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3.3 Estimation <strong>of</strong> <strong>the</strong>rmal energy gain <strong>and</strong> loss through building fenestration 78<br />

optimal value <strong>of</strong> <strong>the</strong> window-to-wall ratio for <strong>the</strong> entire building was equal to over 22 %.<br />

But <strong>the</strong> area <strong>of</strong> <strong>the</strong> south-facing windows was enlarged to 58 % <strong>of</strong> <strong>the</strong> <strong>façade</strong> size. The<br />

lowest value <strong>of</strong> WWR, only equal to about 4 %, characterizes <strong>the</strong> north <strong>façade</strong> <strong>of</strong> <strong>the</strong><br />

building under consideration.<br />

Window Opening Area<br />

- design value (m 2 )<br />

Window Opening Area<br />

- optimal value (m 2 )<br />

Difference between design <strong>and</strong><br />

optimal value (m 2 )<br />

Difference between design <strong>and</strong><br />

optimal value (%)<br />

Optimal value <strong>of</strong> <strong>the</strong><br />

Window-to-Wall Ratio (%)<br />

Table 3.9: Optimal value <strong>of</strong> Window-to-Wall Ratio.<br />

Total<br />

North<br />

315 to 45<br />

deg<br />

East<br />

45 to 135<br />

deg<br />

South<br />

135 to 225<br />

deg<br />

West<br />

225 to 315<br />

deg<br />

768.42 148.11 155.67 205.26 259.37<br />

410.70 17.78 53.77 260.38 78.77<br />

357.72 130.33 101.9 -55.12 180.6<br />

46.55 88.00 65.46 -26.85 69.63<br />

22.15 3.96 11.23 58.07 16.45<br />

It is crucial to note that <strong>the</strong> optimal value <strong>of</strong> WWR can significantly provide a reduction in<br />

energy consumption. As we see in Table 3.10, it is possible to decrease <strong>the</strong> space heating<br />

energy requirements by over 30 %.<br />

Design value<br />

Optimal value<br />

Difference between design <strong>and</strong><br />

optimal value<br />

Difference between design <strong>and</strong><br />

optimal value (%)<br />

Table 3.10: Heating energy consumption.<br />

District<br />

Heating<br />

(kWh)<br />

Energy Per Total<br />

Building Area<br />

(kWh/m 2 )<br />

Energy Per Conditioned<br />

Building Area (kWh/m 2 )<br />

29138.56 21.23 21.98<br />

19963.75 17.32 17.93<br />

9174.81 3.910 4.050<br />

31.49 18.42 18.43<br />

It is important to underline that <strong>the</strong> results <strong>of</strong> <strong>the</strong> optimization procedure, shown above,<br />

cannot be applied to o<strong>the</strong>r multi-family buildings because <strong>the</strong> optimal value <strong>of</strong> WWR<br />

mainly depends upon <strong>the</strong> apartment arrangement, <strong>the</strong> <strong>the</strong>rmal <strong>and</strong> optical performance <strong>of</strong><br />

windows <strong>and</strong> <strong>the</strong> building shape. However, <strong>the</strong> proposed optimization procedure is<br />

universal <strong>and</strong> can be used for single-family as well as multi-family buildings.

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