't match up anymore. But i think the bulk of the confusion comes from the fact that we are in no way discussing anything electrical here, this purely deals with heat. 1 kWh is equal to 3412 Btu. But 1 kW is not. If it was 1 kW for 1 hr, it would be. Sure, there could be something wrong with my calculation, but it isn't so straightforward as that i need to tack on an h to the result. I tried to explain the method as clearly as i could, and how i've done my best to reproduce in metric the calculation as done in Imperial. The trip up comes when the metric unit doesn't mention a time-scale. Think about my point that a 21 MW power plant is actually one rated for 21 MW per hour. Or, i guess it's 21 MWh per hour. Watts are pinned to seconds - joules per second. 21 MJ per second. If it was pumping out 21 MJ in a tenth of a second, it would be a 210 MW power plant. Sometimes time-scales aren't stated, just implied. The 5.678 Btu/ hr x ft2 x deg F = 1 W/ m2 x K conversion rate works, if i assume that the rate is for one hour. I can illustrate the point with an example.... Tomorrow. G'night.