Abstract: A cooling system of compact design includes redundancy and free cold source usage. The system includes two circuits for circulating coolant and heat absorbing medium, and two heat exchanges common to the circuits. The heat exchangers are combined to act on both of the circuits, so that inside air is cooled by cold liquid or by expanding coolant in a combined evaporator-air cooler, and the outside air is used to cool warmed liquid or condensed coolant in a combined condenser-liquid cooler. Free cold, that is, outside cold air, may be utilized when the difference in temperature between inside air and outside air is sufficiently great and the outside air is sufficiently cold. Liquid cooled by outside air in the combined condenser-liquid cooler and then heated by warm inside air in the combined evaporator-air cooler can satisfy the entire heat load. In other cases, the compressor system can provide cooling. The free-cooling system can serve as a redundant system for the compressor system.