AS SECONDARY REFRIGERANTS EVOLVE, END USERS SEE OPPORTUNITY IN NEW TECH

As refrigerants with highglobal-warming potential are phased out, natural refrigerants are being considered for new applications, and the industry is seeing increased use of secondary refrigeration units that allow users to lower their ammonia charge.

Ken Mozek, refrigeration sales manager for Air Treatment Corp., said regulatory requirements are driving adoption of natural refrigerants, such as ammonia, and as a result, secondary refrigerant systems. “We’re seeing a high level of interest even in the commercial side of the business,” he said. “A lot of different innovative technologies are coming into play.”

James Hower, sales director, industrial refrigeration for Danfoss, said ammonia charge reduction has been a popular topic, and utilizing a secondary refrigeration fluid is a viable option to reduce charge while maintaining the robustness of a central system engine room.

Secondary circuits allow the charge of any primary refrigerant to be decreased significantly. “This means that potentially hazardous refrigerants can be used in a safe way in many applications,” said Björn Palm, head of division of applied thermodynamics and refrigeration, Department of Energy Technology at KTH, Royal Institute of Technology, in Stockholm, Sweden.

Bruce Nelson, president of Colmac Coil, said secondary use, whether it is chilled water, glycols, salt solutions or even volatile secondary refrigerants, such CO2 , allow users to manage and mitigate some of the safety issues, such as flammability, associated with the use of natural refrigerants.

“We can select secondary fluids that are foodsafe or benign that don’t have the safety ramification or risk,” Nelson said. “That allows us to really set people’s minds at ease and manage the risk profile. That makes fire marshals and environmental groups happy.”

Using secondary refrigerants with an ammonia chiller, for example, allows an end user to keep the ammonia well contained, well managed and well away from occupied spaces. “Secondary refrigerants allow us to begin to consider really reaching those other cooling applications we haven’t thought a lot about or discussed in a serious way up until this point,” Nelson said, referring to uses such as data-center cooling and pharmaceutical facilities.

What’s more, the use of secondary refrigerant systems offers the prospect of the expanded use of natural refrigerants, Nelson said. “Ultimately it is about addressing climate change and reducing our carbon footprint. What we have all come to understand is that the use of natural refrigerants offers a way to reduce the direct emissions of greenhouse gasses because the natural refrigerants are by definition very environmentally friendly,” he said.

Use of secondary refrigerants also gives designers greater flexibility in secondary refrigerant piping design and material selection. “Depending on the fluid being used in the secondary loop, plastics, thin-wall tubing and other more cost-effective materials could be utilized,” Hower said. “Also, restrictions on routing of the piping and restrictions on equipment placement are reduced when using secondary refrigerants/fluids.”

REFRIGERATION OPTIONS

End users have several options they can consider with their refrigeration systems, and designers work with end users to determine what is the business case that needs to be achieved. “It isn’t a one-size-fits-all answer,” Nelson said. “The correct answer is it depends on the business case, the risk profile and what the customer really needs as a solution.”

Nelson added that in some cases, secondary refrigeration systems are the only way end users can accomplish what needs to be done. “In others, there is a choice between a secondary or a direct system,” he said.

Mozek said users have to consider their goals. “There are no silver bullets out there. There are pros and cons,” he said.

Jim Adler, department manager, refrigeration engineering at Hixson, said users have to analyze their systems and determine what they are trying to achieve.

There are several factors, such as the amount of cooling needed, the number of temperature zones required, the region’s seasonal temperatures, energy and water rates, and local authorities and codes, that dictate which refrigerants will work well in certain applications. “We try to ask enough questions to understand what is really important,” Mozek said, adding that for many users the goal is to optimize the rate of production while making their facilities safer.

Stina Forsberg, managing director of Temper Technology AB, based in Backa, Sweden, said it is important for the designer or end user to choose the right secondary fluid. “There is a wide range of heat transfer fluids and they are all different with different properties to consider,” she said. “This is something that is often forgotten.”

Nelson said, “Just as you’d select from a wide range of natural refrigerants for a primary system based on the application, you’d select the secondary based on energy efficiency targets, environmental concerns you may have and the temperatures you may be operating at.”

When selecting a secondary refrigerant, end users should consider the endof-life disposal of the secondary fluid as well as maintenance needs. Hower said some fluids require inhibitors to be maintained to prevent breakdown, corrosion and biological growth.

INDUSTRY-SPECIFIC APPLICATIONS

Fosberg said she is seeing secondary systems used in many different applications, including huge industrial applications. “This is mainly because the legislation regarding refrigerants and needing to have a lower refrigerant charge,” she said. “In Europe, the legislation is giving the industry no alternative. They need to move toward natural refrigerants and that is what they do.”

In certain food-grade applications, such as dairies or beverage production facilities, ammonia doesn’t fit the cooling needs, Adler said. In those applications, the equipment has to be cleaned with hot water.

“When you do that with ammonia, it would be a problem and would be popping pressure relief valves. You’d have to do some pre-work to make sure that ammonia is out of the system before you ran hot water through it,” Adler said, adding that those systems typically use food-grade propylene glycols as the secondary refrigerant.

