Energy cutting can give foundries real savings.

A good understanding of your company's electric usage and a few energy-conscious steps can save you money.

In the constant struggle to cut costs, foundrymen go to extensive lengths to reengineer processes, boost productivity and lessen material consumption. Yet an easy, effective way to reduce your overhead may be as close as the light by which you're reading this magazine.

Though the possibilities for energy reduction are many, this article offers a few easily overlooked solutions to high electrical power costs--from the type of light bulbs installed to rescheduling your melting operations.

Controlling Your Operations

Many large foundries own and operate their own electrical substations that enable them to purchase their electricity at more favorable rates. For "mid-sized" foundries with demands of greater than 1000 kW per month, it may be worth investigating the possibility of purchasing a substation.

Installed costs of substations vary widely--starting at $15,000 and up. Most utilities will sell customers the equipment that is already in place at a fair market price. The resulting savings can easily make up for the investment.

Foundries are inherently energy intensive, causing most to be placed on a demand rate by local electric companies. With this rate, there is a monthly charge for the highest recorded on-peak kW demand during each billing period. On-peak times vary from utility to utility, but they generally occur between 8 a.m. and 10 p.m. on weekdays.

In addition to the demand charge, which can account for 30-50% of the total monthly energy costs, on-peak kWh charges are typically 1 1/2 times higher than those for off-peak consumption. Foundries should look for opportunities to shift usage to the off-peak period to reduce the demand charges and on-peak kWh charges. Many foundries operate a large portion of their melting operation during the off-peak period, saving significant money on their electric bills.

Load scheduling is another method used to substantially lower costs. By carefully scheduling work, savings may be realized by alternating use of large energy-consuming equipment. For example, if your foundry has two 500 kW furnaces, you would pay for 1000 kW of demand if both furnaces are run simultaneously. Alternating their operation would cut that demand charge in half.

Most utilities offer an interruptible or curtailable rate. Incentives are provided to customers for the right to require customers to shed load during times of system emergencies or capacity constraints. Foundries must reduce or remove predetermined loads to stay below a planned demand limit at the utility's request during an interruption or curtailment.

Another portion of your electrical costs that can easily be shaven is the power factor. Most utilities charge for "poor" power factor and provide credits for "high" power factor. Power factor is simply a method of measuring the proportional amount of what is called "real" and "reactive" power.

For example, an unloaded motor is using power virtually without performing any real work. The electricity is essentially being used only to energize the windings of the motor. This motor would be considered to be causing a poor power factor.

As a motor approaches full load, the proportional amount of real work (power) is large compared to the energy needed to energize the windings. A fully loaded motor will have a relatively high power factor.

Installing power factor correction capacitors can substantially increase the foundry's power factor. These capacitors actually store reactive power and supply it to reactive loads. This is reactive power that the utility does not have to supply.

Demand controlling is another widely used concept. With an uncontrolled melting operation, the furnace is run at full power throughout the entire melt, leading to high kW demands. By applying a lower input power and extending the melt cycle, foundries can melt the same amount of metal with the same amount of kWh, but with less demand charge.

To ensure complete control of a set maximum demand, foundries can install an automatic demand controller. This unit would automatically regulate or limit operation to prevent a set maximum demand from being exceeded. With the monitored demand information, the controller can calculate when an exceedence of demand will occur and delay any electrical load shedding to allow time for the load to be shed normally, without affecting operations.

Variable-Speed Drives

The motors that run much of your materials handling and ventilation equipment use significant amounts of electricity. Quite often, they are run at full speed even when unnecessary.

The use of variable-speed drives (VSD) on these motors is an excellent way of reducing your operating costs and extending the life of your machinery. The most efficient means of capacity control for centrifugal fans and pumps, VSDs control motorspeeds electronically, rather than with traditional mechanical methods.

Most fans or pump motors are over-sized in relation to electrical load by a factor of two or more. What the VSD does is control fan speed by sizing the motor to the delivered electrical load. Power flow drops dramatically when fan speed is reduced. For example, reducing fan speed 20% decreases air flow 20%, but the power consumed is cut by nearly 50%. Again, there is a side benefit in reduced downtime and lower maintenance on the belts, pulleys, bearings and the motors themselves.

To apply a VSD, flow information must be sensed and fed back to the drive. For water flow, a pressure sensor at the pump outlet can be used to send signals to a drive. For an airhandling system, a static pressure sensor may be installed in the ducting. As pressure changes occur, the drive adjusts the speed of the motor to bring the static pressure to the set point of desired operation.

A Foundry's Success

An excellent example of a VSD application may be found at a 320--employee ferrous foundry in Milwaukee. The existing system was a 100 horsepower (hp) constant volume dust collection system required for shakeout, mold production, grinding, and various other processes throughout the plant. Dust collection was done all day at various workstations, even though some were only in use for a couple of hours.

The dust collection system was modified to include air actuated blast gates (dampers), which shut off the system at workstations not being used. A pressure sensor was installed in the duct system to measure static pressure, while a 100 hp VSD was added to control motor speed. The whole project cost $17,920. The results--as shown by actual metered before and after information--were:

* reduction of 75% in kWh consumption;

* kW demand reduced by 70%;

* annual electric bill reduction of $9,418;

* reduced reheat at air makeup units saved $4,919 on the gas bill.

A Look at Lighting

One of the easiest ways to realize electrical cost savings is in the plant lighting system. A well-designed system will provide optimum light levels while consuming the least amount of kWh.

If you look around your foundry, you may find that over the years several different styles of fixtures have been installed. Perhaps you have lights in areas that don't need them, while other areas could use some light. This may be a good opportunity to standardize your fixtures and upgrade the efficiency of the system with fluorescent or HID efficient lighting.

Standardizing your fixtures means less stocking and purchasing worries, while saving on the high cost of spot replacements. The upgraded light sources offer optimum light levels for less kW and kWh.

These are just a few of the measures any foundry can take to cut power costs. The savings can be dramatic, and free up capital for investment in processes and people.