Evohome - poor temperature regulation

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  • G4RHL
    Automated Home Legend
    • Jan 2015
    • 1580

    Originally posted by rcopus View Post
    I think the system could be a lot more intelligent if it actually knew what the boiler was doing.
    For example I have a combi boiler, which means when DHW is being used the boiler relay may be calling for CH but will not get any heat to the radiators at all. However the Evohome system will assume it's added a certain amount of heat to the zones when really nothing at all has been added.
    I don't have a combi boiler. Surely Evohome is not involved when hot water only is requested as those requests would not go via Evohome? As said I don't have a combi

    Comment

    • Bazinga
      Automated Home Jr Member
      • Feb 2015
      • 22

      Originally posted by G4RHL View Post
      I don't have a combi boiler. Surely Evohome is not involved when hot water only is requested as those requests would not go via Evohome? As said I don't have a combi
      My Combi boiler is only able to do one thing at a time, either CH or DHW but not both. If someone is running a bath or having a shower, then regardless of what Evohome wants or does, there is no additional heat to the radiators. I think that the pump also stops on my combi when there is a DHW demand. This is based on hearing noises in the radiators a few seconds after the hot tap is turned off.

      Comment

      • rcopus
        Automated Home Jr Member
        • Nov 2014
        • 49

        Originally posted by G4RHL View Post
        I don't have a combi boiler. Surely Evohome is not involved when hot water only is requested as those requests would not go via Evohome? As said I don't have a combi
        You're correct its not involved with hot water and that's the problem.
        When hot water is being used the boiler doesn't provide the central heating with hot water, of course Evohome is oblivious to all of this.

        This means if someone is using a shower or filling a bath, Evohome will still put the request in to start the central heating and of course the boiler ignores this as hot water has priority.

        Therefore when Evohome thinks it's heating a zone by running the boiler for 'X' minutes when in reality it's having no affect.

        Comment

        • sharpener
          Automated Home Sr Member
          • Jan 2015
          • 78

          Originally posted by rcopus View Post
          It seems Evohome isn't smart enough to realise that the water circulating in a heating system is not constantly at say 70c and available straight away from the second it calls for heat...
          Maybe this and the lack of cycle time and minimum on time settings for UK S and Y plan configurations are because it was first designed for European (i.e. German) scenarios?

          Originally posted by Bazinga View Post
          I think that the pump also stops on my combi when there is a DHW demand. This is based on hearing noises in the radiators a few seconds after the hot tap is turned off.
          The pump will run in DHW mode to circulate the water through the HW heat exchanger, so what you are hearing is probably the diverter valve switching the flow back to the radiator circuit.
          Last edited by sharpener; 25 March 2015, 12:26 PM.

          Comment

          • G4RHL
            Automated Home Legend
            • Jan 2015
            • 1580

            It is now 4 days since I turned optimisation off and still think the system runs better. The frequent firing up of the boiler has reduced quite a lot. I certainly no longer hear the frequent firings of sometimes less than one minute. It seemed to have a turn doing just that for a short period yesterday after I used a Quick Action. Gone though is the system coming on too early and going off too early.

            Does optimisation do anything else than try to work out how long it takes to heat a zone up and then come on in due time for that (or to go off if a lower set point is ahead)? If so certainly in my case it is not needed for it does nothing. I have never set my heat on times to take account of the need for a room to warm up. Heat times for me have always been that is when I want it knowing that it may take 10 minutes for the temperature to go up or down. The effect of it coming on whilst not instant is very quick. There is nothing special about my house. Built 1997, brick with breeze block inner leaf, double glazed, loft insulated, cavity insulation installed.

            Until recently I had never thought of people wanting heating on earlier in order to allow for warm up time but I suppose some do. If you don't then am I right in thinking optimisation is not needed as that is all it seems to do other than cause more frequent firing of the boiler to maintain a set temperature? I.e. Optimisation increases fuel use as opposed to saving it.

