Cooling tower drives save chip maker £30,000 in energy

A semiconductor manufacturer in Plymouth, UK is saving over £30,000 a year in energy costs, since installing six, 37 kW HVAC drives on its three cooling towers. The £15,000 installation is set to give a payback in only six months.

This customer is one of the largest semiconductor makers in the UK. A clean, vibration-free environment is a top priority in semiconductor manufacturing and the company uses large quantities of air and water to maintain cleanliness. The three cooling towers produce chilled water for the manufacturing process.

The drives are used to control six, 37 kW fan motors in the cooling towers.

Originally, the fans were star/delta connected, arranged in cascade style so that they would come in, or disconnect, one by one as demand varied. This meant the final fan would constantly be switching on and off, sometimes as often as every 10 minutes. With a large 37 kW motor, this would draw significant start-up current. Additionally, whenever an odd number of fans were connected, air from the last fan would blow out through one of the other fans.

With the new drives, two fans start on the first towers at 20 Hz when the building management system indicates that cooling is needed. If more cooling is required, the next two fans start at 20 Hz and then the remaining two start if there is demand for still more cooling.

For further cooling, all six fans run together between 20 Hz and 50 Hz. At an installed cost of £15,000, an annual saving of £31,400 is achieved.

Maintenance costs have also been reduced, as drive belts would break at least once a month with the old system.

We worked out the cost at fixed speed, measuring power consumption and power factor and then estimated the savings at variable speed. Erring on the side of caution, we predicted 18 months payback but in the event, they actually got the money back in six months.

“I hadn’t used drives much before our ABB partner came along to give me a demonstration, ” says Senior facilities engineer.

“However, I now see that using variable speed drives is the most effective way for us to save energy. I have a 10-year plan for how to reduce energy use at this site and it will mainly be achieved with drives; 70% of electricity here at the plant is used by motors so there is vast potential for using drives”.

Further energy saving projects with drives have since been carried out, enabling the customer to reduce electricity use by about 5% across the site so far.

” Not many people in my profession are interested in drives, but with electricity prices increasing at the rate they are now, you start to develop an interest, ” says Financial director. “In the past, payback for energy saving projects was often many years, but with electricity prices having tripled in the past three years, the long payback has become short.  The days of cheap energy are gone. The causes of climate change may be under debate, but what you can’t get away from is that in general, energy is used very inefficiently. For me, it’s simply about using what we buy more efficiently. There’s no use buying energy and then sending it up the chimney”.

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