We failed in designing Air Conditioners

Recently, I started using a car-sharing service. I find a car near me, hop into it, drive to my destination, and leave it there. It has been a joy to not worry about parking or maintenance -- and still come out on top financially. There is just one thing that I keep noticing: many of the cars have their climate control set to the lowest temperature possible.

In a Toyota that has climate control, if you dial the temperature down all the way, it shows "LO" (picture above). Depending on the outdoor conditions, that should push the temperature down to 16°C (60°F). I can't imagine anyone being comfortable at that temperature.

The plot thickened when I noticed this trend everywhere. I keep seeing the temperature of wall units being set as low as the interface allows. Who gave the remote control to huskies?

It took me way too long to realize that people don't care about what the target temperature is. They care about how fast the cold is delivered. It's easy to assume that if we tell the AC we need a low temperature, it will work the hardest so we get cooler faster. Perhaps someone's desired temperature is nowhere near what they set the AC to, but they figure when they get cold, they can shut the AC down.

This probably works. Not because it is sound reasoning and not because that trick will make the AC work any harder. The logic in the wall-mounted AC is that it delivers cooling as hard as it can until it reaches the temperature you want -- and then some, so that it doesn't have to turn back on for a while.

The real reason such manual overrides work is because, ultimately, it's the user who has to decide when they have had enough cool air.

I was slow to realize this fact because I am an industry insider. At school, we are conditioned to see reaching an indoor temperature as the objective of HVAC; even though in a previous article, I concluded that air temperature is a poor metric for determining human comfort.

When people are in a space for a long time every day, like their home, they gradually learn what number on the thermostat corresponds with their comfort.

For a shared car that has baked in the sun, however, the person who hops in only wants to cool down -- and cool down fast. At least, dialing down that thermostat all the way does something useful when the climate control is on Auto:

It makes the fans blast more air.