HR92 - open/close 100% or modulating?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • Leigh
    Automated Home Jr Member
    • Jan 2016
    • 32

    HR92 - open/close 100% or modulating?

    So, im now about a week in with my new evohome system and things have definitely changed / been learnt with by the system about the rooms etc.

    One thing i have noticed is that when a valve calls for heat it doenst necessarily open the valve from 0% to 100%, it sounds like its controlling the opening position, perhaps based on current room temp versus required room temp. i.e. it can go from 0% to 40% etc. The reason i ask is that i noticed my farthest rad on the system (living room) had a small whooshing noise last night when operating even though the lockshield is 100% open, this wasnt happening previously either using the HR92 or with the standard TRV head.

    Its not a problem, just wanted to know more about the control philosophy.
  • top brake
    Automated Home Legend
    • Feb 2015
    • 837

    #2
    Originally posted by Leigh View Post
    So, im now about a week in with my new evohome system and things have definitely changed / been learnt with by the system about the rooms etc.

    One thing i have noticed is that when a valve calls for heat it doenst necessarily open the valve from 0% to 100%, it sounds like its controlling the opening position, perhaps based on current room temp versus required room temp. i.e. it can go from 0% to 40% etc. The reason i ask is that i noticed my farthest rad on the system (living room) had a small whooshing noise last night when operating even though the lockshield is 100% open, this wasnt happening previously either using the HR92 or with the standard TRV head.

    Its not a problem, just wanted to know more about the control philosophy.
    Hi

    The HR92 are modulating and can be fully open, fully closed or at a % open position between

    To prevent system noise it is recommended that you have a ABV Automatic Bypass Valve
    I work for Resideo, posts are personal and my own views.

    Comment

    • Leigh
      Automated Home Jr Member
      • Jan 2016
      • 32

      #3
      Thanks, there is an ABV installed as noted in my other thread but i will review the setpoint again in light of this. The manual says set at 0.2 if there are TRVs on the system and its about 0.22-0.25 at the moment.

      Thanks.

      Comment

      • top brake
        Automated Home Legend
        • Feb 2015
        • 837

        #4
        sounds like the issue is with velocity rather than pressure. what system and pump do you have, and what setting is the pump on?
        I work for Resideo, posts are personal and my own views.

        Comment

        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          #5
          Originally posted by Leigh View Post
          So, im now about a week in with my new evohome system and things have definitely changed / been learnt with by the system about the rooms etc.

          One thing i have noticed is that when a valve calls for heat it doenst necessarily open the valve from 0% to 100%, it sounds like its controlling the opening position, perhaps based on current room temp versus required room temp. i.e. it can go from 0% to 40% etc. The reason i ask is that i noticed my farthest rad on the system (living room) had a small whooshing noise last night when operating even though the lockshield is 100% open, this wasnt happening previously either using the HR92 or with the standard TRV head.

          Its not a problem, just wanted to know more about the control philosophy.
          The HR92 is a PI or "Proportional Integral" controller.

          This means that the valve opening is proportional to both the difference between measured and set point temperatures and the length of time at which it has been away from that temperature. The proportional band isn't documented but seems to be about +/- 1.5 degrees.

          This means if the set point is more than 1.5 degrees above the current temperature the valve will open fully, and if the set point is more than 1.5 degrees below the current temperature the valve will fully close. However within that +/- 1.5 degree "proportional band" the valve will adjust to a partial opening somewhere in between to reduce water flow (and thus radiator temperature) but not completely shut it off.

          If you're observant and sitting nearby you will hear it make very small, very brief, (half a second) adjustments to the valve position about every 4 minutes until it homes in on an equilibrium that maintains the room temperature steady and at the target. The ideal situation is that it finds a valve opening that lets just enough water through to make the radiator just hot enough to balance the heat loss of the room - thus the room remains at a constant temperature without oscillating up and down. It's a delicate balance but one that it is often able to manage.

          If there are things changing in the environment such as people entering and leaving, doors being opened and closed, appliances being turned on and off etc, then obviously it would need to make adjustments to compensate for those, so it would make small adjustments every now and then to do so.

          If the valve opening required to maintain this balance is quite small you will hear a small hiss through the valve where it is restricting the water flow. This is regardless of where your lock shield valve is set. If the hiss is unusually loud then it could be too high a flow velocity as top brake suggests, although with your ABV set to 0.25 that seems unlikely. (0.25 actually seems quite low to me)

          The reason you wouldn't often hear a noise like this with a conventional TRV is they are just not very accurate and are unable to maintain such a delicate balance for any length of time like the HR92 can - a conventional TRV will tend to overshoot the target temperature which causes it to fully close, then it undershoots the target in the other direction and opens wide - wide enough that you don't hear a hiss. It spends little if any time at the exact partial opening where you would notice a hiss, but your room temperature is not staying steady either.

          With the HR92 if you hear a gentle but steady hiss from the valve after the room is up to temperature that lasts a long time that is actually a pretty good sign that it has found the correct equilibrium point on the valve to maintain the room at the desired temperature!
          Last edited by DBMandrake; 28 January 2016, 11:45 AM.

