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WHO USED ALL THE HOT WATER!!! Need a simple temperature data logger ** UPDATE **
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floobydust:
It's the huge time-constant... bigger than I expected for cool down of a sensor on copper or iron pipe. So I thought maybe on a manifold of the sink? Here we use 1/2" copper pipe and plastic braided supply line to the tap.
Consecutive water use, I don't think you can ID the culprit with such slow data. Morning showers I imagine it's a lineup, rush and person after person.
Brumby:

--- Quote from: floobydust on August 23, 2023, 11:06:05 pm ---It's the huge time-constant... bigger than I expected for cool down of a sensor on copper or iron pipe. So I thought maybe on a manifold of the sink? Here we use 1/2" copper pipe and plastic braided supply line to the tap.
Consecutive water use, I don't think you can ID the culprit with such slow data.
--- End quote ---
I will ask you two questions:
 1. At what point can you say a particular water usage has begun?
 2. At what point can you say a particular water usage has ended?


--- Quote --- Morning showers I imagine it's a lineup, rush and person after person.

--- End quote ---
There is usually a minute or two as people dry off and get decent for the public traverse.  It's not as if party B is stripped off ready to jump into the shower as party A reaches to turn the water off.
Brumby:
Here is a photo of the setup:

Criteria used:
1. No idea what the optimum setup would be, so wasn't fussed about over-thinking an initial configuration - just wanted to get some data to get an idea of the real world
2. Quick and easy
3. Temporary fixture OK for starters
4. Placed on the hot water outlet pipe to gain maximum temperature swing because:
  a. This would allow easier identification of temperature increases
  b. This would produce the fastest temperature drops when water flow ceased because of the highest difference between pipe temperature and ambient than other locations
5. Placed as far as possible from the tank, to reduce bulk heating effects from the stored water
6. Sampling rate set at maximum available (every 10 seconds) to get best resolution possible
7. Transmitter placed on tank as high as possible for best Bluetooth range (it has magnets  :-+ )
Brumby:
Other considerations for future refinement:

* Place secondary sensor at tank outlet point to see if there is a detectable difference which might indicate flow rate.  (Higher difference implies lower flow rate; lower difference implies higher flow rate.)  I think it doubtful there is enough resolution to achieve this ... but it might be worth investigating

* Fit sensor via a clamp.  While being more permanent, this allows investigation of thermal coupling options.  Thick metal and/or short length provides greater coupling, resulting in the sensor seeing temperatures that are close to the actual pipe temperature.  Thinner metal and/or longer length will reduce that coupling and result in the sensor being more influenced by ambient air temperature.

Maybe something like this...   
In this latter case, while the temperature measured will be slightly less, it will still be notably higher than ambient and a continuing flow of water will maintain this temperature.  When flow stops, the lower coupling will result in the ambient air cooling the sensor more quickly, giving a much more visible indication.  Since absolute accuracy of temperature measurements is of no real importance here, this is not a problem.

* Custom project where:
 - More accurate sensors could be used and configured for best result in targeted temperature range
 - Only recording samples of interest - say 5ºC above ambient
 - Potential for custom software, including computation
floobydust:
I'll ask you once - what temperature delta constitutes the next person and imprisonment?  ;)   One time constant looks like about 7 minutes which may lead to mistakes if the heater turns on temp kicks up possibly and your window is only a few degrees.
I understand you can figure out shower duration by looking at the derivative of pipe temperature. I think you could get one more piece of info by sensing at the shower mixer outlet instead of the hot supply. I'm not sure why you have a mixer right at the tank.

Ideal shower temperature is anywhere between 37°C (98°F) and 40°C (104°F) and no more than 41°C (105°F).
Old showerheads were 5.5gpm or 20.8l/min. US national standard of maximum 2.5 gpm flow rate for shower heads was established through the Energy Policy Act (EPAct) of 1992. California is less at 1.8gpm.

Could I scam your system by taking a shower with master blaster high flow rate, or high temperature? Your graph would not tell you this.

A little math you can check - a 7 minute shower, 50% hot 60°C/15°C rest cold water to get 37.5°C is about 4.73l (10.4l  with high flow head) of hot water. But I like it hot, 42°C would use 5.6l (12.5l) of hot water. Not a big difference unless the cold water is much colder.
Flow.. well it's the big unknown.
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