Calculating Daily Heat Loss

Calculating Daily Heat Loss jls164 Wed, 05/30/2012 - 13:28

Now that you know how to calculate hourly heat loss, how would you calculate daily heat loss?

Since there are 24 hours in a day, you would simply multiply the hourly heat loss by 24.

$H e a t L o s s (\frac{B T U s}{h}) = \frac{A r e a (f t^{2}) \times T e m p e r a t u r e D i f f e r e n c e (^{\circ} F)}{R v a l u e (\frac{f t^{2} º F h}{B T U s})} \times 24 h r / d a y$

Example

What is the hourly and daily heat loss of a 15-ft by 15-ft room with an 8-ft ceiling, with all surfaces insulated to R13, with inside temperature 65°F and outside temperature 25°F?

Cube, Height = 8 ft, Width = 15 ft, Depth = 15 ft, each side = 120 sq ft.

$H o u r l y H e a t L o s s r a t e = \frac{Q (B T U s)}{t (h o u r)} = \frac{(480 f t^{2} \times (65^{o} F - 25^{o} F)}{13 \frac{f t^{2}^{o} F h}{B T U}} = 1, 477 \frac{B T U s}{h}$

Once we know the heat loss rate per hour, we can determine the heat loss per day by multiplying by 24 (hours in a day).

In a 24-hour period or one day, the heat loss would be:

$D a i l y H e a t L o s s p e r d a y = \frac{1477 B T U s}{h} \times \frac{24 h}{d a y} = 35, 448 \frac{B T U s}{d a y}$

$H e a t L o s s (\frac{B T U s}{h}) = \frac{A r e a (f t^{2}) \times T e m p e r a t u r e D i f f e r e n c e (^{o} F)}{R v a l u e (\frac{f t^{2}^{o} F h}{B T U})}$

Area (ft²) is the sum of the area of all four walls. Each wall is 8' x 15', or 120 sq. feet, so take 4 x 120 sq ft to get 480 ft² in the equation.