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3.3 Estimation <strong>of</strong> <strong>the</strong>rmal energy gain <strong>and</strong> loss through building fenestration 76<br />

energy balance is positive for each storey. The difference between <strong>the</strong> first <strong>and</strong> <strong>the</strong> highest<br />

floor is equal to 31 % for balcony-windows <strong>and</strong> up to 66 % for windows.<br />

(Window Heat Gain Energy -<br />

Window Heat Loss Energy)<br />

per 1m2 <strong>of</strong> <strong>glazing</strong> system<br />

[kWh/m2 ]<br />

30,00<br />

25,00<br />

20,00<br />

15,00<br />

10,00<br />

5,00<br />

0,00<br />

Fig. 3.28: Dependence <strong>of</strong> <strong>solar</strong> gain <strong>and</strong> heat loss difference in <strong>the</strong> middle <strong>of</strong> each storey’s height.<br />

The dependence <strong>of</strong> <strong>the</strong> energy transfer Et on windows highest above ground level hs,<br />

shown in Fig. 3.27, we can approximate with a high level <strong>of</strong> accuracy using <strong>the</strong> following<br />

equations:<br />

• for <strong>the</strong> south-facing window:<br />

2<br />

Et<br />

= 0,<br />

099hs<br />

− 0,<br />

07hs<br />

+ 8,<br />

13,<br />

• for <strong>the</strong> south-facing balcony window:<br />

2<br />

Et<br />

= 0,<br />

042hs<br />

− 0,<br />

12hs<br />

+ 13,<br />

78.<br />

South‐Balcony window<br />

South‐Window<br />

Approximation<br />

0 2 4 6 8 10 12 14<br />

Middle <strong>of</strong> <strong>the</strong> storey’s height [m]<br />

3.3.3 Definition <strong>of</strong> an optimal value <strong>of</strong> window-to-wall ratio<br />

(3.2)<br />

(3.3)<br />

To summarize <strong>the</strong> above <strong>analysis</strong>, it should be noted that only south <strong>glazing</strong> systems<br />

provide heat gains for all locations in Germany. As mentioned before, east, west <strong>and</strong> most<br />

<strong>of</strong> all north <strong>façade</strong>s’ contributions to energy consumption increase during a heating period.<br />

So, it is impossible to talk about <strong>the</strong> optimal value <strong>of</strong> window-to-wall ratios with a<br />

reference to <strong>the</strong>se sides <strong>of</strong> <strong>the</strong> building. We can determine WWR only for <strong>the</strong> whole<br />

building with <strong>the</strong> additional investigation <strong>of</strong> each type <strong>of</strong> apartment (zones).

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