            Comment

            • G4RHL
              Automated Home Legend
              • Jan 2015
              • 1580

              On the subject of temperature regulation can someone confirm if there is a difference in the speed a room may heat up dependent on its initial temperature, ignoring for the moment external influences. Its a long long time ago that I did physics at school but at the back of my mind is something about a room will warmer up quicker by degrees if its start temperature is already higher despite that sounding illogical. What brought this about is I have been away from home for a few days, I set the system including hot water to off having programmed 5c as the off temperature. Over the few days I gradually watched the temperature drop from some 100+ miles away. On my return, once I had a signal, I pulled in and switched off the Quick Action Menu so the house would start warming. At that time most of the house was 11C. It took an hour to rise 3 degrees. At home monitoring it I have seen it go from 15c to 18 in 30 minutes. It made me think whether if the starting temperature is low it takes longer to lift it by the same amount. A 30 minute difference in this case. Plus I noticed once the temperature got up to about 16 then it increased thereafter more rapidly. My physics is stale but is this what should happen or???

              Of course it did show that I could watch what was happening on my iPhone (pinned to the dashboard in front of me) and see it automatically updating the reading every so often!

              Comment

              • Mavis
                Automated Home Ninja
                • Oct 2014
                • 322

                Originally posted by G4RHL View Post
                On the subject of temperature regulation can someone confirm if there is a difference in the speed a room may heat up dependent on its initial temperature, ignoring for the moment external influences. Its a long long time ago that I did physics at school but at the back of my mind is something about a room will warmer up quicker by degrees if its start temperature is already higher despite that sounding illogical. What brought this about is I have been away from home for a few days, I set the system including hot water to off having programmed 5c as the off temperature. Over the few days I gradually watched the temperature drop from some 100+ miles away. On my return, once I had a signal, I pulled in and switched off the Quick Action Menu so the house would start warming. At that time most of the house was 11C. It took an hour to rise 3 degrees. At home monitoring it I have seen it go from 15c to 18 in 30 minutes. It made me think whether if the starting temperature is low it takes longer to lift it by the same amount. A 30 minute difference in this case. Plus I noticed once the temperature got up to about 16 then it increased thereafter more rapidly. My physics is stale but is this what should happen or???

                Of course it did show that I could watch what was happening on my iPhone (pinned to the dashboard in front of me) and see it automatically updating the reading every so often!
                Could it have something to do with conduction? By that I mean will items in the room have got cold so any heat expelled from the radiators be absorbed into soft furnishings first. Reading back that probably sounds absurd.

                Edit. that should probably be convection perhaps.

                Comment

                • erik
                  Automated Home Guru
                  • Feb 2015
                  • 244

                  A wild guess: mybe if your radiators have been OFF for a long time, then your insulation first needs to warm up a lot, causing it to take longer to heat up the room?

                  Comment

                  • G4RHL
                    Automated Home Legend
                    • Jan 2015
                    • 1580

                    Possibly that plus the point Mavis raised which is similar. The air temperature could be different to that of furnishings and insulation which retains some heat which when off for a long time needs to regain it first. Seems to me a possibility. Presumably optimisation takes this into account or it may be that in my case it never did for rooms warmed up quicker than the 60 minutes optimisation thought they would take. We must have a heating engineer in the forum who knows the answers! Just odd that Evohome lifts 15C or 16C by 3 degrees quicker than it lifts 11C by 3 degrees. Perhaps we should sell this as an exam question for a physics graduate?!!

                    Comment

                    • Bazinga
                      Automated Home Jr Member
                      • Feb 2015
                      • 22

                      Newton's Law of Cooling describes how energy flows from a hot object to the surroundings via conduction and convention. Despite being called radiators, the vast majority of the heat is transferred by convention, and not radiation. Heat is transferred quicker when there is a greater differential between the object (the radiator) and the ambient air, so a cold room extracts more heat from a radiator than when the room is warm in an identical period of time.

                      As alluded to by others, heat is also transferred from the ambient air to the cooler objects in the room again at a rate determined by Newton's Law of Cooling. This is probably what is happening. Once the fabric of the room has warmed up, the air will warm up quicker since it is not losing the heat it gains from the radiators.

