SensoCOMFORT Room Temp Mod: Inactive, Active or Expanded?

SensoCOMFORT Room Temp Mod: Inactive, Active or Expanded?

In this document we take a deep dive into the Room Temp Mod setting on your SensoCOMFORT controller.

Whether to choose Inactive, Active or Expanded as well as some of the other primary controls of the heat pump.

The Room Temp Mod setting adjusts the behaviour of the SensoCOMFORT controller, with each of the three available options providing variations of behaviour.

We will work through the following topics

• OT switch-off Threshold
• Arotherm Control Methods
• Weather Compensation Curves
• Room Temp Mod Summary
• Room Temp Mod: Active
• Room Temp Mod: Inactive
• Room Temp Mod: Expanded
• Inactive versus Active
• Pump Overrun Observations
• Summary and Recommendations

OT switch-off Threshold

As long as you have a heating schedule set or are in manual heating mode, then the final trigger as to whether your Arotherm heat pump will turn the heating on or off is the outside temperature threshold setting.  

You can find and change this setting via the following menu tree

• Settings
• Installer Level
• 00
• Installation Configuration
• Circuit 1
• OT switch-off threshold

The default value for OT switch-off threshold is 16C, which means that if the outside temperature is below 16C then the heating will activate.  If the outside temperature is 16C or above, the heating will switch off.

Arotherm Control Methods

Once the heating is enabled there are two main ways you can control the amount of heat being put into your house by an Arotherm heat pump.

• Primary Control Method: Weather Compensation Curve
• Secondary Control Method: Room Temp Mod setting

There is also a third element to be aware of, Energy Integral.

Energy Integral is the internal counting system within the heat pump controller that decides whether to start or stop a heating cycle.

In summary, it does this by monitoring the difference between the target flow temperature and the actual flow temperature to determine how quickly the internal counter (Energy Integral) rises or falls.

I wrote a very in-depth article on the site about Energy Integral here, so we won’t cover that again here.  But it is well worth understanding, especially if you’re wondering how cycling works.

Vaillant Arotherm Firmware 351.06.07 Problems (Energy Integral)

I will also make brief comments within this document how Energy Integral works with each of the three options for Room Temp Mod.

Weather Compensation Curves

The Primary way to control the amount of heat coming out of your heat pump and into your underfloor heating (UFH) or your radiators is by choosing the correct setting on the weather compensation curve.

Choose the right setting on the curve so that the heat pump tries to put the same amount of heat back into the house that is being lost to the outside world at a certain outside temperature.

It does this by using a combination of your chosen indoor temperature, curve setting and outdoor temperature to select how hot the water in your radiators and/or underfloor needs to be.

For example, if we look at this table here (a snapshot of the Vaillant weather comp curve)

If you have chosen a target indoor temperature of 20.0C (yellow box, red circle) and a curve setting of 0.6 (green box, blue circle), then at 10C outside (blue box) the target flow temperature of the water to your heating system (rads/UFH) will be 31C (ie, where the green and blue meet indicated by the orange circle).

But if the outside temperature suddenly drops to 0C, the heat pump will automatically increase the temperature of the water in your heating system to 38C (purple circle).

Similarly, if the outside temperature then rises back up to 5C, the heat pump will automatically decrease the water temperature in your radiators and underfloor to 35C (pink circle).

This is weather compensation in a nutshell; the temperature of the water within the rads/UFH is dictated by the weather compensation settings.  Hotter system water is generated when it’s colder outside and cooler water in the system when it’s warmer outside.

If your house isn’t getting up to temperature, you may want to look at increasing the curve setting.  Ie. put hotter water into your rads/UFH.

But this comes at a performance cost, as the hotter your flow temperature goes, the lower your system efficiency.

If you are finding your house is too hot then you may want to look at decreasing the curve setting.

You can find Heat Curve via the following menu tree:

• Settings
• Installer Level
• 00
• Installation Configuration
• Circuit 1
• Heat Curve

You can read more about Weather Compensation Curves and how to choose the right one for your house in this separate more in-depth article.

Vaillant Arotherm Weather Curve Information

Room Temp Mod Summary

After making sure you’ve got the correct weather compensation curve setting you can then look at the secondary control parameter of Room Temp Mod.

The Room Temp Mod setting on the SensoCOMFORT controller relates to what role your room controller plays in adjusting the flow temperature of the system or indeed pausing heating for a while.

