Cold Hard Facts
I n recent years, cooling equipment manufacturers have placed a greater emphasis on energy efficient chiller units. And rightly so: chillers are an integral part of most manufacturing plants, but they...
In recent years, cooling equipment manufacturers have placed a greater emphasis on energy efficient chiller units. And rightly so: chillers are an integral part of most manufacturing plants, but they can also put the largest dent in your energy bill.
However, when purchasing new or replacement chillers, processors should also be mindful of the features that make the chiller more reliable. Since most plants in the plastics industry employ a continuous process, a reliable chiller will reduce downtimes and offer efficient performance.
As a general rule for processors, chiller manufacturers recommend units that have redundancies built into them. “When we work for a medium-sized plant, we select the chiller with multiple compressors,” noted Balbir Anand, vice president of Freeze Co. Systems, Ltd.
As a result, even if one of the compressors goes down, the additional compressors can pick up the slack. Freeze Co.’s WCT series central process chillers come standard with four compressors, and the company’s air-cooled, water-cooled and modular units can be modified to include multiple compressors.
Additionally, today’s industrial chillers are chock-full of features that make them more dependable and efficient over the unit’s lifetime.
GETTING A MOVE ON
Some industrial chiller manufacturers have increased reliability by simplifying the compressor design, and reducing the number of moving parts.
For instance, Thermal Care’s TC Series central chillers feature frictionless, magnetic bearing centrifugal compressors. In addition to offering a reported 50 per cent in energy savings compared to conventional rotary compressors, the units have only one moving part: the compressor shaft. The oil-free design eliminates problems associated with inefficient operation, and the magnetic bearings extend equipment life because there is no surface contact when the shaft rotates.
Meanwhile, Sterling’s S Series central chiller models from 30 to 195 ton capacity feature a compression technology with 50 per cent fewer moving parts than most compressors. Hermetically sealed scroll compressors are used on chillers sized from 30 to 100 tons, and semi-hermetically sealed screw compressors are used on the 60 to 195 ton units.
Additionally, Advantage Engineering, Inc. uses scroll or screw compressors depending on duty and capacity. Although these compressors have been used in the industry for over a decade, scroll and screw compressors are said to have fewer moving parts and lower maintenance costs than some of the alternatives.
Mokon has taken a similar tact, utilizing scroll compressors that cut the number of moving parts in half. The company’s portable and central chillers — from 5F (-15C) to 65F (18.3C) and HTF series chillers up to 650F (343C) — are also equipped with hot gas bypass capacity control to eliminate compressor short cycling under low load conditions; waterregulating valves; and refrigeration low and high pressure switch protection to help protect the compressor from dangerous pressure conditions.
THE MERITS OF MODULAR UNITS
Modular chilling units are ideal for processors when taking future cooling needs into account, allowing the manufacturer to add units as their cooling needs expand. However, chiller manufacturers also note that modular chillers can help reduce downtime.
For example, Freeze Co.’s semi-hermetic modular chillers feature strainers that can be accessed on the front of the unit. Operators can pull out and clean the stainless steel strainer on each unit without having to power down the machine or interrupt the process.
Modular unit suppliers also note that manufacturers can add more modules and expand their chilling capacity with- out major blips in production.
“When you expand your process, a new module can be brought in and installed within a matter of hours with little downtime,” noted Roger Lambert of Temperature Corporation. The company’s high energy efficiency ratio (EER) modular chillers can be field-coupled for large tonnage requirements, and are designed for easy installation and removal for service.
Frigel North America Inc. has taken a completely different approach to modularity. The company has addressed the issue of clean water with its closed-circuit Ecodry cooler, an alternative to traditional cooling towers. The Ecodry system can be used in conjunction with the company’s modular water-cooled Microgel chiller/TCUs, which replace central chilling with machine-side cooling.
ENJOYING THE BAD WEATHER
Many newer chillers are designed for free cooling, where the unit uses the low ambient air temperatures to chill the water for the process. In addition, free cooling can help the unit perform more reliably.
Freeze Co.’s Anand notes that chillers with free cooling options reduce the plant’s dependence on compressors, leveraging the risk of compressor failure. The company offers chillers that allow customers to shut their chillers down during colder months, and rely on the cooling tower, plate & frame heat exchanger and pumping system.
In addition, Anand explains, free cooling reduces the “wear and tear” on the compressor. The use of outside air can extend the chiller’s life.
AEC has developed the AWX Series Winter Kooler, which allows process cooling water to bypass the chiller when outside temperatures are low enough. These supplemental chilling systems are designed to work with existing air-and water-cooled central systems, and are available from 20 to 250 tons.
The AWX Winter Koolers can be pad or roof-mounted, and provide optimum performance in months where ambient temperatures are around 40 F (4 C).
SITUATION UNDER CONTROL
Most suppliers note that a reliable controller is an important consideration, allowing for the early detection of issues that could cause downtime or reduce efficiency.
Berg has used Programmable Logic Controller (PLC) technology to build a chiller controller that offers “large system” features in all sizes of the company’s central and package chillers.
