How home and car air conditioners work. Explain the difference between them and chillers.
■ How home air conditioners work
＜Cooling＞
The basic principle of air conditioning is the use of latent heat caused by the evaporation of liquid.
For example, when water on the body evaporates, it takes away body heat and makes that part feel colder. This is latent heat of vaporization.
After the refrigerant is vaporized, a compressor and an expansion valve are used to circulate the refrigerant again.
The compressor has the function of compressing the evaporated gas and turning it into a liquid again, and the temperature of the liquefied refrigerant becomes high.
In order to cool the refrigerant, a fan is used to blow air on it in the heat exchanger.
Therefore, the air coming out of the outdoor unit is warm.
The refrigerant that has been cooled to a certain extent in the heat exchanger is expanded by the expansion valve to increase the flow rate and further lower the temperature.
This cold refrigerant comes out of the heat exchanger as cold air.
＜Heating＞
The flow of refrigerant during heating is the opposite of that during cooling. During cooling, cold air comes out of the indoor unit and warm air comes out of the outdoor unit.
On the other hand, during heating, cold air comes out of the outdoor unit and warm air comes out of the indoor unit.
This mechanism is called a heat pump.
The refrigerant is heated by exchanging heat between the very cold refrigerant coming out of the expansion valve and the cold air outside (which is relatively warmer than the refrigerant).
Therefore, when the outside air is colder than the refrigerant, heat cannot be extracted.
Does this mean that the heating will not work? No, it is possible to blow warm air using air compressed by the compressor.
You might think that this means it would be better to just use the compressor from the start, but a heat exchanger is used to improve heating efficiency.
However, as explained earlier, efficiency drops when the outside air is very cold.
■ How car air conditioners work
Automotive air conditioners work in almost the same way as home air conditioners.
The heat exchangers are called evaporators and condensers, and the compressor is driven by the engine's power.
When heating, the engine's heat is used to blow out warm air.
This is more efficient because it does not require the compressor to be turned on.
However, the engine is not warmed up immediately after starting, so it cannot be heated immediately.
In cold regions, it can be heated quickly by using a PTC heater in combination.
In the case of electric vehicles, since they do not have an engine to serve as a heat source, their structure is the same as that of a household air conditioner.
■ How a chiller works
A chiller is a cooling water circulator that keeps the temperature of a liquid constant.
By running a liquid kept at a constant temperature through various devices, the temperature of the devices can be kept constant.
This also works in the same way as an air conditioner, except that while an air conditioner cools the air, a chiller cools a liquid.
In addition, in the case of a chiller, the heat exchanger part shown below can be either air-cooled or water-cooled.
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