Figure 10-2 does not represent any particular server system type, and is intended only to  show hot and cold airflow and the arrangement of server aisles. Figure 10-2 Hot and cold aisles Water-cooling system requirements 394  IBM z14 (3906) Technical Guide As shown in Figure 10-2, rows of servers must be placed front-to-front. Chilled air is provided  through perforated floor panels that are placed in rows between the fronts of servers (the cold  aisles). Perforated tiles generally are not placed in the hot aisles. If your computer room  causes the temperature in the hot aisles to exceed a comfortable temperature, add as many  perforated tiles as necessary to create a satisfactory comfort level. Heated exhaust air exits  the computer room above the computing equipment. With the standard z14 rear covers (FC #0160), the exiting airflow direction can be  customized, which provides you more flexibility in placing z14 servers in your data center.  Optional Thin doors (non acoustic, non-vectored) are available also (FC #0161). For more information about the requirements for air-cooling options, see  IBM 3906 Installation  Manual for Physical Planning,  GC28-6965. The water-cooling system requires a chilled customer building water supply to be supplied to  the z14 water-cooling units (WCUs). A z14 server requires four connections to the facility  water: Two feeds and two returns.  Raised floor:  The minimum raised floor height for a water-cooled system is 22.86 cm  (8.6 in.).