ReedRichards

Well done; I really didn't think you were going to make it.

Likewise, I can the offset the water temperature determined by weather compensation by +- 5 C in 1 C steps (LG Therma V).

I have LG. It's straight line only for weather compensation. Flow temp may adapt to room temp but this is not a documented feature (you can control on Water or Air + Water but the difference this makes is not documented).

I'm never sure about the correct way to interpret such temperature distribution curves @SteamyTea. It's typically coldest in the middle of the night and I use a night time set-back temperature of 2.5 C so my heat pump can cope with a colder outside temperature overnight because I'm not asking it to work so hard. And that is if it comes on at all, almost always the retained heat is sufficient that it does not need to come on until it starts warming up the house in time for me to get up. Given that my heat pump is rated to keep the house at 21 C down to -3.8 C outside, I would only be in real difficulty if the temperature did not get as high as -3.8 C for 24 hours or more.

The MCS norm is to specify a heat pump for a temperature that is exceeded 99.6% of the time (if I remember correctly). If you specify it for the lowest temperature achieved in the last 50 years then it will be bigger. Any boiler or heat pump will be oversized to meet your heating requirements most of the time. Does being more oversized cause a heat pump to lose efficiency? I have seen data for a Mitsubishi heat pump suggesting that it does, although I don't know if this is the norm.

The yellow curve shows what I calculate to be the weather compensation required to match my radiators and the straight line is what I am using. There's not a huge difference. Both are based on the assumption that the MCS calculation is correct and I need my maximum flow temperature at -3.8 C or less.

I have always thought that a hallway is a crazy place for a thermostat; hallways tend to be draughty and you don't need them to be particularly warm. So the alternative to what you propose is to throttle back the flow to the radiator(s) in the hallway so that it heats more slowly I too have a third party controller, it's a Drayton Wiser in my case. It is wired so that when there is no thermostat or radiator calling for heat then the heat pump turns off its room heating. This works perfectly well. If you do this then you may lose any load compensation ability that the Daikin may have. This could reduce the efficiency but it's more likely to be significant if your thermostat was not in the hall. Control of my heat pump is set to water temperature only (so it does not care what the room temperature is). Hot water functions are unaffected by this. There is an argument that you should disable all thermostatic controls and just set your weather compensation to give you the temperature you want in the house 24/7. If you buy into this argument then room thermostats, TRVs and zones are all bad for efficiency/performance. I don't entirely believe this myself.

Your installers may be telling you otherwise but I think you will find you are too late. Any heat pump installer that isn't overloaded with work this month surely can't be very good.

Given that the questioner merely wants people to express an opinion, perhaps this statement is the one that we should be challenging?

I both watched the video and read your original post. But there are many "nuggets" in your original post that just aren't in the video and if you have to interpret a video with the aid of a whole load of extra notes and clarifications then it simply isn't a very good video and it leaves itself open to misinterpretation.

Any tips?

If the lesson you are mean to take from the video is that you can install a heat pump without paying attention to the radiators then it's a very bad lesson. If not, then what is he trying to tell us?

I don't know how it works in Scotland but here in England I applied for my RHI online, it took less than 15 minutes and acceptance was immediate. You don't explain what your problem is and why you need to make direct contact.

So why is the guy wearing a cap and a hoodie; could it be that he is not feeling terribly warm? You cannot defy the laws of physics and if the radiators are small then you'll end up with cold house; if the radiators are adequately sized for the 48.5 C flow temperature then you can keep the house sufficiently warm. It all seems a bit disingenuous.

I thought I had commented but my comment has vanished (or I never completed it). You can see what the flow temperature IS in either mode by pressing the semi-circular arrow on the display. In AI mode you cannot see the target flow temperature and you can never see the outside temperature (from which you could calculate the target flow temperature). I would be surprised if you have a significantly different version of the software (go to Settings - Service - RMC Version Information to find out). But if so, ask your installer for an update next time you have the heat pump serviced.

