Originally posted by robbietobbie
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Evohome firmware 02.00.19.31 Beta Trial - Exclusive for Automated Home Members
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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...
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Originally posted by robbietobbie View PostCan 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 economicalOriginally posted by G4RHL View PostI 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.
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; 3 November 2020, 03:03 PM.
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Originally posted by DerekWilliamsUK View PostJust 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
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Originally posted by DerekWilliamsUK View PostJust 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?
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; 3 November 2020, 03:04 PM.
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Originally posted by DerekWilliamsUK View PostJust 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...
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.
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Originally posted by DBMandrake View PostYou don't use any hot water in the morning ?
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Originally posted by DBMandrake View PostThis 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.
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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Originally posted by mtmcgavock View PostThis 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.
I did the same tests you did where I used a set back in the 16-18C range at night and during the working day for the full house and it was unequivocal in my case - gas usage was much lower just scheduling the zones to 5C when we were out of the house (and downstairs zones at night) and letting optimal start figure out when to start heating to get things back to where we wanted them again.
In mild weather like spring/autumn you'll find that when turned off for more than about 12 hours a house will reach an equilibrium temperature - for example it might reach 15C and stay there, so if your set points are below 15C in those conditions you'll use zero gas even if you're away for several days but if your set back was say 18C then you're constantly using gas during that period.Last edited by DBMandrake; 5 November 2020, 10:29 AM.
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Originally posted by DBMandrake View PostThat just means your boiler is a lot less efficient at full pelt than it is at lower output, and this is counteracting the gains had from keeping the house temperature lower when unoccupied. Perhaps it's not condensing properly in those conditions due to insufficient temperature drop across the radiators ? As I don't have a condensing boiler I don't have this factor to worry about - efficiency won't vary much with return flow temperature or whether it's going flat out or not.
I did the same tests you did where I used a set back in the 16-18C range at night and during the working day for the full house and it was unequivocal in my case - gas usage was much lower just scheduling the zones to 5C when we were out of the house (and downstairs zones at night) and letting optimal start figure out when to start heating to get things back to where we wanted them again.
In mild weather like spring/autumn you'll find that when turned off for more than about 12 hours a house will reach an equilibrium temperature - for example it might reach 15C and stay there, so if your set points are below 15C in those conditions you'll use zero gas even if you're away for several days but if your set back was say 18C then you're constantly using gas during that period.
In my tests I certainly found that it uses less gas. It's hard to monitor due to weather conditions, but I try to log them along with my readings. I've monitored for all day usage over a couple of years now (We've lived here 4 years and had HR92s from new) and it's pretty consistent in the readings. Whilst it doesn't use considerably less gas than timings, it does use less. My theory is that you're heating the fabric of the house. A very well insulated house should in theory have little heat loss, so keeping it at a set point all day should in theory use less energy than letting the room cool then reheat - as your then having to heat everything again, not just the room but the fixtures and fittings and any walls etc.
However I do have a very well insulated house (My front door has a U value of 0.87). In a house that's older, poorly insulated, and has lots of drafts then I can see how you'd use more gas. For example my parents have a HR92 in a rear porch where theres a draft from the cat flap. If they use a 16oc set back on this rad it just runs 24/7 - maybe an extreme example but in a house where your heat losses are great then I can see how timings prevent a system from overworking.
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Originally posted by bruce_miranda View PostHad my first experience of seeing what happens to all the fancy weather compensation when broadband goes down. Everything reverts to the set points and then seamlessly goes back into weather compensation mode when things return to normal. Nice.
My thanks to Virgin Media for involuntarily testing this out for me a few times recently.
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If I apply to join the beta now, will I get 19.31 or 19.33 (assuming the beta programme still allows new participants). I'm getting some quite severe overshoots, and from reading here, it seems that 19.33 may help matters. Are there any negatives to be aware of?
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