Posted by: @derek-m

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I doubt whether anyone is going to post on the forum that setbacks are actually causing them to use more electrical energy, even if they knew that to be the case. It is human nature to brag about wins, and conveniently forget about defeats.

Equally, folks might want to complain, not getting the performance they hoped they would get etc etc. There's no shortage of such complaints about other aspects of heat pump installation and use, all very visible in the many posts here on this very forum. Nor is it really a defeat, if you do find setbacks don't save you energy. You tried it, it didn't work, and have gone back to 24 hour running. That shouldn't be painful to report. On other fora, when something is up for discussion, you often get it worked for me/didn't work for me posts.

I suspect it has more to do with data collection, it is not easy to do unless you have a setup that facilitates it, and without the data, you just don't know. Even with the data, it is still apparently not that clear, as you and @jamespa have both helpfully reminded us, and even if it is clear, then generalisability can be a problem. But the potential energy and costs savings do, at least for me, make it worth attempting to get a good enough answer, at least for my system, and in developing a method, it might well pave the way to a general method of determining what savings are possible without materially affecting comfort.    

@cathoderay

Thank you for some of the missing information. I was hoping that you would have the temperature information for the PHE to hand, but don't worry I will search back through the numerous posts to see if I can find the data.

I would have thought that you would be appreciative of spreadsheets, since they helped highlight the serious problems that still exist with your system, which is why I am trying to ensure that the raw data used within the spreadsheet is as accurate as possible. Otherwise the computer world adage 'garbage in, garbage out' may apply.

I don't agree with your assessment that thermal energy is still being supplied when the compressor is in 'cycle off' mode. The primary water is indeed loosing thermal energy, but I don't think it is being lost within the thermal envelope of the building. The fact that the LWT reading drops 11C in 8 minutes, would indicate to me that the small quantity of primary water is being cooled, but the thermal energy being lost is not being replaced by thermal energy from the secondary water circuit, otherwise the radiators would cool by 10C or so. That is why I suggested checking if the secondary water pump was actually running, which would be one possible reason, or it could be that the PHE does not work very well in reverse direction. Also just the fact that you cannot get thermal energy to flow from a lower temperature to a higher temperature, if the primary water is cooler than the secondary water, then thermal energy should be flowing out of the building, not into it.

I will try the calculations with both versions of the average LWT, which you may not deem important, but is nonetheless one of the primary factors in calculating the energy out and COP values, from which energy in can then be derived.

@derek-m I simply have a kwh meter that just reports heat pump usage. I monitored for 24hour period running 24/7,approx 30kwh usage, most days im running 11am-9pm, usage bertween14-16kwh. I don't have any other monitors for heat pump so i wont be getting data for lots of different aspects of different parameters. I simple monitor kwh usage and stat temps in the house. Thats it, simple to me and i can see in my bills how much cheaper they are this winter.

Posted by: @cathoderay

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Posted by: @derek-m

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I doubt whether anyone is going to post on the forum that setbacks are actually causing them to use more electrical energy, even if they knew that to be the case. It is human nature to brag about wins, and conveniently forget about defeats.

Equally, folks might want to complain, not getting the performance they hoped they would get etc etc. There's no shortage of such complaints about other aspects of heat pump installation and use, all very visible in the many posts here on this very forum. Nor is it really a defeat, if you do find setbacks don't save you energy. You tried it, it didn't work, and have gone back to 24 hour running. That shouldn't be painful to report. On other fora, when something is up for discussion, you often get it worked for me/didn't work for me posts.

I suspect it has more to do with data collection, it is not easy to do unless you have a setup that facilitates it, and without the data, you just don't know. Even with the data, it is still apparently not that clear, as you and @jamespa have both helpfully reminded us, and even if it is clear, then generalisability can be a problem. But the potential energy and costs savings do, at least for me, make it worth attempting to get a good enough answer, at least for my system, and in developing a method, it might well pave the way to a general method of determining what savings are possible without materially affecting comfort.    

This is the primary reason I have been developing the spreadsheet, so that it may be possible to predict what conditions favour a setback routine and under what conditions it may be best to avoid doing so. A prime example would be a system that works fine under mild weather conditions and does produce a degree of energy reduction, but trying a similar routine during cold weather conditions may lead to a situation where the home becomes too cold, and the heat pump does not have the necessary additional capacity to recover the IAT in a reasonable time period.

There have also been predicted situations where a setback may have increased energy use rather than decreasing it, which is why it is often better to test out different scenarios in the 'computer world', rather than in the real world. Then try the ones that appear most promising in the real world.

One of the possible reasons why your particular system could potentially show an energy reduction, is because it is not working particularly efficiently at the moment, so switching it off provides an immediate energy reduction, which could equally be achieved by optimising its performance.

Posted by: @derek-m

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I don't agree with your assessment that thermal energy is still being supplied when the compressor is in 'cycle off' mode. The primary water is indeed loosing thermal energy, but I don't think it is being lost within the thermal envelope of the building.

