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Solar storage tank - circulation?

  • 30-04-2013 11:44AM
    #1
    zagmund
    Registered Users, Registered Users 2 Posts: 2,501 ✭✭✭


    We have a new 500l solar storage tank installed, with a gas boiler for topping it up. All seems to be working well on a macro scale - the sun is out, our water temperature is going up.

    However, on a micro scale there seems to be a little weirdness which I don't understand. This morning, before the sun came out we had 22 degrees at the bottom and 34 degrees at the top. Now, after a couple of hours of sun we have 31 degrees at the bottom (good) and 31 degrees at the top (not good).

    I'm 99% sure no hot water was drawn off the top of the tank this morning, so the only way I can explain the drop in temperature at the top is if the water in the tank circulated as it was heating up from the bottom. Is this expected behaviour?

    The drop of 3 degrees is no big deal at the moment, but if the top of the tank was (say) 50 degrees in the morning and we managed to churn cold water up into it and drop it 5 or 10 degrees it changes from being useful hot water to not useful warm water which we have to heat with the gas if we want a shower.

    Is this drop in temperature at the top expected behaviour, or do I have something funky going on in my tank?

    z


Comments

  • #2
    BaldEagler
    Registered Users, Registered Users 2 Posts: 2 ✭BaldEagler


    Hi Zagmund,

    I'm a solar installer and i've seen this a few times.

    First thing to check is did anyone draw hot water off during this period. If not then a drop of a few degrees might be accounted for by the position of the temperature sensor pocket. These are usually located near the top of the cylinder but not at the top so the heat may have risen to the very top where the hot water outlet is.
    Hope this helps

    Paddy


  • #3
    zagmund
    Registered Users, Registered Users 2 Posts: 2,501 ✭✭✭zagmund


    Thanks for the reply.

    I'm pretty sure nobody drew off water. As far as I remember I was the only person at home at the time.

    Your description of the layout is correct - the thermostat is not at the very top of the tank but is a few inches below. It's maybe 95% of the way up the tank from the bottom.

    I'm working on my own set of thermostats (measuring the temperature of the outside of the tank) hooked up to an Arduino. These will give me a better spread of temperature readings than the existing 2 which just tell me that the top is hot and the bottom is cold and provide no granularity.

    z


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