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1 : Air-cooled chiller located on a roof top .
Filiform corrosion – An unidentified enemy to aluminium fins
A HVAC / R coating is used to protect the aluminium fins of a heat exchanger coil from corrosion whilst operating in an aggressive service environment . Despite the protection , filiform corrosion may still propagate at the aluminium-coating interface under certain environmental conditions , which can affect the operational efficiency of the HVAC / R asset . Filiform corrosion is an unidentified enemy to the vulnerable coated aluminium fins , as this type of corrosion is often seen , but not always understood – until now ...
By Craig J R Thomas , HVAC / R Coating Specialist & Senior Managing Consultant – The Pipe-Sol Consultancy Ltd
Heat exchangers are designed and used to transfer heat from one medium to another in both heating and cooling processes , and one of their most widespread uses is for air conditioning and refrigeration . This type of heat exchanger is commonly referred to as a “ coil ”. Heating , ventilation , air conditioning and refrigeration ( HVAC / R ) systems employ various technologies to regulate temperature , humidity , and maintain air quality . HVAC / R systems provide heating and / or cooling for residential , commercial , industrial and institutional buildings . There are multiple types of HVAC / R unit ( See Table 1 ), and the vulnerable coil is what links them all . The aluminium , copper , and galvanised iron metals that are used to manufacture the coil units are vulnerable to different types of corrosion . It is very important that these critical HVAC / R assets are protected to maximise efficiency and extend life expectancy . High performance coatings are applied to the aluminium / copper fins and copper tubes by original equipment manufacturers or specialist applicators . In fact , the whole unit can now be protected . One type of corrosion that is often seen , but not always identified and understood is Filiform corrosion ( FFC ).
Table 1 showing types of HVAC / R unit as well as coil types and designs .
HVAC / R Units |
Coil Types |
Coil Designs |
|
• Air-cooled condenser units
• Chilled water coils
• Fin & tube
|
|
• Air handling units
• Hot water coils
• Finned tube
|
|
• Dry air liquid ( air blast ) cooler units
• Condenser coils
• Microchannel
|
• Rooftop packaged units |
• Evaporator coils |
• Split system units |
• Steam coils |
26 Heat Exchanger World April 2023 www . heat-exchanger-world . com