Posted by: @hughf

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Please don’t think I’m banging the homely drum again like some sort of fanboy, but it’s precisely this ‘figuring out the weather compensation curve’ that homely aims to do, so that installer aren’t tempted to 1. Guess, and 2. Not enable it at all

To my mind, the problem is that there isn't a constant weather compensation curve for a given building. You need a (slightly) different curve when the building is recovering from an overnight setback, another (slightly) different one when there is solar gain, another when you have a party with lots of human radiators, and so on. How do you detect those events, and use them to alter the flow temp in the right direction to maintain the desired room temp? It seems to me the difference between the actual room temp and desired room temp is the best, and most easily obtained, summary measure of whether the flow temp needs to increase of decrease.

@derek-m - surely the reason for all those oscillations is the system controls have not enough gain and/or too much latency? If AI/machine learning does have a place in all this, isn't it to learn the characteristics of the particular building, ie how much a change in flow temp changes room temp, and how fast this happens, and then adjust flow temps taking that information into account? 

The 64m dollar question is can Homely do this? Not in theory, but in practice.

[@hughf - I see you also posted while i was writing this post, but we are I think pretty much covering the same ground, asking the same questions]

@cathoderay it has an indoor temperature sensor… so it always knows the error between the setpoint and the actual indoor temperature.

Posted by: @hughf

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it has an indoor temperature sensor… so it always knows the error between the setpoint and the actual indoor temperature.

Yes, I get that (and I think maybe we should be calling any corrections based on the difference room compensation, so as to give it similar sounding weight to weather compensation) but that's the theory side of things, my big question is does it work in practice? I'm not after vague Homely makes my Samsung Sing types assertions, but facts (real data, charts etc) showing Homely does what it says on the tin.

I'm also rather surprised (and concerned) that Homely appears to be so opaque. You might imagine a bunch of science PhDs might naturally lean towards open source transparency etc. But then again if primary degrees and careers were in economics/investment banking, maybe a different mind set prevails, and intellectual property etc becomes paramount.

Please don't think I am heading into ad hominem territory, it's just that I am asking what I think are legit questions about where Homely is coming from, and where it might go.    

Posted by: @cathoderay

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I'm also rather surprised (and concerned) that Homely appears to be so opaque. You might imagine a bunch of science PhDs might naturally lean towards open source transparency etc. But then again if primary degrees and careers were in economics/investment banking, maybe a different mind set prevails, and intellectual property etc becomes paramount.

As someone who has had recent close hand experience of a retrofit heat pump installation I can see how brave and urgently needed this type of intelligent controller is. Self teaching after a minimal hand over is not a good way forward for most people. Suffice to say we learned a lot as we grappled with programming our own weather compensation curve. (Incidentally-Why are they called curves when most people draw straight lines?)

Even ignoring the private situation of my home heating needs the national/global need for optimised use of energy couldn’t be in sharper focus than right now. So I guess that’s why most of us are here reading these threads. 

As I see it, this ‘Homely’ program attempts to eliminate human error by learning the bespoke nature of a given installation. It then has to integrate with multiple BUS languages and that’s before it then tries to pick out additional localised effects eg solar gain, thermal mass, tariff privileges and  lifestyle needs etc. All this, I can only imagine means that we - the consumer can enjoy living in comfort and don’t have to give even a second thought about how to optimise our energy use but crucially, we know it’s happening. That’s where I see this kind of controller - serving the mass market of rapid transition to new energy tech. With low user interference and simple top layer controls.

I didn’t think Karolis was being opaque in any way but it clearly is an evolving system in a rapidly shifting energy market. He appears to be incorporating educational fields within the system to help inform domestic users on how their heat pump works. 

I think I’m prepared to cut Homely some slack as their system evolves further and keep watching.

Posted by: @sunandair

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I think I’m prepared to cut Homely some slack as their system evolves further and keep watching.

I'm just as open-minded (I started the thread, and note I put Homely in the title as a possible solution) but I am also minded to ask questions because it is the current nature of the heat pump industry to be less than forthcoming about the real world as opposed to nominal claims. The industry has only itself to blame for this situation. The high frequency of installations that fail to live up to expectations is another reason to question things.

