To maintain their shape and structural stability multi-layer ETFE foil cushions require air inflation. The cushions are kept continually inflated at a predefined pressure by a small air handling unit (or AHUs) connected to a control panel which inflates, monitors and maintains the pressure in each individual cushion.
In the unlikely case of a power failure, the air handling unit will cut out until the primary power source can be reconnected or a back up generator can be activated. Without a connected air supply, an ETFE cushion system will maintain pressure for between 3 and 6 hours before deflating (dependant on weather conditions). This is due to the non-return values built into the air inflation units which retain as much air as possible to avoid deflation damage. After this time, there is a possibility that, as pressure drops, heavy rain/snow will pond on the deflating structure, wind will flog the membrane and the roof will become damaged.
As a result we recommend that there is either a standby generator or alternatively a cable bracing system installed to support the cushions should this situation arise. Aside from this, we also recommend that the roof is closely monitored, through our control system or through other means, to avoid problems occurring which could have been forseen.
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Architen Landrell, Station Road, Chepstow, NP16 5PF, UK