Non-Condensables "BAD GAS"

This article is going discuss how non-condensable gases enter the refrigeration system and how to automatically remove these foreign gases.

Industrial refrigeration systems can only operate at maximum efficiency when non-condensable gas (air) is NOT present in the system. How does non-condensable gas enter the system:

• Refrigeration system maintenance (e.g., compressor maintenance, valve replacements, and much more).

• Refrigeration system that operates in a vacuum (below atmospheric pressure). Locations such as a shaft seal on a booster compressor that is not running or any leak on the low-pressure side of the system (below atmospheric pressure).

• Pressure testing of piping and/or components (normally nitrogen or oxygen)

As you can see, non-condensable gases have many opportunities to enter the refrigeration system. Non-condensable gas will not condense at the same temperature/pressure as the refrigerant (hint the name). Liquid oxygen (AIR) boils at -297°F at 14.7psia...... needless to say, but no normal refrigeration condenser system can condense AIR back into a liquid state, it will always stay in a gas state while inside our refrigeration system. Other substances like nitrogen, hydrogen, argon, and many other non-condensable gases will behave the same way and NOT condense.

This is a problem because excessive head pressure on the high side of the system will occur and result in:

• Higher compressor oil temperature

• Higher compressor amp draw

• Higher compressor ratio

• Reduced refrigeration capacity

Anytime atmospheric gases enter the refrigeration system, the air will carry moisture into the system. Over time, air getting into the system can add up to a significant amount of moisture as well. Water in a refrigeration system is just as troublesome as non-condensable gases.

So far, we have learned about non-condensable gases, lets discuss how we can remove these foreign gases & water from our refrigeration system with the help of some "automatic equipment".

Auto-Purgers are totally automatic and designed to separate non-condensable gases from liquid ammonia and to minimize refrigerant loss during the purging process. The auto-purger will cycle through purge points at solenoid valves that traditionally are located at condenser outlets (drains), receiver vessel(s), and thermosyphon vessel(s).

A standard auto-purger is connected to a high-pressure liquid line for supplying liquid refrigerant to the purger and designed to ONLY release non-condensable gases.

The Auto-Purger Plus by Hansen is designed to remove non-condensable gases AND water from the refrigeration system. This design is usually connected to the ammonia pumps on the lowest pressure Recirculator vessel for supplying liquid refrigerant to the purger. Water contamination in an ammonia refrigeration system greatly affects temperature-pressure relationships. Some facilities have a pressure vessel called an Anhydrator that is designed specifically for the removal of water. In addition, depending on oil pot design but routine oil draining can also help remove water from the refrigeration system.

Just because the auto-purger is displaying/reading zero purge counts doesn't always mean your system is "air free". Purgers can have equipment errors that are not obvious without troubleshooting. Checking refrigeration systems for non-condensable gases will be discussed in another article!

To wrap up this short discussion, the goal is to always have ZERO non-condensable gases inside the refrigeration system for reducing energy costs of operating the refrigeration system.

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