@jamespa Again, I’m going to have to read this carefully to take it on board. But I absolutely agree about the piping and the radiators. As I said in the post about my experience I think BG did a good job on the piping, I have I think 28, 22 and 15, which I believe is best practice. All was new. Plus the radiators, or emitters, which is a truer title I think although generic. I never understand how people are putting in heat pumps whilst retaining old radiators and expecting it to work. Briefly though, if in practice my delta t is running about 5 av, and my flow rate is 7L/m always, except when restarting or doing DHW, then surely I already have that impact. But it does raise the question of why they recommend 10 for radiators. It’s said somewhere that it reduces wear on the compressor et al, but that doesn’t really make sense because that would surely be the case too regardless of emitter type and yet they recommend 5 for fancoil and UFH, or at least variable settings. 

In fact this is the perfect opportunity for me to ask two questions that relate to the level of the LWT. Firstly a number of people are saying that this Daikin model ( others too possibly) does not like going to its lower limit of 25 , really gets inefficient  and can cause problems really its lowest limit is much higher, which kind of creates a problem as it gets warmer. I also note that for some reason which I don’t understand for a while now it spends quite a bit of time above the expected target for the WDC at the given temp, this morning for example it’s sitting 1.25 degrees above where it should be. What’s it doing? And to fill in the data points, outside temp is 13c, delta T is 5 and flow rate is 7.

@terry1812 Octopus carried out a very thorough survey with an electrician and a plumber both here for three hours; they measured just about everything from wall thickness to water pressure, window sizes, room dimensions, gaps under internal doors … you name it they measured and took pictures of it too! As, in the end, they were not able to carry out the install as it fell outside their ‘scope’ at the time, I never received any formal offer or paperwork. I was given the heat loss figure of 6.5 kWh verbally. The company who did carry out the installation based their heat loss on the EPC figures carried out earlier that year. The installers based their design on 7.67 kWh. I don’t know for what OAT as neither stated that. I think the Octopus survey was the closer as even in the coldest winter weather, we have not seen the 8Kw heat pump run non-stop, and that is when we are demanding a comfort level of 22.5 degrees. The installers were of course basing their calculations on the flow temperature of 50 degrees C. In their contract details, they state that the heat loss calculation is (according to MCS guidelines) subject to many variables including amount of ventilation and may be up to +20% and - 30%! Anyway, it has worked out well for us and the actual reported COP is somewhat higher than the predicted figure. Regards, Toodles.

@terry1812 Had we gone with OE, we would have done so. Their ‘scope of installations’ did not extend to the peculiarities of our needs at that time though I believe they have widened out their installation capabilities since then. At that time, they had a very narrow and rigid range of designs and capabilities. Regards, Toodles.

@toodles , yes you’re right, there are a lot of variables and all of the figures can be plus or minus. I guess both of your heat loss figures would have popped you into the 8kw choice anyway.

Posted by: @terry1812

↑

@jamespa Again, I’m going to have to read this carefully to take it on board. But I absolutely agree about the piping and the radiators. As I said in the post about my experience I think BG did a good job on the piping, I have I think 28, 22 and 15, which I believe is best practice. All was new. Plus the radiators, or emitters, which is a truer title I think although generic. I never understand how people are putting in heat pumps whilst retaining old radiators and expecting it to work. Briefly though, if in practice my delta t is running about 5 av, and my flow rate is 7L/m always, except when restarting or doing DHW, then surely I already have that impact. But it does raise the question of why they recommend 10 for radiators. It’s said somewhere that it reduces wear on the compressor et al, but that doesn’t really make sense because that would surely be the case too regardless of emitter type and yet they recommend 5 for fancoil and UFH, or at least variable settings. 

In fact this is the perfect opportunity for me to ask two questions that relate to the level of the LWT. Firstly a number of people are saying that this Daikin model ( others too possibly) does not like going to its lower limit of 25 , really gets inefficient  and can cause problems really its lowest limit is much higher, which kind of creates a problem as it gets warmer. I also note that for some reason which I don’t understand for a while now it spends quite a bit of time above the expected target for the WDC at the given temp, this morning for example it’s sitting 1.25 degrees above where it should be. What’s it doing? And to fill in the data points, outside temp is 13c, delta T is 5 and flow rate is 7.

