I found the comments here interesting too in relation to safe hand washing temperatures:
What would you like to see in evohome? (have your say)
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I have almost exactly the same settings as you. 54 with +/- % 5 degrees.
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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.
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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?
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Originally posted by paulockenden View PostI have almost exactly the same settings as you. 54 with +/- % 5 degrees.
[ATTACH=CONFIG]1039[/ATTACH]
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.
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.
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Originally posted by fergie View PostMy 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.
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.
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?
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; 24 May 2017, 12:07 PM.
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I've a 210 baxi stainless tank so the probe had to be installed quite low - maybe not quite a 3rd up where the cover is.
Makes sense what you are saying about the reading dropping fast as cold water enters. I've not checked how often and for how long it reheats if always on. My thinking was if it's heated to 65 and then allowed to naturally cool to 50, it would still be safe.
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Originally posted by fergie View PostI've a 210 baxi stainless tank so the probe had to be installed quite low - maybe not quite a 3rd up where the cover is.
Makes sense what you are saying about the reading dropping fast as cold water enters. I've not checked how often and for how long it reheats if always on. My thinking was if it's heated to 65 and then allowed to naturally cool to 50, it would still be safe.
When you use some hot water causing the reading to drop the water in the top part of the cylinder isn't dropping in temperature and the system only has to reheat the new cold water that has entered at the bottom - so long as the cold patch remains significantly colder than the water at the top the heating process causes convection in only the cold part of the cylinder with the boundary to the hot section at the top acting like a "ceiling" for the convection. So it's not like the reheating process is having to reheat the entire cylinder - only the cold part.
In a way this is all quite theoretical because I think Legionella in household hot water cylinders (as opposed to large commercial hot water systems) is exceedingly rare, but if you do get it I believe it can be quite nasty.
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Legionella in the home setting usually manifests itself in the form of mild cold or flu symptoms. Of the 15 or so serogroups 1 is the worst, most people contract sero group 5-10. In the household situation using a shower (mostly likely source of an infection) every day tends to thermally flush the bacteria out, but it's not guaranteed, so water temperature should ideally be at 60°C or more to help prevent growth. In an industrial environment where legionella is usually controlled by chemical cleaners, the chemicals need to be changed regularly as the bacteria eventually becomes resistant.
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Originally posted by g6ejd View PostLegionella in the home setting usually manifests itself in the form of mild cold or flu symptoms. Of the 15 or so serogroups 1 is the worst, most people contract sero group 5-10. In the household situation using a shower (mostly likely source of an infection) every day tends to thermally flush the bacteria out, but it's not guaranteed, so water temperature should ideally be at 60°C or more to help prevent growth. In an industrial environment where legionella is usually controlled by chemical cleaners, the chemicals need to be changed regularly as the bacteria eventually becomes resistant.
We have an electric shower but a hot water cylinder for two sinks only, which would seem to be the worst case scenario as we don't get through a cylinder of water very quickly...
I do make sure that the hot water is scheduled on and thus between 49-54 degrees during the day whenever the house is occupied though, even if I don't think we would need to be using the water much outside of breakfast and dinner times. For a while I was only scheduling it at times of the day when I thought we might actively use the water but thinking about legionella made me change that to having it on any time the house is occupied. (Except overnight)Last edited by DBMandrake; 30 May 2017, 09:01 AM.
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Originally posted by paulockenden View PostI seem to remember it's water being held at hot (but not hot enough) temperatures that's the problem. The tank becomes a bug farm.
I think if I was getting a new boiler I would switch to a combi as we really have no need for a hot water cylinder with only two sinks and a rarely used bath. (We almost always use the electric shower) The dishwasher and washing machine both also heat their own water so only need a cold supply. That solves the problem completely and probably saves money for infrequent use of hot water. The only reason we have a cylinder is that's what was already there. I just modified it to be an S-Plan system controlled by the Evotouch instead of an old gravity circulation system! Previously the hot water temperature was all over the place - either too cold or too hot depending on heating demands.Last edited by DBMandrake; 30 May 2017, 09:12 AM.
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Originally posted by paulockenden View PostI seem to remember it's water being held at hot (but not hot enough) temperatures that's the problem. The tank becomes a bug farm.
Not sure how all this fits in with the original thread though!!
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Originally posted by paulockenden View PostHas anyone added Stringify integration to the "What would you like to see?" list yet?
I notice a couple of other Honeywell products are there, but no Evohome.
Given how much more flexible Stringify is compared to IFTTT, it's a real pity it isn't supported.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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