I felt on many projects, HVAC (heating, ventilation and air conditioning) solutions could have been better.
The design of these systems seemed an inexact science involving estimates for heat generation and air transfer and treated as a bolt-on to the main design rather than an integral part of it.
My first office build had a plant room which was not large enough so the HVAC plant had to spread out onto the roof.
Space for ductwork, especially in process plants, was frequently underestimated resulting in access problems for maintenance.
An indoor pilot plant had wall louvres and automated roof ventilation which was never needed even on hot summer days.
LEV (local exhaust ventilation) systems for the removal of contaminants from working areas and laboratories were frequently undersized.
We had more success with clean rooms, maybe because it was the primary technology for the project and everything else was designed around it?