Technical definition
Ammonia is a measurement of the concentration of ammonia-related nitrogen species present in the heating system water, expressed in milligrams per litre (mg/L).
When ammonia dissolves in water, it exists in equilibrium between un-ionised ammonia (NH₃) and ammonium ions (NH₄⁺). The proportion present in each form depends particularly on pH and temperature; higher pH favours a greater proportion of un-ionised ammonia.
Within closed heating and cooling systems, ammonia can be particularly significant because it may be associated with microbiological activity and the degradation of nitrogen-containing treatment chemicals. Fernox Laboratories includes Ammonia within its analytical capability and identifies monitoring of nitrogen species as relevant to corrosion and biological growth.
One recognised mechanism in closed systems is the microbiological reduction of nitrite or nitrate to ammonia. This can simultaneously consume treatment chemicals and produce ammonia that can be aggressive towards copper and copper alloys.
Simplified definition
Ammonia is a nitrogen-containing substance that may be present in the system water.
In a heating system, an unexpected ammonia level can be a sign of changes in water chemistry or microbiological activity, particularly where nitrite- or nitrate-containing chemicals are present. High levels can also be harmful to copper and brass components.
Ammonia is important because an elevated concentration can provide evidence of microbiological activity, treatment degradation or contamination within the heating system.
An abnormal or elevated Ammonia result may indicate:
Microbiological activity within the system.
Breakdown of nitrite- or nitrate-containing treatment chemistry.
Nitrite-reducing bacteria being present within the circulating water or biofilm.
Contamination introduced through the filling water.
Introduction of another water or chemical source.
Deterioration or alteration of the system's existing treatment regime.
Conditions within the system that are supporting biological growth.
A significant change in water chemistry compared with previous results.
The relationship between ammonia and nitrite-based corrosion inhibitors is particularly important. In closed systems, nitrite-reducing bacteria can convert nitrite or nitrate into ammonia. This has two potential consequences: the concentration of the protective inhibitor can decrease, while the ammonia produced can increase the risk of attack on susceptible materials. (Waterline)
Ammonia is particularly relevant to copper and copper-alloy components such as brass. Industry guidance on closed heating and chilled-water systems identifies ammonia generated through microbial degradation as aggressive to copper and copper alloys and associates this mechanism with stress-corrosion cracking of brass valves.
Elevated ammonia may therefore be associated with:
Corrosion of copper-containing components.
Deterioration of brass valves and fittings.
Increased Copper or Dissolved Copper concentrations.
Loss or degradation of certain corrosion-inhibitor treatments.
Microbiologically influenced corrosion.
Biofilm formation or other microbiological contamination.
Reduced effectiveness of the intended water-treatment programme.
Increased likelihood of component deterioration where unsuitable conditions persist.
Ammonia can also provide useful information when considered alongside Nitrite and Nitrate. Biological nitrification can convert ammonia first to nitrite and ultimately to nitrate, while other microbial processes in closed systems can operate in the opposite direction and reduce nitrate or nitrite to ammonia.
Testing these nitrogen species together can therefore provide a more complete picture of whether the system water is experiencing chemical or microbiological changes.
Ammonia should therefore be considered alongside parameters such as Nitrite, Nitrate, Copper, Dissolved Copper, pH, Conductivity and microbiological test results when investigating the overall condition of the heating system.
Ammonia should not normally be assessed in isolation. The presence of a small amount of ammonia does not automatically demonstrate that microbiological contamination or corrosion is occurring.
Some ammonia may already be present in the original filling water. The Drinking Water Inspectorate notes that ammonia can occur in water and that unusually elevated concentrations can indicate contamination that requires investigation.
It is therefore particularly useful to compare the system-water result against the original filling water and previous test results.
It is also important to establish exactly how your Fernox laboratory reports this parameter. Laboratories may express ammonia results on different analytical bases, for example as:
NH₃ — ammonia.
NH₄⁺ — ammonium.
NH₃-N / ammonia as N — the nitrogen component of ammonia.
These values are not directly numerically interchangeable, so the Fernox App's definition, units and pass/fail limits should correspond to the laboratory's analytical reporting basis.
The relationship between ammonia and ammonium also changes with pH and temperature, so these factors can affect the significance of the result.
Where elevated ammonia occurs alongside declining Nitrite, evidence of microbiological activity and elevated Copper or Dissolved Copper, the combined results would provide a stronger indication of a potential treatment-degradation or corrosion issue than the ammonia result alone.
