ReedRichards

I do not agree. Some electricity generators cannot be turned off quickly so we tend to have surplus electricity overnight, hence Economy 7 tariffs. Although electric cars may cause this to change, AFAIK they have not done so yet in which case you do not have to burn extra gas to charge them overnight.

I'm on the SVT tariff for single rate electricity and I am paying approximately 34 p per kWh (including VAT but excluding the Government discount scheme).

I got a heat pump in December 2020 at which time I was paying 13p per kWh for my electricity, now I pay 33.76 p per kWh (figures include VAT, exclude Government rebate). The average price I had paid for my heating oil in the two years or so prior to 2021 was 45.19 p per litre (average not weighted for quantity). Now heating oil is somewhere close to £1 per litre, I understand. So the balance has certainly swung in favour of heating oil since my heat pump was installed; oil has gone up in price by a lesser percentage than the cost of the cheapest electricity deal available.

The lower the water flow temperature and the larger your pipe spacing then the lower will be your heat output per square meter of floor. What will work depends on what you need. By chance, earlier today I came across this table: https://www.tradingdepot.co.uk/info/plumbing/polypipe/underfloor-heating-heat-output-tables/ It doesn't help directly because it does not go down below 40 C flow but it gives an idea of the dependencies.

My neighbours are not nearby. it's behind the kitchen and audible inside the house only if you have the kitchen window open. Although the noise is different, I don't feel it is any louder than the external oil boiler it replaced. Seems fine. No issues after the first week (it stopped after 24 hours with what turned out to be a blocked filter; a "known bug" as it turned out). It just works. The controller lacks a "holiday mode", which is a bit annoying. Yes, although I agree that the design of what it is feeding is more important than the heat pump. It does not seem to suffer from the high standby power consumption of some heat pumps.

Paul made one post and has not visited since 4th September. You might get a better response if you pitched the question more widely, @thefoxesmaltings

There is an important feature of heat pumps which in the UK goes by the name of Weather Compensation. It means (if I understand the french correctly) "Les températures d’eau sont calculées en fonction de la température extérieure (intégrée à la machine - loi d’eau)." When it is warmer outside you don't need as much heat from your radiators. So the target temperature of the water leaving the heat pump can be reduced, which makes for more economical operation. The heat pumps in your literature lay claim to this feature but I cannot find how to engage/disengage it or how you would change the compensation curve/line if required. There is another useful feature termed, in the UK, "Load Compensation" which is basically the same as PID ( https://en.wikipedia.org/wiki/PID_controller ). Again I have not found any documentation on this feature. This lack of documentation is not that unusual. My installer had to send me a copy of a training manual he had for fuller instructions on my LG heat pump; they were not supplied as standard.

No, I don't think so. That looks like the Installation Instructions; I don't see anything about how to operate the heat pump when it is installed.

The Technical Dossier doesn't seem to offer any help with regard to ease of operation. You need to track down the Operating Instructions.

Different models of heat pump have different ranges of modulation. I have observed that my 12 kW heat pump seems to be able to modulate down to 2 kW and then upwards in roughly 0.5 kW steps but that was just on one particular day when I was watching it closely. Of course you can regulate the radiators but that will reduce the demand for heat (although possibly not by as much as you would think) so require greater modulation ability from your heat pump. I have not looked at the heat loss model you are using but you must have to assume an outside temperature to calculate a heat loss. In principle my heat pump can match the demands of my house for heat and hot water at -3.7 C with a little bit of headroom. So if it was -10 C outside I might find that I could only heat my house to 16 C instead of the normal 21 C; in which case I would have to light the stove. But when it's +10 C outside, my heat pump can provide the necessary heat without having to cycle on and off too much

If you put in too many radiators or size them for an outside temperature you very rarely encounter then you will need a bigger heat pump. This will cost more and you may find that it has to cycle on and off a lot of the time when it is milder outside because it cannot modulate down low enough to give you just a little heat continuously. Conventional wisdom is that this is a bad thing. My heat pump is sized to give me enough heat at -3.7 C, which in my locale is a temperature achieved 99.6% of the time.

I am fortunate in that my installer did all the heat loss calculations for me (using some software called Heat Engineer). The biggest "room" in my house has a floor area of 48 m2 and was calculated to require about 2.8 kW of heat when it was -4 C outside. Yes indeed; just make sure your installer flushes all the gunk out of it before it is relocated.

Running a heat pump in the night will minimise its efficiency of operation because it is colder at night than during the day. But if you have an Economy 7 tariff or similar it would be worthwhile. In winter I leave my hot water heating on from 06:30 to 22:30 with the temperature set to 50 C; this is to ensure I have hot water whenever it is needed. In summer I heat the cylinder via my solar panels on sunny days.

