EFFICIENCY, REDUCE NOISE HOWDEN KNOW-HOW THERE ARE MANY POSSIBLE REASONS FOR FAN RETROFITS. FANS IN POWER PLANTS, FOR EXAMPLE, WERE OFTEN AIR HEATER LEAKAGE. SOMETIMES, SYSTEM RESISTANCE WAS SIMPLY MISCALCULATED. CHANGES AFFECT THE SYSTEM RESISTANCE. FACTORS LIKE THESE HAVE A SERIOUS PERFORMANCE. AND EVEN WHERE A FAN MEETS ITS OUTPUT TARGETS, NOISE AND VIBRATION CAN CARRY HEAVY COSTS AND CONTRIBUTE THERE ARE THREE MAIN WAYS IN WHICH RETROFITS CAN BE APPLIED OPTIMISED WITHIN THE INSTALLATION. • The existing impeller can be replaced with a high efficiency design, allowing • A tip can be added to the existing blade to increase performance, typically by 10-12%. This is a practical way to increase the capacity of an induced draught fan to cope with system resistance change. Casings, fairings and scrolls can be replaced or modified to improve aerodynamics or reduce noise. • Inlet cone shape and clearance can • The overall system, including the inlet WITH A DESIGN MATCHED PRECISELY • This is a preferred response to changed operating conditions and a demand for extra flow or pressure. • It is an effective solution in situations where severe erosion or corrosion is preventing safe operation of the fan. It is the clear preference where the existing fan is incorrectly matched to SYSTEM RELIABILITY NEEDS BE • Bearings can be modified to cope efficiently with the fan parameters, for example by replacing rolling elements with sleeve bearings to solve problems arising from temperature issues. On-line automatic balancing gear can be fitted on a shaft to reduce vibration during operation. This is an effective solution where here is extensive

Problems are compounded where the fan diverges from the geometry and parameters used for performance testing and design - by, for example, omitting internal fairings or introducing system components which were not present when demands on the fan were assessed. Unless the fan is matched perfectly system loss as well as the application, efficiency will be compromised. The motor may be more powerful than necessary. The fan may be pushed beyond the limits of its aerodynamic ability. Foundations or casings may have become inadequate. And the costs incurred by stalled operation, failures of blades...