11.1.3 Cooling requirements Radiator (air) cooling The z15 cooling system includes with two options: Radiator (air) cooled or water-cooled  system. Single chip modules (SCMs) are always cooled with an internal water loop, no matter  which z15 cooling option is chosen. The liquid in the internal water circuit can be cooled by  using a radiator (for air-cooling option) or customer-supplied chilled water supply (for  water-cooling option). I/O drawers, PCIe I/O drawers, power enclosures, and CPC drawers  are cooled by chilled air with blowers.  The z15 servers include a recommended (long-term) ambient temperature range of 18°C  (64.4°F) - 27°C (80.6°F). The minimum allowed ambient temperature is 5°C (41°F) and the  maximum allowed temperature is 40°C (104°F). For more information about cooling requirements, see  IBM Z 8561 Installation Manual for  Physical Planning , GC28-7002. The following radiator (air) cooling options are available: The radiator cooling system requires chilled air to fulfill the air-cooling requirements. z15  system airflow is from the front (intake, chilled air) to the rear (exhausts, warm air) of the  frames. The chilled air is provided through perforated floor panels in front of the system The hot and cold airflow and the arrangement of server aisles are shown in Figure 11-3. As shown in Figure 11-3, 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. Chapter 11. Environmentals  459 Figure 11-3 Hot and cold aisles GLYPH<SM590000> A-Frame radiator air-cooled feature code (FC 4033) GLYPH<SM590000> B-Frame radiator air-cooled feature code (FC 4035)