          Comment

          • paulockenden
            Automated Home Legend
            • Apr 2015
            • 1719

            #6
            I think one of the important factors that people seem to (initially) misunderstand is that once a room is up to temperature, with an Evohome system the valve won't them completely close, and the boiler shut down. It keeps a small amount of heat trickling into the radiator to maintain the room heat, compensating for any heat losses. This avoids the see-sawing of temperatures that you get with conventional controls.

            Many of the posts on this forum seem to be from people querying why their heating is still running once their rooms are warm.

            Comment

            • DBMandrake
              Automated Home Legend
              • Sep 2014
              • 2361

              #7
              Originally posted by paulockenden View Post
              I think one of the important factors that people seem to (initially) misunderstand is that once a room is up to temperature, with an Evohome system the valve won't them completely close, and the boiler shut down. It keeps a small amount of heat trickling into the radiator to maintain the room heat, compensating for any heat losses. This avoids the see-sawing of temperatures that you get with conventional controls.

              Many of the posts on this forum seem to be from people querying why their heating is still running once their rooms are warm.
              That's a very good point.

              As well as controlling the valve openings it does modulate the boiler as well of course, either by directly reducing the flow temperature via OpenTherm, or using duty cycle modulation via a BDR91 as a crude method of flow temperature modulation.

              I've found that if any zone is out of the proportional band in the "needs more heat" direction, the boiler relay will just go to 100% duty cycle. However if all active zones are in the proportional band near their set points, the boiler duty cycle will drop way down to only that which is necessary to replace the lost heat in the rooms.

              For example in recent weather conditions our boiler has been running at roughly 30% duty cycle on the BDR91 in the evenings once the zones are up to temperature. So during this maintenance period where it is just trying to maintain the room temperatures not only are the HR92 valves only partially open, the boiler is only running part time too, so the average flow temperature is also reduced.
              Last edited by DBMandrake; 28 January 2016, 12:37 PM.

              Comment

              • Leigh
                Automated Home Jr Member
                • Jan 2016
                • 32

                #8
                Thank you all, thats is very helpful. I can indeed hear the valve for around half a second so it is doing exactly as you say DBMandrake and Paul. It doesnt bother me at all i just wanted to understand how the system operates better.

                As for my pump its a Grundfos Alpha 2 which i changed last week to contant pressure mode as per the suggestion in one of my other threads as i have one rad with the lockshield open only a fraction as it got all the flow before the system was balanced and it was noticeably audible. Changing to CP mode has made a lot of difference.

                Comment

                • MrB
                  Automated Home Sr Member
                  • Oct 2015
                  • 80

                  #9
                  Best description of how the HR92s work that I've read.

                  My system (now about 3 months) has settled down and it operates as stated above. We had a completely new heating/hot water system installed - new boiler / rads / pipes / pump /valves / ABV / filter [think that's all ] and of course, Evohome. All Rads were correctly sized and also the Boiler.

                  The Alpha 2 Constant Pressure setting is an absolute *MUST* - just won't work properly on any other setting (and the CP2 setting for our 12 Rads and Hot Tank). The Proportional Pressure is an absolute disaster - will even negate the correct working of the ABV.

                  The way the temperature is now constant, room by room, is amazing. It simply manages itself. We have none of the problems that others appear to have, but I have to say it was a relatively steep learning curve - nothing onerous, but just that you have forget everything you know about "old style" heating and boilers.
                  Last edited by MrB; 28 January 2016, 04:39 PM.

                  Comment

                  • rotor
                    Automated Home Guru
                    • Aug 2015
                    • 124

                    #10
                    Originally posted by MrB View Post
                    My system (now about 3 months) has settled down and it operates as stated above. We had a completely new heating/hot water system installed - new boiler / rads / pipes / pump /valves / ABV / filter [think that's all ] and of course, Evohome. All Rads were correctly sized and also the Boiler.
                    Would you mind telling us what boiler and hot water tank you bought, and why? I'm thinking of replacing my one, and would appreciate someone else's (also an Evohome owner) perspective. Thanks!

                    Comment

                    • benc
                      Automated Home Lurker
                      • Sep 2015
                      • 7

                      #11
                      If you want to check the valve position you can go into the settings (long press on the button) then turn the control wheel anti-clockwise until it gets to 10, short press on the button, turn wheel to 1, then another short press and it will show P XX where XX is the % open. I think it'll stay showing this for a little while then revert to the standard display.

                      Comment

                      • MrB
                        Automated Home Sr Member
                        • Oct 2015
                        • 80

                        #12
                        @rotor

                        Boiler:
                        Ignoring all the logistical and constructional concerns (like the boiler is now floor standing and in a conservatory with a high level vent pipe):
                        It has to be a condenser and 'regular' (ie: not combi or system) see https://www.worcester-bosch.co.uk/pr...lers/explained
                        We changed from an open-vented system (ie: has open fill/expandsion tank in loft) to a closed pressurised system for the hot water and heating pipe system. Needs a bit more space for the expansion vessel etc - but not a lot.
                        This closed pipe system removes all the problems related to air locks and uneven pressure flow through all the pipes/rads/tank. It took a while to get all the air out and the pressure to stabilise, but now it sits at a constant pressure requiring no further air bleeds or water top-ups.

