PhilT

So includes the electricity standing charges and 5% VAT, or not?

Are these numbers gross or net of solar usage/export? Useful to compare what others are achieving. I could probably do more to get my cost down

90 = 5809 91 = 0000 190 = 2001 191 = 0000 The flow temp is modulated to extend comp run time eg at room temp target 20, actual room temp sits at 20-20.5 for longer before switching off comp at top of hysteresis 21, so in warmer ambients it gives a higher ratio of comp on vs. off time

Mitsubishi have just released a new firmware upgrade, which they installed on my ASHP and controller for free. It's designed to extend compressor lifespan, improve overall performance and efficiency. The difference is noticeable

Do you have solar panels and smart meter capable of export? The latter, at say 15p/kWh, makes a huge difference to the financial case

Granted but why call it a heat pump tariff?

I think it's aimed at heat pumps feeding UFH and big concrete slabs

Longer ON period?

what kind of A2A are you considering, individual room units or a central pump/compressor unit supplying a network of fan coils? Have you ruled out a wet system? Would be interested to know why.

you could try this website https://www.visitaheatpump.com/

Me too. Q4 to Q6 not entirely logical so for q4 I already have a heat pump but for q5 have guessed option 4 with reason: replacement of existing

That's absolutely fine, I did that too in the early days, just keep in mind that "Room" is actually "Weather Compensation", overlaid by a flow temp reduction as your room temp approaches your target room temp, to keep the heat pump running for as long as possible at the lowest flow temp possible to achieve your target room temp.

House size (eg floor area)? Are you saying peak heat loss is 5kW (at what ambient temp?) but the heat pump is a 17kW? Hot water set to 60 continuous will cost you a lot of electricity. Mine is set to 42, for 2 people, timed to heat once a day at 2pm. We only take short showers. If the flow temp is fixed at 50 then it's not set to Weather Compensation. There may be some useful YouTube videos on that model possibly?

Why not just leave it on "Room", it already uses Weather Compensation, only much more intelligently, so no need for any more fiddling about. Are your upstairs radiators actually on? If so there is something wrong with your setup.

The MCS tests also record a poor performance for this unit compared to most other models

The Zone 1 setting, yes that's it

If you have the Mitsubishi Ecodan Wireless Remote Controller then the most efficient way to run your heat pump is in "Room Temperature (Auto Adaptive)" mode. I have been doing that for over a year now. Best thing is, you don't have to fiddle about with settings, just let it do it's thing, knowing that it will run at peak efficiency all the time. It uses the WC curve in the background so initially you have to set that to something sensible.

So one could be quoting the existing 1732w @ ΔT of 50 with gas And the other 782w @ ΔT of 27 approx. with a heat pump, which makes sense if the heat pump average radiator temp is 47, less target room temp of 20. Not sure about BUS but certainly RHI specified a MAX heating flow temp of 50, not the average of the in & out. So my heat loss calcs all use radiator temp of avg. 50, 44 = 47 maximum target. In practice it operates way below that 99% of the time But no light yet shed on total lounge heat loss. 4700w seems implausible unless there is a large glass area somewhere

( actual delta T / 50 ) ^ 1.3 ?

I would be very interested to hear if you go for this as I have a couple of friends and relatives who are looking into the same option

My house is very similar in size and spec to yours, with oversized rads and the same peak heat loss of between 5 and 6kW. My installers also spec'd a design flow temp of 50degC but that is the absolute maximum. My guess is that they build in an average downtime for night time set back or timed off. My flow temps only reached 50 at outside temp -12degC. In reality, if you run continuously like I do, with little or no set back, the vast majority of the time it stays between 30 and 40, and only gets above 40 on the very coldest Winter days.

To what temp are allowing your rooms to drop? I never allow mine to go below 18, max 21, on 24/7

Which is not good. There is a significant variation in efficiency/COP throughout the modulation curve, for example this research chart shows peak efficiency at around 40% of the modulation range. JohnMo's heat pump is a 6'er I think, so in mild temps the modulation range could be as much as 3 - 8kW. His chart shows a constant 5kW output which would be around 40% of the modulation range - bang on the optimum according to this chart. Mine does exactly the same in Auto mode, but in straight WC mode it cycles on and off at minimum modulation level during mild outdoor temps, and the performance hit is very clear to see.

That previous post should have said Sensocomfort mode is set to "Incative", which is pure WC mode heating with no roomstat temp influence. "Active" means flow temp is influenced by room temp of any assigned roomstat. "Expanded" is the full monty, outside and room temp influenced flow temp using that wizzo Vaillant Sensocomfort roomstat controller, which suggests that it might work like the Ecodan "Auto" mode, which is highly desirable, as it does many important things over and above pure WC mode; suppresses start up power spikes, flattens out then, if necessary, reduces flow temp as room temp is approached, compensates for solar gain and defrost, and never allows compressor cycling, and works the heat pump at it's optimum efficiency level

Which heating mode are you using? Normal, Eco, Balance Sensocomfort Inactive, Active, Expanded