The system CAV or VAC (Constant Air Volume) is the simplest system for extraction in Fumehoods and other extraction systems. As the name indicates is a system that maintains the volume of air extracted, and there may be variation in the facial velocity of extraction.
A system that uses a speed and volume of constant extraction, which makes it necessary in the case of the fumehoods to resort to bypass so that there is no variation of the velocity to the face of the fumehood less than 0,3m / s or greater than 0,5m/s . The Bypass allows the user to open and close the window without varying the speed and staying within the safety standards.
This system presents a reasonable level of safety but at economic levels becomes very expensive, as it makes extraction volumes which may be unnecessary if the window of the fumehood is closed, and a higher extraction volume means a higher volume of insufflation, all this is then converted into energy consumption which in this type of system can be high.
As this extraction system presents constant air volumes, the HVAC system of the room where it is being inserted can be also simple, since to maintain the temperature and the atmospheric pressure within the parameters does not need to make great adjustments to what is normalized.
As the name indicates the CAV / VAC system, it is a system that maintains an air volume extracted independently of the window aperture, for example, if a fumehood that is extracting at a face speed of 0.4m / s with the window at 100mm height, as the window passes to a height of 500mm the facial velocity drops to below 0,1m / s since the air volume is always constant.
This is only a small demonstration that the CAV is a system that may have variations that may pose risks to the user, however, with the application of the bypass these variations drastically reduce to results that ensure the safety of the user.