How most portable air conditioners work
When a portable air conditioner that is in good working order senses (through a thermostat) that the temperature of the air in the room is too high, or above the threshold set, it begins the cooling cycle. Modern window unit air conditioners typically operate in “dual” phases – and cool using one of the phases. This is set at the factory to ensure the most efficient use of energy.
The first phase uses the internal fan. When the fan turns on, air is blown into the room to circulate it. The only energy used (above normal operation of the unit) is that which powers the fan. The fan can run anywhere between 30 seconds and an hour or more. Typically, the fan is used when the desired temperature is a degree or two off from the room reading.
The second phase kicks in when either the temperature difference is too great, or the fan running alone can not effectively reduce the temperature efficiently. Almost always, the fan is turned on first, then the compressor turns on. The compressor take more power, but it forcibly cools the air inside the room, releases the heat to the outside and blows the cold air into the room via the fan.
A cycle is the time it takes for the fan/compressor to turn on, then turn off. The whole process is one cycle. Thus, your air conditioner goes through several cycles every day.
The key to saving energy on A/C costs is to reduce the number of cycles the air conditioner goes through. It also helps to reduce the amount of time it takes a cycle to complete. In other words, you don’t want the a/c to turn on several times an hour. But having it turned on once a day for 6 hours isn’t great either.
To reduce the number of cycles:
- make sure window coverings such as shades and curtains are drawn closed during the warmest parts of the day.
- turn off lights, especially incandescent ones
- avoid heavy computer usage
- avoid using appliances that generate heat as much as possible
- keep the path to the a/c unit’s vents / registers clear from obstruction. This allows for proper air flow.
- use ceiling fans to circulate the cooled air more efficiently. (Many ceiling fans set on low use only about 20 watts of power)
- make sure the unit is cleaned (especially the filter)
Many A/C units don’t have an “active” thermostat – they simply run when you tell them to. Usually cheap, small room air conditioners of 5000 btu and lower have this problem. Is it a problem? Yes. The reason is because they simply keep spitting out cool air whether it is needed or not. Rotary dial air conditioners are notorious for this. They only have four settings – low fan, low cool, max fan, max cool. (Or something similar to that terminology.) If you select the fans, of course, only the fan will run. But if you select cool, the fan and compressor will run. And they won’t turn off until you specifically change the setting or turn it off. Thus leaving the unit at max cool will make both the fan and compressor run at top “speed” until you turn them off. That’s a terrible waste of energy.