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Thread: Evohome firmware 02.00.19.31 Beta Trial - Exclusive for Automated Home Members

  1. #601
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    Quote Originally Posted by robbietobbie View Post
    Can I ask people with a hot water cylinder how they set hot water - do you do 3 short bursts during a 24 hour period or do you leave on much longer in the day but with a larger hot water differential in the settings? Not sure which is more economical
    30 minutes in the morning! 60 minutes in the evening is fine. I think the 60 minutes is too much.

  2. #602
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    Quote Originally Posted by G4RHL View Post
    30 minutes in the morning! 60 minutes in the evening is fine. I think the 60 minutes is too much.
    Mines on 3pm till 11pm at night. Depends on your usage I suppose....

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    Just thinking out loud here with regards to Hot Water settings, so happy to be shot down in flames !!

    I currently only have my Hot Water ON via Evohome daily in the mornings from 06:30 - 09:00. We always get up at 07:00, so the Hot Water is always OK and ready for our morning showers.
    By 08:00 the Hot Water has already been reheated back up to my setpoint of 58c, so is effectively already OFF before the 09:00 scheduled OFF time.

    The unvented hot water tank then slowly cools throughout the day & following night until the next scheduled ON time at 06:30 the next day.

    BUT... would it make any sense to have the Evohome Hot Water scheduled ON ALL the time??
    It would obviously use some energy to keep to the 58c setpoint throughout the day, but as it would only need to raise the temp by just a few degrees every so often, would this use less energy in total (over 24 hours) than the larger amount of energy needed to reheat from a much lower temperature each morning at 06:30??

    Has anybody modelled this?

    As i say, happy to be shot down in flames...

  4. #604
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    Quote Originally Posted by robbietobbie View Post
    Can I ask people with a hot water cylinder how they set hot water - do you do 3 short bursts during a 24 hour period or do you leave on much longer in the day but with a larger hot water differential in the settings? Not sure which is more economical
    Quote Originally Posted by G4RHL View Post
    I live in a 4 bedroom house. Just self and wife. Hot water comes on in the morning at 07:00 for 30 minutes, which is more than adequate. In fact it is usually up to temperature in about 10 minutes or so. In the evenings it is on for an hour from 18:00 to 19:00.I probably could reduce that time.
    Our hot water is set to 54C with a 5 degree differential and just scheduled to be "on" when the house is occupied (and people are awake) plus a 30 minute warm up time allowance.

    So, Monday to Friday 5am to 7:20am then 4:30pm to 11pm. Weekends 6:30am to 11pm. If we're going to be out for the day on a weekend we use the Away action which turns off both hot water and heating.

    Keep in mind that the hot water being "on" just means that it will try to re-heat it if it falls below the hot water temperature minus differential (below 49C for me) during that time period. If the cylinder is well insulated and the water isn't actually being used you might only have one or two brief top ups in an entire day that don't amount to much gas use particularly if the boiler is already running to maintain room temperatures.

    The problem with scheduling hot water on only long enough to initially heat it up and then continuing to use that water through the day with it scheduled off is that if you do use the hot water a fair bit and allow it to cool down to say 40C-45C there is a significant risk of legionella. Even the 54C we run ours at is marginal if you read the literature. (However I find any hotter than that is just too hot at the tap without an automatic tempering valve)
    Last edited by DBMandrake; 3rd November 2020 at 03:03 PM.

  5. #605
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    Quote Originally Posted by DerekWilliamsUK View Post
    Just thinking out loud here with regards to Hot Water settings, so happy to be shot down in flames !!

    I currently only have my Hot Water ON via Evohome daily in the mornings from 06:30 - 09:00. We always get up at 07:00, so the Hot Water is always OK and ready for our morning showers.
    By 08:00 the Hot Water has already been reheated back up to my setpoint of 58c, so is effectively already OFF before the 09:00 scheduled OFF time.

    The unvented hot water tank then slowly cools throughout the day & following night until the next scheduled ON time at 06:30 the next day.

    BUT... would it make any sense to have the Evohome Hot Water scheduled ON ALL the time??
    It would obviously use some energy to keep to the 58c setpoint throughout the day, but as it would only need to raise the temp by just a few degrees every so often, would this use less energy in total (over 24 hours) than the larger amount of energy needed to reheat from a much lower temperature each morning at 06:30??

    Has anybody modelled this?

    As i say, happy to be shot down in flames...

    I have my Hot Water on permanent it is set to 56c

    I have a 200 Litre Foam insulated cylinder and i figure the heat loss is tiny from it so the hot water really only uses gas if I draw off water other than that I have a full tank of Hot water always available and if I dont draw water off then I am only making up the heat loss which is very small and for me is worth it to always have a full tank of HW

  6. #606
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    Quote Originally Posted by DerekWilliamsUK View Post
    Just thinking out loud here with regards to Hot Water settings, so happy to be shot down in flames !!

    I currently only have my Hot Water ON via Evohome daily in the mornings from 06:30 - 09:00. We always get up at 07:00, so the Hot Water is always OK and ready for our morning showers.
    By 08:00 the Hot Water has already been reheated back up to my setpoint of 58c, so is effectively already OFF before the 09:00 scheduled OFF time.

    The unvented hot water tank then slowly cools throughout the day & following night until the next scheduled ON time at 06:30 the next day.

