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100A should be plenty. 100A = 24KWish You are obviously looking at single phase so the biggest EV charger for single phase is about 11KW. 3-phase you can get 22KW ones but your EV has to support it. Assuming you have electric cooking and are not having instant electric water heating/showers it seems like you should be able to have pretty much everything on at the same time without much difficulty. That is not how things are usually planned, it's assumed that not everything demands power at once and if you do get tight you can set the EV charger to charge at times when you are not in the workshop. If you want more than one EV charger either get smaller ones (which are likely all you need anyway unless you do a lot of miles every day) or you can get ones that can share a limited feed, ie you can program them so that they don't draw more than X between them.

Butting in where not asked but I thought the idea was its the same material. Less likely to get a path for water to get to the rebar and cause rust problems. Whether that really matters on a slab wrapped in plastic like @Duncs I've no idea.

It really doesn't seem like this is enough to spend an awful lot of money on. Deploying a 15KW single phase inverter/battery combo will be more expensive than generator but will be silent and if you add solar might start paying for itself, making it 3 phase adds cost*. 30kwh of battery doesn't cost much these days (Fogstar, Pylonttech, etc) and would likely keep you going for hours if you allocated the additional 20A you are getting from UKPN from your upgrade to supplement the battery. Victron can definitely work in a way that it limits draw on a grid/generator to a set number of amps and provides the rest from the battery. Still a generator would likely be cheaper. * Sounds like you'd need a new electric compressor anyway. Chinese VFDs are cheap these days to convert existing machines if you have the knowledge or know someone that does, though not all machines are easily convertable.

Does cash mean no documentation? What about tagging and liability? Scaffolding can get people badly hurt, want to make sure you have a safety paper trail for that.

Edit: replying to Roger Peak load and continuous are usually quite different (and by this I mean the continuous load when you are actually in the workshop). Inverter/battery system could easily act as a buffer and smooth out peaks. If the 55A is motor start load, then soft start or vfd reduces that a lot also. How big is this compressor? What are you doing with it? 10HP compressor/7500W should do 40-50CFM continuous. That's a lot of air to use for one person. An awful lot of workshop tools are now available in battery versions that are easily equivalent to the air versions and use a lot less power. (Air power is 50% efficient at best, battery ~90%). The 18V tools can deliver many KW power to the tool during use. Obviously there is a cost to buying them but the cost of a generator or inverter system is also high.

As @JamesPa pointed out (and I forgot), if the heating system is designed as a low temperature system (as a system should be in a good quality well insulated house) then its not like the water will be very warm in the first place. So if you want warm towels, skip hooking it up to the central system and just use electric with timers for when you have showers.

I'll leave the main system design for others to comment on (lots of experience here). But: Why not put in towel radiators with water loops + electric heater. In winter, use the main system, in summer use electric if needed (doubt you'd need it much so putting in something that doesn't cost much to install but costs a little more to run if needed makes sense)?

That is my point. The system is running off single phase and transferring the energy between phases (via the DC battery bus). Lose a bit of efficiency but as long as total draw is below the input capacity of the inverter connected to the mains minus the efficiency loss it should run forever. The battery also proivides a reserve for temporary load spikes above the capacity*. Would want soft start on equipment though I'd guess. Anyway I'm not 100% sure Victron can do it but I thought I saw it mentioned in their docs. I know people do similar using big VFDs (instead of one per machine, get a big one and have it generate 3 phases for the shop). But I believe that has downsides, you absolutely need to understand the details and wouldn't be a recommended route. *The Victron Multiplus series can generally run at 2x rated for short periods without sweating. If your compressor is the main draw, why not put it on a VFD and run it off single phase? Even if you put in a way to generate 3-phase for everything else, at least it would reduce the overall load on that system saving cost.

TerryE sounds right. Had a quick search and couldn't find anything though.

joe90 maybe? I remember something about rebar ties between the exterior (uninsulated) brick support concrete and the main slab creating a thermal bridge. Not a fundamental flaw with the system more a product of last minute changes that weren't thought through I think.

I'm not 100% sure on this but I thought you could use Victron to generate the second and third phases using power from the batteries and the battery charger on the first phase. ie it could work without solar at all just using the single phase existing supply. Have you checked this?

This is going to differ depending on manufacturer. Some will make it easy and some will make it hard. Choose a system that supports everything out of the box and you will have minimum problems. Assuming you plan to use an installer, find one who can sell the complete system. Now the planning restriction on heatpumps that cool has been lifted it should be easier to find. When I looked for a system for my current place (before BUS existed) Panasonic seemed to be the goto for this. Ended up staying with gas as getting permission to put a heatpump in a flat (especially back then) was too difficult.

