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  • guyank
    Automated Home Sr Member
    • Sep 2015
    • 73

    #16
    I'm not disagreeing that this is a fundamental physics issue with this type of installation and for a retrofit installation I believe that it is still the best option. I'm sure that now Honeywell have set a standard, other manufacturers must be looking at alternatives that may be better implemented but will still not get over this particular issue unless they also produce small, cheap sensors.

    The point I was making was that if I were doing a new build or a whole house refurbishment, Evohome would not be my system of choice because of the limitations induced by putting a sensor next to the radiator. I haven't looked at this in detail as it is not something I am looking at doing in the near future, but if you used the Heatmiser system or something similar and a heating manifold, I believe that you would achieve a much more accurate level of control. However, it would probably be considerably more expensive.

    Comment

    • top brake
      Automated Home Legend
      • Feb 2015
      • 837

      #17
      Originally posted by guyank View Post
      I'm not disagreeing that this is a fundamental physics issue with this type of installation and for a retrofit installation I believe that it is still the best option. I'm sure that now Honeywell have set a standard, other manufacturers must be looking at alternatives that may be better implemented but will still not get over this particular issue unless they also produce small, cheap sensors.

      The point I was making was that if I were doing a new build or a whole house refurbishment, Evohome would not be my system of choice because of the limitations induced by putting a sensor next to the radiator. I haven't looked at this in detail as it is not something I am looking at doing in the near future, but if you used the Heatmiser system or something similar and a heating manifold, I believe that you would achieve a much more accurate level of control. However, it would probably be considerably more expensive.
      Not sure why so many of you feel that measuring temp at the HR92 is not good. Look around all houses and you will find TRVs. The only issue is if the HR92 is covered by a rad cover, curtains etc

      Majority of evohome installations just use HR92 rather than the other way round.
      I work for Resideo, posts are personal and my own views.

      Comment

      • G4RHL
        Automated Home Legend
        • Jan 2015
        • 1580

        #18
        I have no issues with the HR92 sensor being at radiator level. It is designed to take account of where it is and whilst as a room warms up it may read a degree or so out from a thermometer elsewhere in the room it seems to eventually balance. Plus I don't see it all that important so long as there is something ensuring the room is at a comfortable temperature. When the system is new one can't help playing and fiddling, but leave it alone and it does its stuff. You soon find if you generally need a slightly different setting. Have to say the concerns over the position of the HR92 sensor etc. is a little bit of navel gazing. The HR92 sensor is far better and more accurate than other TRVs I have had.

        Comment

        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          #19
          Originally posted by G4RHL View Post
          I have no issues with the HR92 sensor being at radiator level. It is designed to take account of where it is and whilst as a room warms up it may read a degree or so out from a thermometer elsewhere in the room it seems to eventually balance.
          [...]
          Have to say the concerns over the position of the HR92 sensor etc. is a little bit of navel gazing. The HR92 sensor is far better and more accurate than other TRVs I have had.
          Every room is different though - if you have internal walls that are solid brick/plaster like we do, there is a lot of thermal mass in the room to heat so it can take hours for the bulk of the room to reach an equilibrium at the desired temperature if the temperature is measured at the radiator.

          For example in our living room with the temperature measured at the HR92, say the room is scheduled to 21 degrees at 8am on a Saturday morning. In cold weather the radiator will come on at about 6:30am and "reach" it's target of 21 by 8am. However when we get up soon after this we find the room subjectively feels a lot colder than 21 degrees - a thermometer sitting on the coffee table in front of the sofa confirms it - and only reads about 17-18 degrees even though the heating has been "on" for an hour and a half. It takes about a further 3-4 hours for that coffee table reading that is more representative of the room to creep slowly up to 21 degrees and the room to start to feel comfortable and actually feel like it is 21 degrees.

          It takes so many hours to eventually get there because when the HR92 measures 21 degrees at the radiator it throttles the radiator right back even though the rest of the room is nowhere up to temperature yet. In reality we don't wait, we just turn up the temperature to 22-23 for an hour or so to speed up the process but then need to turn it back down again to 20-21 otherwise the room will eventually end up too hot.

