I work for my state government and as such usually work in a large building. The respective facilities managers always turn off the blowers, heat, or air conditioning at 5:00PM, ostensibly as a cost-saving measure.
1) As many people work in the buildings past 5:00PM, how dangerous does it become with the ventilation turned off?
2) Does it really save money to turn off the heat/air conditioning every day? It seems as if it would take less energy to keep a huge volume of air at a constant temperature than it would to radically change the temperature of that volume once every 24 hours.