Posted by: @batalto

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@marvinator80 put in more batteries - that would be my advice

I might just do that. The AmpiHome system allows adding additional packs. I might take it up to 15KW and see from there.

We used 149kwh yesterday 🙄. We had the car plugged in overnight for four hours using Octopus Go, but most of that will be from the two heat pumps. 

The temperature never got above zero here and it looks like we have at least ten days of similar cold weather. It is going to be expensive!

@marvinator80 I started at 7kwh, then went to 14kwh. After installing the heat pump I realised that I wanted even more so now I have 29kwh. Honestly, I'm going to go even further. With these energy prices the pay back is very very fast. I'm saving over £4 a day with each battery pack 15kwh x 90% x 39p = £4.26 (it costs me £1 to fill it). It's sub 2 years to pay it off. I can't see prices getting better next year.

You'll get a better bang for your buck building, rather than buying a battery. Probably double the capacity

Summary from the Midea app for yesterday: 24 hour ambient -0.12 degrees (whatever that is), 93kWh used, or £35.34 at today's cap price. That's £247.38 per week, or £1060.20 for a 30 day month. Kitchen temp this am 16.0 degrees, 3 degrees below design temp. Over £35 per day, equivalent to over £1000 per month, for a system that fails to reach design temps. Not good, though to be fair, it went down to -3.7 degrees ambient overnight, which is all but 2 degrees below corrected design ambient of -1.8. This is empirical confirmation that there is zero headroom in the system, any suggestion that there is is creative marketing.    

Posted by: @cathoderay

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Summary from the Midea app for yesterday: 24 hour ambient -0.12 degrees (whatever that is), 93kWh used, or £35.34 at today's cap price. That's £247.38 per week, or £1060.20 for a 30 day month. Kitchen temp this am 16.0 degrees, 3 degrees below design temp. Over £35 per day, equivalent to over £1000 per month, for a system that fails to reach design temps. Not good, though to be fair, it went down to -3.7 degrees ambient overnight, which is all but 2 degrees below corrected design ambient of -1.8. This is empirical confirmation that there is zero headroom in the system, any suggestion that there is is creative marketing.    

Not necessarily, there’s only no headroom if your water temp is maxed out and the unit is running at full pelt. What flow temps are you running at. Most curves are set for -2 so you’ll need it to run hotter than that if it’s -4. 

Also was it on 24/7 or do you have a set back or off period?

@benseb - I don't know what the weather comp curve is supposed to do when it goes outside the set parameters. Does it keep the same gradient, or flat line? 

The reason for saying it has no headroom is based on the observation that yesterday, when I set the curve to 55@-2, it failed to reach 55 degrees. Obs every five minutes or so over an hour showed it mostly got up to 53 degrees, once or twice it reached 54 degrees. That strongly suggests it couldn't meet the demand, ie there is no headroom. 

It was on 24/7, no setback. 

You might be more successful at a lower temp. At 55c I imagine it’s defrosting a lot. Whereas at say 45 you might find it’s not as hot but defrosts less. With a shot?

Then I guess the question is, can that heat get into your house… are the radiators etc big enough?

we’ve just added an extra small rad to each bathroom and they are now at 20c. Whereas we have a utility with an undersized rad that’s 16c. So it’s just as much about the emitters as it is the heat pump itself. 

I may even pull up the rug we have over the UFH today for max output. 

It’s also worth remembering the oil or gas boilers have very expensive days too. It was just harder to measure. 

I remember during beast from the east getting through an entire 1100L tank of oil in 3 weeks. At todays prices that’s about £1000 in 3 weeks. 

Thankfully these cold spells are short lived. Saying that if they were more common maybe installers would pay more attention to good design!

Posted by: @benseb

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You might be more successful at a lower temp.

I doubt it, the system was designed with a flow temp of 55 degrees. Lack of available wall space for rads was a major constraint, necessitating a higher than ideal flow temp, But, as designed, the system needs these flow temps, any lower and the rads will not put out enough heat.

I agree it is absolutely a whole system thing, ASHP => circuits => emitters, as I have said many times. Each part of the system needs to do its bit. As designed, the rads can put out enough heat at 55 degrees flow, the weak link in the system is the heat pump which does not put out the 12.4kW plus headroom claimed by Freedom. It's going flat out, and doesn't get the system up to design flow temp.

For anyone wondering whether I am going to flip the dips, the answer is not yet, because doing so is bound to increase consumption, and as I am already using ~100kWh a day, I really don't want to push that up any further. I'd rather put on an extra layer of clothing. The point under discussion here is whether the heat pump as part of the designed system is adequate or not, not what I do if it turns out it isn't adequate.    

yesterday was the coldest ever my system faced. Average of 2 degrees ambient over 24hrs - It used 61 kW (according to the Midea App) and 73.8kW total for the house (from Octopus). I'm inclined to agree with those numbers as we use about 10-15kW for ovens, lights, washing machine etc and the sun was shining yesterday so we did make quite a bit of solar. However I still think the midea app over estimates power use.

HEATING : Used 61kW : Delivered 159kWh : 2.61 COP

Last year at 3 degrees ambient my system used 73kW to deliver more heat, 189kW at the same COP. I can easily see my system is currently more efficient how its set up. Or at least more heat seems to be making it into the house.

The effects of the batteries are shown below

kW off peak @ 7.5p/kWh = 39.1kw : £2.93

kW on peak @ 39p/kWh = 34.4kw : £13.42

Cost at Cost Cap @ 34p/kW = £25

@cathoderay three other courses of action for you might want to try?

1. More loft insulation?
2. Swap the rads for more efficient ones? e.g K3 type
3. Remove the heat exchanger and go direct from pump into the house