What is Energy Integral

[JohnMo]

7 minutes ago, Dreadnaught said:

could easily be set at 15º.

Not really that practical, basics are

 

House at 20,  floor has to be at or above 20. Your return temp will be at or close to the average floor temp before a compressor cycle starts. So then you would need a minimum of 35 flow temp. Not practical, too hot, poor CoP.

9 minutes ago, Dreadnaught said:

run for longer – a good thing for CoP

Not really the longer you run generally the hotter you run, the worse the CoP.

 

Great CoP isn't the only parameter it's also cost to run and comfort. Big screed and overshooting target temperature isn't comfortable, you can take 12 hrs to cool down, then you undershoot target temp. Bigger/thicker the screed floor the more gentle or very well controlled you need to be, to eliminate yo-yo temperatures.

[Dreadnaught]

15 minutes ago, Dan F said:

buggy firmware

 

Good question. Short answer "not any more, I think".

 

Long answer: when I bought the UniTower it had the bug in the controller yes. Then my installer got in to a bit of a pickle and called in the Vaillant flying squad to help (the problem turned out to be installer-error 😄 but that's another story). In problem solving, the Vaillant engineer (with a little bit of encouragement from me) swapped out the controller board inside the controller, which, as you would imagine, I was very pleased to see him do!

 

I now have "351.09.01" on the controller in my UniTower but the version in the heat pump itself is still with the bugged "351.06.07", hence "I think" above.

Edited September 16 by Dreadnaught

[Dreadnaught]

@Dan F, turning to these settings …

• "Room temp. mod."
• "Set-back mode"
• "Set-back temperature"

I am in two minds about these.  The best way to run a heat pump is "low and slow", which would suggest running it 24/7 at the lowest temperature commensurate with a comfortable internal temperature. 

 

But the CoP at night will be worse. So turning the compressor off at night could lead to better CoP overall.

 

These settings above could allow a half-way house. Leave the heating on at night but lower the "target flow temperature" overnight to minimise the impact of the lower temperatures during that period.

 

Any thoughts, @Dan F?

 

 

[Dan F]

12 minutes ago, Dreadnaught said:

but the version in the heat pump itself is still with the bugged "351.06.07", hence "I think" above.

It's the heat pump board that matters, so your unit has the bug and:

i) The default -60º min behaves like -30º min

ii) It ignores any attempt to change the value, eg. to -100º min,

 

This is bad news for over-sized systems and for systems like ours where adjusting this makes sense.

 

See https://energy-stats.uk/vaillant-arotherm-firmware-351-06-07-problems-energy-integral/\

 

I had Vaillant switch mine out FoC, but I don't think anyone else has had any sucess.

Edited September 16 by Dan F

[Dreadnaught]

8 minutes ago, Dan F said:

It's the heat pump board that matters

Ah I see, that's unfortunate news. I will have to see how much Vaillant will charge to swap mine out in the heat pump itself.

 

Did you ask Vaillant to change yours?

 

Edited September 16 by Dreadnaught

[Dreadnaught]

14 minutes ago, Dan F said:

I had Vaillant switch mine out FoC, but I don't think anyone else has had any sucess.

 

Ah, I see. Well done. I have emailed them. Let's see how they reply. 

[Dan F]

22 hours ago, Dreadnaught said:

 

Ah, I see. Well done. I have emailed them. Let's see how they reply. 

Don't ask them for a price. Tell them it doesn't work as designed and you want it fixed under warranty.

[Dreadnaught]

25 minutes ago, Dan F said:

Don't ask them for a price.

 

Good advice.

[ReedRichards]

On 16/09/2024 at 12:34, Dreadnaught said:

Leave the heating on at night but lower the "target flow temperature" overnight to minimise the impact of the lower temperatures during that period.

 

I'm not @Dan F but my thought is that this is more about the temperature you want to achieve.  If you like your house to be a bit cooler overnight then use the set-back mode.  If you like the same temperature 24/7 then don't.

