Posted by: @eliuccio

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So I guess I am left with Vaillant unless 21degrees will come back with their updated quote.

Is that because the only people who will quote for 45C also quoted for Vaillant?  

Might be worth doing a stare and compare (between the quotes) on the rads and house loss estimates.  In the end the operating FT will depend on the rads fitted, not on the heat pump.  So if, for example, the guys offering Samsung are actually fitting the same or bigger rads as the guys offering Vaillant, the FT will end up the same (and almost certainly different to either 'design' temperature!)

Unless of course you have already decided to go for one or the other anyway.

@jamespa I will wait for smart heating to come back with a newer quote (45C) and ask Sustain to provide their 45C quote based on a Vaillant pump.

Posted by: @eliuccio

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@jamespa I will wait for smart heating to come back with a newer quote (45C) and ask Sustain to provide their 45C quote based on a Vaillant pump.

Very sensible.  Get the 'second round' quotes in, hopefully puts you in a position to make a decision.

@eliuccio Why don't you talk to Midsummer Wholesale in Cambridge who are not too far from you (0223851535). They stock several brands including Samsung. As a major distributor, they may be able to help you clarify the technical issues and recommend specialist installers in the area who know the kit. For the Samsung, beware that there are 2 different R290 units, one with pump inside (....BEK £2975) and normal dumb one without (....DEK £2653). Your installer did not specify which R290 he was supplying, probably the cheaper one as he obviously doesn't know the difference.

Posted by: @jamespa

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There is only limited evidence to support the comment and absolutely no evidence to support the suggestion that its detrimental.  Of the top 25 air source heat pumps on heatpumpmonitor.org, 18 are Vaillant and 1 is Samsung, so whatever design choices Vaillant have made, they appear not to be negatively impacting performance!

Regarding lack of evidence vis a vis constant flow rate of Vaillant, I attach 2 examples over same period from heatpumpmonitor.org of 2 "top performing" HP's, one Vaillant and one Daikin. The Vaillant shows a fixed flow of c. 14 l/min with cycling to reduce average heat load with dT all over the place. Daikin has reduced constant flow matched to the power output with steady dT around 5C. I have no axe to grind here as I use neither but I know which one I would choose. As an engineer, constant on-off switching does not bode well for long term reliability, even if COP is claimed to be somehow superior. Daikin appears to have the same facility I was talking about. Maybe its Jap AI! 😊 

Posted by: @heatgeek

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Regarding lack of evidence vis a vis constant flow rate of Vaillant, I attach 2 examples over same period from heatpumpmonitor.org of 2 "top performing" HP's, one Vaillant and one Daikin. The Vaillant shows a fixed flow of c. 14 l/min with cycling to reduce average heat load with dT all over the place. Daikin has reduced constant flow matched to the power output with steady dT around 5C. I have no axe to grind here as I use neither but I know which one I would choose. As an engineer, constant on-off switching does not bode well for long term reliability, even if COP is claimed to be somehow superior. Daikin appears to have the same facility I was talking about. Maybe its Jap AI! 😊 

Noted but (a) constant vs variable flow rate doesn't materially affect cycling, that is determined by the how far the heat pump can modulate down its energy output (which is determined essentially by frequency of the inverter-driven compressor) relative to the demand from the emitters and (b) these are two different systems in two different houses so the onset of cycling will therefore be at a different temperature, so this one-off comparison is meaningless if the intent is to 'prove' that the Vaillant is more susceptible to cycling than the Daikin (I suspect that, if you look into it, the Vaillant is more 'oversized' than the Daikin in these two plots)

Unfortunately you continue (I think) to confuse modulation of the energy out/delivered to the emitters with modulation of the water pump speed.  The heat pump can modulate the energy out (by changing the compressor frequency/fan speed) to match the demand with or without modulating the water pump.  

If you can provide evidence that heat pumps with variable flow rate have a materially greater output modulation range (and thus will cycle less when exposed to the same conditions), then that would be interesting, as would evidence that they have a materially greater COP or lifetime.  So far I have seen (and know of) none and nor has anyone presented a theoretical argument why such differences would exist.  

