Evohome: temperature regulation

[paulockenden]

My system is setup as 8 zones and by 22:30 they are all set to 15deg until around 06:30. The challenge is that only two of the zones ever get down to 15deg and one of them stays at 17.5deg all night (the remainder stay between 1.5 and 2deg above the setpoint 15deg).
I do not understand this behaviour or how to troubleshoot it.

Are those zone still demanding heat? Check whether the radiators are hot / warm / cold during this period. It could just be that the zones are well insulated parts of the house, or perhaps upstairs where the day's heat from downstairs rises.

P.

[guyank]

RobCee, 8 degrees overshoot seems very extreme. Must be some error in the setup. Normally a zone stops demanding 1.5 above setpoint. So there must be another zone asking for heat. Normally your HR92 would close at 1.5 above setpoint too, so 8 overshoot shouldn't ever happen. Probably better to start a new topic for this case.

Guyank, thanks for the comment. You're saying it hits 22 when set to 20. Does it cool down towards 20 afterwards? What happens when it hits 20? Does it go to 21 or 22 again? Or stay nicely on 20?

It does come back down again to the set point of 20C, but this takes about an hour and its quite uncomfortable at first. It does then stay around 20C but there are variations of approximately ±.5C. This I can cope with, although slightly surprising given the amount we are paying for this equipment.

[RobCee]

Are those zone still demanding heat? Check whether the radiators are hot / warm / cold during this period. It could just be that the zones are well insulated parts of the house, or perhaps upstairs where the day's heat from downstairs rises.

It is a bit tricky to check for the zones demanding heat, as I am usually asleep!
I do not believe that these zones are particularly well insulated (although the coolest zone is very poorly insulated). The property is over 100years old and is fairly well insulated for it's age, just not the same standard as modern properties. The slow to cool zones are a mixture of downstairs and upstairs, so that doesn't appear to be the direct issue. It just strikes me as odd that some zones can stay so hot during the night. I could try requesting 10deg instead of 15deg as an overnight temperature, but that seems a little extreme.

[paulockenden]

Can you tell whether the boiler is firing overnight? Can you hear it? Or maybe read the gas meter morning and night.

It's just that some of my rooms stay warm- ish overnight, but it's just the built-up heat in the building structure.

[f1arp72]

My only observation regarding the massive overshoot noticed by f1arp72 was that I had the same at one point and couldn't figure it out. I ended up resetting the system and rebinding the valves and it sorted itself out. It appeared to be a system software corruption that had occurred. Never happened again.

Thanks for the suggestion, but it would appear to me that every time an issue is raised, the solution always seems to be to reset and rebind the system. When I first set this thing up, I must of reset and rebinded half a dozen times. I have very very carefully set my system up, having not only spoken to Richard at Evohome Shop but also follow his guide to the letter. Every radiator works and responds to the controller and I can open and close each radiator using the controller. I'm 100% sure they system if configured and set up correctly as there is absolutely nothing I would or would do differently if I reset it. Apologies if I sound like I do not appreciate your suggestion or if I'm being ungrateful, I assure you I'm not, but there are only so many times I can reset it.

The system does appear to work AFTER the initial overshoots, as the temperatures come back down to 20C and seem to maintain that temperature give or take 0.5C. It's just that I have to endure a very uncomfortable period of 23C in some rooms. I appreciate positioning of thermostats have an effect, but oddly, the 3C overshoot I had in the hallway is on the radiator which I would say has the best positioning, with nothing limiting or obstructing the airflow.

Not if you have an S-Plan system, as those boiler control parameters aren't available. That's my biggest bugbear with Evohome.

P.

Which is correct, I do have an S-Plan so I have to listen to my boiler fire up every 10 minutes for no reason whatsoever !!

[paulockenden]

To be fair, it's not for "no reason" - it's TPI maintaining temperatures, compensating for the natural heat losses which occur.

[top brake]

What system setup do you have?

Thanks for the suggestion, but it would appear to me that every time an issue is raised, the solution always seems to be to reset and rebind the system. When I first set this thing up, I must of reset and rebinded half a dozen times. I have very very carefully set my system up, having not only spoken to Richard at Evohome Shop but also follow his guide to the letter. Every radiator works and responds to the controller and I can open and close each radiator using the controller. I'm 100% sure they system if configured and set up correctly as there is absolutely nothing I would or would do differently if I reset it. Apologies if I sound like I do not appreciate your suggestion or if I'm being ungrateful, I assure you I'm not, but there are only so many times I can reset it.

The system does appear to work AFTER the initial overshoots, as the temperatures come back down to 20C and seem to maintain that temperature give or take 0.5C. It's just that I have to endure a very uncomfortable period of 23C in some rooms. I appreciate positioning of thermostats have an effect, but oddly, the 3C overshoot I had in the hallway is on the radiator which I would say has the best positioning, with nothing limiting or obstructing the airflow.



