Putting the Freeze On Energy Consumption

Chilling systems have always been essential to the thermoplastic molding process. The problem, however, is that they can be greedy, often consuming more energy than any other of the machines in a plastics production facility.

But for today’s processors, the good news is that modern chillers offer real energy savings, especially when compared with energy output levels of previous models from even a few short years ago.

And buttressed by more recent developments in compressor technology, there’s less excuse than ever for processors to hand extra money over to the hydro companies — but many continue to do just that.

Processors have saved significant amounts of energy by switching to all-electric injection molding machines, despite their high cost, Jon Gunderson, vice-president of sales and marketing at Advantage Engineering Inc., of Greenwood, Ind., said. Unfortunately, they can be stingier when it comes to their cooling systems, and often aren’t willing to pay an even slightly higher acquisition cost regardless of the fact that significant energy savings could be achieved, he added.

Christian Weiss, Wittmann product manager at Nucon Wittmann Inc., in Markham, Ont., agreed. “Buyers need to be convinced that energy savings are important enough to justify the increased capital investment of a truly energy-efficient chilling system,” he said. “The problem is that buyers rarely see or have responsibilities to the power bills, only the process uptime. Energy savings can be a tough concept to convey.”

UNDER COMPRESSION

Chiller manufacturers agree that the best way to streamline energy usage in the central system is to take advantage of developments in compressors.

And the first step in this direction is to recognize which types of compressors offer which benefits.

“[The compressor] is the heart of the system, the part of the unit that pumps refrigerant. The compressor maintains adequate pressure to cause refrigerant to flow in sufficient quantities to meet the cooling requirements of the system,” Jim VanderGiessen Jr., CEO and general manager of chiller manufacturer Pro Refrigeration Inc., in Auburn, Wash., explained.

In fact, optimizing the compressor is the only way to improve the efficiency of the central system, Roger Lambert, president of Temperature Corporation in Markham, Ont., said.

Centrifugal compressors, for example, are widely held to be more energy-efficient than the traditional reciprocating and screw compressors — and with new developments such as variable speed drives, the use of water as a lubricant rather than oil, and the use of multiple compressors, reciprocating and screw compressors are being left further and further behind.

CENTRIFUGAL FORCE

“A centrifugal compressor is inherently a more efficient compressor than the screw,” Tom Benson, vice-president of sales and marketing at Thermal Care Inc., a chiller manufacturer in Niles, Ill., said. “Centrifugal compression technology has been available for 7 to 10 years, but it is becoming more and more common.”

As the name implies, centrifugal compressors use centrifugal force — the movement of something away from the centre around which it revolves — to propel coolant through the system.

“In the past, you have not been able to get centrifugal compressors for less than 150 to 200 horsepower (hp), but now they are available down as low as 60 hp,” he noted.

And the energy savings offered by centrifugal compressors can translate into significant dollar savings.

For example, chiller manufacturer Sterling, based in New Berlin, Wis., estimated that its new RTCW chiller, with a frictionless centrifugal compressor, will save 24 kilowatt (kW) per hour compared with energy consumption of a non-frictionless design. This translates into an annual saving of approximately U.S. $20,000 per machine, the company said.

A SUCCESS STORY

A notable development in thermoplastics chilling came within the last three years with the introduction of the Turbocor compressor, a high-speed centrifugal compressor from Danfoss Turbocor Compressors Inc., in Dorval, Que.

The Turbocor compressor uses a friction-free, magnetic drive instead of oil, and has a built-in variable speed drive (VSD) device, which offers the most efficient method of unloading by reducing and regulating electric power according to a chiller’s operating load. According to Danfoss Turbocor, its compressor — available in nominal 60 to 150 ton capacity — can achieve average energy savings of 33 per cent or more compared to competing technologies such as screw compressors, and up to 50 per cent compared to reciprocating compressors.

Joseph Orosz, president of Danfoss Turbocor, said Turbocor is significantly more energy-efficient, especially at part load, than competing products.

The unique design of Turbocor won the firm the 2006 Frost & Sullivan Technology Leadership of the Year Award in Heating, Ventilating, Air Conditioning & Refrigeration (HVAC&R). Frost & Sullivan is a market analyst firm based in San Antonio, Tex.

“A range of new technologies incorporated in this centrifugal compressor makes it highly competitive over existing compressors used in the mid-range air conditioning market,” Frost & Sullivan said in a statement.

In fact, the Turbocor design is an industry-first, according to Frost & Sullivan, and the analyst firm predicts it will spark a new trend in chiller models.

The Turbocor has also won the approval of chiller manufacturers, who are now incorporating the device into their chilling systems.

“The Turbocor compressor is perhaps the most significant energy saving design in modern [plastics processing] history,” Jackson Ball, director of business and technology at ArctiChill, a chiller manufacturer in Newberry, S.C., said.

“It can vary its speed to as low as around 10 per cent, and its in-rush current to start the compressor is only 2 Amps, thus avoiding high peak load costs…[and] because there is no oil in the system, the heat exchangers are far more efficient and responsive,” he added.

