Assumptions

The fume cupboard is active for 8 hours per day on a VAV system, or 2 hours per day with Autosash, with the extraction rate at 100%. The remainder of the time, the extraction rate is 30% of the volumetric flow rate at 0.5m/s. On CAV fume cupboards, the extraction rate is 100% during all hours of operation. This is active 52 weeks a year, 7 days per week.

The weather is based on an average at Manchester Airport over 3 years taken up to 2024. Energy cost is 6p per kWh for a gas fired heater with a heater efficiency of 56%.

Fan energy consumption is not included within these calculations. The extraction fan is assumed to operate at a constant speed, independent of sash position. In systems comprising multiple fume cupboards, the range of possible extract and supply fan configurations is sufficiently complex that it cannot be robustly represented within a simplified modelling framework.

The fume cupboard has 12% design leakage and is valid only on Clean Air fume cupboards. The sash opening is 1200mm to account for the width of the side panels which aid containment. The sash opening is the height between the bottom of the sash handle and the aerofoil, as per BS EN 14175-1.