A basic summary of the three options would be

• Inactive = Pure Weather Compensation (WC) mode. Flow temperature is chosen based on outside temperature and indoor target temperature as per the WC curve setting. The SensoCOMFORT room stat is therefore nothing but a display.
• Active = Weather Compensation, same as Inactive, but with added Room Influence. Room influence means that depending how far away the current room temperature is from indoor target temperature the system can adjust the flow temperature, i.e. increase flow temperature if the room needs a little more heat or drop the flow temperature if the room is over target.
• Expanded = Uses both WC and Room influence from Active, but also acts as on/off stat, switching the heating off if room temp is exceeded.  

Note: To use Active or Expanded modes successfully you need to have your SensoCOMFORT controller placed in a sensible location, like a habitable room.

There is no point having the SensoCOMFORT controller in a plant room, airing cupboard or cold garage and choosing Active or Expanded.  As the room temperature measured needs to be from your living space to make use of room influence within Active and the on/off feature of Expanded.

You can find Room Temp Mod in the menus here:

• Settings
• Installer Level
• 00
• Installation Configuration
• Circuit 1
• Room temp. mod.

Let’s now dig a little deeper into each of the three Room Temp Mod settings

Room Temp Mod: Active

• Active = Weather Compensation with added Room Influence. Room influence means that depending how far away the current room temperature is from indoor target temperature the system can adjust the flow temperature, i.e. increase flow temperature if the room needs a little more heat or drop the flow temperature if the room is over target.

Room Temp Mod: Active is the setting I recommend for most users and is the one I’ve been using through the first couple of years with my Arotherm Heat pump.

Here is a classic example of Room Temp Mod: Active, in action.

It was around 4C outside in this 5 hour heating snippet and at 9:20am I decided to open the back door for 20 minutes.

The indoor temperature (black line) started to drop, so the SensoCOMFORT adjusted the target flow temperature (grey line) upwards to combat the shortfall.

Side note: On the flip side, if the temperature in the room had started to rise based on solar gain or from another internal heat source, the target flow temperature would lower to counter the room temperature rise.

You can see this sharp increase in flow temperature (red line) as well as an increase in heat output (yellow).

This is Active mode in a nutshell.  It reacts to indoor temperature changes by adjusting the target flow temperature.

From my experience, Active works really well if you’ve got the weather compensation curve nicely dialled into your rooms/property.  It doesn’t need to be exact, but there or thereabouts.

But what I’ve found is that there is a limit to how much extra it increases and decreases the target flow temperature.  Don’t expect Active to make up for massive discrepancies, like many degrees between target room temperature and actual room temperature.  It only seems to add a degree or two to the flow temperature when trying to catch up.

I wish there was some kind of setting to adjust how aggressive the room influence is.

If you are finding that Active mode cannot compensate enough for wild internal swings you may be better looking at Expanded mode.

Energy Integral Behaviour: Using Inactive or Active, Energy Integral is the primary control for starting and stopping cycles (aside from OT threshold).  Heating cycles stop at 0 and restart again at -60 (default).

Room Temp Mod: Inactive

• Inactive = Pure Weather Compensation (WC) mode. Flow temperature is chosen based on outside temperature and indoor target temperature as per the WC curve setting. The SensoCOMFORT room stat is therefore nothing but a display.

In the above Active mode example when the back door was opened, the controller would have not changed anything being set to Inactive.

The heat pump would have just carried on at the same flow temperature because it would have been only using the outside temperature as a guide.  Not knowing anything about the indoor temperature had started to drop.

So you’d imagine in most cases, like the door being opened, the room may have struggled to get back to target indoor temperature in a reasonable timescale.  I.e it would have needed more heat to make up for the shortfall, but it never tried to put more in.

I can see why there is a puritan lure to use “pure weather compensation”, ie Inactive.

But I cannot see why you wouldn’t use Active to have the small benefit and advantage of room influence.

In Active you can have your cake and eat it.  You might ever need room influence, but it is there as a fall back.  If you stick with Inactive, you’ll never have that option.

Is there an advantage to choosing Inactive over Active that I’ve missed?

Energy Integral Behaviour: Using Inactive or Active, Energy Integral is the primary control for starting and stopping cycles (aside from OT threshold).  Heating cycles stop at 0 and restart again at -60 (default).

Room Temp Mod: Expanded

• Expanded = Uses both WC and Room influence, but also acts as on/off stat, switching the heating off if room temp is exceeded. 

One thing to remind everyone of, is that the SensoCOMFORT controller can be used on both Heat Pump and Gas Boiler systems.  So Expanded acts more like a traditional on/off thermostat to cater for gas systems.

The SensoCOMFORT manual explains that Expanded deactivates the zone if the current room temperature is 0.125C greater than target and only re-activates if room temperature drops 0.1875C below target.

So a very narrow bandwidth of temperatures.

You get best efficiency with a heat pump by having long runs, low and slow.  By using Expanded there is a danger that you are turning the heat pump off and back on more times than you would be compared to Inactive or Active.

