EDITOR ’ S CHOICE FUME FAN MAINTENANCE
AXAIR FANS
As the Summer sees a busy time for school facilities and maintenance teams upgrading or replacing old laboratory parts , Axair discuss how their complete fume fan pack can simplify school fume cupboard maintenance
Installing , maintaining and testing fume cupboards can be problematic for schools and universities because of a lack of experience . Senior management of schools rarely understand the problems which may arise when ducting and the fume cupboard itself are installed and commissioned . These problems then differ for maintenance or health and safety inspections .
A fume cupboard is intended to minimise exposure to hazardous gases , vapours or dusts . A secondary function can be to act as a safety screen to protect students and staff from minor explosions or splashes . Protection is achieved by a flow of air created by an exhaust fan which is designed to ensure the contaminant remains inside the fume cupboard .
If the airflow rate is too low , hazardous fumes may escape , especially if the air is disturbed by cross-draughts or people moving about nearby . On the other hand , if it is too high it may destabilise Bunsen burner flames , waste energy and be noisy . Airflow rate is very much dependent on the fan , the ducting , the sash height , the presence of a baffle , bypass , damper , and inverter .
A centrifugal fan that is part of a fume cupboard system is mounted on the outside of the building or on the roof space . This ensures that the ducting inside the building is under negative pressure , compared to atmospheric pressure , and that any leakages are into the duct and not into the rooms . Older fume cupboards used to have axial fans mounted just above the fume cupboard . These noisy fans put the whole of the ductwork under positive pressure and caused leakage of fumes to surrounding spaces . The exterior stack height must be sufficiently high above the building to prevent the air re-entering , which can be a problem for schools that
Airflow rate is very much dependent on the fan , the ducting , the sash height , the presence of a baffle , bypass , damper , and inverter .
are situated in residential areas due to unsightly stacks .
The fan and ducting must be correctly sized to give the required face velocity , without requiring major adjustment by a damper or inverter . While a damper should be fitted , it should not be required to do more than make small adjustments to the air flow . Fitting an over-powerful fan and using the damper to reduce the air flow to an acceptable level is a waste of money . EC fume fans were introduced to save on average 20 % of fan energy consumption without affecting performance . As an alternative to a damper , some fume cupboards may have an inverter , which is used to adjust motor speed allowing a slow ramp up time and a reduction in start-up costs . Whichever option is used , once set , it should be locked into position and not altered during normal use . Dampers may also increase noise levels if they are used to produce a considerable reduction in velocity from an unnecessarily powerful fan .
All parts of any fan in the airstream should be resistant to the airborne contaminants which may be present . Corrosion resistant centrifugal fans made form polypropylene with either backward-curved or forwardcurved blades should be used . Antivibration fan mountings should be used , to ensure that vibrations are not transmitted from the fan to the building or to the duct .
The customisable fume fan pack from Axair Fans offers a complete fume cupboard extraction fan set along with complementary accessories such as inverter , isolator , wall mountable pedestals and AV mounts for simple school and university installations . Contact our team to discuss your fume fan maintenance and airflow requirements .
For further information , please visit www . axair-fans . co . uk
10 PECM Issue 57