JamesPa

I agree entirely, this device seems like a game changer for getting WC right. Its function should be built into every HP controller and installers forced by law to use it. That just leaves balancing. Balancing the traditional way by matching deltaTs might be a good enough approximation, provided emitters are correctly sized (does balancing present any challenges for installations done in the summer?)

In principle I agree with you. But people are profoundly lazy and uneducated about this stuff, and our government is profoundly stupid (all as you have yourself intimated). So in the real world things have to be made extremely simple and also deliver the necessary result (a house that is warm without tweaking) otherwise they will be clobbered as you say. It's not ideal but systems have to be designed for the majority not for those on this forum. Calculating anything is probably more than we can realistically expect, taking into account individual usage patterns etc is well beyond reasonable expectations in the real world. I think your system setup is likely correct, the question is how installers can tune it without any instructions that are too complex in whatever small number of hours (minutes?) they allocate and more or less guarantee no callbacks. Today it's too easy to do mode 1, quick, familiar and warm house guaranteed

There is a severe danger that the perfect gets in the way of the good, to the advantage of the bad. If doing it perfectly is too complex most will default to mode 1. I wonder if anyone has done some calculations to work out where an easy compromise lies (and what penalty is paid for the compromise) something that's easy and good, if not perfect. Something like the Lizzie curve plus balancing the emitters for consistent delta T (which is easier than balancing for room temperature) maybe. I wonder what the Germans do, they have had weather compensation on their boilers for decades.

This excellent summary made me think about the motivations of both installers and customers, and what is needed to change behaviours so that are least most pumps are installed at worst in mode 2. The underlying problem is that mode 1 is quick, thus cheap, and more or less guarantees a warm house. Modes 2 and 3 take progressively more time to set up, more probably than most will pay for, and don't guarantee a warm house unless done well and then tweaked. But an installer needs to set up quickly and leave, not come back when the ambient temperature has changed so (s)he can adjust the slope correctly or wait around while things stabilise etc, and most homeowners don't want to fiddle with the plumbing. So perhaps the question is (given that the motivations are unlikely to change) what technology, information or practical rules of thumb are needed (and can it be made cheaply) to make modes 2 and 3 no more difficult and expensive to set up than mode 1, and just as reliable. Discuss!

Well doesn't that comment, to the best of my knowledge accurate, say something deep about how the profit motive (or laziness or ignorance) can lead us to dumb down things to the point where the point is negated. I doubt many install an ASHP because its the cheapest or most convenient option, the point is that its eco friendly (whilst possibly being no less convenient and no more expensive). Clobbering the efficiency thus clobbers the point. If your analysis is correct this is clearly immoral, and should be illegal under trading standards rules. Profoundly sad! Of course the knowledgeable will simply ignore the instructions and do the right thing. it would be interesting to know whether that's a majority.

its worth watching the heetgeek videos on 'balancing'. Basically adjusting the flow through the radiators so that, with the TRVs set to max (or the head removed) so they never close down, your rooms heat to the same temperature (or alternatively so that the temperature drop across each radiator is the roughly same - much easier but arguably less accurate). Its not exact, but making some effort at balancing is a good idea. You do this using the lockshields or, if you have TRVs - eg Drayton, with the ability also to apply a fixed restriction - the restriction adjustment on the TRVs. The manufacturer data on the radiators tells you how much water is in them (sometimes for each radiator, sometimes per metre). If they are all the same height and type (11, 20, 21, 22 etc) then you can just add the lengths together to get the total. No need to do it exactly, +/-20% gets you in the right ballpark. Then you add something for the pipework the volume of which is calculable using pi r squared times length (which you can estimate). I had nightmares about fluid dynamics at uni, so I cant comment 'from first principles'. maybe there are plumbers on this forum who can, My understanding is that bends basically add resistance which means your pump will need to work a bit harder. Thats unlikely to be significant unless there are lots more bends in the route to one radiator than others. Balancing sorts this unless its an extreme problem. Very possibly, but just watching (and recording) the behaviour in various periods of different stable outside temperatures might suffice. Of course sophisticated monitoring would be nice. It should definitely improve things. Whether its enough to get the system up to expectations is another matter (quite probably not), but best first to eliminate the obvious shortcomings before exploring the obscure.

