Evohome without HR92s

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  • fezster
    Automated Home Sr Member
    • Dec 2017
    • 72

    Evohome without HR92s

    Hi All.

    Having browsed this forum for a few hours, I'm being tempted to spend some money to improve my heating.

    I always thought Evohome was about having individual TRVs on each radiator, but it seems Evohome paired with Opentherm can allow smart controls to be used on a regular S Plan Plus heating system, and gain efficiency by controlling flow temperatures (in my case, on a Vaillant 438, by adding a VR33 controller).

    Ideally, I'd have HR92's on all of my radiators, but with 25 radiators in total, it's going to cost a small fortune. So I wanted to know if anybody started off with a system without the HR92's and if so what the recommendations are on the controls to purchase. Requirements are:

    1. Have thermostats on 2 CH zones with radiators, which can adjust temperatures at various times of the day automatically (and weekday/weekend adjustments)
    2. Control boiler flow temps based on the internal temperature (and ideally, with weather compensation too).
    3. Have hot water priority to boost the flow temp to an unvented cylinder (if necessary, by using a separate sensor in the cylinders dry pocket).

    And finally - is there any benefit to using HR92's on only some radiators and adding more as funds permit? Or is it an all or nothing affair?

    Thanks!
  • Dan_Robinson
    Automated Home Ninja
    • Jun 2012
    • 347

    #2
    You could have one hydraulic circuit of hr92 years heads, and one zone on a single thermostat.

    A hydraulic circuit is either all (except bathrooms IMHO) hr92s, or not.


    If the house is very well insulated, then sub zoning isn't a massive saving over proper compensated controls.
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

    Comment

    • fezster
      Automated Home Sr Member
      • Dec 2017
      • 72

      #3
      Originally posted by Dan_Robinson View Post
      You could have one hydraulic circuit of hr92 years heads, and one zone on a single thermostat.

      A hydraulic circuit is either all (except bathrooms IMHO) hr92s, or not.


      If the house is very well insulated, then sub zoning isn't a massive saving over proper compensated controls.
      Thanks Dan - doing half the house would definitely be more palatable in terms of cost than the whole lot at once. You mentioned the bathroom rads and I was thinking that the HR92 would look quite ugly on the chrome towel rads that I have. However, they are plumbed into the CH circuit, so there's no way of isolating them from all of the other rads. Is there another solution?

      Comment

      • Dan_Robinson
        Automated Home Ninja
        • Jun 2012
        • 347

        #4
        A few...

        You could do what I've done and have the valve outside the bathroom. Moly towel rail doesn't have anything on the pipes in the bathroom, but in the cupboard on the other side of the wall is the hr92. I have a remote sensor I made up giving sensor readings to Evohome.

        Alternatively, and this is what I tell clients.... Ku6have a regular trv and let them come on Al year round to dry towels. If it gets too hot, the trv will trim the heat in the room

        Massively drops installation costs too.
        Kind Regards - Dan Robinson (Jennings Heating Ltd)

        Comment

        • fezster
          Automated Home Sr Member
          • Dec 2017
          • 72

          #5
          Originally posted by Dan_Robinson View Post
          A few...

          You could do what I've done and have the valve outside the bathroom. Moly towel rail doesn't have anything on the pipes in the bathroom, but in the cupboard on the other side of the wall is the hr92. I have a remote sensor I made up giving sensor readings to Evohome.
          Thanks Dan. I assume you mean have the TRV on the pipework going to the radiator (and assuming the pipe is only feeding that towel rail, and not any other rads). Only problem for me is that all of the pipework is under tiles, and outside of the bathroom is under the floorboards.

          I'm actually thinking to just leave the towel rails without TRVs. They'll simply heat up when any zone is calling for heat. Not ideal, but not the end of the world either. The towel rails don't do a particularly great job of heating the bathrooms. We have underfloor electric for that. So could be an OK compromise.

          Comment

          • fezster
            Automated Home Sr Member
            • Dec 2017
            • 72

            #6
            Originally posted by fezster View Post
            Hi All.
            <snip>
            1. Have thermostats on 2 CH zones with radiators, which can adjust temperatures at various times of the day automatically (and weekday/weekend adjustments)
            2. Control boiler flow temps based on the internal temperature (and ideally, with weather compensation too).
            3. Have hot water priority to boost the flow temp to an unvented cylinder (if necessary, by using a separate sensor in the cylinders dry pocket).
            Thinking this through further, EvoHome with OpenTherm bridge is probably more expensive than just having an OpenTherm thermostat which can modulate boiler heat output. I'm not sure if any of these thermostats can control HW flow temp independently (Nest V3 can control HW, so I'd assume it boosts flow temp to 80 degrees to do so, but it's not clear from the documentation).

            On the other hand, using EvoHome, I can definitely achieve this with the HW kit, and then leaves me the option of adding HR92's as and when funds permit. Decision decisions...

            Comment

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