EGEE 102
Energy Conservation and Environmental Protection

Calculating Daily Heat Loss

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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.

Heat Loss( BTUs h )= Area(f t 2 )×Temperature Difference ( o F) R value( f t 2 o F h BTUs ) × 24hr/day

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.
Hourly Heat Loss rate= Q(BTUs) t(hour) = (480f t 2 ×( 65 o F 25 o F ) 13 f t 2 o Fh BTU =1,477 BTUs 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:

Daily Heat Loss per day= 1477 BTUs h x 24 h day =35,448 BTUs day
Heat Loss( BTUs h )= Area(f t 2 )×Temperature Difference ( o F) Rvalue( f t 2 o F h BTU )

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.