Which is correct, I do have an S-Plan so I have to listen to my boiler fire up every 10 minutes for no reason whatsoever !!

[PaulB]

@ PaulB - I have DM'd you.

Ok quick update!

Rameses passed on my details to a chap at Honeywell, who I had a very good conversation with & actually things did make some sense! Sorry I can't remember the name of the person I spoke to, but the main focus/ideas of the chat was:

• Balancing radiators (they may be oversized for the rooms so will need adjustment on the valves to restrict the flow. House is only 7 years old and other than the boiler being replaced by the previous owners due to it 'blowing up', nothing else has been changed other than fitting the Evohome kit, but will measure & work out the radiators properly)
• Reducing the running temperature of the boiler itself (Ideal Logic 18+). It was set to 'Economy' mode, however, I've now turned the temperature down further.
• Perform a calibration on all HR92's again (pull batteries, wait 10 secs, put batteries back in)
• Let the system then settle for a further week or so to 're-learn' how the house appears to be working.

One area of concern that was mentioned with my setup, was how quickly the rooms were heating up. This is what brought into question the size of the radiator in comparison to the room, and also the suggestion of turning down the boiler to reduce the rate at which the temperature increases. As the HR92's will learn how quick the room heats up, if it's too quick, then this can cause some very strange results. Trying to find the balance however of what setting to have the boiler on so it produces enough heat to also warm up the storage heater may take some further tweaking, but I think I'm on the mark with it now.

The second was a suggestion to reduce the flow to the radiators by adjusting the lock shield, or even the TRV valve itself by limiting how much it opens, although I've not had chance to look at this just yet.

I was also asked how I was collating the information & where the data was coming from, to which I said it's coming directly from the Evohome kit via the API.

But for now, I'll continue to monitor how it progresses over the next week or so with the boiler turned down, but from just this morning & last night, the bedroom radiators didn't 'bake' like they normally would!

[dmsims]

I think most boilers come with a suggested optimum outlet temperature, do you know what yours is / was ?

[SteveP]

SteveP and G4RHL, since the system works fine for you, could you answer the following questions (wich have to do with section A in the opening post):

1: do you most often heat 1 room, or multiple rooms at the same time?
2: to what temperature do you heat your rooms?
3: do you use Opentherm? Or on/off?
4: does your boiler have fixed pump speed, or adaptive?

.

Apologies for the delay but I don't seem to receive all the notifications and so hadn't seen this.
1 - I have 11 zones and I can be heating from 1 zone to all zones at the same time - I really use the scheduling and change temps throughout the day. That's why I love the system
2 - varies from some rooms at 16, some at 19 some at 21 and bathroom and separate en-suite at 23. The utility is set to 22, conservatory at 20. These temps are varied during the day via the schedule as I work from home but the rest of the family is at school so the schedule changes the room temps as demand changes.
3 - no sadly my boiler is too old for Opentherm - it is also a combi and that is no mean feat for Evohome due to the kids liking loooooooong showers when the heating is optimising. Evohome though seems to cope nicely.
4 - pump is fixed speed set at number 2. Ideally a combi prefers number 3 but that a) creates noise in the system b) did lead to overshoots as the water rate varies too quickly when valves are closed. The whole system is tightly balanced but as soon as you close one rad then effectively the balancing goes out. So a slower pump speed is better I found. Only causes a minor drop in hot water temperature as I have a large combi. The actual boiler is well oversized for the heat demand due to the hot water demand. However, the boiler does modulate its output to match so deals well with the demand with just infrequent manual adjustments to the heating temp control on the boiler and only when the temp outside changes significantly.

Other points I have seen raised:
a) Software system reset. I agree it is a pain and I have actually in 3 years of having the system only had to do the whole system once. I have had a few zone issues and for that I had to delete the zone and rebind the rads. That has happened twice. That is the one issues with parameter driven software solutions as sometimes a change in one parameter upsets another as it is almost impossible to test every scenario (Yes I am an IT software designer so have some sympathy with this complex solution)
b) Yes the system must be balanced correctly with all valves open otherwise it will not operate correctly and will get worse as valves close altering the water flow rate
c) I haven't altered the cycle and min on time as the boiler also does that. Leaving the parameters at default meant the boiler really controls things and the defaults work well with my boiler. I did play around with these in the early days until I worked out that changing them means the boiler and evohome will work against each other if changed from the default
d) I use optimum start but not stop. without optimum start I would be second guessing the weather and room heat up rates on a daily basis. I have used optimum start controllers since I first came across them 20 years ago (quite specialised back then)
e) other than changing temperatures if room demand changes from norm which I predominantly do via the android app, I tweak the temp schedules when we go from summer to winter and back as temperatures feel different. Otherwise I now leave the system well alone and it does a great job

I hope the above helps