PS Im actually not sure the graph shows a constant flow rate, its difficult to tell which blue it is (but none of the blues are constant) - not that I think it matters see above

PPS I dont have an axe to grind either.  I joined this forum a couple of years ago before I got my own heat pump.  I stay with it because its interesting stuff (in a slightly nerdy sort of way) and I enjoy getting to the bottom of physics/engineering related things that pop up in everyday life.  If Im wrong on anything, Im wrong, and will admit it.  

As an academic (and scientist; as you can guess I teach and research at Uni of Essex) I am very much intrigued by how much heat pump tech has advanced (or at least I perceive as such because I am naive and with no engineering background.

@jamespa @heatgeek this is indeed a very interesting comparison. But it requires ceteris paribus, which seems particularly difficult in this case unless some controlled experiement/test has been done by independent professionals (perhaps without disclosiong the brands but only with an interest in comparing fixed vs modulated).

Thanks!!

E

I confess I had to look up 'ceritus paribus', but having done so it is the problem with almost anything to do with domestic heating and heat pumps (possibly with domestic heating generally).  The paradox is that the physics is incredibly simple, but the application of that physics to a real environment rather complex, and experimental evaluation of many interesting questions made nigh on impossible by the uncontrollable variations in the environment. 

As a concrete example, we don't even know under what circumstances it is sensible (from a cost standpoint) to turn a heat pump down at night, because we cant establish an adequate control to do the experiment and the simple theory (based on the first law of thermodynamics - which is pretty inviolate) is (a) too simple and (b) gives results which depart from the very few reported, totally uncontrolled and under-instrumented, experiments we have which, because they are so few, we must suspect suffer from confirmation bias and (c) even if they dont suffer from confirmation bias, since we cant explain them, we dont know to which systems (house + heating system + heat pump) other than the specific one in question we can apply the results.

There is a warehouse somewhere in the country (I cant remember where) with two houses built inside, where controlled experiments are done.  So far as I'm aware there is only one, and its not difficult to imagine that its in high demand (I have a feeling its owned by a couple of developers).  Presumably there are dsparate facilities where heat pumps and boilers are tested, but for that you don't need a whole house!

I am a physicist by training (ie my degree was in physics) following which I spent nearly 30 years in telecoms engineering and 15 years in local government (yes its an odd combination).  This stuff is remarkably fascinating, probably because of the contrast between the simplicity of the physics and the complexity of the real environments.

Until such time evidence is produced to the contrary, I stand by my statements above  (specifically that maintaining a constant deltaT across the emitters by modulating the water pump speed does not confer an advantage).  This is on the grounds that

• no theoretical basis for the contrary view has been advanced and there is some theoretical arguments against the contrary view
• no evidence from the monitoring has been produced that the contrary view is correct and some evidence has been produced that it may be incorrect, and
• several well renowned heat pump brands do not bother maintaining a constant deltaT, even though they have the hardware capability (as for example Vaillant does) to modulate the water pump. 

However if someone can produce a contrary argument and/or evidence then I remain open minded.

Welcome to the fascinating world of domestic heating with heat pumps!

Incidentally, similar questions can be asked about boilers, but they are far more linear in their response so somewhat easier to deal with.  Nevertheless its becoming ever more clear that our collective ignorance of how heating systems work has led the UK (unlike some mainland European countries, most notably Netherlands and Germany) to make some silly decisions over the past decades, most particularly the failure to mandate low temperature heating and weather compensation for our condensing boilers.  As a result most don't condense, evidenced by the plumes of vapour emitted by most flues, an consume 10% more gas than they need to as well as compromising comfort.  Its also far from clear that the micro-zoning (in both time and space) that the controls industry and building regulations have encouraged us to adopt is actually beneficial.  Its now becoming clear that it is not beneficial in the majority of cases with a heat pump, and probably is not in a significant number of cases with a boiler.

PS

IMHO we need an engineering department of a UK university to become serious about understanding whole-house heating systems.  There are surely loads of PhDs in it and doubtless some spin off software/hardware companies.  I know Univ. Ulster do already have an interest, but I cant help feeling we need more. 