I will answer in a different order in the hope of shedding some light.  Before I do though I would make the general remark that, in order to analyse these things, it helps, I find, to think of four separate actors in the system, namely the heat pump, the emitters, the house and the owner.  If you disturb an otherwise stable situation they all respond until a new stable situation is reached.  You may have to go round the loop a couple of times before you work out what that is.  I will illustrate that in one of my later answers.

Posted by: @terry1812

↑

I also note that for some reason which I don’t understand for a while now it spends quite a bit of time above the expected target for the WDC at the given temp, this morning for example it’s sitting 1.25 degrees above where it should be. What’s it doing?

At 13C OAT its unlikely that it can modulate its output down sufficiently to operate 'steady state'.  So it will likely be dumping more power into the water than the radiators lose to the house/the house is losing to the outside.  This normally results in cycling, where the heat pump starts up, the flow temperature rises and overshoots, then eventually the flow temperature reaches the point at which the heat pump shuts itself down for a while. 

There is, in principle, a point on the threshold of cycling where it settles at a slightly higher FT than the target, but within the permitted deviation (the flow temperature hysteresis).  Because the flow temperature is higher than the target the radiators will emit a bit more and this might be enough to bring the required power back within the modulation range.  Of course as a result of the radiators emitting more the house will get slightly warmer.

Posted by: @terry1812

↑

In fact this is the perfect opportunity for me to ask two questions that relate to the level of the LWT. Firstly a number of people are saying that this Daikin model ( others too possibly) does not like going to its lower limit of 25 , really gets inefficient  and can cause problems really its lowest limit is much higher, which kind of creates a problem as it gets warmer.

I doubt that there is anything magic about 25C or about Daikin.  All heat pumps will eventually get to the point where the energy demand is so low that it has to cycle with a long off time.  At this point it is indeed inefficient relative to the 'perfect' pump, but you will still be getting a higher COP than at lower temperatures and the amount of energy you need is anyway small so some loss of efficiency doesn't matter.  At these temperatures (typically when its a fairly stable 13-16C OAT) it can become more efficient to heat part time, if your house has sufficient heat capacity and it suits your lifestyle.

Posted by: @terry1812

↑

But it does raise the question of why they recommend 10 for radiators.

Obviously I dont know what was in Daikin's mind but I would surmise that they felt this would reduce the frequency with which pipe upgrades were necessary, having regard to the retrofit market.  Radiator based systems tend to have been designed for high flow temperature and high deltaT, thew switch to a heat pump changes it to low flow temperature and low deltaT.  The radiators may need upgrading because of the lower FT.  Changing radiators, whilst a bit of a pain, if really not difficult.  To operate at a lower deltaT requires more water passing through the system which may require pipework upgrades.  These are much more distuptive.  UFH is normally designed for low FT/deltaT.  Its difficult to comment on fancoils, they arent common (yet) in the UK so there isnt an established practice afaik.  

The truth is (with any heat pump) that one should operate at the lowest deltaT practical to get maximum efficiency.  This is because higher deltaT means lower average emitter temperature for any given LWT, and so the LWT has to be higher for any given emitter output, reducing COP.  Conventionally we design for ~5 with heat pumps, its a reasonable compromise.  There is nothing wrong with designing for 10C or anywhere in between and, if it made the difference between having to rip out all the pipework and not having to do so, this may be a good design trade off (in many cases a better design trade off would be to put in a bigger water pump!)

OK so lets now return to the effect of reducing the target deltaT.  Remember the four actors in the system.  Now lets suppose we start with a system perfectly in equilibrium.  The heat pump is supplying water at some LWT and at some flow rate which means that the radiators are losing just the same amount of energy as the house is losing to the outside world.  That amount of energy lost causes the water flowing through the radiators to reduce in temperature by 10C as it passes through.  Because the radiators are emitting the same amount of energy as the house is losing, the house stays at the same temperature.  To complete the equilibrium this temperature is the temperature you want it at.  All four actors are satisfied.