Plastics processor Universal Plastic Mold (UPM), in Baldwin Park, Calif., recently had Thermal Care replace a 150-ton water-cooled chiller and a 106-ton water-cooled chiller with custom designed chillers built with 70-ton Turbocor compressors.

“[The new chillers] use about 40 per cent less energy than the reciprocating units that we were relying on earlier,” Walter Pipan, engineering manager for UPM, said.

Keys to the Turbocor compressor’s efficiency are that it’s oil-free, and that the shaft and twin impeller assembly are its only moving part; the impeller shaft rotates on magnetic bearings to eliminate friction.

But while centrifugal compressors offer undeniable energy savings, the willingness of processors to adopt them may be impeded by their higher cost. In particular, the loftier price may frighten away manufacturers of lower tonnage cooling systems, Thermal Care’s Benson, said. For lower tonnages the cost per ton is higher, while for higher tonnages the compressors are very cost competitive, he explained.

“Because the compressor is basically the same (in cost and architecture) in all units, you have a fixed cost of whatever that compressor costs so the cost for a 60-ton unit is the same as for a 90-ton unit,” Benson said.

MIXING OIL AND WATER

The success of the Turbocor compressor demonstrates a broader trend in energy-efficient chillers: Lubricating cooling systems with water rather than oil.

“Moving away from oil is significant because when you have a compressor with oil you need to maintain sufficient refrigerant pressure so that the oil gets returned back to the compressor for proper lubrication and that consumes energy,” Thermal Care’s Benson said.

“When there is no oil, you can run a condensing temperature as low as you want. From a practical perspective, this means as the temperature outside gets
cooler, you can let the temperature that the chiller runs at continue to go down with the ambient air. Whether it is water-cooled or air-cooled, this dramatically increases the efficiency of the compressor,” he explained.

MULTIPLE REDUNDANCIES

Another method of improving the energy efficiency of chillers is through the use of multiple compressors, and the system that controls these compressors is key to these savings.

Redundancy is the chief benefit offered by a multiple compressor control system; it toggles the compressors’ use to keep the volume and pressure of the compressed air within specified parameters. By allowing unnecessary compressors to be cycled off, this can be accomplished in the most energy-efficient manner.

Many in the industry are advocates of water chillers that incorporate multiple small compressors because they provide good staging while reducing energy usage.

“This way, if the load is less than 75 per cent, you can shut one compressor off and if its less than 25 per cent you can shut three compressors off. Whereas if you have one big compressor and you’re not running at 100 per cent, you’re wasting energy,” Christopher West, manager of research and development at Berg Chilling Systems Inc., in Toronto, said.

Although multiple compressor chillers offer the potential for enormous energy savings, many processors make a critical mistake that causes them to miss out: They waste energy by operating at the maximum installed capacity all the time, regardless of the actual flow rate.

Aside from a possible lack of familiarity with compressor technology, Advantage Engineering’s Gunderson suggested this common error could simply be psychological.

“All processors want to look and feel as though they’re busy,” he said. “They don’t want to envision only running at half capacity,” he said.

NO CHILLER IS AN ISLAND

But new developments in chiller technology are only effective at saving energy if the devices are viewed as part of the entire plastics processing system, rather than isolated as ‘islands’.

Unfortunately, that’s exactly how chillers have been traditionally viewed, according to ArctiChill’s Jackson Ball.

“Now [however,] there is an increased emphasis on viewing the ‘system’ as a whole to derive efficiencies,” he continued.

Nucon Wittmann’s Weiss agreed. “You can’t look at the chiller in isolation,” he said. “You have to look at it as a piece of the bigger picture of achieving energy reduction.”

And putting this picture together relies on the processors’ abilities to quickly collect accurate energy consumption data. And in this area, too, developments in data recording and transmission are making it easier for plastics processors to gauge before and after energy consumption figures.

Manufacturers of programmable logic controllers (PLC) have been hard at work to improve data collection processes as well as improve the format in which results are made available.

This involves developing systems that collect data from each machine and put it in a form that management can understand and evaluate to determine if energy is being wasted or if machines are not performing efficiently, Berg’s West said.

For example, an important aspect of the chillers that Thermal Care installed at UPM’s Baldwin Park facility is the remote monitoring capablility connected to the new cooling system, which provides either UPM or Thermal Care’s own service specialists remote access to 79 points of diagnositc information per compressor, including amp draw.

“This capability [allows us to] quickly assist with any chiller performance questions by having one of our service specialists communicate directly with the chiller through the Internet and view [data about] kW usage,” Thermal Care’s Benson said.

In the end, there is no single, magic energy-saving solution in plastics production. But when information technology is combined with the latest in manufacturing technology — such as recent developments in compressors — thermoplastics processors can get one step closer to eliminating excessive energy use in their chilling systems, and put their overinflated energy bills on ice for good.