Manual vs. Automatic Purging in Ammonia Refrigeration Systems | Blog No. 112

In ammonia refrigeration, removing non-condensable gases is not optional maintenance; it is essential for system performance. Air and other non-condensables raise discharge pressure, increase compressor workload, and reduce overall capacity. Over time, even small amounts can translate into measurable energy penalties and unnecessary mechanical stress. The two primary methods for removing these gases are manual purging and automatic refrigerated purging. Both methods are used in the field, but they differ significantly in efficiency, safety, consistency, and refrigerant loss.

Why Purging Is Necessary:

Non-condensable gases collect on the high side of the system, typically in condensers and receivers where temperatures are lowest, and gas velocity is reduced. Because these gases do not liquefy with ammonia, they add pressure without contributing to cooling. The result is higher head pressure, increased energy consumption, elevated discharge temperatures, and accelerated wear on compressors and lubricating oil. Prolonged operation with excessive non-condensables can also contribute to oil breakdown, contamination, and reduced equipment life. Regular purging keeps the system operating near its design conditions, stabilizes performance, and prevents gradual long-term efficiency decline that often goes unnoticed until utility or maintenance costs increase.

Manual Purging:

Manual purging involves an operator opening purge valves at strategic high-side points, usually condenser outlets or receivers, to release trapped gases. The vapor mixture is commonly routed through a hose into a container of water, so ammonia is absorbed while air escapes to the atmosphere. This process may be performed with the system offline or, when shutdown is not practical, carefully conducted while the system is operating.

Advantages

• Low equipment cost

• Can be performed without installing additional hardware

• Useful when automatic purgers are unavailable or temporarily out of service

• Flexible for unusual system configurations or short-term corrective actions

  
  

Limitations

• High refrigerant loss – Manual purging can release significantly more ammonia compared to refrigerated purgers.

• Labor-intensive – Requires trained personnel and continuous monitoring.

• Higher safety exposure – Direct handling of ammonia vapor increases risk.

• Operational disruption – Off-line purging may require partial or full shutdowns.

• Inconsistent results – Effectiveness depends heavily on operator judgment and timing.

Manual purging can be effective, but it relies heavily on operator skill, strict adherence to SOPs, and proper PPE. It is typically best suited as a corrective or backup measure rather than a continuous control strategy for modern facilities.

Automatic Refrigerated Purging

Automatic refrigerated purgers are designed to separate ammonia from non-condensable gases before venting. The device chills the foul gas mixture so ammonia condenses back into liquid and returns to the system, while the remaining non-condensables are discharged usually through a water column. These units operate automatically based on pressure or temperature controls and are often tied into multiple purge points across the high side.

Advantages

• Minimal refrigerant loss – The refrigeration process retains most ammonia within the system.

• Continuous operation – Removes non-condensables as they form rather than waiting for accumulation.

• Reduced labor – Limited manual intervention once installed and configured.

• Improved safety – Less direct exposure to ammonia during routine operation.

• Performance monitoring – Timers and counters provide early warning of leaks, contamination, or abnormal air ingress.

• Consistency – Provides repeatable, predictable purging performance independent of operator availability.

Limitations

• Higher upfront equipment and installation costs

• Requires maintenance and periodic inspection

• Dependent on the correct setup and manufacturer guidelines

• Electrical and control components introduce additional maintenance considerations

Automatic purgers are the industry standard for modern ammonia systems because they maintain consistent efficiency with minimal refrigerant waste and provide ongoing system protection rather than periodic correction.

Safety Considerations

Regardless of the method, purging must follow written procedures and include:

• Proper PPE, including eye and respiratory protection

• Ammonia detection devices in the work area

• Two-person operations are required by policy

• Lockout/Tagout and site-specific permits as applicable

• Clear communication with operations personnel before and during purging

Manual purging presents a higher immediate exposure risk, while automatic purgers reduce routine handling but still require scheduled maintenance, inspection, and verification of proper function.

Choosing the Right Approach

Most facilities use automatic refrigerated purgers as the primary solution and reserve manual purging for exceptional situations such as equipment failure, unusually high contamination levels, commissioning activities, or temporary system configurations. The decision ultimately depends on system size, operational demands, staffing levels, and safety policies. However, in large or continuously operating facilities, the long-term energy savings, reduced ammonia loss, and lower labor requirements of automatic purging typically outweigh the initial capital investment.

Conclusion

Manual and automatic purging both remove non-condensable gases, but they are not equal in outcome or long-term value. Manual purging is reactive and labor-dependent, while automatic refrigerated purging is proactive, consistent, and more efficient. Facilities that prioritize stable performance, energy control, regulatory compliance, and reduced ammonia loss generally benefit from automatic systems supported by clear procedures, routine maintenance, and informed operators. In practice, the most effective strategy is often a combination: automatic purging for continuous control, with manual methods available as a trained and carefully managed backup.

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Previous Blog: Compact Efficiency in Ammonia Refrigeration Part 2 of 2: Plate and Frame Heat Exchangers | Blog No. 111

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