OK several thoughts: The difference between calculated demand and measured could be real or not. If its real then the most likely explanation is pessimistic assumptions about air changes or building materials, or just that you have the house colder than the design 21C. All the calculations for my house says it needs about 11kW continuously to keep it warm when the external weather temps is -2, actually the measured value during the cold spell earlier in the season was 7kW. I am pretty certain that's due to a combo of lower than assumed air changes and slightly better than assumed fabric, plis we aim for 20 not 21C. But it could be that your measured output is underreported by the Ecodan. Difficult to tell unless you have an independent way of determining the actual load. Assuming that the measurement of delivered heat is correct, the efficiency does seem poor. I would suggest that as a starting point you get weather compensation going. As it is currently operating it must either be cycling a lot (other than at the coldest design temp) or the TRVs or the main thermostat must be shutting down to compensate for hotter than required flow temp. Weather compensation has been mandatory in Germany for decades (and Im talking gas boilers which don't benefit anything like as much from WC as do ASHPs), but of course our government deems the British (or British installers) too stupid, lazy or ill-educated to cope, or is too influenced by developers protestations about the extra cost (a few £100). Fundamentally (in the physics) the efficiency of an ASHP is linked irrevocably to the difference between the source air and the flow temp, so keeping this as low as possible at all ambient temperatures is rule no 1 for efficiency. Ideally the ashp should be running and heating the circulating water continuously with all the zone valves/TRVs (if any) open whatever the ambient temperature, delivering water continuously to the radiators at a temperature just sufficient to get the room to the temperature you want. Neither the TRVs nor the thermostat should be doing anything at all, other than to limit the heating if there are exceptional conditions eg high solar gain. Then, as others have pointed out, you need to consider (short) cycling (ie cycling on and off with a short on perios eg <10mins) because of the limited modulation depth of the machine (ie the extent to which it can turn down when the the heat demand is low). You cant avoid cycling when the heat demand is lower than the minimum output of which it is capable (guess - around 2kW, its somewhere in the spec), but its better if the cycles are long. That is achieved principally with sufficient thermal mass, ie volume of water in the system (radiators plus pipework). Do you happen to have an estimate of your system volume. If you have only small radiators it could be quite low and its possible that you would benefit from additional volume from a volumiser/buffer tank, but I wouldn't personally conclude that until you have eliminated other causes. One other thing you might do by way of diagnostic is to look at the figures during moderately stable periods of low, medium and high ambient temperature. That might give you an idea of whether the problem lies in a particular part of the temperature range. Unfortunately we dont often have stable temperatures for an extended period (although we did back in December have a stable period of very low temperatures followed by a stable period of unseasonably high temperatures - perfect for testing Central heating systems) I don't know if that makes sense or helps. Keeping the message simple - get weather compensation going and see if it helps, get an estimate of your system volume to see if short cycling is likely to be a problem.

... Further to the above it would also help to know how its controlled eg is everything just left to the ecodan controller or is there also one or more roomstats/TRVs and if so are they actively controlling the system most of the time or set above the desired temp as 'iimiters' . Given this information and the information above it might be possible to work out whats going on

In fairness this thread has gone down a bit of a rabbit hole about the summer consumption, which is a minor part of the story. Having established that its as per spec, about 25 W, and yes you can turn it off, and furthermore, given you have solar PV, your DHW is heated nicely by your solar diverter in summer and most probably autumn and spring also (so heating it from the ASHP in winter would be nice, but not essential(, perhaps its time to think about the bigger picture ie 1560kWh per year. You say that the house is 37W/sqm, how big is it/whats the estimated annual heating requirement, what flow temp is it running at and has weather compensation been properly adjusted?

Fair comment. I might try running the stats based on PVGIS when I have some spare time, unless someone else already has the spreadsheet!

Im interested in your thoughts/findings on this one. Solar diverters rely on modulating the immersion element down to match the instantaneously available excess solar power. With a resistive heating element that easy to do, not so with an ASHP. I cant quite see how to use an ASHP efficiently to mop up excess PV generation with currently available technology. Of course if export and import charges were more closely matched, then all would be sorted. Simply turn on the ASHP to heat the water, and whatever energy deficit/surplus you have gets netted off and the energy would be used as efficiently as possible (and therefore global warming minimised). Sadly that would require that energy suppliers pay nearly the same for export as they charge for import, and there is no business or regulatory incentive to do that. Obviously this logic applies only in the sunny months, in winter (other than on very bright days) solar is most likely to be inbsufficient to heat the water and in that case ASHP surely makes sense.

I admire you for turning off a 9W load, most, sadly, wouldnt. Unless the ashp is heating the dhw then it can be turned off. It might need a few hours to start up again (but probably won't).

Fair enough if you have gone to strong efforts to reduce your baseload. Your router, computer and other sundry items will consume 10-30W doing nothing. Your fridge probably averages a lot more, freezer ditto. But if 25W concerns you (which it should, every little helps the planet) then just turn it off! I'm not saying that 25W should be ignored, just that for most it will be a small proportion of the baseload so perhaps not the most important thing to worry about.

20kWh per month is only 27W. That's almost nothing (and consistent with the spec). I bet your baseload is 10 times this.