Posted by: @jamespa

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Unfortunately you continue (I think) to confuse modulation of the energy out/delivered to the emitters with modulation of the water pump speed.  The heat pump can modulate the energy out (by changing the compressor frequency/fan speed) to match the demand with or without modulating the water pump.  

If you can provide evidence that heat pumps with variable flow rate have a materially greater output modulation range (and thus will cycle less when exposed to the same conditions), then that would be interesting, as would evidence that they have a materially greater COP or lifetime.  So far I have seen (and know of) none and nor has anyone presented a theoretical argument why such differences would exist.  

@jamespa @eluccio. OK, the gauntlet has been thrown down. Let me first explain the context. I have been using a Samsung Split with PWM pump for 10 years without drama and got interested in what modern technology has to offer. After looking at heatpumpmonitor.org, around 60 of the 92 users have Vaillant pumps so I became curious as to what the secret was to this HP’s popularity. I did an analysis of the data of a number of Vaillant HP’s and posted a spreadsheet on another thread, posing some questions. Some things stood out like the very low dT’s and the fact that the bigger the over-size of HP, the smaller the dT. As the Vaillant monobloc has an internal pump, I surmised as to whether this unit had flow modulation capability. I was slapped down by a Vallaint user on heatpumpmonitor.org and given examples of Vallaint having fixed peak water flow at all loads with small dT’s and much increased cycling at higher OAT’s. This was pronounced to be a super-efficient method. I was summarily chastised. Yeah, right.

So let’s do some academic math. The heat power delivery from a HP is given as follows:

Power (kW) = Specific Heat of Water (4.2) x Flow (l/sec) x dT (C)

From the data tables attached, it is clear that the Vaillant has a 14.474 l/min flow or 0 flow (5kW unit). The Daikin has current average flow of 6.54 l/min with peak flow of 23.835 (8kW unit). Both units are outputting around 2 kW.

Daikin Power = 4.2 x 6.54/60 x 5 = 2.28 kW

Vaillant Power = 4.2 x 14.474/60 x 2 = 2.03 kW

So, as can be seen, the Daikin maintains its 5C dT by modulating the water flow rate. If the Vaillant were to be more over-sized, the dT will fall off a cliff. In another thread, Brendon Uys of British Gas stated somewhat facetiously that several installers have told him that the Vaillant operates best when under-sized (or filter blocked). It is easy to see why. He is unequivocal that dt's must be 5C minimum or more. In the case in question, the 5kW Vaillant is struggling to meet the 2kW partial load with very small dT and is cycling. This suggests that it is over-sized for the application. Could be a compact house with 3kW heat loss! 😶

The 8kW Daikin however takes the 2kW load seamlessly within its stride. Impressive.

In the light of this, if the new 5kW Samsung BEK R290 with integrated PWM pump can be proven to work like the Daikin, this would make it the best value unit on the market currently IMHO given its natural refrigerant and price. However, a competent installer is needed! On the other hand, the Daikin R32 has a 4kW unit which is less over-sized for E. and, on the evidence above, could modulate down to 1kW. Just what the doctor ordered! Given its high price and questionable design whatever the COP, as an unbiased observer, the Vaillant is IMHO a lousy unit. Never took notice of the Daikin before but a new R290 unit when it arrives would definitely be worth a look.

In another observation of the Daikin case, the room temperature is varying from 24.6C to 20C therefore suggesting that it is uncontrolled herd open-loop. If temperature was controlled at 21C within 1C through use of thermostats, a large amount of energy would be saved and the Daikin will modulate temperature and water flow rate accordingly. Maybe that is why Part L Building Regulations stipulate that a thermostat must be provided in every room. The problem is that the HP and house design must however be compatible with this aim which, with the current level of installer competence, is pie in the sky.

Therefore, I stand by the advice I gave E. with modulating flow rate, WC, lounge thermostat and TRV’s in the bedrooms. It is up to E. to choose whether to go with the herd……or not. If one really must have a Vaillant, under-size it (if that is possible). Quad erat demonstrandum.

@eliuccio  Here is a response for you from Midsummer Wholesale.

