S-Plan vs Y-Plan for Evohome ?

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  • jvallis
    Automated Home Jr Member
    • Feb 2018
    • 29

    Originally posted by DBMandrake View Post
    But you can't frost protect the pipes because unless the rooms are below 5C the HR92's won't open therefore no flow through the pipes. In contrast a conventional system with manual TRV's will generally have the TRV's set to normal room temperatures when the system is scheduled "off", so the TRV's are open and ready to flow should a frost stat somewhere in the system fire the boiler.

    I haven't worked out an elegant solution to this problem.
    I think you have. Because if the boiler does it's frost thing, then the pump-controlled zone valve will open, and you'll get defrosted pipes. If you're on a recommended Fig 4 set up, same thing. If an HR92 demands frost protection, the whole shebang needs to circulate, and the pipes will be fine too, irrespective of whether the rest are open or closed. The worst case scenario is the ABV on the heating circuit will bypass (which is why the ABV should be in the longest/furthest away heating loop).

    In any case I feel the issue is moot. Who would have a setback temperature with evohome, even if away from home of less than 8-10C? To allow a building to fall to such a low temp you're going to have many other problems with heat expansion/contraction (e.g. plaster cracking, brick movement), and the only time I can think of - when doing building works - you'd probably have drained the system.
    Last edited by jvallis; 3 December 2018, 12:38 PM.

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    • DBMandrake
      Automated Home Legend
      • Sep 2014
      • 2361

      Originally posted by jvallis View Post
      I think you have. Because if the boiler does it's frost thing, then the pump-controlled zone valve will open, and you'll get defrosted pipes.
      No, because if all HR92's are closed there will be no flow through the pipes beyond the automatic bypass valve whether the zone valve is open or not. Water can't flow if there isn't a complete loop.

      Also in a standard S-plan configuration the heating zone valve will NOT open if the internal frost protect in a boiler triggers. However in my modified S-Plan configuration which tries to keep the heating zone valve open most of the time it would.
      If an HR92 demands frost protection, the whole shebang needs to circulate, and the pipes will be fine too, irrespective of whether the rest are open or closed.
      Which pipes ? Only the branches that are actually flowing will heat up, so depending on the topology many of the pipes will remain cold. For example in my system there is a 22mm manifold from the boiler that runs under the floor to a central point and there is then a star configuration from the end of the manifold to each individual radiator. Upstairs is handled by a completely different branch and doesn't go via the main underfloor manifold.

      So a single HR92 being on would ensure the 22mm mainfold was protected, but all the branches to the other radiators would remain cold, and some of them are many metres long. The only way to fully frost protect pipes is for all TRV's to flow in frost protect mode.
      The worst case scenario is the ABV on the heating circuit will bypass (which is why the ABV should be in the longest/furthest away heating loop).
      How many installations have their ABV anywhere other than the boiler closet, realistically ? In my installation it would need to be in the middle of the house under the floor in a very inaccessible position. No thanks. Not to mention that the ABV has to be installed before a heating zone valve, which is often in the boiler closet as well.
      In any case I feel the issue is moot. Who would have a setback temperature with evohome, even if away from home of less than 8-10C? To allow a building to fall to such a low temp you're going to have many other problems with heat expansion/contraction (e.g. plaster cracking, brick movement), and the only time I can think of - when doing building works - you'd probably have drained the system.
      You're confusing room temperature with under floor temperature.

      We have a raised floor with about a 1 metre ventilated crawl space under the house with pipes running willy nilly in the crawl space. On a cold windy winter night it can get very cold under there - much colder than inside even unheated rooms.

      Comment

      • jvallis
        Automated Home Jr Member
        • Feb 2018
        • 29

        Originally posted by DBMandrake View Post
        You're confusing room temperature with under floor temperature.

        We have a raised floor with about a 1 metre ventilated crawl space under the house with pipes running willy nilly in the crawl space. On a cold windy winter night it can get very cold under there - much colder than inside even unheated rooms.
        If I were you, I'd get those pipes lagged. Also for efficiency, so that you can further keep your flow temps lower.

        Comment

        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          Originally posted by jvallis View Post
          If I were you, I'd get those pipes lagged. Also for efficiency, so that you can further keep your flow temps lower.
          I've lagged quite a few of them a couple of winters ago, but some of them are REALLY difficult and unpleasant to get to as it means crawling through very tight holes in the brick support walls under the floors and.... well... I'm not as skinny as I once was and nearly got stuck in one last time... As they are long runs of 8mm microbore some of them are also quite twisted and wriggly so don't lend themselves well to standard foam pipe lagging without spending a lot of time in difficult locations trying to straighten the kinks out a bit. I intend to grit my teeth and do some more next summer though.

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