trevor hedman kendall hill. assumptions: outside wall is exposed to convection due to wind. ...
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Trevor Hedman Kendall Hill
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Assumptions:
Outside wall is exposed to convection due to wind.
Convection is approximated by flow over a flat plate.
Inside Wall temperature is constant at room temperature.
Radiation is neglected.
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Measurements:
Outside temperature of 20 degrees F
Inside temperature of 70 degrees F Outside wind speed of 8.8 mph used
(monthly average) The section parallel to the wind was
measured to be 22’ long and 8’ high
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Convection Coefficient Calculations
520,731
)/(13
44.29.3Re
26
sme
msm
vL
78.844Pr871Re*037. 3
1
5
4
lNu
Km
WNu
L
kh l 2
14.8
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Thermal Circuit Analysis
T
ios R
TTAq
T
ios R
TTAq
..1)
11( bdgyp
insstudsplywoodfinishconvT R
RRRRRR
kA
LRcond
AhR
o
conv
1
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Four Wall types were analyzed: 2x4 Stud wall with
Stucco finish Brick veneer wall CMU 2x6 Stud wall with
Stucco finish
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1st Wall: 2x4 Studs
Composed of: Stucco finish Plywood sheathing 2x4 Douglas fir studs Insulation (R-13) Gypsum board
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2nd Wall: Brick Veneer
Composed of: Brick covering Plywood sheathing 2x4 Studs Insulation Gypsum board
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3rd Wall: CMU
Composed of: Filled Cinder block 2x4 Studs Insulation Gypsum board
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4th Wall: 2x6 Stud
Composed of: Stucco Finish Plywood sheathing 2x6 Studs Insulation (R-19) Gypsum board
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Heat Transfer of each Wall
BrickBatt Insulation
Cork MasticExpanded Polystyrene
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Monthly Cost of each Wall
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Conclusions:
2x4 Brick Wall and 2x6 stucco wall types are very similar when insulation of k=0.5 (typical batt insulation) is used
CMU wall has the highest thermal resistance for most k values and the best monthly savings. It costs more to begin with but will save you money in the long run.
At k values greater than 0.7 changing insulation type does significantly reduce heat transfer in walls. Don’t spend extra money to upgrade insulation unless the k value is less than 0.7.