I agree with Mark re MEV.
Neighbour is building a tiny 8m2 well insulated guitar workshop that needs constant temp and RH. It has 300mm+ insulation all round, air tight, no thermal bridges, triple glazing etc.
We assumed a small single room HRV but thought we should model it in PHPP.
Attached shows energy balance assuming MEV and 0.37 airchanges average vent rate (higher when in use then turns off or to trickle).
Adding efficient MVHR would only reduce the ventilation by a bit as there is still leakage and door opening etc is more significant in tiny building.
Result really surprised me and I got Alan Clarke to check it.
So model in PHPP and be prepared for a surprise if you think you can achieve 15 kWh.m2.a or 10W/m2!
In practice for small buildings the internal heat gains will be higher per m2 than the assumed domestic level and you can work them out in PHPP, I didn't, my fee was a couple of pints down the pub!