So I can’t personally recommend Expanded unless there are exceptional circumstances.

I think it’s much better to get your weather compensation curve dialled into the right ballpark and then use Active to take advantage of room influence.

I tried Expanded for a week or so and here are some thoughts and observations.

In this short example, the room temperature rises to 20.2C at 17:12 (target is 20C), so it goes higher than the 0.125C ‘Expanded’ cut off.

In ‘Inactive’ or ‘Active’, the heat pump would have just carry on putting a low amount of heat into the room.  Because my heat curve is pretty well configured I know the room wouldn’t overheat excessively.

Especially in Active mode where it would have also tried to lower the flow temperature to combat the room temperature rise.

But here in Expanded, the heat pump shut off for almost an hour until the temperature dropped to 19.8C (0.1875C lower than target) and fired up again (red circle) just after 18:00.

A heat pump uses a lot of electricity when starting up the compressor (blue trace at the bottom), so for performance, it’s better to try and avoid stops and starts.

For the nerds: The Energy Integral setting was only at -38 when Expanded chose to turn off the heating cycle at 17:12.  So the heating would normally have carried on in Active or Inactive modes in this circumstance.

More on Energy Integral behaviour in Expanded later.

Another thing I didn’t like about Expanded is the setback behaviour.

From 21:30 each day my unit goes into normal setback mode, dropping the internal target temperature from 20C to 19C.

In Inactive or Active modes, the heat pump would continue to output heat, even if the current room temperature (20C in this example) is over the setback indoor target (19C).

Normal Setback mode still uses the curve, but drops the flow temperature because not as much heat is required to maintain 19C indoors compared to 20C indoors.

So in essence, you are limiting the heat loss of the room/house by trickling a smaller amount of heat in.

You can see in this ‘Active’ example, that at 21:30 the target flow temperature (grey) drops, the unit carries on putting cycles of heat into the house, but at lower (setback) flow temperatures.

But if we go back to the Expanded example, the area highlighted in the Blue circle, we can see that because the room temperature (20C) is above the setback target temperature (19C), the heat pump does nothing for 3 hours (21:00 to 00:00).

So you get a much more dramatic indoor temperature drop off during that period (black line).

As you can see in my example, this period of no heat is then followed by a hot water run, so the indoor temperature drops even further.

That means that once you come out of hot water mode, the heat pump has to work much harder to try and get back to target indoor temperature.  Working less efficiently because it’s starting from a much colder indoor temperature.  It is much easier for the heat pump to maintain a temperature once achieved than trying to raise the temperature.

Normal Setback in Active mode seems a better way of keeping heat in the building overnight than just letting the house indoor temperature drop like a stone.

I really don’t like letting the house drop cold like this, it’s not comfortable having such temperature swings

I have found it much more comfortable putting heat into the house frequently in Active mode.

Another observation (and potential downside) of Expanded mode is that you’ve got the SensoCOMFORT in one room and you are measuring whether that single room hits target temperature before deciding whether to switch off the heating for the whole house.  What if other rooms are still under temperature?  

Sensitivity of the SensCOMFORT as a room stat?

Perhaps it’s because I’ve got the RF wireless version, but it does seem very slow to react to temperature swings and to trigger the turning off and turning back on of cycles in Expanded mode.

I have 3 other temperature sensors in the same location as my SensoCOMFORT and whilst all 4 seem pretty accurate at recording temperature, the SensoCOMFORT seems the slowest to react to changes.

Perhaps this is to preserve battery life?  Maybe it only wakes up every once in a while?

As part of my ebus > MQTT > Home Assistant workflow I only see updates every 5 minutes when reporting the indoor temperature. 

So if this 5 minute reporting timescale continues back to the heat pump and you ‘miss’ a temperature change by a minute, it could be nearly 10 minutes before the temperature change is noticed and threshold triggered.

Then miss that again when it’s time to turn back on, again, could be almost another 10 minutes.

Energy Integral Behaviour: 

When indoor temp is below target, Energy Integral will cause cycles just like in Inactive or Active.

But when target indoor temp goes 0.125C above room temp, Expanded kicks in and shuts the cycle down, regardless of Energy Integral.  And then keeps the cycle off until target drops 0.1875C below room temp, ignoring Energy Integral.

Once the cycle starts again, triggered by the temperature requirement, Energy Integral comes back into play.

All the time from when the cycle stops to when it starts again, Energy Integral stays the same value, i.e. it is paused and static.

Although when it fires back up, because the actual flow temp is starting from pretty cold (with the heat pump having been off) and desired temp is quite a way away higher, the Energy Integral drops off quickly when the cycle starts before then starting to rise.

