ProDave

Regarding DHW, be careful of over complicating it. I am heating HW to 48 degrees with the heat pump. Most of the time the HP does not need to defrost. However we had a 1 week cold spell recently with an average temperature of 0 and about -6 overnight. For the first time during that cold snap I did see the HP defrost when heating HW (I can confirm even at -6 it did not need to defrost when heating 37 degree water for UFH) the consequence of that is the HW for that week consumed 30KWh compared to a normal week of 22KWh. So it was using roughly 1KWh more per day either to defrost, or through a lower COP (probably a bit of both) I am shortly to be implementing a "boost" system using a modulating instant in line hot water heater. This is being installed mainly to cover those "oops ran out of hot water" moments, but it will allow the HW tank to run at a lower temperature with the electric heater boosting it as it is used. If you are going to use resistance heating then doing so real time heating just what you use will be more economical than heating the whole tank that last bit with the immersion heater. Once this is installed I will experiment with reducing the tank temperature during very cold weather to reduce or eradicate HP defrosting.

I would treat the buffer tank as a thermal store where the "heat in" and "heat out" are usually separate control loops. So the heat out is simple, whenever any room calls for heat, the UFH controller will have a "call for heat" output that will turn on a pump and / or open a valve and draw heat from the buffer. The heat input control will be in it's simplest form: whenever the buffer tank cools down, the tank thermostat will call for heat from the ASHP. That on it's own would be too simple as the buffer would be maintained 24/7/365 which you don't want. So add in a timer so the buffer tank is only being kept heated when the heating is on. In my house I have chosen only to have the UFH working only in the daytime, mainly because I want the house silent at night (the noisiest component of my entire heating system is the UFH circulating pumps) so that is controlled by a conventional central heating controller. That timed output could power both the heat in and heat out control loops so the buffer would only be heated when the heating is on.

I think the lesson here is don't just believe the instructions, actually LOOK at the thing and see if it really behaves as it should.

There are very many ways to tackle a low energy house and you cannot say one is right and the others are wrong. We are in the Highlands a little north of Inverness. We are in a sheltered glen far enough inland that the sea has little influence, and a couple of weeks in winter when it sits at -10 is not uncommon. I very much doubt any house would work well with no heat input at all in that so UFH is a must as far as I am concerned. I have opted for a small 5KW ASHP heating UFH downstairs only (and just bathrooms upstairs) and also doing the bulk of my water heating. Even if you only need say 3KW a little larger is better as it will run at a low level rather than running flat out. I find the heat loss from an UVC to be tolerable it seems they might generally be insulated a bit better than a thermal store but obviously not as good as a Sun Amp for instance. I will be fitting solar PV to try and cut down my electricity bill. So far space heating and water heating is a minor part of my electricity bill. Other "stuff" uses more, thinks like the dishwasher, washing machine, tumble dryer, fridge/ freezer etc. So anything that can help power those will be a big energy saver. The ability to use surplus to also heat hot water makes it even better. Solar thermal would not work for us due to so much shading from trees so it could not go on the roof. You can mount PV remotely from the house to overcome that, but solar thermal would not work mounted remote from the house. If however you are using solar thermal, then turn off any legionairs heating function, let the solar thermal do that. But we had a discussion about that and under certain circumstances there is no need to do that anyway.

I don't believe it is in Scotland, just that the door does not swing over the "activity space"

They work very well to let light IN. When viewed from outside at night they are just a faint glow so I don't think you will have a problem.

We found the 11KW instant shower in the caravan "poor" not helped by the incoming water temperature here in winter can be a lot less than 8 degrees.

We had ordinary timber joists and UFH with a biscuit screed upstairs in our last house. But definitely pleased we used posi joists in the new house. The vent pipes for the mvhr would have been a real challenge with anything else.

I will bet our shower flow rate form the UVC is at last 3 times that of a 7KW electric shower

According to this picture: The stairs are in place and so is the door. Not ideal but all you have to do is scribe the architrave around the newel post and you can keep the wider door.

