PhilT

Yes to both, it depends on how much you enjoy the tech involvement. I paid extra for a smart thermostat so I can set to auto adapt, which incorporates load compensation, to take care of everything for me in the most efficient way possible, but I have rads, it's an unknown quantity with UFH. Others prefer managing the tech to achieve a "Goldilocks" WC setting. Either system can be made to work well.

Ah yes of course. I must admit I was doing a lot of this until the temps dropped below zero then I gave up. Especially when I saw the power spikes after several hours off, even with adaptive, which is a lot gentler than straight WC

Could you please clarify what this is saying exactly?

I have Cosy but in these cold temps I'm running mine 24 hours a day at a very steady 20 room temp. I still get 8 hours at half price. The extra cost of the 3 hours 4pm to 7pm is partly offset by the better efficiency of constant running and the comfort of constant warmth and not having to worry or fiddle about with the controls and timer

If your Water Law (WC) with no adjustment was, for example, set as:- Outside 15>>>>>>>>>>>>>>>>> -2 deg C Flow 35>>>>>>>>>>>>>>>>>50 deg C your adjustment of +5 to the flow temp takes effect across the whole range, so the Water Law becomes:- Outside 15>>>>>>>>>>>>>>>>> -2 deg C Flow 40>>>>>>>>>>>>>>>>>55 deg C so either you should be feeling a lot warmer, or your room stat cuts the heating sooner, or both.

Yes this might happen the first time but that's why it's called "adaptive" - the idea being to leave it for however long it takes (a few days, a week maybe) in a steady state at your chosen room temperature setting, so it can "learn" from the micro-incremental temperature changes how your room temperature reacts to your flow temperature, with reference to your target room temp. If, the first time, the flow temp climbs too fast, the next time it will choose a more gradual increase in the flow temp, and repeat this "learning" until the flow temp behaviour achieves a steady state vs. your room temp target. Then if the sun is shining through your window it will reduce the flow temp further according to the higher rate of room temp increase.

that's precisely why adaptive is more efficient

Are you able to activate? This mode is designed to operate the compressor in the most efficient way possible given flow, outdoor and indoor temps.

-18degC that's what the met office weather record is for Northern Ireland

Neither can be justified on purely financial grounds if you have any kind of export and off peak tariff. It costs me 4p/kWh (12p/COP of 3) to heat my DHW. I get 15p/kWh credit for excess solar exported so it would cost me 15p/kWh to heat my DHW if I used a diverter, not to mention the up front cost. The up front commercial cost of a battery just takes too long to pay back, but do the spreadsheet to satisfy yourself that is the case.

That would be risky in an area which gets as low as -11°C to -18°C. The heating would be off for much of the time during lots of defrost cycles and while the heat pump struggles to get your hot water up to temperature. You talk of "payback" but what value do you put on comfort, convenience and lack of worry?

Or maybe there's a forum member who can help if nearby, in which area are you?

There are also 2 of us and the domestic hot water takes 30 minutes each day to heat up for everything we need, that's it. I don't think you have a problem.

21kW ??? You could try one of these in each room! https://www.hotspotenergy.com/DC-air-conditioner/#:~:text=An all-DC system means,for many years without maintenance.

I would also very much like to get rid of ghastly tank in loft. I have a heat pump but the 2nd video in the original post specifically refers to a gas boiler application at 09:00

Banning R32 seems like a sledgehammer to crack a nut, because there are well established processes to recover the miniscule amounts of refrigerant. I worry that it will screw the already fragile UK heat pump market unless the site location regs for R290 are relaxed.

The base Cosy calc at the moment uses the % hour split but it matters not - it's just another scenario. Interesting to play around with the numbers

Cosy 2 is a no brainer for me, at least for the room heating months anyway. I used Cosy 1 when it was launched but that extra 22:00-00:00 low rate makes a useful difference. Re the spreadsheet I reckon I will still export around 50% of my solar, without the battery, at 15p/kWh, but obviously most of that will be in the summer months.

One other thing I just noticed is that Cosy cheap rate hours I think are 8, not 7? Definitely useful as a directional steer, obviously you can debate the assumptions till the cows come home but that's where the "modelling" bit comes in based on your own particular circumstances. O

Ah, VisiCalc, the first commercial spreadsheet. I used it on an Apple IIe. Cue jokes about 5" floppy drives.

Good effort. Cosy "normal" rate = 25.81

Take a lot of time and care in working out the justification for a battery. With no export it is marginal at best so why go through all the hassle to install a potential fire bomb in your house. With export I would say impossible to justify on purely financial grounds. If someone has a spreadsheet which proves otherwise, more than happy to concede

I beg to disagree. If you already have a heat pump then Cosy makes financial sense without a battery. Getting a battery by itself just for Cosy would not be financially justifiable. For a heat pump consuming say 3,000kWh pa there would be a potential maximum saving of (3,000 x 12p) = £360 pa, with no up front investment, having already bought the heat pump. For a battery only, for an average consumption of 3,000kWh pa, the potential maximum saving would be the same at £360pa, but with a big up front investment. Considering the alternative use of your money at a few % interest on a fixed deposit account for 10 years after which you get all your money back, I would not consider getting a battery just for Cosy. Happy to be challenged on this.

is this what your controller looks like?

It still does that at warmer outside temps, say 12 - 15, but not at around the 10 or lower that we had over a week ago. Looking at the power draw curve, the behaviour suggests that AA manages the compressor to run as near as possible to its efficiency sweet spot around 40% of maximum capacity, and if it can't, then if the run has been long enough (never less than 20 minutes), AA allows the compressor to ramp up and either switch off while keeping the flow pumps running, or when target room temp +1 is reached.