Smart TRV question

Discussion in 'Plumbers' Talk' started by fabro, Jan 8, 2019.

  1. fabro

    fabro Member

    This may not be a smart question at all...just to confirm, if I change one TRV for a smart TRV and set the temperature specifically for this room, will it control the boiler? or do you need all the TRV to be smart and then either change the transmitter or leave the boiler on the ON position. Not sure how to do multi-zones either.
  2. MGW

    MGW Well-Known Member

    In a way yes, all TRV heads can control the boiler by altering the flow of the return water and temperature of return water. But to electrically control the boiler is more complex.

    First thing is the boiler has to be designed so there is access to the boiler bus. Without access to the bus, the only way to modulate the boiler output is with the return water temperature, you can of course switch the boiler off/on, but that rather defeats the whole point of having a modulating boiler.

    I have looked at the whole idea of electrically controlling the boiler, and theory is easy, if target is lower than current on any TRV head then boiler runs, and with multi TRV heads then that could work. However what is really wanted is a device that uses algorithms the modulate the boiler, not switch it on/off, I think the EvoHome thermostat may do that, but not sure, and it would not work with a single TRV head.

    I did try first with two and then four TRV heads, since a bosch boiler only access to bus is with Wave which only controls a single room, so I used two wall mounted thermostats mounted opposite end of house. Idea is if house is cold boiler runs, whole house warm it stops. And I have set the TRV head just on the thermostat temperature so only when the weather is warm will the thermostat switch off boiler.

    Nest it seems is designed to pair with MiHome so in theory using the 'follow' command with an OpenTherm enabled boiler Nest could control the boiler bus, but my stupid bosch is not OpenTherm so option not open to me.

    So all my great ideas failed, and I just use two on/off thermostats. Also found the TRV needs to be on the feed, again theory the TRV is bi-directional, but in practice radiator heats up fully before the TRV gets warm so it over shoots if feed at lock shield valve end. By carefully trimming the lock shield valve it can be made to work, however the idea of rooms varying in temperature over the day does not really work, as they take too long to cool down, even if you can heat them quickly.

    Once trimmed in and set yes the electronic TRV does keep the room spot on set temperature, but I am sure a cheap Terrier i30 would have worked just as good as my Energenie MiHome heads which cost three times the price so I can access with phone rather than set on the head its self.
  3. dcox

    dcox Active Member

    The smart TRV on its own will just turn off that one radiator when the local air temperature gets to the set point. As far as I'm aware, the 'smart' bit just means you can adjust that temperature set point from your phone.
  4. MGW

    MGW Well-Known Member

    As said "Smart" seems to mean phone controllable. However as far as TRV heads go, we do seem to have levels of smartness, have I invented a new word?

    It seems to start with the Terrier i30 which has no wifi, but is programmable so the room can be set to different temperatures through the day. Not read the spec, but many electronic TRV heads measure water temperature as well as air temperature so compensate for heat from radiator, so are far more accurate than simple mechanical types.

    With an old boiler it had two states, off or on, but with modern boilers they modulate, as a result they should run longer, in heart of winter never turning off, output varying from 6 to 30 kWh so the TRV will directly control boiler by controlling return water temperature.

    However a simple off/on thermostat, or motorised valves with micro switches can completely mess up the whole idea, just as the boiler starts to modulate, the wall thermostat turns it off, and if the boiler is not running, then the TRV can't turn up the heat.

    However using the TRV (wax or smart) to control temperature, even in summer the boiler will need to fire up, to test if heat required.

    So there needs to be a method to turn off boiler in the summer, this was traditionally the wall thermostat in a room kept cool, with no outside door, or alternative heating, on the ground floor, set so it will allow boiler to run in winter 24/7 and in summer off.

    The other option is a modulating wall thermostat, this will mean again the boiler runs nearly 24/7 so an electronic TRV head will work.

    The third option is to use the TRV head to send information to a central hub, which in turn controls how much the boiler is modulated.

    So answer to original question, yes is set correct then all TRV heads should control boiler output, but the question is it set correct?
    Last edited: Jan 10, 2019
  5. The Teach

    The Teach Well-Known Member

    There are so many add on gadgets available for retro fitting to existing heating systems,most are just a sales opportunity directed to the uk diy market :(

    Maybe just wait untill you need to renew the gas boiler,then choose a gas boiler with direct open therm capability. Having spent the last few weeks in a cold country with 2 foot of snow every day,i can confirm the internal apartment comfort level was excellent although the boiler never stopped running there was no on-off cycling all the time (reducing boiler wear out time and noise). The boiler just used sufficient gas via the OT room thermostat to maintain comfort levels.

    fitting so called smart controls to many uk systems is actually no so smart :(
  6. retiredsparks

    retiredsparks Well-Known Member

    I have just 'invested' in a new TRV.
    It is fully 'digitally' (fingers) controllable and ergonomically (round) designed to allow 'infinite' adjustment. (ON to OFF)
    It is also fat and sugar free and suitable for vegans.

    In addition it is recommended by chiropractors to stretch the back muscles if used 2 twice a day.
    RS trv.jpeg
    The Teach likes this.

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