PhilT

MCS-020 section 3.1 (b) (page 15) https://mcscertified.com/wp-content/uploads/2021/10/MCS-020.pdf contravention enforcement probably unlikely unless a neighbour complains about noise or visuals

I wouldn't be at all concerned about that. I'm in a similar postion, having switched from a 22kW boiler to an 11.2kW R32 Ecodan which has turned out to be around 100% oversized! At the current mild temps the auto mode manages it pretty well so it doesn't cycle more often than once an hour. My COP so far this year is 4.1, better than data table specs on any given day, and that's for a microbore/radiator system with two pumps and a low loss header. There's an intersting view here on cycling https://www.shenlingglobal.com/blog/unlocking-efficiency-understanding-your-heat-pumps-three-operation-cycles/ "What Is the Ideal Frequency for Heat Pump Operation? The frequency at which a heat pump turns on and off depends on your specific home and heat pump setup. The cycle duration should be sufficient to heat or cool your home effectively without putting undue strain on the system. Typically, a cycle length of 10 to 20 minutes, followed by a shutdown, is considered normal. Ideally, your pump should complete two or three cycles per hour at most. Under normal conditions, your heat pump should not run continuously, except during extended periods of freezing weather when it needs to maintain the temperature"

how would you operate? If it's anything like JohnMo, using the slab as a night storage heater to utilise cheap rates, then you would need a pump that is much more powerful than the design steady state continuous heat loss/energy input of 8kW at -2degC

Need a lot more detail please! "up to temperature" - what does that mean - as per the system design? What do you mean by "normal" radiators - are they the old small gas boiler size, or new extra large/low temp radiators? Are you running in "fixed flow temp", "weather compensation" or "auto (target room temp)" mode? The focus of your post is all on flow temp but the fundamental question is - despite your issues, are your room temps getting to where you want them to be? In current seasonal daytime conditions my average flow temp (large-radiator system) is typically around low to mid 30's when my room temp is at or approaching target temp, so possibly things may be working as designed?

Did you try this search site? I dialled in a Cornwall postcode and it listed a few MCS heat pump installers https://www.renewableenergyhub.co.uk/search-installers

When I first read about the launch of the new R290 "Cosy" heat pumps (made by RED, now part of Octopus), initially promoted as as a high temperature boiler replacement, I called them to find out if it they would also fit that as part of a low temp/large radiator application and they said yes, and conceded that it would be more efficient. No prescription about flow temp was mentioned, but anyone interested should certainly double check with them.

I'll add my name to the ever growing list of people who suggest Octopus - have you looked into this yet? I have a heat pump already but if I was in your position that's what I would be doing. They are offering leading edge R290 technology at not a lot of money net of £7.5k grant or even, as ReedRichards mentioned, free if you are able to use all of the plumbing you have already.

I actually spoke to them about that recently. They now do either direct boiler replacement with existing rads or a more efficient low temp system with large rads, at cost of course.

Ta. It would be so much easier to to use the calorie Cp version of 1 !!!

Or "half as good", the pure substance having Cp of 2.3 compared to water 4.184 (joules per something or other). The commercial offerings are diluted plus additives. Fernox Alphi-11 (20% in my system) has Cp of 3.99, so mixed Cp 4.15, so nothing much to worry about.

The business would likely move more towards the most commercially progressive big energy companies like Octopus who will probably use the benefit of increased electricity sales to support financially attractive heat pump deals without grants, and particularly compared to gas boilers.

The planning portal says https://www.planningportal.co.uk/permission/common-projects/heat-pumps/the-microgeneration-certification-scheme this page seems pretty clear "One of the limits of permitted development rights for wind turbines and air source heat pumps is that equipment must be installed by an installer who has been certificated through the scheme using a certificated product", and "the installer of the equipment should check to ensure that the installation complies with the Microgeneration Certification Scheme planning standards (MCS 020), including requirements on noise"

I think it means that due to lower conductivity the compressor has to work harder to deliver the same unit of energy to the water/glycol mix. Would love to be proved wrong!

The specific heat capacity of ethylene glycol is 2.36, propylene glycol 2.5, at 25degC, so a 20% mixture of either would have Cp of around 3.8 at 25degC I wish it wasn't so as my system has 20% antifreeze source = https://waterbaths.net/blogs/blog/thermal-conductivity-and-specific-heat-of-bath-and-chiller-fluids

Interesting point, the formula for delivered energy being Q = M x Cp x delta T, so water Cp reduces from 4.18 to around 3.8 for a 20% glycol mix, but increased flow rate M would cause a decrease in delta T, which seems to suggest the conventional wisdom may be correct

The Hydro Pro 8.3 has the same specs as you quote and also specs "Slow Fuse 15A"

Depends entirely on how many solar panels you want, and their power rating, but anyway you have posted this in the Heat Pump section. Try posting to the PV (solar panel) section.

Yes

You can if you keep daily track of the month figure which is the cumulative to the most recent midnight I.e in whole day batches - includes no energy measurement for the current day.

In your first post you ask how can FLOW temp go to 60 - in which FTC6 screen are you seeing a flow temp of 60? Is there some confusion with the Legionella hot water temp which is set at 60?

Depends on what type of emitters you have. 25 minimum might be ok for UFH but probably too low for radiators unless they are well oversized. If you have radiators try minimum flow temp 30 at 12 outside, up to maximum flow temp 50 at -8 outside, which rather neatly works out at matching increments of exactly one degree for both flow and outside temps. You need the max/min to both be higher than required in case there is a situation where the room temp drops further than normal below target room temp, otherwise it will take too long to get room temp back to target. For normal day to day operation, Auto mode will override WC and keep the flow temp limited to only that required to keep your room temp on target.

Indeed but once balanced solar gain could potentially cause throttling in many or most rooms. Isn't it better to have some form of automatic modulation of heat pump output according to room temp?

22 is a very low minimum for a radiator circuit, and the badly named (as you rightly implied) WC "curve" is probably on the conservative side, but try it out to see if it keeps your house at the temp you want.

That's a great example, one of many, where auto adaptive mode, for those lucky enough to have it, is a big step improvement over pure WC mode

Do you have a radiator circuit? My max is set to 50degC flow temp at -3degC outside temp, minimum 35degC flow temp at 15degC outside temp. BUT - If you plan on switching to Auto mode this range is not critical, because the max flow temp is governed by the room temp - mine rarely goes above 40 and from what you said I don't think yours will either. At time of writing here it's 11degC outside and the flow temp is 33degC. As you can see from the chart below this is how Auto mode reacts as room temp is reached. Domestic hot water temp is down to personal choice, no. of inhabitants, size of tank, lifestyle etc. Mine is set to 42degC and I never run the legionella cycle.