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convert cold water tank/vented cylinder installation into vented heat store with HIU for DHW

Discussion in 'Plumbing and Central Heating' started by mafj, 19 Sep 2020.

  1. bernardgreen

    bernardgreen

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    You need to think carefully before adopting your hypothetical final set up.
     
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  3. oldbutnotdead

    oldbutnotdead

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    I do wish you'd make your mind up- either 'no part of system is sealed' or 'no part of system is vented'....
    Your Phase 1 (twin coil cylinder) is fine (as in will work) but it lacks the elegance of split hot water (so unless you're careful with the pipework you'll get significant shower flow and temp variations if another hot tap is operated).
    Your Phase 2 might work and might not- the cylinder may not work as a neutral point with that pipe setup, you might end up pumping primary hot up into the F & E tank, expensive and dangerous. If you are going to replace the cylinder, get one with a fast recovery coil at the bottom as well as the top coil.
    Header tanks taking up valuable space- move them (subject to keeping feed & vent runs as vertical as possible).
    Shower pressure poor- put a pump and a Surrey flange on.
    Nothing stopping you (apart from cost) fitting a combi for kitchen hot water and keeping the cylinder for bath/shower (or the other way round).
     
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  4. mafj

    mafj

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    Thanks guys that is really helping a lot to run this through you. I see your points and am getting a bit hesitant myself.
    The last thing I want is to needing to bath in a kitchen sink in cold water and to flush toilet with a bowl for a week,
    with some bits and bobs dragging for months. And to get my family through this process.


    I kind of realize now that instead of making some piecemeal solution it would be better to do this properly:
    • build new system in the loft next to cold water tank with new cylinder with either some really powerful coil or PHE for the whole house unified pressurized system
    • when all is ready - switch to the new system
    • decommission old tank and boiler

    The switch would involve
    • move overflow pipe
    • switching the boiler loop - two connections
    • connect mains cold water
    • switch cold and hot water of:
      • bathroom bath/basins/cysterns
      • shower
      • kitchen hot water - just cold

    So in total 8 connections - I would have the piping prepared - just cut old copper and reconnect


    Just a quick schematic thanks to systemdesigner.co.uk.
    Comments:
    * Left hand side (boiler/heating) is in fact is currently a bit different : just common inlet/outlet from boiler + tri-state valve and controller
    works good I would not change it (the tool was unable to model it on the picture below).
    * The tank I'd take the simplest - just six connections in total.

    I'll come with more accurate drawing in due time.


    upload_2020-9-20_21-59-36.png
     
  5. mafj

    mafj

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    Where have you sourced this cylinder from?

    Would there be any affordable cylinder for my design with either coil or PHE?
     
  6. mafj

    mafj

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    Last edited: 20 Sep 2020
  7. oldbutnotdead

    oldbutnotdead

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    Have a look at this lot https://store.heatweb.co.uk/product-category/heatbank-pandora/
    Lot cheaper than Gledhill.
    Then take a breath and decide what OUTCOME you want rather than continuing with a scheme primarily designed with what you had available.
    With a single bathroom and a single controlled heat source (your gas boiler) there are many cheaper less disruptive options than a thermal store. Shower pumps work very well, cost including the mods to your existing cylinder £200 or so, if you want the shower pump to give you a turbo bath fill thats possible too.
    Thermal stores work well when combining heat from woodburners, wet solar, pv solar, gas, oil.
     
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  9. mafj

    mafj

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    I have been just looking at https://www.plumbnation.co.uk/site/gledhill-pulsacoil-stainless-thermal-store-cylinders/
    And perhaps I misunderstood and the price £945 is for cylinder alone? while I initially thought the price is for cylinder and PHE/pump.
    ... on the pictures it looks like one integrated unit - the same in datasheet - would you be able to tell me?

    Pandora seems to be £1600+ for the smallest tank.




    TBH I started with considering the idea of the pump. Then I thought it is not really that much less work than swapping to PHE/pump integrated module, with
    the latter having benefits of swapping over the entire system to mains pressure over time.

    Finally, I got thinking that I could get the entire system for £945 minimizing effort on my part to swapping over the pipe connections.
    And gain all the benefits - mains pressure on all the premise, instant hot water at high rate, emptier loft space, space for water conditioning system, free airing cupboard.
    And no reg work needed (no gas nor pressurized tanks).
    For £945 VAT inclusive I could take a punt.

    I could imagine myself just going after my primary drivers:
    and as you suggest getting pump for shower and pump for kitchen.
    It would be easy job - for shower: 4 pipe cuts in the loft and few speed-fit connectors, plug the pump and voila,
    slight extra work I'd need to do another pump for the kitchen - just hot water - well easy as well. That would make two pumps - some £300-£400 altogether
    (perhaps I could use one pump and feed the sink off the shower hoping aerator would limit the use to prevent interference).

    The drawback is that if - further down the line - I would decide I needed to switch over to some more comprehensive system,
    the pumps would be a sink cost. Well, I'd benefit with some 3000 showers and aerated kitchen faucet and happy wife).
    Probably not that big a drawback.
     
  10. oldbutnotdead

    oldbutnotdead

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    Must have linked you to the wrong page, there are cheaper (£600) units on there.
    I'll repeat- the space occupied by the tanks in your loft is not wasted if you don"t have any other use for that space.
    Gravity feed to kitchen and bath taps if plumbed correctly (22mm pipe) can be fine even with 2m head-pressure may be tiny but flow rate will exceed most combis. Single shower- fit a pump & flange.
    Big bonus with vented & cylinder & shower pump- your local water board can reduce your supply to statutory minimum (10 litres/min at 1 bar) and it won't affect your shower or bath experience at all. Combi or mains pressure hot water- well that would be a sad waste of cash wouldn't it.
    End of the day its up to you but you do seem determined to throw a lot of cash in an erroneous direction
     
  11. mafj

    mafj

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  12. bernardgreen

    bernardgreen

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    Newark Copper Cylinder Company

    upload_2020-9-21_2-28-4.png
     
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  13. mafj

    mafj

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    Update,
    I have eventually went on with a shower pump (RP50PT) that feeds shower (both hot and cold) and feeds kitchen (hot only).

    It is a bit of love and bit of hate.
    * Flow at shower went up from 2L/min to 6L/min mixed and pressure is sensible now.
    Less than expected but you can tell from numbers - much more.
    Pressure at 1.3 bar... does not feel as strong.
    * Flow in kitchen is 3L/min hot ... bit low, up to 30s waiting (some 10m pipe in 15mm, meaning 1.45L volume)
    * temperature regulation is an issue - pump kicks in at 2L/min flow - meaning a bit surprise at shower when cold flow drop below 2L pump switches off and hot water dominates.

    One source of my issues is having gone for positive pump. I reckon universal pump would trigger on drop of pressure not on flow.
     
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