Monitoring results

Monitored data from an apartment building in Freiburg, Germany, confirm the extent to which direct solar gains reduce heating peak load (Voss et al, 2004). In Figure 2.3.7, the upper straight line represents the theoretic heating peak load as a function of ambient temperature with no solar radiation, no internal gains and a constant 20°C indoor temperature. The dashed line assumes a demand reduction resulting from 2.1 W/m2 of internal heat gains (100 per cent usability). The points represent measured heating peak load, keyed by the intensity of solar radiation at the time. The diamonds indicate heating

Source: Lars Junghans, AEU

Figure 2.3.6 Reduction of heating demand as a function of window/ façade proportions and glass quality for a top-middle and middle-middle apartment peak load when solar radiation was less than 25W/m2, triangles 25 to 90 W/m2 and circles greater than 90 W/m2.

From the data, two observations can be made:

1 The extent that heating peak load decreases with increasing solar radiation: this reduction would be even greater were the south-facing windows of this project not shaded by balconies and trees.

2 As the ambient temperature decreases, measured heating peak loads are furthest from the theoretical demand (dashed) line. This is explained by the fact that the 8 W/m2 heating system capacity was unable to maintain the design 20°C. As the room temperature fell below the design temperature, the heating peak load decreased accordingly.

Source: K. Voss, Fraunhofer ISE, D

Figure 2.3.7 Heating peak load versus ambient temperature for the apartment block living and working areas, Freiburg i.B

Source: K. Voss, Fraunhofer ISE, D

Figure 2.3.7 Heating peak load versus ambient temperature for the apartment block living and working areas, Freiburg i.B

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