Data if possible should include LWT, RWT, IAT, OAT, setpoints, any setback periods, flowrates if you know them, energy in and energy out, and anything else you think may be useful.
I am not convinced you are going about this the right way. Normally you take a hypothesis (model), use it to make a prediction, and then test that against the real world. Earlier you said your independent variables were the DT between IAT and OAT, the length of the setback period, the thermal capacity (Heat Mass) of the property, and how quickly recovery to desired IAT needs to be made. I think you should be asking for those inputs, rather than the dependent variables, as you do above. For example, let's say I have:
an inside/outside delta t of 10 (this being an average, as it varies over time)
a six hour setback
thermal capacity of building (not property, that includes the garden/shed etc): this is problematic, in that I have no idea what it is, apart from having a hunch that it is 'relatively high', and on this, google is not my friend: I can find plenty of descriptions of what it is, how it works, and even numbers for individual materials, but nothing on values for typical buildings. You will have to use a suitable number, and explain why it is suitable, or, failing that, find a proxy variable of some sort that can be obtained, and use that in the model; and if that isn't possible, then it is back to the drawing board
a three hour recovery
then you should tell me how much energy that particular setback will save (or cost) me, over and above what I would have used anyway.
Midea 14kW (for now...) ASHP heating both building and DHW
The monitoring system creates a record for each minute. For energy, it logs 1 pulse per watt hour and counts how many of them there are in each minute. So 35 means 35 watt hours per minute. Which is 60x35=2100 watt hours per hour, which means that for the minute in question, it's running at 2.1kW. Maybe there is an easier way of explaining this! Just multiply by 60 and that's watts.
I do something similar behind the scenes, though my inputs for energy in are amps and volts. I then average them over the hour (I found this gives the same result as doing minute by minute calculations) and then the average (amps x volts)/1000 for the hour gives the kWh for that hour. I also tried using complicated area under the curve methods and again got a very similar results, and so ended up using just the simple average calculation.
As I have mentioned before, the energy in values obtained this way do underestimate the amount of energy in shown on the external kWh meter. I don't know why this is the case: maybe it is because Midea don't measure all the amps going used by the entire heat pump assembly, maybe they don't include the secondary circulating pump, which gets its mains supply from the heat pump (that's the most likely explanation, I think), maybe their measurement device is inaccurate. I am currently recording daily external kWh meter readings, and when I have enough, I will compare them to the calculated values, and if the error is constant, add a suitable correction factor. From the readings so far (ten days worth of readings), the error does appear reasonably constant, with the calculated value coming in at around 80% of the metered value.
In the fullness of time, when the stars are aligned in the right way, I might swap my current external kWh meter for another one of the same model/brand (meaning an easy swap) that does have a modbus connection.
Midea 14kW (for now...) ASHP heating both building and DHW
Here is the last 24 hours' data. The spike on the left hand side is a manually triggered DHW cycle, and on the right hand side we have the setback and recovery period:
The OAT has gone into defrost cycle territory over the last few hours, at 4 degrees, but no defrost cycle occurred (they can be identified by the fact the LWT drops below the RWT); instead, we have less cycling, with longer periods of steady state running. We can also see, from the popup box, that the actual IAT has recovered to within 0.2 degrees of the desired IAT by 0700, from a nadir of 17.2 at the end of the setback period. The heat pump does use more energy during the recovery period, but it would have done so anyway, because the OAT was lower. Before the setback, it was using just over 1 kWh per hour, after the setback it is around 1.7 kWh per hour - let's say around 0.6 kWh more per hour. Let's say half of that is because of the drop in OAT, ie it would have been used even without a setback. That leaves an extra 0.3 kWh extra energy used to speed up the recovery over a four hour recovery period, a total of 1.2 kWh extra energy used. But I saved at least 6kWh, probably nearer 7 kWh, during the setback,
These results are extremely useful and exciting, but nevertheless something has been bugging me about this. I couldn't quite put my finger on what was bugging me until now.
Taking the example I reproduce above, your standing energy out (which must in the long term equal your house loss) is about 4.3kW at a temp diff between IAT-OAT of about 9C, so about 470W/C.
During your six hour setback your IAT falls from 20 to about 17 roughly linearly, so an average 'setback' of 1.5C,.lets generously say 2C to allow for the slight curve. It then recovers over about 3 hours also roughly linearly. Thus the 'saved' loss from the house (due to the fact that the house temp is lower) is roughly 2*470*9 Wh=8.4kWh.
Your COP is consistently over 4, so that would correspond to saving of energy in of about 2kWh. Yet you are claiming, and I agree that the mark one eyeball integrator would suggest that you are correct, that the saved energy in is about 6kWh. Unless my math or reading of your graphs is all wrong, something doesn't stack up.
My first guess is that the mark one eyeball integrator doesn't adequately account for the small increases in demand, possibly throughout the day, which eventually add up, however I am very definitely open to other suggestions (including 'wrong math') to reconcile the savings in loss from the house, due to the mild setback, with the apparent savings in energy out/in. @derek-m any insight you may have would also be appreciated!
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
In my limited knowledge opinion, set backs will work for some houses better then others. Last night my heating went off at 9pm. Got to as low as 4deg oat overnight. My living area was still at 20 and kitchen still at 21 at 7am. If i had kept heating on all night i would have used up near 15kwh as lowest per hour usage overnight while im asleep as i have seen is approx 1.5-1.7kwh per hour in middle of evening after heating has been on for good few hours. My heating will come back on 3 today as nobody in house all day and will be nice and warm by 6pm for the evening until it goes off at 9. In colder weather i have turned heating on at midday so a 9hour run time with little to no cycling as far as i can see at fixed flow@30deg. My point is calculations can only go so far, real house data for each individual is all that matters at the end of the day.
