[Reading Science] Does Turning on the Air Conditioner in Winter Make It Warmer?

Will the room get warmer if you turn on the air conditioner in winter? The photo shows an air conditioner advertisement screen from a company.
[Photo by YouTube screen capture]

[Asia Economy Reporter Kim Jonghwa] Although temperatures dropped below freezing at times this winter, they generally stayed in the single digits, making it relatively warm. No matter how warm it is, winter is still winter, so heating devices need to be turned on.

Nowadays, ceiling-mounted HVAC units regulate office temperatures throughout all four seasons. However, there are still places where the power of these shared heating units does not reach. In offices that are not perfectly square, there tend to be more cold spots.

At times like this, a colleague might look at an air conditioner standing stubbornly in a corner that was used before and say, "Let's at least turn on the air conditioner." That colleague probably thought that since the outside temperature is lower than the air conditioner's lowest setting, setting the air conditioner to about 27℃ and turning it on would warm up the room.

Assuming the outside temperature is -2℃ and setting the air conditioner to a desired temperature of 27℃, they calculated that the air conditioner would raise the indoor temperature close to 27℃. But if you turn on the air conditioner as that person calculated, will the indoor temperature really warm up to 27℃?

When it’s hot, wind feels cool because sweat evaporates due to the wind, taking heat away from the body. When a substance changes state?from solid to liquid, or liquid to gas?it absorbs heat from its surroundings. The heat absorbed when a solid melts is called the heat of fusion, and the heat absorbed when a liquid vaporizes is called the heat of vaporization.

An air conditioner uses the heat of vaporization to cool the air. For an air conditioner to operate, it requires a substance that can change from gas to liquid and liquid to gas, called refrigerant (air conditioner gas). When the air conditioner is turned on, the compressor compresses the gaseous refrigerant, raising its temperature to 80?100℃.

This heated refrigerant moves to the condenser. Although the outside temperature in summer is generally above 30℃ and hot, it is still very cold compared to the heated refrigerant. Therefore, as the refrigerant passes through the condenser, its temperature drops and it changes from gas to liquid. When the gas changes to liquid, heat is released. This heat is expelled outside through the outdoor unit. That’s why hot air comes out of the outdoor unit.

The refrigerant, now liquid after passing through the condenser, moves to the expansion valve. The expansion valve’s passage suddenly narrows and then widens again. This causes the refrigerant’s speed to increase, and its pressure and temperature to drop. In this process, the refrigerant, still liquid but now in a state ready to vaporize, is sent to the evaporator.

In the evaporator, the refrigerant meets the hot indoor air and changes from liquid to gas. During this process?evaporation?the refrigerant absorbs heat from its surroundings. This cools the surrounding air, and this cooled air is sent indoors through the indoor unit.

The gaseous refrigerant then returns to the compressor, repeating the cycle and turning the indoor air into cool air. When the indoor air cools after running for a while, there is no hot air to evaporate the refrigerant, so the outdoor unit stops operating. Have you now properly understood the air conditioner’s function? The indoor unit only cools hot air.

In winter, the indoor temperature is not much different from the air conditioner’s set temperature. Ultimately, the outdoor unit does not operate even if the air conditioner is turned on. This means the air conditioner’s function does not work when turned on. For the air conditioner’s cooling mode to operate, the outside temperature needs to be between about 21℃ and 43℃. It also operates when the indoor temperature is between about 18℃ and 32℃. This means the indoor temperature must be at least 18℃.

If the functions of the air conditioner’s outdoor and indoor units are reversed, it becomes possible. This type of air conditioner is called a 'heat pump,' which absorbs heat from external sources such as air, water, or the ground outside and sends warm air indoors. The colleague who said, "Let’s at least turn on the air conditioner since it’s cold," was mistaken.