So depending on what value Energy Integral was at when the cycle ended, Energy Integral can drop as low as -180 before starting to rise again.  Which means you could get a very long first run coming back into that first cycle.

Quick side note: This is the same Energy Integral behaviour seen at the start and end of hot water runs.  It starts again where it left off, ie, it is paused though a hot water runs.  Which can lead to short initial heating runs directly after hot water.  And because the flow water is still hot from the hot water run, you don’t get the same boost you do from coming out of Inactive.

As mentioned earlier, if you want to know more about the underlying Energy Integral counter, check out this article:

Vaillant Arotherm Firmware 351.06.07 Problems (Energy Integral)

Inactive versus Active

In this example I was initially running ‘Inactive’ mode, which is pure weather compensation, but I switched to Active to show the difference in behaviour.

The first cycle is using Inactive, then I switched to Active part way through the second cycle.

You can see at the end of this first cycle (15:59) the room temp is 19.5C (black line), whilst the target room temperature was actually 20C.  So at 16:20 I swapped over to ‘Active’ mode.

Instantly, the target flow temperature increased (grey line) because the actual room temperature (19.6C) was a little away from the target (20C).  This leads to an instant increase in flow temperature.

But then as expected, as the room temperature got closer to 20C at 16:40, 16:50 and 17:00, you can see the target flow temperature lower (the grey line dropping).  Proving that ‘Active’ works both ways.  Both increasing and decreasing target flow temperature when required.

You can also see that it wasn’t the outside temperature (purple line) that adjusted the flow temperature (i.e. weather compensation) as that was rock solid at around 9C.

Pump Overrun Observations

• Inactive mode: The circulation pump continues to overrun non-stop between cycles that are caused by Energy Integral (albeit at a reduced flow rate)
• Active mode: The circulation pump continues to overrun non-stop between cycles that are caused by Energy Integral (albeit at a reduced flow rate)
• Expanded mode: The circulation pump continues to overrun non-stop between cycles that are caused by Energy Integral (albeit at a reduced flow rate) but DOES NOT run between cycles when indoor target temperature is met where this causes the heating to stop. The circulation pump does not fire up again until start of next cycle (ie, room temp is 0.1875C lower than target)

Summary, Flaws and Recommendations

Before playing with and relying on Room Temp Mod settings, try and get your weather compensation curve dialled in.  Use the information in the Weather Compensation curve article to help with that.

Inactive Mode: If you are adamant you’ve got your weather compensation curve dialled in 100%, then absolutely give Inactive a try if you want.

If you have got your SensoCOMFORT controller installed in a plant room, airing cupboard or a garage, then you have no choice but to only choose Inactive.  If this is you, I’d highly recommend speaking to a heating engineer about getting the SensoCOMFORT moved to a habitable room where you could take advantage of Active or Expanded modes. 

There is no point having the SensoCOMFORT controller in the plant room or cold garage and choosing Active or Expanded.  As the room temperature it measures needs to be from your living space to make use of the Room Influence and on/off features.  You will just get wacky results otherwise.

If you do have your SensoCOMFORT in a habitable room then I would always first choose Active Room Temp Mod.  As the deep dive showed, it really helps with subtle swings of indoor temperature.  Think cooking, solar gain, humans or appliances etc that can all heat a room up and windows and doors being left open that can cool them down.  Active mode can automatically adjust to this, to a certain extent.

If you have rooms with mega amounts of solar gain, south facing with large windows perhaps, then maybe Expanded would be better for you.  But be careful with how Expanded deals with setback mode compared to Inactive or Active and adjust the setback temperature accordingly. 

But remember, cycling kills heat pump efficiency.  So I’d only use Expanded as a last resort.  

Much better to try and get the weather compensation curve really dialled in and use Active.

It’s completely rosy with Active though.  I sometimes find that I have to tweak the weather compensation curve.  Increasing the number when it’s colder outside and dropping it again when it is milder. I’m only flip flopping from between 0.45 and 0.5 for example at the moment, but still having to make manual changes from time to time.

This is not helped by the fact that the room influence is not aggressive enough. I wish that it could be more reactive to the room requirements.  Increasing or decreasing the flow temperature by more than it does to try and achieve or maintain the target room temperature.

Feature request:  For homeowners that don’t want or need to understand all this stuff, the room influence needs to be more dynamic.  More set and forget. A homeowner Auto mode!!

Big shout out to the guys at Open Energy Monitor for their heat pump monitoring system.  This article would never have been possible without their kit.

You can monitor my system here: https://emoncms.org/energystatsuk

My system is also part of the growing list of systems taking part in the https://heatpumpmonitor.org/ project.