Now I reduce the target deltaT on the heat pump.  The heat pump will (we presume - because thats what the 'second' control loop is designed to do) respond by increasing the flow rate to achieve the new target deltaT.  The radiators will lose more heat because their average temperature is higher.  Eventually the heat pump/radiator combination will settle at a flow rate that causes the deltaT to be the new target value with the increased energy emitted by the radiators.  This will also cause the heat pump to dump more energy into the water so that it balances the increased energy lost by the radiators.

However the story doesnt end there.  Because the radiators are emitting more energy the house will get hotter, until its temperature is raised to the point where the energy emitted by the house matches the energy emitted by the radiators.  Of course as the house gets hotter the latter will reduce, because the temp difference between the radiators and room reduces.  Eventually this will also settle, and cause small adjustments to the operating points of the heat pump and eventually it will all settle.

However the house is now hotter than you want it to be so now the fourth actor intervenes.  He or she reduces the FT (by turning down the WC curve) until the house is again at the correct temperature (which will occur when the average temperature of the emitter is what it was previously).  The various loops all readjust but eventually we reach a new equilibrium where everyone is satisfied, at a higher flow rate, lower deltaT, the same average emitter temperatur, loss from the radiators and output from the heat pump as those that we started with, equalling the same loss from the house.

The overall result is that we reduce the flow temperature by about half of the reduction in deltaT.  Because reduced flow temperature = higher COP and the energy output from the heat pump hasnt changed, you will consume less electricity.

I hope that helps

Posted by: @terry1812

↑

. Briefly though, if in practice my delta t is running about 5 av, and my flow rate is 7L/m always, except when restarting or doing DHW, then surely I already have that impact.

If in practice your deltaT is 5 when its in a quasi steady state (ie cruising), then the pump speed control loop isn't really doing the job it seems to claim to do.  Perhaps, in fact, it interprets the target flexibly knowing that the optimum will always be lower deltaT subject to the pipe velocities not being too high (which it can sort of infer from the back pressure).  This would be something 'decided' in firmware, and of course manual and firmware may not always reflect each other perfectly.  The only way to find out is to try it by changing the target deltaT and see what happens!

@jamespa Thanks for that. I think from what you have said that we seem to disagree, if we disagree at all, about the way the system responds in relation to Heatpump output. Your experience tells you that when running a pump in pure weather comp mode using a WDC as the only tool somehow the flow rate will increase to maintain maximum output. My original query, maybe badly expressed was how does it does this, because I can’t see that it does. I see it having the 3 priorities we discussed previously, and in priority order, get to Target LWT, get to target Delta T , and get to Target flow temp. Once it has satisfied these, why would it subsequently increase flow rate? 

Secondly I do understand that a lower delta T effectively increases radiator capacity, but it drastically reduces ASHP heat output. Such that increasing the capacity of the radiators, unless they were way too small isn’t helpful. I,ve attached a print of my spreadsheet model. The radiator info is based on my radiators, the heat output based on the altherma 3 8kw, manufacturers specified heat outputs. I have assumed the heat output can’t exceed maximum. But that situation wouldn’t arise for long anyway. 

One can see ( assuming I haven’t got some basic logic errors built in) that at a 45c flow temp with a delta T of 10, a flow rate of 11l/m is need per to get max output. But as soon as priority 3 has been attained , the flow rate of 7, brings output down to 4.88kw. A huge drop. If at this point one had a Delta T target of 5, then the output drops to a catastrophic 2.44kw. This is the crux of my issue. What is going to tell the heat pump you want more heat? It has met its priorities, it is doing what has been asked of it. It has no idea what temp I want because that is not a parameter. Nothing I can see is going to persuade it to up its flow rate. 

For this model I have also used the design spec figures of -2c and 21c. I have modelled , as you will see, various tweaks to see the impact.

And in answer to your point about changing Target Delta T ( aside from that it might breach my warranty) as it’s already at that level I can see that the flow rate seems largely invariable. Actually I did catch it going a little bit lower, for a nano second, I just happened to be taking a photo of the  sensor page, wouldn’t have captured it otherwise. 

