The ducts get very large, so trying to fit them in existing infrastructure is a big challenge. Also consider that much of original 'spare' space has been repurp

The ducts get very large, so trying to fit them in existing infrastructure is a big challenge. Also consider that much of original 'spare' space has been repurposed for additional systems (CCTV, PA, additional power etc). It's different for new infrastructure where this can be allocated more readily at a smaller marginal cost.