Example An office building

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An office building has a total external exposed wall area of 1875 m2. It is proposed to fit metal framed windows to a total area of 732 m2, and the windows will be fitted with 16 mm air gap low-E (sn = 0.05) argon filled double glazing, U = 2.1 W/m2K (Table 4.2). The building is to have metal part-glazed personnel doors of U-value 3.3 W/m2K to a total area of 15.9m2. There are no rooflights. Check for compliance by the elemental method. The requirements are:

• From Table 3.2, that the total area of openings does not exceed 40% of the exposed wall area, and

• From Table 3.1, that the average U-value of windows doors and roof-lights does not exceed the figure for metal window frames, i.e. U = 2.2 W/m2K.

The total area of openings is 732 + 15.9 = 747.9m2. Thus:

747.9 x 100

Openings as a percentage of exposed wall area H--——-= 39.9%


732 x 2.1 + 15.9 x 3.3 + 0 1589.67 Average U-value uwdr =-747-9-= 747 9

Taken together, these results satisfy the requirements of the elemental method for openings.

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