Façades and summer performance of buildings

External cooling loads of a building façade are caused mainly by shortwave irradiance transmission, but also secondary heat flows from the internal glass panes and through ventilation gains from the façade. In a double façade with sun-blinds in the air gap, thermal energy is produced through absorption on the blinds. The work quantifies the thermal performance of single and double façades under summer conditions using laboratory and full scale building experiments. The experimental results were used for model validation and parameter studies were done using dynamic building simulation tools.While the measured sun-blind surface temperature reached up to 45 °C, the air temperature increase in a one storey high double façade was between 3 and 5 K, with peak values of 8 K. For typical absorption coefficients between 10 and 30% the summer thermal energy produced ranges between 50 and 100 kWh mfaçade−2. Depending on the ventilation rates between façade and room, only an air flow fraction of about 10% enters the room and adds to the cooling loads. Additional summer cooling loads through façade ventilation of 2–5 kWh m−2 room surface were obtained. The measured total energy transmittance of shaded double façades was about 10%, nearly independent of blind position and opening cross section, so that short wave irradiance can be effectively blocked with sun-blinds. Secondary heat flows only play a role if no shading system is used and are otherwise negligible.