EWI = external wall Insulation I presume. If so then that makes sense, if the house is very well insulated then you don't need much heat input so the radiators aren't so big. It sounds like you may have happened across a pragmatic and thoughtful installer who doesn't insist on putting in every component under the sun as an insurance policy ... or of course a complete chancer!

I honestly don't know, suggest you interrogate your installer and see if his/her answers are credible, or see what others here have to say. The possible problems I can think of are: UFH is commonly designed for a flow temp of 35C. Radiators are commonly designed for a flow temp of 45C or above (historically around 70C but ASHPs aren't efficient at that temp, which is why they 'need bigger radiators'). Of course you can run radiators at 35C, but they would be mighty big. That might just work well with undersizing the bedrooms, you'd need to do the calcs. Im not sure if there would be any problem with balancing between the UFH and the radiators. Your installer seems to be suggesting 'not' - and he might be right. Unlike some on this forum I'm not an installer, just an amateur with a university degree in physics (which is good for understanding this stuff!), a general interest in how almost anything works and a specific interest in renewable technologies both at work and at home. I am also a great fan of Occam's razor which is one reason I always ask 'why' when anybody proposes adding to a system a component for which there is no obvious function (buffer tanks in a suitably large system where no mixing is required being the case in point).

In this case the freeze protection function needs to be left on. I don't know if there is any parameter you can adjust, but I certainly wouldn't turn it off altogether.. The a/f valves are just a backup to the ASHP freeze protection to cover the situation that its both cold and the power has failed.

That messes things up. My current panels, Sanyo HIT 250, have a current rating of 7.2A. Modern 400W panels appear to be typically 11-12A, the increased power comes from increased current rather than increased voltage. I haven't yet had a response from SMA solar as to whether my existing inverter can tolerate a situation where the available input power exceeds the spec, but neither the voltage nor current does. if this comes out in the negative, Id be looking at fitting separate (micro) inverters anyway. I had hoped that it would come out in the positive and I could just tack the new panels onto the existing inverter as suggested by Dillsue, using optimisers to match them. But it seems Tigos might not do the job.

Sounds like (as Temp suggests) the freeze protection function. It is most likely configurable if you want to switch it off (but I wouldn't unless you have glycol in the system). If it only happens on cold days then almost certainly that. My boiler does this and every ASHP I have read up about also.

OK I read the Calefi article so now understand the concept of 3 port buffer tanks. Essentially they combine the functions of a 2 port buffer tank/volumiser with that of a bypass valve. When the load is active they are pretty much bypassed on the flow and only the return passes through, adding system volume but not much else. When the load is inactive (because the zones are shut down) they serve as a bypass/heat store. That seems prima facie like a reasonable idea (although Im not clear whether its better than a 2 port tank and a bypass valve). The diagrams all show two pumps though, is there any reason, I wonder, why a 3 port tank could not be run with only 1 pump?

Thanks for this, it looks like a rather good 'text' on heat pumps and related technology which perhaps ought to be better known. Thats apart, of course, from the crazy (ie non-SI units). However, given that Btu (have I got the capitalisation right?) means 'British thermal unit' I guess we cant complain too much. A 'ton' as a unit of power is a new one on me though, 'the average heat transfer rate associated with melting one ton of ice in a period of 24 hours' - 12000Btu/hr (3.5kW).

That would indeed be interesting, a good experiment to do and as you say pretty much isolate the effect of buffer mixing. There is an argument hat this should be followed by an experiment where all ports are bypassed, which reduces the system volume of course, but remains an interesting case (and an interesting comparison) if the system volume is 'sufficient'.

Intrigued by this one, what's a 3 port buffer (beyond the obvious) and do people fit them?

Agree entirely Unless I have missed something it's almost certainly inevitable. With mixing you get hot and cold water producing warm water. This increases entropy (disorder) and you can't restore that without inputting energy from outside the system (or violating the laws of thermodynamics). In practice this manifests itself in a requirement for higher flow temp=lower efficiency. Also mixing (unless it's purely conduction of heat in which case the 4 port buffer isn't needed) implies some circular flow (ie from hp via tank to hp, or distribution system via tank to distribution system). That can't happen without either injecting energy from outside or creating a perpetual motion machine. The latter violates the laws of thermodynamics. In practice the pump(s) need to do more work to force water round the system. Sadly, getting something for nothing usually violates the laws of physics (this may sound trite, but its largely true). Sometimes the sacrifice is of no consequence (a heat pump reduces the external air temperature, but we don't care because the volume of external air is near infinite, solar panels collect energy from the sun, but we don't care because the available energy is more than we can use). Most of the time, however, the sacrifice has to be paid for somewhere.

Thank you, I will definitely investigate