Adjusted Calculations for R-value Framing

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This article discusses the conductive Heat loss calculations that affect HEAT's walls, attics, windows and doors and basement/floor screens.

The calculations for the adjusted R-values after selecting a framing option are done in U-Values which are the reciprocals of R-Values, U=1/R.

For the annual heating season, conductive heat loss through walls, ceilings, windows, doors, and floors uses the following calculation:

Where n = the discrete temperature bin midpoint (in 5 degree intervals) for all bins under 60oF; h = hours at each temperature annually, U = U-value of the buildings component, and A = the area.

For annual cooling season conductive heat gain through walls, Attics, windows, doors, and floors:

 

 

Where n = the discrete temperature bin midpoint (in 5 degree intervals) for all bins over 80oF; h = hours at each temperature annually, U = U-value of the buildings component, and A = the area.

 

U-values that are used in the bin analysis are generated using assembly U-value methodology by generating a material weighted U-value for each shell component. An example calculation for a wall is as follows:

 

Example for an R- 13 insulated 2x4 stud wall with wood siding

 

R-value

 

Building Component

stud

cavity

 

outside air film

0.17

0.17

 

wood siding

0.8

0.8

 

plywood sheathing 1/2"

0.63

0.63

 

3 1/2" stud

4.38

13

 

1/2" drywall

0.45

0.45

 

inside air film

0.68

0.68

 

 

 

 

 

 

percent of wall area

0.15

0.85

 

total wall component r-value

7.11

15.73

 

wall component u-value

0.141

0.0636

 

total wall assembly u-value

 

 

0.075

total wall assembly r-value

 

 

13.3

 

 

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