During the scorching summer heat, cool pleasant air is just a switch away. Just turn on the air conditioner and within minutes you can feel the cold air around you. Apart from the various factors that determine which type of air conditioner is better, there is an age-old debate as to which type of coil is better – Copper or Aluminium. Before we see the pros and cons of each type, let us first understand the importance of these coils in the air conditioning process.
Importance of coils in Air Conditioners
The core to air conditioning is a refrigerant gas that goes from gaseous state to liquid state by compression and then again changes back to gas by absorbing heat available in the room. It goes through a refrigeration process that is mainly divided into 4 parts:
- Compression: The gas is pressurized and converted into a high-pressure hot liquid.
- Condensation: The liquid flows through a coil where the high-pressure hot liquid refrigerant is converted into cooler liquid by releasing heat into the outside air. This is a part where coils are used.
- Expansion Valve: A valve then converts high-pressure liquid to low-pressure liquid.
- Evaporation: The low-pressure liquid again goes through an evaporation coil where it absorbs heat from the room and changes from liquid to gas. This process happens in the indoor unit while all other happen in the outdoor unit (in case of split ACs).
Basically the heat from the inside air is transferred to outside air and this transfer of heat takes places in the coils.
The refrigerant in the evaporation coils evaporates (changes from liquid to gas) by absorbing the heat from the air (air from the room) passing over it. The air (from the room) cooled in this process is directed into the room. The gaseous refrigerant is then passed through the compression process and condensation coils where the refrigerant condenses by releasing the heat into the air surrounding it. This warm air is blown out with the help of exhaust fans.
This working principle remains same in all types of HVAC systems; just the size of the system keeps on varying.
Hence the type of coils used in them affects the efficiency of HVAC systems. The size of the coil, the material used to make them, their ease of cleaning and maintenance; all play a very major role in the functioning of the HVAC systems.
History of Air Conditioner Coils
In past the most popular choice for making these coils was copper. For many years only copper was used to make the coils in HVAC systems due to the various benefits it had, but that made air conditioner expensive and not everybody could afford them. By around 1970, General Electronics took a step that was a game changer for the air conditioning industry. The started using aluminium to make coils. The cost of using aluminium was much less than that of using copper, which brought down the subsequent rates of ACs making it a luxury that most people could afford.
Since then there has been a debate about which material is better for making coils.
Differences between Aluminium and Copper
1) Heat transfer characteristics:
As the transfer of heat takes place in the coils, it is very important for the metal to have good heat transfer characteristics. Copper has a heat transfer coefficient higher than aluminium. That means, copper is a better heat exchanger than aluminium.
2) Cost and Pliability (The quality of being easily bent):
Copper is costlier than aluminium, which increases the cost of making an air conditioner and thereby the price of air conditioner. To reduce the unit cost of manufacturing ACs, aluminium has become the favorite choice of manufacturers.
Another factor to be considered is pliability. Aluminium as compared to copper, has a better ability to be bend into the shapes desired. Hence to make a coil of same size and shape, approximately three times more copper is required, making the process costlier.
However, to bring down the cost of AC with copper coils, thinner and thinner copper coils are being made now days.
3) Strength and reliability:
Copper is much easier to repair on field than aluminium. Many times, when aluminium coils are damaged they need replacement. The coils made out of copper are much more stronger than aluminium. Hence they are durable.
4) Ease of maintenance:
As the condenser coils are placed in the unit that is usually placed outside the house; it is exposed to harsh climates and dust and this needs regular cleaning for better functioning. Having said that, copper coils are easy to clean and maintain, as they are durable. While aluminium coils are not strong and so need to be kept in heavy-duty cabinet to protect them from damage. This makes them difficult to clean and maintain.
Corrosion plays as very important role in determining the life of an Air Conditioner. Corrosion damages the coils that hampers the heat transfer process and also results in leakage. Hence it is very essential to protect the coils from corrosion. Corrosion damages are higher in humid climates and for people living near seacoasts and salty water bodies, as the moisture content in air is higher in such areas.
Due to these corrosion, a non-conducting layer is formed over the coils, which reduces its heat exchange capacity. Today many modern technologies have been developed to protect the coils against corrosion and thus increase the life of ACs. (Tip: Look for corrosion protection techniques while buying AC such as coating over the coils etc).