Opentherm Weather Comp and Intergas HRE 24 OV

[mike42]

I haven't seen much information about exactly how and why you'd want either or both of these. I suspect those that don't know just say "...the boiler will use the WC and OT to work more efficiently..". Yeah but how ?

What problem are we solving? Lets deal with that first. So its said that with a traditional on/off boiler controlled by a room stat, the boiler will overshoot and undershoot its target. So in the real world, Mrs Miggins sets the temp to be 21 and what actually happens is that it cycles between 19 and 23. Doesn't sound too terrible to me. Then we get told well the boiler will also by "cycling". Perhaps on and off every 30 minutes? Lets put that into perspective. My old boiler an Ideal 3100 ran for 30 years and was still running fine when changed. However it would cycle every MINUTE - that's right you set the temp to be 21, the boiler was well oversized and so the rad water temperature hit its boiler-maximum and so the boiler would shut down even when the temp of the house was say 15. It was doing that all its operational life - 30 years. Obviously that was all badly specced and configured but if a boiler can last that long cycling every minute of its operation then I can't see how its such an issue for a boiler to cycle every 30 minutes or so once the home has reached temperature.

On to the how to solve this (non existent?) problem. The OT tells the boiler what the stat's target temperature is and presumably tells it what the temp is now. The WC part tells the boiler how long it is likely to take increase the home temperature by say 1 degree - the colder it is, the longer it takes to heat up. Armed with both, presumably the boiler outputs its highest allowed temp until it gets close to the target temperature. It can see how long it is taking to reach that target temperature so I'm not sure how helpful the WC is when OT is in operation. And yet my boiler has connections to both OT and WC but there is zero information about what it does with that info.

Even though I'm obviously a bit sceptical about the whole thing, I'm planning on connecting up the OT to a yet-to-buy-controller like a Nest (anyone have any suggestions on what is a good OT controller?). Then I can look forward to perfectly stable 21 degree temps. Perhaps I'll put an independent digital controller on the wall so I can start shouting at the stat if the temperature exceeds 21.5 . A modern day fawlty towers if you will....

 

[Harry Bloomfield]

I haven't seen much information about exactly how and why you'd want either or both of these. I suspect those that don't know just say "...the boiler will use the WC and OT to work more efficiently..". Yeah but how ?

If you don't understand the how, and more importantly the why - then why bother doing it at all?

 

[mike42]

If you don't understand the how, and more importantly the why - then why bother doing it at all?

I look forward to your explanation as to why you think WC and OT work well together......

 

[RandomGrinch]

I look forward to your explanation as to why you think WC and OT work well together......

The main point you seem to be missing is OpenTherms ability to control the boilers modulation.
Here's a recent report that explains the theory of modulating controls, load compensation controls (along with weather compensation) and their potential energy efficiency gains, when combined with a modulating boiler.

https://www.beama.org.uk/static/7f5ebe31-04e1-470e-9befd249359959d9/15d07ed2-35d0-4c9f-90f958f81e9425f6/Salford-tests-on-load-and-weather-compensation.pdf

The upper efficiency gain, commonly stated for OT controls is around 15%.
This report suggests annual gains of around 12% (although, that may be a slight underestimate), over the use of a standard room stat.
It also suggests that smart stats with proportional on/off load compensation could achieve energy savings of up to 10%.
Although interestingly, correctly commissioning the system, including range rating the boiler, setting the correct temperature curves and balancing the system, produced noticeable efficiency gains, that reduced the effectiveness of the OT gains.
They also found that a known issue in weather compensation set up, improved efficiency, but didn't allow the room to actually come near to the set point temperature - it was noted that weather compensation is often disconnected, when OT is used to work around this issue.

Although real world savings could be anywhere up to around 15%; there is a genuine potential for energy savings by utilising OT, load compensation, smart stats, or correct commissioning, in part, or in any combination.

 

[mike42]

I'm not missing that point as yes that's the entire idea isn't it?

The main point you seem to be missing is OpenTherms ability to control the boilers modulation.
Here's a recent report that explains the theory of modulating controls, load compensation controls (along with weather compensation) and their potential energy efficiency gains, when combined with a modulating boiler.

Maybe I'm guilty of not restating that fact in my post. As you say that's the entire idea. I leapt forward and asked what problem does it solve?

None of this explains how and why OT AND WC (or load compensation AND weather compensation if you prefer that terminology).

I admit to just reading so far the summary in that report partly because even though conducted by a University, it was paid for by a Heating Control company so is not exactly unbiased.

Intuitively, does it even make sense? Yes overshooting is going to use more energy (but undershooting less) and cycling is bad (but not that bad as I suggest above).

I was hoping to get some insight and debate how how, why and whether or use one the other or both. Maybe we will all learn something although appreciate my first post was perhaps too much for many folk to wade through and is certainly no introduction to the topic.

 

[Harry Bloomfield]

Although real world savings could be anywhere up to around 15%; there is a genuine potential for energy savings by utilising OT, load compensation, smart stats, or correct commissioning, in part, or in any combination.

My system is not OT, rather it is Vaillant's system. Since installing it I have noticed some savings in gas use, but I am reluctant with so many varibles involved, to even make a guess at how. The more obvious benefit, is that the house temperature, remains completely steady, no wild swings, between stat switching off, and back on.

 

[RandomGrinch]

Maybe I'm guilty of not restating that fact in my post. As you say that's the entire idea. I leapt forward and asked what problem does it solve?

At least to me, it wasn't clear exactly what you were getting at, and as boiler modulation wasn't mentioned, I had to make the point.

I admit to just reading so far the summary in that report partly because even though conducted by a University, it was paid for by a Heating Control company so is not exactly unbiased.

