How "smart" is the hot water system

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  • StuartG
    Automated Home Jr Member
    • Mar 2015
    • 45

    How "smart" is the hot water system

    My Evohome system is being installed at the moment, and I'm really looking forward to using it. I have a question about optimisation with respect to hot water.

    Does the system learn how the water system responds, in a similar way to how it optimises for rooms? e.g. if I know I want my hot water to be ready for 0600 do I need to anticipate warm up time and schedule an earlier start myself? Or does the "on" time tell the system that's when I want the water by and it will come on to suit?

    To be honest, the heat loss from the tank is so small it's more of a hypothetical question, but I was just wondering
  • HenGus
    Automated Home Legend
    • May 2014
    • 1001

    #2
    Originally posted by StuartG View Post
    My Evohome system is being installed at the moment, and I'm really looking forward to using it. I have a question about optimisation with respect to hot water.

    Does the system learn how the water system responds, in a similar way to how it optimises for rooms? e.g. if I know I want my hot water to be ready for 0600 do I need to anticipate warm up time and schedule an earlier start myself? Or does the "on" time tell the system that's when I want the water by and it will come on to suit?

    To be honest, the heat loss from the tank is so small it's more of a hypothetical question, but I was just wondering
    I have had the HW kit installed for nearly a year. My experience is that if it is set for 0700 hours it will come on at 0700 hrs PROVIDED that the temperature is outside of the temperature range that the user has set. My setting is 60C with a -7C variation; i.e., a range of 60 to 53C cylinder temperature.

    Comment

    • paulockenden
      Automated Home Legend
      • Apr 2015
      • 1719

      #3
      I don't /think/ there's optimisation on the DHW side, only on the rad controls.

      Comment

      • Fursty Ferret
        Automated Home Sr Member
        • Oct 2014
        • 84

        #4
        There's no "optimal start" but there's definitely an optimal stop. I noticed that if I increased the target temperature it overshot for the first day or two but now nails it every time.

        Comment

        • G4RHL
          Automated Home Legend
          • Jan 2015
          • 1580

          #5
          I ran optimisation for some time and there was no noticeable affect on the Hot Water. It came on and went off when asked and kept the temperature to that set. I do not think optimisation works at all with the Hot Water system. Indeed why should it? You don't need it.

          By the way Fursty Ferret is a very nice beer!!

          Comment

          • Fursty Ferret
            Automated Home Sr Member
            • Oct 2014
            • 84

            #6
            Originally posted by G4RHL View Post
            I ran optimisation for some time and there was no noticeable affect on the Hot Water. It came on and went off when asked and kept the temperature to that set. I do not think optimisation works at all with the Hot Water system. Indeed why should it? You don't need it.

            By the way Fursty Ferret is a very nice beer!!
            Because convection in the tank means that there is hysteresis between the probe temperature, the average water temperature, and the boiler flow temperature, especially if the tank is cold to start with. It would be highly inefficient if the controller shut off the heating at the target temperature and every time overshoots by 5 degrees.

            Comment

            • paulockenden
              Automated Home Legend
              • Apr 2015
              • 1719

              #7
              But there isn't a target temperature. There's a target temperature range. The default is a huge 10 degree differential.

              That'll mop up any problems caused by convection in the tank.

              Having said that, get a thermal image camera and look at your tank (assuming it's not one of the newer foam covered jobbies), you'll be amazed at the stratification. You'd think convection would mix things up in there, but it doesn't. The 'warm line' moves down as the tank heats up.

              Comment

              • Fursty Ferret
                Automated Home Sr Member
                • Oct 2014
                • 84

                #8
                Sorry, but there is a target temperature. The differential is solely to prevent short cycling as the temperature fluctuates around the target, but in my experience the evohome controller hits its target with remarkable accuracy.

                Comment

                • StuartG
                  Automated Home Jr Member
                  • Mar 2015
                  • 45

                  #9
                  Thanks all! I'm going to play with the system a bit and see what happens. Installation finishes this week so I'll see what happens once I start using it in anger!

                  Comment

                  • Rameses
                    Industry Expert
                    • Nov 2014
                    • 446

                    #10
                    No HW is not subject to 'optimisation' that the rooms/zone are subject to. The HW tank is more controlled and static environment. Also as conduction takes place (not convection via Air) the heat up process is A LOT quicker. Also the thermal decline should be (assuming proper insulation) very gradual. Meaning Hot water change occurs when you 'use' it - rather dissipate than in room/zones. Possible savings are there and being investigated but right now small considering the larger system view.

                    So my advice - set it for when you need it. Eg in my instance 7-8am in morning - I have never had a cold shower getting up early - because the tank is still 'insulated' from previous evenings 'top up'

                    PS Paul's comment about the tank is also valid - correct placement of the sensor( plural if you have both insertion and outside) is key - see guidelines for more info.
                    Last edited by Rameses; 26 May 2015, 10:03 AM.
                    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

                    • jonstatt
                      Automated Home Guru
                      • Feb 2015
                      • 111

                      #11
                      The thermal decline will be larger, if like me, you have a hot water circulating system that means that hot water is instantly available at any tap. This is particularly useful in a town house otherwise you can wait, quite literally, 2-3 minutes for hot water to come through. The downside is the thermal decline is much higher and therefore operating efficiency is significantly reduced.

                      As mentioned, the placement of the probe is important. Typically they seem be optimally placed about 1/3 up from the bottom of the tank.

                      Comment

                      • Rameses
                        Industry Expert
                        • Nov 2014
                        • 446

                        #12
                        Originally posted by jonstatt View Post
                        The thermal decline will be larger, if like me, you have a hot water circulating system that means that hot water is instantly available at any tap. This is particularly useful in a town house otherwise you can wait, quite literally, 2-3 minutes for hot water to come through. The downside is the thermal decline is much higher and therefore operating efficiency is significantly reduced.

                        As mentioned, the placement of the probe is important. Typically they seem be optimally placed about 1/3 up from the bottom of the tank.
                        Jon - this is on our radar to see if we can squeeze any extra efficiency out of the system.
                        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

                        • jonstatt
                          Automated Home Guru
                          • Feb 2015
                          • 111

                          #13
                          Originally posted by Rameses View Post
                          Jon - this is on our radar to see if we can squeeze any extra efficiency out of the system.
                          That could be interesting! You know where I am if you need a beta tester

                          Comment

                          • Kevin
                            Moderator
                            • Jan 2004
                            • 558

                            #14
                            The system really should take notice of the hot water temperature to initiate some form of optimised start. If people get up unexpectedly early and run the hot water off then it should be aware of that and compensate. In any hot water priority system, as mine is, you can't provide any room heating until the hot water is up to temperature so the knock on effect can be lack of hot water and / or cold rooms. Hot water circulation, again as in my system, means pre-heating the cylinder isn't as efficient. Optimised start for heating zones could fail as no heat will be available

                            As this situation can be anticipated by inspection of the setpoints, time settings and current cylinder (and room) temperatures, all information that evoHome has, then a 'smart' system marketed as 'saving you money' must surely implement this or it's just not living up to it's capabilities.
                            Last edited by Kevin; 16 June 2015, 02:39 PM.

                            Comment

                            • paulockenden
                              Automated Home Legend
                              • Apr 2015
                              • 1719

                              #15
                              Surely in your case (where the water needs to be up to temp before the heating will come on) you'd just schedule the hot water to come on an hour or so before the heating? I don't think any scheduled system could be expected to cope with "someone getting up unexpectedly early".

                              Comment

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