In principle, a smart efficient control system that works, with simple top level controls is almost the ideal: it works, and anyone can understand and use it. The only reason it isn't 100% ideal is that it (the system) is opaque, and there will always be a small but not trivial percentage of people - 5%, maybe 10% - who want to go beyond the simple top level controls, be it out of curiosity or because they want to tweak some feature. There is also the question of data ownership. As householder end users of these systems, it is not at all unreasonable to say we should have access to detailed data, if we want it (not all will). All, however, should know what their energy in/energy out/COP is. Only the reckless or those with too much money to burn don't know the mpg of their car, the same should apply to heat pumps.

I've said it before and I'll say it again for good measure: the piece of the Homely jigsaw that is missing is the real world experience/data/feedback from everyday households on how it works in practice. So far, the only evidence to come to light along these lines in this thread (n=1) has been negative. But like you, I shall keep watching. I actually want Homely to work, not fail!

I should perhaps add that one of the reasons I want Homely to work is to gain the ability to recover from overnight setbacks. Last night, running a 24/7 steady state system with no set back, I burnt 12kWh of energy keeping the house in a steady state. If I had a small setback, I would save some if not all of those overnight kWhs, but at the moment, my system, using a fixed weather comp curve, takes not hours but days to recover. Yes i could manually tweak the LWT everyy morning, but all very tedious. It would be wonderful if Homely could do that automatically.

Yes, I know there is the steady state vs up and down total energy consumption debate, but what better way to answer that than by doing it in the real world, and seeing what actually happens over a sufficiently long time to get a meaningful answer.   

Posted by: @cathoderay

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Last night, running a 24/7 steady state system with no set back, I burnt 12kWh of energy keeping the house in a steady state. If I had a small setback, I would save some if not all of those overnight kWhs, but at the moment, my system, using a fixed weather comp curve, takes not hours but days to recover. Yes i could manually tweak the LWT everyy morning, but all very tedious. It would be wonderful if Homely could do that automatically

Yes, at the moment, I switch off every night at 9.30 for that same reason (£/kWh) but in the morning our house is only 18.5C and within 1 hour of the HP activity we are up to  20C in the coldest room. (4 bed old house using 8.5 ecodan running @ 34PFlow current ambient of 9). 

I struggle with the concept of steady state continuous heating when we are up to temp in one hour the next morning. Isn’t the priority to eliminate unnecessary energy/carbon?

if the off time was added to our COP where would our SCOP be at then?

I struggle with the concept of steady state continuous heating when we are up to temp in one hour the next morning. Isn’t the priority to eliminate unnecessary energy/carbon?

Chucking a YES here, I think the "run it all the time" folk may (may not) be missing the wood for the trees on this 

Posted by: @hughf

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@derek-m the same oscillation would occur if the weather comp didn’t match the property, and the system was running on an on/off stat.

Please don’t think I’m banging the homely drum again like some sort of fanboy, but it’s precisely this ‘figuring out the weather compensation curve’ that homely aims to do, so that installer aren’t tempted to 1. Guess, and 2. Not enable it at all

There’s a perfectly good reason (in my mind at least) why the heavy lifting (the flow temperature requirements for a given property, efficient recovery from a setback period etc) are done on AWS, and that’s to remove any requirement for field firmware upgrades when evergreen want to roll out new features or fix bugs. 

Hi Hugh,

I'm not against Homely, but I'm also not a fan of such systems, unless they provide actual benefit to the homeowner. As Heat Geek stated during the video, from the point of view of assessing the weather compensation curve, Homely may do what he does through knowledge and experience. The spreadsheets that I produced previously for Ecodan and Midea user's could be used to assess the initial starting values for the weather compensation curve, and if the heat pump controller provided auto adaptation or something similar, then the setting of the weather compensation would not be that critical.

I would need to see feedback from long term Homely users, about the benefits and cost savings, to be convinced to recommend such a system.

My posts are aimed at educating not only homeowners, but also any installers who may hopefully be on the forum, that providing a home heating system that works in an efficient and cost effective manner is not impossible. It is a matter of understanding how the various pieces of equipment function and interact with each other, the layout of the home and any restrictions that may pose, and having at least a basic understanding of control systems and how to configure and commissioned such systems.

Posted by: @ecodannewcastle

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I struggle with the concept of steady state continuous heating when we are up to temp in one hour the next morning. Isn’t the priority to eliminate unnecessary energy/carbon?

Chucking a YES here, I think the "run it all the time" folk may (may not) be missing the wood for the trees on this 

This is a date stamp post…

Following our recent discussion this morning and probably by coincidence.. A new post has just arrived on YouTube, a few hours ago from Heat Geek. No surprises there then….

