In the past, it was common to waste energy, even in wood manufacturing plants. Energy costs are a small component of the overall woodworking manufacturing costs, when compared to other industries. Rising energy costs, nevertheless, are affecting our profits.

Energy today in North America is plentiful, but not as cheap at it was a few years ago. This three-part series looks at ways to reduce energy costs and consumption without affecting production or safety.

Understanding your energy usage

The initial step in any energy savings program is an energy audit. Audits indicate where energy is being used, at what rates and which equipment and operations are determining your electrical demand. The audit reveals which processing areas to target for reduced energy use. Many electrical utilities offer free energy use audits.

It is also important to understand how you are being charged for the electricity your shop uses. This knowledge applied to the audit will direct you to high payback, energy saving ideas. See the sidebar, Components of an electric bill, to better understand your bill. The examples will show that the true cost of lighting a light bulb or running an electric motor can be 3 times more than what you thought it was.

The Bill

Assume a plant used 10,000 kWh in a month. They operated for 200 hours during the month, giving an average demand of 50 kW (10,000 kWh / 200 hours). This is equivalent to five 10-hp motors. The peak demand for the month was 74 kW. The typical monthly electric bill was:

 

The bill represents the charges for using 10,000 kWh, so the average charge is 11.7 cents per kWh, even though the basic tariff is only 5.5 cents per kWh! This illustrates the impact of the demand charge, and why further discussions on reducing peak demand are so important.

Reduce peak demand

Utility companies have developed many special rules concerning the peak demand charge. In one Southern utility, if you are willing to close down by 12:30 PM every day in June through September (the peak air conditioning hours), they will reduce your bill by 50 percent or more. If you are able to reduce your energy consumption, but not your demand, you save only the 5.5 cents per unused kilowatt hour.

Consider two plausible examples, using the basic charges from the above bill:

Example 1

Ten 100-W light bulbs are used for security lighting. They are on 24 hours a day, 30 days a month. The monthly power usage would be 720 kWh (10 bulbs x .1 kW/bulb x 24 hours/day x 30 days). The demand is 1 kW (10 bulbs x .1 kW/bulb). The energy cost is $39.60/month (720 kWh x $0.055), and the demand charge is $7.50/month (1 kW/month x $7.50/kW). The cost of running the bulbs, then, is $47.10 per month ($39.60 +$7.50).

Now consider that the bulbs are turned off in the morning, at least 15 minutes before the plant is started, and then turned on again in the evening, at least 15 minutes after the plant is shut down. The bulbs will not contribute to the demand charge and the bulbs are run only 12 hours a day. Now the cost is $19.80 per month for the electricity, with no demand charge. Shutting these 10 bulbs off during the day saved $27.30 a month or over $300 per year! Of course, if you forget to shut them off just one day, they will boost the month's demand charge by $6.00.

Example 2

Two pieces of machinery uses 25 kWh of energy and has a 25 kW demand (roughly 30 hp). We typically run both machines 8 hours a day. If we could shut off one of the machines for 4 hours every day, we could save $5.50 per day (25 kWh x $0.0550 x 4) over $100 per month in electrical usage. If we can also arrange it so that the two machines are NEVER on at the same time (and NEVER means NEVER EVER), the demand charges will be cut in half. The savings would be $187 in demand charges every month (25 kW x $7.50/kW).

Monitoring the demand of a mill can be very cost-rewarding. You can purchase a demand warning alarm that lets you set a maximum demand level. If your demand approaches the limit, an alarm sounds, and perhaps, some machines are automatically shut down. (Special note: Stagger starting of electrical motors does NOT reduce the peak demand.)

View  Part Two   and  Part Three  of this series.

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