[ELI-REVIEW: IIAR-2] is the industry standard (published by the International Institute of Ammonia Refrigeration) that governs the design of closed-circuit ammonia refrigeration systems in the United States, and it sets requirements for pressure vessels used in those systems on top of the pressure-boundary rules already covered by [ELI-REVIEW: ASME Section VIII, Division 1]. For vessel design specifically, [ELI-REVIEW: IIAR-2] mainly addresses how design pressure and MAWP are established, what relief protection is required, minimum liquid hold time, and liquid level instrumentation and control — it does not replace [ELI-REVIEW: ASME]’s wall-thickness formulas, it adds requirements around them.
What [ELI-REVIEW: IIAR-2] covers that [ELI-REVIEW: ASME VIII-1] does not
[ELI-REVIEW: ASME VIII-1] governs how a pressure vessel’s shell and heads are sized once a design pressure and material are chosen; it does not tell a refrigeration engineer what that design pressure should be for a given ammonia system, or how much liquid retention time a recirculator needs. [ELI-REVIEW: IIAR-2] fills that gap for ammonia systems specifically.
| Topic | What it covers |
|---|---|
| Design pressure / MAWP basis | [ELI-REVIEW: how high-side and low-side design pressures are established from saturation conditions and ambient design basis] |
| Pressure relief | [ELI-REVIEW: requirement for code-sized relief devices on refrigerant-containing pressure vessels] |
| Liquid hold (retention) time | [ELI-REVIEW: minimum liquid retention time by vessel type, referenced in §11.3] |
| Liquid level control | [ELI-REVIEW: level instrumentation, alarms, and control requirements for refrigerant vessels] |
How this shows up in vessel sizing
In practice, an [ELI-REVIEW: IIAR-2]-governed vessel design chains together: an [ELI-REVIEW: IIAR-2]-derived design pressure feeding an [ELI-REVIEW: ASME VIII-1] thickness calculation (see the [ELI-REVIEW: UG-27] shell thickness formula), an [ELI-REVIEW: IIAR-2] hold-time check against the vessel’s usable liquid volume, and a separation-velocity check for the vapor space. All three checks have to pass together; none of them is optional just because the others are satisfied.
Run it
ColdCalcs' Vessel Sizer and HPR / Thermosyphon Sizer run the [ELI-REVIEW: IIAR-2]-referenced hold-time, level, and separation-velocity checks alongside [ELI-REVIEW: ASME] thickness sizing, on screen, free.
Open the Vessel Sizer →FAQ
Does [ELI-REVIEW: IIAR-2] replace [ELI-REVIEW: ASME Section VIII, Division 1] for vessel design?
No. [ELI-REVIEW: ASME VIII-1] remains the pressure-boundary design code (shell and head thickness, MAWP, materials). [ELI-REVIEW: IIAR-2] adds ammonia-system-specific requirements on top of that, including design-pressure basis, relief protection, hold time, and level control.
Is [ELI-REVIEW: IIAR-2] mandatory, or is it a recommended practice?
Adoption depends on jurisdiction; many U.S. jurisdictions reference [ELI-REVIEW: IIAR-2] (or an equivalent edition) as the applicable standard for ammonia refrigeration systems through building or fire code adoption. Confirm which edition applies for a given project and location.
What is the liquid hold-time requirement roughly based on?
It sets a minimum time a vessel's usable liquid volume can supply the system's liquid draw before running dry, varying by vessel type (for example, pumped recirculators vs. flooded chillers), which gives operators margin to respond before a low-liquid condition becomes a problem.
Does [ELI-REVIEW: IIAR-2] size the pressure relief valve itself?
[ELI-REVIEW: IIAR-2] sets requirements for when and how relief protection is required; the actual relief valve sizing calculation is a separate exercise (commonly referencing [ELI-REVIEW: ASME VIII-1 UG-125]) that ColdCalcs' calculators do not perform.