Tracking down random boiler demand with Evohome

[G4RHL]

agreed - (I think we're saying the same thing in different ways) - but it's (IMO) it's essentially irrelevant to the way that optimisation works

Whilst jonstatt has said Evohome does not need to know the outside temperature the guidance when you go to settings indicates it does take account of it. Without an outside sensor it is not possible bearing in mind it works without the Gateway so cannot always access a weather forecast. It will know current temperature inside and what is called for and then presumably calculates how long is needed to bring it up the set point. In my case, taking my lounge as an example where it set at weekends to come on at 06:40 at 20C because I know almost without fail optimisation will click in around 05:40 which is when I want the heat, it is at a comfortable temperature within 10 minutes or so and at the set temperature usually well before 20 minutes all from a start temperature of around 15 to 16C but then last weekend when the start temperature was around 14C within 10 minutes the room was comfortable. It certainly gets it up to set point well before the heating is needed which is why I have it set so that I am using the optimisation period as one where I need the heat on.

[top brake]

Here's what the carbon trust say about optimisation

https://www.carbontrust.com/media/131445/ctl035_how_to_implement_optimum_start_control.pdf

[Rameses]

Its a 'red herring' for the UK (unless you just fancy looking at the weather onscreen and happen to have one of the hometronic sensors) - but for other regions outside weather function is useful for other countries like the German market where boiler control is directly performed this way - with no radiator demand and different system altogether. Thanks for posting up my previous post on this.

[Mavis]

[QUOTE=G4RHL;21316]

Right, last night I went to bed with the controller and kept watch.

Thats not a nice name to give your husband!

At least it doesn't hog the duvet and does what I tell it (most of the time)

[G4RHL]

Here's what the carbon trust say about optimisation


https://www.carbontrust.com/media/13...rt_control.pdf

Useful article. I note it talks of an external sensor. Do Honeywell do an external sensor that links wirelessly to Evohome?

[jonstatt]

Useful article. I note it talks of an external sensor. Do Honeywell do an external sensor that links wirelessly to Evohome?

They do, and the system will even let you link it in, but as Rameses says above, it does absolutely nothing for the EVOHOME system for UK users.

[orange]

Recommend that you log a call with consumer support, thanks

and a big radio silence from consumer support

[emmeesse68]

They do, and the system will even let you link it in, but as Rameses says above, it does absolutely nothing for the EVOHOME system for UK users.

I have an external temperature sensor wired to my boiler, that could be used to set OTC (Outside Temperature Compensation) on the boiler itself. I'm not using this feature right now because I'd like to keep it simple until I learn how to move all the levers.

Anyway... since I'm using the R8810 OpenTherm boiler gateway, I'm sure my EvoHome is asking my boiler for this parameter value - and my boiler answers with the actual reading. I might try checking again, but I did it a few days ago and I couldn't find an option in the installer menu to show external temperature.

EvoHome asking my boiler the temperature makes me think it's using it to some point...

[G4RHL]

Optimisation.

Continuing a check on what is happening this morning I monitored what happens in my Living Room. It is set to be 20c at 06:40 but I have done that on the basis that with optimisation on it will come on around 05:40 when I will be using the room. The following was recorded:

Heating came on at 05:40, TRV temp 16, thermometer temp at desk height 16.5
05:50 TRV read 17, thermometer 17.5
06:09 TRV 18, thermometer 18
06:18 TRV adjusted self, heating went off, initially TRV read 19 for short period then 20, pump still on
06:29 TRV reading 20 heating off, pump off, thermometer reading 19.5
06:40 TRV reading 21.5, thermometer 20

It therefore took 49 minutes to lift the room temperature from 16 to 20. It seems to show the system making allowances for the fact heat is still coming through to be utilised and switching off because of that. Indeed this is evident by the fact that it shut off the boiler at 06:29 but at 06:40 the temperature was 21.5 although it should have been 20.

On this basis optimisation should have brought the heating on at 05:51 and not 05:40 but I always know it comes on 60 minutes before hence the settings I have. Optimisation is set to come on no sooner than one hour before

What was interesting is that although I had a separate thermometer alongside it was an HR92 which is not bound, just left there whilst we complete the conservatory, throughout it consistently read the same as the TRV on the radiator.

So yes, optimisation works but it is not that efficient for it comes on 11 minutes sooner but that might be part of the inbuilt tolerances.

[erik]

If you would use a simple old Honeywell Round, it would probably be easily able to heat the room to exactly 20 instead of over-shooting to 21.5. Because, in my experience, the over-10-year-old Honeywell Round acts smarter than the new Evohome system. Even though it's 20x cheaper too.

[erik]

Test result of the heating behavior of the Honeywell Round Wireless (connected to my boiler through BDR91 relay). I've been monitoring the temperature reading on the Round Wireless and on my own thermometer. Also, I've been monitoring the BDR91 and boiler through a webcam.

Setpoint was set to 17.5.

It takes about 1.5 hours to heat up the room from (according to my own thermometer): 17.1 to 18.2 degrees, it's requesting heat for a minute or two or three from the boiler every 10 minutes. The closer it gets to 18.2, the shorter the requests for heat become.