Food-grade propylene glycols are popular in cooling rooms, but if temperatures get too low, the fluid gets too thick, too hard to pump and the heat-transfer characteristics get worse, said Bob Czarnecki, chairman of IIAR’s Standards Committee. He noted that calcium chlorides or salt brines can be used for colder temps, but are highly corrosive.

including Temper’s, are treated with corrosion protection. She added that end users can check to see if a product has undergone corrosion testing and what type of corrosion protection the product has.

Hower said that traditionally, industrial secondary refrigerant systems were dominated by recirculated glycol, which has energy efficiency penalties and disadvantages when it comes to heatexchanger equipment size.

Forsberg said there are a lot of alternatives to choose from today. “The industry has learned that heat transfer fluid or secondary refrigerant doesn’t have to be a glycol,” she said.

Temper Technology’s secondary refrigerant, also called a heat transfer fluid, is based on organic salts, potassium formate and potassium sulfates together with an advanced corrosion protection package. “From our point of view there is no life limit to this fluid because it is chemically stable. Glycols can chemically change and break down,” Forsberg said.

Hower said CO2 recently has become a popular secondary refrigerant choice. It is a fluid that the industrial refrigeration industry is quite comfortable with, and it has largely removed many of the downsides of using a secondary refrigerant loop.

Hower said that due to differences in viscosity and the reduction in mass flow, which result from latent heat transfer versus sensible heat transfer, CO2 volatile brine systems benefit from a reduced energy penalty compared to glycolbased systems. “This can approach a 20 to 30 percent improved energy efficiency for CO2 volatile brines,” he said. “Due to those same differences, heat transfer surfaces are greatly reduced resulting in smaller equipment sizes as compared to water-based heat transfer fluids.”

With a CO2 volatile-brine secondary system, thought must be given to the options available for defrosting lowtemperature evaporator coils, Hower explained. Options could include electric, glycol and CO2 hot gas via a gas generating system, so CO2 compressors would not be required. “To increase energy efficiency when using glycol defrost, the heat for the glycol could be provided from the waste heat of the primary refrigeration system,” he said.

The most popular secondary refrigerant is water, but water can’t be used at near-freezing temperatures. “That limits your applications to space cooling,” Czarnecki said.

Nelson said some of the latest interesting technologies today include salt solutions that allow users to operate at very low temperatures, lower than they would have considered in the past, even down to blast freezers. “Some new developments and technologies with potassium salts, silicone-based fluids, aqua ammonia or citric-based fluids are really extending the range of secondary systems,” Nelson said.

New pump technologies are expanding end users’ options. “A number of pump manufacturers are making variable-speed circulating pumps that have their own onboard intelligence and technology. It makes these pumps smart, in that they can regulate the speed and circulation rate depending on the target set-point they are watching,” Nelson said.

That makes it possible to match the flow rates to the cooling load and dramatically reduce the pumping power required. “Between the fluids themselves and some of the pumping technologies, our industry is really in a good place and in a position to build these systems in a wide range of applications that minimize energy penalties,” Nelson said.

END-USER CONSIDERATIONS

Although secondary refrigerants have several benefits, these systems may come with a higher operating cost due to the additional pumps required and the electricity needed to run them. “A lot of people in the industry don’t do it because of their concerns with potential added cost,” Czarnecki said.

Czarnecki added that new technology advancements now allow systems to utilize secondary fluids that have easier pumping, which enables designers to use smaller pumps with lower costs.

Servicing secondary refrigeration units is easier, Czarnecki said, because operators don’t have to take time to get the ammonia out of the way. What’s more, users don’t have to install ammonia sensors throughout a facility. “There are intangibles, but it is often going to cost you more to put in and more to run a secondary refrigeration system,” he said. “The advantage is that it is safer and easier to deal with.”

PRIMARY REFRIGERANTS

As for the primary refrigerants, Palm said ammonia is already used in large-scale industrial plants and could possibly find a broader use in new applications in the future. He added that CO2 is already used in supermarket refrigeration and in domestic hot water heat pumps in Japan.

With hydrocarbons, isobutane is already used in almost all domestic refrigerators sold in Europe and is common in other parts of the world Palm said. Propane and propylene are used in some heat pumps, AC equipment, and commercial refrigeration equipment. Regulations are being changed, allowing larger charges than before, so use can be expected to increase in the near future.

“Regardless of the primary refrigerant used, regular testing of secondary refrigerant/fluid should occur to detect contamination of the primary refrigerant into the secondary caused by a failure of the primary to the secondary heat exchanger,” Hower said.

LOOKING AHEAD

Given the critical role secondary refrigeration can play in the industry, IIAR’s board of directors has embraced the idea of expanding IIAR’s scope of activity to include secondary refrigeration on a greater level. The association has formed a task force to examine what IIAR can do to expand its best-practice information, safety information and also educational opportunities within the Academy of Natural Refrigerants in regard to a secondary system. The task force will share information this March at the association’s meeting in Orlando. Also, the meeting will feature an educational session devoted entirely to technical issues and topics surrounding secondary refrigeration, Nelson said.

He added that the ozone depletion potential of natural refrigerants is zero and the global warming potential of natural refrigerants is extremely low and in some cases zero. “It’s really making the world a safer place,” Nelson said.