The shop (7m x 8m) has no opening windows apart from in the small WC, I have insulated the loft using 350mm mineral wool and will be using 50mm PIR for IWI. The ceilings are 3m high.

There is also a basement which has no insulation whatsoever....

What form of ventilation should I use? A single heat recovery extractor fan? A MVHR unit located in the basement with exhaust and supply and the inlet located in the basement and the outlet floor level in the shop?

Heating will be by an ASHP/Air Con unit

Ideas please?

I'm just thinking of any wiring etc... before I board the walls this weekend.

Should the box be in the heated envelope? Given the layout anyway the basement is part of the building anyway really I guess.

How about heating/air conditioning? Where to mount it? Considering it will end up heating the whole building anyway being a one room affair. Split air con unit with outlet in the shop?
All wiring from the basement and then external to the air con unit?

Have you looked at an A2A HP, they are cheap to buy and you can easily introduce ventilation to the airstream with a bit of crafty boxing in. They run of a normal 13amp socket too.

you just have to duct in some fresh air beind the room outlet (forget about the heat recovery side as you are getting a CoP advantage anyway).
You will also not be heating the place at the coldest times of day, and the advantage of A2A is that it quickly heats the place up compared to a wet/convection heating system.

I can't see how it would work, for ventilation you need an in and an out and a fan on one or the other.

I would put in a relatively small duct to the outside rather than one with the same surface area as the fan unit.
It is just for a bit of warmed outside air after all, not trying to make it a fully balanced MVHR unit.
I am sure that air can leak out via 'other' orifices.