Shower Techno

got one of those instant gas hot water heaters for the shower that has 1 degree increments for temperature adjustment.

For no good reason I have plotted how I adjust the water temperature with respect to the seasonal changes in air temperature (the Sydney monthly average at 9am).

In the plot below the blue dots show the air temperature, the red dots my blood temperature, and the green ones the shower setting.

I’m still struggling to see why this is interesting. But it is.

A little googling later; it’s reasonable to suggest that the water delivered at the shower head is 1 degree colder than on the dial.

Also, over the 6 foot drop (yeah, yeah I’m mixing units) the water temperature will cool by about 4 degrees or so by the time it hits your feet, depending on so many factors that they aren’t worth noting.

Assuming the head and shoulders are near the centre of your temperature perception, let’s say the water delivered is 2 – 2.5 degrees colder than the that shown on the shower dial.

Surprisingly, the shower is used as a cooling device for a good fraction of the year!

I guess this makes sense; our bodies are adapted to maintain temperature with air that is usually cooler than our blood temperature. Therefore, so should the water be.

The required temperature gap between the water and the body is less than the temperature gap between the air and our body because there is much more efficient heat transfer between and liquid and a solid, as compared to a gas and a solid.

It’s all consistent.

All of this since it’s easier to maintain body temperature at a value which is at the higher end of the regularly experienced air temperatures because the body’s internal heating systems are very good. They work by various exothermic chemical reactions going on in the organs.

However the body’s cooling relies entirely on heat transfer at the skin surface; a much more problematic proposition.

In total, it’s much easier using a temperature on the high end of the atmospheric values if, say, one were going to design such a human system and insist it had a stable temperature.

A final note – an invention of the day. A shower unit which automatically adjusts the temperature as per the plot below. Minor adjustments could be made on a daily basis and an initial calibration could occur to allow for differences in piping, roses and personal preferences. The plot could be used to automatically adjust the temperature and could be created according to the local climate, or, better still, the temperature adjustment unit could even just measure the current temperature and humidity, and adjust the temperature accordingly. This could even change during a shower as the room saturates with hot, humid water vapour and heats up.

That’s actually a good invention!