Refrigeration Insights series. Season 3: The IIAR standards, part 5 of 10.
There is a moment in the life of every plant when the system stops being a construction project and becomes an operation. That moment has its own standard, and it has just released a new edition: ANSI/IIAR 5-2025, Start-up of Closed-Circuit Ammonia Refrigeration Systems.
It is one of the three IIAR standards revised in 2025, together with IIAR 6 and IIAR 7. If your last project was commissioned under the 2019 edition, this article is for you.
What it covers
The standard specifies the minimum requirements for the start-up of new systems and also of additions or modifications to existing systems. That second point is often overlooked: expanding a machine room, adding an evaporator or modifying a circuit is also a start-up, and it also falls under this standard.
Portable systems listed under other ANSI standards are excluded. And as with the entire IIAR family, legally adopted codes (building, fire, mechanical, electrical) prevail in case of conflict.
The sequence that governs start-up
The structure of the standard is the commissioning sequence itself: ammonia specifications, activities and requirements prior to charging, the charging itself, and the start-up process. Within the pre-charging activities there are three verification blocks: the mechanical system, the electrical system and the safety systems.
That logic has a practical consequence: start-up is not an event, it is a process with control gates. Each verified block is a gate that closes before the next one opens.
Pressure and leak testing: what the standard requires
Two definitions that prevent accidents and cost overruns:
What to test with. The standard expressly prohibits the use of the following for pressure and leak testing: oxygen or any combustible gas, carbon dioxide, halocarbon refrigerants, and water or aqueous solutions. Each has its reason, from the risk of explosion to contaminating the circuit with moisture, the silent enemy we have already covered in this series. It also requires a supply regulator or equivalent method to control the test pressure.
How to test. Pressure testing of the piping system is performed in accordance with section 538 of ASME B31.5. For leak testing, the minimum pressure is the design pressure or the pressure specified in the engineering design, the system is kept pressurized until tightness is confirmed taking temperature effects into account, and every leak is repaired and retested until the system is tight. There is no shortcut: repair and repeat.
Why the 2025 edition matters
The ANSI five-year revision cycle did its job: the 2025 edition replaces the 2019 edition and incorporates six years of commissioning experience. For contracts in progress, it is worth checking which edition is referenced: a specification that cites "current IIAR 5" today means the 2025 edition.
Practical advice
Before the first ammonia charge on your next project, ask for the start-up plan in writing and check three things: that pressure and leak tests are planned in accordance with ASME B31.5, that the test medium is not on the prohibited list, and that mechanical, electrical and safety verification records exist before charging. The ammonia charge is the point of no return; everything before it is cheaper to correct.
Next week: IIAR 6-2025, the standard for inspection, testing and maintenance, the backbone of mechanical integrity.
Source: ANSI/IIAR 5-2025, Start-up of Closed-Circuit Ammonia Refrigeration Systems, International Institute of Ammonia Refrigeration. Thermomac is a corporate member of IIAR.
