The decision to turn off your air conditioner when leaving home depends on several factors, including how long you'll be gone, the climate, your home's insulation, and the type of AC unit you have, according to Patrick Phelan, a professor of mechanical engineering at the University of Arizona. Modern inverter AC units maintain a stable temperature more efficiently than constantly turning the unit on and off.
If you're only leaving for 10-15 minutes, turning off the AC might actually use more electricity because the unit has to cool the entire space down again. It can also cause wear and tear on the system, as it takes 15-30 minutes for an AC unit to reach optimal efficiency. Phelan recommends using a timer or smart controls to raise the temperature a few degrees while you're out. This helps circulate air, maintain humidity, and reduces the load on the system when you return.
In humid climates, running the AC in dehumidification mode for a short period each day can prevent mold and mildew and protect furniture. Raising the AC temperature by about 0.6 degrees Celsius can save approximately 3% on cooling costs.
If you're only gone for 15 minutes, turning off the AC offers virtually no benefit, says Elizabeth Hewitt, a professor and urban planning expert at Stony Brook University.
If you're away all day, 8 hours or more, turning off the AC generally saves energy and money. In dry climates, raising the temperature a few degrees while away is reasonable. However, in humid areas, turning the unit off for extended periods can lead to mold growth because the AC helps control humidity.
The efficiency of your AC and your electricity costs also depend on the type of home and the installed equipment. Gregor Henze, a professor of architectural engineering at the University of Colorado Boulder, explains that homes built with heavy materials like concrete or brick retain cool air longer, while older homes are prone to drafts and heat up quickly. For poorly insulated homes, raising the AC temperature a few degrees when leaving for several hours is sensible.
The type of air conditioner also affects energy savings. Window units are often less efficient because they are installed in open windows, making it difficult to completely block out hot air. Hewitt recommends using spray foam insulation around windows or drafty areas to maintain a stable temperature.
Simple measures can also help keep your home cool. Blocking sunlight reduces indoor temperatures, and opening windows at night in dry climates allows for air circulation. The International Energy Agency (IEA) states that shading and good insulation can reduce cooling energy by 5-15% in residential buildings.
Ngoc Ngan (Japan Times)
