ReedRichards

Okay @JohnMo , I was probably confusing a volumiser with a 2-port buffer. Is the description here https://blog.heatspring.com/2-pipe-versus-4-pipe-buffer-tank-configurations/ an accurate representation of what you mean? It seems to rely on having the heating system pump flow rate broadly matched to the heat source internal pump flow rate. My 4-port buffer is underneath the DHW cylinder and integrated with it. It's "short and fat" and so would probably not achieve the stratification shown in the reference illustrations; how important is that?

Not really. A 4-port buffer is absolutely the conventional way of plumbing a heat pump. I have been thinking about whether my 4-port buffer could be converted to two ports and I'm not sure it could. I have two zones. Suppose it's the middle of a cold night and the heat pump wants to defrost but my set-back is in operation and neither zone is calling for heat. Currently my ASHP would just turn on the internal pump and take some warm water out of the buffer. But with a 2-port buffer it could not do that because the closed zone valves would block any flow. Maybe @JohnMocan see an answer to this conundrum but I can't.

I would agree except that if you have a bathroom with an extractor fan then you are just wasting heat whilst that fan is running so any heat you can pump out of that exhaust is saved rather than wasted. Whether the durations match I would not like to say; can you extract enough heat to keep your water hot in the amount of time it takes to get the moist air out? Another issue to consider with an internal heat pump is the amount of noise it makes.

Heat has to go somewhere and the heat from UFH on the first floor must surely stay inside the house unless you have a severe problem with drafts. So I don't see there is necessarily any link between your cold first floor and the amount of electricity you are using. However if you have UFH throughout you surely cannot need a water flow temperature of 50 C, wouldn't 40 C or less suffice? Reducing the flow temperature to as little as you can will pay dividends in cutting your electricity use.

I had the majority of my heating pipes (which had been just under the floor, unprotected, in screed) moved to the loft at the same time as my heat pump, 14 replacement radiators and a new hot water cylinder were installed. That required 3 fitters for the first 2 days and 2 for the next four days plus an electrician for about a day. So that's 15 man-days of labour - and they worked hard.

Off topic but what does this message mean?

I bought a gas boiler 25 years ago (Atag) that did both weather and load compensation.

I don't know if it is achievable but I strongly suspect that the balancing would take longer than any installer would wish to spend or that you would wish to pay for. So you might well end up doing that yourself.

Yes. You may well need hotter water for the rads than you do for the UFH. If so, when the rads are not calling for heat you want the heat pump to react to this by reducing its output water temperature to match the UFH. If you cannot do this then you cannot derive any economic benefits from the UFH.

Yes, of course the system should include a hot water cylinder. It should be of a type designed to be compatible with a heat pump so with a particularly large surface area coil so it can be heated quickly with not-very-hot water. And you are going to want the water in the cylinder to be heated to 50 C (or less) so when you run a bath (or similar) you will need more hot water and less cold, so the cylinder needs to be generously sized to take this into account.

There are many people on this forum who are "handy" and advocate installing a heat pump yourself. My opinion is that your decision should be taken in context with what other contributions you will make to the house build; will you do your own plumbing for example?

Field mice get into my loft in the autumn; I cannot work out how. They love to chew up all types of foam pipe insulation but don't touch the aluminium-coated phenolic pipe insulation or, I think, anything covered with aluminium foil.

Have you read the Product Installation and Training Manual? Page 12 lists the various models including Therma V High Temp (heating only) so perhaps your model is not capable of cooling? Page 91 says that Dip switch 4, if set on, allows both heating and cooling (off is heating only).

Unless you have the option of Load Compensation. That can maintain a very stable room temperature.

I'm pleased that you got your heating working again. My heat pump installer tells me he is now busy with solar. Since there is no plumbing involved in solar PVs and solar water panels are out of fashion I don't really know how he is being occupied but I did not question him further. I don't think the water pressure will affect the pump and once you have got up to 1 bar I doubt that you would need to add much more water to increase the pressure. If you have any leaks this would make them leak faster.

On my system the ASHP, and it's controller, and the third party heating controller, and the internal central heating pump are all on the same (electrical) circuit. I had assumed this was the norm.

I found these two statements confusing. You mean you can heat the hot water with the ASHP but you don't?

I've been giving the experiment and the comments some thought. Isn't the "best" experiment to compare two scenarios where everything if the same except that two of the ports on the buffer (say the two flow ports) are bypassed and sealed so you compare the effect of a four-port buffer where mixing can occur with a two-port buffer where it can't? Everything else, including the volume of water circulating round the system remains the same. The control method remains the same. That would show you exactly what effect mixing in the buffer has on performance.

I may be mistaken but it looks to me as if the experiment is set up so that the heat pump and the buffer tank (when used) are at the same temperature, being the 7 C temperature inside the chamber. If I am correct this means that the buffer tank in the simulation is essentially external, equivalent to a real situation where the buffer tank is outside the house. I think the text also indicates that the pump on the "house" side runs all the time, whether or not there is a call for heat. That's not the way my system works, if there is no call for heat the pump circulating water round the radiators turns off. And I would consider a room thermostat with a 2 C difference between the off and on temperatures to be totally unacceptable.

Yes, you're right, I misread that; I don't know how. But we don't (I think) know how the Weather Compensation parameter were set. The use of Load Compensation in Scenario 3 could compensate for a poor choice of Weather Compensation parameters. So I see the difference between Scenarios 2 & 3 as making two changes. None of the scenarios compare the same control methodology with and without a buffer tank.

I understand it is a test devised by someone with a limited understanding of heat pumps. Scenario 1 uses a buffer tank and no Weather Compensation (although simulating an outside temperature of 7 degrees). A third party thermostat was used but there's no particular reason for that, I'm sure the heat pump allows you to disengage Weather Compensation on its own controller. Scenario 2 eliminated the buffer tank and uses Weather Compensation. So that's two different variables changed, which means you can never attribute any change in outcome with certainty to one or the other of the two variables. Scenario 3 is the same as Scenario 2 but uses Load Compensation as well as Weather Compensation. The average COP is a lot higher which is surprising. Perhaps the Weather Compensation settings were not optimal?

You can set the Therma V to control based on the just the Leaving Water Temperature or on both the LWT and the room temperature read by the controller, "Air + Water". In the Air + Water mode the controller will try to reach and then maintain whatever room temperature is set. When trying to maintain a set room temperature then modulating the central heating pump could be used to increase or decrease the heat output from the heating so might be a useful control feature.

The picture shows what is probably your central heating pump (too much in shadow to be certain). I have an LG Therma V and AFAIK mine is completely unaware of the presence of the central heating pump. I don't think there is even any option to take control of a central heating pump. In my case I'm not using the Air + Water control option with Load Compensation so there wouldn't be any point anyway. I can also see a pressure gauge which appears to indicate a disparity between the actual water pressure and the indicated pressure. And what looks to be the top of a motorised valve actuator.

Locking the arm in the "manual" position should open the valve. I don't know if there is a convention for whether this gives you heating or DHW but if the valve is the problem I think it should give you flow one way or the other.

Or oil. Before I got my ASHP I had an external oil boiler. The exhaust made a roaring noise that was audible from some metres away but as far as I can tell such boilers are subject to no noise restrictions whatsoever. There are various new regulations on oil boilers pertaining to efficiency but none on noise.