That does sound a lot, BUT in the initial 24 hours is the heat up from cold of the sun amps, so the next 24 hours will be more representative of your actual usage. For us (as a comparison) we seem to be using a pretty constant 22KWh per week heating hot water with the heat pump. Even guessing an optomistic COP of 3 that would be 66KWh of hot water, so just over 9KWh of hot water per day. That's for 3 of us. It is probable less than that as I doubt the COP is much more than 2 when heating hot water (unfortunately mine does not even guess at what the COP is at any given time)

The general accepted norm is a recirculating cooker hood with a charcoal filter and the mvhr extract vent nearby.

The issue with a garage is the vehicle door. My garage walls and ceiling are insulated to the same standard as the rest of the house, except no air tightness membrane. It is still cold as heat leaks from the "insulated" garage door like it is going out of fashion. So I would say cheap rockwool type is all you need.

A resistance heater is to all practical purposes 100% eficcient.* But if you put 9KWh of heat into a tank, you will not get 9KWh of hot water out as some of it will have been lost to the room as standing heat losses. A Sun amp will lose a lot less of it's heat to the room. * this makes me laugh when you see some makes of electric panel heater claiming to be more eficcient than other makes.

Would in not be a whole lot simpler if instead of labelling them A and B or DHW / Heating, they just labelled them NO (normally open) and NC (normally closed) like a relay?

What about a house with a "certificate of temporary habitation" ? (possibly Scotland only) A self builder close to me reported being able to move onto ordinary insurance once he had that and I am hoping to do the same next May when the building site insurance is up for renewal. By then I should have a fairly complete house, but the en-suite won't have been done, a lot of rooms will be missing joinery e.g skirtings, window boards and quite possible even doors. But the big issue is the sun room (orangery) is just a shell with a roof. It will be some time before we have the funds to buy the windows to complete that. At the last renewal of the building site insurance I tried to negotiate a discount on the basis all the digging and heavy work was long completed and it was only interior work ongoing so the risks should be lower, but they would not budge.

Ours is the traditional UFH setup with 1 thermostat per room so for example in the kitchen I want the heating to go off when there is heat from cooking etc.

Glad it's working. You must have had a worrying moment until you found the stuck fan.

An important "feature" of an air tight house, is if you open one window or door, you get very little in the way of a draught even if is blowing a gale outside. So unless a thermostat is right by the door, I would not expect the temperature around a thermostat to drop quickly.

There are many ways to skin a cat. One thing that is clear in our house is the temperature will never change quickly. A cold night with the heating off is barely noticable, and when the UFH comes on, it only warms up slowly. I am finding (contrary to others experience) that an ultra simple mechanical thermostat set at 20 keeps the room comfortable all the time. I also have mine on a standard central heating timer so I can set the on off times of heating and hot water easily. That is partly so the house is dead quiet over night (the most noisy part of the heating is the UFH circulating pumps*) and partly for when we eventually fit solar PV to try and do as much of the heating in daylight hours as possible. * When I get around to it I am going to try swapping one of the UFH pumps for a different make to see if I can make it quieter

In our old house, the "1000 impulses per KWh" light flashes when exporting, but I checked that the usage reading was not counting up.

Those were the "rent a roof" schemes where you leased your roof to a company who paid for the install and collected the FIT. All you got was the free electricity.

^^ but the mortice is into the newel posts, you are not going to tell me that will weaken them?

From that article "under Ofgem licencing rules energy firms must pay homes the exact amount of energy they export if they have a smart meter. " So if you have a smart meter they are not supposed to pay you a deemed export figure of 50% rather they should pay actual export. How is that going to even work if your FIT contract is with a different provider to your supply? Bad news if you self use most of it. And yet another good reason to refuse a smart meter.

I just tried googling "Grid Trade Tariffs Available Through Solar Panel Funding" and it came back with 5 hits, all on foreign facebook pages, and when I followed the link, no sign of this advert.