where does one put the heat from the overnight boost?

the options I can see are

a) heat whole house to a high temp at night. then house will cool over the day. hopefully its still at a comfortable temperature by the next time the heating comes on.  hopefully the occupants don't cook in their beds.

if the heat loss of the house is high, then you'd need to heat to an uncomfortably high temperature in order to have enough left 16 hrs later.

If the heat loss is low,  perhaps you could indeed use it without having to overheat by much in the first place, but if thats the case, you probably don't need to muck about with this approach anyway?

b) heat something else to a high temp and then deliver it slowly to the house over the day. Water based thermal stores to hold enough heat for a typical house over an entire day would have to be enormous (35kwh with a DT of 10 needs 3000 litres!) so where on earth do you put it?

Does this approach work if and only if you have a large UFH slab that can be preloaded?

@iancalderbank I just run the downstairs UFH only, so no one gets hot whilst asleep, saves about £1.50 a day in terms of off peak vs peak prices.

Its not a thick slab as its retrofit but today at 4C outside it was enough to prevent the heating coming on for 7 hours.

@gary I am the same. None is cooking upstairs, the radiator is set to everyone comfort max 21. Downstairs UFH is on for about 7 hours 22t concrete  ( hand mixed 💪 back in the day  when we built it, We put 150mm Kingspan under it using 20mm piping for UFH.)

I when I go  to bed usaly is is around 21.2c when I get up it is about 21.8c . As underfloor seems to heat up slow once the heating off temp still rises a bit for a few hours and the concrete giving out the heat till it reaches about 22-22.3c then starts falling by 10 pm is about 21.2c again.

As the heat rises still keep upstairs ok. When the heating comes on it does go to about 19.5 but then the heating kicks in as the flow temp is only about 35c. It takes a while to heat upstairs but always stays comfortable.

Posted by: @cathoderay

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Another point to consider: what happens if time of use tariffs become commonplace, and many more people time their electricity use according to their tariff? What if demand in peak periods falls, and rises in non-peak periods? Given the fact an ASHP will be the major electricity consumer in most settings that have an ASHP, shifting their use to off-peak periods might substantially reduce peak load and increase off peak load, and in so doing remove the basis for time of use tariffs...

I suspect there will always be a peak time for domestic heating need which will always result in some peak/off-peak differential worth reflecting in a time of use tariff. No-one is going to be heating their home only while everyone's in bed.

If load-shifting was that easy, heavy-using industry would have done it years ago and things like Economy7 would have ended.

Batteries probably have far more potential to change this than varying ASHP time of use.

Posted by: @mjr

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No-one is going to be heating their home only while everyone's in bed.

But that is pretty much what has been proposed in this thread... The point I am making is that if this happens widely, it may mean the tariffs end up changing to make it less attractive.

Batteries are an obvious solution for domestic load balancing, apart from the fact the technology isn't there for mass market yet, and then there are the problems many choose to ignore, like the 12 year old kids operating in toxic mining conditions, what happens to end of life batteries etc. 

@cathoderay I don't think it can happen widely. to be honest I'm a little bit puzzled by the original post. I can see how this works with a large UFH slab (as @gary and @andris confirmed) but not any other way.

Posted by: @iancalderbank

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I'm a little bit puzzled by the original post

You weren't the only one. There is another recent truly bizarre post here, to which I nearly replied '"The broader challenge calls for a collective introspection..." as to how on earth I can get away with posting 486 words of AI generated gibberish which says absolutely nothing'. Perhaps the poster's name is a clue - Nathan Gambling.

Posted by: @cathoderay

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Batteries are an obvious solution for domestic load balancing, apart from the fact the technology isn't there for mass market yet, and then there are the problems many choose to ignore, like the 12 year old kids operating in toxic mining conditions, what happens to end of life batteries etc. 

Even more so given that, in 20years time, we will all have at least one 60kWh battery sitting on the drive.

Seriously electric cars should make an enormous difference to load balancing opportunities, although 5-7pm may well remain a problem.

