Process Water Cooling Tower Drive System

The Opportunity...

A new cooling tower was to be installed at a large automotive parts plant employing plastic injection moulding machinery.

The injection moulding machines were electrically heated, and much of the process heat had to be removed via water-cooling into the injection moulds.

The amount of heat to be removed could vary with the number of machines in use. Since the cooling tower was sized with the assumption that all the machines could be calling for cooling water at the same time (and for future machine installation) it is apparent that there would be scope for optimising the cooling to the machines requirements.

The cooling tower has two direct coupled fans each of 15KW @ 980 REV

The Solution...

Newton Tesla devised a control panel system based around two 15kW Mitsubishi Electric FR-A540 'Flux Vector' inverter drives, with one being employed for each fan motor.

The system was housed in a proprietary free-standing enclosure system, with a main incomer section, drives section, separate control section for the 110V AC control and safety circuits etc.

Using a PT100 temperature sensor in the water return from the cooling tower a 4-20mA signal was given to inverter No.1 which was programmed using it's internal PID control loop.

The 0-10V DC signal from the inverters AM terminal was connected to inverter No.2 which was set to follow exactly the frequency of the "lead" inverter. If the "lead" inverter tripped or it's motor required attention, then the "slave" inverter would be brought up to 50Hz by activation of a preset speed.

The cooling water set point was set at 15ºC and under test the temperature remained around that regardless of the heat load from the machines, so much so that the actual temperature never varied by more than plus or minus 1.4ºC from the set point!

The immediate benefits to the customer were:

1. Consistent cooling water temperature regardless of ambient air temperatures and machine loading.
2. Danger of overcooling and ice formation in winter is eliminated.
3. Energy is saved on the two 15KW fan motors by speed reduction but also a benefit and moving by not overcooling the machine moulds, thereby reducing electrical heat input to the machines.