Explanation Given information: The face brick size is 4 in , the size of concrete block is 4 in , the thickness of cement mortar is 0.5 in , the thickness of air space within concrete block is 20 mm , thickness of gypsum wallboard is 0.5 in , the thickness of furring is 0.75 in , the temperature difference is 30 ° F , the mean temperature is 50 ° F , the heat transmission area of air space is 80 % and the heat transmission area of studs and headers is 20 % . The below figure represent the schematic diagram of the masonry cavity wall and different element used in the construction of masonry wall. Write the expression of the total unit thermal resistance ( R − value ) between furring R b = R 1 + R 2 + R 3 + R 4 + R 5 + R 6 + R 7 + R 8 ....... (I) Here, the R-value between furring of Outside surface is R 1 , the R-value between furring of Common brick is R 2 , the R-value between furring of Airspace is R 3 , the R-value between furring of Concrete block is R 4 , the R-value between furring of small Airspace is R 5 , the R-value between furring of Vertical furring is R 6 , the R-value between furring of Gypsum wallboard is R 7 and the R-value between furring of Inside surface in air is R 8 Write the expression of the total unit thermal resistance ( R − value ) at furring R a = R 1 a + R 2 a + R 3 a + R 4 a + R 5 a + R 6 a + R 7 a + R 8 a ....... (II) Here, the R-value at furring of Outside surface is R 1 a , the R-value at furring of Common brick is R 2 a , the R-value at furring of Airspace is R 3 a , the R-value at furring of Concrete block is R 4 a , the R-value at furring of small Airspace is R 5 a , the R-value at furring of Vertical furring is R 6 a , the R-value at furring of Gypsum wallboard is R 7 a and the R-value at furring of Inside surface in air is R 8 a . Write the expression of the U-factor between furring. U b = 1 R b ....... (III) Write the expression of the U-factor at furring. U a = 1 R a ....... (IV) Write the expression of overall U factor. U overall = U b f b + U a f a ....... (V) Here, the heat transmission area fraction of air space is f b and the heat transmission area fraction of studs and headers is f a . Write the expression of overall thermal resistance or R − value . R overall = 1 U overall ....... (VI) Calculation: Refer to table "Unit thermal resistance of common components used in building" to find the R − values of different material as shown in below table. Construction R-value between furring R-value at furring Outside surface in winter 0.17 ft 2 ⋅ h°F / Btu 0.17 ft 2 ⋅ h°F / Btu Common brick ( 100 mm ) 0.43 ft 2 ⋅ h°F / Btu 0.43 ft 2 ⋅ h°F / Btu Airspace, ( 90 mm ) 0.1 ft 2 ⋅ h°F / Btu 0.1 ft 2 ⋅ h°F / Btu Concrete block ( 100 mm ) 1.51 ft 2 ⋅ h°F / Btu 1.51 ft 2 ⋅ h°F / Btu Small airspace, ( 20 mm ) 2.91 ft 2 ⋅ h°F / Btu NA Vertical furring ( 20 mm ) NA 0.94 ft 2 ⋅ h°F / Btu Gypsum wallboard ( 13 mm ) 0.45 ft 2 ⋅ h°F / Btu 0.45 ft 2 ⋅ h°F / Btu Inside surface in air 0.68 ft 2 ⋅ h°F / Btu 0.68 ft 2 ⋅ h°F / Btu Substitute 0.17 ft 2 ⋅ h°F / Btu for R 1 , 0.43 ft 2 ⋅ h°F / Btu for R 2 , 0.1 ft 2 ⋅ h°F / Btu for R 3 , 1.51 ft 2 ⋅ h°F / Btu for R 4 , 2.91 ft 2 ⋅ h°F / Btu for R 5 , 0.45 ft 2 ⋅ h°F / Btu for R 7 , 0 for R 6 and 0.68 ft 2 ⋅ h°F / Btu for R 8 in Equation (I). R b = [ ( 0.17 ft 2 ⋅ h°F / Btu ) + ( 0.43 ft 2 ⋅ h°F / Btu ) + ( 0

5th Edition

ISBN: 9781307573060

Author: CENGEL

Publisher: MCG/CREATE

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Chapter 3, Problem 169EP

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The winter R−value and the U−factor of a masonry cavity wall.

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Chapter 3, Problem 168P

Chapter 3, Problem 170P

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Chapter 3 Solutions

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The winter R − value and the U − factor of a masonry cavity wall.

The winter R−value and the U−factor of a masonry cavity wall.

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Chapter 3 Solutions