American units to SI problem

WilcoYHF

Im doing a problem on heat gain through windows and the particular example im working on from an american book says:

"787 (Btu/h.ft^2) x 64 (ft^2) x 30 days x 57% = 0.86 million Btus"

but when I convert the individual numbers to SI units I cant get the same answer;

asuming 1 Btu/ft^2 h = 3.2525 W/m^2
1 ft^2 = 0.0929 m^2
1 Btu = 1,055.06 J

I get: 2481.018 (W/m^2) x 5.9456 (m^2) x 2592000 (s) x 0.57 = 2.18^10

but 0.86 million Btus = 9.09^8

Can someone please help me with this I'm sure I'm doing something wrong with the 30 days part of the sum but I've hit a dead end.

Thanks

spideog7

While I don't know anything about heat transfer my impression would be that since the quantities you're given are per day then you should convert them to per second if you're going to do your calculation in seconds. Or alternatively just leave it at 30days.

EDIT: It's not per day it's per hour Btu/h looks like a mistake in the original text or else you left out the actual question that puts it in context??
You can't multiply Btu/h * days and get BTU that's basic arithmetic you can't cancel hours with days.

His answer is 0.86million BTU/30hrs which is 2.11million BTU for 30 days, which means you're answer is correct give or take some rounding.

Unless of course the US decided they wanted to make their own day which now has 30hrs... wouldn't be surprised

backboiler

Someone's after leaving out a factor of 24.
Haven't done the calculations so don't know if it's you or the example.