Viessmann Weather Compensation

[needyahelp]

Cripes! Id better get on with floor and some sort of wall insulation! I do have ancient aluminium double glazing as well so lots of room for improvement measures to take!

 

[tech749]

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

I'm using normal, mainly because I didn't know what TPI was. I know now. I think it's irrelevant at present because because the temperature never reaches the setpoints anyway, I just let the weather comp do it's thing. It may be handy if temperature goes below 18 in the house on very cold nights. Not really sure.

 

[tech749]

Cripes! Id better get on with floor and some sort of wall insulation! I do have ancient aluminium double glazing as well so lots of room for improvement measures to take!

Yes we had loft insulation installed last month, and the difference in the bedrooms is really noticeable, of course part of that could be the new WC and boiler. It's about 19 deg overnight, so retains heat quite well, used to get quite cold at bedtime and in the morning! That is quite a lot of gas you're using, should be able to reduce that.

 

[Johntheo5]

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?

If the controller is set to 23C then wont the boiler control the room(s) temperature to 23C/23.4C and WC will just change the boiler flow target temperature, if you set it at say 18C, the coldest your room(s) fall to overnight, wont it switch off the boiler at say 18.4C and if the room temperature doesn't fall below that for the remainder of the day then, the boiler will "never" again start, in either case WC has no control over the boiler control?. and your running in effect with just roomstat control (+WC)

 

[tech749]

If the controller is set to 23C then wont the boiler control the room(s) temperature to 23C/23.4C and WC will just change the boiler flow target temperature, if you set it at say 18C, the coldest your room(s) fall to overnight, wont it switch off the boiler at say 18.4C and if the room temperature doesn't fall below that for the remainder of the day then, the boiler will "never" again start, in either case WC has no control over the boiler control?. and your running in effect with just roomstat control (+WC)

Basically the controller is used as an ON/OFF switch and set up that way on the boiler, you're right on the first line, the WC will control the target flow temperature, but only to whatever you have set the boiler to using the WC curve that is comfortable for you in your home, i.e. my boiler is set to 20 deg, and you just adjust the curve to achieve that temperature, if it doesn't do it already.
If for any reason the room temp reaches 23 deg, the boiler will just shut down until it is below 23 deg again, at which point it will switch on and the WC will do its job. At the 18 deg setting which I only use overnight from 2300 - 0730, if it gets below that temperature, then the boiler will switch on, and the WC will now control it again. Obviously as the boiler is set to 20 deg, it will try to achieve that, but won't because the controller will switch the boiler off again at 18 deg, or close to it. During the day it switches to 23 deg again so WC works normally. The only reason I had an overnight set point instead of just turning boiler off, is that I didn't want the room to get so cold maybe 15 deg, that it would take quite a while to get it back up to 20 deg again using WC. It hasn't come on at all overnight as the temp is 19-20 deg depending how cold it is outside at the moment. So summing up, the controller is only used to switch the boiler on and off at set temperatures, according to what schedule works for you in your home, and has no control over the actual temperature. Hope this clarifies, but feel free to ask if you want me to explain further.

 

[monkeysballs]

thats exactly what i want to achieve but on my 200w my only option as £279! for the 300e controller as we dont sell the much cheaper zigbee roomstats in the uk for some reason!

 

[tech749]

I thought you could connect any controller to achieve this to any Viessmann boiler, think they all have same control inputs?

 

[monkeysballs]

not the 200w it only supports wc or this controller (in theuk) (there is a wired one too but im not doing wires and its more than the wireless one)

there is also the zk03839 wireless temp sensor that isnt sold in the uk for some reason

 

[Johntheo5]

Basically the controller is used as an ON/OFF switch and set up that way on the boiler, you're right on the first line, the WC will control the target flow temperature, but only to whatever you have set the boiler to using the WC curve that is comfortable for you in your home, i.e. my boiler is set to 20 deg, and you just ust the curve to achieve that temperature, if it doesn't do it already.

OK, I understand the WC curve, which adjusts the boiler flow temperature target value or setpoint, you have choosen curve 1.4 where a OT of -5C sets the boiler target temp to 56C, 0C sets it to 51C, 5C sets it to 44C, 10C sets it to 39C and so on, you say "my boiler is set to 20C" what does this mean?, IF you are using the controller/roomstat to switch the boiler on/off and for example if the OT is 5C then the boiler will fire up and maintain a target flow temperature of 44C, it couldn't care less what the room temperature is, it will keep firing the boiler until your roomstat is satisfied and switches the boiler off?, WC does not control the room temperature, it controls the boiler target flow temperature.

If you want WC only to "control" the room temperatures then you need a switch in the programmer that switches the boiler on permanently and the roomstat has no role whatsoever to play in the room temperature, now, you could have TRVs which will contol individual room temperatures but the boiler never switches off until programmed off or you switch it off.

@monkeysballs is using WC only with no roomstat (I think), he may have TRVs, but I think he wants to be able to connect a basic programmer/roomstat to control his room temperatures (like yours) but not sure if he wants the option of switching the boiler on permanently and reverting to WC control only?

