PhilT

I have an Ecodan but as you are with Octopus, I would recommend you have a look at their latest heat pump offering "Cosy 6". If they can use your existing installation and tank it could be free with BUS.

reasons being? Surprised at this - sounded like potentially a good way to size a heat pump and provide some comfort regarding a detailed heat loss calc. Say during a very cold day this month, if you could run your gas boiler for a few hours with the house in as near to steady state as you can get it - say 21 inside and -3degC average outside (or whatever are your preferred design parameters), note meter readings, ideally flow temp to get a good idea of boiler efficiency (plenty of tables/graphs around), couldn't you work out with a fair degree of accuracy the kWh supplied and hence what size heat pump you need, and wouldn't that be better than a detailed heat loss calc?

Good summary, and reason to be optimistic about the potential for mass conversion. In the last couple of years I organised new boiler replacements for 3 of my relatives with existing rad installations more than 15 years old, and made sure the flow temp was set to 55degC. They do the job fine, all that happens is - longer boiler runs

Does this happen all the time or only at colder temps? I had this same issue at colder temps in the early days and it was the freeze stat setting which I turned off completely as I have antifreeze.

It uses WC as a start point then learns the curve of roomstat temp vs heat output. On Melcloud you can clearly see the flow heat curve flattening out more and more as it approaches target room temp, over the course of a few days, until it achieves a consistent control pattern. The end result is steady long runs, typically in the high 30s in these mild temps, with rads. It also manages much gentler starts than WC, I.e. no power spikes, and automatically compensates for defrost cycles by upping the flow temp slightly post defrost.

Mitsubishi does auto adaptation very well indeed, but most effectively with rads, ufh is an unknown quantity. I stopped using WC months ago, full auto being so much better, the numbers suggest around 15% more efficient than WC mode.

totally agree - that's what Octopus are leading with, and my bet would be that the rest of the energy suppliers and hp makers will follow

I wish the Octopus campaign highlighted in the original post had been around 3 years ago, I would almost certainly have gone for it. All I would have needed to do to get a free installation would have been to simply replace my gas boiler, which was running small rads at 70degC, with an efficiency of no more than 70%, meaning real gas costs of c. 11p currently, compared to electricity 27p therefore only need to achieve SCOP of at least c. 2.4 to be worth it

Lol, not so bad if inside the heated part of the house hopefully!

It will be though, if heating engineers are increasingly employed by energy companies and heat pump manufacturers running properly organised boiler upgrade schemes, with proper training etc.

Not if they can demonstrate with real world examples that running costs are at least on par. They invest a huge amount on research and are extremely media savvy, so it's only a matter of time

https://www.theengineer.co.uk/content/news/octopus-raises-the-temperature-with-cosy-heat-pump/ Following up on the original post, the Octopus strategy (and others will almost certainly follow) as demonstrated by their media splurge of their Cosy 6 heat pump, will offer simple boiler replacement which could cost net nothing with the BUS grant, or modest extra cost with larger rads. I wouldn't be at all surprised if this is the way things go now, with energy companies taking the lead, and is a potential game changer in terms of mass conversion of old housing stock. It would be really interesting to see how such an installation performs especially in terms of running costs.

It's interesting that the media focus is increasingly on flow temperature, 70 or even 80degC now being quoted. That suggests to me that heat pump manufacturer's strategy is mass conversion of old housing stock via mass produced, low cost, high temperature heat pumps as direct replacements for old gas boilers, working with existing small rads and which, because of technological improvements, can achieve comparable energy running costs. This doesn't stop those who can afford it from going one step better with large rads/UFH to reduce running costs further.

Interesting background to the Cosy 6 heat pump mentioned in OP link, capable of 80degC flow temp:- "Design: Developed in-house by Octopus's team led by Dr. Jason Cassells, CEO of Octopus Heating (formerly Renewable Energy Devices acquired by Octopus). This involved innovative design features and boasts six pending patent applications. Manufacturing: While not directly owned by Octopus, the physical production takes place in Craigavon, Northern Ireland, through a partnership with Red Engineering. This allows Octopus to influence the manufacturing process closely while ensuring efficient production. Overall Control: Octopus Energy maintains complete control over the Cosy 6 ecosystem. This includes the heat pump itself, the Cosy Hub control system, Cosy Pods room sensors, and even the bespoke smart heat pump energy tariff. So, while Red Engineering handles the physical manufacturing in Northern Ireland, the Cosy 6 is very much under the creative and strategic direction of Octopus Energy. It's truly their baby, designed and managed to seamlessly integrate with their wider home energy ecosystem"

Weather here this month has been shite, hardly any sun at all, wind, rain, dismal nearly all the time, but freakily mild. Solar panels will have generated c. 85kWh by the end of the month compared to 232kWh in Jan'23 just after they were installed. Average temps here +8 this Dec so far compared to -1 last Dec when we had two weeks of sub zero, including two nights of -12 minima! My ASHP energy used for heating only will be c. 520kWh this month compared to 837kWh last Dec.

Not sure about Scotland but down here in Buckinghamshire this December is very much milder than last December, so our total usage will be c. 800kWh compared to 1,119kWh last December, nearly 30% less, the heat pump obviously accounting for most of that.

Is this actually causing you any discomfort? Isn't that same sun shining through your windows during the late morning and compensating for the lower flow temp?

I think this is an excellent idea and one I was also considering but couldn't find a suitable location. It has an advantage of enabling better efficiency at low ambient temps. "A thermometer on most weather stations is taken 2 meters (or about 6 feet) above ground level (AGL). Because cold air sinks relative to warm air, and because the ground radiates heat very efficiently during calm, clear nights, the temperature at or near ground level can often be several degrees cooler than the temperature at the 2 meter thermometer height". https://www.weather.gov/abr/frost_fall2012#:~:text=Because cold air sinks relative,the 2-meter thermometer height.

Heating, cooling and dehumidification. It's a winning combination. I had a 2kW Fujitsu split installed a couple of months ago in a downstairs hobby room. Whisper quiet and does the job really well. A significant installation though, with through wall electrics, pipework for condensate etc.

In a workshop you will probably also get extremely warm in summer. All modern air cons are also heat pumps so well worth the cost of a few hundred quid (if doing it yourself)

I get annoyed when I read this nonsense. They are not noisy, unless old, poorly maintained, badly fitted, or any combination of the above.

Indeed. Its a bit mad that gas price has dropped back from 30% to 25% of electricity prices despite the need to incentivise heat pumps, although all the people I know with gas and small radiators are running their boilers at or near maximum, well over the condensing temperature range and so probably not much more than 70% efficient, making gas cost 10p. With a realistically achievable SCOP of at least 3.5 it still makes heat pump running costs very favourable to gas.

Manufacturer's own software is pretty good. I have found input to be spot on based on verifying against meter readings. Not sure if it's possible to get any better than a calibrated software estimate for output, but mine looks reasonable compared to expectations (heat loss calcs etc.)

This user monitor is quite encouraging. Things have definitely improved, but the usual caveats still apply. https://heatpumpmonitor.org/

No. DHW at 45 is for the water in the tank, not the heating flow temp - that is determined automatically and would likely exceed 50 to achieve DHW of 45. Regarding space heating the general recommendation is to use "weather compensation" - select "Mode" on your control panel and see what options is displayed - probably fixed flow temp. There is a video featuring a later version here but hopefully the steps will be similar for yours.