But the discussion was between Adam and the Daikon representative Rob Stiby. The conversation drifted on to the popular topic of Continuous Overnight Heating with Heat Pumps (see 27th minute onwards)

The discussion plays out that Rob Stiby wants to know more factual information about overnight set backs and what limitations are there on this approach to space heating. Adam replies “well for sure I’d rather have 2 hours of cop2 that 24hours of cop5”.

I see this as a significant shift in the interpretation or, dare I say it… the panacea of 24 hour heating. 😉 

Perhaps the second panacea to come under review is that of “Thermal Mass”. Because it’s an incomplete theory (there are different forms of thermal mass within the home, some useful and some detrimental to optimal space heating.)

I hope you find this interesting and relevant to the topics under discussion.

you tube link below

https://youtu.be/9ggvh02trBY  

Posted by: @sunandair

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Adam replies “well for sure I’d rather have 2 hours of cop2 that 24hours of cop5”.

I suspect getting your head round this quote is crucial to this debate, though the intervals are probably better thought of as 2 hours of COP2 vs 8 hours of cop5, ie the overnight period from 2200 to 0600. Lets also make it a more likely 8 hours of COP 3.5 (which is about where I am at the moment) and see how it plays out.

Scenario 1: 24/7 always on heating:

Last night, my house needed 2kWh input per hour to keep it in a steady state at design temps. LWT was around 45 degrees. These are real figures. At COP3.5, that is a total of 8 x 2 = 16 kWh input, 16 x 3.5 = 56 kWh output over the 8 hour period (= 7 kWh output per hour).

Scenario 2: six hour setback to 16 degrees 2200 to 0400, superboost 0400 to 0600:

Setback period (2200-0400): 0 kWh in, 0 kWh out (the house cools slowly, at the end of the setback the house is 2 degrees below design temps, not quite low enough to cause the setback stat to call for heat. The rest period may or may not extend the life of the heat pump. If the mean time before failure is xx,xxx hours of running time, then the rest will significantly increase the life of the heat pump.

Superboost period (0400-0600):

I need to make an assumption here, as I don't have the relevant calcs to hand. Lets assume the building needs twice the amount of energy per hour for two hours to get it back to design temps as it does to maintain it at design temps. Steady state needed 7 kWh per hour (see above) so recovering from the set back needs 14 kWh per hour. This can only be achieved by rasing the LWT to 60 degrees (I know, I am just trying to make a point), and the COP falls to 2. To get 14kWh per hour at a COP of 2, I need an input of 7 kWh per hour, or 14kWh over the 2 hour period.

Summary (for this scenario, over the 8 hour period):

Steady state uses 16 kWh, setback plus superboost uses 14 kWh.

Setback plus superboost wins. There may be other benefits eg extended heat pump life. A 2 degree setback while asleep is minimal, condensation etc not likely to be a problem.

Of course this is all crucially dependent on how big the boost needs to be. I guestimated it to be twice the steady state demand. Obviously, if less was needed, the savings would greater, if more was needed, steady state might overtake SB2 (abbreviation in the spirit of tw3). We could either calculate a more accurate figure, or alternatively (and much better) just run the frigging thing, and see what happens. Unfortunately that is not possible on a Midea timer, and I am absolutely not getting up at 0400 and 0600 to adjust the LWT.

Any and all comments welcome, including if necessary this is all a load of cock and bull.   

I have just done my weekly data update, a very tedious manual transfer of data from the Midea app into a spreadsheet, and the updated charts look like this (time period is last six weeks or so, and includes the cold spell in December, intervals are daily). First up: heating (only, DHW not included) energy in vs heating energy out, and then calculated COP for both heating and DHW: 

 No real surprises here. The DHW COP is rather suspect in places.

And now, ambient vs set LWT (this should be the weather comp curve) and ambient vs actual LWT (should also be the weather comp curve):

The weather comp seems rather approximate at best, though this may be an artefact of the way Midea records the data. Bottom line is it appears, at least in this data, that both the set and actual LWT temp can vary a lot for a given ambient.

Finally, set vs actual LWT:

This sort of confirms an implication from the previous two graphs, the actual LWT only sort of follows the set LWT. 

These charts are examples of the sort of charts that a monitoring system should be able to produce, both automatically, and for different (and smaller eg hourly) time intervals. I need to get a modbus hat for my raspberry pi...