Ammonia (NH3) Refrigeration Systems for Cold Storage

Direct-expansion (DX): Refrigerant expands directly in the evaporator. Simple. Lower refrigerant charge. Standard for smaller systems and DX condensing units.

Pumped recirculation: Liquid refrigerant pumped from receiver through evaporators at higher mass flow than required for cooling. Excess refrigerant returns to receiver as wet vapor. Better evaporator utilization. Larger refrigerant charge. Standard for large industrial systems.

Pumped recirculation is more efficient at industrial scale. DX systems are sometimes specified for retrofits or applications where reduced refrigerant charge is preferred.

Screw compressors

Standard for industrial ammonia refrigeration at scale.

• High capacity per unit (100–1,500+ tons per compressor)
• Smooth operation, low vibration
• Efficient at partial load
• Long service life (30+ years with maintenance)

Manufacturers: Vilter, FES Systems (Sabroe parent), GEA, Mycom, York/Frick (Johnson Controls), Howden.

Reciprocating compressors

Standard for smaller ammonia systems or specific applications.

• Lower capital cost than screw at smaller sizes
• Higher efficiency at certain operating conditions
• Simpler service requirements

Manufacturers: Vilter, Carlyle, York/Frick.

1. Calculate design load per ASHRAE Refrigeration Handbook
2. Determine redundancy level — N+1 standard for frozen; N+2 for critical
3. Total capacity = design load × (1 + redundancy factor)
4. Match capacity ranges — compressors operate efficiently in 25–100% range
5. Smaller multiple compressors stage more efficiently than single large

Example: 150,000 SF frozen DC, 600-ton design load, N+1 redundancy. Total capacity 720 tons. Possible configurations: 3 × 240 ton screws + 1 × 240 ton standby, OR 4 × 180 ton screws (3 active + 1 standby), OR 2 × 360 ton screws + 1 × 240 ton variable.

IIAR-2 (Standard for Ammonia Refrigeration Systems) is the design and installation standard for ammonia refrigeration systems. Published by the International Institute of Ammonia Refrigeration (IIAR), adopted by reference in most US jurisdictions.

IIAR-2 covers:

• Mechanical integrity requirements for piping, vessels, and equipment
• Pressure relief device specifications
• Refrigerant containment
• Emergency ventilation
• Safety devices and alarms
• Operating and maintenance documentation requirements
• Inspection and testing protocols

USCB designs and installs all ammonia systems to IIAR-2 standards.

OSHA 29 CFR 1910.119 (Process Safety Management of Highly Hazardous Chemicals) applies to ammonia refrigeration systems with refrigerant charge above 10,000 lb.

1. Process Safety Information
2. Process Hazard Analysis (PHA) — repeated every 5 years
3. Operating Procedures
4. Training (initial and refresher)
5. Contractor Management
6. Mechanical Integrity Program
7. Hot Work Permits
8. Management of Change
9. Incident Investigation
10. Emergency Action Plan
11. Compliance Audits
12. Trade Secrets
13. Employee Participation
14. Documentation Maintenance

PSM compliance adds significant operational overhead — but it's manageable. USCB provides PSM documentation and procedures as part of project handoff for systems above threshold.

Strong fit: Frozen storage at 0°F to -10°F, sub-zero applications, large refrigerated facilities (100,000+ SF), heat recovery integration, HFC phase-down jurisdictions, single-tenant operations.

Marginal fit: 30,000–80,000 SF facilities (DX or CO2 sometimes more economical), mid-size 3PL multi-tenant operations, facilities in restrictive ammonia jurisdictions.

Poor fit: Walk-in coolers and freezers, refrigerated facilities in heavy multi-tenant urban environments, facilities in jurisdictions with strict ammonia exclusions.

Tell us about your cold storage project — facility size, operating temperature, jurisdiction, regulatory considerations. We design and install ammonia refrigeration systems to IIAR-2 and OSHA PSM standards. Houston-headquartered · Design-build · Nationwide.