So back to the nitty gritty , I feel you know the answer to this, what is going to tell the Ashp to up its flow rate when it has met all its targets and is happy? Is there another priority somewhere that says “but ensure you are delivering max output.”?

I really appreciate your help I just want to get to the bottom of this.

Posted by: @terry1812

↑

. I see it having the 3 priorities we discussed previously, and in priority order, get to Target LWT, get to target Delta T , and get to Target flow temp. Once it has satisfied these, why would it subsequently increase flow rate? 

That's actually two priorities, lwt and flow temperature are the same thing.

Posted by: @terry1812

↑

So back to the nitty gritty , I feel you know the answer to this, what is going to tell the Ashp to up its flow rate when it has met all its targets and is happy? Is there another priority somewhere that says “but ensure you are delivering max output.”?

If the radiators demand more heat, the only way it can maintain ft is to supply more heat to the water.  So it will do so because maintaining ft is it's priority.  It knows that, to carry the heat away, it needs a certain flow rate (it can do the mass flow calculations in your spreadsheet too!) so it could calculate the flow rate and adjust accordingly.  Alternatively it could monitor some internal temperature,  which will initially rise because more heat is being supplied, and adjust flow rate accordingly.  There are probably other mechanisms I haven't thought of, including monitoring return temperature and thus delta t of course (this might require a bit of thought to avoid a destructive circular feedback loop between the two control systems, but ultimately there is only one equilibrium condition that satisfies all requirements, so it must be possible). 

I don't know which it uses, or indeed why it bothers adjusting flow rate at all rather than leaving it it's maximum and allowing deltat to fluctuate.  However it is clear that, unless it operates insanely and treats the wc curve as secondary to deltat/ flow rate, it must use one of the mechanisms I have suggested (or another I haven't thought of) to compensate for the fact that it is forced to put in more heat to maintain the ft and to take heat heat away and conduct it to the radiators to avoid it boiling itself.

I'm grant that I am assuming that the heat pump strives principally  to maintain ft.  If it doesn't then my argument fails.  However in this case the weather compensation curve becomes meaningless.

@jamespa The third priority was a type, it was meant to be flow speed. Which was the whole point I was making. Also I notice you refer to radiators calling for heat. Surely radiators are simply passive recipients of whatever heat gets sent their way?

With my vast experience of 1 heat pump it seems that getting to Target LWT is the easiest thing for heat pumps to do. 

We are both guessing now it seems. That’s why I had hoped that Daikin would answer my query. Although thanks to you and others I am much clearer in my question and it is a practical question, because knowing the answer to it, I believe, will enable me to potentially tune the hp. I still don’t see setting the Delta T Target to 5c as benefificial. Mind you the system does it anyway, regardless of what Daikin is saying in their manual. The only thing fixed about the 10 is that it’s a max but not a minimum too.

Posted by: @terry1812

↑

Surely radiators are simply passive recipients of whatever heat gets sent their way?

Not really, and thinking of them this way can mislead.  Its also misleading to think of the heat pump sending a fixed amount of heat.  It sends hot water, and the radiator is in principle 'free' to extract all the energy in that water until the hot water reaches room temperature.  Thats way more than the flow rate * deltaT calculation.

A better way to think of it is that radiators will emit an amount of heat determined by their average temperature (which principally is determined by the flow temperature), not more , not less.  This will determine how much the water temperature falls as it passes through.  Essentially its the radiators (and ultimately the house) that are in control here, not the heat pump.  Equilibrium will only occur when the system adjusts so the heat pump is sending out exactly the amount of heat the radiators emit.

For any given flow speed/flow temperature combination there is exactly 1 equilibrium condition, which will eventually be reached.  If the heat pump has done what it appears to say on the tin then this will be when the heat pump is measuring a deltaT equal to whatever its target is (if it has a target) and a flow temperature equal to whatever its target is (if it has a target).  Until then it will keep adjusting the things it can adjust (namely flow rate and amount of heat dumped into the water).  If these are outside its operating parameters then a different equilibrium condition will be reached, with either FT or DT or both not 'on target' 

Posted by: @terry1812

↑

The third priority was a type, it was meant to be flow speed.

