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zone control using 2 port valves

Discussion in 'Plumbing and Central Heating' started by jamesBen80, 9 Jan 2019.

  1. jamesBen80

    jamesBen80

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    The whole system is balanced including the HW and i re-checked it after swapping the TRV's in case it upset anything. But even if the rads are completely unbalanced, when the TRV sensor head detects the room is at the correct temperature or above, it should shut and stop flow through the rad regardless what the valve the other end is set at as they are in series so either valve can limit the flow through the rad? If the rad was still hot when the room was 32C and the TRV was set on 1 of 1-5 what do the number relate to? Drayton say in their instruction that it has a range of 10C-27C so i assume 1 is 10C and 5 is 27C right? Also why does it matter how the radiator gives out its heat conduction, convection or radiation the result is still the same, the room is way too hot and the TRV seems to have no control over the room temperature.
     
  2. slippyr4

    slippyr4

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    It should detect, and it will. It’s not a complex device.

    Your rads may be balanced - in that the lockshields have been adjusted for 12, or 20 degrees temperature drop above the radiator, but that probably isn’t enough.

    When the TRV shuts off, the radiator is still hot and will then cool by warming the room. Some types of radiator have a high heat capacity (if they hold a large volume of water (and to an extent, if they have a lot of metal). Cast iron column radiators are pretty bad for this.

    You’re almost certainly seeing overshoot because of this. Is your pump speed set appropriately? If it’s not, you may be flowing far too much heat through the radiator when the valves are shutting, which won’t be helping.
     
  3. jamesBen80

    jamesBen80

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    Thanks Slippyr4, i'll try a slower pump speed as it's set on 2 at the moment, so i can slow it down to 1 and re-balance the system. One of the reasons I've gone for cast iron column rads is they hold the heat better than the pressed steel ones. Having lots of windows, all single glazed Crittle, with leaded light meaning it can be draughty, and most rooms have 3 external walls making the heat looses massive, hence the large rads.
    On a slightly different note. I've spoken to an old colleague of mine who used to work for the council as a boiler engineer, and he said they had lot of problems when they came to retro fit TRV's to the big old cast iron rads in public buildings, schools etc.. He found it improved the control-ability if the large rads were split in to 2 or 3 smaller sections and joined with a single pipe at the bottom and then 1 TRV and 1 lockshiled installed at the ends. Neither of us can work out why this would help, other than reduce the temperature across the 2 or 3 sections or rad slightly more maybe?
     
  4. DIYnot Local

    DIYnot Local

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