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I recently installed weather compensation on my Ideal Vogue Max and I'm very confused by the settings menu item called "outside sensor slope", which lets me select a number between 0 and 40. The manual states that this adjusts boiler performance relative to the building insulation, but doesn't tell me what unit that is measured in. Also, the picture in the menu and manual looks very much like a weather compensation graph (outside vs flow temperature), which I can also adjust by changing the room temperature (nominal, not actual).

When I change the room temperature, the boiler immediately reacts as I would expect it to, but when I change the outside sensor slope, nothing happens at all. Does anybody know what that is supposed to do?
 
Outdoor temp 5C - Indoor Temp requested 21C
Boiler operates to temp set on boiler. ( 70C ) ?

Outdoor temp 15C - Indoor temp requested 21C.
Boiler reduces temp of heating water to 50C.

In a nutshell, as the temperature outside goes up, the temperature the boiler heats the water to is reduced.
I'm not sure of the temperature gradients from indoor to outdoor temperatures, and as for the insulation rating of the home to the reduced temperature that the boiler is working to, would be minimal.
 
What are the model numbers of the boiler and weather compensation kit?

The Ideal Vogue Max systems I've seen had a setting to choose the weather compensation 'curve' by selecting a curve number, IIRC, between 10 and 30. The curves were plotted in the installation or user guide. (A change of 1 in the curve number, roughly speaking, offset the curve by 1°C.)

I think it's possible that the word 'slope' on your display may be a mistranslation of the word 'curve'. The weather compensation curves are maps between T_flow and T_exterior so the (mathematical) slope is [°C/°C], i.e. dimensionless. The slope (gradient) of these curves is typically around one (i.e. not 40) and varies over the operating range, because the heat output from radiators is not a simple linear function of (T_flow - T_room).

So much for the theory. In practice, if hunting through manufacturer's manuals doesn't provide the answer, try calling the Ideal Vogue helpline. If still no joy, try the middle setting, i.e. 20, and see how the system behaves. In cold weather, if the house is up to temperature and the boiler is cycling on and off several times an hour the compensated flow temperature is too high. On the other hand, if the boiler is running continuously but the house is not getting up to the desired set point temperature the flow temperature is too low. Change the setting up or down by, say, 5 units and see what the effect is. Tweak as necessary.

The aim, as @oz-plumber explained above, is to end up with a system that reduces T_flow to its minimum by the time T_exterior = T_room and increases it at a rate that matches the radiator outputs to the building losses as T_exterior falls. It can be a bit of a fiddle, but it's worth putting a bit of effort in to get the system working correctly. When properly implemented, weather compensation noticeably improves both comfort and fuel consumption.
 
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Can you post a link to this Christoph?

As stated above the normal weather compensation curve looks like below so if your rooms require a boiler temp of 72C at -5C outside temperature then you set (this particular curve) the heating curve to 1.4 which means it should reduce the boiler temperature to 58C at a outside temperature of 10C and so on as you probably know anyway.

1674733247247.png
 
Thanks all for your answers, I already understand it a bit better than before!

The boiler is an Ideal Vogue Max 32 (manual attached, pages 40 and 45) and the weather compensation kit is from Ideal too (manual attached, page 7).

The compensation kit instructions make sense to me (except that I find it hugely confusing that they use the term "room temperature" for something that selects a curve...). The graphs look like this:

1674759406608.png
1674759444750.png


(And yes, set at 22C it can't keep up with the heat loss of my house during coldish periods!)

What doesn't make sense to me is this:
Boiler performance can be adjusted relative to the insulation level of the building. To change the slope press MENU and the following screen will be displayed ...
1674759651703.png


To me, this feels like it's exactly the same as the "room temperature" setting, except that it seems to have no effect at all. Both settings only are available when the weather compensation kit is fitted, so I suppose it must have some kind of effect. I could imagine that "17" was supposed to read "1.7" though. I just changed it from 17 to 30 and the boiler did not react in any way other than shifting the red line further right on the display (I can see the OpenTherm data ID values; none of the numbers change). But, when I change the room temperature even by one degree, it immediately adjusts the modulation and flow temperature.

Maybe "17" is the recommended thickness in inches of the insulation foam :)

Thanks for taking the time to look at this everybody!
 

