Heating curve

vicentiu
Posts: 27
Joined: 13 Jan 2022, 17:02

Re: Heating curve

Post by vicentiu »

I don't have a netatmo weather station. My understanding from Netatmo's documentation is that the thermostat gets the outside temperature from the internet. The closest weather station to me that has data on the internet is 3 km away at an airport.

I got the graph by taking many measurements. My boiler's diagnostics menu has a function to show the flow temperature commanded by the thermostat.... so I took repeated measurements.
At a certain outside temperature, I would set the heating curve in the app to the values above, and observe the commanded temperature on the boiler display when in the diagnostics mode.

I made measurements when outside temperature was between -4 and +8 degrees celsius.
sergeantd83
Posts: 80
Joined: 12 Nov 2020, 13:21

Re: Heating curve

Post by sergeantd83 »

vicentiu wrote: 27 Jan 2023, 10:38 Now that setting the heat curve is working again, I'm observing that it's completely flat... meaning the flow temperature does not increase as outside temperature decreases.
My boiler shows the temperature commanded by the thermostat and it's the same for all outside temperatures between -4 and +8 degrees celsius.

Here are the values I observe:

Heating curve ---- flow temperature

0.1 ---- 22
0.2 ---- 25
0.3 ---- 28
0.4 ---- 31
0.5 ---- 34
0.6 ---- 37
0.7 ---- 39
0.8 ---- 42
0.9 ---- 45
1.0 ---- 47
1.5 ---- 61
2.0 ---- 74

I tested on multiple days where the outside temperature varied between -4 and +8 degrees celsisus, and it's always the same flow temperature as listed above.

Anyone else observe similar behavior?
This behavior probably happens because you have the advanced algorithm enabled. So my assumption about how the thermostat handles the boiler is the below:

1) The thermostat sets a relatively high Control Setpoint value based on heat curve.
2) Sets the Max Relative Modulation Level to 0%.
3) Handles the ON/OFF times of the boiler with an embedded PID algorithm.

You can check your boiler settings if my assumption is correct and report back.
This kind of control is surely advanced because the Modulating Thermostat can keep the room temperature constant and at the same time prevents the wear of the boiler due to cycling ( fewer oscillations in flow water temperature ).
Last edited by sergeantd83 on 03 Feb 2023, 05:41, edited 1 time in total.
vicentiu
Posts: 27
Joined: 13 Jan 2022, 17:02

Re: Heating curve

Post by vicentiu »

You may be on to something... I do have advanced algorithm enabled.

I didn't think the advanced algorithm would affect the heat curve. Since the setpoint is not visible in the application, I assumed the setpoint was always fixed.

At -1 outsisde temp during the night, the boiler runs about 90% of the time (at 28 degrees flow temp, heat curve 0.3) to maintain the temperature. I'm expecting at -3 and below outside temperature it won't be able to maintain the target temperature.... so I guess the hypothesis is that at -3 and below outside, I need to observe an increase in flow temp.

The next two nights will be -5 :) .... so I will report back.
vicentiu
Posts: 27
Joined: 13 Jan 2022, 17:02

Re: Heating curve

Post by vicentiu »

I made the following updates to my original post with the chart:
  • Corrected the temperature range: I observed up to -1 degrees, not -4
  • Made the chart to show for which temperatures I made observations: 8, 7, 6, 4, 3, 2, 1, -1
  • Added the slightly different values observed for temperatures 3 and 4 that I initially discounted since +8 and -1 had the same values.
jaburgoyne
Posts: 5
Joined: 17 Jan 2023, 22:15

Re: Heating curve

Post by jaburgoyne »

Nice graph! Like some other users, I don’t have an easy way to record the flow temperature other than going in person to look at the boiler itself, but I’ve been checking more often since the recent server problems and trying different values to get the system back in check. We currently have the heating curve at 1.5, we also use and are very happy with the advanced algorithm, and there are definitely temperature fluctuations in flow temperature throughout the day, as it gets warmer or colder outside.

I’d be very curious if anybody has seen more detailed documentation about which heating curves Netatmo uses. It seems like there is quite a lot of variation between manufacturers, from simple straight lines with a slope of the heating-curve parameter to more elaborate curves that take into account the physical properties of radiators, etc. The official documentation only gives the almost uselessly general fact that higher heating curves cause higher flow temperatures. It would so helpful to know *how* much higher, and how that depends on the weather outside.
vicentiu
Posts: 27
Joined: 13 Jan 2022, 17:02

Re: Heating curve

Post by vicentiu »

I opened a ticket asking for the heat curve graphs. I didn't receive an answer yet.
Support is currently assisting me with my flat values.
jaburgoyne
Posts: 5
Joined: 17 Jan 2023, 22:15

Re: Heating curve

Post by jaburgoyne »

Please share if you hear back from them! This would be very interesting.
vicentiu
Posts: 27
Joined: 13 Jan 2022, 17:02

Re: Heating curve

Post by vicentiu »

My observations exactly match the Viessmann heat curve chart.
So my thermostat thinks it's always -6 outside. And for the lower flow temp values ( at 3 and 4 degrees outside temp in my chart) the thermostat thought it was -1 outside.

I think it's safe to assume these are the heat curves being used.
Attachments
viessmann chart.PNG
viessmann chart.PNG (522.89 KiB) Viewed 1760 times
vicentiu
Posts: 27
Joined: 13 Jan 2022, 17:02

Re: Heating curve

Post by vicentiu »

jaburgoyne
Posts: 5
Joined: 17 Jan 2023, 22:15

Re: Heating curve

Post by jaburgoyne »

I think I’m actually now having the problem that an earlier post mentioned during the Netatmo server problems. For a while, it worked to set the heating curve, but now all of a sudden its using a flow temp of 77º even though is 7º outside. Our heating curve is set to 1.5, and on the chart above, that would imply that Netatmo thinks it’s –20º outside.

Is anybody else noticing something like this, or is it just our house?
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