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  1.  
    I have two questions about heat sink radiators that I'd be grateful for any advice on.
    (1) is it possible to have a valve that only directs the circuit for a stove back boiler through the heat sink radiator when the cold return flow is above a certain temperature? (see schematic).
    (2) is it even necessary to have a heat sink radiator if you can instead have a valve to circulate excess heat through the underfloor heating if there is a risk of the thermal store overheating? (see second schematic).
      20170304 Plumbing Schematic.jpg
  2.  
    Second schematic:
      Screen Shot 2017-03-04 at 19.51.39.jpg
  3.  
    A heat sink rad must be fail safe.
    So to answer 1) - You should not have the situation that requires a valve to operate by electricity in the event of over heating. Also valves can jam and if they are rarely used they are more likely to jam. Would you actually remember to test it say monthly?

    And the answer to 2) is much the same as 1). with the addition that you are also relying on a pump - that needs power - sods law says it will be needed during a power cut!

    Having said that if you are running a wood burning stove with a back boiler why would you be putting on so much fuel so as to over heat the TS. You should be running your stove with an eye to what heating is required. If the room is too hot don't load up the stove, if the TS is up to temperature don't load up the stove.

    Stoves with back boilers are always a compromise between space heating and water heating - You have to learn your system and what to put on the stove and when. And put up with the limitations that a dual function stove gives.
  4.  
    Thanks Peter! Is it not possible to get valves that operate without electricity?

    I was surprised at 2, as well. It was recommended by Morso though, so it's hard to discount. One thing they say is that heat sink radiators have trouble dealing with modern boilers anyway.

    I also agree with you about the stove. You wouldn't be stoking it without some thought or knowledge about what is happening in the thermal store. Then again, there are times when others not so familiar with the heating are left in charge.
    • CommentAuthorGotanewlife
    • CommentTimeMar 5th 2017 edited
     
    Posted By: ComeOnPilgrimIs it not possible to get valves that operate without electricity?
    Yes, my wood burner has a valve on the quench coil that opens at 90 deg C and then it closes once the water temp comes down. I guess that this type of valve doesn't need a head of water to work and as that is the only difference between a gravity fed heat dump radiator and the quench coil set up I assume it would work. Radiator TRVs use the same type of technology and this is even more obvious if using the remotely operated TRVs - ie a thin wire to a sensor. Getting the heat dump radiator sized correctly (genuine worst case) and the pipes to and from sized and fitted correctly is of course critical.

    I would definately not consider an electrically operated valve in any type of safety scenario let alone a solution needing a pump to work!!!
    Posted By: Peter_in_HungaryA heat sink rad must be fail safe.
    Not so sure - fail safe is a very high bar indeed - eg if the valve fails on my quench coil my boiler would become a giant 400 litre kettle and once most of the water had gone....melt down.... yet quench coils are the standard solution for most (all?) big wood burners! I think such valves must be up to the job of opening a heat dump radiator and so if not fail safe they must be really, really reliable.
  5.  
    Posted By: GotanewlifeNot so sure - fail safe is a very high bar indeed - eg if the valve fails on my quench coil my boiler would become a giant 400 litre kettle and once most of the water had gone....melt down.... yet quench coils are the standard solution for most (all?) big wood burners! I think such valves must be up to the job of opening a heat dump radiator and so if not fail safe they must be really, really reliable.

    Heat sink rads are normally installed with at the most manual valves which are left fully open (only used for maintenance or to remove the rad for decorating) This is as close to fail safe as you can get (short of someone deliberatly closing the valve - but then I have seen heat sink rads installed without valves).

    The quench coil is perhaps the third in line of safety, the first being the operator not overloading the system, the second, in the event of a power cut the Laddomat will open circuit and allow gravity flow from boiler to TS and the same power cut will turn off the fan in the boiler which drastically reduces heat output, and then if you still have problems the quench coil comes in to play.

    Posted By: ComeOnPilgrimI also agree with you about the stove. You wouldn't be stoking it without some thought or knowledge about what is happening in the thermal store. Then again, there are times when others not so familiar with the heating are left in charge.

    A lot of solid fuel heating systems need a level of awareness by the operator not to screw things up. Overloading wood burners when the system can't cope is probably the best example, choosing how much wood to put on depending on the heat in the system and the type of fire wood to hand is a more refined skill set to get the most out of the system.
    If you are having people unfamiliar with the system use the stove then perhaps a temperature gauge on the TS with a repeater gauge next to the stove with instructions not to put more wood on the stove if the gauge reads (say) 85 or more. A simpler (cheaper) solution would be to have a thermostat switch on the TS set to 85 deg. which operated a warning light near the stove with instructions not to load the stove if the light is on.

    For what it's worth my TS has 5 temp gauges from top to bottom which I use to guesstimate the amount of heat in the TS and so fill the wood burner accordingly. IMO some sort of temperature sensing/monitoring on the TS will be needed otherwise how will you know where you stand. And I don't think one gauge ant the top and another at the bottom is enough because if the stratification is good then those two don't give enough information.
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