For a moment I thought you were building a new shed for chickens using ICF! Welcome and best wishes for your build.

These look good. I quite like the idea of hidden emitters as part of a wall. If DIYing likely loads cheaper than fancoils too (though with some likely downsides)

Noted thanks. Not for systems used exclusively for cooling AFAIK. If you get an A/C system that can heat then you have the issue with BUS.

Well this sent me down a little rabbit hole with Copilot. Not worth muddying this thread with that though as I think the main point is as long as the system is quiet enough to sleep through any system (water or refrigerant) would work well to offset this. For me personally this pushes me towards wanting UFH for cooling in the bedrooms too to avoid fans running overnight as I'm particularly sensitive to that. I feel out of my depth talking about this more so I will let others address this. Either way, planning permission is still an issue.

It would admittedly be tricky to find a company to do it all for you within the grant. But more self directed options exist like Cool Energy that you could likely get pretty close to fully covered by the grant. Yes I was thinking of the radiator replacement/wall hung units. Surprised you say they are noisy, as people on here who've got them say they are pretty silent. Personally I'd be more worried about ducted ones transmitting noise between rooms. I'm a light sleeper so personally I wouldn't want any fans running when I'm trying to sleep (I notice even 'silent' ones), but I'd hope in a well built modern house if you control the temperature of the structure during the day then the room should carry through the temperature while sleeping without the unit needing to run. If installing FCUs in a new build at least with a decent amount of DIY labour I don't see why you wouldnt want to run pipes for condensate drains and insulate the pipes well. It's a something you could do DIY following behind a plumber to if you didn't want to do the plumbing yourself (tell the plumber to use preinsulated MLCP and just deal with the junctions). If the FCUs are fully ready for below dew point operation then in the event that a mistake was made in the design and you need more cooling than planned then you always have the option to modify the system to support below dew point feeds to the FCUs (with some changes in the plant room and the tradeoff of slightly lower efficiency). Would suggest you want to size the system to cover heating/cooling needs without operating below dew point though. You'd have to sequence this carefully though as it would be violating the BUS grant. MCS wouldn't install if the AC system was already there and MCS might not want to install anything if they can't satisfy themselves that you have provided adequate heating for all rooms (which you might not if it depends on the a2a system). You would also need planning permission for the a2a system. My thought is if you are going a2a, go the whole way and just do an a2a system (they can heat as well) and rely on immersion HW heating using solar/cheap rate. Don't do both.

Unless you have (or can easily get) 3-phase. With that you are allowed 3.6kw per phase = 10.8kw.

It's available to self-builders too. Search the forum, plenty of examples.

You can get the BUS grant to install a water based ASHP (including the cost of fancoils if you want). Have to be careful as lots of MCS installers around bumping up the costs to suck up the grant and more. But plenty of experience on here. If you are careful and have UFH downstairs then won't need many fancoils and should be able to keep the costs close to the grant amount so the system will be free or almost free. Referring back to my previous post and your tight budget. The more different things you need, the more quotes you need, the more contractors you involve, all adds drain on your time and the more likely you will get overwhelmed dealing with so many things. When that happens the chances of costly mistakes goes up. Try to keep things as simple as possible. Fewest components, minimal complexity.

Believe they are concrete: https://nextdaysteel.co.uk/products/concrete-square-bar-spacers-1m-length

There's a lot here that maybe deserves point by point responses but I can't help feeling you are getting stuck into the details without actually knowning the scope of the problem. Have you done the heat loss/heat gain calculations? Before you spend time thinking about how to solve the problem it would seem best to figure out whether you have a problem and, if so, how big the problem is. You have said you are on a fairly tight budget. So if you want to get this project done without delays or blowing the budget I think you need to apply a razor focus on what you actually need vs nice things to have.

Good result. I assume you are just running the pump in an on/off form. Any thoughts about speed control? Reason for mentioning is when I've thought about what I might want to do, if it ever happens, is that the pump might serve as a useful way to distribute heat/cold between rooms to try and keep things equalised despite some rooms having higher heatloss/gain than others. Edit: Clarification, idea being that to do that equalisation you'd likely want to run the pump more than for a short period every 40 mins. Running slow for longer might be better than more frequent full on pulses. I've done no maths on this as don't want to start detailled work until I actually have a project.

Wouldn't this be a better solution in this case @ProDave? Saves doing anything inside the wall or serial switching. Can still replace the external cable if needed but just use a wireless external switch (they sell IP67 versions).

I've seen a thread on here in the past about how the insect screens they had installed ended up being about perfect for shading too. Relatively cheap (as its simple roller blind) and maintains the view while cutting a lot of light. There are probably downsides too but worth considering as they will serve a dual purpose (though you will need curtains too if you want to black out the room).