Review of Sharp AH-XP18MV 1.5Ton Eco-Inverter Air Conditioner [Part-III]
Sharp & LG outdoor units uses complete all-aluminum, much lighter, more efficient & durable condensers having canalicular tubing resulting in superior refrigerant flow velocity, improved heat exchange efficiency and decreased heat transfer loss from tube to fin as fitted in their outdoor units.
I think pretty much all companies are shifting to aluminium condensers only because its cheaper, less corrosive, easy to recycle, etc. Copper actually has better heat exchange properties than aluminium.
It is Trane who made the Aluminium thing successful or invented the Tech which made Aluminium more durable in ACs after GE left in the middle.
Recently I have observed a lot of hotly debated threads in different forums (except TE
) relating to the performance of:
1) The newly used all-aluminum micro-channel (canalicular tubed) condensers
2) The older round copper coil/tube with aluminum plate fin (bi-metal) RTPF condensers
By nature copper is a better conductor of heat than aluminum. All thermal properties of copper are better than aluminum. Copper is also costlier than aluminium. Aluminum’s advantage is that it is lighter and easier to machine.
RTPF condensers have serpentine internal coils to carry the refrigerant to be cooled. These copper coils are further assisted with aluminium fins when air passes through them. Let us consider three types of RTPF condensers:
RTPF-1: Copper coil with copper plate fin condenser (all-copper)
RTPF-2: Copper coil with aluminum plate fin condenser (copper-aluminum)
RTPF-3: Aluminum coil with aluminum plate fin condenser (all-aluminum)
Here definitely RTPF-1 (extremely rare in AC's) will have the best thermal performance due to (all copper) and most costly to implement. It will be followed by RTPF-2 (most widely used in AC's) and then by RTPF-3 where performance in concerned as price goes on decreasing. I have observed there are few people who have this conception or rather misconception that RTPF-1 and even RTPF-2 will have better thermal performance than the new micro-channel condensers variants, reason being micro-channels are all aluminum.
THEY ARE WRONG.
So let me state again for two identical shaped, volumes, face areas, and fin densities condensers one being RTPF-1/ RTPF-2 and the other being all-aluminum micro-channel, the micro-channel condenser will
ALWAYS have better thermal performance. This is not just due to the metal used but by the inherent design advantages that micro-channel rejoices over RTPF.
All-Aluminium Micro-channel Condenser VS Copper-Aluminium RTPF Condenser
Before we dig deeper let us revise the work cycle of an air conditioner in layman’s terms to get a full picture. Air conditioners follow a simple rule where they absorb heat from air situated inside the room in question and reject that heat to the outside atmosphere. For split ACs when the cross-flow fan situated inside IDU starts to rotate it sucks air from above the IDU passing it through the cold evaporator unit situated inside which is finally blown out from below where the louvers are situated to guide the cool airstream. While passing through the evaporators the residence time the air spends causes heat transfer from indoor air to the evaporator via convection. This heat absorbed is then carried by the refrigerant gas via dedicated copper pipes to the ODU situated outdoor and are finally ejected to the outdoor atmosphere via convection. The component that does this very important job is known as the condenser unit or heat exchanger. An outdoor fan is provided to aid the heat exchange by expulsing the air through the condenser fins. The overall efficiency of an air conditioner is highly dependent on how efficiently these heat exchange of the both indoor and outdoor takes place. And this is where the micro-channel all-aluminum condensers have a distinct thermal performance advantage due to their inherent design advantage.
Micro-channel condenser technology is not new. It was first introduced as a viable heat exchanger/ condenser option in the late 1980’s in the automotive industry. These types of condensers are used to replace R22 by R134A, R410A and R407C. The change in refrigerant type introduced new thermo-physical properties. What the industry required was a coil with heat transfer properties equal to or better than the oversized RTPF condensers were being evaluated – but with a reduced size, reduced weight and increased leak protection. Micro-channel coils brazed in a controlled environment offered the solution. Since that time, all-aluminium micro-channel technology has taken over the automotive industry.
