The mechanical systems usually decrease its performance after a period of time. Hence, the systems are to be optimized in order to get maximum output from them. The optimization of the fans utilizes different kinds of steps like using series of fans on the shafts or using multiple shafts with series of fans.
Multiple fans in series or parallel
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- Fans are combined in series or in parallel as an alternative to a single set of fan.
- A set of two smaller fans are less expensive than a single set of larger fan and they give better performance than the larger one.
- The operation and arrangement of this kind requires a special care and special operating arrangements.
- Fans are to be installed in series close to each other to increase pressure locally.
- Parallel arrangement is done for single or dual operation for varying air flow rate.
- Series and parallel arrangement has its own advantage.
- Series arrangement is preferable in systems, having long duct or large pressure drops.
- In draft systems either induced draft or forced draft, the fans in series will minimize the amount of pressure in the duct.
- In parallel arrangement high efficiencies are achieved in system air flow rate,
- In parallel arrangement lower noise is generated.
- Parallel configurations are feasible for systems with large changes in air moving requirements.
Better matching of fans with the system
- The fans are selected to match the maximum pressure and flow requirements of the system.
- The system may not require the operation at maximum conditions all the time.
- The motor selected for a drive system must be capable of supplying the fan with required driving power.
- The fans in the system are usually driven by alternative current.
- The motor selected for driving the fans is usually a squirrel cage induction motor, because of its durability, low cost, reliability and less maintenance.
- These motors provide 3600 RPM when used a 2 pole 60 Hertz system and 1800 RPM when used a 4 pole 60 Hertz system.
- When there is a need of continuous range of speed variation, variable frequency drives are used to effectively vary the speed of the motor.
- In some cases when loading on motors is not high, the predicted savings from varying frequency drives may not materialize because of the impact of the losses associated with variable drives.
- Care must be taken in situations where increased air flow rate or system pressure due to clogging of air filters causes an overload on the system motor.
There are some optimization steps that needs to be followed to increase the performance like control of inlet vanes, use of multiple speed motors for driving fans etc.