issue: April 2007 APPLIANCE Magazine
Refrigeration Systems & Compressor Technology
Pushing the Envelope
Email this Article
by Lisa Bonnema, Senior Editor
An innovative supplier-OEM team has created a cutting-edge refrigeration system that is bringing cost and energy savings to the supermarket industry.
Close collaboration between OEMs and their key suppliers is nothing new to the appliance industry. In fact, it is basically the industry norm. But once in a while, these partnerships spark more than a new or improved product; they can create true industry innovation.
A new distributed refrigeration system from Kysor//Warren (top) features capacity modulation thanks to a redesigned Copeland® Scroll Digital™ compressor (bottom) from Emerson Climate Technologies.
That was certainly the case for Emerson Climate Technologies (Sydney, Ohio, U.S.) and commercial refrigeration manufacturer Kysor//Warren (Columbus, Georgia, U.S.). Calling themselves “Alliance Partners,” the two companies developed an exclusive product that is changing the way supermarkets use small refrigeration systems.
The system, called the Distributed Scroll Pack (DSP), is a small distributed refrigeration system that uses three compressors—two fixed and one variable-speed compressor.
Jim Knudsen, vice president of sales and marketing at Kysor//Warren, says one of the main drivers behind the project was reducing refrigerant leaks. “The Environmental Protection Agency is becoming more and more concerned about refrigerant loss in large refrigeration systems,” he says. “A grocery store may tend to lose 10 percent to 30 percent of their refrigerant charge in a given year, and that releases a lot of refrigerant into the atmosphere.”
Distributed refrigeration systems address this issue by enabling supermarkets to put the refrigeration closer to the end-use product. “By doing that, you reduce the length of refrigeration runs and the amount of refrigerant that is in those lines,” Knudsen explains. “By reducing the amount of refrigerant, you reduce the potential for leaks.”
The DSP’s small size provides further benefits. “By having a lot of small systems as opposed to one very large system, the most you can leak is the total in the system, which is a small percentage of what the big system would have been,” Knudsen explains.
Although it weighs less than a packaged air-conditioning unit, he says the system was configured like one so that end users could easily install it on rooftops. “The goal was to keep it about the same size and if possible, use the same cabinetry as a packaged a/c system,” he says. “Emerson was working on something similar, which started the thought process in terms of size.”
In fact, Emerson had approached Kysor//Warren about producing a small distributed refrigeration system around the same time Kysor//Warren was looking into the concept. “They came to us with a prototype of a distributed scroll pack, and said that they had interests in this but they didn’t want to build it because they weren’t a refrigeration supplier,” Knudsen says. “We would build the product; they would help us market it. In all ways, it was a joint project, much closer than we worked with them or any other component supplier on any other project.”
According to Knudsen, the thought behind the product was to create a unique refrigeration system that could bridge the gap between a full rack system and single condensing units. “Before, it was difficult to do because of the capacity control question,” he explains. “You use a few small compressors, and you don’t get a lot of capacity steps.”
What enabled the system, he says, was pairing two traditional scroll compressors with the Copeland® Scroll Digital™ compressor from Emerson. “This product was basically not possible if it wasn’t for the digital compressor,” Knudsen notes.
The new compressor solved the capacity modulation issue because it provides continuously variable capacity. “With large rack refrigeration systems, you turn multiple compressors on and off, therefore generating different levels of capacity. So there are various amounts of combinations that you can turn compressors on and off to get the levels of capacity,” explains Kurt Knapke, market manager of Supermarket and Industrial at Emerson Climate Technologies. “When you switch to a distributed system, you normally have fewer compressors, which results in fewer capacity choices to choose from. But with digital technology, the compressor can provide anywhere from 10- to 100-percent capacity. So if you vary that compressor along with additional fixed capacity compressors, you can achieve an infinite number of capacity choices.”
The digital scroll compressor allows users to turn capacity on and off at will by averaging “on” time over 20-second intervals. “If you run the compressor loaded for 10 seconds and run it unloaded for 10 seconds, it would generate 50-percent capacity,” Knapke explains. “And if you would leave it on for 15 seconds and leave it off for 5 seconds, you would have 75 percent capacity, and so forth.”
