CHILLERS: A discrete question

As every plastics processor knows, there’s only one alternative to a central chilling system: portable chillers — small units mounted on casters that can roll from application to application.

Right? Actually, no.

Another option goes by several names — usually either “discrete” chiller or “dedicated” chiller — but the idea is simple enough. Think the opposite of portable: stand-alone units that are attached permanently to a specific work cell or use point, cooling a single process or processing machine.

It’s a set-up that’s more common than you might think. “We sell hundreds of portable chillers and the majority of them are for dedicated applications, although they’re still on wheels and can be moved around,” said Bob Smith, director of plastic markets with Thermal Care Inc. “We don’t call it a discrete chiller: we call it a portable chiller for dedicated use.”

Call them what you will, they’re not always the same, from a technical point of view, as a portable chiller that’s simply left in place with one application. “A discrete chiller can have an outdoor remote condenser, which isn’t very portable, or an elaborate ductwork system to exhaust warm air in the summer and provide supplemental heat in the winter, which is also not very portable,” said Jon Gunderson, vice president of sales and marketing with Advantage Engineering Inc. “Also, a discrete chiller can provide 30, 40, or 50 tons of cooling capacity, making the units larger than traditional portable units.”

GET FLEXIBLE

So why, if you’re not going down the portable road, might it make sense to dedicate chillers to manufacturing cells rather than simply cool with a central system? In a word: flexibility. 

“Discrete chillers offer the advantage of unique fluid setpoints for each use point, which can eliminate the need for having both a central system and separate mold temperature control units that are often required to tweak the bulk fluid temperature provided by the central system,” said Jon Gunderson. “In addition to saving capital costs, this option also allows the processor to select the best temperature for each process, without compromise. If you change to a new mold, you simply change the temperature to accommodate that mold’s particular needs.”

A second advantage relates to easy information access. “A discrete chiller’s control system provides processors with information on parameters such as to-process fluid temperature and pressure at the use point, which lets them address fluctuations more quickly,” said Giorgio Santella, global marketing director with Piovan SpA. “Also, some discrete chillers can provide additional data, including flow rate and from-process temperature, allowing the molder to truly understand what’s going on in the process to optimize cycle time and part quality. A central chiller system often lacks this information at the use points or requires an additional investment in components and installation costs.”

And then there’s the question of minimized risk and exposure in the event of equipment trouble. “If you have a problem with a discrete chiller, it impacts the production of only one machine,” Jon Gunderson said. “Even with multiple refrigeration circuits, a circuit problem with a central chilling system can take multiple machines out of production.”

Discrete or dedicated chillers also offer certain control and flow capacity advantages. “A processor with a central system has to run it as cold as the coldest required temperature. Also, if one or two machines in a central system require very high flow rate, the entire pumping system has to be sized for that higher flow rate — which means that you’re over-sizing your pumping system, and over-pressuring everything else, just to satisfy the two hungry processes,” said Bob Smith. “Since a dedicated chiller is close-coupled to one process, the fluid flow and temperature are consistent and not dependent on other machines operating in the plant, providing more consistent production rates and process quality.”

EASY INSTALLATION, MAINTENANCE

In these post-recession days, when business is beginning to pick up again, discrete chillers take less time for your supplier to produce and can be installed relatively quickly and inexpensively. “Many discrete chillers are available from stock or with short lead times and require only power and hoses to get into production, whereas central systems require vast, expensive piping networks and long lead times,” said Jon Gunderson.

And once installed, discrete chillers usually require little in the way of maintenance, even compared to their portable counterparts. “Even if it’s running 24/7, a properly-sized dedicated system generally receives less wear and tear than a portable unit, especially when the portable unit is operating at 20 per cent capacity, for example, with compressors cycling on and off,” said Tim Miller, heat transfer product manager with The Conair Group.

And while it’s true that having a number of discrete chillers escalates the parts count relative to a central system, these components are generally much smaller on discrete chillers, and therefore less costly to repair. “Also, the complexity of a central chiller system, with high-level PLC-based con­trols and specialized compressor technology, often requires highly skilled and hard-to-find refrigeration technicians,” said Jon Gunderson.

Finally, there might be a processor or two out there who leans towards discrete chilling because it complements their management philosophy. “Using dedicated chillers instead of a central system satisfies the cell management/ownership mentality that a lot of processers have, by giving them slightly better control over operational problems,” said Tim Miller. “They feel more aware of what’s going on, and the operator gets a sense of ownership over the production process.”

THE DOWNSIDES

This isn’t to say that dedicated units are the silver bullet solutions for every processing situation. “Redeploying a discrete chiller can be problematic if the production cell changes,” said Don Berggren, president of Berg Chilling Systems Inc. “In a lot of cases, a discrete cooling unit is probably a single-pump design. If your demand for cooling a new production cell is up and down, that fluctuation might negatively influence the efficiency of the cooling unit or limit the performance of a production cell if moved to another application.”

And then there’s the all-important issue of dollars and cents. “A few discrete chillers with total cooling capacity of around 60 tons or less can often have initial cost for equipment and installation that are far lower than a small central system,” Jon Gunderson said. “But for larger system capacities, the cost of multiple discrete chillers is often higher than a comparable central system.”

In the end, the central system isn’t about to be replaced by row upon row of discrete chillers anytime soon. “When considering discrete versus central chilling, do what’s best for your facility, production re­quirements, and budget by clearly defining the expectations of the unit, and the variation it will have to handle,” said Don Berggren. “And remember to use your industry resources whenever you can.”