What is microchannel coil and how it works

TECHNOLOGY OVERVIEW

Micro-Channel all-aluminum coils are designed to use less refrigerant and facilitate better heat transfer. Because of the aluminum, the units are lighter, and not susceptible to formicary corrosion.

Unfortunately, because it is a newer design to residential HVAC products, there is a wealth of misleading information available on online platforms – such as forums and videos. Some believe these coils are more difficult to install. However, installation is no different than traditional tube-in-fin coils. Micro-Channel coils require proper charging, but what HVAC system doesn’t?

Micro-Channel indoor and outdoor coils are made up of three main components. The “channels” or “tubes”, aluminum fins and two manifolds. These components are brazed together during a hydrogen/nitrogen process. This process uses no water or oxygen, ensuring an uncontaminated, sturdy joint. Additionally, for every one braze on a Micro-Channel coil there are approximately 28 braze points on its tube-in-fin counterpart. That means there are far fewer opportunities for joint repairs on a Micro-Channel coil.

Micro-Channel indoor and outdoor coil installation is very similar to traditional methods. Contractors must:

  • Braze with nitrogen
  • Install a liquid line filter drier
  • Perform a thorough system evacuation
  • Carefully weigh in and fine tune any additional charge (For additional information, check out our How to Charge page.)
 

If there are questions about Micro-Channel coil installation, contractors should talk directly to the manufacturer or distributor – not immediately turn to online forums.

Nortek Global HVAC features Micro-Channel evaporator and condenser coils in models starting at 13 SEER and going up to 20 SEER. In fact, our air conditioners are 100% Micro-Channel, both indoor and outdoor. For further repair and installation instructions, heating and air conditioning contractors can watch free videos available on this site, EdgeTek or YouTube.

Using Microchannel Coils for Process Cooling

Used in process cooling equipment such as condensers, chillers and environmental chambers, microchannel coils provide process benefits.

As emergent technology for the process industries, microchannel air-side coils are having a favorable impact because their performance exceeds traditional copper tube/aluminum fin coils in many OEM applications. Long term, microchannel coils have a bright future in process cooling, process chillers, cooling coils, environmental chambers and rooftop system air-handling equipment. Microchannel coils are used as refrigerant condensers (ranging in size from 0.5 to 400 ton systems), evaporators (cooling coils), and fluid coils for air-side cooling and dehumidification.

The microchannel coil story began approximately 30 years ago in the automotive industry.  Design engineers needed an air-side heat exchanger for condensers, evaporators and radiators that weighed (and cost) less than the traditional copper tube/aluminum fin design. The microchannel heat exchanger was developed as a result. The all-aluminum microchannel heat exchanger coils have a flat-tube design and air-side fins. Since their introduction into the automotive industry, four variations in their design have been developed to serve as radiators, air-conditioning condensers, evaporator/cooling coils and cabin heaters.

Beginning in the mid-2000s, the microchannel coil technology progressed into use in process cooling and HVAC/R applications. At four to 50 times larger than the original automotive designs, they are designed to provide robust performance (and less susceptibility to galvanic corrosion) for more demanding conditions, yet they are lighter weight and smaller in physical size. When integrated into process equipment, the microchannel coils may provide better energy efficiency with closer thermal approach temperatures.     

Heat Rejection in Process Equipment

With improvements in compressors, variable-speed fans and plate heat exchangers, process equipment energy efficiency has increased rapidly over the past 30 years. Microchannel air-side coils help continue that progress as they have been put to use in the process cooling and chiller equipment industries. Applications include refrigerant condensers, process chillers, environmental chambers and other compressor-driven systems.

One application where microchannel air-side coils are helping to provide energy efficiency advantages is process chillers with mechanical refrigerant cooling systems, where the microchannel coils are used as condensers. It is estimated that up to 30 percent of the process chillers worldwide use microchannel coil technology, and some industry insiders expect this value to increase in the next five to 10 years.

Reliability and Corrosion Resistance in Microchannel Heat Exchangers

It is worth repeating that unlike fintube designs, microchannel coils are all aluminum and do not contain copper. With dissimilar metals such as is found in the fintube coils, the natural copper-to-aluminum eutectic is susceptible to galvanic corrosion. This is especially true in marine environments and processes with various vapors in the airstream.

The galvanic copper/aluminum corrosion potential is not present in all-aluminum coils because there is no copper to make the aluminum anodic. As such, there is less potential for the aluminum to corrode and fail over time.

Microchannel coils specified for highly corrosive applications with vapors that can cause corrosion on copper or aluminum should be ordered with an epoxy electrocoating. This type of coating, which is widely used on traditional fintube coils, also can protect all-aluminum microchannel coils from a range of chemicals and vapors. The coating can extend the coils’ durability and maintain efficiency over the useful lifetime.

When it is time for maintenance, microchannel coils can be cleaned and washed with a regular water hose or low pressure spray. Soap and water can be used instead of harsh chemicals. Routine maintenance allows process equipment to be maintained at peak performance and reliability.

Today, microchannel coil technology has shifted from your car to process cooling and beyond, being integrated into process chillers, cooling coils, air-handling equipment and more. Where microchannel coils will go in the next five to 10 years as equipment providers recognize the benefits of this new technology remains to be seen. 

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