Knowing Your AC System Makes a Big Difference in Energy Savings and Electricity Bills

Is your AC usage increasing power consumption?

Daikin Industries, Ltd.
Content Production: TOYO KEIZAI BRAND STUDIO

Chikashi Shigemasa
PR Group
Corporate Communication Department
Daikin Industries, Ltd.

Advice can often be heard on the efficient operation of air conditioners: “Set airflow to as low a setting as possible,” “Cover the entire outdoor unit to prevent exposure to direct sunlight,” “Regularly turn off the AC when not in use, even for a short period of time,” or “Set the airflow direction downwards to focus cooling on the area near the floor where people are interacting.” Surprisingly, all four of these methods may be counterproductive. You might even call them “misleading techniques for saving energy.

“It’s important for us to know how an air conditioner cools a room and which part of the air conditioner uses electricity and how much. Knowing this gives us a hint to what actions will be effective in saving energy and enable us to confidently act in the future,” says Shigemasa.

“What’s especially troubling is when people avoid turning on their air conditioners in an effort to save energy and then end up damaging their health. As a manufacturer specializing in air conditioning, I feel that we have a strong obligation, now more than ever, to carefully educate people in the effective use of air conditioners so that they can experience both comfort and energy savings.”

“The compressor, which is said to be the ‘heart,’ actually accounts for roughly 80% of the electricity used to operate the air conditioner,” explains Shigemasa. An air conditioner cools by having its indoor unit draw in air from inside the room to collect heat before returning that same air as cool air that has lost its heat. The heat collected from the indoor air is transported to the outdoor unit via a gas called refrigerant that flows through pipes connecting the indoor and outdoor units. The outdoor unit then expels the heat outdoors. In this process, the compressor is essential for compressing the refrigerant and circulating it inside the pipes to collect and release heat.

“To try and save energy, I recommend against reducing the airflow volume (fan speed). In fact, lowering airflow results in the air conditioner taking longer to collect heat from the room, putting a heavier load on the compressor. When you increase airflow, the indoor unit will make more noise, and it may seem like you’re using more electricity; however, the motor operating the fan consumes far less power than the motor driving the compressor. For this reason, I think it’s far better to set airflow to ‘auto.’ After initially increasing the airflow to quickly collect heat, the unit will then automatically switch to steady operation that reduces compressor load while running more efficiently in maintaining a comfortable room temperature.”

The compressor also undergoes an increased load when the air conditioner starts operation. That’s why the advice “regularly turn the switch off” can actually increase power consumption, depending on the time of day and frequency. An experiment conducted by Daikin discovered that leaving the air conditioner in operation for around 30 minutes during the day resulted in more energy savings than turning it on and off.

“When you consider the way air conditioners work, which is to collect heat from inside the room and release it outside, a vital point for energy savings is keeping air passages unobstructed,” advises Shigemasa.

“To ensure that air passages remain unobstructed, it’s important to clean the filter of the indoor unit and keep the area around the outdoor unit tidy. If dust builds up on the filter, the amount of air intake decreases, which will reduce the capability of the unit to cool the room. This means that the unit will need to operate at a higher load for a longer period of time to cool the room, leading to a higher electricity bill. Furthermore, failing to clean the filter for a year is estimated to result in unnecessary electricity consumption of approximately 25%.^*1 Likewise, when the filter in the indoor unit has accumulated roughly three years' worth of dust and there are objects around the outdoor unit that prevent good ventilation, the amount of electricity consumed can more than double. That’s why I recommend cleaning the filter once every two weeks.”

As previously mentioned in the misleading energy-saving tips, some people cover their outdoor units to protect the units from direct sunlight. However, when an obstruction blocks the air passage of the air intake or exhaust vents, heat is prevented from dissipating efficiently. Keeping the area around the outdoor unit neat and tidy by removing any objects nearby will help prevent unnecessary consumption of electricity.

*1

Annual electricity cost ratio calculated based on operating conditions in accordance with JRA4046-2004 with and without filter cleaning (1145kWh) and 1432kWh based on dust volume of 2g after one year (Source: Daikin Industries).

Shigemasa points out that in order to reduce the load on the compressor, it is also important to reduce the “uneven temperatures” in the room.

“Air conditioners detect room temperature from the temperature of the air that the indoor unit draws in from inside the room. In a room with uneven temperatures, the air near the ceiling is warm, so when an air conditioner draws in that air, it determines that ‘room temperature has not yet reached set temperature.’ Even if the area near the floor where people interact is sufficiently cool, the air conditioner will continue to operate more than necessary, which will lead to an increase in power consumption. For this reason, we must be sure that airflow from the air conditioner during cooling is directed horizontally, not downward. Cold air is heavy, and it tends to accumulate near the floor, so if you send cool air horizontally along the ceiling, the cool air will naturally fall to the floor from above, making it easier to reduce uneven temperatures.”

Sending airflow horizontally also helps prevent people from experiencing discomfort from the air conditioner blowing air directly on their bodies. To keep uneven temperatures to a minimum, air purifiers, fans, and air circulators can be used to mix the air. The motors that run these devices consume very little power compared to the air conditioner's compressor. When uneven temperatures are minimized, the load on the compressor can be reduced, which leads to lower power consumption and energy savings while maintaining a comfortably cool temperature.