ReedRichards

UFH is always slow to respond so you will need to keep it on most of the time. If it follows the same timings as your rads then it may not be on long enough and that is why its not getting the rooms warm enough. But if you make it stay on for longer you won't get the economic benefits of running the UFH at a lower flow temperature because that flow temperature has to be whatever your rads need.

Is your system smart enough to reduce the flow temperature when the UFH is calling for heat but the radiators upstairs are not?

My LG heat pump lets you manually move the weather compensation curve up and down by 5 degrees either way but this is a manual adjustment, it's not programmable. AFAIK only a small minority of heat pumps would let you program a change to the weather compensation settings at particular times.

I used to have an Atag gas boiler in my old house (now I don't have mains gas). I really liked it and it was way ahead of its time when I got my first one in 1998. However since it did both Load Compensation and Weather Compensation there was no need to set the room thermostat at anything other than the temperature you wanted because it would modulate the output to maintain that temperature very precisely. It was not thrown by TRVs elsewhere in the house. Using a thermostat as a "limit stop" is effectively abandoning the use of the thermostat and to me that is hard core. I use my thermostat to gradually increase the house temperature during the day and then set it back overnight, something difficult to do unless you have a controller that allows you to program multiple changes to the Weather Compensation settings (which few of us do). This may cost me slightly more than the thermostat-free Weather Compensation advocated by Heat Geeks, although I'm not sure it does.

The Heat Geek website preaches a very hard core style of weather compensation. You can still use weather compensation to reduce your running costs without abandoning the use of thermostatic controls. And when it's very cold outside, weather compensation will make the least difference.

How do you measure the heat output?

Panasonic have a wireless room thermostat that works with some(/all?) of their ASHP models. Maybe that could be used to talk to the controller and override the controller's internal temperature sensor?

So what does it mean when the curve reaches an impossibly high target flow temperature?

-7°C must be very rare on the Isle of Wight, in which case you have probably gone off the end of your weather compensation curve and 43°C must be the maximum heating setpoint.

Your heat pump needs a heater or a heat source to defrost. So an easy option is to use the warm water in the buffer vessel as the heat source.

That's what I have. If you installed a heat pump during the latter years of the RHI you were obliged to have a dedicated electricity meter for the heat pump. But I can only measure the electrical energy in, not the heat out.

I think what your wife is actually complaining about is the fan. Blown air will dry you (or the clothes on a line) much faster than still air. In summer a fan is cooling because it blows away the moister air close to your body so your skin can evaporate more sweat, which cools you. With a fan heater blowing air over you, you get the same drying effect but because the air is hot you don't notice the cooling. But you may feel the drying.

This is from an Ecodan brochure explaining the capabilities of the Wireless Remote Controller and Receiver Accessory. I did a copy and paste but the formatting was lost; the original is here: http://library.mitsubishielectric.co.uk/pdf/download_full/798

There's terminology. If the controller works by adjusting the leaving water flow temperature (or perhaps it's the return water) according to the outside temperature it's called Weather Compensation. A lot of heat pumps and gas boilers can do that but its more effective in reducing the running cost with a heat pump than a gas boiler. If the controller adjusts the water flow temperature according to the difference between the setting on the room (i.e. house) thermostat and the actual temperature in the room it's called Load Compensation. For economy, the benefit of Load Compensation is that it enables the heat source to modulate down its output when the room temperature is close to the set temperature. A lot of gas boilers can do this and some heat pumps, but in the case of heat pumps, only if you use the manufacturer's thermostat. I'm not sure if this terminology is used outside the UK. Consequently, foreign-made heat pumps may use their own terminology but for the same two types of control.

You need to allow the heat pump time off from heating your house to allow time for heating your hot water and for defrosting in cold weather. My heat loss was calculated to be 8.95 kW at - 3.7 C. But if my heat pump takes two hours a day off doing other things then it only has 22 hours with which to heat my house so the output capacity I would need would be 8.95*24/22. In actuality I got a 12 kW heat pump.

I strongly suspect that the more common opinion is that you should do the heating calculations. You will doubtless be encouraged to do those yourself but there's no shame if you choose to employ an expert to do them for you. You don't want to end up with a heat pump that is smaller than you need and there are disadvantages to getting one that is significantly larger also.

What I gathered is that some but not all Ecodans have a standby power consumption so high that you would want to consider strategies for turning them off when you don't need heating. Some other makes of heat pump may suffer the same issue but other heat pumps have a reasonable level of standby power consumption that you wouldn't worry about.

How enclosed is the courtyard? Is the air in the courtyard still or does the wind whistle through it? Even if you can overcome the problem of getting sufficient air flow through a grille in your door, you could end up just cooling the courtyard if it is too enclosed. That wouldn't make your heat pump inefficient and you wouldn't be very popular with the neighbours.

But your ASHP efficiency depends on how hot it has to make the water. So having to make the buffer even hotter than the heating water must hit efficiency, surely?

Well it's nice and simple but can you do a night time setback? I don't want my house to be at one constant temperature for 24 hours; perhaps you do? Then if you did have a setback then the rads would recover faster than the UFH so that might be awkward.

Does this work? It looks to me as if when neither the cylinder or radiators are calling for heat then there is no supply of heated water to keep the UFH up to temperature. Perhaps there is an invisible buffer in there somewhere or I am misinterpreting the drawing?

Could the graphite be a lubricant, helping the polystyrene spheres fill the cavity rather than getting stuck somewhere and leaving some of the cavity unfilled?

You may have heard that UFH and an ASHP is cheaper to run than radiators and an ASHP. This is likely to be true because you typically need a higher water temperature for the radiators than for the UFH. Unfortunately a combination of UFH and radiators is no cheaper to run than all radiators. That's unless you have a sophisticated system that can work out when the radiator zones are not demanding heat and then reduce the water flow temperature. I doubt that your Grant heat pump is capable of that and if it was it would need to be using its own controller, not your Honeywell system.

Does your Honeywell Home Control know that it is controlling a heat pump? Controllers usually have a setting for "heat source" although it can be hard to find. If there is no option to set heat pump, the next best option would be Oil Boiler. This should force your controller to use a minimum cycle time of 15 or 20 minutes so if the heat pump turns itself off after 10 minutes then the controller won't allow it to turn on for another 5 minutes or more. That will limit your cycle time.

25 kWh per day is not too terrible, it's about the same consumption as keeping a 1 kW fan heater on all the time but that is keeping your whole house warm(ish). For comparison, my worst monthly average was 27 kWh per day for last January and I keep my house at about an average of 20 C during the day. But different houses can have very different heat requirements so a comparison with somebody else means very little. How were you heating the house before you got the heat pump and how much energy did that use? How do you control your heat pump? Do you use a third party programmer or is it the one Grant supplied? Your heat pump will cool the surrounding air and this will cause condensation inside the body of the heat pump. Ideally this would be piped to a nearby drain but in the absence of any drainage system it will drip onto the patio slabs. If your brickwork remains dry then it's probably not an issue but if your house bricks get damp then I think something needs to be done.