Maybe not unbiased, but funded by the manufacturers trade body and not an individual heating control company.
The fact that they show that a properly commissioned system reduces the effective efficiency increase of OT controls, does suggest some level of impartiality.

Intuitively, does it even make sense? Yes overshooting is going to use more energy (but undershooting less) and cycling is bad (but not that bad as I suggest above).

Whatever your feelings are about this, we are fighting for the last 10-15% improvement in efficiency. Eventually this hits the law of diminishing returns.

Having weather compensation AND OT probably gets you another couple of percentage point towards the target.

If you take Nest for example, the weather compensation is already calculated within its algorithms, from its Internet connection to Google.
Having additional local weather compensation, may gain a tiny fraction of a percentage point of efficiency - how much more accurate is your thermocouple, compared to Googles forecast and data from the network of other local Nest users?
Even if the forecast was less accurate, would it make a huge difference?
Houses are not precise.

What interests me, is the fact that a load compensating on/off stat can nearly match the efficiency improvement of OT.
Basically, by treating the on/off cycle as pulse width modulation, the boiler can be controlled more efficiently.
This is an extremely crude method of control compared to OT, and it may wear out the boiler quicker, but this imprecise method still works remarkably well.

 

[mike42]

A couple of interesting replies - thanks.

What controller are you both using ?

I started looking into EPH and liked what I saw. The main down point seems to be cosmetic - it looks crap. Nest v3 is another option I suppose. It seems there aren't many....

 

[RandomGrinch]

What controller are you both using ?

I'm afraid my place is an example of why chasing efficiency might lead to diminishing returns.
I have an 1890's solid stone walled house - no external wall insulation.
However, it is mid-terrace - 2/3rds of its walls have perfect (or better) insulation.
I have a non-condensing combi, that is coming up to 20 years old.
My gas usage so far this year has been 3700kWh, 1500 of which was for hot water.
With this little gas usage, even chasing the efficiency benefit of a condensing boiler doesn't make financial sense to me - the boiler will only be changed when it eventually fails.

For the controls, I have a 2nd gen Nest, and as @Harry Bloomfield says above, regarding his Vaillant; the greatest benefit for me, is how stable the Nest keeps the indoor temperature - and it looks good!

 

[mike42]

Lots of old threads and questions about opentherm on an S-plan. Anyone know if any of the controllers solve the issues? i.e. open the respective MVs then allow opentherm to take over when its heating? HW to take priority and run at max temp etc ?

 

[Harry Bloomfield]

Lots of old threads and questions about opentherm on an S-plan. Anyone know if any of the controllers solve the issues? i.e. open the respective MVs then allow opentherm to take over when its heating? HW to take priority and run at max temp etc ?

On my system, a Y-plan, it has to service CH separately from the hot water. Logically, there is no way it can service CH, at a completely different boiler flow temperature than is demanded by the HW - simultaneously.

 

[mike42]

Not simultaneously obviously but for example if your heating is on and has reached steady state and then your controller suddenly wants to heat up the HW then it should instruct the boiler to go to max temperature and when finished revert back to opentherm (or in your case the Valliant system equivalent) ? I assume your system has its own Valliant controller too?

 

[Harry Bloomfield]

Not simultaneously obviously but for example if your heating is on and has reached steady state and then your controller suddenly wants to heat up the HW then it should instruct the boiler to go to max temperature and when finished revert back to opentherm (or in your case the Valliant system equivalent) ?

I have the HW, set to come on, when there is less likely to be demand for CH. The worst possible situation, is walking in to the house, when the house is cool, at a time when it is set to deal with HW. My old system was able to share it's heat output, between both HW and CH, using the mid-position.

I assume your system has its own Valliant controller too?

Yes, I have all the bits installed - VRC 470F wireless stat./ display/ control panel, outdoor wireless sensor, the extra receiver unit in the boiler, the unit in the airing cupboard. The latter, connects to the boiler via a bus wire, the 3-port, and a thermistor cylinder temperature sensor - replacing the old joint box. All very easy to install, much easier than my old wired system, which it replaced.

All it needed, was the bus wire, plus pump supply, from boiler to airing cupboard. Boiler is at far end of kitchen, airing cupboard above near end. I managed to simply fish the two cables, along the gap behind the kitchen coving. Once fitted, it began learning how the house responded to temperature and boiler input.

Operation wise, it is mostly left to just get on with it most of the time. If I decide we need it a bit warmer, temporarily, I just nudge it up, and it does its clever calculations, to increase the temperature to the new one, in a reasonable time, without any overshoot. One thing the manual said it did, but it didn't - was that is said it auto-set it's date and time, from a time code receiver in the outdoor sensor. I spent ages moving the outdoor sensor around, trying to get it to receive, and set it's clock up. The UK version, does not include this Hamburg time code receiver. No biggie - it retains all of it's settings and program, through a power cut, or battery swap - it just needs the time/date to be set, if you take too long swapping the batteries.

 

[mike42]

I'm definitely warming to the idea (so to speak) but the problem I have is my system is an S-Plan. So I would need the controller to open the MVs over 240v AND then talk Opentherm over the twin data cables.

I've read that some people have done this but not convinced as I think it would need the boiler to understand it is to ignore the OT commands until it gets the "ON" signal via the 240v connection.

I'm still scratching my head......

 

[mike42]

Very interesting thanks - does appear to be a solution. Only issue is we have 2 heating zones. The second one is for just two rooms with its own controller and isn't used that often. Maybe I could leave that MV as a NC type and leave that zone as non-OT. If that called for demand I guess the boiler would think it was being asked for HW and set temp to max - maybe that's ok as such a small area....