When building a trading floor and its associated data centre/technology room the designer will need to think about how much fresh air should be pumped into the room. Depending on external climate conditions the delivery of fresh air will need some energy to process it before introducing the air into the building. It may need heating/cooling/dehumidification and it will definitely require filtering.
Keeping the fresh air to a sensible minimum in an air conditioned building will reduce energy costs. If the building has a lot of people present you'll need more fresh air. If the building contains only machinery there will not be a great demand for fresh air. Some basic building ventilation systems will be designed to deliver a certain percentage of fresh air to ensure X air changes per hour. However in practice many buildings are occupied only 60% of the day. Some rooms such as conference rooms are often empty with little need for fresh air, but when fully occupied the demand for fresh air increases.
Demand air ventilation systems incorporate carbon dioxide sensors to detect whe the people load is increasing the need for fresh air. Such systems are usually capable of air conditioning of the fresh air delivered, so only the specifically required fresh air will need energy. It reduces waste and improves the environment for the building occupants. Here is one such system. Here's a useful (12mb pdf) document. from Carrier Corporation