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Thread: What would you like to see in evohome? (have your say)

  1. #221
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    Quote Originally Posted by fergie View Post
    Apologies if already suggested, but a couple of things I would like:

    1. Option to let the hot water temp drop more than 10 deg before kicking in again. This would be useful where I only want it to reheat after say a bath has been run.
    Just adjust the hot water differential ? The default is 10 degrees but you can change it in the system configuration.

    I actually have my differential reduced to 5 degrees as I only have my hot water set to 54 degrees and a 10 degree differential would let it get too cold.
    Last edited by DBMandrake; 24th May 2017 at 11:40 AM.

  2. #222
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    I can change it by 10, but it would be good if I could vary it by 15 or 20.

    My understanding is the water should be heated to 60-65 to prevent bacteria etc.

    So basically I'd like to be able to heat to 65, then let it drop back to 45 or 50 before kicking in again.

  3. #223
    Automated Home Legend paulockenden's Avatar
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    But in this case when the water has dropped to 46, say, the tank will contain a lot of water that hasn't been heated to 65. (When you've used the very hot water the tank has been replenished with cold).

    Legionalla thrives and multiplies quickly in the mid-40s. I think that's just asking for trouble, especially if the tank is likely to remain at that temperature for some time.

    P.

  4. #224
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    Quote Originally Posted by fergie View Post
    I can change it by 10, but it would be good if I could vary it by 15 or 20.
    I don't understand what you mean ? Are you saying you cant set the differential to any more than 10 degrees ? I'd have to check mine when I get home but I'm pretty sure you can set the differential to at least 20 degrees.
    My understanding is the water should be heated to 60-65 to prevent bacteria etc.
    There is a long running debate in the industry about what temperature hot water should be set to...

    In theory hot water in a tank should be heated to 60 degrees or more at least once a day to kill legionella bacteria, but 60+ degrees is up into the dangerous range where people can suffer scalds and burns from putting their hand in the flow of a hot tap. Not good if you have children using taps...

    Personally I can't put my hand in the stream of a hot tap for more than a moment if its any more than about 55, and even that is very uncomfortable.

    The ideal solution is to have the hot water cylinder quite hot, 60-65 degrees, and then have thermostatic mixer tempering valves installed at each hot tap - the legionella will be killed in the cylinder and then when you run the hot tap it automatically blends in cold water to bring the temperature down to a safe temperature like 47-50 degrees.

    http://www.ciphe.org.uk/consumer/saf...-water-scalds/

    I considered installing these last year but in the end I didn't do it mainly due to the cost of the valves (even though I only needed 3) and difficulty of intercepting the pipe work to the bath to install one on the bath.

    So without a mixer valve like this hot water temperature is always going to be a compromise between risk of bacteria or risk of scalding and burns.

  5. #225
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    Quote Originally Posted by paulockenden View Post
    But in this case when the water has dropped to 46, say, the tank will contain a lot of water that hasn't been heated to 65. (When you've used the very hot water the tank has been replenished with cold).

    Legionalla thrives and multiplies quickly in the mid-40s. I think that's just asking for trouble, especially if the tank is likely to remain at that temperature for some time.

    P.
    This is one reason why I went for a narrow 5 degree differential despite it causing more frequent reheats - to keep the minimum temperature up above the dangerous 20-45 range for bacteria multiplication without having the maximum temperature being too high.

    55 (at the tap) is the hottest I can stand to use a hot tap (even for briefly washing hands or squeezing out a sponge) without blending in cold water, so I have it set to 54 (since I use a one minute hot water overrun which causes 1-2 degrees overshoot sometimes) and 5 degree differential.

    A higher cylinder temperature with TMV's on all the taps to lower the tap temperatures would definitely be safer from both a bacteria and scalding point of view but absent those valves I think I've found a reasonable compromise.

    On the rare occasion where the system has overshot to 62 degrees (ahem - still doing that occasionally...) it really is just too hot to safely put your hands in.

