ReedRichards

There is "hard core" weather compensation and "soft" weather compensation. If you want go "hard core" then you fine-tune your weather compensation settings so that the house holds your desired set temperature without the aid of a thermostat and if you want to adjust the temperature, e.g. for a night time set back, you adjust the weather compensation setting to achieve that. Or you can do "soft" weather compensation where your weather-compensated water temperature is a bit higher than it would be if fine-tuned but you have more wiggle room, in particular the ability to warm up the house a bit faster. And you don't need to spend however long it takes to get the fine-tuning sorted. But you need thermostats.

I have not come across this formula before, do you have a reference? I don't know my flow rate, in fact I have two pumps so potentially two different flow rates, one from the heat pump to the buffer and one from the buffer around the radiators.

Hello @Garald, I was wondering what had become of you. I know nothing of FCUs but with a quick search online I could not find anything that did not look ugly and industrial. Surely with your classy Parisian apartment you would want something stylish in keeping with the decor?

Remember, the nearer you get to the "perfect" Leaving Water Temperature, the longer it will take your heating system to increase the room temperature. So you may need to be patient when running tests. Or you may want to reach a compromise between economy of operation and response times, it depends on the heating schedule you use. If you actually use Air + Water control this need for patience may not apply if the Load Compensation overrides the Weather Compensation in order to reach the set temperature more quickly (which I imagine it does).

I live in an old timber frame house. The exterior walls have about 100 mm of rockwool insulation but so, it appears, do all the interior walls. So in principle I could turn the heat off in some rooms and just reduce the effective volume of the house (provided I remember to keep the doors closed).

At 10 degrees outside my target water temperature would be about 37 degrees. If you really want to experiment, you should decrease your fixed temperature from 38 C to find out how low it can be and still keep your house at 21 C. If the water temperature is warmer than it needs to be then the heat pump is using more electricity than it needs to and so your running costs are higher than they need to be. "Weather Compensation" is UK terminology for a particular control feature commonly used by both heat pumps and gas boilers and intended to cause the heat source to operate more efficiently.

I've read that the Vokera AriaPRO supports OpenTherm - but their website isn't working at the time of writing this. If it does support OpenTherm it's the only one.

Isn't what you describe the intended function of a radiator valve once it reaches the set temperature? In my experience automated radiator valves are too close to the water pipes and the radiator to accurately determine the room temperature so you might need to compensate for this by setting the requested temperature to something a bit different to what you actually want.

@Transition do you know what (maximum) temperature your radiators were sized to work at? And what outside temp was assumed in the calculation? Or if you don't know those design parameters, have you ever yet encountered an outside temperature so low that your heat pump could not keep your house warm enough? Here it could get to -5 overnight in winter but only rarely would the temperature stay below -5 for 24 hours or more. It's only for an extended period below -5 that my heat pump might not have enough output to cope, at least in theory.

I have just radiators and a 12 kW (monobloc) Therma V. I assumed that my average radiator water temperature was 2.5 C less than the LWT. My heat pump is specified to heat the house when the outside temperature is -3.7 C the inside temperature is 21 C and the LWT is 50 C. So that's a temperature difference, inside to outside, of 25 C (rounded to the nearest degree). And a Delta T for the radiators of 47.5 - 21 = 26.5 C. I assumed that the heat loss from my house varied linearly with the inside to outside temperature difference and used a lookup table for how the heat output from my radiators varied with Delta T to calculate what LWT I would need for a range of outside temperatures between -4 C and 18 C. Then I found a straight line that gives a reasonable fit to what is actually a gentle curve. By coincidence @Ronny has a heat pump specified for the same operating parameters as mine so If I have calculated my weather compensation line correctly then it should work equally well for them. But it's only as good as the heat loss calculations for my/their house are accurate.

To use Air + Water control I would have to override my third party controller by setting it to make the room so hot that it is on all the time then setting the indoor Air temperature to be lower on the LG controller. I keep thinking I should try this to see what happens but I haven't yet been brave or bored enough to try.

You're a southerner from my perspective @Ronny , I live near Berwick-upon-Tweed. You are probably right that our climates are similar. I may be near enough to the sea for that to have some moderating effect on the outside temperature but I don't know. If my sharing my own experienced has helped you then I'm very pleased. Unfortunately I can only use the "Water" control mode, I don't know how "Air + Water" control changes things.

It shouldn't be a "standard". The LWT of 50 C was the choice of my installer. It was probably done on the basis that a few of my pre-existing radiators could not easily be replaced. 50 C was the maximum temperature for normal heating operation and it squeezed a bit more heat out of the too-small-but-fixed radiators. -3.7 C is supposedly based on readings from nearby weather stations and is intended to be an outside temperature that is exceeded for 99.6% of the year. I'm almost as far north as you can get in England, about 4 miles inland.

