|Here are 10 opportunities for contractors to help their industrial refrigeration clients increase their systems’ efficiency, along with the cost, operational risk, and overall value.|
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 HVAC&R Center at the University of Wisconsin-Madison, spoke at a joint AHRI, ASHRAE, CRAA (China Refrigeration and Air-conditioning Association) technology forum that took place during the 2015 AHR Expo. He said there are both direct and indirect benefits to be gained by taking a closer look at industrial refrigeration facilities, and offered a number of suggestions to help increase their efficiency.
The direct benefits include reduced energy costs, reduced equipment downtime, and the potential for increased equipment life.
“By upgrading equipment, by making it run less, and by running it more efficiently, you’re going to improve the system’s reliability,” Dettmers said. “Ask any food plant manager how much it costs for every hour that a single production line in their facility is shut down. The number is usually tens of thousands of dollars 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 — that undertake energy efficiency improvements also benefit from improved public perception of their companies. Knowing this can help you improve your relationships with “green” customers.
“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, many were designed (and have been modified) “on the fly,” and 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 the contractor arrives on site with the owner informing him, ‘OK, I have a load that requires x tons 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.” This often means there are many opportunities to improve the efficiency and operation of the refrigeration system by looking for the opportunities left from these 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 control of refrigeration system compressors.
When identifying opportunities for energy savings, look for the low-hanging fruit. Start where most of the energy is being consumed: at the compressor, and it’s a 300 to 1,000 hp (or larger) motor. Determine if the head pressure or the discharge pressure can be reduced.
“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 setpoints can be changed, and update the system to automatic control valves that can run off the control system’s setpoints.
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:
• Reduce the system’s head pressure. This involves low risk and low capital cost but the savings can be very high and it pays off almost all year.
• Raise the suction pressure. Operators could see 1 to 2 percent energy savings for every pound of suction pressure increase, and the savings persist all year, no matter what the weather. This also gives a boost to system capacity.
• Install variable-frequency drives (VFDs) on 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, then VFDs aren’t necessary,” Dettmers said. “But there isn’t one facility I’ve ever seen that runs — or needs to run — their compressor at 100 percent capacity all the time.”
• Install VFDs on condenser fans. This gives the operator control to vary and lock in their system’s head pressure.
• 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.
• Take advantage of heat recovery. Compressors in industrial refrigeration systems using 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.
• Improve the compressor sequencing and capacity control.
• 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.
• Convert liquid injection oil to external oil cooling. According to Dettmers, 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.
• Reduce parasitic loads. Reduce infiltration from the outside by replacing leaking doors or broken strip curtains. Make sure the facility isn’t overcooling product, or cooling areas or products that don’t need to be cooled. Any load you can take off the compressor is helpful.