Applicability of European standards for the calculation of thermal properties of membrane cushions

In today's world of constructions engineering membranes play such an important role that they are often referred to as "the fifth construction material". One of the particularly innovative application areas is the use in tensile architecture. Membrane cushions form the envelopes of buildings like swimming halls, atrium-roofs or sport arenas for example. As the same requirements apply for buildings with membrane roofs as well as for regular buildings, standard indicators are needed to describe the thermal performance of the building. Regarding energy transmission lightweight building elements made of transparent membrane cushions show a different behavior compared to monolithic building parts or even windows. Existing standards relevant for U-value or g-value calculations are developed for conventional building structures. The defined range of application of these calculation methods does not include curved building elements or large locked air spaces. The U-value of membrane cushions depend disproportional high on the boundary conditions. Angular dependencies of reflection and transmission as well as orientation of the cushion influence the result of the g-value. All limitations and restrictions of existing standards for their application on membrane cushions will be discussed in the paper. Calculation methods described in DIN EN 673 and DIN EN 410 will be applied on membrane cushions. Parameter variations for panel thickness, number of membrane layers and different heat flux directions show the deviations between the standards. The results will be compared to measurements. Differing outcomes can be explained by simplifications made in the standards. The underlying physics need to be discussed to adopt standards for membrane cushions. This paper provides an overview of relevant calculation methods to describe the thermal performance as well as their applicability on membrane cushions. Furthermore it points out critical cases, where the calculation does not meet the requested accuracy and shows the demand of modification.