What is CAV - VAV
1. CAV
The exhaust air volume flow is changed in relation to the fume hood sash position so that the face velocity remains constant. The fume hood exhaust air volume flow is regulated either by a motor-driven damper (in hoods connected to a central exhaust air system) or by an integrated exhaust air motor with a frequency inverter.
Constant air volume (CAV) ventilation provides a constant flow of air, regardless of whether or not the fume cupboard is in use and the sash is open or closed, wasting a significant amount of energy.
Closing the sash on a CAV hood will also increase the face velocity (or ‘pull’ at the front of the fume cupboard) with consequences including the disturbance of equipment, slowing of experiments and potentially even pushing contaminated air back in to the room.
2. VAV
In terms of energy efficiency, this mode of operation is the most expedient and the best method of fume hood control. A very fast and yet stable control algorithm is the most notable technical feature of this control mode.
The operating mode seamlessly regulates the exhaust air volume fl ow in relation to the fume hood sash position. The fume hood exhaust air fl ow is regulated either by a motordriven damper (in hoods that are connected to a manifold air system) or by an integrated exhaust air motor with a frequency inverter.
This type of system, which can be fitted as part of a new installation or retrofitted to any existing laboratory, has several significant benefits.
- Energy efficiency: Using a VAV system, fume cupboards operate at minimum exhaust volumes when the sash is closed so energy usage is highly responsive to user needs. The exact saving depends on user behaviour but in general the less the hoods are open (in terms of height and time), the greater the energy savings.
- Cost saving: VAV systems may incur higher initial costs than CAV systems but VAV controllers can reduce energy costs
- Improved safety: VAV systems provide better protection for your staff from potentially hazardous fumes and substances, helping you stay compliant with relevant health and safety regulations.