"The Samsung R290 HP is a modern monobloc heat pump designed with a focus on environmental sustainability (R290 refrigerant), ease of installation (integrated hydraulics in some models), and high-temperature performance.
Yes, It's accurate to say that advanced models like the Samsung R290 HP, are designed to regulate both temperature and flow, and they do aim to manage the delta-T."

So, when counter arguments are made to the above methodology, I am sure that, as an academic, you would also love to have some justification in terms of calculation or data, would you not, not just love.

I think you are covering two points, namely water pump modulation and control strategy (weather compensation and/or room thermostats.  I will deal with them separately as either alone is sufficiently complex and so we shouldn't confuse the two

Water Pump modulation

Sorry but again I think you are mistaking modulation of water flow rate with modulation of heat output and then making linkages which have no apparent basis and statements based on what others have said without any supporting argument or evidence.  You have provided a lot of data, but I apologise that I still cant follow your argument that maintaining a particular deltaT specifically of 5C is advantageous.  Perhaps you could summarise why this would be the case in a sentence or two in order than can better understand what you are trying to say.  

Control strategy

I think you go on to suggest that its somehow better to operate a heat pump on Thermostats and TRVs, rather than (or possibly in addition to?) weather compensation.  I think this might be based, at least in part, on

Posted by: @heatgeek

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In another observation of the Daikin case, the room temperature is varying from 24.6C to 20C therefore suggesting that it is uncontrolled herd open-loop. If temperature was controlled at 21C within 1C through use of thermostats, a large amount of energy would be saved and the Daikin will modulate temperature and water flow rate accordingly

You do not provide any evidence for the assertions or conclusions nor do you know how this particular machine was controlled or what the circumstances were (for example the sensor may be in a room subject to lots of solar gain!).

I think you may also believe that weather compensation is either new or specific to heat pumps.  It is in fact neither, its decades old and has been mandatory for boilers in some mainland european countries for some decades.  Had we followed suit most of us would have used 10% less gas to heat pour homes for the past two decades, but we didnt.

There are good reasons why weather compensation is fundamentally a better control strategy - essentially its a leading indicator of what the heat source needs to do as opposed to a lagging indicator, which circumvents problems that occur in control loops with time delays (there is a whole branch of engineering devoted to this!).  There are also good reasons why operating a heat pump (or a boiler!) at the lowest flow temperature possible is generally optimum (which of course WC ensures), its fundamental to the physics of heat pumps and described in the Carnot equation.  I can go into more detail on request but the upshot of this is that almost any heat pump not operated on weather compensation will be less efficient and also will likely result in lower levels of comfort (again I can go into more detail if you wish).

As I have said earlier, for some houses layering on top of weather compensation an element of control based on house temperature helps.  Popular strategies including using TRVs as limiters (by setting them a couple of C above the desired level) or some sort of auto adaption.  In all cases however the principal control is the WC if the objective is maximum comfort and minimum running cost and the other controls are secondary.  For many houses these additional controls don't improve stability/comfort or aren't needed. 

Heat pump sizing

Finally I would not advise to undersize any heat pump, I would advise to right-size it!  Undersizing leads to cold houses, oversizing leads to excessive cycling, right sizing gives a warm house with only modest cycling at very mild temperatures, which is efficient and imposes a low level of strain on the machine.

Finally please note that the above argument is designed to favour any particular unit, just get to the bottom of the fundamentals!

@jamespa Perhaps I can chip in to say that our Daikin 8 kW monobloc does modulate the flow rate between ~5 - 35 lpm (it does seem to hover at approx. 15 lpm a lot of the time) The system also varies the flow temperature (ours is set within the limits of 30 - 50 deg C).

We originally used WC and the output was well matched to changing conditions of weather and temperature - the only exceptions were at the extremes of the OAT where I found I needed to intervene with a little tweaking. It may have been that in time, I might have mastered the art of the curve for all weathers. We had the homely smart controller fitted before the following winter and from the Dashboard plots, I can see that the Delta T is still approx. 5 deg. C at all times other than defrost. So with or without smart control, the Daikin can maintain a Delta T of 5 degrees. We have a secondary pump set to run at ~ 15 lpm but I am unsure what happens to efficiency when the Daikin pump starts to run at a flow rate of 30 lpm or more. Regards, Toodles.