@jamespa When I had my first Powerwall 2 installed in 2022, my installer suggested I think hard before installing a second unit. I have 8.1 kWp. of solar PV and they thought a second unit would never show any ROI. Though my PV installers knew of my intention to have a heat pump installed soon, they still did not feel that more energy storage would be a benefit. The solar PV provision has not changed but with the NG and energy suppliers encouraging us to ‘load shed’ and also the initiative to support the grid during times of highest demand has, I feel moved the goal posts! Once I had the heat pump installed - I felt doubling my capacity would have multiple advantages. 27kW/h of storage arranged around a TOU tariff would be a good move. Not only do I feel the flexibility of TOU charging rates help reduce costs, I have the comfort of being more resilient in the event of power outages … and the benefit of ‘helping the grid out’ whilst being reimbursed well for doing so goes a fair way towards recouping some of the cost of paying for Mr. Musk’s holidays. 😉 Regards, Toodles.

Posted by: @cathoderay

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Posted by: @mjr

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No-one is going to be heating their home only while everyone's in bed.

But that is pretty much what has been proposed in this thread... The point I am making is that if this happens widely, it may mean the tariffs end up changing to make it less attractive.

Batteries are an obvious solution for domestic load balancing, apart from the fact the technology isn't there for mass market yet, and then there are the problems many choose to ignore, like the 12 year old kids operating in toxic mining conditions, what happens to end of life batteries etc. 

I remember discussing this sort of thing years ago with people with varying technical backgrounds.

The first point is that using car batteries for load shedding etc only works if your batteries are good enough to take the extra cycling.  They weren't back then, they might be in some years time. 

Without specific gvt intervention to specific aims, tariffs will change to meet the need of the company to make profit.  Simple as that, so you can expect lower tariffs only when it suits them, e.g. there is too much wind power.

Finally, I'm sure someone could do the modelling, but it probably isn't efficient to have 20 million little home batteries for load balancing, somewhat regional setups would probably work better.  I also wonder what the fire rate would be when you get to tens of thousands of home batteries. 

As for the child labour, that is how the world works and is solvable with appropriate political will.

Battery recycling is only an issue because the omnipotent market is not actuall omnipotent and there is always drag and inefficiency, which is where a sensible gvt intervention to get it up and running properly would be a good idea.  E.g. these disposable vapes thing, if you had a deposit scheme that would probably help.  But anyway, battery recycling won't be a problem soon because once supply chains are setup and so on, there will be proper facilities etc for it.  Money needs to be put into it though. 

Thanks for sharing your tips on reducing energy bills. One more tip is to make sure you have your thermostat in the right spot. If it's too close to a fireplace, in direct sunlight, or in a room that's much cooler or warmer than the rest, it might not get a good read on your home's overall temperature. This can make your heating or cooling system work harder than it needs to. Moving your thermostat to a place that better represents the average temperature of your home can make a big difference.

@ken 

I agree that this approach is more cost effective, but not necessarily the most efficient way to run a heat pump.

I have a 12KW Samsung on the Octopus Cosy Tariff.

I run it for 3 hours 4am to 7am on the off-peak tariff (house is warm when I get up) by setting the timer to a 20C target (it overshoots by 1C), then set it back to 18.5C. On really cold days, it might come on again mid morning for an hour or so. I then set it back to 20C at 1pm, for 3 hours, during the second off peak session (1-4pm), so the house is again warm when I get back from work. I set heating and DHW off 4pm to 7pm as this is the peak period. I then set it to 19.5C at 7pm, and then set back to 18.5C at 10.30pm. The heat pump rarely runs between 10:30pm and 4am which is fine with my neighbours.

So the house average is around 19.5C +/-1C throughout the day and night, getting coolest at 4am and warmest at 4pm. So the majority of the heating effort is done using off peak electricity. 

I also run the dishwasher, washing machine and tumble drier in the off peak windows and this also makes a huge difference to lowering the bills.