                        We looked at all the plumbing/heating websites/forums to get a feel for what is recognised as the Good, Bad and Ugly Boilers- we had a Baxi which was not the best. Reading about what Plumbers have to repair the most (and why) is the best insight.
                        Came down to a Valiant or Worscester-Bosch. Price/Guarantee and models were next.

                        As we have Solar PV and Solar Thermal the plan was to use the most economical and 'greenest' - and of course using Evohome to drive the overall efficiency via HR92s on all Rads and the remote Temp Sensor on the Hot Tank etc.

                        It came down to the W-B Greenstar FS CDI and then had to decide on the power output. As all Rads were being replaced with modern ones each room was correctly BTU sized base on volume, doors, windows and compass direction. The total amount of BTUs plus the total BTU to heat a 250L hot tank to 63C gave the boiler requirment. Originally I though that it would need the 40KW boiler but the company doing all the work stopped that. Said you'll be wasting heat (simply returned via the ABV) and get overruns on the rads because water would heat up so quickly. The actual total was about 35Kw, but 30Kw would be fine. Which is what we have and it's generally running at about 80% capacity - which proves the point.

                        The Evohome can directly control the boiler, but we have the Evohome controlling the 2-way values (nb: not 3-way values, which is what we had before and that prevented simultaneous rad and hot tank heating) and the 2-way valves are wired in parallel to fire the boiler. The boiler controls the Grundfos pump.

                        All works very well and the boiler is regularly pumping condensate water so that shows it's running efficiently.

                        The HR92s are in 12 Zones (all have single Rads apart from main Living Room Zone which has 2 rads) and their individual heat requests combined with the hot tank request means I see little short cycling of the boiler. Although, I still haven't been able to figure out why the Hot Tank is not acheiving the required temp as quickly as expected - as it approaches the required temp it just gets slower and slower - WIP that one.

                        Hot Tank
                        Nothing really special - we disposed of the old blanket wrapped smaller tank and replaced with modern sprayed insulation tank that was custom sized to fit the required space and also has dual heating loops - from gas boiler and from solar thermal panels on the roof. I'm currently in the process of merging the controls so they don't fight over the heating, but the crap weather hardly makes it a priority.

                        That's about it - if I can answer any question for you then only too happy to.

                        Comment

                        • rotor
                          Automated Home Guru
                          • Aug 2015
                          • 124

                          #13
                          Thanks MrB, I really appreciate the time you took to write this up.

                          Am really impressed with the company you used, in terms of sizing and BTU calculations. That's not in London, by any chance, is it?

                          One question about radiator sizing: how do they take into consideration how much insulation / draught-proofing each room has? Our hallway has single-glazing on the door and the window, and I had to disable open-window detection as the cold coming from the glass was enough to trigger it on cold nights.

                          Also... you mentioned your boiler seems to be running at 80%, but we've had really mild weather this winter, so it seems to me that you haven't had a true test of how much heat you're going to need during a really cold winter...?

                          Sorry if these are all obvious!

                          Comment

                          • MrB
                            Automated Home Sr Member
                            • Oct 2015
                            • 80

                            #14
                            @rotor

                            1. Not London 'fraid.
                            2. Rad sizing - it's too coarse for small things - lots of online sites will do good rad sizing for you (if they are too simple don't bother - find another site). They should consider things like cavity walls and single glazing. I expect some lurking heating engineers could also advise on sites.
                            3. Correct about efficiency, but it's also a by-product of Evohome and HR92s managing everything. They keep it all topped-up in small increments and the Optimisation predicts how to obtain required temp at a certain time and works well - there's no big rush to blast the heating and then cool down on timers like old systems. Our rads/rooms maintain an incredibly balanced temperature - never feel hot or cold (and it's by room of course).

                            Comment

                            • morpheus
                              Automated Home Sr Member
                              • Apr 2016
                              • 68

                              #15
                              Does anybody know how the HR92 does in order to find the "completely closed" and "completely open" states of the valve body ?
                              I have a colleagu of line who used the M30 adaptors, and he saw the valve was never completely closed, so that the radiator was always heating if there was a demand on another zone.

                              Comparing with the M28 adaptors, we discovered that the pin is longer on that adaptor ...

                              M28 and M30 adapters.jpg

                              so he replaced all the shorter pins of hiw M30 adaptors by the pins of the M28 adaptors ... but this is not normal ....

                              Now assuming you have the correct adaptor with the correct pin length, how is the HR92 doing to find the exact "completely closed" and "completely open" states of the valve body ??

                              I have also seen there was the pamareter 6 on the HR96 which puts a standard or integral course, but according to the feedback I got this is only to play on the motor power for valve heads which would be blocked or harder for example ...

                              Many thanks !!

                              Comment

                              Working...
                              X