The last concept of air circulation when designing dedicated cooling for IT devices are closed circuits. This solution is more suitable for LAN applications, however, its deployment is also possible in data centers.
The closed-circulation circuit can be created using glass doors on server racks instead of standard perforated ones. The closed circuit can be built up as 1 or 2 rows of cabinets and the use of row based cooling units is required.
The advantage of closed circuits is the absolute separation of the airflow for active devices from the surrounding environment. Moreover, in a LAN environment, this solution can be installed outside the dedicated technical room.