I have a proposed underfloor air distribution system (UFAD) for a one level office in a temperate climate. Typically the demand for heating and cooling in this climate is about even for offices. However the building is well insulated and has a fair amount of (shaded) low U-value glazing on the sun facing elevation.
Now the question boils down to whether the thermal mass of the slab will be beneficial overall or not. At the moment I tend to have insulation within the plenum, i.e. excluding the impact of the thermal mass to create a more controlled supply, instead of having the insulation under the slab.
Based on some handwavy assumptions though, I could see some benefits of including the mass of the slab in order to reduce cooling loads (which I expect to be somewhat dominant due to the glazing and amounts of insulation).
However what would happen once the slab is fully heated, i.e. runs out of capacity? Would I night purge it? Can someone share their thoughts/experiences? When I insulate the plenum, should I include or exclude the slab?