Pressures in the racks are constantly kept positive (or negative) to the atmospheric pressure of the rearing room with high precision control of exhaust and supply air volumes.
Conventional technologies involved a problem that if the racks are connected to the main duct, a positive (or negative) pressure could not be maintained constantly because instabilities of exhaust and supply volumes are prone to be caused by external disturbances (such as fluctuations in pressures in the main duct, changes in operating status of other rearing rooms, sudden gusts of wind outside, etc).
Phoenix Controls' pressure independent type airflow volume control valves can maintain a constant airflow irrespective of disturbance of the air from external causes.
This technology enabled to keep a constant positive (or negative) pressure in the racks even when the exhaust and supply ducts of individual racks are connected to the main ducts.