ReedRichards

New build bungalow yet you have radiators rather than underfloor heating. That's a bit surprising. I suspect that new builds are the most likely type of dwelling to have heat pumps installed by people who don't really know what they are doing.

Your Ecodan has a nominal 11.5 kW of output. That's the same size as I have for my 1980 bungalow so it's a lot for a new well-insulated house unless it's a large one.

Heat pumps installed to MCS specifications are sized to provide sufficient heat 99.6% of the time at minimum (you may have some headroom). Look-up tables enable a calculation of an outside temperature that is exceeded 99.6 % of the time. If the calculation was accurate and your heat pump was sized to exactly match this specification then when it is 2 degrees colder outside than the specified 99.6% temperature then the inside of your house will fall 2 degrees below its specified temperature - and so on. Therefore it's possible you did nothing wrong except not leave yourself any headroom when sizing your heat pump. You will have to reconcile yourself to needing auxiliary heating during particularly cold weather. Gas boilers are usually greatly oversized for the demand of the building but have a greater range of modulation than a heat pump. So for a gas boiler cold weather is not such an issue and they may be able to modulate down enough to avoid cycling in warmer weather.

I don't have UFH, just radiators so I have no direct knowledge of how the controller works with UFH. In my case the top number in the top section is the temperature of the room where the controller is installed, whereas yours says "Lo". And the number before that is the same as the outlet flow temperature, as with you. I think the inlet and outlet temperatures are exactly as they say and are measured within the outdoor unit. My buffer tank has no electrical connections at all so I know it cannot report its temperature. Inlet and outlet temperatures both 43 imply to me that the buffer tank is at 43 C and there is no demand for heat. Sorry, I don't know enough about UFH to offer more advice.

I have an LG Therma V. Mine has no means of knowing what the buffer tank temperature is.

The table isn't right as such but the way you enter the parameters is correct. It's just an idiosyncrasy of the LG Therma V controller.

What about your hot water requirement?

Your understanding is correct, at 1 degree outside your target flow temperature would be 40C with those settings. By implication your system was specified to operate at a maximum 45 C flow temperature and your heat pump and radiators were sized so that the heat output would meet the demand (i.e. the building rate of heat loss) when the outdoor temperature is -4 (with whatever spare capacity was deemed advisable).

At these low outside temperatures your "water law" settings (if correct) probably won't make much difference because you would expect your heat pump to be running at close to its maximum output temperature. It's in spring and autumn when getting those settings right can save you money.

kW per annum is not a viable unit. You probably mean kWh per annum. The other evaluation you should make when installing a heat pump is the rate of energy loss at some specified outside temperature. For example the heat loss calculation made by my installer says I require 8.95 kW of heat to keep my house at 21 C when the outside temperature is -3.7 C. My worst case electricity usage, earlier this week was 65.84 kWh used in a day, so an average of 2.74 kW when the average outside temperature here was probably around - 3. In that context 2.74 kW seems remarkably good (the average temperature of my house is probably around 19.5 C as I use a night-time setback).

My ASHP is way too large to fit through the loft hatch and too heavy as well, I would think.

I replaced an oil boiler with an ASHP and I am very satisfied with the result. But almost all of my radiators were replaced with ones having a much larger output and two new radiators were added where there wasn't room for a bigger radiator. You were badly misled when advised that you did not need to replace your radiators and equally misled that running a heat pump at 55 C or more is a good idea.

Unless you are somewhere warmer than most of the UK, the outside temperatures are likely to be too cold for weather compensation to make much of a difference. In my case if the temperature outside is -5 or less then I'm outside the range of weather compensation and at anything below zero it makes very little difference.

I think you may be overreacting. If your heat pump keeps your house warm then it is doing its job and performing. It will use a lot of power in unusually cold weather and make up for this in spring and autumn by using much less power. Whether the economy of operation is good or bad depends on the heat loss from your property. The company that supplied your heat pump presumably made an assessment of this. It would give a context with which to assess your electricity use.

