Opaque vented façades are innovative and widely-used
technological systems adopted both in new constructions
and in building renovations. According to European
Directive 2010/31/EU (EPBD recast) on the energy
performance of buildings, each Member State should give
priority to passive cooling techniques in order to enhance
building performance during the summer period. For this
purpose opaque vented envelope could be an appropriate
technological solution to reduce the summer peak loads
and the energy consumption. Although the EPBD recast
has submitted the development of calculation methods
for the energy performance evaluation to the European
Committee of Standardisation (CEN), there is a lack in
European Standards on the calculation of non conventional
building envelope performance, including
vented façades.
The object of the present work is the thermal
performance characterization of vented vertical opaque
enclosures in real conditions of use, through simplified
parameters.
Starting from EN ISO 6946 and EN ISO 13786, new
equivalent thermal parameters are defined, such as the
equivalent steady state thermal transmittance, the
equivalent periodical thermal transmittance and the time
shift.
Equivalent parameters are obtained by evaluating surface
inside face conduction in the opaque components, under
stabilized periodic external conditions, for the summer
design day. An equivalent outside temperature is used,
which considers both the convective and the radiative
thermal exchanges (solar and infrared waves), for
different boundary conditions (orientation). The tool
used for calculations is based on the conduction transfer
function – CTF – method, as implemented in the thermal
dynamic simulation program Energy Plus.
Through a sensitivity analysis, different opaque
enclosures are analyzed, varying the design parameters
such as the thickness, the height and the length of the
vented cavity
