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Potential Domestic Unvented Hot Water Cylinder Issue.

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Mornin' All,


yesterday I visited a horse stable block in the middle of nowhere. One of the stalls has been converted into a "utility room" for caravaners. It contains a cheap dim L.E.D. ceiling light, a washing machine, a tumble drier and a small domestic unvented water heater for hot water, containing two 3kW heating elements, all run on a 4.0mm2 underground S.W.A. cable about 100 metres away in a house. But that is not the issue here.


The unvented cylinder has lots of copper pipework attached, all with no thermal insulation. Bearing in mind that this "room" is a very well ventilated horse stall outside, what are the main safety concerns regarding the unvented hot water system?


Thoughts please.


Z.

  • 0
    Dad, could this happen?

    https://www.youtube.com/watch?v=5pVQryuKMj8



    Z.
  • 0
    It is still happening in our day and age son.

    Water Heater Explosion - YouTube


    Z.
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    Do they drain it in winter ? A lot of scout sites have toilet/washroom blocks that are little more than unheated sheds that protect little more than the embarrassment of the user,  and can be cleaned by hosepipe at the end of the day during the muddy season.  Frozen pipes  have almost disappeared off the RADAR of the  modern centrally heated house, but in such case it is common if provision is not made to drain down at the end of season.

    The other hazard, perhaps less so on an adult campsite is fiddly fingers doing silly things and turning the power off while someone else is using it, or in the case of the gas ones, shutting the valves on the cylinders as a practical joke.


    I'd expect some sort of overpressure feature on the tank or plumbing, a deliberate weak link if you will, and in the demos of exploding tanks, such safety devices are bypassed.

    M
  • 0
    mapj1:

    Do they drain it in winter ? A lot of scout sites have toilet/washroom blocks that are little more than unheated sheds that protect little more than the embarrassment of the user,  and can be cleaned by hosepipe at the end of the day during the muddy season.  Frozen pipes  have almost disappeared off the RADAR of the  modern centrally heated house, but in such case it is common if provision is not made to drain down at the end of season.

    The other hazard, perhaps less so on an adult campsite is fiddly fingers doing silly things and turning the power off while someone else is using it, or in the case of the gas ones, shutting the valves on the cylinders as a practical joke.


    I'd expect some sort of overpressure feature on the tank or plumbing, a deliberate weak link if you will, and in the demos of exploding tanks, such safety devices are bypassed.

    M


    I believe that the system is used all year round, as one couple lives full time in a caravan. These people are gormless (there's an old term) and have a nearly overflowing cess pool sunk into the lawn of a holiday let home. I attended to estimate for a cess pool pump system.


    Also,  the highly educated man who looked over my shoulder and gave me advice about a faulty immersion heater of the unvented system, had not turned up the thermostat for the one remaining good immersion heater thus that is why the water would not get hot.


    Z.


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    Steam explosions can indeed be very powerful. Any modern cylinder should have at leat three levels of protection though - on all electric ones it's usually the immersion thermostats, a non-auto resetting thermal cut-out and then a temperature/pressure relief valve. Freezing shouldn't really defeat any of those if it's installed correctly - since the problem will only arise when the water temp exceeds 100°C - at which point it's unlikely anything in contact with the cylinder will be frozen. There should be a tundish after the PRV so even if the outflow pipe has frozen water in it, pressure should still escape harmlessly.


    Freezing could well ruin the pipework and cylinder itself of course - but not an explosion risk I would have thought.


    It's all a bit different to the old back boilers behind open coal fires - which used to explode quite regularly when the feed/vent pipes to the cylinder or cistern in the loft froze.


       - Andy.
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    I perceive some risk of explosion in frosty weather.

    If the pipes freeze and the water in the cylinder cools, then when the heater is turned on the cylinder contents will expand, and with pipes blocked by ice where is the expansion to go ? I think that the tank might then burst at normal operating temperatures.


    A vented system would be safer IMHO, and with trace heating tape applied to the vent pipe.


    It would be better to insulate and slightly heat the utility room to avoid frost damage not only to the water heater but to the rest of the installation.
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    Zoomup:
    These people are gormless (there's an old term) and have a nearly overflowing cess pool sunk into the lawn of a holiday let home. I attended to estimate for a cess pool pump system.


    Re the Cesspit, only one answer really:-  https://www.youtube.com/watch?v=eOwven0Rt94

    Enjoy!

    Clive
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    AncientMariner:

    Zoomup:
    These people are gormless (there's an old term) and have a nearly overflowing cess pool sunk into the lawn of a holiday let home. I attended to estimate for a cess pool pump system.


    Re the Cesspit, only one answer really:-  https://www.youtube.com/watch?v=eOwven0Rt94

    Enjoy!

    Clive


    Well Clive, I am now considering putting in a medical claim after I split my sides. Blaster Bates is hilarious.


    Z.


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    If the pipes freeze and the water in the cylinder cools, then when the heater is turned on the cylinder contents will expand, and with pipes blocked by ice where is the expansion to go ?

    Hopefully into the internal air gap or closely associated expansion vessel - expecting the supply pipework to take up expansion is a bit old hat these days - too easily defeated by by water meters (which usually prevent backflow) and risks of warmed water (with associated risk of bacterial growth) being supplied to cold drinking taps.


      - Andy.
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    When we had our plumbing replaced recently due to low water flow on our main supply (what do you expect in a small hamlet 4 miles from a city?) and they thought the solution was an unvented hot tank. As you need a minimum of 20 litres a minute flow it's still sitting unused in our loft if any one wants a direct hot water cylinder with coils for solar panel, boiler  and 2 I/H.

    Real bargin, v/Cheap if you get it down again as it took 3 to get it up.


    Plumbers!!

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