Thermal performance of pneumatic cushions: an experimental evaluation

In the recent past coated textiles and membrane structures have been increasingly implemented in architecture as either temporary or permanent external building envelopes. Double or multiple layer pneumatic cushions are frequently adopted. Therefore, one of their tasks is to guarantee suitable thermal conditions for the enclosed environment and/or limit HVAC energy consumption. The key thermal-physical parameter is then the cushion thermal resistance, which is usually assessed through simple calculations based on the assumption that cavities are approximated as rectangular enclosures. However, the impact of the actual shape of the cushions on the heat transfer has not been clarified yet. In this work, the thermal resistance of two cushions is experimentally assessed using a double chamber thermal setup. More precisely, two (double and triple layer) small vertical samples (1.1 m x 1.1 m) are exposed to a 25 °C steady-state temperature difference, to replicate Milan winter design conditions. Their exterior surfaces are divided in thermally homogeneous sub-surfaces of various sizes and temperatures are locally sampled on every sub-surface of both skins, along with the heat flux density on one side. Data are collected every 5 seconds for a time span of 12 h, in order to verify the steady-state assumption, and the average values for both temperatures and heat flux in every subsection are calculated. These data are then area-weighted and used to calculate the overall thermal resistance for each sample investigated, which are then compared with various correlations from literature.