Friday, February 13, 2015

Wanted: A Better Shower Controller

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?

23 Comments:

At 8:40 AM, February 13, 2015, OpenID whswhs said...

How do you get hot water to come out of the hot water pipe if the cooled water hasn't come out yet?

 
At 8:46 AM, February 13, 2015, Blogger Mark Kaminsky said...

Great ideas all! Another advanced feature should be to adjust the shower temperature based on the ambient temperature (and perhaps even the user's skin temp!) - giving a colder shower in the summer and warm in the winter.

 
At 9:11 AM, February 13, 2015, Blogger Leslie Birt said...

Yes, some of these exist.
http://www.us.kohler.com/us/DTV-Custom-Showering-Experience/content/CNT2400429.htm

http://www.moen.com/whats-new/innovation/iodigital;jsessionid=3e996b0f7fc77d73771296c73214

http://www.faucetdepot.com/resources/building-your-luxury-shower.asp

 
At 10:09 AM, February 13, 2015, Blogger David Friedman said...

whswhs: I only thought of that problem after I made the post. Presumably the shower diverts the not yet hot water directly to the drain instead of through the shower head.

 
At 10:25 AM, February 13, 2015, Blogger Leslie Birt said...

whswhs + David Friedman: or you could have the "Not Hot" water redirected back to the heater until you get the right temp coming through..

 
At 10:57 AM, February 13, 2015, Anonymous Art Justart said...

Recirculating hot water system exists, as well.
http://www.taco-hvac.com/uploads/FileLibrary/100-41.pdf
Diverting it to the drain is essentially what you do now as you wait for it to warm up. What would be nice for drought affected areas is a shower with flow that could be stopped while soaping up and turned on again at the same temperature.

 
At 12:16 PM, February 13, 2015, Blogger John said...

Unfortunately since the government already regulates the amount of water allowed out of the shower for conservation I will predict that they will deem it their business to regulate the temperature also. Won't someone think of the scalded children.

 
At 12:18 PM, February 13, 2015, Anonymous Chris Wegener said...

Europe has many controllers which separate the temperature sand pressure functions into to separate control. It is then trivial to set the temperature to the desired value and only use the pressure control to turn the shower on or off.

 
At 4:27 PM, February 13, 2015, Blogger Ricardo Cruz said...

Chris, I am from "Europe", and I have never seen anything like that. Do you have any picture?

Older houses have stuff like this: http://www.sanitana.pt/imagens_produto/amb_torneira_grecia_chuveiro.jpg

More recent ones are something along these lines: http://www.drogariasantoantonio.pt/image/cache/data/afj/TORNEIRAS/torneiras%20(026)-500x500.jpg

 
At 6:18 AM, February 14, 2015, Blogger pjt said...

Ricardo, for instance look at this:
http://www.reuter-shop.com/oras-optima-thermostatic-shower-mixer-a32496.php

That's what I have at home. There are of course many other models from this manufacturer (Oras, a Finnish family company) and others.

The mixers have thermostats so that the water is right temperature (after some flow, of course, because it takes a moment before the hot water pipe fills up).

I'm rather surprised that America does not have this. It's been standard technology in Finnish bathrooms for years.

 
At 6:47 AM, February 14, 2015, Blogger Kri.st said...

Thermostatic shower controls have been standard technology in Swiss, and German bathrooms as well.
Basically standard feature everywhere that Nordic design is popular...

 
At 5:15 PM, February 14, 2015, Anonymous Elias said...

You'll only waste water for the first 10 seconds of turning it on. Assuming a reasonable flow rate of 3.5 gallons/ minute and the price of water being $0.004278/ gallon you'll waste about $0.0025 by just flushing your 10 initial seconds worth of cold water down the drain. I doubt you can build pipes redirection the water back to the heater at those rates.

 
At 2:19 AM, February 15, 2015, Blogger pjt said...

