Why Are There So Many Fins in a Coil?
If you look really close at your air conditioner’s evaporator or condenser coil, you’ll see a ton of tiny fins sandwiched between two tubes. You might ask yourself, why are we making this so fragile. A screwdriver could puncture these fins with just the smallest bit of force, let alone what some ice could do. Why are we using such tiny parts instead of just a few, massive fins or something more robust?
Let’s start with a trip to the past: the classic heating radiator. A radiator like this is just another type of heat exchanger, almost the same thing as your air conditioner’s coils, but designed to heat the home or office. These were massive, robust pieces of equipment. They weighed hundreds of pounds of cast iron and could break your foot, leg, and back all at once during a botched installation.
These work on the same principle as other heat exchangers: we change the temperature of the heat exchanger, and it in turn changes the temperature of the air. With such beefy components though, it requires a lot of water or steam to make any significant changes. Sure, the radiator will get hot enough to fry an egg or reduce just about anything to a piece of charcoal, but it doesn’t have a lot of contact with the air. It ends up being slower as a result.
When we radiate or absorb heat, we need to maximize our contact with the air. That means more surface area. The only way to increase the surface area is to make a ton of tiny pieces of metal. Then we fall into a second problem: we need to have constant contact with our fluid or gas too. The heat will only radiate so far down an extrusion of metal. It’d be inefficient if we had a just a few long cooling fins.
We need to maximize surface area and thermal contact. To do this, we need, essentially, large stretches of pipe contact short fins. If we make the fins in a wave shape, we can easily suck or push air through them and improve our efficiency even further.
This sort of efficiency plays a major part in making air conditioning affordable, both in terms of hardware and operating costs. We can reduce the amount of refrigerant needed, which reduces the size of the compressor, reduces the amount of material in the radiator, and reduces the amount of power required to compress less fluid.
This crucial weakpoint in the equiment makes it essential that you maintain the casing on your air conditioning equipment. If you have the casing off for maintenance, try to keep the heavy equipment away. All it takes is a lawn mower or a weed wacker and a pebble to total an expensive coil.