You may be right. I had in mind a sort of over-running, heat that has been generated, and is visible in the LWT, but has yet to be distributed. Consider this chart (from this morning):

Posted by: @derek-m

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That is why I suggested checking if the secondary water pump was actually running, which would be one possible reason, or it could be that the PHE does not work very well in reverse direction.

This may be worth thinking about. The flows are still contraflow, but now the direction of heat flow is in reverse.

I'm still as sure as can be it runs through the whole cycle. When I took those PHE temp readings, I just happened to catch the nadir of a cycle, and the secondary pump was running at the time. Also, I have never seen the pump off (LEDs always on) when the heating is on.

The problem is catching a cycle in real time, so I can check in real time whether the pump is running.  

Posted by: @derek-m

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I will try the calculations with both versions of the average LWT, which you may not deem important, but is nonetheless one of the primary factors in calculating the energy out and COP values, from which energy in can then be derived.

I'd forgotten that in effect you reverse engineer the energy in from the energy out via the COP. That needs both the energy out and the COP to be correct, and we know from the scatter plots that the energy out is far less stable for a given OAT than the energy in. Likewise, the COP - I think you get it from the Midea engineering data - is potentially subject to errors. That's why I think it is important to test the model's predictions against the observed values. 

Posted by: @newhouse87

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@derek-m I simply have a kwh meter that just reports heat pump usage. I monitored for 24hour period running 24/7,approx 30kwh usage, most days im running 11am-9pm, usage bertween14-16kwh. I don't have any other monitors for heat pump so i wont be getting data for lots of different aspects of different parameters. I simple monitor kwh usage and stat temps in the house. Thats it, simple to me and i can see in my bills how much cheaper they are this winter.

Your bills are lower, because the tariff may possibly be lower, but also because forum members helped your sort out all the issues and get your system working efficiently. To be able to state that you have achieved an energy reduction of 50% using a setback, you would need to perform detailed testing using fully calibrated test equipment under specified testing conditions.

It is therefore probably best to state that under certain conditions you appear to have achieved a reduction in energy usage. I am not trying to put words into your mouth, but for the forum to maintain its credulity, any claims should, whenever possible, be backed up by test results or appropriate mathematics.

During the November cold spell did you not say that you had to stop using a setback because it was taking too long to get the temperature back up again?

@Derek-m

Your bills are lower, because the tariff may possibly be lower, but also because forum members helped your sort out all the issues and get your system working efficiently. To be able to state that you have achieved an energy reduction of 50% using a setback, you would need to perform detailed testing using fully calibrated test equipment under specified testing conditions.

It is therefore probably best to state that under certain conditions you appear to have achieved a reduction in energy usage. I am not trying to put words into your mouth, but for the forum to maintain its credulity, any claims should, whenever possible, be backed up by test results or appropriate mathematics.

During the November cold spell did you not say that you had to stop using a setback because it was taking too long to get the temperature back up again?

No offence but I'm not that stupid that i cannot calculate my bills using different tariffs. Only for this forum i would not have the reductions, you in particular helped me alot. It was me however who decided to go off wc and find lowest fixed flow temp for my house and that seems to have worked well, i have warm house and lower bills.During the cold spell i was in Scotland and stats were set to come on at4pm and off at 9 as previous weeks weather was mild so i will need another cold snap to get better view of the situation. All i know for certain, math's or no math's is that during these mild weather conditions and above setbacks are saving energy for ME and house still very comfy heat wise. I might try 24/7 run in these conditions and see kwh usage again.

@derek-m - another reason why folks might be wary of posting their observations is that they know if they do, they are likely to get a pasting. Also a forum by its very nature doesn't have a view, only it's participants do. It is of course perfectly legit for you to question things that are posted, but as yet no one has a definitive way of answering the underlying question that all can agree on. 

@newhouse87 used his bills as back up evidence, his primary evidence is based on kWh use, which is independent of tariffs.

There is I suspect a vague general consensus among users of setbacks that have posted here that setbacks are more effective in mild weather, in colder weather the recovery boost struggles to get the IAT back to where it should be. It's visible in my charts, and yes I also recall @newhouse87 stopped the setback in colder weather. 

For arguments sake i will extend running at 9pm tonight when its due to go off and see what it uses until 9pm tomorrow. I know in these conditions its 14-16kwh for 10hour day period. I will do24hr run and compare.

Posted by: @newhouse87

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Currently with setback from nov5-jan5th, im trending at35% less usage then last winter. That is the difference from 7 zones to 1 and not using stat on/off. Its constant running from 11am-9pm nowadays.  

Thats excellent and doubtless a true reflection of reality or thereabouts (I say thereabouts only because I dont know whether this years weather conditions are better or worse than last year)

Posted by: @newhouse87

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I know running 24/7 costs me roughly 30kwh, running from 11-9pm is 14-16 both include dhw.

