With the rapid growth of cloud computing

the number of data centers (DCs) continuously increases

leading to a high-energy consumption dilemma. Cooling

apart from IT equipment

represents the largest energy consumption in DCs. Passive design (PD) and active design (AD) are two important approaches in architectural design to reduce energy consumption. However

for DC cooling

few studies have summarized AD

and there are almost no studies on PD. Based on existing international research (2005-2024)

this paper summarizes the current state of cooling strategies for DCs. PD encompasses floors

ceilings

and layout and zoning of racks. Additionally

other passive strategies not yet studied in DCs are critically examined. AD includes air

liquid

free

and two-phase cooling. This paper systematically compares the performance of different AD technologies on various KPIs

including energy

economic

and environmental indicators. This paper also explores the application of different cooling design strategies through best-practice examples and presents advanced algorithms for energy management in operational DCs. This study reveals that free cooling is widely employed

with Artificial Neural Networks emerging as the most popular algorithm for managing cooling energy. Finally

this paper suggests four future directions for reducing cooling energy in DCs

with a focus on the development of passive strategies. This paper provides an overview and guide to DC energy-consumption issues

emphasizes the importance of implementing passive and active design strategies to reduce DC cooling energy consumption

and provides directions and references for future energy-efficient DC designs.