Outside sensor slope vs room temperature setpoint

[John.g]

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.

 

[Chuck]

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.

 

[Silvinho]

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

 

[Christoph]

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.

 

[John.g]

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.

 

[Christoph]

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.

 

[Knappers]

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...?

 

[John.g]

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.

 

[Knappers]

You need an R8810 bridge.
Don't forget opentherm was developed by Honeywell.

 

[ian.]

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.