To meet the needs of the distributed refrigeration system, Emerson had to redesign its scroll platform to improve compressor efficiency and expand the feature set to include digital modulation technology. According to Knapke, the modulation was made possible by controlling what the Emerson calls “axial compliance” of the scroll sets. “Axial compliance allows our compressors to deal with debris, liquid and other particles that are introduced into the scroll set,” he says. “It actually separates the scroll vertically apart by a small distance, stopping the compressor from pumping or providing cooling.”
The design challenge, then, was finding a way to control the separation of the scroll sets to enable the capacity modulation. “There is actually a fixed scroll and an orbiting scroll, and we accomplish this modulation by lifting up the fixed scroll,” Knapke says. “We needed to come up with a method to do that, and we achieved that by using pressure balances across a piston that we developed in the top cap of our compressor.”
Once the mechanism was in place to raise the fixed scroll away from the orbiting scroll, the next step was developing a way to control the pressure balance and ensure the system could reliably withstand the number of cycles it would go though during its life. The answer was a new solenoid valve that controls the axial movement of the fixed scroll. “The challenge was getting the solenoid valve to live through 40 million cycles, which we project is equal to the compressor operating for 15 years at a 10-percent duty cycle,” Knapke says. “After extensive reliability tests—inside Emerson and outside in the field—we were confident that we had a good product that exceeded our reliability standards and was ready to be launched into actual field applications.”
Another design challenge was creating a controller that could control both the variable-speed digital compressor and the fixed-capacity compressors on the same system. “The biggest challenge in the whole project was finalizing the control aspect for the digital scroll,” says Knudsen of Kysor//Warren. “There are some unique requirements for the control that the digital scroll presents that had to be resolved before we could complete the project.”
The Retail Solution Division of Emerson Climate Technologies provided the solution. The E2 controller was designed to analyze the various readings throughout the system and determine how much cooling capacity the system requires. Based on that requirement, it decides what compressors to turn on and off and at what percentage the variable-speed compressor should be running. “That is the brain,” Knapke says. “It makes the decisions.”
But the challenge wasn’t over yet. The supplier then had to find a way to provide a variable voltage signal to the compressor so it could decide how to generate the needed capacity. “We had to develop a separate controller—which we call the IDCM module—that interprets the voltage signal from the E2 and converts that into the control scheme of the digital technology, giving you the requested variable capacity,” Knapke explains.
Even with all of the design obstacles overcome, Knapke says the biggest challenge was yet to come—educating the industry. “I think the hardest thing was to get the industry to accept and understand the differences between the traditional rack technology system and the distributed scroll pack technology system,” he says. “The industry was very used to quoting and developing their work orders and instructions off of a rack system, so we had to let them know that when you go to a distributed scroll pack, you’re really dealing with a completely different system and installation.”
Together, Emerson and Kysor//Warren got the word out by attending trade shows and presenting customers with hard data. “We’ve taken it as far as having a hypothetical store designed by an architect. We then had different construction companies provide quotes for what it would cost to build and install the units,” Knapke says. “With the help of Kysor//Warren, we shared those results with the industry in order to prove that distributed systems are economically feasible.”
And so far, the success has been even better than both companies had estimated. “At the beginning of the fiscal year, which was in October, we made a guess how much volume we could do with this product,” says Knudsen of Kysor//Warren. “As of January, we’ve exceeded that volume. It’s going to be 2 to 3 times more successful than we forecasted.”
In fact, customers are finding value in several different applications. “For someone who is using it for distributed duration and wants to minimize the amount of refrigerant in their store and distribute the refrigerant for energy efficiency reasons, it’s probably the least expensive option,” Knudsen says. “For a remodel, where they are putting in a line of cases rather than several different single units, now they have one distributed system, which reduces installation costs. In other words, we’re finding the value proposition for this product is a lot better than even we thought it would be.”
Both companies agree that their partnership is what made this product a success. “Throughout the development of the project, Kysor//Warren and Emerson developed the ideas and knew there were benefits to distributed systems; however, we needed to, one, prove that distributed system performance was comparable to rack systems, and, two, make it cost-effective for the end user,” Knapke says.
“I think we had the technology ready before the industry was actually ready to adopt it,” he continues. “I think you’re going to see over the next few years a large shift from traditional rack technology to distributed technology.”