Refrigeration Insights Series. Season 2: The Enemy Within, installment 3.
In our article on contaminant agents we saw that every real ammonia system lives with intruders: water, oil, air. We already devoted a full article to water. Today it is air's turn, guided by a classic of the IIAR's Spanish-language catalog: the paper by Ernesto Rodríguez (Hansen Technologies) on non-condensable gas purgers, presented at the 2004 conference.
What non-condensable gases are
The paper explains it precisely: during normal operation, the system collects gases that do not condense at the circuit's pressures and temperatures. "Air" is the generic label, but the family is broader: air itself, hydrogen, nitrogen and hydrocarbon gases.
Each one has its own way in. Air enters during maintenance, refrigerant charging and oil recharging. Hydrogen and nitrogen appear from the dissociation of the ammonia itself under heat and pressure. Hydrocarbons are a product of the lubricating oil's reaction.
The uncomfortable conclusion: there is no system that does not accumulate non-condensables. The question is not whether you have air in the circuit, but how much and what you do about it.
Where it hides and what damage it does
Air migrates to where the refrigerant condenses and stays there. The damage mechanism is elegant in its simplicity: air is a good thermal insulator. As it accumulates, it forms a film over the condenser's heat exchange area, and that invisible film forces the system to condense at higher pressure.
High condensing pressure is one of the most expensive problems in refrigeration: more pressure means more compression work, more power consumption, more compressor wear, less available capacity. All because of a gas you cannot see or smell, and that does not show up on any gauge by itself.
The purger: how it works and why it fails
The non-condensable gas purger is the equipment that solves the problem: it takes the mixture from the condensing zone, cools it to condense the ammonia and return it to the system, and expels the air in a controlled, safe way.
The paper insists on the point where theory meets reality: installation. An inadequate installation causes inadequate purger operation and, as a consequence, the efficiency loss persists even though the equipment has been bought and connected. Purge points must be located where the air actually accumulates (the paper documents the typical arrangements), and the lines must allow the mixture to reach the purger in the conditions its design expects.
A poorly installed purger is worse than no purger at all: it gives the feeling of a solved problem while the air keeps collecting its toll.
The connection with the series
Readers of this season will recognize the pattern: just like water in the evaporator, air in the condenser is a contaminant that degrades silently, without breaking anything overnight. The difference is the side of the system where each one acts: water attacks the low side and evaporator performance; air attacks the high side and the power bill.
The practical takeaway
A simple check for this week: compare your actual condensing pressure against the one that corresponds to the temperature of your condensing medium. If there is a persistent gap that condenser cleaning does not explain, you have a firm candidate: air in the system. And if you already have a purger, the right question is when someone last verified that it is actually purging and not just switched on.
Next week: corrosion under insulation, the enemy that works exactly where you cannot look.
Source: E. Rodríguez, "Non-Condensable Gas Purgers", Spanish Technical Paper #1, IIAR Ammonia Refrigeration Conference, 2004. Thermomac is an IIAR corporate member.
