SteamyTea

And then it is 'No'.

Depends on the size of the heat pump and radiators. Not necessarily, may be more noticeably when it turns off. This does really depend on how noisy it is, and how sensitive the occupants are to the noise. I cannot stay in a place with barking dogs or crying babies, wailing women and dot matrix printers.

And just think how much better it would have been if you had had all your windows sealed they way you wanted.

Isn't that set on the thermostat. In the olded days, these were very basic, bi-metalic strips that just turned off at a set temperature, then turned on again when the room had dropped a couple of degrees. For some reason they were often placed in a cold and drafty hallway. There was usually a secondary timer used to set the on off times. These where mechanical as well, and you had to pull or push pins in or out. These days they have electronic units that can be set up for different temperatures at different times, and even different settings for weekends. They are often wireless and can have other sensors attached to them, wirelessly. It is this unit that can be used to set different temperatures at different times, and by setting the 'set back' temperature very low, effectively turn the ASHP off. Do you have one of these? If so, send a picture of it or the make and model number.

Here is today's outside data. I think my sensors has got flooded.

So does this ASHP only do Hot Water.

To a certain extent, the timings can be set with trial and error. Do you now how your MVHR fan speed is controlled?

Sample every 5 minutes, if second value is equal to previous value +5%, then switch on. If next value is previous value -5%, switch off. (Switch on and off could be a change in fan speed) May need a bit more polishing i.e. if switched on, delay next reading for 15 minutes.

Would a simple logger with inside and outside temp/RH sensors be useful. Once the scale of the problem us known, it is fairly easy to design a switching system to cope with it. Though I think @MJNewton has the right idea, rate of change.

I think I have the same problem with my front door. South facing, but the porch is SW facing. When I get home I shall open it. Pretty sure it will let out half a cup of water. Been like it for 15 years that I know of, probably longer.

Refresh all our memories. Did you already have a wet system in and when the ASHP was fitted this pressure/water loss first started. Or did you already have to repressurise the system before the ASHP was first installed.

As a kids bike from Frog costs about 300 quid, I don't think they are competing with mainstream manufacturers. But this must be why MG don't sell many cars in the UK, Bentley have stolen the market.

I shall have to come over and see if that logger is still l logging, that had a couple of the better DHT22 on it. Though you do then your MVHR off in the summer.

Any chance you can log some numbers when the tank is in different states i.e. heated but unused, after use, in use and being heated. Be interesting to see how much turbulence is created. It will if the thermal outputs are equivalent, not if the ASHP is smaller. During those times you can heat the tank up to a higher temperature with a normal immersion heater. Just remember to turn runoff when they leave.

It probably only hits 80% sometime after peak temperature. Suppose the trick is to predict this time of 'not very nice to sit in' combination of temperature and humudity, and start to force more dryer and cooler air in before it becomes uncomfortable.

Large bodies of salt water tend to stabilise the RH. Trouble is there is not enough salt in it to reduce the RH to a comfortably low level.

That is tackling the same problem, but with different technologies. First thing to know is your DHW demands. Do you need 50, 100, 1000 litres a day. Without knowing that, it is just speculation based on guesses. And don't get temperature, energy and power mixed up. They are different things.

electricity prices are pretty stable, and now that the government has committed to supply all housing with RE (and nuclear probably), and with the cheapest form of new generation being wind and solar. I can see prices dropping in real terms. We can generate from wind and solar cheaper than gas now.

Isn't this looking at the problem from the wrong perspective. Rather than say 200lt at 50°C, if you calculate it as the effective energy stored, say 17 MJ, then within a tiny bit, a UVC and a TS, or even a traditional WH cylinder of the same size and the same temperatures, store the same amount of energy. If you extract water (energy) at the same rate, I am really (not being difficult) struggling to see the difference. Now you can 'average' the stored temperature out by allowing turbulence within the store i.e. constant pumping, but that is not the same thing.

Yes, and this is why I am claiming that sizing is important. There will be a slight temperature drop due to the heat exchanger efficiency, but that leaves more energy in the store. If space heating load is also being drawn off at the same time as DHW, then sizing is even more important.

Is there some sort of different physics going on then.

Those prices seem rather high, but a factor of 5.

Something like this, maybe. https://www.ebay.co.uk/i/324152361393

That is just sizing correctly isn't it. My cylinder is 200lt, heated to about 40°C. If I did the same with a 50lt cylinder, I would run out of hot water while filling a bath. Just sizing really, not temperature as such.

I genuinely do not under stand why they will not get 'hot enough', because of the type of cylinder/store.