New technologies have led to improvements in energy efficiency, but it will take a new and smarter approach to industrial refrigeration system design to harness the full potential of energy savings – systems that are environmentally sound and costeffective.

“The rules of thumb that engineers still go by, because that’s how they were trained, may have been accurate in the 1950s, ‘60s and ‘70s, but those systems were not like the enormous, process critical ones we have today,” said Steve Jackson, president of PermaCold Engineering Inc.

Taking a more forward-thinking approach means that refrigeration systems can be designed more efficiently. And that can mean something as simple as renewing a focus on load.

First, by stopping heat from entering a facility in the first place through lighting, doors, walls and variable frequency drives on evaporator fan motors. And second, by optimizing the system for its purpose-built application, a.k.a. design conditions, component sizes and computerized control systems.

More load means greater costs, more chemicals, more time spent on maintenance, more sewage and higher electric bills. Being clever in managing refrigeration load can produce greater energy efficiency without sacrificing reliability, Jackson said.

Not only are evaporators, compressors and condensers oversized, but so are pipes, valves, support systems and anchorage systems. “Contractors should not just look at condensers [when designing for efficiency], but at compressors and evaporators that are too big, at suction piping, at the insulation package and the hangers. You’ve got to scale it all back,” he said.

Here are Jackson’s five steps toward a smarter, more efficient refrigeration system.

More load means greater costs, more chemicals, more time spent on maintenance, more sewage and higher electric bills. Being clever in managing refrigeration load can produce greater energy efficiency without sacrificing reliability.

–Steve Jackson, president of PermaCold Engineering Inc.

1. DROP HEAD PRESSURE/ TEMPERATURE

By dropping head pressure from 160 to 90 pounds-per-square-inch discharge pressure, a facility will save 25 to 30 percent on energy, mainly due to the lower horsepower needed to run the compressors. “We did this at a plant in North Dakota where they were running 150 to 160 psi discharge pressure year-round because that’s the way it had always been done,” Jackson says. “We had to upsize some piping because they had pre-existing issues with high pressure liquid and hot gas feeds, but they now maintain 90 psi head pressure for much of the year.”

For years, engineers have designed for a 150 to 180 psi head pressure (85-95 degrees), regardless of wet-bulb temperature and winter operating conditions. With current technology, given the correct ambient conditions, a 130- to 140-psi design condensing pressure can be achieved in most locations.

Additionally, one should ask why water is running through the condenser if ambient conditions allow for dry operation. An engineer must look at the ambient conditions and operating characteristics of a plant to intelligently design a condensing system to match. A hybrid system is often the best solution, allowing for both lowering head pressure and saving water, sewer, chemicals and energy.

2. RAISE SUCTION PRESSURE/ TEMPERATURE

Depending on the engineer, refrigeration systems are commonly designed using evaporators with a 10- to 15-degree temperature differential (TD). By using larger and more efficient evaporators, that TD can be dropped, which will result in significant compressor efficiency gains, leading to increased savings.

3. PROPER COMPUTER CONTROL SYSTEM

A well-designed computer control system will allow suction pressure to rise and discharge pressure to fall when conditions are satisfied. In addition to this, it will control VFDs on evaporator fans, condenser fans and compressors to work together to maintain the highest efficiency level for the system as a whole.

“With an old system, you can walk into an engine room and see four compressors running, two at 100 percent and two at 50 percent, because the control system isn’t smart enough to shut any of the compressors off,” Jackson said. “If you don’t have a load, compressors should be staged to turn off.”

4. THE LED SOLUTION

Modern LED lights are vastly superior to those used even five years ago and can result in as much as 35 percent reduction in refrigeration load. Interior lights used in older facilities, such as halogen, high-pressure sodium and metal halides, generate a tremendous amount of heat, thus consuming energy. LED lighting systems emit heat at a 90 percent slower rate than conventional lighting systems, while using half the power.

They also instantly illuminate, which means they only need to be lit when the facility is in use. “Whether they are turned on by motion sensors, timers or manually, the LEDs operate only when the facility is in use to further reduce the heat output and the amount of horsepower needed in the refrigeration system engine room,” Jackson said.

Finally, LEDs last thousands of hours longer, and are water resistant and shatter resistant, reducing replacement costs and maintenance.

5. BETTER DESIGN OF DOORS

More efficiently designed doors can reduce the load significantly. Quickopening doors, tied to motion sensors so they automatically open and close, minimize external heat coming into the system, along with cooled air leaving the system.

In the final analysis, the “Rule of Thumb Engineering” is no longer valid for modern freezing and storage processes in a modern refrigeration system. Instead, one should consider how to prevent heat from entering the system in the first place, and how to design the system so it is inherently more efficient.

Simple engineering decisions, such as placing VFD’s on evaporator fans, can have a ripple effect throughout the refrigeration system because they not only reduce the energy consumed by the fan but also the heat released by the fan into the space that then must be removed. These ripple effects, along with simply removing load from the space by switching from fluorescent to LED lighting, must be considered when designing a modern refrigeration system.

Ambient conditions for the year must also be considered during the design to avoid missing the ability to run dry, run at lower head pressure, or both. This may sound like an expensive approach, but, it is by far the more economical approach when life-cycle costs are considered, as it gives you optimal savings during operation.