FRENIC4600 Series Medium-voltage direct output inverters Application and effect examples

Facility: Energy-saving cooling tower cooling fan

The capacity requirements of a cooling tower vary by day and by night, by the temperature conditions of the season, as well as by the operating power of the cooling fan's motor. Electric power can be saved by operating at the optimal power that matches the load by means of the inverter drive of the electric motor. The following is an example of detecting the temperature of the cooling water to automatically control the speed of the operation.

Key points

  • Because cooling towers are not generally designed for 100% capacity, they are a target for energy conservation.

  • Constant temperature control is applied based on the actual temperature value of the cooling water.

Calculation conditions

Motor output  600 kW, for annual operation time8,500 h
Operation pattern85% of flow rate         4,250 h
         60% of flow rate         4,250 h

Calculation example

  • Constant speed operation of motor (using flow valve control)

At an 85% flow rate   Required power = 91% x 600 kW = 546 kW
At a 60% flow rate    Required power = 76% x 600 kW = 456 kW
Annual power consumption546 kW x 4,250 h + 456 kW x 4,250 h = 4,258,500 kWh

  • Inverter operation

At an 85% flow rate   Required power = 61% x 600 kW = 366 kW
At a 60% flow rate    Required power = 22% x 600 kW = 132 kW
Annual power consumption366 kW x 4,250 h + 132 kW x 4,250 h = 2,116,500 kWh

Annual energy savings

4,258,500 - 2,116,500 = 2,142,000 kWh
If 1 kWh = 10 yen, the total value of the annual energy saved amounts to 21.42 million yen.

Annual energy savings