  6. #226
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    I found the comments here interesting too in relation to safe hand washing temperatures:

    http://food.cieh.org/is_hot_water_to...estId=73791d84

  7. #227
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    I have almost exactly the same settings as you. 54 with +/- % 5 degrees.

    chart (4).jpg

    At first I assumed the 5 degree differential would give me a 10 degree span, bit it doesn't. Only the minus bit of +/- 5 degrees is used.

  8. #228
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    When I tried to change the offset, it let me select between 0 and 10deg only.

    My thinking is I only want the tank to fully reheat when water has been used for a bath or shower. I don't see the point of it kicking in every time a tap is run or the tank has naturally cooled during the day. Yes I could leave the water off more often, but being able to alter the offset more would be a very easy implementation.

    Another option would be to allow the hot water to be programmed to different temps at different times of the day, but that might be harder to do?

  9. #229
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    Quote Originally Posted by paulockenden View Post
    I have almost exactly the same settings as you. 54 with +/- % 5 degrees.

    chart (4).jpg

    At first I assumed the 5 degree differential would give me a 10 degree span, bit it doesn't. Only the minus bit of +/- 5 degrees is used.
    Yes, like most thermostats the set temperature is exactly the cut-out temperature, and the cut-in temperature is the set temperature minus the differential. So a 5 degree differential means exactly that.

    If I don't use any hot water when it is scheduled to be on I still only get about 3 reheats (each only lasting about 5 minutes) in a full day, so I don't think the smaller differential is costing me too much.

    If the differential was greater it would do less re-heats but each reheat would take longer so it wouldn't save much.

  10. #230
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    Quote Originally Posted by fergie View Post
    My thinking is I only want the tank to fully reheat when water has been used for a bath or shower. I don't see the point of it kicking in every time a tap is run or the tank has naturally cooled during the day.
    If the sensor is properly positioned about 1/3rd of the way up the cylinder it shouldn't reheat just because you run a tap for a short time. I've only got a fairly small 95 litre cylinder and I can still run at least two full sinks of dish water in the kitchen before it drops the 5 degrees necessary to trigger a reheat. Only when the cold water entering the bottom of the cylinder starts to approach the sensor location will the reading start to drop. (It will not drop at all for quite a while as the tap runs then will drop quickly as the cold water rises to and passes the sensor location)

    And if the tank is naturally cooling during the day without use that means the entire tank is cooling and if it cools down below about 45 degrees it encourages the growth of legionella. So during the day when you might use the hot water unexpectedly you want to ensure that it can't get below 45-50 degrees at any time you might be using the water.
    Yes I could leave the water off more often, but being able to alter the offset more would be a very easy implementation.
    Just keep in mind that if you're deliberately leaving it off during the day and letting it cool naturally and then still using the hot water that there is increased risk of legionella.

    Also important to keep in mind that there are two different things that can cause the reading to drop. If the tank cools gradually through lack of use then the temperature reading reflects the temperature of all the water in the tank. So for example if it dropped over many hours to 45 degrees, all the water in the tank is now at 45 degrees, roughly, and at risk.

    However if you start at 55 degrees and run the hot tap with hot water disabled, and then turn the tap off when it has dropped to 45 degrees, the top of the cylinder will still be 55 degrees and the bottom will be cold around 15-20 degrees and the part where the sensor is will be somewhere in between, eg 45 degrees due to stratification. So the water that is coming out of the cylinder is still hot enough to be safe and the cold water going in won't have had time for bacteria to grow, provided that hot water is enabled so that the system will heat it up quickly and not let it sit cold for a long time and then exit the cylinder into a tap.
    Another option would be to allow the hot water to be programmed to different temps at different times of the day, but that might be harder to do?
    Impossible to do - the evohome doesn't support scheduling different temperatures at different times of the day for hot water.

    And when you consider the balancing act between not being too hot to scald and not being too cold to allow bacteria to grow having a customisable temperature schedule for hot water really doesn't make sense. You find the best compromise temperature and differential for your circumstances and stick with it.
    Last edited by DBMandrake; 24th May 2017 at 01:07 PM.

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