[Dreadnaught]

On 16/09/2024 at 12:55, Dreadnaught said:

Let's see how they reply. 

 

Update. After a bit of "persuasion", Vaillant swapped the board in my Arotherm Plus free-of-charge. All good. 

 

Many thanks for everyone's help and suggestions.

[Dreadnaught]

On 23/09/2024 at 08:03, ReedRichards said:

If you like your house to be a bit cooler overnight then use the set-back mode.  If you like the same temperature 24/7 then don't.

 

Yes, good point. You are quite right.

 

My new-build house has huge thermal inertia. The concrete raft foundation for my bungalow acts as a 55-tonne heat store. The UFH pipes are embedded deep inside it. The internal temperature for the dwelling changes on a time scale of days (sometimes even weeks). 

 

This means that it is far less important when I add heat to the dwelling. Day or night makes no real difference.

 

This all means that I can control the heat pump somewhat differently from most homes and I can try to maximise efficiency … to save money (and the planet).

 

Hence the unusual slant of my questions here.

[JohnMo]

1 hour ago, Dreadnaught said:

My new-build house has huge thermal inertia. The concrete raft foundation for my bungalow acts as a 55-tonne heat store. The UFH pipes are embedded deep inside it.

We also have about 50+ tonnes of slab, but its only 100mm thick. Once you start to monitor what happening you actually see solar gain, slab average temp starts to rise (seen in a rise of the return and flow temp) in the tenths of degree. I have reverted to straight WC away from batch charging because its more efficient in terms of kWh through the meter, and if the daily temperatures follows the normal pattern of colder at night and warmer in the day, suits our E7 tariff quite well. Basically the bulk of the heating gets done as the outside temps drop, charging the floor, as the day temps rise the target flow temp also lowers so heat pump naturally stays off. But the important bit is, floor temp isn't allowed to cool, resulting in the heat running at elevated flow temps for long period to recharge the floor.

 

Yesterday we had 3 degs overnight and the day went up to 10 degs during the day. 

 

Even running in the time of 3 degs was still getting a cop of 4.8, so 2.7p per kWh, the bits of running in the day and evening all came from the battery, but was getting a CoP of around 5.3 so 2.4p (maybe zero as battery was being charged by solar during the day). Note the 2x greyed sections are DHW heating.

[Dan F]

4 hours ago, Dreadnaught said:

 

Update. After a bit of "persuasion", Vaillant swapped the board in my Arotherm Plus free-of-charge. All good. 

 

Many thanks for everyone's help and suggestions.

 

I know various people, including a Vaillant-approved installer, who have had to purchase and install their own replacement boards!

 

What kind of "persuasion" was required?  Is the new board already installed now?  (make sure they move your cooling resistor over, and don't take it away with the old board. if you have one installed)

[Dreadnaught]

1 hour ago, Dan F said:

What kind of "persuasion" was required?  Is the new board already installed now? 

 

Persuasion: happy to discuss offline. (Vaillant after-sales had mentioned a cost of £490 to replace the board.)

 

Yes the new board is now installed and, as you say, I took care not to forget the cooling resistor (I even wrote a reminder note in big-black-pen and stuck it on the appliance ahead of time 😄).

 

Firmware versions now …

• Heat pump: 351.09.02
• HP controller: 351.09.01

Interestingly, the Vaillant engineer also modified the opening on the other side of the appliance, the opening for the power connections. As you may know, there have been some reports of water ingress there causing a short-circuit and I believe that newer models have been modified as a result.

 

In my case, he removed that panel and put a clear sheet of thin self-adhesive acrylic over the entire opening before refitting the panel. This gives an extra layer of protection for the underlying circuit board. He said it was Vaillant's chosen mitigation method and was done for me as a precaution. I have read online that others have solved the issue with a line of sealant along the top of that panel, which I was considering adding but it is now no longer needed.

