Does tado modulate the flow temperature?

Alex474728

Hi, I'm wondering if tado actually modulates the flow temperature when using open therm? If so, based on what?

I have the tado X system, wireless thermostats and smart radiator valves in 3 separate rooms.

Also, how does the automatic max flow temperature play into this? I have been playing with the setting and it seems to always set it to 80% or so of whatever max I set.

In my mind, tado would calculate the optimal needed flow temp and use that or the max, whichever is lower. But it is not the case, if I set it to 40 it uses 36, if I set it to 60 then it uses 54, if I set to 80 then it uses 72 and so on. What is the point of this feature then? Note that outside temps are quite mild still.

The issue that I have is that the rooms never reach the target temps due to flow temp being too low, but despite that the automatic max flow temp feature still does not use the max limit I set but a lower value

Rob

@Alex474728 @policywonk

It depends a bit on the protocol, but let's stick to Opentherm only. For Opentherm, you set a maximum flow temperature in the app. This is the maximum value the boiler cannot exceed. But it will accept something lower.

Modulating and maximum flow temperature

With modulating-capable protocols like Opentherm, the thermostat modulates its heat request. If there is a low heat request from the thermostat, the thermostat tends to ask for a lower water temperature than the max setting from the boiler. A% or B degrees less than the maximum setting. If there is a large heat request, it asks for the maximum value.

So if the max is set at 60 and the heat request is low, the thermostat might ask for 45 or 50.
If the max is set at 70 and the heat request is equally low, the thermostat might ask for 50 or 60.

These are some hypothetical numbers, to illustrate the principle only.

So, here we ask for a flow temperature based on:
A. the heat request from the thermostat and
B. the maximum set flow temperature.

Flow temperature optimization

Now with this optimization feature enabled, you set a maximum of the maximum, if you will. We look at the outside temperature and the maximum flow temp you've set, to set the maximum flow temperature of the day. Is it very cold outside; we will take your maximum value. If it's not that cold outside; we will take a lower value than your max value. This relative 'how cold is it?' is calculated once every 24h (and based on a night temperature around the address you've set in your account), so if you play around with the settings on the same day, you will see similar values. If you do so on a 'warm' day, you will see something else than on a 'cold' day.

Here, we ask for a flow temperature based on:
A. the heat request from the thermostat and
B. the daily maximum set flow temperature, as determined by
__C. the outside temperature and
__D. your manually set maximum flow temp in the app.

I have been playing with the setting and it seems to always set it to 80% or so of whatever max I set.

This makes sense, as long as you've been playing with the settings on similarly cold days. Now, if you do the same on a day that is much colder or warmer, you should see a different result.

policywonk

My understanding is that Opentherm, or digital controlled boilers, as opposed to those which use on-off switching at low or mains voltage, is that there are thermal sensors on the outbound and inbound pipes in the boiler. These boilers then throttle themselves on the basis of the difference in temperature between the two, also controlling the speed and pressure of the pumps. That algorithm can be set in the boiler's own control table, or delegated. The boiler manufacturer's firmware defines what can be delegated to the external controller to inform its heat development curve- and the level of external development can sometimes be set on the control panel at the boiler.

The instructions are usually provided in the boiler's installation guide. Have seen some Tado installation guides for the specific boiler setting this out clearly. This video is worth a watch: The ULTIMATE 3rd Party Boiler Controller!

There are a few people on this forum who know lots about this. @Rob ?

Alex474728

Thanks both for the answers! It's clear now, the part I was missing was that the modulation is based on an offset applied to the configured max temp.

Indeed I adjusted the optimization feature multiple times on the same day.

Is there a way to see the requested flow temp? Would be interesting to track

Irek85

Thanks for clarification. Is it possible to check what one wave/two waves/three waves stand for? Is it certain % of maximum temperature? Is it on Tado side or does it differ boiler to boiler?

Rob

@Alex474728

I cannot see the requested flow temperature, so I don't think you can either.

@Irek85

My guesstimate is that the waves stand for a heat request like this:

• 0: 0%
• 1: 1-33%
• 2: 34-66%
• 3: 67-100%

Now how is the heat request percentage calculated? With a PID (Proportional–integral–derivative) controller. So it looks at:

• Difference between measured temp and setpoint. Proportional.
• The slope; to what extent is the temperature in/decreasing. Integral.
• "anticipatory control". What do we expect will happen? Derivative.

What exactly we send to the boiler is something I don't really know. Not every OT boiler has the same OT implementation either. I believe, but don't quote me here, that for higher heat requests it tends to be a specific water temperature request, and at lower heat requests there is some kind of low load mode. But I'm no expert here and, like I said, there are big differences in OT implementation on the boiler manufacturer (/boiler age/generation) side.

SPT

Good posts in this thread but if I set my boiler to 60c, then Tado only goes that high..it will use open therm up to that temperature. Is that correct?