Microchannel Coil Technology : Let’s Cut to the Chase
When placing a chiller enquiry, the various suppliers are always surprised by our insistence that the condensers be of the copper tube / aluminium fin type. In fact, our general specification clearly states that Microchannel Condensers are not permitted (by the way, the same will apply to plate heat exchangers and the use of hermetic type scroll and reciprocating compressors) when it comes to our specifying chilled water generators.
The main reason behind our rationale is to combat the refrigerant leak issues commonly found with MCHC (microchannel) coils and likewise, to address the fundamental pitfalls associated with the wide-spread use of multiple hermetic compressor circuits serving the same common refrigerant system.
In recent years (microchannel coils are relatively new technology) we have experienced an unusually high occurrence of refrigerant leaks on this type of coil, many occurring between 3- and 10-years following installation of the chiller. In cases of clearly premature failure (3 years or so) the supplier has opted to replace the offending coil panel with new, at their own expense.
I might add that replacing even one microchannel panel is not a cheap exercise. Try R200K for starters. You can only imagine the clients’ disapproving response when handed the quotation. After all, he has only recently forked out 2 Bar plus, for his new chiller.
Currently, we are involved with three complete chiller replacements as a result of terminal microchannel condenser failure (multiple refrigerant leaks). The Powers-that-be have taken the decision to cut their losses in all three cases, and purchase new chillers, rather than replace the condensers. Sounds drastic? Maybe, but in all probability, the best solution in the longer term, given the top-tier status of their property assets.
Have we opted for microchannel condensers for the replacement chillers? No way Jose! You must be joking. It’s not to say that microchannel condensers are inferior in any way. Certainly not. In fact, they offer a number of distinct advantages over the conventional copper tube / aluminium fin condensers ; inter-alia :
- Cheaper to produce (making for more cost-effective chiller offerings)
- Less refrigerant charge
- Higher efficiency
- Smaller footprint (less weight)
- Improved corrosion resistance
Where they don’t quite match up, is in the maintenance and durability stakes :
- They are prone to premature clogging (due to the microchannel design)
- Less durable due to their all-aluminium construction (handle the chiller with care from production line to site)
- Leak repair is difficult (two epoxy process or gas torch repair)
- Requires precise refrigerant charge (easy to overcharge system) : Proper charge is critical
- Prone to leaking due to ultrasound harmonic vibration, incorrect cleaning methods, overcharging the system etc.
Our regular choice will invariably be in favour of the tried and tested copper tube / aluminium fin coil construction, for as long as these remain available. (However, if a “tight budget” dictates the chiller selection, we will ensure that the client is made aware of the risks involved.)
Currently one has the choice, “New Age” microchannel super-efficient condenser, or the “Old School” well proven durable Aluminium fin on copper tube condenser.
Going forward, we firmly believe that the problems besetting the MCHX coils will in due course, be overcome, as new materials and technology evolves. We can only wait and see.
In the meantime, both “budget cost” chillers and the higher-cost more robust (durable) offerings are readily available to the end-user, thus, catering for both sides of the spectrum.
Nevertheless, like everything in the “Engineering” world, proper communication, instruction, and user training is essential when encountering any new form of technology. Never, and I repeat, Never, simply apply the “old way” of doing things. You could land up with a great deal of egg on your face, not to mention the damage to your own, and your company’s reputation.
Remember, when all else fails, read the instructions, then read them again for good measure.
At the end of the day, the client needs to get what he is paying for, nothing more, nothing less. He must be made completely aware of the pros and cons determining any final decision. That’s your obligation and commitment. Achieve this and you will have a client for life.
Patrick Burke FSAIRAC
RPM Consulting Engineers
“Regular Cleaning is Essential for Maintaining optimum efficiency”