Attachments

  • Vogue-Max-Combi-Installation-Servicing-222378-1_lowres-REDEUCED.pdf
    13.8 MB · Views: 7
  • Weather_Compensation_Kit_User_Guide.pdf
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The room compensation bit looks straight forward enough anyway!!
Say you want your rooms at 17C and select "17" this is curve 6th from the left so OT of -5C sets the boiler to 61C, 0C sets it to 54C & 10C sets it to 38C
If you require room temps at 20C...curve 9th from the left so -5 sets 67C, 0c sets 62c & 10C sets 46C

A room temp selection of 22C = curve 11.

If you know the present OT then go vertically upwards until it intercepts whatever curve you have selected and the Y axis will show you the present boiler setpoint temperature.

Will have a look at the other bit in a minute.
 
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I think what they mean is that if you have super duper insulation and you find the your selected curve is setting the boiler temperature too high then you simply select a lower room temperature which will then lower the slope and consequently the boiler set point?.
 
Thanks all for your answers, I already understand it a bit better than before!

The boiler is an Ideal Vogue Max 32 (manual attached, pages 40 and 45) and the weather compensation kit is from Ideal too (manual attached, page 7).

The compensation kit instructions make sense to me (except that I find it hugely confusing that they use the term "room temperature" for something that selects a curve...). The graphs look like this:

View attachment 81143View attachment 81144

(And yes, set at 22C it can't keep up with the heat loss of my house during coldish periods!)

What doesn't make sense to me is this:

View attachment 81145

To me, this feels like it's exactly the same as the "room temperature" setting, except that it seems to have no effect at all. Both settings only are available when the weather compensation kit is fitted, so I suppose it must have some kind of effect. I could imagine that "17" was supposed to read "1.7" though. I just changed it from 17 to 30 and the boiler did not react in any way other than shifting the red line further right on the display (I can see the OpenTherm data ID values; none of the numbers change). But, when I change the room temperature even by one degree, it immediately adjusts the modulation and flow temperature.

Maybe "17" is the recommended thickness in inches of the insulation foam :)

Thanks for taking the time to look at this everybody!
I see what you mean now by the outside sensor slope which is selected from the menu.
can you take a few screen shots, say 3, one with the temp setpoint the same as the weather one, one with it say 5C lower and one with it 5C higher.
 
20 dc room temp try setting on that one and see how you go
 
Doesn't make a lot of sense although it does seem to look at the temperature set in the OT compensation curve, 22C, in this case, The number inputted then one would think might influence/modify the actual compensation curve but does nothing.
 
Doesn't make a lot of sense although it does seem to look at the temperature set in the OT compensation curve, 22C, in this case, The number inputted then one would think might influence/modify the actual compensation curve but does nothing.
I suspect that the installation instructions were written some time ago and need to be updated so they are a better match to what the user sees on the display with the installed version of the boiler software.

Anyway, it seems clear how the OP needs to proceed. First set the 'room temperature' parameter to the desired building temperature. The current value of 22°C is probably close enough. Next select the 'slope' for the region below room temperature. Looking at the examples shown I'd go for curve '15'. Then see how things go. If more heat is needed in warm weather, raise the 'room temp' setting. Then get the cold weather behaviour right by tweaking the slope.
 
Christoph, did you resolve this in anyway. I've just experienced the same confusion with the Outside sensor Slope. My initial thoughts were to set the red line so at my theoretical worse case outside temp of minus 3, I get a 60deg C flow which is what I've calculated my radiator sizes for. Strange that after picking a 'curve' from the graph, inputting it into the Sensor Slope means the values do not correlate at all with the comp curve graph..Very confused
 
I must confess I still don't understand it completely. My current belief is that this is only meaningful without a room thermostat. In theory, a boiler can heat the house without knowledge of any room temperatures, just by looking at the flow/return delta (e.g. full power until the return gets too hot). In this operating mode, it can approximate the actual room temperature if it has weather compensation (i.e. at least a precise outside temperature).

