JohnMo

My view and there are others that will say no. Your heat pump is not doing cylinder heating, so there is no need to have a mixer to protect the floor from 55 deg flow. So use pump that comes with the ASHP and no mixer or pump on the CV UFH manifold.

Here you go, controller manual and technical details. If you search google for Maxa i-32V5, the user/install instructions come up in English. You need the installer password, which is 195 Controller-Manual-i-32V5.pdf Technical-Bulletin-i-32V5-1.pdf

Most efficient way to add volume is either a 2 port buffer, that sits in parallel to heating system, or a volumiser, it sits in either the flow or return piping and flow passes through it - it is connected to only flow or return, not both. Neither add hydraulic separation, so only a single pump is required. One zone - no wiring centre needed, single thermostat (normally your heat pump controller), no buffer/volumiser, simple system is all that's required for heating only, couple of isolation valves (use a filter ball valve in the return). Get your rooms where you need them by balancing loop flows.

You need to meet minimum manufacturer heating system, which is normally around 30 to 40 L, which you should exceed, as long as you don't zone and leave it as an open system. Min volume, is the smallest zone plus interconnected piping. My install will be open on a single zone no buffer.

@NickfromwalesIt was a one off on eBay, there is a 9kW still there. Item number 266070280966 The seller got them direct from Italy, as the postage bits were still on the packaging. I paid £300 less than the original asking price on eBay.

If you have a buffer you may well get a temperature drop across the buffer so will have to compensate. Increase your second floor flow rate, that will increase the mean flow temperature to increase energy input to the room.

Just compared @ReedRichards figures with the Brendon test, and interesting that the flow temp in test two is 38 to 40 and the flow temp in test 3 is 35. Almost exactly the same figures. But more importantly the use of a buffer is causing the heat pump to run hotter than it would without a buffer. For your bathrooms it may be worth increasing the loop flow rates a little so they are putting more heat in to the floor. Higher flow rate would give a higher mean flow temp, without increasing the actual flow temp.

Your EPC should have an energy usage figure on it, that will give you a start

What is your flow temp setting on the boiler?

So cost update as I been shopping, cost includes a 2 zone UFH manifold and 100m of 16m pipe. All pricing include vat and delivery. New Maxa 6kW heat pump (same as Viessmann, Vitocal-100 normally £4k) £1300 28mm Fill flush manifold and filter ball valve £78 Computherm thermostat £50 Manifold and UFH pipe £208 Wiring centre, expansion kit, 2x auto vent valves £86 AVM feet and flex hoses £147 Viessmann 1" Flow and return isolation valves, electric meter and isolation switch £158 28mm 3 way valve £59 Total £2086. Only have add inter connection piping. Hope this give people an idea of what the costs are or can be to do it yourself. Will do all plumbing myself, will need an electrician for a day.

Test 3 has less water in the system, so would be more susceptible to short cycling. So wouldn't that make test 3 perform less well or what's the point of a buffer. But in test 3 CoP gets better. More water may have improved CoP further. Question If you have a buffer why not record your own findings and post them. It's better for us to see real life installation, rather than experiments. So what is the a temperature change across the buffer or is there no change in flow or return?

No. To many variables. The house side of things stays the same, same energy loss on each test, same flow into the simulated emitter. He sets up up test 1 fixed flow to match a low temp as it enters the heating emitters equal to design flow temp at min outdoor temp. Test 2 same test but with WC engaged so at the test temp of 7 degs outside, the flow temp is lower, but with a slight uplift due to buffer. The flow temp into emitter is always the same temp. Test 3 same as 2 but no buffer, flow temp in to emmiters the same as previous tests. So test compares the cop at the same weather conditions and heat going into the house. Only two variables fixed flow temp and or a buffer with weather comp.

Heat pump efficiency is directly linked to flow temp, the lower you can get the more efficient. What are your flow temps? Can you fit bigger radiators?

Because we historically had a few days a year when Aircon was needed, historically they were also expensive to run, unlike now. Toshiba make a water heating module for A2A. But generally for commercial sized units.

And if it's in the thermal envelope those losses go in to the house and are not wasted heat loss. So zero loss

I have a mixer / pump, they are pretty crap with WC, due to the mixing, they generally just mess the flow temps up. Your delta T will change as the flow temp moves up or down, so think the moving delta is normal I think?

If you are running all your loops open (single zone) and don't have opening closing loops all the time (lots of zones), they offer zero advantage, other than making you wallet lighter. I had them, then removed and use open circuits on a single zone, with loops set up via the flow meter that comes with the UFH manifold.

They are just the same as any other actuator, if powered the allow flow if you remove the power they switch it off. They only added function is auto balancing to maintain a fixed delta T. They don't care They have a probe on the loop supply and return pipe and monitor/measure the flow temp and temperature change as heat is transferred to floor. As said any system will do, they open or close the flow rate to get a fixed delta T.

Main differences I see Brendon is actually using a modulating ASHP, trying to simulate real conditions, and controlling heat absorption rates within the simulated house. This goes a long way to represent real life conditions of wanting your house a set temperature. The Kiwa is testing with electric immersion heaters, and seems not to report or include output monitoring or compensation. As you say

If you are not after hot water on demand from the boiler, no need for a combi. If you are just doing central heating any suitably sized system gas boiler will do, you may be better having it as a pressurised system, just to keep air out and therefore less corrosion build up. Will be a simple system.

Auto balancing actuator is there to do one thing. Maintain a set delta T on the loop it is attached too. If flow temp is below 30 degs, it maintains 4 degs over 30 it maintains 7 deg delta T. As zones open and close, this delta is sometimes lost, the actuator open or close to ensure the delta T doesn't change. They don't care or know what they are attached too.

Not sure it does say a different conclusion, but that report is now very old and only really applied to fix speed heat pumps. Report are written early 2000s when most heat pumps didn't modulate. Recommendations states - for Installers Buffer tanks are unlikely to be required when the heat pump can modulate (i.e. if the heat pump is not fixed speed). 3 configurations of buffer, one a 4 port, the other 2 are actually not buffers but used as a volumiser in either the flow or return piping, so no mixing occured between flow and return water. Fig 41 shows a lower return temp for all test when no buffer was installed. Fig 42 shows a long on time time for all buffers, especially so for those in volumiser format. This really is showing the volume of the water system to be inadequate for the kW input. But a volumiser being better than a buffer to combat limited water. Fig 43 clearly shows if you split your system in small zones you do need an extra volume of water. But why not save money by not splitting in small parts? Fig 45, 46 47, when hysterisis was at 10, the highest CoP was in a no buffer configuration. Fig 48 shows by just running one rad with no buffer, you are running low on system water capacity But generally the report shows how much heat pumps have moved on in the last 20 years, they were cops of less than 3.

https://renewableheatinghub.co.uk/how-to-correctly-install-heat-pumps-so-that-they-work-properly-and-efficiently

Basically a buffer and LLH are the same thing, a buffer just has more capacity, both give hydraulic sepereration between the the heat source(s) and heating system. Both add inefficiency to a system; if added to a system that can be run without them being added. Managing zone size, can in most case delete any requirements, in a domestic situation, for a buffer or LLH. Saving capital costs and adding simplicity and efficiency. No LLH or buffer, less thermostats and zone valves, easier system balancing

Most if not all Viessmann products are designed to run weather compensation via their own controllers, and can run two zones at different flow temps if required via a fully open system without thermostats or trvs. So why mess with that? By putting a third party thermostat that will give less control or worse efficiency. Run as the Germans intended