Jeremy Harris

Yes, they have been on sale here for two or three years; the current model is the Powerwall 2 I believe. I'm not convinced that Tesla have optimised them for use here, though, as I've heard a few tales about them playing up in cold weather, failing to switch to charge mode and turning on internal heating elements that then drain the battery. I'm sure there will be, or probably are, over-the-air firmware fixes, but the stories remind me very much of the early days of Tesla cars, where they were released to the market full of bugs and had to be continually updated to fixed them. I'm not sure I like the business model of buying a partly-tested product and then having the manufacturer fix it through the first year or two of ownership, but have to say Tesla are far from being alone in adopting this approach, it seems.

I agree with @Declan52 and @Cpd, it doesn't sound as if you don't have a particularly well-sealed build, and that will impact pretty heavily on your heating requirement, unfortunately. I also think that the DG, rather than TG, will also have a negative impact on the overall heating requirement, and if the overall house insulation level matches the airtightness performance then you could be looking at having relatively high energy bills in cold weather. Knowing the EPC details should help us see whether or not your heating requirements can be met OK with the system you have, so getting that would be very useful.

Not sure if this helps, but I did my own building regs "full plans" submission, using LABC, and all the documents I submitted can be downloaded from here: http://www.mayfly.eu/2013/09/part-fifteen-the-site-is-finally-ready/ It may give you an idea as to what they need to see, although this will vary a bit with different build methods, I'm sure.

I'm afraid you're probably spot on with this observation. When I was looking around at ASHP suppliers/installers initially I was given some really wild options to meet our requirement. It was getting some barking mad specifications for systems, together with very high installed prices, that made me investigate buying and installing a ASHP myself. That turned out to be both a big cost saving and also a useful exercise in learning about the way heat pumps work in a real installation.

FWIW, I've found that our re-badged Carrier ASHP seems to modulate over a wider range than 30%. Input power seems to vary from around 700 W minimum, to around 1,800 W maximum (although the manufacturers maximum input power rating is 2,320 W). I've no easy way to accurately measure output power, but the rated maximum output is 7 kW and a rough calculation based on ∆t and the UFH flow rate indicates that the UFH tends to use around 2.8 kW when running. The ASHP rarely ever runs at maximum power for more than a minute or two; when running the UFH it throttles back to around 700 W to 800 W input within a few minutes of starting up and will just sit running at that level for hours on end, without defrosting. When I initially installed it I did experiment a lot with the settings, primarily because, as supplied, the settings were hopeless for the typical conditions we have in the southern part of the UK. The biggest problem was defrosting, which has a pretty big impact on efficiency, as the heat pump reverse-cycles to defrost. By experiment I found that the worst case for ice build up was at an outside air temperature of around 4°C to 5°C, when the RH was high (typical cold, wet, winter weather). As soon as the outside air temperature dropped below zero the icing pretty much went away and the performance improved markedly as the temperature dropped below zero. By limiting the ASHP flow temperature to 40°C maximum I found that I could restrict the heat output power to a level where the ASHP stopped needing to ever run a defrost cycle. Our ASHP is significantly over-sized for our heating requirement though, and this definitely seems to make a big difference, as by modulating the compressor and fan speed down it seems to operate with a high COP (always better than 3.5) in cold weather.

Sadly this doesn't work well, as an ASHP shifts a lot of air, many times the volume of an outbuilding per hour. Also worth looking at the variation in the amount of heat available in the air for a given outside air temperature. The heat energy in the air is zero at absolute zero, -273°C, so air at -10°C has about 3.5% less heat than air at 0°C, or about 5.3% less heat than air at +5°C. The effect of varying air temperature isn't that great, in terms of heat pump performance, at least until you get down to the lowest working temperature of the refrigerant used (typically around -20°C for R410A).

I don't know, as it was a closed panel system that was designed to meet the performance spec and be quick to put up. The inner panels are 12mm thick, and taping the joints after assembly looked to be much quicker and easier than fitting a separate VCL membrane, particularly as the surface of the inner panels is very smooth, because of the vapour sealant on the outer surfaces of the board.

