Noncondensable Gases in Ammonia Refrigeration Systems

Noncondensable gases in industrial refrigeration systems are common, and although it may take years for those gases to accumulate, they must be addressed. If not, the steady accumulation can become problematic and have an adverse effect on systems.

Tony Lundell, director of standards and safety at IIAR, hosted a webinar to help owners, designers, in-house refrigeration operators and technicians understand the adverse effects that noncondensable gases can have on industrial refrigeration systems.

Lundell explained that the noncondensable gasses are vapors that accumulate and have their own pressure. If noncondensable gases accumulate in a system, head pressure increases – due to the insulating properties of the noncondensable gases on condenser surfaces, which restricts the heatexchanging process.

He added that the total condensing pressure is additive because the total condensing pressure is equal to the pressure due to the refrigerant plus the pressure due to the noncondensable gases.

Higher head pressures cause higher compressor discharge temperatures, longer compressor and condenser fan runtime, and increased wear and tear on equipment. They can also lead to a possible increase in system leaks, reduced system efficiency, a risk of reduced facility production capabilities and an overall increase in system energy costs.

Water infiltrates into the system with air infiltration and, like noncondensable gases, must be removed. However, there is a difference in the techniques between a purger that removes the non-condensable gas contamination and a distiller that removes the water contamination.

Lundell said a purger chills the foul gas — the term for refrigerant contaminated with noncondensable gases — so the refrigerant condenses out and separates from the noncondensables, allowing the foul gas to be removed from the system. A distiller heats the refrigerant to boil it off, separating it from the water so the water can be isolated and removed.

Overall, this results in an increase in system maintenance. “The elimination of any existing noncondensable gases in the ammonia refrigeration system will reduce your energy usage. This is a quick return on investment,” Lundell said.

During the webinar, Lundell reviewed the infiltration of noncondensable gases from inadequate evacuations and vacuum leaks, dissociation of the refrigerant, and compressor-oil breakdown.

He said there are several sources that can expose internal surfaces to the elements: rain, snow, sleet, high humidity, construction, inadequate evacuations after installation and before start-up, as well as after maintenance service in which the closedcircuit system needed to be opened.

Lundell said the “purity” of the ammonia is critical and said that complex chemical reactions occur between the system’s oil, oxygen, water and ammonia refrigerant. Problems can arise if a system is inadvertently filled or the system’s charge is replenished with contaminated or non-refrigeration grade ammonia.

“Unless steps are directly taken to control the amount of infiltration, there will be a continuous increase in contamination in the system over a period of time,” Lundell warned.

The webinar covered the increasing difference between the observed condensing pressure and the saturation pressure corresponding to the liquid refrigerant temperature exiting the condenser, as well as how to measure for excess pressure.

Operators must remove the contamination of noncondensable gases using a purging technique. Lundell said condenser coil outlets with appropriate drain traps are typically the most used location for purger-point connections.

Purging can be done either manually or automatically. Lundell said manual purging is troublesome and wastes refrigerant. What’s more, discharges may cause nuisances and regulatory issues and the contamination is easily neglected until problems exist.

With automatic purging, neither time nor refrigerant is wasted, Lundell said. Simple training with minimal risks can be easily provided and the contamination does not get neglected.

An automatic purger counts the purge point and purge times. The purge cycle and times are automatically reduced with the elimination of the foul gas and nuisances and regulatory issues are avoided.

“The adverse effects of noncondensable gases in an ammonia refrigeration system may [occur for] years before the problem is recognized and addressed.”

Tony Lundell, director of standards and safety at IIAR

Lundell said use of a “bubbler” dilutes any residual amounts of ammonia particles into water before it exists, containing the foul-gas contamination to a drain line.

Estimating purger refrigerant loss amounts was reviewed and discussed utilizing a developed chart. Purge rates can be verified by the purger manufacturer and used to estimate the amount of refrigerant lost. The estimate results can be used for the annual Form R submissions.

“The adverse effects of noncondensable gases in an ammonia refrigeration system may [occur for] years before the problem is recognized and addressed,” Lundell said.

In the meantime, room temperatures may have been compromised, more compressors may have been operated, suction pressures may have been lowered and additional electrical energy may have been consumed and wasted.

As a result of the contamination, energy cost increases and capacity is lost. “If an excess pressure of 20 pounds per square inch gauge condition exists, there is a 10 percent consumption increase and the compressor capacity is reduced an estimated 5 percent,” Lundell said.

During the session, Lundell went into detail on what the estimated savings could be in lower energy costs from removing the contamination. IIAR members can access Lundell’s webinar via the IIAR member website in the member only section.