April 2006

Reaching Beyond Energy Star
By Mike Sherer

Ever wonder why reach-in refrigerators and freezers were among the first categories of foodservice equipment rated for Energy Star approval? Since reach-ins are always running, tons of data had been gathered by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, and it was relatively easy for the California Energy Commission and Environmental Protection Agency to graph the energy efficiency of every reach-in made. From that data, they set efficiency targets.

When we did our last story on reach-in refrigerators about three years ago, the first wave of Energy Star-approved equipment was coming to market. For some manufacturers, getting approval was relatively easy, involving only test procedures and paperwork. For others, it required some minor modifications to their existing boxes.

The results were good for you, as Energy Star is an easy way to identify energy-efficient reach-ins, and good for manufacturers, as Energy Star provides a new avenue for marketing their better models.

But there’s been a downside, says Ramin Faramarzi, manager of the Refrigeration and Thermal Test Center in Irwindale, Calif. Once manufacturers meet a minimum standard for their reach-ins, there’s little incentive to continue incorporating increasingly more efficient technology.

“When the standards for energy efficiency were developed,” Faramarzi says, “the California Energy Commission said they wanted reach-ins to be 10% more efficient than a certain number of the total population, for example. But they didn’t recommend specific technologies. They just said that if you’re 10% more efficient, you’re energy efficient.”

Carry On, Developers

Now, improving efficiency by 10% is certainly laudable, but there’s more that can be done to improve reach-in performance. The RTTC, run by Southern California Edison, researches and tests all types of refrigeration equipment, so the folks there are up on the latest technology. They say manufacturers have taken various paths to efficiency, but Faramarzi adds that in order to continue improving reach-in performance, equipment developers should focus on six major areas.

1. Minimize heat migration. The principle behind mechanical refrigeration is removing heat, not creating cold, and conduction heat transfer is a big challenge. Heat anywhere outside the box—from the fan motor, compressor or even ambient air—is conducted into the interior of the reach-in itself. The box is made of metal, after all, which is of course a great conductor of heat. In a typical two-door reach-in, heat gain through the walls accounts for more than a third of the load on the compressor.

The fist step toward energy efficiency is a box that is exceptionally well insulated. Increasing the amount of insulation, especially in the doors, or changing to a more efficient insulating material can improve almost any supplier’s efficiency numbers.

Gaps anywhere should also be addressed. One manufacturer re-engineered the way the liner was attached to the cabinet, which eliminated an inch of steel around the doors that was conducting ambient heat into the cabinet. Door gaskets should also provide a good seal. Same with hinges.

2. Use high-efficiency fan motors. Evaporator and condenser fans account for more than 20% of the energy used in reach-ins. In the good old days—think three to five years ago—most evaporator and condenser fan motors were either shaded-pole or split-phase electric motors. They’re inexpensive and good for small horsepower or light-duty applications like fans, but not very efficient.

More recently, refrigeration manufacturers have been purchasing permanent split capacitor motors from their component suppliers. Like shaded-pole and split phase motors, PSC motors have low starting torque and are best suited for light-duty fan applications. But they also have low starting currents, making them excellent for applications with high cycle rates, and they’re about 25% more efficient.

Even better, electronically commutated motors, first introduced by GE in 1969, use transistors or electronic switches to pulse power to the coils in the motor, essentially converting a single-phase motor into three-phase operation. They’re quieter, have no rotor brushes to wear out, and are generally 60% more efficient than old split-phase motors.

3. Increase heat transfer capability. If you understand the basics of refrigeration, it’s easy to see why heat transfer capability is so important. As liquid refrigerant circulates through the evaporator, it removes heat from inside the box. As it circulates through the condenser, heat is transferred to the air outside the box. The more efficient both the evaporator and condenser coils are at transferring heat, the better.

The first step in improving heat transfer capability, says Faramarzi, is to make both the evaporator and condenser coils bigger. The more area in which to accomplish heat transfer, the more efficient the process will be. That’s easier said than done, of course, because more materials add cost, and it can be tough to design larger components into the same size or slightly larger footprint.

The second step, he says, is to use coil materials that do the best job of conducting heat. Titanium is a good one, he notes, but obviously too expensive for manufacturers. Some combination of copper and aluminum is likely best.

Third, manufacturers should consider enhancing the tubing used in both the evaporator and condenser. Most reach-in makers now etch some sort of rifling pattern on the inside of the tubing. The idea is to create a more turbulent flow to stir up the refrigerant as it passes through and thus enhance heat transfer, sort of like stirring your soup to cool it. A more advanced approach, however, is to create a diamond pattern, which increases turbulence and efficiency.

4. Downsize the compressor. Interestingly, increasing the size of the evaporator and condenser coils reduces the load on the compressor, because larger coils can lower condensing temperatures, which provides more cooling effect per pound. Ultimately, the compressor doesn’t have to work as hard, which means the system likely can be balanced with a smaller compressor.

5. Use expansion valve technology. Until recently most commercial refrigerators, like their consumer counterparts, used a capillary tube to meter liquid refrigerant into the evaporator. This approach, however, doesn’t respond quickly to temperature changes inside the box. 

