dropping the cold setpoint for FT from 50 to 45 is likely the cause of the improvement.

Also even if you can get 55C of useful temperature drop out of it (heat to 95, cool to 30) it stores only 190kWh, enough for an not atypical 8kW house for a day.  (We didn't, until relatively recently, bother to insulate our houses, because we have a mild climate and very cheap gas/coal - our gas is still very cheap).

For reference, my house heat loss only gets to 8kW with an inside temperature of 22C when it's -40C outside...

In a UK context, the space that the cylinder sits in is the size of a bedroom, which in the South of England affects the house price by north of £100K (for some reason we sell houses principally by number of bedrooms not floor area, which, together with sky high land prices, incentivises tiny rooms in small houses).

Also even if you can get 55C of useful temperature drop out of it (heat to 95, cool to 30) it stores only 190kWh, enough for an not atypical 8kW house for a day.  (We didn't, until relatively recently, bother to insulate our houses, because we have a mild climate and very cheap gas/coal - our gas is still very cheap).

If you want to store in a tank for later space heating you would need a much bigger tank and different pipework.  Its possible in principle but the scale of storage needed makes it difficult or impossible in practice.

Yes, you need something like this:

This kind of set-up is very common in places that use wood boilers here in Finland. The tank you see in the picture (the white/red cylinder) has a capacity of 3000L. The picture was taken while I was installing the wood gasification boiler (the red thing in the middle) and heat pump at my house. i can store heat for several days for both heating the house and hot water.

And by that I mean a tank used to keep heat that is used later to warm the space.  

Buffer tanks can best be thought of as part of a 'production line' for the heat, ie the heat passes through them but is not stored in them for any length of time.  If you want to store in a tank for later space heating you would need a much bigger tank and different pipework.  Its possible in principle but the scale of storage needed makes it difficult or impossible in practice.

The way to store energy for space heating is either in a battery or in the fabric of the house itself.  In particular houses with ufh buried in slab concrete flooring over insulation can be sometimes be heated quite effectively this way.  You 'batch heat' the floor when leccy is cheap, and it slowly releases over the next few hours.  Essentially is the old idea of a storage radiator.

Thanks, none of us posting much on this forum are typical users. I doubt many would have embarked in these HP upgrades without having first understood the key aspects to consider. We all seem to have systems thinking and most agree that each householder will expect to look after their own interests. 

My objective discussing heatpumps is just that when we will discuss ours, we will want to have an appreciation of what to balance and consider. One angle I was focusing on is the fact that much more space is required than with a combi boiler. Systems could work without a hot water tank. At the moment it would seem to me that buffer tanks could be a sensible choice for ROI. 

My perspective is that, given the wide range of considerations involved in the choices for these energy systems for each house (electricity tariffs, battery, PV, heat loss, lifestyle, disruption accepted, etc), it is not fair to expect the installer to be able to advise anyone to reach some optimal choice. I am someone that believes in standardisation, but the housing stock and all these factors differ too much. So it is probably a space where at best we have relatively standard system designs that need to be customised and sized.. If we ever get close to that 600k a year, the installers will be more specialised. So are our neighbouring heat pump installers going to be able to supply it?   

And last but not least, much the same applies to DHW heating, We have to ditch the fossil fuel thinking, and instead go low with Steady Eddie, ie abandon the idea of instant hot water

Steady Eddie it will be. 😀

@batpred, English does not seem to be your first language

I too had exactly the same thought, and agree 100% (note I did not write 110%...) with the Major, in such cases, the simpler the language the better. If you must use technical terms, define them the first time you use them, so that we are all clear what a word or a phrase means.  

...

I suffer from communicating in too many languages! One of the early ones was IT Infra language. I appreciate this is not common here. Also when people use heating engineer language it is not always understood. That does not really explain most of the "misunderstanding" in that exchange. 

....

No, that is not what we mean. "IT Infra" is not a language; it's not even clear what you actually mean by this. If you mean "IT Infrastructure jargon", I can understand your sentence better, but that underlines that you're missing the point.

Your sentence structure and grammar, to pick just two examples, clearly tell me that whatever language you spoke in childhood it was not English. If communicating effectively in English is already a challenge for you, complicating what you're saying with technical jargon of any kind makes it immeasurably harder to actually understand what you mean. Your post just above suggests you think your English is fine and that it's just a matter of me not being familiar with IT terminology, but that unfortunately is incorrect in every sense.

I have no wish to criticise your language skills, but for effective communication you really need to move towards using much more basic English, construct simpler and shorter sentences and avoid technical terms where possible.

@batpred, English does not seem to be your first language

I too had exactly the same thought, and agree 100% (note I did not write 110%...) with the Major, in such cases, the simpler the language the better. If you must use technical terms, define them the first time you use them, so that we are all clear what a word or a phrase means.  

😂😂

I suffer from communicating in too many languages! One of the early ones was IT Infra language. I appreciate this is not common here. Also when people use heating engineer language it is not always understood. That does not really explain most of the "misunderstanding" in that exchange. 

As someone deepening knowledge about another domain based on a broad scientific base, I may assume X is the norm whereas it is the exception at the moment. Like I remember going over youtube videos that include buffer tanks. And by that I mean a tank used to keep heat that is used later to warm the space. 🙂 

There will be times when the 8 kW heat pump starts up with a surge much higher than 2 kW and also when adverse weather drags the COP down, there may well be periods where that same pump could draw far more than that 2 kW for an extended period of time. Regards, Toodles.

The max power I've recorded on my Home Power Monitor from my cosy6 is 1.56kW, at todays grid of 237.7V thats 6.56A; the HP has its own 16A mcb.

You're right there’s a startup surge, typical 6-10x running current; more when the motor is cold. There’s also a shutdown collapsing field voltage spike that needs suppressing too.