Measure temp inside hot water cylinder

  • Ok bit of background I have solar at home and have built a power wall . Still have excess 9 months of the year so want to heat some water for free, only snag have a combi boiler

    Discovered mine will accept main water temp upto 60 Deg so thinking add a hot water tank before the boiler use less gas.

    Only problem I want to ensure that the temp in the tank reaches 60 Deg at least 30 mins each day to limit bacteria

    My solar system has mqtt do turning the heater on and off shouldn't be to hard.

    Any recommendations for measuring the water temp ?

  • Water sensors at the top and bottom of the tank could vary wildly.

    Infra red sensor could tell the temp on the outside of the tank, but that's about it.

    With my tank I put the sensor (DS18B20) in a small gap of the insulation and then covered it over with more insulation to try and avoid draughts etc. But I am not sure it is enough for health and safety with regards to bacteria. You really don't want Legionella spraying from the shower!....

    At the moment that's about all I can think of.

  • @arden Think you have this concept in reverse, boiler and solar feed a common tank called a buffer tank, boiler feeds direct, solar via an internal exchange coil.
    Read about such an arragement many years ago, but it would not have been a combi then.
    He used two thermostats in cylinder pockets at 1/3 and 2/3 levels, one triggered the boiler, another triggered the solar circulation pump. The solar was probably controlled by the lower thermostat, the boiler only cut in if the solar had insufficiently charged the tank.
    It got rather complicated from memory and was many years ago, but what stuck in my memory was the buffer had to be stainless cylinder.
    As above, DS18B20 would be fine attached to the inner tank wall, if you could extend the one-wire to the solar manifold, even better as you could read all off one pin..

  • @zboblamont , @arden

    An impeller to stir the water in the tank would be a good idea if you have access to the internals of the tank and can fix it.

    There are 3D printable ones (search for lilly impeller) that are very small that produce a huge amount of movement of the water available to make.

    This would greatly help even out temperature fluctuations.

  • A little of topic, but is it really that important to have the water heated so high before it comes out of the shower? I have a gas instantaneous heater and I set the temp using a control panel. When I shower I set it somewhere between 37 and 41 degrees C and then turn the hot water on to shower with no cold water. The heater is just heating up the cold water that comes into my house. The town water here has lots of chemicals added to it to kill bacteria so it should be ok, but this post got me thinking...

  • @skywatch Ehm, no...
    Thermal layering is the natural state, and one which enables you in this case to control the two heat sources.

  • @homer Chlorine is in the system to prevent biological growth in the pipes and destroy any bacteria encountered, a fairly uncommon occurence if the network is properly maintained/scoured.
    Chlorine residual falls over time, it's depletion accelerates with heat.
    Most boiler manufacturers cite 60c as free from legionella formation, instant hot water units generally mix hot and cold to achieve the selected temperature, so no need to bump your life insurance cover.... ๐Ÿ˜‰

  • @zboblamont

    its solar electric I have not thermal
    this will explain what I'm trying to achieve

  • @arden I realised about an hour ago that a typical combi diverter for the heat exhanger to heat potable water is triggered by flow, so diverter valves would be needed in any case...

    Understood on PV reserve, presumably an inverted supply to a standard AC immersion element is envisaged, they used to come with built in thermostat...

    You could place multiple DS18B20s against the inner shell to get an even better picture of the temperature gradient and better control if you wished.
    I had looked at a buffer tank for the combi here which was as I described earlier, but it was so crazy expensive I didn't proceed with it...

  • If you really care about your health, call the manufacturer of measuring devices or the manufacturer of containers and specify how to correctly measure the temperature of the water to make it safe.

    I have a problem with drinking water, after boiling it is worth it to pass through additional filters, such as these Of course, when I asked the manufacturer and the seller, they all shouted that it was vital, but I doubt their words. Now Iโ€™m just buying bottles of drinking water and itโ€™s awful, tired of it.

  • thanks all the design has changed I plan to heat some medium and have the water pass though a head exchanger what way standing water will never be consumed later

    there is a commercial product called sunamp which is designed for this purpose

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