Wasteful AC use is caused largely by, well, wasteful AC habits. But these habits are not entirely a fault of the user. Current AC units are limited in the comfort they provide and often times a user does not understand their AC well enough to engage modes that provide indoor comfort more effectively.
In an upcoming post, we’ll explore the reasons why ACs are insufficient at maintaining thermal comfort in greater detail. But for starters, here are a few you may be able to identify with:
ACs cannot hold the temperature you set them at for very long. We found users will try to compensate for the ACs inability to maintain temperatures by keeping their AC at a low set temperature, like 22°C. Unfortunately, this is also why users find their room too cool.
ACs are unable to account for thermal comfort variables such as occupancy, movement, radiant heat and changes in outdoor weather. Your AC cannot discern whether you are exercising in your room (which could require a lower set point temperature) or reading (which would allow for the room to be a bit warmer).
The primary function of an AC unit is to control indoor temperature and most units are not equipped with a humidity sensor. Add to the fact that many residents don’t fully understand how their AC works (i.e. “Auto” mode does not mean your AC will automatically select the best mode for you) and the root of poor AC habits becomes quite clear.
So, whether you have developed poor AC usage habits because ACs can be mystifying machines, or you have simply acclimatised to cooler indoor temperatures, it is easy to adopt habits that may be driving up your electricity bill, more than you may realise. Check to see if you do any of the following and you may have an energy-saving solution on your hands.
Here are 3 AC Habits That May Be Spiking Your Energy Bill
At night, do you sleep with the AC turned on? What temperature do you set it at? How thick are the clothes you sleep in? Do you use a heavy quilt? A recent study by Lin Zhongping of Hong Kong Polytechnic University  studied comfortable sleeping temperatures of Hong Kongers and found that over 55% of survey respondents used a temperature below 22°C, with nearly 20% of respondents choosing settings below 20°C.
Lin monitored 10 locations and found average indoor sleeping temperature and humidity were cooler than what users would prefer during the day, which is peculiar considering our body temperature drops while we sleep. Lin then found that the need for cooler thermal environments appeared largely due to the sleepwear habits of Hong Kongers: almost half of the respondents slept in full length sleepwear or used heavy quilts to insulate themselves at night.
Clothing is a significant variable for thermal comfort – the difference between comfortable sleeping temperatures can range greatly depending on how much clothing you wear to bed. According to Lin’s study, at a relative humidity of 50%, the difference in comfortable sleeping temperature between 3 clo and 1.5 clo (1 clo = western business suit) can be as much as 8°C.
It’s likely these respondents could sleep with lighter sleepwear, set their AC to a higher temperature and still feel comfortable. If you insulate yourself from your AC at night by using thick quilts or sleepwear, you can afford to turn your AC temperature up and give your AC a break. Either that or you will be paying to keep your AC on at unnecessarily cool levels.
Don’t underestimate the usefulness of a fan – this simple appliance can help to ventilate your home using very little energy. If you rely heavily on your AC, try using a fan with your AC set at a higher temperature. A study by Leung Wai Ho Wil of Hong Kong Polytechnic University  found that participants who used their fan together with their AC were able to maintain a thermal comfort at warmer thermal conditions by increasing the airflow rate.
His study also showed that an AC set at 28°C augmented with a fan provided an energy saving between 24-33%! In another study by TEPCO , using a fan together with the AC resulted in a 9% energy saving when the AC was set at 27°C and a 22% saving when set at 28°C. The moral of the story: using a fan with your AC set at a higher temperature allows you to maintain indoor comfort using less energy.
Did you know that solar radiation from windows accounts for 45% of your AC’s cooling load? That’s no small number. In fact, according to a study by Joseph Lam from City University of Hong Kong , it’s the most significant contributor to the thermal load on ACs, even more so than heat generated by occupants (14%) or heat conducted through walls (24%). Installing reflective blinds is an easy way to block out solar heat and keep your home cool. The US Department of Energy estimates that highly reflective blinds can reduce solar heat gain by 45% and even good curtains, such as those with a plastic backing, can reduce heat gain by a third.
Wearing lighter materials to bed, using a fan with your AC and installing blinds are fairly simple ways to hack your energy costs and depend less on your AC. Try applying these tips to your home AC and let us know if you experience any change in savings or come across interesting observations!
 2005, The HK Polytechnic University, Lin Zhongping
 2002, HK Polytechnic Univeristy, Leung Wai Ho Wil
 2002, TEPCO, “エアコンを省エネに使うポイント”
 2000, City University, Joseph Lam. “Residential sector air conditioning loads and electricity use in Hong Kong”