Shower Control
By: Martin Vetterli
Tags: Algorithms, Computer Science, Climate Change, Self Driving Cars, Engineer

Where we learn what a common house shower has in common with airplanes, self-driving cars and the climate

Photo by Davies Designs on Unsplash

You probably all know this uncomfortable moment when you want to take your morning shower in a hotel abroad, and you’re trying to adjust the water temperature. You switch on the water, and it is cold. Hence, you shift the lever to “hot”, but the water temperature stays cold. So you shift to even hotter and suddenly, it is too hot and you nearly need to jump out of the shower! Did you ever wonder why this happens, and how it could be fixed?

The engineering principle behind this procedure is called feedback control, and was invented by the British engineer James Watt in 1788 to control the speed of a steam engine. The process is based on a measuring device that lets off steam if the speed is too fast, avoiding a run-away steam engine. With his fundamental invention, Watt initiated the first industrial revolution, which was driven by steam engines.

Feedback control works by measuring the difference between your ideal target, in our example the water temperature that we want, and the current temperature. Based on this difference, the system decides to shift to hotter or colder. Once you reach the target, the difference becomes zero, and no correction is needed. But if the difference increases again, the system will automatically correct.

The most critical part for such a feedback control to work properly is a fast enough response time of the system. Take again the shower example: the water system may react slowly to our manipulation of the taps for example because the water heater is far away and hot water has to travel through a long pipe before reaching the spout. As a result, the response to our manipulation is slow, and it will be hard to get to the right temperature! By the way, the measuring device in this shower example is us, the humans, but you could also have a thermostat that drives to the right temperature.

In fact, feedback control is a process that occurs naturally and unconsciously in humans. We do it all the time. Here’s another example: imagine you try to walk a big distance with your eyes closed, for example across a football field from corner to corner. Now, most likely, you will miss the target. But with open eyes you would reach the goal with certainty, right? This is because with the eyes, you constantly check and correct your path. In other words, the eyes are reading the surrounding and feeding back to your brain, which controls your legs, thereby adjusting your path.

Apart from showers and baths, technological feedback controls are crucial for the control of many things, such as airplanes or self-driving cars. These are autopilots that make sure the plane stays on track, or that the autonomous cars stay on the road and avoid obstacles. An autonomous car is packed with sensors that constantly give feedback, such as cameras, radars and speedometers. Thanks to these feedback, the car expertly manoeuvers unknown territory full of obstacles, just like a human driver.

Speaking of feedback, which is too slow, like in the shower example, there is the case of CO2 emissions into the atmosphere. As it accumulates, the greenhouse gas leads to slow but steady warming of the atmosphere. But by the time humanity wakes up to this threat and reacts, it might be way too late. A typical case of delayed feedback control, but with dire consequences, much worse than a hot shower.

The most critical part for such a feedback control to work properly is a fast enough response time of the system. Take again the shower example: the water system may react slowly to our manipulation of the taps for example because the water heater is far away and hot water has to travel through a long pipe before reaching the spout. As a result, the response to our manipulation is slow, and it will be hard to get to the right temperature! By the way, the measuring device in this shower example is us, the humans, but you could also have a thermostat that drives to the right temperature.

In fact, feedback control is a process that occurs naturally and unconsciously in humans. We do it all the time. Here’s another example: imagine you try to walk a big distance with your eyes closed, for example across a football field from corner to corner. Now, most likely, you will miss the target. But with open eyes you would reach the goal with certainty, right? This is because with the eyes, you constantly check and correct your path. In other words, the eyes are reading the surrounding and feeding back to your brain, which controls your legs, thereby adjusting your path.

Apart from showers and baths, technological feedback controls are crucial for the control of many things, such as airplanes or self-driving cars. These are autopilots that make sure the plane stays on track, or that the autonomous cars stay on the road and avoid obstacles. An autonomous car is packed with sensors that constantly give feedback, such as cameras, radars and speedometers. Thanks to these feedback, the car expertly maneuvers unknown territory full of obstacles, just like a human driver.

Speaking of feedback, which is too slow, like in the shower example, there is the case of CO2 emissions into the atmosphere. As it accumulates, the greenhouse gas leads to slow but steady warming of the atmosphere. But by the time humanity wakes up to this threat and reacts, it might be way too late. A typical case of delayed feedback control, but with dire consequences, much worse than a hot shower.