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PhilT

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  1. £2300 for an 8kW and a 300l tank sounds like a very good deal in this era of grant based pricing
  2. My mistake, hp-5c specific heat capacity at 40degC = 4.09, water 4.18, so 20% mixture (4.09*20% + 4.18*80%) = 4.16 so only a 0.5% reduction in heat capacity.
  3. Hardly at all, it turns out, thanks to this post. For example hp-5c at 20% reduces specific heat capacity by around 2%. Nothing to be concerned about
  4. It won't be able to adapt if you move the thermostat from room to room. I leave mine always in the living room in the same position, in a place where there is no possibility of it ever being in the sun.
  5. Are you in target room temp (auto adaptive) mode? If so the flow temp will not follow the WC curve directly, it will "learn" from repeated runs the point at which flow temp maintains room temp, which may take a few days. At mild ambient temps, if your heat pump is oversized it will not allow short cycling, which may explain what you are seeing - that even at minimum continuous power level the flow temp increases from 25 to 40, then the heatpump switches off for a while. Mine is doing exactly this, in approx one hour cycles (it's been 16degC today)
  6. That's surprising, you must have a very noisy heat pump. I can barely hear mine from 5m away never mind 20m and two fences
  7. 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
  8. 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"
  9. 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
  10. 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?
  11. 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
  12. 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.
  13. 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.
  14. 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.
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