    BUT... would it make any sense to have the Evohome Hot Water scheduled ON ALL the time??
    It would obviously use some energy to keep to the 58c setpoint throughout the day, but as it would only need to raise the temp by just a few degrees every so often, would this use less energy in total (over 24 hours) than the larger amount of energy needed to reheat from a much lower temperature each morning at 06:30??

    Has anybody modelled this?
    Heat loss from the cylinder is proportional to the temperature gradient through the skin and insulation of the cylinder. The hotter the water inside is relative to the surroundings the more energy lost and the more energy it takes to replace it. So the more time it spends at full temperature the more heat is lost. So it should be more energy efficient to let the cylinder temperature fall when the hot water is not needed and reheat it than keep "topping it up" in small increments.

    This applies to rooms and house walls as well by the way, which is why our heating goes off completely at night (except bedrooms) and completely in all rooms while at work - as it takes less energy to reheat it from whatever chilly temperature it falls to than it does to maintain it at a moderately reduced temperature let alone at full temperature.

    However the difference with a hot water cylinder is probably fairly small or negligible if it is well insulated. For example if you schedule hot water off at 9am and back on at 4pm and nobody is using the water in that time period, you're not actually saving any energy if the cylinder temperature doesn't drop far enough in those few hours to trigger a reheat anyway...

    You also have to consider Legionella risk, which trumps energy efficiency IMHO. Legionella multiplies rapidly at temperatures between 20-45C and isn't really killed off until at least 55C, so if your hot water is routinely falling down into that 20-45C range, spending a long time in that temperature range and then being used at the tap before being reheated, that is risky.

    For this reason we schedule our hot water to be on whenever the house is occupied and people are awake as in my previous post. It goes off when we're at work and overnight but is back on by the time we come home or wake up.

    Although our cylinder can fall into the low 40's overnight or during the day while we're at work it is always reheated to 54C again before hot water is actually used, so this still gives energy saving benefit over just running 24/7 but minimises risk.

    Personally I would not heat water once in the morning and once at night and then be using that hot water in between when the temperature is not being maintained at an adequately high temperature.
    Last edited by DBMandrake; 3rd November 2020 at 03:04 PM.

  7. #607
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    Quote Originally Posted by mtmcgavock View Post
    Mines on 3pm till 11pm at night. Depends on your usage I suppose....
    You don't use any hot water in the morning ?

  8. #608
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    Quote Originally Posted by DerekWilliamsUK View Post
    Just thinking out loud here with regards to Hot Water settings, so happy to be shot down in flames !!

    I currently only have my Hot Water ON via Evohome daily in the mornings from 06:30 - 09:00. We always get up at 07:00, so the Hot Water is always OK and ready for our morning showers.
    By 08:00 the Hot Water has already been reheated back up to my setpoint of 58c, so is effectively already OFF before the 09:00 scheduled OFF time.

    The unvented hot water tank then slowly cools throughout the day & following night until the next scheduled ON time at 06:30 the next day.

    BUT... would it make any sense to have the Evohome Hot Water scheduled ON ALL the time??
    It would obviously use some energy to keep to the 58c setpoint throughout the day, but as it would only need to raise the temp by just a few degrees every so often, would this use less energy in total (over 24 hours) than the larger amount of energy needed to reheat from a much lower temperature each morning at 06:30??

    Has anybody modelled this?

    As i say, happy to be shot down in flames...
    As others have said it is more efficient to let the tank cool then reheat, it will also reduce boiler cycling. A condencing boiler gives best efficiency when running at low flow temperatures, but often go to high output when heating the water.

    In the winter, when the house requires heat, it may be that any heat lost from the tank and associated pipework is not lost but simply helps to heat the house and the boiler cycling may not be increased much, so down sides would be minimal and you would have the benefit of constant hot water.

    My tank is centrally located, very well insulated, is closed to the boiler and the house is currently occupied all day, so heat loss would not be an issue. However any day with a bit of sun means that my solar thermal and solar PV can heat the tank with little or no input from the boiler so the boiler is only used for hot water, manually when required.

    As always it depends on your installation and usage requirements.

  9. #609
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    Quote Originally Posted by DBMandrake View Post
    You don't use any hot water in the morning ?
    Our usage is very minimal in the morning (We shower in the evenings), hand washing and that's about it. Our cylinder heats to 56oc, and looses 8oc overnight - so it usually sits at around 48oc in the morning. Heating until 11pm in the evening is more than enough to get us to 3pm the next day, and even if we wanted we can still get a shower or two in the morning (I do usually boost it though if we do).

  10. #610
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    Quote Originally Posted by DBMandrake View Post
    This applies to rooms and house walls as well by the way, which is why our heating goes off completely at night (except bedrooms) and completely in all rooms while at work - as it takes less energy to reheat it from whatever chilly temperature it falls to than it does to maintain it at a moderately reduced temperature let alone at full temperature.
    This isn't quite true. After taking numerous Gas readings over the course of 4 years i've concluded it's actually cheaper (Usage is less) to heat our home all Day whilst we're at work than it is having it on in the morning then drop down to the set back at 16oc, then back up in the evening. Obviously every property is different due to insulation levels, but for ours it's certainly better to leave it on all day rather than timings. If you've got an old, poorly insulated house with lots of drafts then it's a different story.

    My next experiment was actually to see if it was cheaper to leave on 24/7. However I haven't got around to that one yet....

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