Stated N+1. Real-world N+0 at 48°C ambient.
Design specified N+1 cooling redundancy across the IT hall. Walking the CDU headroom against the actual ambient envelope, peak-day GPU duty, and the DLC adoption curve in years 2–3, we found one CDU's redundancy entirely consumed before any equipment fault occurred. Stated N+1 was actual N+0 at the conditions the building would see by its second summer.
Caught at Gate 2. 14 racks reclassified, 2 additional CDUs added pre-tender. Mitigation cost: $880K. Estimated cost if caught in commissioning: $4.6M and seven weeks of slipped energise date.