This research review focuses on air conditioning systems that cool high-heat-generating machines like computers and telecommunications equipment, and reports on various aspects related to air-flow systems and air conditioners. In particular, we introduce current R&D work on air conditioning flow systems, especially raised -floor blowing systems, and describe methods for allocating air flow for equipment with and without fans, calculating indoor temperature distribution, and evaluating energy conservation. We also describe R&D work on various types of air conditioners that operate at low compression ratios, apply the thermo-siphon principle, and have indirect and direct outside-air cooling functions to achieve efficient cooling operations when outside temperature is low, considering the need for year-round cooling.