In general, one can state that energy consumption in Australia is the largest in commercial buildings, not residential. The biggest energy savings and efficiencies can be realised in these commercial buildings. Corrosion is a huge contributor to unnecessary energy and efficiency loss. It causes a loss in cooling performance, reduced indoor air quality, reduced reliability, reduced energy efficiency and a reduction in service life.
These issues will cause such things as discomfort and health risks to building occupiers, higher running costs, higher capital costs and more CO2. There are ways to limit or prevent this corrosion from occurring.
Corrosion of HVAC Equipment
With air-cooled systems, oxidation of the heat exchangers is a major problem. Aluminium is proven to be one of the most suitable materials for this kind of equipment. The advantages of aluminium are:
- Lightweight metal,
- Easy to shape,
- Good heat transfer
The corrosion resistance of aluminium should be an advantage as well; unfortunately, this is not the case. Aluminium forms an oxide film as soon as it is exposed to air. This action is damaging in that it reflects the tendency of the metal to return to its natural oxidation state. If the oxidation layer were evenly spread, it would protect the metal from corrosion. However, the oxidation layer is patchy and because of the humidity and atmospheric pollution the process of oxidation or corrosion may accelerate here.
Another problem concerning air-cooled systems is the construction of aluminium heat exchangers. Most aluminium heat exchangers use copper pipes. When two different metals in a conducting liquid are in direct contact with each other, corrosion of the least noble metal may be the result. The parts closest to the noble metal will be particularly affected. This corrosion depends on:
- The potential difference between the two metals,
- The relationship between the two metals; the larger the cathode surface (the noble metal) compared to the anode surface (the base metal), the more corroded the latter will be,
- The conductivity of the solvent, and
- The presence of oxygen.
A good solution would be aluminium – aluminium. Although this type of coil is becoming more and more popular, some reasons why manufacturers are not using aluminium – aluminium in general yet are:
- Tubes made from aluminium are difficult to weld,
- The tubes damage easier because aluminium is softer than copper,
- It’s easier to repair copper then it is aluminium.
Sources and Effects of HVAC Corrosion
HVAC corrosion is a widespread problem. Australia’s population is concentrated in industrialised, urban, coastal strips and agricultural regions. All these areas contain sources of corrosion on HVAC equipment. Salt and humidity in coastal regions, sulphur oxides, nitrous oxides, hydrocarbons, chlorides, ammonia, electrolytes, and contaminated dust all contribute to corrosion.
Examples of sources are Aluminium production plants, fertiliser production, petroleum & chemical production, mining and metallurgy, power generation, paper and pulp mills, sewage treatment plants, steel production, swimming pools and farms.
Environmental corrosion of the fin surfaces and galvanic corrosion at the tube-fin breaks down this mechanism which reduces maximum cooling capacity and energy efficiency as the refrigerant condensing temperature is raised to recover cooling performance.
Preventing Coil Corrosion
There are two ways in preventing HVAC corrosion. One is through materials selection to suit environments or protective coatings.
Mono-metal coils such as copper tube and fin or aluminium tube and fin will avoid galvanic corrosion but do not provide complete protection. For this method to be effective, expensive air testing and environmental assessments would be required to provide the best advice on what construction would be best suited for a particular environment.
A protective coating is the most readily available and most frequently applied protection measure. Protective coatings for HVAC can be classified in two separate areas.
- Pre-coat: applied prior to coil assembly, and
- Post-coat: applied after coil assembly
Most manufacturers offer an epoxy pre-coat applied to the aluminium fin as the lowest cost option for improving the corrosion resistance of bare metal.
Post coatings are the alternative to pre-coats. So, what do we need to consider when looking for corrosion prevention options for HVAC equipment?
Epoxy pre-coats generally have a low resistance (1000hours) to prolonged exposure to salt and acid spray. A polyurethane post coat will protect for more than 11000 hours.
Pre-coats only protect the aluminium fin, not the tubes or headers. After the fin is pre-coated, it is cut to size and holes punched in them for fitment to the copper tubes. This cutting exposes the aluminium which then meets the copper tubes, the beginning of the galvanic corrosion process. Polyurethane post-coat will cover all surfaces and joints of the fins and tubes.
Due to epoxy pre-coats low thermal conductivity, it creates an insulation layer at the critical fin-tube junction when fins are formed, and coil is assembled. This can create a capacity loss of up to 15%. A Polual XT post-coat by Blygold, contains an aluminium pigment which boosts thermal conductivity. Combine this with a low 25-micron dry film thickness (DFT) and you will minimise thermal and pressure losses. Capacity losses with this type of coating are 0-3%.
With age and exposure to the elements, epoxy pre-coats lose adhesion and have a lower mechanical resistance. The polyurethane post-coat has excellent adhesion to most metals; aluminium and copper, plus have the added benefit of excellent UV and chemical resistance.
The post-coat treatment can be applied in the workshop or on site and is maintainable, repairable, and cleanable. Pre-coats are generally applied with no further ability to maintain or service on site being available.
With a lower life expectancy, pre-coats will generally cost the client more in the future. The post-coat treatment is there for the life of the unit.
BLYGOLD – First Choice for Corrosion Protection on HVAC Equipment
HVACR efficiency loss accounts for a significant proportion of Australia’s energy consumption, business costs and CO2 emissions. Asset owners and managers are now even more aware of this plus the high maintenance and replacement costs and are looking for alternatives to prolong the life of their equipment.
Corrosion of heat exchanger coils is a widespread problem and one that adversely impacts the performance and energy efficiency of HVAC systems.
Applying the most effective post-coating treatment to these units will limit or prevent HVAC coil corrosion and its adverse impact thus saving energy and money and making our environment more sustainable to live in.
Blygold is the market leader in high-end corrosion protection of HVACR equipment. Since its inception in 1976, Blygold has designed and manufactured patented protective coatings dedicated to the HVACR and related industries. Next to corrosion causing economical damage, it also affects health, safety and environmental issues. Blygold products and services will extend the economic lifetime of your equipment and will keep the efficiency high. Our solutions focus on lifetime extension, energy saving and cost reduction measures for your HVACR equipment.
Blygold works with a global network of trained and licensed applicators, creating the same high level of quality applications all over the world. Through our network, we create awareness of global trends on a local level. Blygold focuses on services and products that offer sustainable solutions for the problems that our clients face. We have superior knowledge and understanding of the products, the market, and our clients. Blygold has served many clients worldwide including office buildings, shopping malls, airports, hospitals, universities, hotels, museums, mining, and many others.
Blygold provides services like tube sheet treatments and coatings that can withstand an extreme chemical and salt load. Through its unique application methods, Blygold can execute these treatments on location or in our workshops. This not only makes us the perfect partner for preventive measures, but also for onsite maintenance and refurbishments.
Blygold treatments can save up to 30% on energy use, triple the lifespan of equipment & ensure the highest level of performance of heat exchangers. The coating is heat conductive, surface impact and scratch resistant and has been independently tested and certified to international standards.
Blygold is an innovative and forward-thinking company offering unique and sustainable high-quality protection against corrosion. We have the know-how and state-of-the-art products and techniques to solve any corrosion problem. Our multitude of success stories says it all.