Over here (again, Finland), the standard way to build water pipes is to have a loopback of hot water circulation, i.e. the hot water is pumped in a loop all the time and the "one-way" branch from this loop to the faucet is quite short. Thus, you get warm water nearly instantly.

The cost of building this loop surely exceeds the cost of water that you'd let run if you had a one-way pipe only - particularly because we're not at all short of clean water - but we have this for convenience. The hot water circulation naturally also means using heating energy, but usually this doesn't matter because our climate is so cold that houses need heating almost all the time, so the heating energy is not really lost.

 
At 6:38 PM, February 15, 2015, Anonymous Alex said...

"In practice, almost nobody wants a cold shower"

I heard that cold showers have health benefits like stimulating the immune system. I can't quite bring myself to take true cold showers, but I have lately been turning my dial to 0.5 for the second half of the shower, which for most folks is probably 0.4 because my hot water isn't that hot. I wonder if this is doing any good.

 
At 4:52 PM, February 16, 2015, Blogger Benjamin. said...

I happened to recently be thinking of exactly the sort of temperature control you described in the last paragraph. It would just wait for the correct temperature and only let it out.

 
At 7:10 AM, February 18, 2015, Anonymous Anonymous said...

My comment here is not relevant to shower controllers, and I hope David will forgive me, but I've been a huge fan of David's since reading "Machinery of Freedom" in the mid 1970s, and I wonder whether David will read and comment on the just published book, "Climate Shock: The Economic Consequences of a Hotter Planet" by Gernot Wagner and Martin L. Weitzman.

 
At 10:16 PM, February 18, 2015, Anonymous Anonymous said...

You don't have to tell the shower who you are: the tub can sense how much you weigh, figure out who you are from that, then it can tell the shower.

 
At 6:32 AM, February 21, 2015, Anonymous Anonymous said...

Use nail polish. Find the perfect position. Put a dab of nail polish on each section, lined up exactly opposite each other. If you align the dots for future showers, the temperature should be perfect.

 
At 7:47 AM, February 25, 2015, Anonymous Anonymous said...

"Do any of these already exist?"

Yes.

There are also more basic valves.

 
At 7:49 AM, February 25, 2015, Anonymous Anonymous said...

This is the more basic valve I meant to link above. The one previously linked is a basic volume control valve, not temperature control.

 
At 4:01 AM, March 09, 2015, Anonymous Nigel Sedgwick said...

Apologies for being late in on the discussion.

One of the problems with shower thermostatic temperature controllers is that the mixing valve mechanism accumulates limescale. This affects the operation of the valve and means that there is a gradual deterioration, in effectiveness and in speed of control. Recalibration of the mixing according to the chosen setting is required from time to time (and even that becomes less useful over time). But providing this recalibration is not actually practical in passive control systems; it is probably too costly and poorly corrective in electronic systems.

It can help, IMHO and especially with passive control systems, to exercise the valve on every shower use. After the hot water has started to flow, keep it directed away from yourself and turn the thermostat control first to minimum temperature and then to maximum temperature (for say 2 or 3 seconds each). This causes the valve to try to move through its whole operating range, thus reducing the build-up and adverse effect of limescale. Then turn the setting to that which experience tells you is about right. Lastly redirect the mixed hot and cold water onto yourself and make any necessary (and modest) final changes to the thermostat setting.

Best regards

 
At 10:21 AM, March 21, 2015, Anonymous Alex Tabarrok said...

The second generation of Friedmans tries to solve the fool in the shower problem!

 
At 11:27 AM, April 23, 2015, Blogger Alan Geal said...

Perhaps this British kit will fit the bill:

http://www.aqualisa.co.uk/mixer-showers/axis-thermo-concealed-mixer-shower-with-adjustable-head/

We're had an Aqulalisa Axis Thermo for some 3-4 years, with the usual (i.e. heavy) family loading... it's been effective and reliable throughout. Con: they're not cheap, although the range - cost and specification - is wide.

 

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