A "MONEY-saving" tip doing the rounds online claims that leaving an air-conditioner running all day costs less than only turning it on when needed and switching it off when no one is in the room.
The reasoning is that the unit guzzles electricity because it has to cool the room again.
So, is it really cheaper to leave the air-conditioner on all day instead of switching it on and off?
Verdict:
FALSE
No, leaving the air-conditioner running all day generally uses more electricity than switching it off when you don't need it, although keeping it on when leaving the room for a while may result in some savings.
The idea that it is cheaper to leave the unit on comes from the belief that an air-conditioner has to work extra hard to cool the room again.
That restart does use more power – but only for a short while.
According to the US Department of Energy, a higher indoor temperature slows the flow of heat into a home, which saves energy on air-conditioning.
In other words, a room kept icy cold all day is constantly soaking up heat from outside and the air-conditioner has to keep pumping it back out.
Switch it off and that heat flow slows down because the gap between indoor and outdoor temperatures shrinks.
The department says that adjusting the thermostat by about 4°C to 5.5°C for eight hours a day can save as much as 10% a year on heating and cooling.
A peer-reviewed study published in the journal Energies in 2022 put the question to the test in two identical west-facing rooms in a subtropical climate.
Researchers switched the air-conditioner in one room off and on at intervals, while the other ran continuously.
Every time the unit restarted, there was a spike in power use.
Even so, total power consumption in the room where the air-conditioner was switched off and on was 2.9% lower than in the room where it ran non-stop.
The trade-off was comfort, as switching the unit off for 15 minutes saw room temperatures increase by 4°C to 5°C.
Air-conditioner maker Daikin ran its own experiment in two similar apartments in Osaka, Japan, during the scorching August of 2016.
It found that when residents step out for just 30 minutes during the day between 9am and 6pm, leaving the air-conditioner on worked out cheaper than switching it off.
However, when compared to a full day of continuous use from 9am to 11pm against switching it off whenever residents went out, non-stop operation cost about 35 yen more per day.
Daikin concluded that running the unit all day was counterproductive and recommended combining both approaches depending on the situation.
Closer to home, Tenaga Nasional Berhad (TNB) has advised the public to switch off appliances when not in use.
TNB also recommends setting the temperature between 24°C and 26°C and cleaning its filters regularly.
So the next time someone insists on leaving the air-conditioner running while the family heads out for the day, the electricity bill is on your side.
Source:
1. https://doaj.org/article/
2. https://www.energy.gov/es/
3. https://kyodonewsprwire.jp/
5. https://www.tnb.com.my/assets/
