Intermittent use does bring with it a set of different problems and 300 occupants would do enough heating without a heating system if you could get them there as and when needed

I would try to keep the slab and do perimeter insulation, wet and/or damp ground behave very much the same as dry ground so long as the water is not flowing, the ground would also tend to dry out as the building on top warms it.

Like the sound of super-insulated, what U-values are you aiming at? do include MHRV

Tony,

It's only a 'thought experiment' at the moment but since the brief requires 'zero carbon in use', the intention is to focus on fabric heat loss ahead of micro-generation. Thus I think we'd aim at U-values of 0.15 for roof and walls. Windows are trickier (the budget is small) and I'm not sure what the appropriate space heat load would be (I've read 39-46 kWh/m² for zero carbon residential, but presumably this would be different?) Any tips on where to look?

Defintely intending to use MVHR and the rensmart website gives a PV generation average of 18kWh/day for the area, so I think we should be able to run this comfortably.

joe90,

Thanks for the tip about french drains - was hoping to adopt the LECA backfill approach mentioned elsewhere on here. Not had a chance to visit site yet, so I need to find out a bit more about the existing foundations before I can develop things much further.

I'd ignore the slab - insulate over it

You are effectively going to have a big internal volume with variable occupancy load and intermittent occupancy times.

Build tight and well insulated, balance the windows against heat loss, heat gain (300 people in a space with bright (glare) and big windows will result in blinds) and electrical demand for daylight top up. Also consider location of windows (unoccupied community buildings are a target for all and sundry). Think of that also with regard to where your insulation is and what external finishes you have.

You have a nearly square building so envelope area to volume is good and daylight penetration will be crap unless you use roof lights - see my comments about glare.

Zero carbon in use is challenging and can often lead to loads of bolt on renewables rather than get the demand down in the first place - innapropriate use of technology springs to mind.

I'd agree UFH is probably a good prospect in larger rooms but you'll really want to pay attention to the ventilation - 300 occupants is going to need a big AHU and you will need sensible control over fan sped to meet low occupancy loads - get an analysis on costs for UFH and minimum vent and one where you go "all air" which lends itself to big volume, intermittent use buildings. You may also need to consider cooling if you have 300 people in a small(ish) space - all air would help you here as the volumes will probably be bigger than those required for just fresh air. Consider CO2 tracking for the fan. Solar thermal for the HWS would be a starting point - deciding on your building heating fuel will be the challenge.

Good luck

Regards

Barney

Well you can have all air with low temperatures - you just need more of it as it's delivering less heat energy (low delta T). Ultra low temp UFH with minimum ventilation air is still a good solution - as I said, get each option tested simply - anyone with a bit of thermal modelling software can give you answers to initial what ifs - if you're an Architect there must be a building services engineer somewhere who's still talking to you :-)

Lobbies are always good with any heating system - and they are useful in community buildings if you want to have different functions in different areas - security is an issue - and give you zonal seperation between functions (age groups etc - you know the sort of thing) that is useful for temperature control as well - you'll not want the ganglam dance class at the same temp as the over sixties sewing circle

Regards

Barney