ReedRichards

My MCS calculation specifies slightly different temperatures for different rooms. But a conservatory, if it really is a conservatory, probably needs to target a room temperature of around 5 C. That can't be too demanding for the heat pump, but maybe the calculation software can't cope?

I checked my LG Therma V monobloc and that 13 deg C appears to just repeat the number for the outlet water temperature (which is lower than my outlet water temperature ever gets). This is probably because I use a third party room thermostat so my heat pump doesn't know what the target room temperature is. Does the screen show "Outdoor unit operation"? That should appear a few seconds after what you see in the photo. Are you sure your heat pump heats your hot water without using the immersion heater?

As originally wired, my heat pump had sole control of the immersion heater. This meant that when my heat pump broke down (a filter blocked very soon after it was installed) then I could not use my immersion heater. I got it rewired to fix that problem; don't fall into the same trap.

This must be based on a price per kWh of electricity, an annual requirement for heating and hot water in kWh and an SCOP for heating and for hot water. You'll gain more insight if you break this down into these numbers.

Okay, @JohnMo, you're specifically considering trying to heat up a cold floor with a huge thermal mass. But, I presume, enough thermal conductivity that all the floor remains at much the same temperature. Does concrete/screed have a high thermal conductivity? I've always assumed that it doesn't, like stone. But if it manages to extract a lot of heat from the pipes then I suppose it must. Sorry, I can't work out your picture as it has no labels.

But I don't have a big delta T, why should I? When the heat pump starts up my radiators don't give out much heat so the return water temperature is only slightly different to the flow temperature. The gap widens as the flow temperature increases but it never gets more than the about 5 C or so that the radiators are balanced at. @JohnMo, you'll have to explain the mechanism by which you could get such a large heat loss as to give you a big delta T.

You're never going to have a fixed 5.8 kW hot loss, though.

That's not at all the way my LG heat pump works; it will ramp up to the set flow temperature without caring about the return temperature. When it gets to the set temperature it will continue at a fixed pump speed or an "optimum" pump speed or it will target a specified delta T between flow and return temperatures. And it does all this at a much much better COP than the 1.5 suggested above (unless it was very very cold outside).

Hopefully no one is disputing this. Except possibly @nodwhose earlier comment displayed a lack of understanding.

Either you have a new installation with a low-temperature gas boiler. Or you replaced your rads with larger ones at some time in the past. Or the rads were massively over-specified when they were installed to work with a much higher flow temperature than the 30-40 C you now use

Well if the system was set-up to operate with third party thermostats you most probably DO need them. You might ultimately be able to disconnect them when you have found your way around the controls but it's too ambitious to do this in the first instance. My advice would be to disable use of weather compensation and set a fixed water temperature near the high end of what your heat pump is capable of. This is not the most economical way of operating your heat pump but it removes a level of complexity and potential for error and therefore should give you a better chance of telling if there is a fundamental problem or not.

Would you set the heat pump at its maximum fixed leaving water temperature to do this?

A fact which I acknowledged in my reply. I've had a heat pump for 4 years now and warm radiators can provide all the heat you need.

My Atag gas boiler was installed in the spring of 1998 and it had both Weather Compensation and Load Compensation. From memory it was a 24 kW system.

This is entirely dependent on the size (I.e. surface area) of the radiators. Make that surface area big enough and they will be fast to heat a room, even though they don't get very hot. Make that surface area big enough and they will heat a poorly insulated house perfectly well. Or if you haven't got room for a radiator with a suitably large surface area, get one that is fan-assisted.