The settings are "LWT temp auto mode" and "Outdoor temp auto mode". Each setting has a pair of temperatures which you can change to suit your house. Auto (Ai) mode engages weather compensation. My settings are: LWT temp auto mode 29 50 Outdoor temp auto mode -4 18 This means if the outdoor temperature is -4 or less my target Leaving Water Temperature will be 50 C (which is my system max.) If the outside temperature is 18 C or more then the target LWT will be 29. At intermediate temperature the target LWT varies linearly with the outside temperature. So, for example, if the outside temperature was 7 then the target LWT would be 39.5.

Whereas I have a much larger 12 kW LG heat pump yet is has never (yet) used as much as 70 kWh in a day.

I puzzled over this. I thought maybe they were the hysteresis values for the air temperature when using Air + Water mode. So with the Type 0 setting the unit would turn itself on if the room temperature dropped 0.5 C below the set temperature and off if the room temperature exceeded the set temperature by 1.5 C. If so these would be end stops if it could not modulate to remain closer to the set temperature or if the water temperature did not get "out of bounds" first. The thing that you can do that will most influence the power consumption is to get the weather compensation settings to match the needs of your house. But if you are experiencing the cold weather that I am, then weather compensation probably would not make much difference at the moment. There's a long thread on your/our type of heat pump here:

You design the inside of your house for a heating water flow temperature of as low as you can manage and 50 C at maximum. You get a large capacity hot water cylinder that can be kept at 50 C or less and with a large enough coil that it can be quickly brought to temperature with water at 55 C. You install a buffer tank with 28 mm pipes between this tank and your heat source. Internally you don't use microbore pipes. You opt for an external heat source. Do all that and (I think) you have hedged your bets by getting a system that is compatible with a heat pump or an external oil boiler. You would need an oil boiler that is capable of low output water temperatures or it would short-cycle.

When I installed my heat pump two years ago I was buying electricity for less than 13p per kWh and the average price I had paid for heating oil over the previous two years had been 45.2 p per litre. With these numbers I expected the heat pump to be cost competitive with oil - and I think it was for the first year. Now electricity costs me 33.67 p per kWh whilst heating oil, currently is less than 90p per litre, I understand. So now my heat pump is probably cost competitive with mains gas but heating oil is the cheapest fuel you can get. Who knows what the situation will be like in another two years.

I'm sure it is very gratifying to find that your heat pump really can do the job it is meant to do and keep your house warm. Just don't read the meter to see how much electricity it is consuming at the moment. Yesterday I beat my personal record with 65.8 kWh in 24 hours.

@JohnMois an advocate of "hard core" weather compensation. This may be highly effective if you want to keep your house at the same temperature 24/7 but if you don't then the system can become very slow to change the temperature when you want it to. And your controller may not have the capability to change the weather compensation settings when you want to change the room temperature - which is what you would need to do. Personally I would decide how long I am prepared to wait for my main room the increase in temperature by, say one degree. I would have thought that 2 hours is the longest I would find acceptable. If it takes longer than that I would conclude that the high setting is too low and increase it by a couple of degrees. The end result would be weather compensation settings similar to those determined by @JohnMo's method but with water temperatures a bit higher (you would have to repeat in spring when its warmer out and change the low setting to suit). This won't give you the ultimate in low running cost but it will give you the capability to easily change your room temperature if you want to.

Which is good for heating your house quickly and making sure it is warm enough but not so good for your running costs.

Even if you had a fixed flow temperature without weather compensation, you would see a big difference between -5oC and 5oC outside.

Will it actually let you apply the settings either way round? You would hope there would be an error message if you got it wrong.

That's excellent. But if your heat pump is consuming a lot of power just trying and failing to get your UFH up to temperature then either it is keeping something somewhere very hot (giving rise to a poor COP) or there is some other type of fault giving rise to a poor COP. It doesn't make much sense.