Microchannel coils: how to optimise maintenance

The maintenance of microchannel coils in HVAC equipment requires great care; if the various stages are not carried out properly, the performance and longevity of the entire system may be compromised.

Considering that these components are made from aluminium alloys, often with protective coatings, they are actually quite delicate and therefore require specific cleaning methods which are thorough but not too harsh, in order to ensure they remain in excellent working condition.

What are microchannel coils?

Before taking a closer look at the most efficient microchannel coil maintenance methods, it is important to understand exactly what these devices are and why they play such a central role in HVAC equipment.

Microchannel coils are technically advanced components used inside heat exchange systems, especially in the heating, ventilation, air conditioning and refrigeration sectors.

They are usually made from aluminium, which despite being a relatively light material, makes them resistant to corrosion as well as being recyclable.  They are used to boost thermal efficiency and they enable a reduced environmental impact compared to the use of traditional technologies.

Their structure features a series of small channels, known as microchannels, through which the refrigerant fluid flows.  These grooves are arranged in flat tubes, connected to the heat exchanger’s fins.

General operating principle

The refrigerant fluid flows along the microchannels, while air passes through the external surface of the coil.  The larger contact area between the refrigerant and the internal walls of the grooves provides better heat transfer compared to that possible with traditional coils, which consist of rounded copper tubes and aluminium fins.

Microchannel coils also provide other benefits, as listed below:

1. energy efficiency: most heat exchange surfaces enable energy consumption to be reduced, increasing the system’s overall efficiency;
2. compactness and reduced weight: microchannel coils are lighter and more compact compared to conventional alternatives, making them ideal for use in situations where space and weight are critical factors;
3. less refrigerant required: thanks to their optimised design, they require a smaller quantity of refrigerant fluid and this helps to reduce their environmental footprint;
4. durability and resistance to corrosion: the fact that they are made entirely from aluminium reduces the risk of galvanic corrosion, increasing the equipment’s lifespan.

Thanks to the qualities they offer, these components are used extensively in many sectors, including air conditioners for residential and commercial buildings, industrial refrigeration systems and vehicle cooling units.  Their use has grown rapidly due to their ability to meet high standards of energy efficiency and sustainability.

Recommended cleaning methods

Now that we have looked at their key role in HVAC devices, it is clear why regular maintenance is so important in order to ensure that the microchannel coils work optimally and problems caused by the accumulation of dirt can be avoided.  Professionals recommend that for best results, the following practices should be adopted:

1. removal of superficial dirt: the thin structure and close positioning of the fins mean that dust and dirt can easily be removed using a soft brush, a vacuum cleaner with a suitable attachment or compressed air at low pressure (3-5 bar). To avoid damage, it is important to brush lengthways along the fins;
2. rinsing with water: in order to remove accumulated dust and dirt, water with a pH of between 4.5 and 8.5 can be used. A nozzle should be used to vapourise the water and tilted at 25 degrees in relation to the coil.  It is essential to keep the pressure below 40 bar and maintain a distance of at least 400 mm from the coil, so as to avoid mechanical damage.  Cleaning must always be carried out in the opposite direction to the normal air flow;
3. drying: after rinsing, any residual water must be removed, via drying or blowing air onto the device. This prevents corrosion and ice formation in cold environments.

As outlined in the third point above, in sub-zero conditions, when the use of water could cause it to freeze, compressed air is an efficent alternative and almost as efficient.

Chemical products: to be avoided

The use of chemical detergents for the cleaning of microchannel coils is not recommended, as they can damage the protective coating and the material of the coil itself.  Although there are many products on the market which are advertised as safe, tests show that none of the universal detergents available are in fact suitable for this kind of surface.

The use of unsuitable chemical products can lead to progressive corrosion or a reduction in performance, which, over time, will inevitably lead to the the entire coil having to be replaced.

Microchannel coil maintenance frequency

A regular maintenance program is essential to enable microchannel coils to operate optimally.  In particularly aggressive environments, this frequency will need to be increased.

Clear signs, such as a decline in the unit’s performance, a rise condensation temperature or the fans moving too rapidly indicate that immediate intervention is required.

A lack of adequate maintenance not only risks reducing the the equipment’s efficiency, it can also invalidate the manufacturer’s warranty (which could be extremely costly in the case of a unit breakdown).

If microchannel coils are damaged due to inappropriate cleaning methods being used, it is important to remember that repairs are often not practicable.  The protective coatings which are subsequently applied can be very expensive and are not always reliable.

In such circumstances, replacement is the only option in terms of efficiency.  Luckily, many manufacturers offer a wide range of replacement coils and keep a good their warehouses well stocked; this ensures that the equipment downtime is kept to a minimum.

Translated by Joanne Beckwith