          The remote DT92 completely solves this - because it measures the temperature well out into the room the radiator keeps going full tilt until the room itself nears 21 degrees and only then does it throttle the radiator back. The warm-up time of the true room temperature is vastly faster when measured remotely like this as it avoids the radiator being prematurely throttled back. We find that when it claims the room has reached it's target 21 degree temperature as reported by the remote sensor it does indeed feel like it has, and there is no need to make a manual adjustment and no chance of the room ending up too hot later due to forgetting to turn the temporary temperature boost back down again.

          In short, it becomes set and forget. Up to temperature quickly and efficiently and at a comfortable temperature no matter what the prevailing outside conditions are. I'm no longer having to make any corrections to set points with changes in weather conditions outdoors. Call it navel gazing if you like, but my decision to use a remote sensor in the living room is not just based on theory, its based on months of temperature monitoring at various different locations in the room and comparing those to both the HR92's internal sensor and how we subjectively feel the temperature, and the verdict is clear - the remote sensor gives a reading that tracks much more closely with the feeling of comfort in spite of weather changes while the HR92's measurement does not, and it also optimises warmup times.

          I won't argue with you that the HR92's sensor is far more accurate than a conventional TRV - this kind of goes without saying as manual TRV's are horrifically inaccurate for multiple different reasons that I won't go into, (why do you think they're only labelled 1-5...) and under fixed conditions like consistent prevailing outdoor temperatures the HR92 can maintain a very steady and consistent temperature in the room, once that long equalisation period has happened through the room. (which can take many hours however)

          However make a radical change to the conditions such as a sudden cold snap in the weather and you will still find yourself having to make changes to your set point to maintain subjective "comfort" because the temperature offset between the HR92's sensor and the real room temperature has now changed.

          People are so conditioned to "turning up the TRV" in colder weather that they don't stop to realise that if they have to do this it means the temperature measurement and control system is flawed and is not actually maintaining the temperature at the part of the room where the humans reside... You do not need a higher temperature in the room just because the outdoors is colder during a cold snap, what's really happened is that the room is actually colder than it was previously, despite the same set point.

          This is especially so with a manual TRV for multiple reasons. An HR92 eliminates some of those errors (such as elimination of proportional offset error) so the need to make adjustments to the set point with changes in weather are significantly reduced with an HR92 vs manual TRV but not completely eliminated. A well chosen remote temperature measurement point eliminates the remaining sources of error so that measured temperature corresponds closely to subjective comfort no matter what the prevailing conditions are outside.

          BTW for those already using domoticz to measure their room temperatures with independent (non honeywell) temperature sensors, it is apparently now possible to bind those temperature sensors to the evohome via domoticz, and thus utilise them in place of a DT92 etc...



          It still looks fairly experimental but for anyone already using domoticz this could be a solution to the "remote sensors are too expensive and/or obtrusive" issue, and while I don't use domoticz at the moment it is an interesting development.
          Last edited by DBMandrake; 15 June 2016, 04:49 PM.

          Comment

          • Bazinga
            Automated Home Jr Member
            • Feb 2015
            • 22

            #20
            We've gone down the external sensor route for one of our bedrooms that never warmed up properly, and the DTS92 made a huge difference.
            Our main room has the evotouch controller in it, and this room is usually OK, but it's got a very high ceiling and it's south facing, so I've been using the HR92s' temperature offset to try to keep the room under control. This method does work (-2 in winter, -1 in Spring /Autumn, 0 in Summer), but it's hardly "set and forget". Can I use the internal sensor of the evotouch as the remote sensor for this zone, or do I need another DTS92 or a T87RF, etc. for this zone?

