Taking a shower this morning I was struck, not for the first time, by how badly designed the mechanism for controlling the temperature is. Turn it a little to the right and the shower is uncomfortably hot. Turn it just a little back to the left and it is uncomfortably cold.
What is going on is pretty clear. The controller maps its position to the amount of hot water in the mix in a roughly linear fashion. All the way to the left is straight cold, all the way to the right is straight hot, any intermediate position is a proportional mix.
In practice, almost nobody wants a cold shower or, unless the temperature of the hot water is pretty low, a straight hot shower. What almost everyone wants is a mix within a fairly limited range—say from .6 hot to .8 hot—with the exact range varying both with the temperature of the hot and the cold water and the preferences of the person taking the shower.
Imagine, to make life simple, that the controller has a handle that can be rotated through an arc of a hundred degrees. In the simplest version of my improved controller, the zero degree position is still pure cold, since there may be some masochists who like a cold shower to wake themselves up in the morning. The hundred degree position is still pure hot, since the water heater might be malfunctioning and producing only lukewarm water. But the first ten degrees of rotation map into the range from 0 hot water to .6 hot water. The final ten degrees map into the range from .8 to pure hot. The other eighty degrees of rotation cover the range from .6 to .8, giving me much better control over the temperature in the range I care about. A slightly improved model, designed to take account of variations in the temperature of the hot and cold water in different houses and hotels, has an adjustment that shifts exactly where the central range is, used once and then left alone unless something changes those temperatures.
For the Silicon Valley market we have the intelligent version, which keeps track of what temperature the user actually takes a shower at and adjusts its central range accordingly. Its high end variant allows for up to four users with different tastes in shower temperature. Step into the shower, tell it which you are, and it automatically chooses a mapping that makes it easy to control the temperature over the range you care about.
For the next generation, we have the thermostatic version, which maps the setting of the controller not to the amount of hot and cold in the mix but to its temperature. Turn on the shower and for the first few seconds nothing is coming out, because the "hot water" isn't—it has cooled in the pipe between the water heater and the shower. When the temperature of the hot water reaches the level set on the controller, the shower turns on. Thereafter it adjusts the mix to give the temperature it is set for. As in the previous versions, the position of the controller maps to the temperature of the water in a non-linear fashion, designed to use most of its range to cover the range of temperature that the user cares about.
Do any of these already exist?