Hi, Need some advice as I am in a "disputed" teritory. I have asked my service provider to confirm if the Air Change for baby's nursery in a healthcare facility is within the desired requirement (specs say "The ventilation for the newborn nursery shall: i) have a minimum ventilation rate of twelve air change per hour which is provided by mechanical supply and exhaust air systems;") The vendor measures the total supply air rate through the supply air diffusers in CFH of the room and devides by room volume to arrive at Air Change. That is ((CFM per diffuser X Number of diffuser)X60mins/room volume) I disputed this method as to me it only indicated the "movement" of air due to recirculation and does not tell me the ventilation required. In my opinion the method of calculation should be based on how much fresh air (Outside Air) is injected into the AHU such that 12 times the room volume will be injected in the room in one hour by way of diluting the supply air. That is (12XRoom volume)/60mins to give fresh air intake rate in CFM measured at the fresh air intake grill/duct leading to the AHU. Hope someone will be able to correct me if I am wrong.