@Carrerahillclearly knows vastly more than I do but I can tell you that the man who came to change my mains fuse assured me that these are very slow blow and you could exceed the nominal current rating of the mains fuse for some time without harm.

You only have to look back one page on this thread to see details (in a post by me) of how to change the Weather Compensation settings. I have a programmable thermostat and use Auto mode; there is no problem with that whatsoever. Auto mode does not need to know your room temperature .

I use Auto all the time with a third party controller and two zones so I see no reason why you should not be able to do that too. However if your heat pump is set to control by Air and Water rather that Water (as mine is) then your LG controller might possibly conclude it is hot enough already in the hot water cupboard (since I do't use that option I don't really know). A heat pump that could not accurately tell what the outside temperature is would get itself into all sorts of trouble so I doubt that that is your problem. The other way to proceed is to reduce the water temperature in the Heat setting and see how low it will go and still keep the house warm. You need to record the outside temperature and the water temperature and make a chart so you can construct your own weather compensation line. You should also look to see what your weather compensation settings actually are. Your radiators should be fine for the job. My installer used an over-size factor of 2.4 for 50 C output water flow.

"Auto/AI" is weather compensation. So it will tend to reduce the water flow temperature when the weather outside is warmer. This works because when it is warmer outside you house loses heat less quickly so can be heated less quickly also. The weather compensation parameters will have been set by your installer and can by changed if you access the installer settings. My installer was instructed to use very conservative settings. The ones I set myself are Outside Temperature: min -4 max 18 and Flow Temperature max 50 min 29. This means that the flow temperature will only be 50 C when the outside temperature is -4 C or less. -4 C is the temperature used for heat loss calculations on my MCS certificate (which assumes the flow temperature is 50 C). If, for example, the outside temperature is 10 C then the flow temperature will be about 37 C. The AI values add the set number of degrees to the calculated flow temperature. So if the calculated flow temperature was 37 C then AI +5 would make it 42 C and AI -5 would make it 32 C. Therefore in principle if the room temperature does not ever reach the desired value you should increase the AI number. However rather than flying blind I recommend that you check what values your weather compensation is using. Finally, your energy usage should be about 1/3 of the energy usage you would need to heat the same house with a gas boiler. But if you replaced an ordinary gas boiler with a heat pump and did not change all your radiators at the same time you would be likely to face the double whammy of very high heating costs yet not being able to keep the house warm enough. If you look back through all the posts on this thread you will find more information which may be of use.

I had my heat pump serviced a few days ago by the engineer who installed it. He said that heat pumps are in very short supply at present, stuck at the port, waiting for chips to complete the build etc. etc. I think any notion that there is still time to order one and get it installed before the RHI deadline will prove to be wrong. It's unfortunate for the OP but he who hesitates....

Does anyone use the Air and Water control option? I'm tempted to see what this does. I would have to set my third party controller to some high temperature so it loses control (except on/off).

Maybe you should post a new specific question about Acond in case not every Acond owner cares to read about someone with an RHI dilemma? It would help if you could identify which other brand names Acond units are sold under.

It's very difficult to make the call based on running costs because they change. When I installed my ASHP in December 2020 I could buy electricity for 13p per kWh and for the previous 2 years I had paid an average of 45p per litre for heating oil. Come April the price of my electricity will have more than doubled whereas the current price of heating oil is a little less than 50% more than my average. So for most of 2020 my ASHP was cheaper to run than my old oil boiler but since October 2020 it has switched and oil is cheaper. If you are looking for at least 10 years of life for whichever heat source you choose then you have to predict fuel prices 10 years into the future to try to compare running costs!

You would probably find that lack of time to complete the work has made up your mind for you.

I use one of these https://www.timeguard.com/products/time/immersion-and-general-purpose-timeswitches/wi-fi-controlled-fused-spur for timed/remote control of my immersion heater. But it's an all-or-nothing control, unlike the iBoost which can regulate its output.