Ah, sorry.  Actually to be precise the heat pump cant directly control deltaT, that is controlled by the radiators.  The only things it can control are LWT and flow speed so really there are only two variables. 

Posted by: @terry1812

↑

With my vast experience of 1 heat pump it seems that getting to Target LWT is the easiest thing for heat pumps to do. 

My experience is of one heat pump also, plus a couple of years on this forum and a bit of a general appreciation of control theory.

Im not sure controlling LWT is easy, but at least it is in direct control of it.

Its not in direct control of deltaT but, thinking about the matter overnight, it could control water pump speed in proportion to the heat it dumps into the water, which would have the effect of keeping deltaT approximately constant and ensuring that the heat it generates is taken away.  This would be a simple and effective way to maintain DeltaT if that were its objective!

Posted by: @terry1812

↑

We are both guessing now it seems.

To an extent yes

We know pretty much for certain what its internal control objective is as regards FT, and can surmise how it gets there knowing what it is aiming to do and the system constraints. We dont know exactly how it gets there (ie its control algorithm), but in most cases it doesn't matter.

We are certainly guessing what its internal control objective is as regards deltaT.   It may be to achieve the 'target' according to the set emitter type, it may be something else.  We dont know.  We certainly don't know its control algorithm.  We do know it cant control deltaT directly, but we also know it has a lever which it can pull -namely the flow speed.

I would say thats a good start with the sole exception of not knowing the internal control objective as regards deltaT.  Obviously in this case that matters.  

'

Posted by: @terry1812

↑

I still don’t see setting the Delta T Target to 5c as beneficial.

If, in practice, doing this doesn't increase the pump speed and reduce the actual deltaT, then there is no benefit. 

I apologise that I assumed that your heat pump did what it appeared to say on the tin.  From what you now say it doesnt, and of course that changes the conclusions.  This means that we dont know (or at least I dont know) what effect changing the 'emitter type' setting will have on water pump speed and thus on deltaT.

This being the case it remains a mystery (at least to me) what meaning the deltaT targets have for this particular heat pump and why it bothers with them anyway!

What I do know however is that, if I had a heat pump that was in fact operating at a deltaT of 10 when 'cruising', I would be interested in easy ways to reduce this figure (if there were any) in order to save perhaps 6-8% on operating costs.  If that just involved increasing a water pump speed I would definitely try it.  However I don't, and from what you say you don't, so the question doesn't arise!

Daikin isnt unique in having obscure settings that only give a vague description of what they actually do, there are a few on my Vaillant that are equally obscure.  And it seems like tech support people dont always know precisely either.  Eventually someone usually works it out (usually by experiment) and posts an explanation!

I hope that helps and apologise if it doesnt!

Hello, I am fairly, OK very, new to this forum, but here goes.  In late 2023 we signed with a company called Evergreen Energy for an ASHP and, if I am honest, wish we hadn't.  "Why?" you may ask.  part of the deal was having to use their partner control system called 'Homely', which feels anything but.  It ('Homely') is only available on an app and comes with a thermostat the size of a postage stamp.  Let me outline what we have; a Midea R32, a tank that is branded 'Tempest Heat Pump', 14 solar panels (3.9kw), a SMART meter and Tesla Powerwall 2 (10kw).  Our house is a chalet style built in the 1950s and most of the radiators are fed (unfortunately) by 10mm pipework - I know that is innefficient. But we are continually having to 'boost' the heating.

So My questions are:

Is there a company nearby (in Cheshire) who might provide servicing and advice

Is it possible (I have been told it is) to have a controller that can be used on Mac as well as phones et al?  

Posted by: @unclehefty

↑

Is there a company nearby (in Cheshire) who might provide servicing and advice

I might be able to connect you with a few reputable installers in the Cheshire area. I will reach out to a few today and see if this is in their remit, and if they are, I'll connect you via the email address you used to register on the forums.

@editor Thank you, it would be appreciated.