Just noticed that I posted a chart of my weather compensation line a while back:

And something you would have with any gas boiler paired with any controller (suitably wired together) if they both support OpenTherm.

If you still have these settings then you have a 17 degree range in your LWT for a 32 degree range in the outdoor temperature. So to be strictly accurate your target LWT will be greater than 35 C if the outdoor temperature is less than 18 C. I don't know how this is influenced by your indoor temperature because I don't use that mode of control. Also, I'm concerned that you say you control your heating by varying the AI setting. You can possibly do this if your system is perfectly "tuned" but if you are unsure about the correct settings then it seems to me that this is trying to run before you can walk. When I started with my heat pump I had AI off and experimented with what LWT I needed to achieve the indoor temperature I needed in winter. This and figures for how radiator output varies with temperature, and the specified minimum operating temperature in the MCS Compliance Certificate enabled me to estimate a weather compensation line that was more ambitious than the one originally set by my installer. Then I switched AI on and I've been running that for 9 months now and so far it has worked. Possibly I could be more ambitious still but I'll try what I have for a full year first. For what it's worth I have LWT temp auto mode 29 50 Outdoor temp auto mode -4 18 The heat loss calculation for my house were based on an outdoor temperature of -3.7 C and a LWT of 50 C so I used those for the lower limit.

Thanks @Transition. I have downloaded your uploads for future reference.

According to my installer, heat pumps don't generally have the modulation range of a gas boiler (i.e their minimum output is a larger percentage of their maximum output}. But it should be much easier to get a heat pump with a small maximum output matched to a well-insulated house than it is to get a gas boiler with a small maximum output. It seems to me that short cycling might be worse for the life a boiler that works via combustion compared to one that does not (i.e. a heat pump). I got my heat pump with a third party controller. Originally there wasn't the option to tell it that it was controlling a heat pump so I was advised to choose "oil boiler" which limited the number of cycles to 3/4 per hour. Now there is an option to select "heat pump" but it does the same thing.

Not this again; it's the basis of a lot of mis selling of IR heaters in my opinion. IR heaters will heat you directly if you are close by one but as a radiative source it follows an inverse square law with distance so if you are 2 metres away you get 1/4 the heat that you would at 1 metre, 1/9 the heat at 3 metres from the heater etc etc. The radiation that misses you will warm the solid objects in the room which will in turn warm the air. So in the longer term it may not make any difference if the heater is powerful enough to keep the room warm. In the short term it only works if you are near to the heater.

When we were looking for a house in 2018 we looked at one which had recently purchased infra-red heating panels that were suspended from the ceiling. Talking to the owners made me strongly suspect that these has been mis-sold on the basis of false promises that they were economical to run. In reality these would be no better than the two-bar "electric fire" I had to heat my room as a teenager. In fact they would be worse because they couldn't be moved according to where you were seated and did not have the parabolic reflector that my electric fire had. They put me off that house completely.

Yes, the Zehnder heaters referred to by @Dan F seem to me to be a type of water-filled radiator. But whereas conventional radiators are misnamed because they mostly transfer heat by convection, the Zehnder heaters claim to transfer heat mostly by infrared radiation so really would be radiators. When filled with cold water and suspended from the ceiling they would presumably just condense water and drip it on your head.

It's not an assumption. Any conventional heater converts electrical power to heat with 100% efficiency. Not all of that heat is necessarily useful, for example if you have electric UFH then (hopefully) most heat will rise and heat the room but some will go down and heat the ground. But basically you won't get more than 100% efficiency - except with a heat pump. Heat pumps do what the name implies, they pump heat from outside to inside your house and with a decent heating system based around a heat pump you can aspire to 300% or more efficiency, that is you would get 3 kWh of heat for every 1 kWh of electricity used. So the running cost of a heat-pump based heating system should be 1/3 that of the infra-red heaters you are looking at. Heat pumps tend to be expensive to buy and install; I have no idea about the cost of infrared heaters.

So even further from one end to the other than if it were a box. You'll need to take some pains to avoid long pipe runs for your hot water.

The Zehnder product video makes it look more like ceiling mounted radiators! Infra-red heaters are typically electrically powered and instantaneous which makes them the most expensive type of heating you can get.

I'm not sure an hour is an SI unit. There's an amusing article here: https://www.electronicsweekly.com/blogs/electro-ramblings/weird-wireless/weird-wireless-how-did-we-end-up-with-a-kilowatt-hour-2009-08/ . Personally I would rather have mega joules.