Return water temperature or ebus to modulate boiler?

[ericmark]

Clearly likely to change make to make both boiler and thermostat used, but I see the two different methods and really not sure which is the best.

So I see have does not connect to ebus, it uses the "heat on demand" protocol to keep boiler running if any TRV head reports it need heat.

Nest, and Tado it seems use OpenTherm and EvoHome needs the addition of the OpenTherm module R8810A101 to work with OpenTherm.

Other makes have their own special but in some cases they don't link to the TRV so only control one room.

When I first heard of OpenTherm I thought it was a great idea, however the advent of the Hive TRV head raises the question is it any better than using the return water to control output?

I hope some one can give benefits of all the systems and show why each should be selected.

 

[vulcancontinental]

To many variables. Any one of the four Boiler Plus efficiency improvements will save you perhaps £60-80 a year.

The one thing OT can do is give you remote control of the boiler as well as the heating if you choose a pairing, that may be of no interest to you though. Ebus may do the same, I don't know it, if you have a Vaillant.

 

[ericmark]

I would love to do a test, basic set up with cheap wall thermostat to stop cycling, and programmable TRV's in each room. Compared with Evohome, both set spot on, I suspect little difference? However in the main the cheap set up is not set spot on.

It would depend on the boilers own algorithms, but one would hope the likes of EvoHome would have boiler on minimum output and minimum temperature before it starts to cycle, so less heat is lost out of the flue each time it switches off? But what I don't know is the boilers sweet point, with a boiler output ranging from 8 to 28 kW at some point in that range it is likely more efficient to the rest, where the percent of heat up flue to heat around system is the best.

If I compare with a motor vehicle, with my car, drive around accelerating very slowly with lot top speed and I get more miles per gallon, but with my Yamaha RD200 motor bike it did not matter, driving it slowly with low acceleration or twisting throttle to stop, around 60 MPG drive manor had very little effect, likely down to being a two stroke engine with disc valves, but it seemed not to matter how driven.

So I suspect some boilers nearly straight line on efficiency and others a very defined sweet point.

It was Hive's method which got me thinking about which method, the "heat on demand" link between TRV head and wall thermostat would seem on paper to very well control room temperatures and get around the problem of switching off boiler rather than allowing it to cycle, not sure why the wall thermostat even measures temperature, it would seem from the adverts it could be set at 10°C and still run boiler as long as the rooms are under the temperature set on the TRV heads? But it would seem the boiler modulates using return water temperature, so how would it compare with same boiler using OpenTherm and Tado for example? What advantage is there in using the ebus be it opentherm or boiler manufacturers own system, to using return water temperature to do the same thing?

 

[vulcancontinental]

You're over thinking things and making a couple of errors.

I remember listening to military officers on the news one time when some war or other was brewing and the politicians were in a spin wondering what to do. The officer said the problems is nobody will tell us what they want the result to be. Once we know that we will come up with a plan.

With heating go back to your early paragraph, it makes little difference. Gas is very cheap and depending on the user any system can be operated to give similar running costs.

1: What is the end result you are looking for? 2: Choose the system that gives you what you want.
3: If you can't afford it choose the next best thing.

 

[ericmark]

I looked at what to me seemed simple,

the PC shows both target and current so all it needs is a switch so if any TRV head reports target above current then boiler runs, other wise boiler stops, the unit supports IFTTT so it should be easy enough to do.

But when I looked for an app to do that, nothing.

 

[vulcancontinental]

Evohome

 

[ianmcd]

Stop trying to reinvent the wheel, the technology is available but not viable in the domestic market, the savings against supply and install costs just dont add up yet, will they ever ? who knows depends on how many manufacturers want to get involved