In my case, I always run the system with a room thermostat (usually multiple). In this mode, the weather compensation only forwards the outside temperature reading to the thermostat and the actual compensation is performed by the thermostat. Thus, the outside sensor slope setting has no effect. The "room temperature" setting still works and it limits the maximum flow temperature according to the selected slope. For example, as I type this, my thermostat wants 80C, but the boiler delivers only 60C while it's 16C outside. In this context, the term "room temperature" is completely wrong and misleading and I think Ideal should update their manuals and the boiler UI.
 
Your boiler is probably Opentherm compatible, if so maybe this is selected and the WC disabled, some say that both can be run together, the only way I can see this is if the WC curve is set by selecting the curve as normal, Opentherm might then influence the boiler target temp based on the room temp?
Have a look in the menu to see does it mention both WC and Opentherm and settings.
 
That's a good point! I don't have any non-OpenTherm thermostats to test this, but I can imagine that the outside sensor slope would be taken into account in that configuration. I don't think the manual or the UI ever mention WC+OpenTherm, not even the WC kit manual.
 
This isn't very clear and it could work in various ways.
Worcester has weather comp and 'room influence' which boosts flow temps when re-heating.
I would expect opentherm controls to work similarly but opentherm is just a protocol and manufacturers don't seem to advertise the specifics of how they use it in their controls.
Others I suspect have a fixed curve/slope and weather comp just performs the function of keeping the boiler in condensing zone untill it gets really cold (With the added benifit of regular heat up times and smoother peaks and troughs in actual room temp).
The 'european' way is to run continuously without a room stat and use weather comp setting to control temp but this would work best with UFH and/or really good insulation.

Evohome is the gold standard as far as I'm aware...?
 
I don't think Evohome cares what the boiler flow temperature is, it just cycles the boiler on/off to give any particular room it's required room temperature in combination with throttling/controlling the motorized valve(s) to give the necessary mean rad temperatures required. I think it only calls for continuous boiler operation if one room is something like 1 to 1.5C below it's setpoint temperature.
 
Spoke to Ideal to clarify the outside sensor slope settings on my Vouge Max System 18 which was installed in April 23, so this is its first winter, my system design is 55C @ -3C and larger radiators have been installed as per the heat loss calc.

Room temperature control is via the boilers flow temperature, set in the menu for room temp of 21C, I have hive legacy TRVs, but these have been set to 24C to keep them open.

Hope this helps:
The key at the top of the page is not temperature, but curve reference number, which in my case is 16, therefore, the number in the grey box on the outside sensor slope page is adjusted to display this value.

As a new owner I'm sure there will be plenty of 'test and adjust', but this is my starter for 10.
 

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  • Weather Comp Curve.jpg
    Weather Comp Curve.jpg
    315.8 KB · Views: 13
Correct Website, sorry for confusion.

Best of luck Ian controlling with WC only, at least you have TRVs as supervisory, is your boiler enabled all the time from the programmer?, if so the circ pump will run continuously and the boiler will cycle on/off if its minimum output is more than the heat demand which it often will. Viessmann have very fancy WC where you can change the WC level as well as the slope but still very difficult to control room temperatures especially during milder periods.

I will post a link shortly, it may be of help.

 
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Correct Website, sorry for confusion.

Best of luck Ian controlling with WC only, at least you have TRVs as supervisory, is your boiler enabled all the time from the programmer?, if so the circ pump will run continuously and the boiler will cycle on/off if its minimum output is more than the heat demand which it often will. Viessmann have very fancy WC where you can change the WC level as well as the slope but still very difficult to control room temperatures especially during milder periods.

I will post a link shortly, it may be of help.

I must admit this is a new control philosophy for me, especially as I have heavily invested in Hive TRVs, but as this is my first condensing boiler and I thought I'd try and get the best efficiency from it and I've read that using the boiler flow temperature control in conjunction with weather comp will deliver this.

The Hive controller has scheduled CH times, allowing for earlier ON times, with a room temp (hall stat) of 24c and a set back temp of 16C.

Room temperature controlled and limited by the boiler temp control does sound odd as its based on the heat output of the radiator in that particular room being a match for losses but not too large as to overheat the room, time will tell if I've sized these correctly.

I value warmth over economy, so if this is a spectacular fail, my fallback position is to revert the control back to Hive TRV's being set to 'Heat on Demand' and increase the flow temperature, watch this space :)
 
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