In addition to performing the chiller’s day-to-day operations, the controller monitors all system and compressor safety controls, issuing an alarm and plain text message in the event of a problem. The controller also monitors process fluid inlet and outlet temperatures and compressor pressures, and alarm values can be setup to provide maintenance messages in advance of chiller shutdowns to avoid downtime.
Over at Advantage Engineering, Inc., chiller control systems are a big part of the business: Advantage owns the company that makes the systems.
“Advantage control systems are ‘tailor made’ for process chillers and for the way our customers operate them,” the company said. “We have designed in features that help to prevent the user from operating their chiller when conditions might cause damage to the chiller.”
Meanwhile, Temperature Corporation provides a microprocessor controller for each chiller and a remote master control with its “intelligent chiller control program” to signal potential problems. The control system has its own unique maintenance program, which operates in the background and manages such functions as lead-lag compressors, equalize compressor run time, totalize compressor starts and compressor run time for viewing.
Photos courtesty Conair
10 TIPS FOR IMPROVING CHILLER EFFICIENCY
Conair’s Heat Transfer Team offers the following tips on how to make sure your chiller functions properly and efficiently.
1. Maintain water quality. Anything that contaminates your water will reduce its efficiency, so make sure that both process-cooling water and condenser water (on watercooled chillers) stay clean. You may want to consult a local water treatment professional for advice on addition inhibitors. Weekly biocide treatment of cooling tower water may be advisable.
2. Flush process cooling and condenser lines. Periodically fl
ush out your process cooling water to remove any bits of rust or other debris, and back-flush the watercooled condenser with a dilute concentration of boric acid.
3. Check strainers for debris. If the strainer becomes even partially blinded, power consumption will increase as the pumps work harder to maintain necessary flow rates. Access to screens is provided and they should be pulled periodically and cleaned.
4. Clean air-cooled condenser. Generally, it is sufficient to vacuum out the condenser and straighten any bent fins. Outdoor units should be power washed with a mild cleaning solution. Clean the screen on the air-intake side as well to prevent excessive compressor power consumption.
5. Check refrigerant charge. Loss of refrigerant is a rare issue, but check the refrigerant sight-glass if you notice your chiller is no longer cooling properly. If you see mostly gas, your refrigerant level is low and you probably have a broken pipe or seal. Bring in a certified refrigerant technician to find and repair the leak.
6. Check pipe supports. Any abnormal vibration of internal refrigerant pipes and components can cause a connection failure and leakage, so make sure all lines are firmly supported and all vibration isolated.
7. Verify reservoir level. Low levels in your process-water pump inlet can allow vortices to form and cause air to mix with water in the pump. Any air in the water will reduce cooling efficiency. Check these levels after every mold change or whenever process water has had an opportunity to leak out.
8. Pull and clean temperature sensors. Deposits on temperature sensors reduce the responsiveness of the sensor. For peak performance, the sensors should be pulled without damaging the connecting wires. Wipe the sensors down with a clean cloth and replace.
9. Autotune your chiller. Use an autotuning temperature controller (if equipped) it whenever you move the chiller from one application to another, especially important when the cooling load is substantially different.
10. Check electrical connections. Turn off and lock out the main power to make the chiller safe to work on. Then check that all contactor screws are tight and wire terminations are firmly seated in the terminals and making solid contact. Replace any damaged wire.
CLEAN AIR INTAKE SCREENS
CHECK ELECTRICAL CONNECTIONS
CHECK REFRIGERANT LEVEL
Advantage Engineering, Inc. (Greenwood, Ind.);www.advantageengineering.com; 317-887-0729
Chillers Inc. (Newmarket, Ont.);www.chillersinc.com; 905-895-9667
AEC, Inc. (Schaumburg, Ill.);www.aecinternet.com; 847-273-7700
AEC-Equiplas (Toronto, Ont.); 416-407-5456
Lutek Plastics Equipment (Dorval, Que.);514-421-8963
Berg Chilling Systems Inc. (Toronto, Ont.);www.berg-group.com; 416-755-2221
Conair (Pittsburgh, Penn.); www.conairnet.com;800-654-6661
Hamilton Avtec Inc. (Mississauga, Ont.);www.hamiltonavtec.com; 905-568-1133
Freeze Co. Systems Ltd. (Brampton, Ont.);www.freeze-co.com; 800-339-8982
Frigel North America Inc. (Lake Zurich, Ill.);www.frigel.com; 847-540-0160
Mokon (Buffalo, NY); www.mokon.com;716-876-9951
En-Plas Inc. (Toronto, Ont.);www.en-plasinc.com; 416-286-3030
Sterling (New Berlin, Wis.); www.sterlco.com;262-641-8610
CNSmith Plastic Machinery Sales Inc.(Georgetown, Ont.);www.cnsmith.com; 416-917-3737
Equipment Resources Northwest (Portland, Oreg.); 905-773-7122
Thermal Care (Niles, Ill.); www.thermalcare.com; 888-828-7387
Dier International Plastics, Inc. (Unionville, Ont.); www.dierinternational.com; 905-474-9874
D Cube (Montreal, Que.); www.dcube.ca; 514-272-0500