Edited September 26 by Dreadnaught

[sharpener]

1 hour ago, Dreadnaught said:

Interestingly, the Vaillant engineer also modified the opening on the other side of the appliance, the opening for the power connections. As you may know, there have been some reports of water ingress there causing a short-circuit and I believe that newer models have been modified as a result.

 

May also reduce the likelihood of slug damage(!)

 

Edited September 26 by sharpener
Fix link

[MikeSharp01]

7 hours ago, Jungs said:

only found one explanation through google

 

https://www.physicsforums.com/threads/what-is-the-integral-of-energy.966184/

Hmmmm... not sure they got to the bottom of it either - interesting watching them work through it though.

[Dreadnaught]

Just to clarify… the Energy Integral for the "Vaillant Arotherm Plus" heat pump is the name given to a way that the heat pump's microprocessor controller decides when to turn off the compressor pump, and hence stop heating. And the same Energy Integral also then informs the controller when to subsequently to turn it back on again. (There is also another way the compressor turns on and off unrelated to the Energy Integral, but that's by-the-by).

 

The Energy Integral in this case has the units of "º minutes" ("degree minutes"); note this is not degrees "per" minute.

 

Simplified and only dealing with heating … the controller calculates the number of degrees that the "flow temperature" deviates from the "targeted flow temperature" each minute. This is then summed cumulatively each minute to keep a running total.

 

For example… if the flow temperature in the pipe leaving the heat pump is 42º and the controller is targeting a 38º flow temperature then (42-38) = "4" is added to the Energy Integral at the end of that minute. If in the next minute the figures are 45 and 38 then "7" is added at the end of the subsequent minute. And so on minute by minute. 

 

This cumulative sum is the "Energy Integral".

 

Then… when that cumulative sum of these figures reaches zero (from its negative starting point; default is "-60" but this can be changed in the settings) the controller turns the compressor pump off and heating stops.

 

There are more subtleties than I have mentioned above … such as overrun of the sum and the control of the separate building-circulation pump … but that's the essence of it. It's simple and elegant.

 

I suspect that cumulative counters are used commonly in electronic control-systems. Perhaps an engineer here could confirm this.

 

Edited September 29 by Dreadnaught

[JamesPa]

36 minutes ago, Dreadnaught said:

I suspect that cumulative counters are used commonly in electronic control-systems. Perhaps an engineer here could confirm this.

You are correct.  The classic PID (proportional, integral, differential) controller uses  the current deviation of the variable (eg temperature) from the desired value, the cumulative difference between the target and actual value, and the current rate of change of the variable into account (in various proportions) to decide the change made in the controlled parameter (eg energy input) 

 

PID controllers appear in many control systems, there is a raft of theory on them and tuning them to get the right proportions of p, I and d can be 'interesting', particularly if there is long delay between changing the input and when the output changes (as there is in a heating system) or nonlinearity.

Edited September 29 by JamesPa

[sharpener]

42 minutes ago, Dreadnaught said:

Perhaps an engineer here could confirm this.

 

The energy integral is the I part of a standard PID control loop (Proportional, Integral, Differential).

 

Weather compensation is a feed-forward Proportional term. The closed-loop Integral term takes out any residual error and avoids long-term drift.

 

I do not know if there is a differential term, this would be needed to cope with sudden changes of room temp or OAT which are unlikely - the classic theory was developed for radar tracking of fast-moving targets. It might though be included in the Room Temp mod settings (if used, I don't).

 

@JamesPa Snap!

 

 

Edited September 29 by sharpener
Great minds!

[JohnMo]

Big question - do you need the Energy Integral? Does add to system efficiency or house comfort?

 

Suspect the answer is maybe or sometimes. But generally a good marketing tool, has kept this thread talking about it for a few years.

[Dan F]

On 29/09/2024 at 11:08, JohnMo said:

Big question - do you need the Energy Integral? Does add to system efficiency or house comfort?

 

Suspect the answer is maybe or sometimes. But generally a good marketing tool, has kept this thread talking about it for a few years.

