Brings together purely natural and mechanical ventilation means Mechanical ventilation is activated when purely natural airflow isn’t adequate, for example in the course of peak periods or in additional enclosed regions of the vehicle park. You should buy an air exchanger like this Tjernlund X2D Reversible Basement Admirers from Amazon https://mylespgvky.iyublog.com/35507549/new-step-by-step-map-for-car-park-ventilation