Viessmann Weather Compensation

[Johntheo5]

Is it your understanding that Viessmann are saying that you can't have WC and any form of Roomstat control, ie they are saying that if you choose WC that it wll solely control the house temperature?, if so then they mustn't be living in a real world and even know that WCs almost sole purpose is the give lower boiler return temperatures, enhanced condensing, = higher boiler efficiencies and lower gas/oil consumption.
Obviously wouldnt expect WC and say opentherm to work together (opentherm controls flowtemperature as well?) as no man can serve two masters. Last night my room temperature (where my digital roomstat is installed) fell by 1.8C over 7 hours but the outside temperature fell by over 7C, WC on its own IMO wouldn't stand any chance of giving any semblance of proper control, also in the daytime the solar effect makes a big difference, my boiler stays off sometimes for double the time when the sun comes up but the outside temperature may only rise by 1 or 2 degrees.
Can you/someone confirm that the above is as Viessmann are seemingly saying?.

 

[needyahelp]

Johntheo5 - based on my recent experience with having this model of viessmann installed for me - yup. But maybe viessmann assume its a smart/modulating thermostat rather than an on/off one.

 

[tech749]

Tech749 now the weathers getting colder hows the weather comp going? I have the same boiler and originally chose it specifically for weather comp but my installer was eventually told by Viessmann techies that you cant have a a roomstat/timer and WC together (Viessman sales people were not aware of this either and the viessmann brochures covering the 050 are misleading in the way they market weathercomp especially for typical uk homes and traditional use of timers) so ive gone with room stat/scheduling for now as i was concerned with leaving it permanently on (gas cost) but im keen to hear if WC is worth a try.

needyahelp, the weather comp is doing great for me, I have the boiler set to 20 deg, which adjusts the weather comp curve. On the app I have the heating curve set as follows Slope 1.4, Level 0, which is what the installer recommended for my house. I have attached a graph of house temperature over the last month.

I have an EPH controller which is essentially a cut off switch. So I'm not sure why Viessmann are saying that. Basically I have the controller set to come on at 0730 with it set at 23 deg, doesn't usually reach that unless we're cooking or sun is in room or somethong. If cooking I usually move it to the cooler living room to stop heating going off. that temperature (23) is set until 2300. After that overnight I have a setback temperature of 18 deg, but so far the heating hasn't come on overnight as the temperature hasn't been below 19 overnight, even though it has dipped to 6 deg some nights outside. So essentially my heating is set to ON all the time, which is what is recommended. My gas use is averaging 25 to 30 kwh per day, so just over £2.00 per day including hot water, we don't use a great deal of hot water as its only two of us and we have an electric shower. The loft is insulated to the max level and we have a terraced 3 bed house. Obviously in the colder months it will be more , but the boiler is modulating at 10%, which is really good, as its using less gas. Radiators are just warm, but rooms are comfy. Currently 10 deg outside.

Just stick it on for a week and see how it goes, thats what I did. I'm pretty sure (depending on insulation and type of house) you should use a lot less than coming off and on using temp stat, as your boiler will be condensing more. Just a question, how did you disable the WC, or is it load comp now using Opentherm, on mine there is no control of that, unless you whack the curve right down, in which case it wouldn't come on at all? Or did you disconnect it?

 

[tech749]

Is it your understanding that Viessmann are saying that you can't have WC and any form of Roomstat control, ie they are saying that if you choose WC that it wll solely control the house temperature?, if so then they mustn't be living in a real world and even know that WCs almost sole purpose is the give lower boiler return temperatures, enhanced condensing, = higher boiler efficiencies and lower gas/oil consumption.
Obviously wouldnt expect WC and say opentherm to work together (opentherm controls flowtemperature as well?) as no man can serve two masters. Last night my room temperature (where my digital roomstat is installed) fell by 1.8C over 7 hours but the outside temperature fell by over 7C, WC on its own IMO wouldn't stand any chance of giving any semblance of proper control, also in the daytime the solar effect makes a big difference, my boiler stays off sometimes for double the time when the sun comes up but the outside temperature may only rise by 1 or 2 degrees.
Can you/someone confirm that the above is as Viessmann are seemingly saying?.

It seems to work ok for me, obviously will have to monitor what happens when its colder overnight but the outside temperature dropped 5 deg the other night all night, but it will all depend on how warm your house is normally. As you stated WC couldn't cope with large temp changes, it would take a while to recover from say 15-16 deg, especially if weather next day is mild, which is why I set it to 18 deg to keep it topped up in case. As stated in my previous reply, it hasn't been required yet, and I don't know why Viessmann have said that, my room stat works ok with it.

 

[monkeysballs]

you have your room heating from about 19/20to 24c!! are you a lizard!

 

[tech749]

you have your room heating from about 19/20to 24c!! are you a lizard!

 

[tech749]

Haha, with the weather comp its about 20 deg, what can I say, we're really old (76) and in most days, I'm married to a lizard. The bill isn't that bad at the moment anyway

 

[Johntheo5]

It seems to work ok for me, obviously will have to monitor what happens when its colder overnight but the outside temperature dropped 5 deg the other night all night, but it will all depend on how warm your house is normally. As you stated WC couldn't cope with large temp changes, it would take a while to recover from say 15-16 deg, especially if weather next day is mild, which is why I set it to 18 deg to keep it topped up in case. As stated in my previous reply, it hasn't been required yet, and I don't know why Viessmann have said that, my room stat works ok with it.

