Wise consumption

July 1, 2008
With energy costs projected to rise as much as 12% this year, and carbon footprint (total amount of greenhouse gases produced to directly and indirectly support human activities) an issue of increasing importance, cold storage facilities are taking a hard look at their energy consumption

With Energy costs projected to rise as much as 12% this year, and carbon footprint (total amount of greenhouse gases produced to directly and indirectly support human activities) an issue of increasing importance, cold storage facilities are taking a hard look at their energy consumption. Facilities can save tens of thousands of dollars in yearly electric costs, and cut harmful emissions by thousands of tons by implementing a handful of simple, cost-effective efficiency measures to reduce electrical consumption and have a payback period of three years or less.

There are three main areas of “low-hanging fruit” for a cold warehouse facility seeking to lower electric costs: refrigeration, electrical motors, and lighting, said David Simon, chief executive officer of Evergreen Energy Solutions, a Nevada-based an energy consulting firm specializing in reducing electricity use and cost (www.evergreensolves.com). Typically, refrigeration represents the largest component of the electric bill, generally accounting for 50% to 80% of the total cost.

“The efficiency of refrigeration systems can be improved three ways,” he said. “Put into operation controls to optimize the operation of refrigeration components, add oil lubricants to refrigerant, and treat fans and compressors to improve operating efficiency.”

Various controls can be used to improve the efficiency of refrigeration components. Such controls include:

  • Fan speed control — uses pressure or temperature signals to control fan speed, reducing electrical consumption when operating at lower speeds.

  • Lube oil control — monitors and controls compressor lube-oil circuits to ensure proper lubrication and efficient operation.

  • Defrost control — improves the efficiency of the defrost cycle by defrosting on demand rather than on a simple timer.

Electrical motors

“Implementing a set of refrigeration controls can lower a refrigeration system's electricity consumption by 10% or more,” said Simon. “With payback periods as short as one year in some cases, refrigeration controls are a great place to start lowering electric bills immediately.”

Another way to improve a refrigeration system's efficiency is to add oil lubricants to the refrigerant. Oil lubricants serve to reduce friction in the compressor's moving parts, improving mechanical efficiency and lowering power consumption. Such additives may also provide other benefits, such as reducing wear on bearings and improving seal life.

A refrigeration system's electrical consumption also can be lowered by improving the efficiency of rotating motors found in equipment such as refrigeration units, chillers, fans, boilers, and air handlers.

Rotating electrical motors often account for 20% to 30% of a cold storage facility's monthly electric bills, Simon said.

Motors are inherently inefficient in two ways. They typically lack the ability to vary their speed, so they run at full speed even when the device they are driving, such as a fan, pump, or blower, doesn't require it. Secondly, motors rely on both active and reactive power to run.

“Imagine pushing a ball across a field that slopes to the side,” he said. “Active power is the force that drives the ball across the field, and reactive power is the force that keeps the ball from rolling down the slope. The power factor measures the relationship between active power and reactive power.

“If the field in this analogy were level, requiring no reactive power, the power factor would be 100. Motors typically run at a power factor of 80 or 90 out of 100, representing a potential efficiency loss of 10% to 20%. An idling motor, or one not under load, runs at an even lower power factor — sometimes as low as 50.

A motor running at a power factor less than 100 is inefficient in two ways. First, the motor demands extra current to compensate for the power factor deficiency, which increases the electric bill. Second, the extra current causes the motor to run hotter, which reduces its lifespan.

“Correcting a motor to reduce its electrical consumption by 10% can increase the motor's life by 50%,” noted Simon.

Motor efficiency

One way to improve a motor's efficiency is to regulate it with a variable frequency drive (VFD). A VFD allows the motor's speed to change with the changing demands of the device it is driving, reducing a motor's electrical consumption by 10% or more.

Another way to help a motor run more efficiently is to increase the power factor by attaching a capacitor to the motor, said Simon. A capacitor acts like a short-term battery, regularly storing and discharging current as necessary to provide power to the motor in a more efficient manner.

“Attaching a capacitor to a motor fitted with a VFD will help both the motor and the VFD operate more efficiently,” said.

“When addressing low power factor, it may be prudent to install capacitors in banks at electric panels, individually at particular loads, or both.”

Low power factor is generally a problem in cold storage facilities because of the prevalence of motors, Simon said. Electric utilities impose a surcharge when power factor falls below a designated threshold, such as 90.

A facility can determine if it has a power factor problem, he said, by checking its electric bill for any extraordinary charges related to power factor, such as a Power Factor Adjustment, he said.

Facility lighting

The third major opportunity for fast-payback electrical savings is lighting, which can account for up to 10% of a facility's electric bill, said Simon.

“The obvious first step is to replace incandescent with fluorescent lighting. The next steps include replacing high-intensity discharge (HID) lights with fluorescents, treating fluorescents to reduce harmonics and regulate voltage, and adding lighting controls to reduce or eliminate light in areas with adequate ambient light or no occupants.”

HID lighting is commonly found in warehouse areas with high ceilings.

While fluorescents historically could not match their output, and thus were a poor substitute for HIDs, lighting advances have led to the development of high-intensity fluorescents (HIFs) that are superior in most respects to their HID counterparts, Simon said.

HIFs can have a number of advantages over HIDs. Among them: lower energy consumption, less loss of light output over product life (lumen depreciation), better dimming abilities, faster start-up and restart times, and reduced glare. “Thus, in most applications, fluorescents are both more cost-effective than HIDs and able to provide light of better quality.”

Where a facility has already replaced incandescents and HIDs with fluorescents, significant further savings can be achieved by fine-tuning the fluorescents in one of several ways. One way is to correct harmonic distortion, a kind of electrical “feedback” or white noise that increases heat in the light fixture and reduces its electrical efficiency, Simon said. Harmonic distortion arises in electrical systems with many “non-linear” loads — those drawing current that does not travel in a sine wave.

Fluorescent lights are a predominant non-linear load in most facilities, but other examples of this kind of load are computers, monitors, printers, and photocopiers.

Simon said harmonics can be corrected by the use of harmonic filters or cancellers placed either at a lighting fixture or at the lighting panel to reduce harmonics in the lighting system for reduced electricity consumption and increased efficiency.

Another way to reduce fluorescents' electrical consumption is by means of a voltage regulator, he said. A voltage regulator causes a small, often undetectable, drop in light levels, reducing current to a light fixture by 15% to 30%, with a corresponding drop in electrical consumption.

Automated lighting controls also can help reduce a light's electrical consumption. The main types of lighting controls turn lights on or off depending on ambient light, time of day, or area occupancy.

“By correcting refrigeration, motor, and lighting inefficiencies using the fast-payback methods noted, a cold storage facility can lower its electric usage by 10% or more,” Simon said. “For a facility using 500,000 kilowatt hours monthly, a 10% reduction would lower annual electric bills by $60,000 or more, and bring down carbon emissions by 500,000 pounds.”

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