Chillers: Think plant-wide for energy savings
When it comes to saving energy with chillers, it's important to realize one thing from the start: treat it l...
May 22, 2010 by Canadian Plastics
When it comes to saving energy with chillers, it’s important to realize one thing from the start: treat it like a piece to a puzzle.
“There’s no single magic bullet to achieve an energy efficient chilling system,” said Don Berggren, president of Berg Chilling Systems. “Instead, the process requires a plant-based approach that looks at the whole picture.”
Why isn’t it as simple as just buying energy efficient chillers? “From an energy efficiency perspective, chillers haven’t progressed much over the years because the focus has tended towards reducing ozone-depleting refrigerants, not on cutting energy consumption,” said Ziggy Wiebe, owner of Chillers Inc.
Achieving energy savings with chilling systems is difficult, then…but not impossible. Luckily, operating in a northern country like Canada gives processors an opportunity right off the bat: free cooling, which is the use of “free” lower external ambient air to assist – or bypass entirely – the mechanical cooling systems during winter months.
THE JOY OF FREE COOLING
“Free cooling of a chilled water system during winter and even into part of spring is an effective way to cut power consumption,” said Don Berggren. “In a regular cooling system, chilled water loops cooled by mechanical refrigeration operate continuously. Using free cooling, refrigeration compressors can be turned off in the winter to save energy.”
It gets better: many newer models combine a central chiller and outdoor free cooling in one unit, to allow process cooling water to bypass the chiller when outside temperatures are low enough.
The potential of free cooling can best be realized when combined with another efficient solution, variable frequency drives (VFDs), which can be installed to reduce fan/pump motor speed to 80 per cent full speed, in turn reducing a cooling system’s energy consumption by as much as 50 per cent. “VFDs are important in allowing motors to run at a lower speed, which saves energy usage,” said Balbir Anand, vice president of Freeze Co. Systems. “There’s a cost to installing VFDs, of course, but processors usually find that it will be paid back relatively quickly.”
The only real drawback to free cooling is – you guessed it – temperature fluctuations. “If the weather isn’t conducive, free cooling won’t provide much in the way of energy savings, particularly when temperature fluctuations cause energy spikes, ” said Don Berggren. “The differing demands of each manufacturing system play a role here: processors who are running molds at lower temperatures will have shorter periods of time to take advantage of free cooling than will those with higher mold temperatures.”
HEAT RECLAIMING AND BEYOND
A second energy saving strategy is heat reclaim. In a traditional chilled-water cooling system, heat is transferred from the indoors (at the air-handler chilled-water control) to the outdoors (at the cooling tower). “Not only is this heat wasted, but energy is consumed at the cooling tower and condenser-water pumps in the process,” Ziggy Wiebe said. Whether or not a heat reclaim system is feasible for your shop boils down to whether or not it can accommodate continuous and peak hot-water demand while providing a controlled source of service hot water. If so, a heat reclaim system might be a valuable energy saving addition. A way to further build on these savings is to include a heat-reclaim chiller, a device that generates high-pressure refrigerant that can be used to produce higher-temperature condenser water.
And although it sounds obvious, proper sizing and application of equipment shouldn’t be overlooked – but often is. “Too many chilling systems are oversized, resulting in higher than necessary power and energy consumption per ton of cooling delivered,” said Henry Van Gemert, president of Regloplas Corporation. “By better matching current loads with chiller units, processors can get better performance and energy efficiency.” Modular chillers are particularly well suited for this; they can be installed in hard-to-reach places, require a only small footprint, and make it easier to better match current and future cooling demands.
Other recent chiller technical developments can also help. Piovan‘s new PET chiller, for example, is designed for energy efficient performance for chilled water systems. Developed for PET perform production lines, the unit is equipped with inverter controlled compressors for self-tuning of the refrigeration capacity necessary to provide cooling to the utilities.
Another energy efficient technical development is Advantage Engineering’s new Maximum portable chillers with digital scroll compressors. Combined with Advantage’s proprietary control, the digital scroll compressor modulates cooling capacity from 20 to 100 per cent, while also consuming less energy than traditional portable chillers that use hot gas bypass capacity control. “Portable chillers are often applied to a wide range of load profiles, making energy efficient capacity control an important feature,” said Ziggy Wiebe.
It doesn’t hurt to reiterate that these developments remain a piece of the bigger puzzle. “In the end, a processor has to be prepared to examine its entire process and make changes anywhere in the system to get the best cooling efficiency,” Wiebe said.