In an era where energy costs have become a focus of attention, many people have authored articles with reducing energy as their theme. Saving money is always a good thing. Perhaps we can gain a little clarity on where the real savings are.
Start with the big loads. Plant air handling, building HVAC and lighting are generally a lot more significant in total Watts or equivalent horsepower. 1 Horsepower is equal to 746 Watts. If you are located in the northern states, winter heating uses a lot more energy than summer air conditioning. In the southern states, it’s the opposite. There is one study that puts the northern thermal cycle at a much higher overall cost, so everybody needs to move their manufacturing to the south.
Check all the integral horsepower motors in the plant. A recent DOE study shows that over time, many motors get replaced with whatever is readily available in the next larger frame size. This is in reaction to plant failures where the exact replacement motor is not handy or on the shelf. The result is that the plant power and power factor can be very poor because there is a lot of excess capacity that is not being used efficiently.
Industrial plants also suffer from peak demand billing practices. The utility company agrees to provide power, but large users get billed extra when they have peaks above their average usage. Again, look at the large loads, and see if some or all can be put on soft starters or inverters with longer starting profiles. AC motors try to get to full running speed and spend several seconds at poor power factor and huge inrush currents during starting. Most motors require at least 4 seconds to get to speed. So, is there a savings opportunity if you can get by with a 6 to 10 second starting period? Yes, there absolutely is.
The smaller loads like individual plant floor machines are a little harder to regulate. Some production machines consist of dozens of individual motors and sub-systems. In large conveyor installations, newer control system turns off whole zones of equipment if there is no traffic for that section. Use the same strategy in production equipment. If there is nothing coming into the machine, turn off as much stuff as possible.
Again, look for the largest loads. In CNC machines, the spindle is usually the dominant load. Turning off a 10kW spindle motor will save lots more money than turning off 400 Watt positioning axes. However, don’t pass up an opportunity if one exists. If there are a large number of individual axes of motion that have low duty cycles, it may be cost effective to put brakes on the load and turn the motors off when they are not in use.
Prudent planning can be turned into real cash savings.