Promoting Energy Efficiency

The flow from most fans and pumps is either constant or controlled by restricting the flow by mechanical means, e.g. dampers are used on fans and valves are used on pumps. This mechanical constriction will control the flow and may reduce the load on the fan or pump motor, but the constriction itself adds an energy loss that is obviously inefficient. Hence if the flow can be controlled by reducing the speed of the fan or pump motor, more efficient means of achieving flow control could be offered.

[ from EMSD HK: Energy Management - Application Guide of Variable Speed Drive VSD link ]

• As the speed of the fan or pump is reduced, the flow will reduce proportionally, while the power required by the fan or the pump will reduce with the cube of the speed. This level of potential energy saving makes the use of Variable Speed Drive (VSD) a cost-effective investments in energy efficiency which can be considered for motors.

• [Energy saving effect and amount of CO2 reduction by inverter drive]
  - Capacity of fan, pump: 30kW
  - Control speed by inverters: 60%
  
  * Efficiency of fan, pump at 100% operation: 92%
  
  * Necessary power of damper control: (60% speed = 84% power)
      30kW / 0.92 x 0.84 x 24h x 365days = 239,948kWh
  
  * Necessary power of inverter control: (60% speed = 21% power)
      30kW / 0.92 x 0.21 x 24h x 365days = 59,987kWh
  
  * Energy saving effect
      239,948?- 59,987 = 179,961kWh
  
  * Amount of CO2 reduction
      0.555kg / kWh x 179,961kWh = 99,878kg/year

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