By Liz Nekesa
Fan system refers to all components attached to a fan, for example an industrial fan system may include, fume hoods, ductwork, control dampers, filters, motors, belts drive and other electrical connections. Fan system performance optimization is mostly overlooked yet it can offer considerable cost savings, improve reliability and prevent unwanted downtime.
There exists three opportunities in industrial fans to improve fan system performance:
- Initial system design: Specifically the selection of the fan in the initial stages. The following considerations are essential: Knowledge of system operating conditions, air properties such as temperature, moisture, density), air flow rate and system layout. Awareness of these factors aid in choosing the right fan.
- Trouble shooting : When maintenance of fan is required, energy mangers may use the opportunity to bring forth long term solutions angled at improving efficiency
- System capacity modification: creates opportunity for existing fan system to be assessed opening a window to float an optimized system to accommodate the change.
Common problems that affect fans systems, indicators of an inefficient system include:
- High operating and maintenance costs
- Poor airflow or insufficient delivery affected by system configuration and flow controls
- Noise from possibly worn out bearings
- Contaminant build up on some of the fan blades
- Fan degradation due to blades wearing out
- Pressure loss across dirty filters
- For belt driven fans, belt could lose tension over time resulting in inefficiencies.
- Oversizing of fans as fan systems are initially designed to meet highest expected loading.
- Unstable operation caused by operating at low flow rates or interaction of multiple fans operated at parallel
Most of the problems above can be solved by routine maintenance categorized into preventative and predictive maintenance to improve reliability and avoid expensive failure. Solutions that can be adopted for preventive maintenance include:
- Create filter changing schedule
- Lubricate bearings
- Replace and properly adjust tension and alignment of belt drives (applies to belt driven systems)
- Verify correct operation of dampers. A damper that is mostly closed throughout operation is a red flag.
For large fans and critical loads, predictive maintenance can be conducted to monitor motor health, bearing health and vibration levels.
For oversized fans some specific corrective measures include:
- Replace entire fan or motor with a smaller one
- Decrease fan speed by use of variable speed drives on the motor. Theoretically using affinity laws (shown below) reducing speed by half reduces power consumed to an eighth of initial consumption
- Use of multiple fans to cater for the load.
In general, a well-designed system can avoid higher than needed operating costs. Overall system efficiency is key to savings.
A mistake done at the early stages of early design is focusing on the initial cost only, where the lowest bidder wins. Overall system efficiency is key to savings. The life cycle costs should be used to bring into perspective the required fan system, these cost include: Initial equipment cost, energy consumption and maintenance cost