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Water that changes temperature as soon as you turn the control
  [vote for,

If one were to make a shower mixer that took separate hot and cold inputs (as most do) but also had separate hot and cold outputs, you could run both of these outputs separately to where the shower rose attaches to the wall.

Now, instead of joining them with a tee you could plumb them concentrically, with one connector going around the outside and connecting to a regular pipe, and the other going to a smaller outlet in the middle of the former, and with a barbed outlet to which you could attach a plastic tube. That plastic tube runs right down the shower head itself (whether that be on a long hose or just a pipe fixed to a wall).

So rather than the water mixing at the mixer, it mixes in the shower head itself (mostly; please just ignore what happens when things get too close together while still being separated by a thin plastic wall).

This matters because the shower mixer changes the flow rate of the water in the two pipes, which changes the proportions when they are finally mixed, but if you mix them in the shower head then you don't have to wait for that mixture to get from one end of the pipe to the other to decide if it's the right temperature.

Simple as that!

b153b, Aug 24 2023

Like this? https://a.co/d/gvAhfgh
Water Heater for Bath Instant Hot Faucet Kitchen Heating Thermostat Mini Tankless LCD Digital Water Heater [21 Quest, Aug 25 2023]

Lo Hevanti Mila https://www.youtube...v=2IobZt-J3Lc&t=38s
Not understood a word! [pashute, Aug 27 2023]


       Even better to mix them at your skin i.e. have separate hot and cold nozzles. Just like a proper old fashioned sink with a hot tap and a cold tap. None of this mixer shite
pocmloc, Aug 24 2023

       // Even better to mix them at your skin i.e. have separate hot and cold nozzles //   

       Mix it at your core. Have a hot sauna and then plunge into ice water afterwards.
b153b, Aug 25 2023

       The other way you could make a shower instantaneously adjust temperature would be to have only cold water fed to the shower but have the water that’s falling between the shower and you be heated by a powerful microwave ray. Obviously this shower will have a maximum user height limit
hippo, Aug 25 2023

       I like it! In the past I had briefly considered this problem and concluded that it would be a pain too get the valves and controls all the way at the end of the faucet. Leaving the valve at its current location, but extending the separate hot and cold before mixing is a great way to enable that.   

       It seems like you might want a temperature sensor in each pipe by the shower head so it can automatically compensate for the heat transfer (that we are instructed in the original text to ignore) that occurs in the concentric pipes.   

       This is a much better solution than the link from [21 Quest] since that still has a long hose before the sprayer, and uses resistive electric heating. [b153b]'s idea gets control right up to the sprayer and takes advantage of whatever efficient heat source you already have (gas, solar, heat pump) rather then just using resistive heating. One thing this idea doesn't address is the water wasted waiting for hot water to fill the lines from the central water heater, but at least this can run just water from the hot line, then start regulating immediately to avoid overshooting.   

       You might almost make this work with a retrofit kit. Just have a small flexible hot water tube that you thread up the existing outlet pipe to be near the shower head. You could even have the two temperature sensors mounted and wired to the inside and outside of this flexible pipe so it measures the temperature just before mixing. Maybe add something at the end of the pipe to promote turbulent flow to help mix the hot and cold before it comes out as well.
scad mientist, Aug 26 2023

       Lo Hevanti Mila. [+]
pashute, Aug 27 2023

       I don't think this will have the effect you think it will have. The first problem with the standard hot-cold mixing shower is the warm up period where the "hot" water initially, isn't actually hot and so when you first turn the shower on, you essentially have two room temperature feeds. Slowly the cold water cools down a little and the hot heats up. This is annoying and is fixable with hotel-style hot water loops.   

       Anyhow, in your model there won't be much difference compared to the standard system since the dead volume up to the shower head is minimal compared to a fairly brisk flow rate (at least in civilized countries). You also want a little mixing as a safety feature.
bs0u0155, Aug 28 2023

       I respectfully disagree with [bs0u0155].   

       This invention doesn't create a "perfect shower". However, for whichever type of shower system it is applied to, it will improve the experience.   

       For example, I have a standard pressure balance valve in my shower. I initially turn it too full hot to flush the cold water from the hot line. I know that as soon as the water coming out starts to warm up a little, I need to turn the temperature down and let it warm up slowly, otherwise it will overshoot to nearly scalding. Then as I'm fine tuning the temperature (or adjusting to account for pipes heating or cooling) I have to make small adjustments and wait several seconds to see what the result was. I   

       On a high end system, you might have a recirculation pump or a local on demand water heater to reduce the wasted water and time waiting for it to warm up, and a thermostatic mixing valve to hold the temperature exactly where you set it, but if you decide you want to adjust the temperature of your shower, it will take several seconds for that to go into effect. I imagine that people who pay for a high end system would gladly pay a little more to reduce that response time from a few seconds to a half second.   

       I do agree that there needs to be some volume of water that is being mixed to avoid uneven temperatures from the shower head, but considering that most shower heads have some mechanism to reduce the flow, it should be fairly trivial to modify that mechanism so that it mixes the water well without having to have a lot of water volume in the mixing area.
scad mientist, Aug 30 2023

       OK I think I see your point. So the problem you're looking to solve is the dead volume between the mixer and the shower head. This should be something like a 0.5" (1.27cm) pipe for something like 1.3m. Which is about 160ml. A US standard flow* is 2.5gpm. So running the numbers means your dwell time between adjustment and felt temp change is about 1s. That ties in well with the length of time I wait between switching from bath tap to shower, so it passes common sense. Raising the mixer to nipple height and having a scalp-skimming shower head might reduce this by ~30%. Upping the flow rate to 5 could get you down to a 250ms dwell. Time saving in the ms is for a seriously pressed section of the population.   

       *Because saving water is important in a city that sits between two rivers with a flow considerably larger than all England's rivers combined.
bs0u0155, Aug 30 2023

       I have a rain shower which is probably 3m of wriggling around studs and joists and other pipes, but also the handshower is on the end of a hose on the end of a bunch of in-wall plumbing. I've also seen mixers a few metres away from the shower because apparently that means luxury or something. Those ones have a _really_ long delay. But maybe that's the price you have to pay for being fancy.
b153b, Sep 01 2023


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