Industrial Refrigeration: Big Systems Equal Big Opportunities
Ten Tips to Increase System Efficiency
Industrial refrigeration customers — those in businesses that use hundreds of thousands of pounds of refrigerant, such as food or pharmaceutical processing facilities — can benefit dramatically from the expertise and advice of a knowledgeable refrigeration contractor. These larger refrigeration systems present tremendous opportunities for energy-efficiency improvements that can lead to significant operational savings.
Daniel Dettmers, a research engineer with the Industrial Refrigeration Consortium and the HVACR Center at the University of Wisconsin-Madison, spoke at a joint Air-Conditioning, Heating, and Refrigeration Institute (AHRI); ASHRAE; and China Refrigeration and Air-conditioning Association (CRAA) technology forum during the 2015 AHR Expo, noting both direct and indirect benefits are to be gained by taking a closer look at industrial refrigeration facilities. During his presentation, he offered a number of suggestions to help increase their efficiency.
The direct benefits, according to Dettmers: reduced energy costs, reduced equipment downtime, and the potential for increased equipment life.
“By upgrading equipment, which causes it to run less often and more efficiently, you’re going to improve the system’s reliability,” he said. “Ask any food plant manager how much it costs for every hour a single production line is shut down. The number is usually $10,000 per hour. You never want refrigeration to be the cause for those line outages or a plant-wide outage.”
The indirect benefits include increased refrigeration capacity, increased safety thanks to closer attention to detail on the part of the operators, and the ability to add future electric equipment without expanding the electric infrastructure.
“Many large industrial plants in the U.S. have their own transformers,” Dettmers said. “If, thanks to your improvements in their electric consumption, they can expand their operations while staying within the capacity of that transformer, that’s several million dollars they don’t need to invest.”
Customers, especially large wholesalers or retailers, who undertake energy-efficiency improvements also benefit from improved public perception of their companies, which could help improve budding energy-conscious customer relationships.
“Being green and having a low carbon footprint gives retailers a little extra to sell to their customers,” Dettmers said. “They’re always looking to boost their green score.”
There are difficult challenges to improving the efficiency of refrigeration systems in industrial facilities. The systems are all different and many were designed (and have been modified) on the fly, said Dettmers.
The facilities’ internal production processes are always in flux. When facilities add a new processing line, Dettmers noted, someone should step back and look at how it fits into the overall refrigeration system design to determine how it could be installed to operate the most efficiently. But, that’s usually not the way it works.
“What’s more likely is that a contractor arrives on site with the owner informing him, ‘OK, I have a load that requires X amount of refrigeration as part of our new process line. I have a liquid supply pipe right here and a suction line over there, can you hook them up and get refrigeration going to the new line?’” Dettmers said. “There is not the time or budget to evaluate the new refrigeration load because the plant is waiting to run a new product.”
Future refrigeration system improvement and efficiency opportunities are often created in the wake of such rapid changes. In addition, the control systems all differ from facility to facility. Dettmers said one of the biggest opportunities in this industry is better sequencing and controlling refrigeration system compressors.
When identifying opportunities for energy savings, look for the low-hanging fruit, hinted Dettmers. Start, at the compressor, where most of the energy is being consumed, and look for 300- to 1,000-hp motors, or larger motors, if applicable. Determine if the head pressure or the discharge pressure can be reduced, added Dettmers.
“Often, it’s worthwhile to go back to the manufacturer and ask, ‘How low can I go?’” Dettmers said.
Also, determine if the suction pressure in the compressor can be raised, look at the entire system to determine if the set points can be changed, and update the system to automatic control valves that can run off the control system’s set points.
The Top 10 Opportunities
According to Dettmers, these are the top 10 opportunities for contractors to help their industrial refrigeration clients increase their systems’ efficiency:
1. Reduce the system’s head pressure — This is a low-cost and low-risk action that often yields extraordinary savings that pay off almost all year long.
2. Raise the suction pressure — Operators could see 1-2 percent energy savings for every increased pound of suction pressure, and the savings persist all year, no matter the weather. This also gives a boost to system capacity.
3. Install variable-frequency drives (VFDs) — VFDs can be applied to the trim compressor for each suction pressure level in the plant. “If you’re running your compressor and your equipment at 100 percent capacity all the time, VFDs aren’t necessary,” Dettmers said. “But, there isn’t one facility I’ve ever seen that runs, or needs to run, its compressor at 100 percent capacity all the time.”
4. Install VFDs on condenser fans — This gives the operator control to vary and lock in a system’s head pressure.
5. Install VFDs on air unit evaporator fans — VFDs on the evaporators can help make facilities like refrigerated warehouses less noisy and windy, contributing greatly to increased worker satisfaction.
6. Take advantage of heat recovery — Compressors in industrial refrigeration systems that use ammonia have a large oil separator that allows the oil to be pulled out and cooled before it’s re-injected into the compressor. Use the heat removed from that oil to heat glycol for underfloor heating. If heat recovery can be installed at the time of construction, it’s a very low-cost addition with huge benefits.
7. Improve the compressor sequencing and capacity control — This can reduce power and energy consumption, provide better dehumidification, reduce compressor cycling, decrease the starting load, and provide good oil return, if properly piped.
8. Improve the hot gas dwell period — In the summer, a system needs to be defrosted more often and for a longer time than it does in the cool, dry winter months. If the defrost cycle isn’t being reset in the winter, it creates a parasitic load on the space.
9. Convert liquid injection oil to external oil cooling — Liquid injection is much easier to install, but it reduces a compressor’s life expectancy and decreases its efficiency. Converting an entire system in a retrofit might be cost-prohibitive, but, on new systems, it represents only a small and incremental upgrade that pays dividends in the future.
10. Reduce parasitic loads — Reduce infiltration from the outside by replacing leaking doors or broken strip curtains. Make sure the facility isn’t overcooling or cooling areas or products that don’t need to be cooled. Any load you can take off the compressor is helpful.
Publication date: 5/4/2015