ReedRichards

Radiant heating, if the radiation is not focused, follows an inverse square law with distance so if you want it to heat you, you need to be close to the heater. Otherwise it mostly heats whatever solid objects it hits and these heat they air so the room warms up. But it's no more efficient than any other form of direct electrical heating, you get 1 kWh of heat per kWh of electricity. Electricity is expensive; are you sure this "closed family member" has your best interests at heart?

1000 litres is 1 cubic metre so a <1m2 footprint is feasible if it's >1m tall (depending on insulation thickness). But how are these 1000 l tanks used?

I held my tongue when I first read this but I can't help wondering how sensitive is this valve to orientation? I can see that flow in the wrong direction will tend to close the flap but the valve could be mounted vertically so that gravity, via the weight of the flap, could tend to open it. Could you reach a state of equilibrium where the valve remains slightly open and allows a little back flow or is that not going to happen? Or could it be so wide open that a sudden burst of reverse flow could fail to close it?

Assuming the flow temperature reaches 55 C before the heat pump gives up?

It is without doubt a load of old tosh. Either your installer did not know what they were doing or they knowingly did something wrong but don't want to own up.

Local demand at a price below the international market rate; you are fortunate indeed.

I think their units will be kWh per year. The kiloWatt hour is a unit of energy consumption and you will be billed for your electricity consumption expressed in kWh (or you are in the UK). Your current electricity per kWh cost is about half what we are paying in the UK. I hope your electricity market is regulated or suppliers may work out that they can make more money selling electricity abroad than domestically and that could push your price up.

So that gives you some warm water quickly but does it ultimately get the cylinder hotter than if you just ran the immersion heater at the bottom?

Putting aside the space considerations, if you pay 35% more for the more efficient heat pump, how long will it take to get that money back through spending less on electricity?

This fundamentally is not true. You just need one immersion as low down the tank as you can get it. The second immersion at the top is just for circumstances when you have run out of hot water and need a bit more. This probably isn't going to happen very often and when it does the chances are the sun won't be shining and you will use the ASHP.

My water tank has one immersion heater in the middle. But it has an integrated buffer tank at the base so that did not give me much choice. It turns out that there is a safety cut-out fitted to the tank at about the same level as the immersion heater. That is triggered when the measured temperature (as reported by the heat pump controller) is about 75 C and stops the heat pump from heating the tank. It's easy enough to reset but I don't want to keep doing that so even with a single immersion heater I have to make sure that the water at that level in the tank does not get too hot. A destratification pump would help but I doubt that a lower immersion heater would improve matters significantly.

Those large "American style" fridge freezers are pretty expensive and their volume is not huge compared to the volume of a typical dwelling. Scale up a fridge freezer by volume and an ASHP looks pretty cheap. The installation cost must depend largely on how much of the necessary infrastructure you have. If you are starting from scratch then central heating with a ASHP should cost much the same as central heating with a gas boiler except for the difference in cost between the boiler and the heat pump. You'll need a hot water cylinder with the heat pump whereas you might have a combi gas boiler and the radiators, if you have them, need to be larger surface area so a bit more expensive.

Back here in the UK even gas boilers are shifting to operating at 50 C output. Running your rads at 70 C flow is old fashioned and unnecessary, you just need finned radiators with a larger surface area for (say) 50 C flow.

I think most people have a blind spot to the benefit of running your ASHP at times of day when it's warmer outside. It seems very sensible to me but it's just not a "done thing" here, perhaps because the day and night time temperatures don't vary so much. Or perhaps because the only thermal store most ASHP owners have is their hot water cylinder. But why go to all the trouble and expense of making your ASHP perform at peak efficiency and then squander your savings on topping up the thermal store temperature with an immersion heater? And how are you dealing with DHW if not via the thermal store?

Must be some form of immersion heater. But not both at the same time. My ASHP heats water up to 60 C but only by taking control of my immersion heater for the final 5 C or so.

I don't think IR ceiling heaters are remotely smart. Now I did invent an IR heater attached to a drone so it would fly around and always keep 1 m away from me. That way I got the most benefit from the heat as I moved around the building. The drone noise was a bit of an issue but the main problem was that it kept strangling me with the flex. My next iteration will have an array of tracks on the ceiling and will work in the manner of an electric tram.

My hot water is off overnight then comes on at 6:30 at 50 C for showers. At 10:00 I drop the required temperature to 40 C and keep it there until 16:00 when it is set back up to 50 C. In both cases the "hysteresis" is set to 5 C so the water is not heated until it drops more than 5 C below the set temperature. All this is done using the scheduling function of my Therma V controller; you can choose your own times and values to suit If you wanted to wire-in another controller for DHW you would need a mains voltage to logic converter; somebody on this forum has done this. The main benefit of using another controller is that the Therma V controller does not have a 'Holiday' function and you need to delete (or modify) all programs in order to stop the DHW heating when away. At this time of year I use spare electricity from my solar PV to heat the water via my immersion heater. This is set to cut-out at about 72 C so on a sunny day I get enough hot water to last quite a while.

Only if your boiler is 100% efficient. It would be nearer 12.5p per kWh if the boiler were 80% efficient, perhaps a more realistic value. In which case if your ASHP could achieve an SCOP of 3 then electricity would need to cost 37.5 p per kWh to match the cost of oil.

An ASHP is NOT a drop-in replacement for a gas (or oil) boiler. Because their output temperature is (typically) 50 C or less you will probably need to replace most of your radiators, possibly add a few and replace your hot water cylinder (if you already have one).

At the end of 2020 I paid roughly the same for a 12 kW ASHP (LG), controllers, expansion vessels, buffer tank, 300l DHW tank, 12 radiators, radiators completely replumbed via the loft (instead of underfloor pipes). The vast majority of the time taken (2 people for over a week) was fitting the new pipes for all the radiators. My local plumber quoted more than this!

I would have hoped there was not much to go wrong; what happened?

I checked a few years ago and nobody nearby had a smart meter that actually worked. If I try to apply for one online from my electricity supplier (Eon.next) the link dumps me back at the overview page so I really don't think I can.

@SteamyTea A heat battery is cheaper than an electrical battery, kWh for kWh, so if the Sunamp product, or something similar, was cheap enough I would be tempted to get one. But I don't have a night rate tariff or a meter capable of running one so I could only use a Sunamp in conjunction with my solar PVs and it would only benefit me on a cloudy day or two following a day of sunshine (like today, as it happens). If there were 50 such days a year and i could save myself £1 each day then for me the payback period would still be too long.

Sorry, i should have written "order" rather than "specify". What i mean is, how do you ensure you get the right Phase Change Material when Sunamp seem reluctant to acknowledge there are different options?

So how do you specify one of those (instead of the standard product which has a transition temperature of about 56 C)?