Fume Cupboard Face Velocity Control
When assessing laboratories for energy saving opportunities, ventilation is often quickly cited as area with great potential. Laboratories require constant ventilation for a safe and comfortable working environment.
Biological safety cabinets and fume cupboards add to the complexity of research facility ventilation as their requirements can vary frequently. While the running of the equipment itself utilises notable amounts of energy, there are greater losses in conditioned air. Much of the air that is ventilated either through rooms or research equipment has been warmed or cooled for the environment, and it is the loss of this conditioned air which can be particularly costly. Ensuring that the rates of flow are high enough to ensure safe conditions and yet low enough to not be wasteful is one of the continuing challenges in managing research facilities. With this case study from Kings College London, we take a look particularly at fume cupboard flow rates and how the introduction of one policy can significantly reduce energy waste across research sites, and save money.
Each fume cupboard maintains a ‘face velocity’, which measures in meters per second the volume of air passing through the opening when the sash is at a safe working height. Currently most fume cupboards operate with a face velocity of 0.5 m/s or above unless otherwise evidenced through containment testing. Many fume cupboards state to operate at 0.5 m/s will actually end up far higher with time. Fume cupboards are inspected every 12-14 months under law to ensure that they are maintaining safe flows and in good working condition, during which face velocities may be altered.
There are hundreds of fume cupboards in operation across 3 hospitals and 5 campuses. King's staff will work with all of them, with many managed by the NHS, PFI contract holders Bouygues, and soon the Crick Institute. Upon inspection many of these fume cupboards are operating with face velocities well above the 0.5 m/s requirement, with some buildings averaging 0.7 m/s. While still safe, such flow high flow rates will expel much conditioned air outside the building, wasting energy. Thus lowering the face velocities on all fume cupboards to a consistent 0.5 m/s could lead to significant savings. To ensure fume cupboards are consistently maintained for safety and efficiency across the college, we have introduced a fume cupboard maintenance policy. As fume cupboards will receive their annual inspections, engineers will ensure that face velocities will be maintained at a consistent 0.5 m/s (unless high velocities are required for special purposes). Furthermore new installations will have their face velocities set to 0.35 - 0.4 m/s.
Likely savings can be massive. Assuming air is conditioned an average of 10 °C per day, reducing a fixed fume cupboards face velocity from 0.6 m/s to 0.5 m/s will reduce the annual energy bill by approximately £300. The policy was recently put to work in the recent installation of 19 new fume cupboards for teaching in the Franklin Wilkins building. By ensuring the face velocities were set to 0.35 m/s instead of 0.5 m/s as well as being VAV, the college will save a minimum of £8,550 per year. When fully applied to all fume cupboards at King's and its partners, significant savings are expected.