Central chilling vs. portable
By Cindy Macdonald, Associate Editor
Both the blessing and the curse of portable chillers is that if you buy more than one, you are buying redundancy. That redundancy is one argument in favor of central chilling systems. Redundancy impli...
Both the blessing and the curse of portable chillers is that if you buy more than one, you are buying redundancy. That redundancy is one argument in favor of central chilling systems. Redundancy implies multiple pumps, multiple compressors, more heat in your plant, more crowding of floor space and more maintenance worries, but it also suggests a more robust system because one component can fail without shutting down cooling for the entire plant.
Victor Gardiman, president of International Cooling Systems Inc. says the majority of his business in Canada involves central systems, and that the U.S. market is moving that direction.
“Larger companies are leaning to central systems, for the floor space, the convenience and the cost savings. With a central system, everything is remote, located in a mechanical room, so the noise and heat problems are removed from the plant floor,” explains Gardiman.
Gardiman installed one system recently where the central chiller was actually housed outside of the plant. A Lawson Mardon facility in New Jersey was being upgraded, and floor space was tight, so International Cooling built a central system enclosed in its own building that simply links to the plant by pipes and wires.
Another new twist in the chiller market is all-electric injection molding machines with their reduced cooling needs. Roger Lambert, president of Temperature Corp., notes that 65 to 70 percent of all cooling capacity in injection molding plants is used to cool the machine hydraulics; the rest is used to cool the mold. A switch to all-electric means you don’t have to cool the hydraulics, so a portable or central system is still be needed, but cooling towers may be unnecessary.
Innovations start in the compressor
The use of scroll compressors in both central and portable chillers is increasing the reliability of cooling equipment. “In central systems, the big change in technology has been a switch from reciprocating compressors to scroll and rotary screw types,” reports Lambert. A single scroll compressor is limited to 15 tons of cooling capacity, but they can now be used in parallel, mounted on a common frame, to give much higher capacity.
“The advantage is lower costs (it’s cheaper to buy two scrolls than an equivalent capacity in reciprocating compressors), and fewer moving parts so they last longer,” says Lambert.
Thermal Care Inc. offers a six compressor/two circuit design of central chillers, the TSW 90/100, available in sizes from 20 to 100 tons. The chillers have an Allen-Bradley PLC with touch-screen control interface, and Trane scroll compressors.
The Iceman SC Series portable chiller from Mokon Div., Protective Closures Co., uses a scroll compressor which has 50 percent fewer moving parts than standard reciprocating compressors. Inherent to the compressor’s design is its ability to be more tolerant of liquid refrigerant or debris due to the radial orientation of the scroll members, says Mokon. This is said to improve durability and reliability, and enables the unit to operate more smoothly and quietly, with less vibration.
Hot gas bypass a hot topic
Electronic hot gas bypass valves are making more frequent appearances on portable units, but not all manufacturers feel they are necessary. The valve has a vast number of options between full open and full shut positions, to closely control temperature. “Under normal conditions, they will hold temperature to +/-1F or less,” says Lambert. They permit processors to run less than 100 percent of the chiller’s capacity and still maintain accurate temperature control.
The hot gas bypass valve is especially beneficial for blown film, explains Lambert, because the frost line of the film bubble moves up and down if cooling is not constant. Temperature Corp. built a five-ton chiller with an electronic hot gas bypass valve that Future Design will show with its film extrusion equipment at NPE.
Lambert explains that hot gas bypass valves are also useful for custom injection molding companies, where plant conditions may vary from day to day (number of machines, size of molds, etc.). These valves add only four to five percent to the cost of a portable chiller.
However, there are drawbacks. IMS Co. explains that its TrueTon chillers do not use hot gas bypass. The benefit, says IMS, is that the compressor will not be running constantly so the processor can save money on energy costs.
It’s all in the details
Thermal Care has improved its complete line of refrigeration equipment by replacing high and low refrigerant pressure and freezestat safety switches with new solid state and electronic technology. All chiller lines now use solid state, encapsulated, direct-mount refrigerant pressure switches, which act more quickly and eliminate the potential for broken capillary tubes. The freezestat has been changed to an electronic temperature controller with a solid state thermister sensing element. The new controller has a faster response time and increased accuracy and reliability.
Eurotherm Controls’ Series 2000 controller is now available on water and oil circulating temperature control systems and chillers from Mokon. The Series 2000 offers automated PID tuning setup, with automatic adaptive and self-tuning functions that give precise, stable, straight-line control of the process. Eurotherm’s Series 2000 also provides advanced protection, from a simple on/off to PID with advanced overshoot protection.
IMS has announced five new Summit Series chillers that have additional standard features without added cost. All five are equipped with electronic control boards, low reservoir warning lights and discharge pressure gauges. The electronic control boards have an easy-to-read display that shows information for the compressor, the water pump, control switches and the high temperature alarm.
The low reservoir warning light is activated by a float switch that can sense when the water level is low. This feature acts as a safety device to protect the pump and it indicates when the level of fluid is below the desired amount needed for your application.
The discharge pressure gauge indicates water pressure. Maintaining a constant pressure keeps the cooling process more consistent, says IMS. Molders can also use the gauge to check for blocked lines.