Example An office building

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For the office building described above, it is found that the proposed 16 mm air gap low-E argon filled double glazing units are unavailable, and that it is necessary to use 12mm air gap low-E (sn = 0.05) air filled double glazing units instead. These have a U-value of U = 2.5W/m2K (Table 4.2). As both the windows and the doors have U-values greater than the maximum average of 2.2 W/m2K, the average U-value must also be too high. Therefore compensatory measures are required, and in this case it is proposed to reduce the window area. The calculation may proceed as follows:

40 2

Maximum heat loss = 2.2 x 750 = 1650 W/K Actual heat loss = AWUW + ADUD + ARUR = 2.5 AW + 15.9 x 3.3 + 0

Equating these two heat losses gives the maximum area of the windows:

Therefore the building will satisfy the requirements of the elemental method for openings provided that the area of glazing is reduced from 732 m2 to a maximum of 639 m2.

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