You can buy steel radiators much more cheaply than 650 euro but if you want them to be the same style as your existing radiators I don't know; I'm sure those will be more expensive. Yes, that's exactly the right idea. In my case I had a towel rail in my bathroom already but added an extra radiator to make the room warm enough. Yes it does. You need to click to view the full specifications: That's 2561 Watts at delta T = 50 C and, as you correctly observe, 0.41 times this, 1050 Watts for delta T = 25 C (sorry about the error in my earlier comment).

I concur that adding fans to existing radiators may well be a more efficient way of boosting the heat output to your house than the alternative of turning up the maximum temperature on your gas boiler so the radiators run hotter.

Don't get it into your head that there is such a thing as a "low temperature radiator". All you need is an ordinary radiator with a large surface area. The radiators you already have probably have quite a high output (and some of the more modern styles would look wholly out of place in your apartment). The one in your style that I Iooked-up appears to have an output of about 2 kW per square metre at delta T = 50 C which would be about 400 W per square metre at delta T = 25 C. Maybe you can move some of your existing radiators around so you don't need a complete new set? Or perhaps some of them are so over-specified that you can use the ones you have?

How old are the radiators you have now? Do they have internal fins to increase the effective surface area? Could you cope with "fat" radiators that protrude almost 20 cm off the wall? I ask because some of my new "low temperature" radiators occupy less area than the old ones they replaced. The old ones were were just double panel (c 1980) and my new ones are mostly double panel double fins with a couple of "fat" triple panel tripe convector types.

Fans enable you to get more heat out of a radiator of a given size. But this is not "free" heat, your boiler or heat pump will have to work harder to supply it. As gas prices are high, this extra heat will be more costly than it used to be.

If you know why a high temperature heat pump is less desirable then I don't see why you are asking the question. You will have to pay an extra 5k but you will eventually recoup that investment through running cost savings. The only reason against would be if you could invest that 5k and generate enough income from the investment to pay the extra running costs. That seems unlikely unless your expenditure on heating is very small. And you would have to persuade your contractor to leave things as they are and hope that that works.

A monobloc air-to-water heat pump that can be installed indoors? How does that work? It's fundamental to the physics of heat pumps that a high temperature heat pump will be less efficient and so more expensive to run than one that operates at a lower temperature (all else being equal). My one regret over getting a heat pump is that the target water temperature (50 C for my system) is too high and I should have made it a bit lower with even bigger radiators.

If water is circulating too slowly the temperature drop across your radiators will be larger than specified. For heat pumps the specified temperature drop is typically 5 C; I presume this is just so the average radiator temperature does not fall too low. On the other hand there are modern gas boilers that seem to target at 50 C flow and 30 C return so a much larger temperature drop requiring radiators with a larger surface area. I don't understand why there should be such a disparity between low temperature gas boilers and heat pumps.

Quoting a reply about this on another forum:

I have a third party controller with my heat pump, similar to the Nest, and it does not stop me using Weather Compensation. When the third party thermostat calls for heat, the heat pump comes on and uses a maximum output water flow temperature that is set according to the weather compensation curve. This doubtless means I need a Weather Compensation curve a tad higher than if I was trying to do it thermostat-free but I doubt that it will make a huge difference. This is called "Load Compensation". That, regretfully, I cannot with my third party controller because the heat pump does not know the desired room temperature. There isn't the equivalent for heat pumps to the Opentherm control system for gas boilers that would allow you to do Load Compensation with a third party controller. But I think if you use Ecodan's own controller you can have both Weather and Load Compensation.

That may well be true. The OP is trying to keep their house warm with no heating on the second floor and finding that the heating on the first floor is insufficient; cause and effect? If so, then the heat pump will be on all the time, struggling to get the house up to temperature using fewer radiators than was envisaged, having to raise the output water temperature to try to do this at the cost of degraded efficiency. If it was winter now they could observe the heat pump to see if this seems to be true. On the other hand, the although the COP figures are reported to be very poor, the actual electricity being consumed seems to be broadly what was predicted. So the most fundamental problem is that the house, or some of it, is not warm enough. What should the OP do? I would begin by setting the flow temperature to a fixed 45 C (as per the MCS spec) turn on all the radiators and check that the house is as warm as they want it to be. It's relatively mild out so the heat pump, set to 45 C, should cycle. Then reduce the set temperature until the heat pump is on the majority of the time but the house is still warm enough. Check that the new set temperature is broadly in line with what the weather compensation, if engaged, would set. If it is, that may well be that, engage weather compensation and everything should be fine. If not then the weather compensation settings would need to be reviewed and altered. Do you agree, @JohnMo ?

No, I was reiterating it but adding a dash of scepticism. For as long as I could program a room temperature (about 25 years now) I have made it cooler in the morning when I'm active, edged the temperature up during the day so it is warmest in the evening when I tend to be more sedentary, then set back the temperature overnight. To my mind this is the most desirable pattern of use for any form of heating but those Heat Geeks don't even countenance it. When the starting assumptions are wrong, and they're wrong for me, then this makes me sceptical about the conclusions.