PhilT

I disagree. You use less energy to heat less volume, and that saving dwarfs any miniscule heat loss between a heated and a non-heated room.

Thanks for sharing. Do you know if that is just for the heat pump itself, or for both pump and controls?

In the UK I don't really see the point in having a max flow temp above 60 it defeats the idea of having a heat pump in the first place. My RHI is invalidated if I go above 50 for heating and the DHW works very well at 55. Vaillant and Samsung make a big thing of the high temperature feature, aimed at those who think they need higher temps because they either don't want, or cannot afford, larger rads or UFH, which is self defeating because operating at flow temps that high utterly screws up the efficiency and operating costs. Although I grant you the situation may be different in -20degC parts of the globe

https://docs.lib.purdue.edu/iracc/1577/#:~:text=From the results%2C R32 has,can keep compressors stoke volume.

R32 is cutting edge for practical commercial application, which is why most of the major manufacturers have now adopted it in their latest models, a notable exception being Vaillant using R290 which is slightly less efficient but enables higher flow temperature but needs a siting position that meets fire regs. My monobloc ASHP has no central heating pump. I have both primary and secondary pumps, the latter to boost radiator circuit flow rate. Looks like you may need at least that for your very large UFH floor area.

Yes say the average UK boiler is 75% efficient, using 16k kWh pa gas to supply 12k kWh pa heat. A modern ASHP will use 3k kWh pa, which takes around 4kWh pa of gas at the generating station. Currently the UK grid is using less than 50% gas so only 2k kWh pa on average. I grant you the overall grid demand will increase massively but there are plans (haha!) to increase that through installation of renewables and nuclear, and reduce fossil fuel still further.

For me the overriding objective of having a heat pump is to reduce our dependence on fossil fuels generally but especially from Russia and the middle east, mainly for reasons of energy security. The intention is for gas heating to be phased out. Whether that happens or not remains to be seen but gas supply will reduce and gas prices increase. Yes obviously insulation, air tightness are important but you still need a heat source. A heat pump is the logical choice as it uses a fraction of the energy of even the most efficient gas boiler. Costs are a major stumbling block but should come down over time with economies of scale - it's a very basic form of technology.

Please do. My experience has been similar to yours, house spec, floor area etc. 11kW ASHP using electricity at 3k kWh pa on an MCS/EPS of 16k kWh pa (two different surveyors came to the same result) implying COP of at least 5. The installer estimated annual electricity usage of 5k kWh. In retrospect the ASHP is well over capacity but that musty be giving it the ability to work in an efficiency sweet spot most of the time.

That puts a whole new perspective on the life cycle cost comparison, if my calcs are correct, at that rate it looks like you're going to use around 8k kWh gas for a full year. Before installing my ASHP my last full year gas consumption was 21k kWh for a 120sqm property. So on a per sqm basis your gas boiler consumes around 25% of mine. The cost comparison with my heat pump would be you = 8,000kWh gas x 10.46 + 365 x 26.84 = £935pa, = £4.87/sqm, me = 3,000kWh electricity x 34.23 + 365 x 42.77 = £1,183pa = £9.86/sqm, around double the running cost per sqm. The only mitigation for the ASHP is the CO2 and energy consumption which, given gas contributes less than half of grid generation, means my equivalent gas consumption is roughly 1,500kWh pa

Impressive. Passive build?

It's a really interesting revelation I had no idea such low temp high efficiency gas systems existed. What's your annual gas kWh usage and size of property?

It is now but it will get louder as the temp drops to frost levels and the fan speeds up a lot. Everyone should be inside at those times so not really a problem

with only 2 of us of course, and so will the majority of the other 9m (18m people) 2 person households in the UK (when they all get heap pumps!!!) so it's a potentially useful case study

We only run it daily at 3pm (the warmest part of the day, on average), in Eco mode, and it takes between 20 and 30 minutes to reach the 40degC set temp.

impressive for Cairngorms. There are only 2 of us and our daily DHW demand is 0.8kWh but we have it set to the minimum 40degC, which easily gives us two good hot showers and enough for the various other minor washing requirements

Yes, now divided up between a cycle lane 60% and pedestrians 40% but I only ever saw one cycle since the line was painted about 10-15 years ago - ???

and filming of "A Clockwork Orange". Sigh - the gold ol' days

22/23°C ! It's interesting how peoples comfort criteria vary. We're comfortably warm at 19-20 during the day and 20-21 during the evenings. Our average electricity usage during October has been around 10kWh per day total, for a 5 bedroom detached 30 year old self build, with the heat pump using around 5kWh per day, although here in Buckinghamshire it has been a mild October so far. Heat Pump = 11.2kW

Our you could get the one with the best performance/price irrespective of standby power draw and switch it off for 4 months of the year, if you have suitable alternatives for DHW

yes sorry picking up bad habits. Power draw = 40W. Daily = around 1kWh

Just did another check over 2 hours with everything else switched off. Main meter readings give 40W per hour total which is 15W for the compressor heater (per data sheet) and by difference must be 25W for the control system. Model is Ecodan R32 11.2kW

Yes but even though I have an 11.2 version of that I would consider the latest offerings from Vaillant (R290) and Samsung (R32). The Coolenergy model appears to be using R410a, unless I am very much mistaken, so I would not recommend, but each to his own. Are you are able to assess the air tightness accurately enough before buying an HP?

The recommended model in that SAP document is an old tech 16kW twin fan unit which is hard to understand given the calcs. Go for one of the latest models featuring R32 or R290 and a scroll compressor in the 7 to 8kW range

Auto Adaptation only works with a Mitsubishi controller and they advise against using AA with UFH so probably WC mode best as others have said.

I'm a little surprised by this I wasn't aware a stat was fitted to the actual FTC. Surely you need some kind of room stat for ultimate control, that's why your temp is running away to 24. Your WCC is way different from mine which is set to 50 at -3degC down to 35 at 15 ambient above which the heat pump almost never comes on as my room temp rarely falls below my target temp of 18 during the day. The advice I have received is that heat pump efficiency starts to fall when flow temp goes much lower than 35 due to more regular cycling.