Tracking down random boiler demand with Evohome

[orange]

it's possible if you change the optimisation time to 2 hours that the controller will need to relearn the room curve again - so will start up 2 hours early anyway....I know it shouldn't need to do this but we know that evohome has some programming quirks, so any fundamental change in the optimisation settings might mean a relearn.

interesting to see what happens.

also FWIW I've still had no reply to my support request from a few days ago - or any response from the dataprivacy email.

[HenGus]

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.

I must be missing something here. With a target/temp set point of 07.10am, the HR92s in my bedroom whirred at 06.50am yesterday and 06.55am today. Even on the coldest night, with an OAT below zero, the longest optimisation period I have had is 45 minutes. So what's different: bigger room, less insulation, smaller radiators, Evohome set up .......?

[orange]

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.

In certain situations (single zone requesting heat) I can see why balancing would be irrelevant - but it's basically no different to having manual thermostats.

Imagine if you had all radiators demanding heat - ie all valves open. If the system wasn't balanced then you would find some radiators/rooms heating much faster than others....in fact on a very badly balanced system some rooms might not heat at all.

[HenGus]

In certain situations (single zone requesting heat) I can see why balancing would be irrelevant - but it's basically no different to having manual thermostats.

Imagine if you had all radiators demanding heat - ie all valves open. If the system wasn't balanced then you would find some radiators/rooms heating much faster than others....in fact on a very badly balanced system some rooms might not heat at all.

Yes, but the USP of zoning systems is that the user can control the rooms in which heat is required. I know that the jury is still out on whether heat is needed in all rooms all of the time but this is not how I use my system - or how I used my basic TRVs before Evohome. Last night, for example, we had heat in our living room and hallway/stairs and bedroom just before we turned in for the night. The other rooms were on frost protect. As I type, the lowest temperature in my 5 bed room is 12C in our downstairs loo.

[jonstatt]

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?

I think what you are getting at is that the system assumes this 11 degree drop from one side of the radiator to the other (for a conventional boiler). If it is only 4-5 degrees, then the system will tend to overshoot and cause the HR92 to close and open more extremely using more battery power as well as perhaps having less stability on the temperature.

[top brake]

I think what you are getting at is that the system assumes this 11 degree drop from one side of the radiator to the other (for a conventional boiler). If it is only 4-5 degrees, then the system will tend to overshoot and cause the HR92 to close and open more extremely using more battery power as well as perhaps having less stability on the temperature.

Think of it another way

If you have a car with a small steering wheel to travel in a straight line you will be constantly correcting the steering angle

It's called control authority

Another analogy is trying to drive a racing car to the shops, one prod of the loud pedal and you're off, then you'll need to be on the brakes.

To achieve responsive and stable control the control system needs to be able to modulate the heat output with small actuator movements and controlled applications of heat

[erik]

Racing car: you could tap the paddle for a short time and get up to speed , then wait a while untill it slowed down enough and then tap the paddle again shortly. Wait a while. Tap it again. etc.

That's much better than holding the paddle for a longer while or too often without enough waits. The latter will get you way above the wanted speed and causes having to wait very long for it to slow down again.

Short taps + short waits = more constant speed than long taps + long waits.

Old Honeywell Round does short taps + short waits so the room sticks at the desired temperature. New Round Wireless and Evohome do long taps without enough waits, causing it to get way above desired temperature and then a long wait to cool down to the desired temperature, after wich it does long taps again to get way above desired temperature again, etc.

[G4RHL]

In certain situations (single zone requesting heat) I can see why balancing would be irrelevant - but it's basically no different to having manual thermostats.

Imagine if you had all radiators demanding heat - ie all valves open. If the system wasn't balanced then you would find some radiators/rooms heating much faster than others....in fact on a very badly balanced system some rooms might not heat at all.

My system is 17 years old, I have never balanced it. I have 14 radiators including towel rails, apart from one "at the end of the line" I do not find any radiator getting hotter quicker than another and from what I read it is for such an occasion balancing is desirable. Evohome means zoning and logic is telling me that balancing begins to become irrelevant if a radiator gets hotter than another unless all are asked to come on. My end of line radiator is in my conservatory. The pipes have a longish route under a cold floor to get to the radiator. They connect to the circuit from my living room. If I turn the living rooms radiators off or all other radiators off the time the conservatory radiator takes to get hot does not change. I will know better in two days as we have replaced the conservatory with up to date thermally efficient glass etc. the radiator has been off and needs a second coat of paint before I turn it on again. Incidentally the conservatory temperature with its new glazing is noticeably warmer and that's with no heating on in it.

[Wally©]

Your system is not that old... Rad balancing is for systems which do not use a collector from where the water is distributed to each individual radiator...image.jpg

[G4RHL]

I must be missing something here. With a target/temp set point of 07.10am, the HR92s in my bedroom whirred at 06.50am yesterday and 06.55am today. Even on the coldest night, with an OAT below zero, the longest optimisation period I have had is 45 minutes. So what's different: bigger room, less insulation, smaller radiators, Evohome set up .......?

The room is roughly 21 feet by 12 feet, has two outside walls, one protected from the elements by the next door property. Cavities are filled, windows are double glazed. It heats up quickly. It certainly does not need to be on an hour in advance to get to temperature but that is what is happening and yet it switches down within around 40 minutes and that is 20 minutes before the desired heat level is wanted.

Have adjusted the advance time to 2 hours and appreciate the point elsewhere that I might have to let it settle in again before I get an accurate position but strictly speaking that should not be necessary. If the system has learned that it takes 40 minutes to get up to temperature then it should not matter what the setting is, whether 3, 2 or 1 hours, for it should come on 40 minutes before. But it doesn't, it comes on 60 minutes before. Probably 120 minutes tomorrow!

[G4RHL]

Your system is not that old... Rad balancing is for systems which do not use a collector from where the water is distributed to each individual radiator...[ATTACH=CONFIG]498[/ATTACH]

Looks like a plumber's nightmare!

[Wally©]

Why you think so...looks pretty ok to me...everything is easily accessible...+ I would rather have it on the groundfloor next to my boiler instead of in a cold basement...

[G4RHL]

Yeh, I suppose so. I'd have them all labelled. At least I have nothing like this!

[SensibleHeatUK]

Using a distriubtion manifold helps enormously with system balancing and if fitted with suitable valves it allows controls to be fitted on the manifold (using the same kind of thermal actuators that would be used on an underfloor heating manifold). It is popular where architectural rads are being fitted and you don't want to spoil the look of the rads with unattractive TRVs. The more enlightened plumbers/heating engineers also use similar manifolds for hot and cold water distriubtion too - the manifolds are close the the rooms requiring hot and cold water, and allow simple isolation per appliance and improved flow (or flow reduction where needed). It also allows plastic pipework to be fitted without any breaks/fittings in ceiling/floor voids. We see this a lot in the residential properties we work in.

[Ubarrow]

I can see the need for basic balancing, but I've assumed that Evohome takes away the need for fine adjustment as the system itself effectively destroys any finely balanced system - or have I got this wrong?