Then, after reaching 18.2 it totally stops requesting heat for about 2 hours, during wich the room cools down to 17.1 again.

Then it starts requesting heat again, every 10 minutes, taking about 1.5 hours to reach 18.2 again.

Then it cools down again to 17.1, taking 2 hours.

Then it starts heating up to 18.2 again, taking 1.5 hours.

And so forth and so forth... During all this, the Round Wireless is continuously showing a reading of 17.5.

So: pretty bad behavior, just like when using Evohome. Temperature going up and down by at least 1 degree. Heating going on for 1.5 hours, and then off for 2 hours. Etc. etc. Very uncomfortable.

Again: when using a simple old skool Honeywell Round on/off, the temperature stays way more constant, to a precision of about 0.1 degree up/down. The old Round on/off skips a 10-minute heating cycle sometimes. Sometimes even 2 in a row. But it never stays off for 2 hours. And it never goes go way above setpoint. It's near perfect. If only it could do schedules and zoning...

[G4RHL]

I repeated the check I did yesterday and posted above, this morning. The boiler fired up exactly one hour before the set point. Start temperature was 16c and it took the same time to get up to temperature, with similar readings. I note that whilst the TRV reads 21.5 when the setting is 20, and the boiler is not then on, the actual temperature at living height, as opposed to virtually floor level, is 20C. Am happy with that. Indeed the room is prefectly comfortable within 10 minutes of the system firing up. The set point for 08:00 is 18C, it is now 07:24 and I note optimisation has checked in, the app reads 18C in readiness obviously happy with what heat is now in the system.

Also nice last night when out for a meal to turn up the heat in the bedroom (now that sounds interesting!) from the restaurant for when I get home.

Still puzzled about balancing and the need for it. Without Evohome I can understand it, but if in any event all radiators heat up at similar times and/or if only one zone wants heat, is it that important?

[jonstatt]

I repeated the check I did yesterday and posted above, this morning. The boiler fired up exactly one hour before the set point. Start temperature was 16c and it took the same time to get up to temperature, with similar readings. I note that whilst the TRV reads 21.5 when the setting is 20, and the boiler is not then on, the actual temperature at living height, as opposed to virtually floor level, is 20C. Am happy with that. Indeed the room is prefectly comfortable within 10 minutes of the system firing up. The set point for 08:00 is 18C, it is now 07:24 and I note optimisation has checked in, the app reads 18C in readiness obviously happy with what heat is now in the system.

Also nice last night when out for a meal to turn up the heat in the bedroom (now that sounds interesting!) from the restaurant for when I get home.

Still puzzled about balancing and the need for it. Without Evohome I can understand it, but if in any event all radiators heat up at similar times and/or if only one zone wants heat, is it that important?

You mentioned that the heating was coming on exactly 1 hour before. This makes me wonder what would happen if you had the maximum optimisation time set to 3 hours. The fact it comes on "exactly" means in it's own little ideal world, it would possible come on even sooner!! (I.e. it's hitting the hard limit you set of 1 hour) Would you try this to satisfy my curiosity? If it comes on at 3 hours, then something is really wrong here.

[G4RHL]

You mentioned that the heating was coming on exactly 1 hour before. This makes me wonder what would happen if you had the maximum optimisation time set to 3 hours. The fact it comes on "exactly" means in it's own little ideal world, it would possible come on even sooner!! (I.e. it's hitting the hard limit you set of 1 hour) Would you try this to satisfy my curiosity? If it comes on at 3 hours, then something is really wrong here.

Have compromised and set it for 2 hours. There is no possible need for it to come on 2 hours early as it should know it takes 40 minutes or so to get up to set point. We'll see! Many weeks back before I fully understood what optimisation was meant to do I had left it at the default of 3 hours, my bedroom radiator seemed to come on far far too early. If I remember rightly some 2 hours or more too early. But it may have been in learning mode then.

[top brake]

I repeated the check I did yesterday and posted above, this morning. The boiler fired up exactly one hour before the set point. Start temperature was 16c and it took the same time to get up to temperature, with similar readings. I note that whilst the TRV reads 21.5 when the setting is 20, and the boiler is not then on, the actual temperature at living height, as opposed to virtually floor level, is 20C. Am happy with that. Indeed the room is prefectly comfortable within 10 minutes of the system firing up. The set point for 08:00 is 18C, it is now 07:24 and I note optimisation has checked in, the app reads 18C in readiness obviously happy with what heat is now in the system.

Also nice last night when out for a meal to turn up the heat in the bedroom (now that sounds interesting!) from the restaurant for when I get home.

Still puzzled about balancing and the need for it. Without Evohome I can understand it, but if in any event all radiators heat up at similar times and/or if only one zone wants heat, is it that important?

Your questioning is unsurprising, I have had a similar discussion with several heating installers over the years, adamant that Evo overcomes this lack of balancing.

The optimal system is one that is correctly sized and commissioned. Controls can work all sorts of witchcraft these days, controlling systems to accuracy and stability levels skin to industrial process control.
But putting it simply why make the controls work harder than they need to? All you will accomplish is to make the overall control less responsive and stable. And wear out batteries in HR92

Hope this helps give a perspective from a controls engineer and a practical real world view?