Now most suppliers use thermostatically controlled expansion valves that react more quickly when demand calls for it. They flood the evaporator without slugging liquid refrigerant into the compressor. That improves pull-down performance and lessens the load on the compressor.

6. Change defrost mechanisms. Most reach-ins have timed defrost cycles. In older models, defrost cycles are initiated at set times and run for a set time to rid the evaporator of frost. Newer and more energy-efficient models still initiate defrost cycles at set times, but end the cycles based on temperature. Often, that lessens cycle time, making it easier for the compressor to pull down cabinet temp once the cycle is over.

Varied Approaches

Now, some of these design approaches have found their way into today’s reach-ins, while others are still to be tried and tested. If manufacturers use the full approach recommended by Faramarzi and other experts at the RTTC, reach-ins will perform better <i>and<i> be more energy efficient.

The challenge, of course, is to incorporate technological advances without increasing costs beyond what you, the end user, are willing to pay. But as more of you adopt lifecycle costing models, the initial price of a truly efficient reach-in may play a less important role in your purchasing. And you can play a role by encouraging your suppliers to keep up with the efficiency improvements.

While you wait for the next generation of efficient reach-ins, what can you purchase now that’ll get your stores the best energy return? Here are some areas current models have addressed:

Electronic controls. As the price of electronics comes down, more suppliers are incorporating them into controls. They help reach-ins respond more quickly to temperature changes, even out demand on compressors, and base defrost cycles on demand as well, initiating more, but shorter, cycles.

Electronics also give new reach-ins monitoring capability. Some can record up to 100 hours of temperature data, letting you know demand patterns and how long food is in the danger zone if your power goes out. They also can be tied into alarm systems and your PC to help you comply with HACCP plans.

Better insulation. As suppliers BASF Corp. and DuPont develop higher-rated insulation, manufacturers incorporate it into their boxes. Reach-in makers are also finding ways to foam it in place more efficiently—one maker heats the cabinets first for better consistency and fewer bubbles—and use more of it. Another manufacturer uses a “vaulted” door design that places more insulation in the middle of the door.

Mixing valves. Used for awhile now on large refrigeration systems for cold storage warehouse and the like, mixing valves may become more prevalent on reach-ins. At least one manufacturer is using the technology now. Placed next to an expansion valve, a mixing valve adds vapor to the liquid refrigerant entering the evaporator. That evens out the temperature in the evaporator, which in turn lessens the load on the compressor.

Air flow. Manufacturers also look for greater efficiency by improving air flow within the cabinet itself. Even temperatures mean less demand. In use now are high-efficiency scroll fans and special ducting that direct airflow around the cabinet.—MS

Future Cool

Refrigerators, for the most part, have been so reliable for so long that technology hasn’t changed much over time. Only in the last five years or so have manufacturers really stepped up with modifications like expansion valves, electronic controls and advanced rifling patterns.

Now that the innovations have started to flow, however, you can expect to see more coming down the pike. Here’s a preview of what’s coming.

Energy-efficient compressors. Scroll-type compressors, versus typical piston-driven compressors, promise big energy savings. Now being used on large refrigeration systems, they’ll eventually make their way down to reach-in designs.

Variable-speed compressors also show promise. The Refrigeration and Thermal Test Center has developed a prototype vending machine using a variable-speed compressor that’s yielding god results. 

Demand defrost. The technology now exists to detect frost on the evaporator and then initiate a defrost cycle. It’s not yet commercially viable, but you can expect to see it before your next reach-in needs replacing.

“Friendly” refrigerants. With CFC-based refrigerants now outlawed, some makers may venture into even more friendly refrigerants like CO2. Coca-Cola Japan, for example, has pledged to use only CO2 vending machines by 2010.—MS

What Else To Look For

In addition to technology that adds to performance and energy efficiency, keep in mind the following when you spec a reach-in:

Construction. Boxes come in a range of configurations, from galvanized steel and anodized aluminum exteriors to more expensive all-stainless exteriors and interiors. Anodized aluminum is fine for both exterior and interior unless it’s exposed to corrosive elements. If you store acidic foods in your reach-in, consider a stainless interior.

Door gaskets. Gaskets are one component you may have to replace at some point. They’re also key to energy efficiency. Look for snap-in-place gaskets, which are easier to replace than the screw-in type.

Door handles. Horizontal or vertical? Recessed or protruding? This is pretty much your call, but remember that handles take a lot of abuse. Higher-end models usually have stainless handles.

Hinges. Hinges also get a workout. Cam-lift hinges that make the doors self-closing are common. They may also have a feature that holds the door open at 90º or 120º. Heavy-duty stainless are best. Also look for field-reversible doors.

Shelving. Stainless pilasters or clips adjustable every 1”and epoxy-coated wire shelves are most common. If you store a lot of sheet or hotel pans, look for pan slide kits. If you don’t handle a ton of pans, wire shelves may do just fine.

Other options. Include alarms, external digital thermometers, temperature recorders, security locks, additional shelves, fluorescent lights, remote refrigeration components and more.—MS