            Comment

            • DanD
              Automated Home Ninja
              • Feb 2016
              • 250

              #21
              Hi,

              Sorry to jump in, but I just saw your question and if I've understood correctly: can you use the evotouch's internal temperature sensor as the temperature sensor for your main room? Yes, definitely. Go into the Installation Menu on the controller by pressing and holding the settings button. Choose Zone configuration, select your main room zone, select Temperature Sensor and then choose Evotouch Sensor. That's it.

              Dan

              Comment

              • DBMandrake
                Automated Home Legend
                • Sep 2014
                • 2361

                #22
                Originally posted by Bazinga View Post
                We've gone down the external sensor route for one of our bedrooms that never warmed up properly, and the DTS92 made a huge difference.
                Our main room has the evotouch controller in it, and this room is usually OK, but it's got a very high ceiling and it's south facing, so I've been using the HR92s' temperature offset to try to keep the room under control. This method does work (-2 in winter, -1 in Spring /Autumn, 0 in Summer), but it's hardly "set and forget". Can I use the internal sensor of the evotouch as the remote sensor for this zone, or do I need another DTS92 or a T87RF, etc. for this zone?
                Originally posted by DanD View Post
                Hi,

                Sorry to jump in, but I just saw your question and if I've understood correctly: can you use the evotouch's internal temperature sensor as the temperature sensor for your main room? Yes, definitely. Go into the Installation Menu on the controller by pressing and holding the settings button. Choose Zone configuration, select your main room zone, select Temperature Sensor and then choose Evotouch Sensor. That's it.

                Dan
                Indeed.

                I use the evotouch's internal sensor as the hallway sensor - not because I'm particularly fussy about my hallways temperature, quite the contrary, but because it always sits on the wall mount in the hallway and is never removed, so I might as well make use of it. I find I have to set the calibration for the built in sensor to -1 to get it to agree with other sensors, including the DTS92, but once that is done it seems quite accurate, so long as you don't hold it in your hands. (which heats it up very quickly!)

                While I'm on a roll, I find another benefit of a remote sensor is when radiators are partially obscured or covered. I'm sure I'm not the only person to hang clothes, towels etc over radiators to dry them in the winter... during my comparisons of HR92 temperature reading to coffee table or other remote sensor I realised that anything you do to reduce the convection of a radiator increases the offset between the HR92's reading and the true room reading.

                You get the most accurate reading from an HR92 when the radiator is fully exposed, eg nothing hung over it... but as you start to cover the radiator, even if you don't cover the HR92, the lack of convection through the radiator causes the sensor to heat up disproportionately as the cool air flow pulled across the floor by convection is reduced or eliminated.

                So I would find in our living room that if it was set to 21 and the radiator was uncovered, the rest of the room would eventually reach 21 with a -1 calibration in effect, however if I even just put some clothes partially over the radiator blocking most of the convection then the room would never reach the set temperature - the HR92 would cheerfully report 21 degrees and shut off the radiator but the room as measured at the coffee table would still sit stubbornly at say 18 degrees forever, and genuinely feel cold to the inhabitants.

                With a remote sensor this problem also does not occur - it doesn't matter whether the radiator is fully exposed or partially covered, the true room temperature will eventually reach and stabilise on the same temperature either way, it just takes a bit longer when the radiator is partially covered. (Assuming that it is not so covered that it can't heat the room even when the radiator is going flat out)

                Same problem with the bedroom radiator - its a pretty large dual panel dual convector that is probably oversized for the room, but if you covered it with a towel the bedroom would be several degrees colder than the HR92 reported, not so with the DTS92 measuring the room at the wall at the head of the bed away from the radiator - a towel can be left to dry on the radiator without upsetting the temperature the room would eventually settle on.
                Last edited by DBMandrake; 16 June 2016, 04:47 PM.

                Comment

                • Bazinga
                  Automated Home Jr Member
                  • Feb 2015
                  • 22

                  #23
                  Thanks for both replies. I agree that remote sensors do work much better than the HR92, but for most of the time the HR92 are good enough. I'll reconfigure our main room's sensor away from one of the HR92s to the touchpanel sometime this week.

                  Comment

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