Is having UFH that heats up quickly a significant advantage over having a system that just maintains a steady temperature? It's certainly a fair bit cheaper to just fit the UFH pipes inside a concrete floor slab, as the only additional stuff needed is the pipe and a bucket load of cable ties.

I fitted a battery powered programmable room thermostat to the heating system at our old house. It was pretty straightforward to just swap the old dial-type thermostat for the programmable thermostat, but it did mean terminating the now unused neutral in the back box, as the old dial thermostat had a small heating element to speed it up. If you replaced your room stats with these, you could then just leave the main programmer on all the time (sound like it may be like this anyway) and you could programme temperatures and times, including off periods, using the programmable room stats. A search for "programmable room thermostat" will throw up lots of these, usually around £50 each for a reasonable one.

I don't think it relates to the heat source, so much as to the design and layout of the house. For example, our primary heating is an ASHP running UFH in the ground floor slab only. The effective heated area of that slab is about 75m². We have no heating upstairs, apart from heated towel rails in the batrhooms, of which only one is used normally, and then only for a couple of hours in the early morning and again in the evening. We have a central hallway that is about 2m wide, 5m long and 6m high so extends right up to the doors that lead to the bedrooms on either side. The UFH in that hallway is undersized for the volume of space it's heating, deliberately so, as we didn't want the upstairs to get too warm. With the ground floor surface running at around 23°C in the rooms either side of the hallway, and around 22°C to 22.5°C in the hallway itself, we find that we have a comfortable temperature in the living rooms (around 22°C to 22.5°C) and a temperature in the bedrooms of around 19°C to 19.5°C. It's very much personal preference, but we like the bedrooms to be a bit cooler than the living rooms. I did fit FCUs in the bedrooms, together with ply backing boards behind the plasterboard, so that it would be no more than an hours work to fit thermostatic panel heaters in the bedroom, if we every feel we need them. I'm inclined to the view that we probably won't ever need them, but the cost of fitting the additional cable and outlets during the build was trivial, probably less than £10, so they are cheap insurance for things not working out as planned. On the subject of MVHR, then I think it's important to reiterate that normal, passive, MVHR will always cool rooms down in cool or cold weather. The air supplied by the fresh air feed terminal will always be colder that the room temperature, not by a lot, but still cooler. During the cold spell recently we were seeing a MVHR fresh air supply temperature of around 18°C with the MVHR running in passive mode. That certainly helps to keep the bedrooms cool, given that the only source of heat to them is whatever leaks up through the (insulated) floor from the rooms below, or comes up via the hallway and landing.

It's buried somewhere in either the Carrier or Glowworm installation manual I think, where minimising noise transmission by using long hoses is mentioned. Looping them works perfectly I found, as we can't tell from inside the utility room whether the ASHP on the other side of the wall in running or not. The only way we can tell is to look at the command unit display.

No, the TRV is the right way around, it's the lock shield that I think needs to be the other way around (although I'm not sure it makes a difference). From what I can remember with valves with an angled stem, the flow should come in towards the bottom of the washer that closes the valve.

Welcome. Sounds like an interesting problem. As you say this is a closed panel system, presumably it was manufactured off-site as prefabricated panels, is that right? If so, then what does the closed manufacturer have to say about the problem? I looked at an MgO closed panel system a few years ago and have to say it looked pretty good, my only concern was traceability of the MgO boards, as the manufacturer was bringing them in from China and I wasn't 100% convinced they had the proper BBA certificate. The only thing I can remember that may have a bearing on your problem is that MgO boards need very rigid fixings, made from materials that will not corrode (because of the possibility of chlorides coming from the panel material if it gets damp during construction). The need for very rigid fixings seems to be associated with the need to try and limit movement from thermal expansion. I've certainly heard of thermal expansion causing problems with MgO boards, but usually bowing off the wall, rather than cracking along the joints. Cracking sounds to me as if the fixings may not be adequate, perhaps. There are special screws for fixing MgO that are both corrosion resistant and have a sharper angle under the head, with little nibs to ensure that they countersink properly. Were these used to fasten the boards?

