Influence of building integrated solar collectors on indoor environment and building performance has been evaluated. Specific winter heat gains and summer cooling loads have been obtained from annual space heating demand and space cooling demand of the investigated building with envelope direct integrated collectors compared to the reference case without collector integration. The characteristics of specific heat gains Aqsh and cooling loads Aqsc are plotted in dependence on collector-envelope (roof, faqade) coverage area ratio Ac/Ae in Fig.5 for atmospheric, evacuated and vacuum solar collectors integrated into building envelope (roof, faqade) operated in combisystems

with different operation temperatures for space heating. Heat gains from the collectors integrated into the facade achieve during the heating season, depending on supply temperature, about 2.3 to

3.5

% of heating demand for combisystem with 10 m2 collector area and 12.2 to 15.5 % of heating demand for total facade coverage (Ac = 42 m2). For the roof integrated case the impact is slightly higher (2.6 to 3.8 % for Ac = 10 m2 and 13.5 to 16.7 % for the extreme case of total roof coverage).

Fig.5a. Collector induced specific gains and loads to building due to integration of atmospheric flat-plate collector into the building envelope (roof integration on the left side; facade integration on the right side).

Fig.5b. Collector induced specific gains and loads to building due to integration of evacuated flat-plate
collector into the building envelope (roof integration on the left side; facade integration on the right side).

Fig.5c. Collector induced specific gains and loads to building due to integration of vacuum flat-plate
collector into the building envelope (roof integration on the left side; facade integration on the right side).

Due to high heat resistance of the envelope (low-energy house) the influence of solar collector integration does not bring large problems for summer overheating. For the most extreme case where the south roof of the building is completely covered by vacuum flat plate collectors (Ac = 42 m2) the cooling load is less than 150 kWh/season.

Similar results are illustrated in Table 2, this time presenting the specific heat gains and cooling loads induced by different types of collectors integrated into the building envelope (roof, facade) and different supply temperatures for space heating for a given solar fraction off = 30 %. It shows that more efficient collectors (vacuum) have higher influence on the building environment than standard atmospheric flat-plate collectors. Furthermore, less collector area is needed to achieve the same solar fraction. The lower the supply temperature of the heating system the better is the performance of the combisystem (less collector area achieving same solar fraction) and the less impact on the building performance can be expected.

Table 2. Specific heat gains Aqsh and cooling loads Aqsc induced by investigated envelope integrated flat-
plate collectors for solar fraction f = 30 %. The required collector area for f = 30 % is shown.

5. Conclusions

Parametric simulation analyses of solar combisystem configurations operated to different types of heating systems and equipped with atmospheric, evacuated and vacuum solar flat-plate collectors integrated into the building envelope or applied separately have been performed. For the solar combisystems the analyses have proved the advantage of building integration of solar collectors. Direct integration of solar collectors thermally coupled to the roof envelope results in higher performance when compared to faqade collectors but leads also to considerably higher stagnation levels and specific stagnation time due to unutilisable summer irradiation peak.

Direct facade collector integration compared to separate installation of solar collectors on the roof (thermally uncoupled) results in lower or equal collector area needed to achieve similar solar fractions but with considerably reduced stagnation periods. The operation temperature of a heating system affects the combisystem efficiency and should be maintained as low as possible for effective use of storage tank although evacuated solar collectors are applied.

The influence of building integrated solar collectors on indoor environment and building performance has been evaluated by means of specific heat gains in winter and cooling loads in summer both induced by heat flow from solar collectors into the building interior. Due to high thermal protection of low energy houses the influence of solar collector integration does not bring large problems for summer overheating even for extreme cases and brings very low heat gains in winter even for high-performance evacuated solar collectors.

Acknowledgement

The research work has been supported by a Marie Curie Early Stage Research Training of the European Community’s 6th Framework Programme under the contract MEST-CT-2005-020498: SOLNET and by research project CTU 880590 “Experimental validation of mathematical model for flat-plate evacuated solar thermal collector”

References

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