Archive for July, 2007

Idea for a new thermostat design

A striking fact: most of my recent roommates — all smart enough to get into MIT — completely failed to understand our thermostat. At first, I attributed this to the notion that MIT students simply lack many everyday, non-academic skills. This may have some truth to it, but the wider conclusion is that the standard thermostat design is just not intuitive.

Here is how a thermostat works: The user sets an (unmarked) temperature with a dial or slider. From this, the thermostat extrapolates a low-temperature cutoff and a high-temperature cutoff. The low cutoff is lower than the user setting, and the high cutoff is higher than the user setting. The thermostat turns on the air conditioning if the temperature rises above the high cutoff. The air conditioning then REMAINS ON until the temperature is pushed all the way past the low cutoff. The temperature then rises naturally until it hits the high cutoff again, and again the air conditioner kicks in. (Switch “high” with “low” in the case of heating.) This makes sense technologically, because air conditioners and heaters are more efficient if they stay on for a while.

The way you are supposed to refine your temperature setting with a thermostat is as follows: If you are too cold, you move the setting until the air conditioning clicks off. This is your way of saying “I don’t want it to get colder than this.” Alternatively, if you are too hot, you move the setting in the cold direction until the air conditioning kicks in. “I don’t want it hotter than this.” If your range of acceptable temperatures is less than the thermostat’s, then you will be changing your setting on every cycle – but you won’t be changing it very much.

Judging from the vast range of settings I have found my roommates leaving the thermostat in, here is how they seem to WANT to interact with it: “Right now I’m really really hot, so I’m going to turn the temperature way down. Five minutes later, I’m still pretty hot, so I’m going to turn the temperature down some more.” At this point, the temperature setting is way colder than the comfortable level, so eventually it will become very cold in the apartment and the roommate will be really really cold and thus turn the temperature way up. Cycle repeats.

So here is my new thermostat design. There is a round dial with no temperature markers — the only markings indicate the “colder” direction vs. the “hotter” direction. If the user is very very hot, they turn the dial strongly in the “cold” direction. This tells the thermostat that the user temperature setting should be set substantially below the current air temperature. Five minutes later, it has cooled down a bit, but the user is still hot. They go back to the thermostat and turn it in the “cold” direction, but not as far as before because they are less hot. The thermostat correspondingly sets a user temperature that is moderately colder than the current air temperature.

In other words, the “user temperature” is determined not by the absolute position of the dial but by the amount of turning in a given adjustment. This design allows people to indicate their level of discomfort, as they seem to want to do intuitively, and avoids the “escalation” problems that occur with the traditional thermostat design.

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