Reducing Ammonia Charge in a Field-Built System

As part of the push within the ammonia refrigeration industry to minimize ammonia system charges, some companies are turning to packaged systems to achieve lower charge, but it is also possible to reduce charge in field-built systems.

“There has been more pressure upon designers to figure out how to reduce the refrigerant charge. For a lot of projects the goal is to stay under 10,000 pounds to avoid Process Safety Management/Risk Management Plan,” said Walter Teeter, chief executive officer of Republic Refrigeration Inc. and chair-elect for IIAR. He added that staying under 10,000 pounds can help the permitting process and reduce some of the regulatory expense in operating the system.

Identifying and combining engineering solutions to reduce charge can be done on new or existing systems, but Teeter said it is always easier to do it from the ground up. “You can be limited on what you can do in an existing location because of space constraints or what local municipalities will allow,” he said.

When determining whether to utilize a field-built or a package system, Teeter said operators have to consider the size of the job as well as the economics involved. “There are certain system-size break points where the packages aren’t as cost effective,” Teeter said, adding that the actual cost on large systems may often be less for field-built systems than for package systems.

Ultimately, the size of the refrigeration system and the amount of ammonia used comes down to the end users’ needs. “They have a certain number of cases or pallets they need to store, which dictates a certain size of building, and they want the most energy efficient building they can get for the best price,” Teeter said.

Every refrigeration system is unique with different operation conditions, varying tonnage requirements and space requirements, but Teeter said operators can use multiple solutions to reduce charge. “It is a matter of doing the engineering mix,” he said.

Republic Refrigeration Inc. recently built a cold storage warehouse that has a refrigeration load of 2400 TR with 1100 TR of that being blast freezing that will have a charge of less than 10,000 lbs. of ammonia when it is completely built out, Teeter said.

To determine the best solution, the customer needs to have a goal in mind. “Sometimes the goal is driven by corporate policies, sometimes it is driven by local regulatory issues because certain localities don’t like to permit large charge systems,” Teeter said. “Some companies may receive discounts in insurance rates by minimizing the potential of product exposure to the refrigerant used in the system.”

If the goal is to stay under 10,000 pounds, it can be done by utilizing new design concepts for the plant site. “Some projects get so big there is no way you’re going to stay under 10,000 pounds no matter what we do,” Teeter said.

However, by using new product and design technology, the total charge of the system may still be resolved, which may reduce the regulatory burden in operating the facility.

To reduce charge, some operators are turning to CO2-ammonia cascade systems, CO2 volatile-brine systems, and secondary coolant systems which can be combined with other engineering solutions, Teeter said. “The big reduction is the decision to get to one of these alternate systems,” he explained.

He added that there has been a move to change to 1.5-to-1 recirculation rates from 3-to-1 rates, which results in charge reduction. “Forever the industry had a rate of 3-to-1 for the recirculation rate which dictates certain liquid-line sizes. When you reduce the recirculation rates you can change the line sizes,” Teeter said. “For a given tonnage, you need X amount of area for liquid to flow to the evaporators. If you go to a 1.5-to-one you cut the amount of liquid you’re using in half. If you’re moving half as much you can have smaller line sizes and significantly reduce the total refrigerant charge through system design.”

With a direct-expansion ammonia design, the system is moving the exact amount of liquid it evaporates. Some manufacturers have been working to make these systems more reliable. Many of these new product designs help reduce the amount of ammonia used in the system. “The penalties of going to the DX aren’t as great as they used to be,” Teeter said.

Teeter said the technology is continuing to adapt and change, which allows the industry to offer systems with lower ammonia charge. That could be particularly beneficial as more and more end users move to natural refrigerants as hydrofluorocarbons and hydrochlorofluorocarbons are being increasingly phased out to meet government and regulatory requirements. “That drives people to look at ammonia systems where they may have not considered ammonia or other natural refrigerants before,” he said.