 

[monkeysballs]

no room stat, no trv's i want room influence as its called to stop unnecessary heating in setback times. my normal day is fine but evening and overnight when i want a the setback to not fire unless the temp is actually at the setback temp now if i have it set at 17c it fires even though its still 19+ in the livingroom i just havent lost enough energy from the house to require it

 

[Johntheo5]

no room stat, no trv's i want room influence as its called to stop unnecessary heating in setback times. my normal day is fine but evening and overnight when i want a the setback to not fire unless the temp is actually at the setback temp now if i have it set at 17c it fires even though its still 19+ in the livingroom i just havent lost enough energy from the house to require it

That's exactly the way I thought it was but IMO you will only consume more gas or have "cold" rooms without a master controller/roomstat, with this you will realize all the benefits of WC, ie lower boiler return temperature, more condensing, more efficient boiler, lower running costs and still maintain very tight control of prefferably, IMO, the most used room where the roomstat is located).

 

[vulcancontinental]

no room stat, no trv's i want room influence as its called to stop unnecessary heating in setback times. my normal day is fine but evening and overnight when i want a the setback to not fire unless the temp is actually at the setback temp now if i have it set at 17c it fires even though its still 19+ in the livingroom i just havent lost enough energy from the house to require it

Although not a huge fan of Viessmann and the 200's intricacies I think your boiler on its own can do exactly what you want.

I am sure others have written elsewhere of it's ability to select 2 if not 3 temperatures between which you can switch on a time schedule embedded in the boiler.

You will not need any internal influence because the accuracy of the weather compensation calculation will not let the property exceed a new lower setback target. It will sense the rise in return water temperature and as it closes toward the calculated set point will know heat is not absorbed in the property so will modulate then shut down.

 

[tech749]

OK, I understand the WC curve, which adjusts the boiler flow temperature target value or setpoint, you have choosen curve 1.4 where a OT of -5C sets the boiler target temp to 56C, 0C sets it to 51C, 5C sets it to 44C, 10C sets it to 39C and so on, you say "my boiler is set to 20C" what does this mean?, IF you are using the controller/roomstat to switch the boiler on/off and for example if the OT is 5C then the boiler will fire up and maintain a target flow temperature of 44C, it couldn't care less what the room temperature is, it will keep firing the boiler until your roomstat is satisfied and switches the boiler off?, WC does not control the room temperature, it controls the boiler target flow temperature.

If you want WC only to "control" the room temperatures then you need a switch in the programmer that switches the boiler on permanently and the roomstat has no role whatsoever to play in the room temperature, now, you could have TRVs which will contol individual room temperatures but the boiler never switches off until programmed off or you switch it off.

@monkeysballs is using WC only with no roomstat (I think), he may have TRVs, but I think he wants to be able to connect a basic programmer/roomstat to control his room temperatures (like yours) but not sure if he wants the option of switching the boiler on permanently and reverting to WC control only?

When my 050 boiler is set to WC mode, which the installer did, you can set the room temp to be 20, 21 etc. I used the app to do it, and this is shown on the boiler display. By setting this the heating curve is set to an optimum setting to heat the house to this temperature. Viessmann obviously base this setting on whatever experiments they've done when designing the boiler. Obviously houses are different depending on insulation, walls, windows etc. hence you can tweak the heating curve to suit your house, it is trial and error, and not an exact science. They do provide examples to base the settings on within the boiler manual or on the app. I.e. 3 bed semi with good insulation etc. should be set to xx slope and xx level. If rooms are too cold or too hot, the app or manual tells you what to do to heating curve to rectify it.
My room temperature remains steady around 20-21 deg no matter what the weather, or it has so far !
My heating system is on all the time, and the thermostat controller just switches boiler off at night because temperature has been above 18 deg all night, and is not required.
I have noticed that during the day the boiler pump is on all the time, but the burner only comes on when the flow temperature drops below where it should be I'm guessing. So it's not using gas all the time, plus it's modulating at 10% (approx 3kw) when the burner is on. Hope that explains things. Feel free to ask if not.

 

[Johntheo5]

Thanks, the reason the pump is running all the time is probably because the minimum output of the boiler is greater than the heating demand which means the burner will cut out when the flow temperature exceeds target temp + 5C, the burner will then refire when the anticycle time has elapsed and when/if the flow temperature is target temperature - 5C.
So do you set the WC curve?, if so then the boiler possibly sets the level depending on the requested room temperature.

What is the rated output of your boiler and what is its minimum output?
I see the minimum output of all these 050 boilers is 3.0kw.

 

[monkeysballs]

Although not a huge fan of Viessmann and the 200's intricacies I think your boiler on its own can do exactly what you want.

I am sure others have written elsewhere of it's ability to select 2 if not 3 temperatures between which you can switch on a time schedule embedded in the boiler.

You will not need any internal influence because the accuracy of the weather compensation calculation will not let the property exceed a new lower setback target. It will sense the rise in return water temperature and as it closes toward the calculated set point will know heat is not absorbed in the property so will modulate then shut down.

thats the opposite of my issue with my setback set it thinks it needs to heat when it doesnt take this morning it came on at 5:40 thinking it needed to top up the heating the setback temp was set to 14c! outside it was 6.2c yet the coldest room in the house (that i care about) was 18c! the absolute coldest was 17c (thats the utility with open fan vent)

if i have it set to a sensible setback temp my heating is on alot more than it should be and id like to use the correct setback temp of 17c so about 2c less than my daytime temp the issue is my house just doesnt loose heat that fast it performs more like its got UFH but it doesnt