                      Comment

                      • G4RHL
                        Automated Home Legend
                        • Jan 2015
                        • 1580

                        Originally posted by Bazinga View Post
                        Newton's Law of Cooling describes how energy flows from a hot object to the surroundings via conduction and convention. Despite being called radiators, the vast majority of the heat is transferred by convention, and not radiation. Heat is transferred quicker when there is a greater differential between the object (the radiator) and the ambient air, so a cold room extracts more heat from a radiator than when the room is warm in an identical period of time.

                        As alluded to by others, heat is also transferred from the ambient air to the cooler objects in the room again at a rate determined by Newton's Law of Cooling. This is probably what is happening. Once the fabric of the room has warmed up, the air will warm up quicker since it is not losing the heat it gains from the radiators.
                        ..and that is what I probably had learned in physics at school half a century ago! Thanks.

                        Comment

                        • G4RHL
                          Automated Home Legend
                          • Jan 2015
                          • 1580

                          It is now just about 14 days since I switched optimisation off. No difference in comfort at all, the heating does not come on unnecessarily early burning more fuel and it's less noisy with far fewer switchings off and on. Occasionally it seems to short cycle but not often. It still seems to my cynical mind that optimisation is about maximising boiler wear and fuel bills than minimising the same.

                          Comment

                          • Rameses
                            Industry Expert
                            • Nov 2014
                            • 446

                            Originally posted by G4RHL View Post
                            It is now just about 14 days since I switched optimisation off. No difference in comfort at all, the heating does not come on unnecessarily early burning more fuel and it's less noisy with far fewer switchings off and on. Occasionally it seems to short cycle but not often. It still seems to my cynical mind that optimisation is about maximising boiler wear and fuel bills than minimising the same.
                            R

                            I will contact you offline - regarding your system.

                            With regards to your comment. If you are experiencing far fewer switching off and on, you are probably likely are burning more fuel. Also within evohome it has optimised 'stop' functionality (will not see the 'opt' logo on zones etc) - so if you have switch this off, so will be unable to benefit from this feature.

                            With regards to 'boiler' wear, the throttling and on/off activity of the boiler is well within most modern (and many older) boiler tolerances. Many are designed with this in mind (like modern cars with start / stop) Boiler firing time in total is what counts, as this takes the heaviest toll.
                            Last edited by Rameses; 5 April 2015, 11:03 PM.
                            getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

                            Comment

                            • Mavis
                              Automated Home Ninja
                              • Oct 2014
                              • 322

                              Originally posted by Rameses View Post
                              R


                              With regards to 'boiler' wear, the throttling and on/off activity of the boiler is well within most modern (and many older) boiler tolerances. Many are designed with this in mind (like modern cars with start / stop) Boiler firing time in total is what counts, as this takes the heaviest toll.
                              Interesting you should say that - we have just bought a car with the start/stop system and the first thing hubby said was 'switch it off as it will wear the ignition (or whatever???) out'. There needs to more information generally - almost like a selling point of these 'new' functions that will quash these immediate thoughts that people will have.

                              Incidentally, yesterday afternoon I noticed for the first time the boiler came on for a short amount of time when no radiators were calling for heat. It will have happened before but it was noticeable as I was sat outside in the sun I went inside to check and all them temps were way over the setpoints.

                              Comment

                              • JohnnyP
                                Automated Home Jr Member
                                • Nov 2008
                                • 38

                                Originally posted by G4RHL View Post
                                It is now just about 14 days since I switched optimisation off. No difference in comfort at all, the heating does not come on unnecessarily early burning more fuel and it's less noisy with far fewer switchings off and on. Occasionally it seems to short cycle but not often. It still seems to my cynical mind that optimisation is about maximising boiler wear and fuel bills than minimising the same.
                                Once Evohome or Hometronic reaches equilibrium it will short cycle your boiler (usually 2mins per 10mins, but can be even shorter, say 30secs). If optimisation is OFF your system will spend less time at equilibrium, therefore less short cycling. As the weather warms, the system will reach equilibrium more quickly and you will notice more short cycling again.

                                Comment

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