Miek

In in South west Wales 40mm clean limestone is about £18/ton delivered. Assumes a 16t load. That's what the locals use for land drain round this way. Pea shingle is £25/t

The main problem is that the pump uses around 30-40W continuously. That's hard to maintain with PV. In the winter in the UK that's roughly 1kW of PV with battery back up to run reliably. Some systems use more power than this too!

What you are planning is possible, but getting a smallholding for the money you are talking limits you to the cheaper areas of Wales, and there won't be much land with it. You won't get a plot & land in Pembrokeshire for 150k! I'm doing what you are dreaming of in SW Wales and I'm at foundation stage. It's taken 20 years to be in a position to finance this. Wales is great, if you like shit weather most of the time . Remember that jobs here are fewer and lower paid than London by a long stretch. And given your age it's clear that you will be looking for work.

You might regret that when the MVHR packs up

The main issue will be fitting. PIR is far more time consuming to to fit tightly, which is important so as to avoid thermal bypass via the gaps around the edges. Mineral batts are far easier to fit. So how confident are you that it will be fitted well? Badly fitted PIR can have most of its better thermal performance wasted if it's done badly enough.

Look up the datasheet for the radiators. You can find the heat output for different temperatures and get an idea of how big you need to go. Obviously you need to know what temperature you are running your system at. The relationship between heat output and system temperature is non linear so you need to have a lot more radiator surface area than you might expect, toughly triple what you would need for a gas system running at 70 degrees C.

If the internals are non load bearing then they are usually built on top of the slab, with no foundation below, I can see your problem. I'd go back to the architect and ask for clarification. You could fill the trenches with concrete I guess.

My small 2kw Daikin unit had 10m of precharge gas. Perhaps look though the specs to see what suits. I found Saturn sales where helpful when sourcing a unit ( no affiliation) Longer pipe runs require extra gas so more tricky to DIY, but easy for an engineer, just costs a bit more

If you are attempting to use PV to run a stand alone system ALL year then you will be sizing it for Dec/Jan insolation (In the UK at least). You will obviously capture more energy if the panel angle is optimised for those months. About 75 degrees or so. PVGIS is the way so model these things.

Not all cells have this. If you can identify the cells then search for the datasheet you should be able to find out.

If you can get each parallel pack to accept charge it might recover somewhat. 4.2v is the max charge level per cell. If the cell jumps from zero to 3.6v that's fairly typical I think , just leave it on and see if it reaches 4.1 at least (4.1v per cell is 90%full), might take a few hours depending on your charger. If the battery does not have a BMS (quite likely) then even if you can charge all the cells up to 4.2 then the pack will probably become unbalanced again when it is cycled as the previously flattened cells will have an increased internal resistance.

Usually a cell below 2.5v won't recover. Sometimes you can charge a zero volt cell by temporarily jump starting the charger with a good cell (the charger won't begin until it sees is expected voltage from the cell). But this is usually done at individual cell level, so tricky to do in an assembled pack. I would check all the cells in the pack or at least every parallel string and see what the voltage is as a starting point. Does it have a BMS? (Battery management system)

Thanks @jamieled , I will bear that in mind when I get around to commissioning mine

You would be surprised. The vast majority of the power comes from the fan blade tip so it can make a big difference reducing diameter. You would need to increase the RPM to get the same flow rate.

Domestic floor? My spec was 150mm compacted sub base with a 100mm concrete floor covering. Insulation and screed on top of that.

Did you compact the ground before concreting? Over enthusiastic whacking can create a lot of outward pressure on the internal leaf, depending on soil type. Possibly the internal ground pressure pushed the wall out or cracked the block bond, and the oversite was the final bit of pressure and pushed the wall over. Just a thought. Weak mix cavity fill below DPM is typical and it is done in order to resist the soil pressure on the cavity. Mike

WTE sell the gauge for £17. I've got one but not used it yet.

To discharge to a ditch you need to contact NRW (in Wales) or the environment agency in your country, not sure who that is in England or Scotland. They grant permission if you can fulfill the requirements.

I've got the dewalt laser and detector, cost about 180 or so. Great tool. use a 30m class 1 steel tape for squaring. Detector is flakey when it's cold in or in direct sunlight. Really useful for drain run fall and foundation layout.

Depends how deep your going ? I'd hire a machine .

I would use 100mm square box minimum, 4 or 5 mm wall, galvanised and concreted in at in least 1m. A 6' gate is not that big a load but you might prefer the aesthetic of 150 or 200 box. A foot on the box is optional , you could plonk it on a pad stone.

I have a DeWalt laser and detector and I find that the detector doesn't work when it's cold (below about 5 degrees); and in direct sunlight it can be intermittent but that's less of a problem as you can shade the unit to get a result. Great tools for by building a house though!

It's really difficult to design an economical & reliable small turbine, really really difficult. Solar just wins the race. PV has dropped in price so much it's quite astounding. I remember when BP PV panels were about £5/Watt , PV is now about 20p/Watt!

You can widen the cavity to get passive standards very easily. A few folk on here building 300mm cavities, myself included.

Beads could also potentially settle over time ( I know they are coated in PVA or something to help them bond). Personally I feel batts are a more reliable method, and I'm doing a 300 cavity, but it's certainly attractive to simply blow in beads at the end and not faff around with batts.