Without doing the precise maths here, for me to mess about with the app on a daily basis rather than the joy of just forgetting about it and leaving it on gets my vote.

Posted by: @westkent

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Without doing the precise maths here, for me to mess about with the app on a daily basis rather than the joy of just forgetting about it and leaving it on gets my vote.

When I had my gas boiler, I had my Honeywell Evohome system set up automatically to turn the heating off when I left the house and back on again when I came within a certain radius of it using IFTTT.

However, IFTTT locational triggers have stopped working and in any event, I need to turn this heating system on about an hour before I need it, the Honeywell system can no longer shut down the heating entirely. I may investigate other automation pathways that allow me to control the myVaillant system using locational triggers, but I use Android rather than Apple so I cannot use Homekit directly.

@jamespetts, there are plenty of threads on this forum basically saying that observation will trump theory every time so I applaud your inclination to test.

I will say, however, that just one observation during a temperate period is not in itself enough to go on, especially when the observed difference is a single kWh. I would strongly urge you to carry out several more of these tests to average out for this kind of mild weather and then several more in the depths of winter when the heat pump's performance may be different. You may find your assumptions change, you may find they are even more strongly vindicated.

Posted by: @majordennisbloodnok

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@jamespetts, there are plenty of threads on this forum basically saying that observation will trump theory every time so I applaud your inclination to test.

I will say, however, that just one observation during a temperate period is not in itself enough to go on, especially when the observed difference is a single kWh. I would strongly urge you to carry out several more of these tests to average out for this kind of mild weather and then several more in the depths of winter when the heat pump's performance may be different. You may find your assumptions change, you may find they are even more strongly vindicated.

Noted - testing is definitely a worthwhile thing! Although the heat differential in this case is perhaps better understood in proportional rather than absolute terms (i.e. a difference of a third rather than of 1kW).

Posted by: @jamespetts

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Noted - testing is definitely a worthwhile thing! Although the heat differential in this case is perhaps better understood in proportional rather than absolute terms (i.e. a difference of a third rather than of 1kW).

Perhaps, but not necessarily, and further testing would show up whether the absolute value and relative proportion change in cold weather in the same proportion. 

One thing I’ve always maintained is that heating decisions are entirely up to the homeowner; it’s all about finding what works for each household. In your case, @jamespetts, if your home can stay comfortable with the heating off for 8-10 hours and only needs reheating when you return, that’s ideal.

In our home, with our particular heat loss rate and emitters, that approach simply isn’t practical unless we’re getting significant solar gain. When that happens, I also turn off the heating, as there’s no point in drawing electricity (even for just 4-5 hours) if it’s not necessary – especially since that still adds up in costs.

Just a quick note: November is still relatively mild, staying above 10°C, but it might become a bit more challenging to manage in January or February when temperatures drop.

@editor Last year, the coldest days in this neck of the woods (south east England) fell in late November and early December when we experienced -7 and -8 degrees C for a few days. Brrrr! Ttttttttttoodles.

In the deep south west we had these temps TWO YEARS running.... we grow palm trees for goodness sake and -7º is not in the script!

Kind of makes a mockery of MCS guidelines too.

I'm always somewhat cautious when claims are made of 30% saving in energy use by turning off/down the heating for part of the day.  I'm not for a moment casting doubt on the data, just sounding a note of caution on the possible explanations and reproducibility in other conditions. 

In practice such savings are made up of

• Savings because the house is cooler, so loses less energy
• Various other things

The first of these is relatively easily calculable from the laws of thermodynamics, and rarely amounts to more than 10-15% simply because the house doesn't cool sufficiently in most cases to make a bigger difference.  The second is not currently easily calculated but includes factors such as standing losses, loads, inefficiencies due to cycling and likely other factors that we don't really understand, which tend to be larger in proportion when its mild, as at present although that is not necessarily the case.  The second group is of course just as real, however if they dominate may indicate that there is an underlying inefficiency in the system which, if corrected, might yield additional savings.

In your case you have already told us that the flow temperature is higher than it needs to be (because the heating system is performing better than predicted - a good thing), which inherently means that the heating does not have to be on all the time to deliver the energy needed to keep the house warm, but is also not running at its most efficient when it is on.  If you want optimum operation I would correct this first and then run the experiment again.  I would also, like others have suggested, run it with an open mind it in a wider range of conditions.  Furthermore I would be careful of coming to conclusions based on results from just one day, unless the conditions were stable for at least 24hrs beforehand.  Houses store a lot of energy and so the energy required to keep them warm on any given day depends a lot on what happened on the day before, and possible even two or three days before.

That said, if the heat pump is turned off during the day and the house cools down then the house will lose less energy, so less energy needs to be supplied by the heat pump to make up for the energy lost.  Provided you don't have to turn the flow temperature up for it to recover in time, and given that the outdoor temperature during the day is unlikely to fall precipitously during the recovery period (which could cause COP to crash just when you are hitting it hardest) then its pretty certain that the heat pump will require less energy in total to power it.  Most, if not all, of the 'other things' are losses not gains so it would actually be surprising if turning it off during the day (provided you don't have to bump up the flow temperature to recover) didn't save energy (although it would be surprising if the saving were as great as 30% when its a lot colder).

Night time setback is a little less clear theoretically because the recovery is likely to happen when COP is at its lowest, but again the 'other things' may well dominate and even if they don't and provided its a modest setback the likelihood is that there will be a saving.

In summary I would say do see if you can optimise your flow temperature to the lowest possible and do continue the experiments as its relatively unlikely, in the circumstance that you describe, that you will increase the energy consumption of the heat pump with a daytime setback/turn off.  But at the same time do keep an eye on it in varying circumstances and don't let 'confirmation bias' cloud observation, or lead you down the path of raising the flow temperature in order to facilitate recovery/remain comfortable.

@lucia I lived in Yeovil in Somerset until until 1973 and up until then, I think we benefitted from the Gulf Stream but I think the influence of its’ warming effect may have shifted slightly. Toodles.

Latest data.

Monday: heating running all day, outdoor temperature 11.5C, heat curve 0.6, 3.3kWh consumed.

Tuesday: heating off between circa 1200h and circa 1900h, outdoor temperature 11.3C, heat curve 0.55, 2.7kWh consumed.