I don't see how you 'know' this  You appear to have made three changes relative to last year

• the difference from 7 zones to 1
• not using stat on/off
• running from 11am-9pm [as opposed to 24*7 ie setback]

yes are apparently assigning all the savings to one change only.  

Unless you have shown that the reduction in energy usage is due solely or primarily to setback then I would suggest that its more likely due to the other two changes.  Do you have evidence that its due to primarily to setback?

For the avoidance of doubt I am not trying to be critical, I am only trying to sound a very strong note of caution to people, to whom this might matter financially, who may not have followed this in detail, may not understand or wish to understand the physics, but might read this and think that setback will save them 35%.  It wont and can't in most practical scenarios, unless you are willing to take a comfort hit during the 'important hours'  If you are willing to take this comfort hit then the best advice currently is to dial down the WC curve/turn down the thermostat 24x7.

Posted by: @newhouse87

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For arguments sake i will extend running at 9pm tonight when its due to go off and see what it uses until 9pm tomorrow. I know in these conditions its 14-16kwh for 10hour day period. I will do24hr run and compare.

Thats great but drawing conclusions based on a 24 hour period unless very carefully controlled is unsafe.

For the avoidance of doubt I currently hold to the view that, on the balance of probability a setback which does not materially reduce the house temperature during the evening period (or whatever is the important period) is likely to save ~5% in many, but perhaps not all, relevant circumstances (by ~ I mean 2.5%-10%).  This view is based on experimental evidence from @cathoderay, modelling done by @derek-m and, crudely, by me and basic physics theory).  That's a 'balance of probability' judgement, taking all the evidence together and could yet be wrong.  However I can confidently say that I would, if I could, personally proceed on the basis of this assumption for now.

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(1) Sadly I dont yet have a heat pump because my planning authority has

a. refused express permission on noise grounds, even though I can do better than the permitted development noise level by 4dB, and can achieve a noise level inside the neighbouring property more than 10dB below the levels which BS8233 deems 'desirable'

b. made it abundantly clear that, if I install under permitted development (which is an option), I might still face enforcement action for noise nuisance notwithstanding the above

c. notwithstanding the above run by a coalition which is majority Green party.

Posted by: @derek-m

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I doubt whether anyone is going to post on the forum that setbacks are actually causing them to use more electrical energy, even if they knew that to be the case. It is human nature to brag about wins, and conveniently forget about defeats.

i am at a loss to know how to interpret your comments Derek,  You appear to be undermining everything anyone may post on these forums. I was about to post some interesting findings on a narrower setback temperature and trialling Weather Compensation instead of Auto Adapt and how that helps with morning recovery and improved, lower flow temperatures.

however, according to you nobody tells the truth apparently, so What’s is the point of posting anything here any more?

Posted by: @sunandair

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Posted by: @derek-m

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I doubt whether anyone is going to post on the forum that setbacks are actually causing them to use more electrical energy, even if they knew that to be the case. It is human nature to brag about wins, and conveniently forget about defeats.

i am at a loss to know how to interpret your comments Derek,  You appear to be undermining everything anyone may post on these forums. I was about to post some interesting findings on a narrower setback temperature and trialling Weather Compensation instead of Auto Adapt and how that helps with morning recovery and improved, lower flow temperatures.

however, according to you nobody tells the truth apparently, so What’s is the point of posting anything here any more?

 

I am absolutely not taking sides here and personally believe that everyone is telling the truth of what they see.

What I do observe is differences of interpretation.  In any field of engineering (or indeed life) observations (on energy use or anything else) can be entirely accurate and truthful, but their explanation may still be a valid subject of debate.  Furthermore the actual the cause for any observed experimental behaviours may well involve multiple factors.  There is a popular  (and very relevant) phrase 'correlation does not equal causality', and its helpful to bear that in mind when drawing conclusions from observations. 

As someone who sits 'on the fence' between experimentation and theory I am happy to believe the truth of any experimental observations, but will not easily be convinced by the interpretation of those observations unless it is reasonably consistent with theory.  Similarly I am happy to believe that any model is what the model says, but will not easily be convinced by the interpretation or validity of the model unless it has some supporting evidence in experiment.  That's just good science.

Surely we can be mature enough on this forum to recognise that interpretations of experimental results that aren't reasonably consistent with (centuries old) theory are suspect, and equally modelling results that aren't somehow backed up by at least some experiment are equally suspect.  Neither is 'wrong' its just that both may be neglecting some (known or unknown) factor which is significant to the conclusion.

Until we have a theory/model which has some experimental verification and vice versa, I personally cant believe we have a reliable answer.  Only by combining the two can we be reasonably certain both that all material factors are accounted for in the, inevitably incomplete, models based on theory, and that any interpretations we may draw from the (inevitably limited and imperfect) experimental evidence we have, are ones we could stand by.

If everyone were to recognise the limitations of the information, whether it be theoretical or experimental, and the value of combining the two, we have might have a much more productive discussion.