With time environmental concerns garnered more and more interest recently there came a similar push in the residential air conditioner market where companies started to shift from older R22 to far more efficient and environmentally friendly R410A refrigerant gas. And with R410A the micro-channel all-aluminum condenser was dragged from the automotive industry.
Let’s be clear, R410A and all-aluminum micro-channel condensers go hand in hand. Micro-channel condenser coils are all aluminum coils with multiple flat tubes containing small channels (micro-channels) through which refrigerant flows. Heat transfer is maximized by the insertion of angled and louvered fins in-between the flat tubes.
Micro-channel Condenser Internal Design
The coil is composed of three components:
1) A flat micro-channel tube.
2) Fins located between the micro-channel tubes.
3) Two refrigerant manifolds.
These components are joined with two refrigerant manifolds using an aluminum-zinc alloy brazing material in a nitrogen-charged braze furnace to make the completed micro-channel coil. Coil circuiting is accomplished by placing baffles in the distribution manifolds to feed the refrigerant through the flat tubes.
The advantages observed over RTPF design:
1) Thermal performance: The higher heat transfer performance is obtained by the flat tubes, which maximize airside heat transfer, and micro-channels within the tubes. The micro-channels maximize refrigerant side heat transfer via multiple tiny refrigerant channels which provide increased primary surface area. Additionally, the metallurgical fin-tube bond resulting from the braze operation maximizes surface contact and increases the heat transfer surface area, further improving the heat transfer performance of the coil.
2) Corrosion protection: The corrosion potential with the all aluminum micro-channel coil is significantly lower than in copper/aluminum (bi-metal) RTPF coils as there are no dissimilar metals to initiate galvanic corrosion. This makes micro-channel coils an inherently better solution for coastal installations or any application where corrosion may be a concern.
3) Refrigerant charge: Micro-channel coils have a smaller volume, lowering condenser refrigerant charge by as much as 75 percent. As such, the use of micro-channel coils provides a more environmentally friendly solution for refrigeration systems to help reduce ozone depletion and global warming.
4) Durability and reduced leaks: Micro-channel coils require only one braze operation versus 50-100 manually brazed joints for RTPF, significantly reducing the likelihood for leaks. Additionally, the flat tubes serve as a fin guard to help protect the fins from damage.
5) Ease of service and repair: Micro-channel coils are easily cleaned and can be field repaired using a two-part epoxy process. These micro-channel coils are less than one inch thick allowing for easy removal of any debris that may be caught within the coil. This is not so with RTPF coils, which are often 2 to 3 inches thick with staggered tube patterns using corrugated fins which make debris removal difficult, if not impossible, in some circumstances. The durability of micro-channel coils also allows for pressure washing (using a broad spray pattern), which is not recommended with RTPF coils. Coil leaks, while unlikely, can also be easily repaired in the field using a simple process. An epoxy based sealant (such as red epoxy), a cleaning solution, a vacuum pump, a few simple tools, and a hot air gun is all that is required.
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All-alumunium Micro-Channel Condenser Internal View
With the advantages of all-aluminium micro-channel condensers stated above I believe it is clear that they offer to be a more performance oriented, durable and viable solution over the old RTPF design and hold to be the future of residential air conditioning solutions. They improve cooling performance (EER), condenser capacity and evaporator capacity compared to the baseline systems using a RTPF condenser. These contributions are caused by the superior heat-transfer characteristic of a micro-channel condenser, lower refrigerant-side pressure drop, and consequently lower condensing temperature -
resulting in requiring less work from compressor increasing its lifespan.
Some time ago I made a comparison between two identical models having different types of condensers. One had RTPF (Panasonic CS-ZC15PKY) and the other all-aluminum micro-channel (Panasonic CS-ZC15PKY-3). Naturally the CS-ZC15PKY-3 had better performance.
Link: Panasonic CS-ZC15PKY-3 VS Panasonic CS-ZC15PKY
I hope no more explaining from my part is required regarding the use of all-aluminium micro-channel condenser in Sharp AH-XP18MV.