What make/model roomstat have you got and what WC slope/level are you using?.

 

[monkeysballs]

my viessmann weather comp is working quite well keeping the rooms between 18 and 20.5 c mostly some get a bit higher due to additional input like monitors and things
it really has improved our comfort as its much more stable then with the way we used to run it and it does seem to be using less gas!

 

[Johntheo5]

my viessmann weather comp is working quite well keeping the rooms between 18 and 20.5 c mostly some get a bit higher due to additional input like monitors and things
it really has improved our comfort as its much more stable then with the way we used to run it and it does seem to be using less gas!

You are using WC only?, is the boiler enabled via a programmer and does it run/cycle all these times?
What WC curve/level are you on?.

 

[tech749]

What make/model roomstat have you got and what WC slope/level are you using?.

EPH CP4 controller, and Slope 1.4, Level 0. Boiler temp set to 20 deg.

 

[monkeysballs]

You are using WC only?, is the boiler enabled via a programmer and does it run/cycle all these times?
What WC curve/level are you on?.

Yes WC only I changed the curve from .7 +2 to .9 today to see what it would do
It's been burning so far 8 times today totaling 10.5 hours since 6am and used 26kw including 2 showers so -2.5 or 3kwh for pure heating usage outside temp started at 6.5c and it's just got up to 11.7c

 

[Johntheo5]

EPH CP4 controller, and Slope 1.4, Level 0. Boiler temp set to 20 deg.

What control mode are you using, ie normal or TPI?

 

[needyahelp]

needyahelp, the weather comp is doing great for me, I have the boiler set to 20 deg, which adjusts the weather comp curve. On the app I have the heating curve set as follows Slope 1.4, Level 0, which is what the installer recommended for my house. I have attached a graph of house temperature over the last month.

I have an EPH controller which is essentially a cut off switch. So I'm not sure why Viessmann are saying that. Basically I have the controller set to come on at 0730 with it set at 23 deg, doesn't usually reach that unless we're cooking or sun is in room or somethong. If cooking I usually move it to the cooler living room to stop heating going off. that temperature (23) is set until 2300. After that overnight I have a setback temperature of 18 deg, but so far the heating hasn't come on overnight as the temperature hasn't been below 19 overnight, even though it has dipped to 6 deg some nights outside. So essentially my heating is set to ON all the time, which is what is recommended. My gas use is averaging 25 to 30 kwh per day, so just over £2.00 per day including hot water, we don't use a great deal of hot water as its only two of us and we have an electric shower. The loft is insulated to the max level and we have a terraced 3 bed house. Obviously in the colder months it will be more , but the boiler is modulating at 10%, which is really good, as its using less gas. Radiators are just warm, but rooms are comfy. Currently 10 deg outside.

Just stick it on for a week and see how it goes, thats what I did. I'm pretty sure (depending on insulation and type of house) you should use a lot less than coming off and on using temp stat, as your boiler will be condensing more. Just a question, how did you disable the WC, or is it load comp now using Opentherm, on mine there is no control of that, unless you whack the curve right down, in which case it wouldn't come on at all? Or did you disconnect it?

Thanks, useful to know. I didnt disable WC, my installer stopped installing it and sourced a vicare climate sensor (modulating) instead so the boiler was never fully comissioned with WC, he did check which one i wanted at the time viessman told him so it was my decision but im a bit annoyed with what viessmann tech advised him in the first place as its clearly not true based on posts here, tbh im not sure their tech support is consistent as i heard the first phone call he had with them and the tech at the time was saying WC doesnt work with the new 050 at all! I may look at getting my installer back to put WC in as i have a spare basic stat but will see how this winter goes. So far i have CH set to run from 5am to 00 at 21c with 21.5 comfort setting in the eve and 9c at night/off time but i too noticed the house doesnt go below about 17c at night when off so i may adjust it a little above that to keep things stable in colder winter. I have a 2 bed terraced (with a 2 inch gap between house and one neighbour) with its solid walls and not great insulation in general. So far the daily gas consumption incl DHW is between 4.5 and 7.5 m3 not sure what that is in kilowatts. Ive set the flow to 49c and burner max to 30% as im not after rapid heat up of the house and this has worked nicely so far with the boiler modulating down to 10-14% after a couple of hours and then goes off late morning for 2-3 hours or more depending on sunshine and then on for the rest of the day modulating at modulating 10-12% until about 9/12pm depending on cooking, front door openings etc. Ive found that the mere circulation of heat in the house (boiler on and minimum burn) even at 19-20 for long periods feels better than heating to 21 and then turning off until the temp drops to 20c (the vicare climate sensor works with a 1 degree differential which i would have liked to be smaller but viessmann say its to reduce cycling). It still seems to be learning (spending increasing time at 10-12% which seems good) so will see how it goes.

 

[monkeysballs]

That's 51kwh to 85kwh! In comparison me in a 4 bed detached so far 40.6kwh Is my highest that was when it was 2c outside to 6c max usually I'm low 20's. Potentially your heating higher than me