 

It's not marketing (and I haven't seen it mentioned in marketing materials), it's a control strategy that is important to control cycling when heating load is less than minimum output.

 

Without an integral-based control mechanism how would ASHP control cycles?  Using simple hystersis would result in more temperature swings impacting efficiency and comfort AFAIU.. 

 

 

[JohnMo]

33 minutes ago, Dan F said:

Without an integral-based control mechanism how would ASHP control cycles?  Using simple hystersis would result in more temperature swings impacting efficiency

Interesting thought, but not sure I agree, many ASHP don't have that functional control. We are currently putting in less than an average of 1kW into the house with a 6kW heat pump, so well below any modulation, controlled on hysteresis and pure WC. House fluctuating a massive +/-0.25 degs and daily CoP generally around 5 for heating, as I get thing optimised. 

 

Generally cycling is good, its an easy way to control capacity, when below min modulation. The only caveat the run time needs to be long enough to do some useful heating, this varies with different systems, this is easy to tweak with hysteresis. 

 

[sharpener]

2 hours ago, Dan F said:

Without an integral-based control mechanism how would ASHP control cycles?  Using simple hystersis would result in more temperature swings impacting efficiency and comfort AFAIU.. 

The obvious way would be to run the HP on a mark-space ratio to give an average power defined by the WC algorithmn. You might want to fine tune it with room temperature feedback but it would surely be better than allowing it to just switch on and off as it oscillates about the room temp setting (bang-band servo mode).

[Dan F]

1 hour ago, JohnMo said:

Interesting thought, but not sure I agree, many ASHP don't have that functional control. We are currently putting in less than an average of 1kW into the house with a 6kW heat pump, so well below any modulation, controlled on hysteresis and pure WC. House fluctuating a massive +/-0.25 degs and daily CoP generally around 5 for heating, as I get thing optimised. 

 

Generally cycling is good, its an easy way to control capacity, when below min modulation. The only caveat the run time needs to be long enough to do some useful heating, this varies with different systems, this is easy to tweak with hysteresis. 

 

Which ASHP is this? What is hysteresis? 

 

My understanding is that with a target flow temp of 23C and a 7K hysteresis (as an example) with an open loop system the ASHP is going to run until flow temp reaches 30C and then shut down. Is this how yours behaves, or does it do something different e.g. mark-space ratio.   I assume you much have hysteresis much lower than 7K?  Otherwise, if flow temp does have to ramp up to 30C before ASHP shuts down, this risks temperature fluctuations and possibiity to overshoot.

 

 

 

[JohnMo]

1 hour ago, Dan F said:

What is hysteresis

You have a start and stop hysterisis for the compressor. So for a target of 25, the return flow will drop by a predetermined amount below the target flow temp, once at that point compressor starts. It will run until the shut off hysterisis temp is reached. How long it runs depends on system volume, heat demand and how deep the heat pump modulates. My settings are based on my system and what it does and doesn't do.

 

Mine at a target flow of 25, start up hysterisis is 5.1, so return temp is allowed to fall to 19.9, before compressor start. Cut off hysterisis is 2.3 so cuts off at 27.3. My total hysterisis is 7.4. All this changes with different heating systems and houses. Mine is 300mm spacing UFH in 100mm concrete screed.

 

Heat pump is a Maxa i32V5.

 

Today excluding DHW the compressor has started 5x times up to 10pm, shortest run time was 18 mins (9 degs OAT) and longest run 2.5 hrs (5 Deg OAT).

 

WC is all about running just enough to top up the energy in the house, so I use the hysterisis and a WC curve to play with the floor heat output. Based on the floor average temperature, to get the correct heat output.  The WC curve starts at 15 Deg OAT at 25, this gives a floor minimum temperature of 19.9 (don't want the heating on really at that temperature), at -9 the WC curve stops at 30.3, so floor temp is a minimum of 25.2 (not tested this temp yet). So far this is working fine down to +3 degs. Depending on actual run times at sub zero this will affect where WC stops and at what flow temp. But once set it's set for ever.