Thermal transfer through membrane cushions analyzed by computational fluid dynamics

The use of membrane cushions in architecture is highly growing. These systems are used as exterior facades or roofs. They need to fulfil all the requirements that are applied to conventional building technologies. In terms of heat transfer a general method or standard to identify the heat loss through the membrane cushions is not available. Furthermore complex processes inside the membrane cushion are not well enough understood to improve the cushions and avoid building physical problems. A test set-up was built to assess the processes inside the cushions. To enlarge the results from these tests computational fluid dynamics (CFD) simulations were performed, where varying boundary conditions in terms of inclination and temperature difference were applied. The simulations showed compareable results for the experimentally measured temperature and heat fluxes. Three different flow conditions were determined by the parameter variation simulations. Surface to surface radiation was determined to be mainly independent from the flow conditions inside the panel. It can therefore be calculated separately. With knowledge of the installation situation and the temperature boundary conditions the flow pattern inside the panel can be predicted. This allows an approximate calculation of the heat transfer through the cushion. Possible improvements of the cushions in terms of thermal performance are shown.