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Thread: How "smart" is the hot water system

  1. #1
    Automated Home Jr Member
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    Default 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

  2. #2
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    Quote 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.

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

  4. #4
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    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.

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    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!!

  6. #6
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    Quote 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.

  7. #7
    Automated Home Legend paulockenden's Avatar
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    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.

  8. #8
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    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.

  9. #9
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    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!

  10. #10

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    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; 26th May 2015 at 11:03 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

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