Should i keep my windows and doors shut after turning off aircon to reduce condensation in aircon?

This is a concept termed as climatisation of air conditioning system, does it really work? Surprisingly No. Why?

If you have big mirrors or glass panels in your room and after running the aircon all night, these glass surfaces becomes cold. If you open the windows immediately after turning off the aircon, the mirror and glass will fog. If you allow the room temperature to slowly climb, meaning the glass surfaces warming up before opening the windows, there is no longer condensation. Climatisation works very well for glass and metal surfaces.

I would like to request air-conditioning guys to stop advising customers to practice climatisation to reduce condensation on the aircon. It doesn’t work that way with aircon. Why?

Unlike a normal cold surface like a glass mirror that slowly gains heat when the aircon is turned off. The aircon fan coil is packed with liquified gas (within the copper pipes), and when the liquified gas evaporates (within the copper pipes), it becomes cold (roughly 3’C).

What that is happening is that when you tun on the aircon, the compressor is constantly pumping liquified gas through the copper pipes into the aircon unit in your room. When this liquified gas reach the fan coil unit, it evaporates in an instance (about 3’C). This is how you get cold air.

The vaporised gas is very cold and it returns back to the compressor. The compressor compresses the gas so much that it becomes a liquid (very hot). Then this liquified gas is sent to the fan coil, evaporates (becomes cold), return to compressor, compressed to become liquid (becomes hot)….and the cycle continues.

When you turn off the aircon, the fan coil in your room is already packed with liquified gas. This liquified gas will evaporate, but much slowly because the fan is no longer running and the aircon flap closes, preventing the cold air from escaping. If the fan is running, the amount of liquified gas in the fan coil will take about 30 seconds to vaporise. But if the fan is not running and the flap closes, it will take hours before the fan coil lose/gain heat.

So what are we dealing with now? We are dealing with with a fan coil, fan blower that is about 3’C. There will be lots of condensation occurring within the fan coil and the internal surface of the aircon. Any air with relative humidity of more that 3-4{fb1d329791d795fe648c75bd713fa46a3cb5b70a471d226a156aa435810d6193} will cause condensation, with such temperature. The warm moist air outside your room in Sinagapore is usually 70-80{fb1d329791d795fe648c75bd713fa46a3cb5b70a471d226a156aa435810d6193} relative humidity. An aircon room is usually 50{fb1d329791d795fe648c75bd713fa46a3cb5b70a471d226a156aa435810d6193} relative humidity. However, when you are dealing with a surface that is 3’C, be it 50{fb1d329791d795fe648c75bd713fa46a3cb5b70a471d226a156aa435810d6193} relative humidity or a 100{fb1d329791d795fe648c75bd713fa46a3cb5b70a471d226a156aa435810d6193} relatively humidity, they both will cause massive condensation. Therefore, by opening the windows is not going to make any difference in managing the moisture within an aircon. There is a better way.

How do you manage this trapped moisture within the aircon then? The technology was around for more than 10 years. Some aircon manufacturers understood this problem and integrated a beautiful solution to this problem. For example, the Daikin Mold proof series do not fully close the aircon flaps and keeps the fan running for roughly 2 hours after you turn off the aircon. By doing so, it helps to reduce the moisture trapped in the fan coil and blower, thereby managing the mold problem. Unfortunately, Panasonic aircon not only doesn’t offer this feature, it has totally removed the fan only function. Consumers cannot manually turn on the fan to dry up the internal parts of the aircon. As such, i see more moldy Panasonic aircon than other brands. This is also because it is indeed one of the coldest aircon (more condensation), but the lack of fan function has greatly sabotaged an otherwise perfect aircon to me.

So, should you immediately open your windows after turning off the aircon? Yes you should and you should do so while the room is still cold. When you room is cold and outside air is warm, the greater the temperature difference, the greater the air movement when you open the windows. It is perfect for air exchange.

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