5.1 Low-Charge Ammonia

Over the past five years, low-charge ammonia systems, driven by safety and regulatory consi- derations, have gained traction in cold-storage and food-processing applications – a trend that is expected to continue throughout the world.98

The low-charge systems have taken the form of single or multiple packaged units, typically installed on or near rooftops, or centralized, machine-room systems. The latter could also include ammonia/CO2 cascade or systems that confine the ammonia to the machine room and use a secondary refrigerant for the refrigerated space. All models take advantage of the inherent efficiency of ammonia as a refrigerant.

These systems have allowed many industrial end users to dramatically cut the amount of ammonia used, compared to traditional liquid-overfeed systems, thereby reducing their safety requirements, while maintaining – or even improving upon – the high efficiencies of traditional ammonia systems.99

An example of the growth in low-charge ammonia can be seen in U.S. OEM Evapco, which recently reported that, since introducing its Evapcold low-charge ammonia packaged units in 2016, it has installed 100 of the units across 25 industrial sites, with each site using between one and 10 units.100

Evapco low-charge packaged ammonia refrigeration units installed at cold storage warehouses in Sioux Falls, South Dakota (U.S.), and Hamilton, Ontario (Canada), were found to have low Specific Energy Consumption (SEC) values, indicating their high level of efficiency.101

The amount of ammonia in low-charge systems varies. Among the lowest charges was devised by Professor Pega Hrnjak of the University of Illinois at Urbana-Champaign and manufacturer Creative Thermal Solutions (CTS), who developed a system using only 0.1lb/TR (0.01kg/kW) of ammonia and with very low-cost components.102

Stefan Elbel, CEO of CTS, recently reported that a two-phase ammonia recirculating ejector for liquid overfeed systems can improve the capacity and COP of an ultra-low-charge ammonia chiller by 28% and 22%, respectively.103 Low-charge packaged systems, paired with glycol, are also being used as chillers for processing or comfort cooling in industrial spaces. The chillers come in both water- and air-cooled configurations, the latter being lower cost and easier to install.

In 2016, the International Institute of Ammonia Refrigeration (IIAR) revised its widely respected IIAR-2 safety standard for ammonia, for the first time addressing ammonia equipment outside the machine room such as low-charge ammonia packaged systems, as well as explicitly covering ammonia/CO2 systems.104

In November 2018, IIAR released Low Charge Ammonia Refrigeration Management (ARM-LC), its first guidelines for users of low-charge ammonia systems that use a charge of 500lbs (227kg) or less.105 The guidelines, which covers packaged and centralized low-charge ammonia systems, are designed to help end users of low-charge systems that may not have used ammonia before.

One of the key advantages of low-charge ammonia systems is that they enable end users to avoid demanding federal regulations on ammonia safety. For example, in the U.S., operators of low-charge systems can abide by the General Duty Clause, which is far less restrictive than stringent rules established by the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA).

Greater comfort level

Low-charge ammonia is bringing ammonia technology into the 21st century, unlocking oppor- tunities for ammonia beyond its traditional market. End users who were previously hesitant to switch to ammonia now have peace of mind thanks to the vastly reduced refrigerant charge and perceived risks. This is expected to lead to the increased uptake of ammonia systems, even in regions where its use has been declining or not popular in the past.