A simple calculation method for the energy performance of double skin facades

Presently the assessment of the thermal behaviour and the energy efficiency of naturally ventilated double skin facades (DSF) is only possible by using complex simulationtools, which allow inter-connections between fluid dynamics, energy balances and optical transport mechanisms. The performance assessment of mechanicallyventilated DSF is slightly easier but still requires simulation tools. Because of the interaction of separate calculation results, extensive iterations are often necessary.This makes it impossible to have reliable predictionson energy efficiency and impacts on comfort in the early planning phase and to sizable uncertainties at designersand investors.Therefore an assessment method was developed in the IEE project BESTFACADE, which on the one hand can be integrated in the assessment methods of the EPBD and on the other hand offers sufficient accuracy of the thermal behaviour and the energy performance of the system. Similar to the standardised approach for the winter gardens, trombe walls and the ventilated buildingenvelope parts of the ISO 13790, annex F, a monthly balanced calculation procedure was developed and evaluatedbased on sensitivity studies performed in earlier projects of the consortium partners. This calculation procedureharmonises with the currently developed CEN-Standards for the implementation of the EPBD. The main work consisted of the approximation of the airflow in the faade interspace and the adaptation of the utilisation factor of the solar gains to the different facade systems.