I'm pretty sure that the lock shield goes the other way around, so that the flow direction is towards the seat where the internal rubber washer seats.

Read it again, in the context of the heading of that section that you failed to quote...

OK if allowable, and our preferred option, but the planners wouldn't countenance it. They wouldn't even let us fit more traditional looking wooden shutters.

FWIW, in the 18th Ed, what were safe zones are now prescribed zones, although AFAICS nothing else has changed. Wiring in walls within prescribed zones does not require metal capping or additional mechanical protection, nothing seems to have changed for a fair while in the regs. The section from the 18th covering this looks much the same in terms of general requirements as that from the 17th:

They can be directional, so the arrows should align with the direction of the flow. I've fitted a TRV the wrong way around and it did work though, although having taken one apart I can see that if fitted the wrong way around then there might be a tendency for the flow to want to close the valve.

Seems very high to me. IIRC we paid LABC somewhere around £700, for a full plans submission with build inspections (no warranty though).

It's probably one of the daftest ideas I've heard of. The idea of hiding wiring behind something that is outside the approved safe zones like this should be outlawed. It's one thing to run wiring outside safe zones within surface mounted trunking or conduit, where it's obvious that wires may be present, but quite another to hide them behind something that no one would suspect has wires behind. FWIW the safe zones on a wall are vertically above and below any switch or outlet, horizontally between switches or outlets or horizontally behind the top edge of the wall. Running cables under floors and in ceilings is also OK. Worth noting that safe zones on stud walls extend right through the wall, so expect wires on the opposite side of a wall too.

Yes. All that's needed is to tape the joins and make sure that the insulation foil faces don't get damaged (no harder to do than making sure any other membrane-type VCL doesn't get damaged). Care needs to be taken with detailing around the edges to make sure the VCL is contiguous, but again this isn't any more difficult that using a membrane-type VCL, or any different to using a panel-type VCL come to that.

The VCL is what it says, a Vapour Control Layer. It can easily be a part of the fabric and doesn't have to be a separate entity that's added on as an afterthought. Take our build as an example; our VCL is an inner frame racking skin of Spano Durelis. In an EPS ICF construction the VCL may well be the inner layer of EPS. With wood/cement fibre ICF construction the VCL could well be a cementitious parge coat on the inner face, before plastering. A VCL doesn't have to be totally vapour impermeable, it just has to have a permeance that is significantly lower than anything within the build outside it. The name gives away exactly what it does, control vapour movement, not necessarily completely block it. Finally, as ICF is a sandwich that may well have a significant amount of insulation on the inside as well as the outside (some ICF seems to be almost 50/50) then the concrete core is going to tend to sit at a temperature part way between the inside and outside temperature. Concrete is a relatively good thermal conductor (around 1.5 to 2 times more conductive than water and around 25 times the thermal conductivity of something like EPS) so it's likely that the core will be at a reasonably even temperature through its thickness with the greatest temperature gradients being through the insulation on either side.

The house will have to have a VCL, and that will be on the inside face of the structure, and that should be airtight as well as being vapour tight. It worries me when we see poor construction allowing cold air in behind dreadful dot'n'dab plasterboard, as it's not the dot'n'dab that's really the problem at all, it's that the builder hasn't ensured there's an effective VCL. Houses like this are going to have interstitial condensation problems, I'm sure.

Down here it looks like it's going to warm up a lot tomorrow. We had forecast temperatures for this morning of -6°C, (although we only saw about -3°C), but the forecast is for the temperature here to rise to around 10°C tomorrow lunchtime.

Just parge coating Durisol should fix that easily enough I'd have thought. Pretty quick and easy to do, just need a bucket and broom.