The contribution of the solar facade to reduce energy consumption derived from the ne­cessity of space heating in a building, has been quantified by means of the solar fraction delivered by the facade. Heating load has been calculated in base to degree-days method (annual base 15: 573 for Barcelona and 1377 for Geneve), considering a typical residential unit of 90 m2 of habitable surface and a volume equal to 225m3. 2m2 of integrated collector (as described in Table 3) is applied in the south wall. The global heat loss coefficient includes the losses by ventilation, considering an air renovation rate equal to 0.5 renovation by hour. Table 7 shows the heating load for different types of good insulated dwellings in Barcelona climate and Table 8 represents the heating load for three insulation levels in Geneve climate.

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Figure 7: Monthly solar fraction and solar efficiency of the facade applied to space heating for both climatic conditions, a — From January to May, b — From October to December

From Figure 7 it is observed that in May and October, the facade is able to deliver the total heating load in the majority of the cases, the rest of the months the solar fraction is lower. For Barcelona climate, the facade is more efficient. Table 9 shows the values of the useful energy (QLOAD) delivered by the facade for both climatic conditions.

For Barcelona climate, it may be obtained average annual values of solar fraction from 32% to 20% depending on the type of construction. For Geneve climate, annual values are about 9%, in this case, larger surfaces for collecting solar energy would be necessary.

Conclusions

Facades play an important role in the thermal behaviour of the buildings or dwellings at which they are addressed. Large glazed areas implemented in double skin facades, allow the combination with partially inner opaque layers. This paper has shown the possibility of using these areas to collect and accumulate significant quantities of solar energy in water tanks placed at the facade. A 2 m2 integrated solar collector implemented as part of the facade accumulating 100 water liters, permits to get annual values of solar fraction of around 41% for a Mediterranean climate (Barcelona) and 31% for a central Europe climate (Geneve) when it is applied to domestic hot water assistance. For space heating applications, the annual solar fraction for Barcelona climate is around 20% whereas for Geneve climate it is
about 9% (depending on the degree of insulation of the construction). For Geneve climatic conditions it would be necessary larger collection areas. Numerical results not shown here, have demonstrated that annual performance does not vary outstandingly with larger storage volumes, since these variation is asymptotic from 50l/m2 [9], [2].

Annual solar efficiencies for both applications are similar, for Barcelona climate it is around 48% and for Geneve, it is about 44%. The geometric configuration and material properties of the prototype analyzed in this paper, was previously optimised by means of a permanent analysis using code. The configuration with lower heat loss coefficient was chosen.

Numerical code AGLA has demonstrated its strength to simulate advanced facades inclu­ding the special features described in this paper.

Acknowledgements

This work has been supported in part by the European Commission under the Fifth Framework Programme, Thematic Programme: Energy, Environmentand Sustainable De­velopment FP5-EESD, Project CRAFT-1999-70967.

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