This thesis examines different methods for the cooling of data centers. Several means of cooling with the refrigeration cycle have been studied, as well as the feasibility of using free cooling in different parts of Sweden. In addition, the possibilities of transferring excess heat to a nearby district heating system were investigated. It was found that in all investigated cases except two, the data center could be cooled solely with free cooling for at least 300 days a year when only the outside air temperature was considered as a constraining factor. The limit was then set to 20 °C. The vast majority of all district heating systems in Sweden get little to none of their heat from other excess heat sources. It is therefore unlikely that this would hinder the possibility for owners of data centers to sell the heat produced by the servers to district heating systems. The data center belonging to the Swedish Energy Agency was especially examined. Experiments showed that when the cooling system temperature was set to 20 °C or below, the power consumption increased by 1 kW. No upper limit was found. Images taken with an IR-camera indicated that some mixing of hot and cold air takes place near the end of the aisle. Moreover, the difference in temperature between the upper and lower parts of the rack increased when the cooling system was set to higher temperatures, indicating further mixing of air.