ProDave

It really should not be frosting up much now. the worst temperature is just above freezing where the evaporator will be below freezing and the moist air will condense and freeze. Once you get a day or 2 of air temperature below 0 there really is little moisture in the air, and icing is very rare. -7 here last night and daytime high of -2 and hardly any defrosting.

Yes that spreadsheet, based on simply physics and some sums, is also pretty much bang on for my house as well. FAR better than the EPC which was fed all the same information that over estimates my heating usage by some margin. Today was one of those "good" winter days here, yes it was cold, but still, and clear blue sky, and plenty of solar gain from the low sun, and as good as it gets PV generation at this time of year.

What I was getting it is radiators or UFH upstairs, or as we have, nothing because the house is so well insulated. Flow temperature should be easy to find on the indoor control panel. You want that as low as possible, radiators upstairs may force it to be higher. DHW can usually be on a timer but if not it will just re heat the tank when it needs to. Keep DHW tank temperature down to no more than 50C, Many of us find 48C is the sweet spot.

Defrost mode is quieter than normal on my unit. But different ones may work differently. To defrost mine seems to do the following. Stop the fan and the compressor. Actuate the 4 port reversing valve. re start the compressor only, not the fan. Run for a minute or 2 until the evaporator has warmed up and thawed (presumably using a temperature sensor) Once the evaporator has thawed, start the fan, and a puff of steam comes out. Stop the fan and compressor Revert the 4 port valve Start the compressor and fan for normal operation. It is a surprisingly quick operation, but it does draw heat out of the house doing so (more correctly sends chilled water to the house while doing so) Mine makes most noise when it is running flat out, compressor and fan at maximum speed, which is usually in the latter stages of DHW heating when the cylinder is nearing it's set temperature so the flow temperature from the ASHP is at it's highest. Some basic questions: Who built the house and how well insulated? What heats upstairs?

For use under 11M which is most domestic buildings?

I would still put ALL the insulation following your green line so all insulation is at the roof level. but that only shows 35mm PIR which is way to little. I assume you will be insulating between the rafters as well, leaving a ventilation gap above it?

I would insulate the whole roof space as in all the insulation follows the line of the roof, easier to detail and you don't have to worry about a cold eaves space. Even better still if it is not too late for you is make it a warm roof (insulation on outside of trusses) really easy to detail and makes a very nice cosy house. This is one of the decisions I am best pleased with.

To adjust the temperature, turn the white valve just below the pump. You can adjust the flow rate through each loop, the flow meters are the two things on the top manifold, prise the red cap upwards and then you can turn the black part of the flow meter in it's thread to adjust the flow rate in each loop, so the one that is heating up too fast, reduce it's flow rate. Be careful you can unscrew it too far and screw it right out, then you get wet.

I can see why yo can't do much above the stairs, but there is no reason you can't insulate the wall below the stairs, that will be about half of it insulated. And a thick pair of curtains over that suicide door / window.

I am not sure the installer is asking the question clearly. There is an optical communication port on most meters, is he talking about that? Or is he suggesting you don't need to install your own generation meter as he thinks the smart meter can do that function? It won't, it will register how much has been exported but not generation, so Iwould fit your own generation meter regardless.

So you will be looking at essentially a petrol generator with an LPG conversion. You will need a proper generator changeover switch, not difficult.

Forget worries about damp. ICF is a good build method, just go ahead and fit MVHR and you will have a very good damp free house.

I better not say my ASHP used 50kWh in the last WEEK heating the house.

I do the same with a wireless operated 600W convector heater, for those times when the surplus PV is more than my immersion heater can absorb which seems to be about 2.8kW

It really sounds to me like it is ignoring the remote call for heat input, and when your heating is "off" it still tries to maintain a now very short loop of pipework up to temperature. I keep hoping someone that knows this particular unit will come along and help you check the settings to make sure it really is reading that input.

My concern is this does not appear to meet one of the basic requirements of a "caravan" that it must be possible to move it in some way. And the frame built so close to the ground level so it will be subject to rain splash which does not seem good. I fear we may have frightened @Tricky from replying? I do hope not.

This is the carrot. A small scale experimental scheme to pay a small number of people to not use electricity. The stick will come later when all those with smart meters will get charged more in peak times with no choice in the matter. Just my humble speculation. That is after all the agenda for a "smart grid"

Certainly on it's own pipe loop so you can reduce the flow in that room to ballance it? do I take it one pipe loop does the WC and some other part of that zone? Our last house, I made the "mistake" (actually the supplier that "designed" the system made the mistake) of a pipe loop and zone to the landing. That NEVER turned on, there was always enough neat from downstairs. Even the large entrance hall zone was questionable as that rarely turned on very little of that was an outside wall.

My LG ASHP when it is "off" will periodically start up the water circulation pump as an ante frost measure, to replace the cold water in the ASHP with something less cold. Is this what you are seeing? It typically takes less than a minute to do that.

The only thing I can pick out from that poor diagram in the manual is that it is expecting terminals 1, 2, and 2a to be used, you only have 2 wires. I wonder if it is expecting a changeover contact rather than an open / close contact? Other than that, if you are SURE the contact is opening and closing (measure the voltage between terminals 1 and 2, relay closed =0V relay open = some higher voltage) then it has to be some setting needed to tell the HP to use the external thermostat. What does the installer say?

42 degrees is not very high. Where are you and what is your outside temperature? The worst for icing up is a few degrees above 0. Is this a new system or has it previously worked okay in cold weather? Is the big air fan on the external unit blowing properly?

So you are putting as much heat in as you can constantly, and the temperature in the room has dropped as the outside temperature has dropped. So as @Radian said above you have reached thermal equilibrium and this is as hot as the room is ever going to get with this outside temperature and the UFH system you have. All you can really do is supplement it with some other heat source in the very cold weather.

What are the details of the building? Insulation levels, calculated worst case heat loss etc? As a trial, remove the actuator heads for a while, this will let all loops run at maximum flow rate uncontrolled, if that can;t put enough heat into the house then it never will.

My question remains HOW does the external controller "call for heat" from the heat pump? I would assume a wired connection probably to a volt free contact. I feel this is the bit not working but you have not provided any details yet of how the external controller talks to the heat pump to call for heat.

Yes I believe the case length is overall length, how deep the hole in the door needs to be, and backset is distance fromt he door edge to the centre of the spindle.