@newhouse87 I'm not sure whether you were responding to my most recent post questioning the current interpretation of the excellent data that @cathoderay has provided, but if so I would comment as below (if not please ignore):
You are correct, but an interpretation of the data which prima facie violates the first law of thermodynamics isn't a valid interpretation, unless we are going to challenge 160 years of very well established and well proven physics.
So whatever measurements may say, the interpretation of/conclusion from those measurements cannot violate the laws of physics, if that interpretation is valid. If the interpretation does violate the laws of physics then either the interpretation or the measurements (or both) are wrong.
I am hoping somebody will point out a fault in the logic of my previous post, because I would be very pleased to have confidence in the interpretation currently proposed. But unless I have made a mistake (which is quite possible) then there is something amiss.
@jamespa Was just general observation really. I wouldn't have the knowledge to question your calculations. All things being considered i know if i kept my heating on all the time my houses would be same level of comfort 24/7 which would be nice, point im making is that for some houses its worth the setback as some houses retain heat very well so may only be 1 degree below desired temp after lengthy setback. Also living habits, if house say is 1/2deg lower in morning while occupants there for 30minutes on way to work and then desired by evening time that suits better and saves considerable energy. I just think telling people run 24/7 universally is not right approach, not saying anybody did that here btw but seems to be consensus opinion universally.
I just think telling people run 24/7 universally is not right approach, not saying anybody did that here btw but seems to be consensus opinion universally
I hope you are right because its obviously more intuitive to turn down when you don't require the heat. However sometimes intuition and fact are at variance! As I said I am hoping somebody will point out a fault in the logic of my previous post, because I would be very pleased to have confidence in the interpretation currently proposed.
My 'working theory', based on the experimental results, with scepticism applied to the interpretation, and the modelling (ditto), it that it probably does make sense to set back when the OAT is moderate (which is most of the time in the South East of England) but quite possibly does not make sense when its low nor for houses which have a thermal mass that is sufficiently high that they 'ride out' daily variations (a situation that likely applies to 'passive' and other well insulated houses with a largish slab). I can't come anywhere close to proving this but the results seem to point to this.
However, for now my focus is on rationalising the thermodynamics in the results posted by @cathoderay (as I set out in this post), in order that we can all have confidence in the interpretation of the experimental numbers we have before us.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
In my limited knowledge opinion, set backs will work for some houses better then others. Last night my heating went off at 9pm. Got to as low as 4deg oat overnight. My living area was still at 20 and kitchen still at 21 at 7am. If i had kept heating on all night i would have used up near 15kwh as lowest per hour usage overnight while im asleep as i have seen is approx 1.5-1.7kwh per hour in middle of evening after heating has been on for good few hours. My heating will come back on 3 today as nobody in house all day and will be nice and warm by 6pm for the evening until it goes off at 9. In colder weather i have turned heating on at midday so a 9hour run time with little to no cycling as far as i can see at fixed flow@30deg. My point is calculations can only go so far, real house data for each individual is all that matters at the end of the day.
You appear to be correct that employing some form of setback will produce better energy savings in some buildings rather than others, which is one of the reasons that I have been developing the modeling tool.
As time has progressed I have been developing the modeling tool to include the effects of as many variables as possible, since it is only by doing so that the tool can mimic what is happening in the real World.
You appear to be in the very fortunate position of having a well insulated home, that also has a large thermal mass, which along with your present lifestyle allows you to achieve larger reductions in electrical energy consumption.
Data if possible should include LWT, RWT, IAT, OAT, setpoints, any setback periods, flowrates if you know them, energy in and energy out, and anything else you think may be useful.
I am not convinced you are going about this the right way. Normally you take a hypothesis (model), use it to make a prediction, and then test that against the real world. Earlier you said your independent variables were the DT between IAT and OAT, the length of the setback period, the thermal capacity (Heat Mass) of the property, and how quickly recovery to desired IAT needs to be made. I think you should be asking for those inputs, rather than the dependent variables, as you do above. For example, let's say I have:
an inside/outside delta t of 10 (this being an average, as it varies over time)
a six hour setback
thermal capacity of building (not property, that includes the garden/shed etc): this is problematic, in that I have no idea what it is, apart from having a hunch that it is 'relatively high', and on this, google is not my friend: I can find plenty of descriptions of what it is, how it works, and even numbers for individual materials, but nothing on values for typical buildings. You will have to use a suitable number, and explain why it is suitable, or, failing that, find a proxy variable of some sort that can be obtained, and use that in the model; and if that isn't possible, then it is back to the drawing board
a three hour recovery
then you should tell me how much energy that particular setback will save (or cost) me, over and above what I would have used anyway.
I have requested as much data as possible to be able to test the accuracy of the modeling tool, which I think will be the most productive way to proceed.
This thread moved on rather quickly after a post I made but I really would appreciate your perspective on my post upthread
So far as I can see something isn't stacking up in the results/interpretation that @cathoderay has posted. I'm hoping I have made a silly error, but I can't see it and, until I do, am not confident in the current interpretation of the experimental data, as it seems to violate the first law of thermodynamics.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
I have some thoughts concerning the data but I would prefer not to comment at the moment, since if I am not 110% correct, anything that I say is likely to be dragged up in 'court' later.
I have some thoughts concerning the data but I would prefer not to comment at the moment, since if I am not 110% correct, anything that I say is likely to be dragged up in 'court' later.
Very prudent.
@jamespa- I'm working on it at the moment, I think I am onto something, but at the moment I am only about 50% sure I have the answer, and I want to get closer to (but not over) 100% before posting it.
Midea 14kW (for now...) ASHP heating both building and DHW
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