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• An air-cooled heat pump unit comprising of two constant rotation speed compressors integrated with PCMs is studied. • Electrical energy and electricity charge consumptions are discussed. • A lower indoor temperature results in a higher electricity charge saving ratio. • A higher cold charging temperature has a positive impact on the energy-efficiency. This paper studies the performance of a cold storage heat pump system integrated with phase change materials (PCMs) for space cooling. An air-cooled heat pump unit comprising of two constant rotation speed compressors is selected. The PCM is an organic material that is commercially available, and has a phase change temperature of 10–12 °C. A coupled computational heat transfer model of the heat pump unit, fan coil units, and a cold storage tank filled with PCM slabs is developed. The simulations are performed under the climatic condition of Fuzhou, China. The operational behaviors of the cold charging and discharging processes of the system are analyzed. Furthermore, the overall electrical energy and electricity charge consumptions at various indoor temperature set points are compared. The results indicate that, the electrical energy consumption of the cold storage heat pump system increases as the indoor temperature increases. However, there is very little difference in the electrical energy consumption of the conventional heat pump system and the cold storage system. While under the demand tariff, the electricity charge saving ratio of the cold storage system over the conventional system is 9.07%-11.28%. In general, as the indoor temperature set point reduces, the electricity charge saving ratio increases. Moreover, the effect of cold charging temperature is also discussed. It is found that higher cold charging temperature consumes less electrical energy, however, takes longer to store the same amount of cold, and the differences relies on the required amount of cold. [ABSTRACT FROM AUTHOR]

• The necessity and uniqueness of TES for data centers are discussed. • TES units and TES integrated cooling systems in data center are summarized and classified. • The designs and performance characteristics of TES units and TES integrated cooling systems in data center are analyzed. • Main trends in TES developments and applications are summarized when utilized in data center. Data center consumes a great amount of energy and accounts for an increasing proportion of global energy demand. Low efficiency of cooling systems leads to a cooling cost at about 40% of the total energy consumption of a data center. Due to specific operation conditions, high security and high cooling load is required in data center. To achieve energy saving, cost saving and high security, novel cooling systems integrated with thermal energy storage (TES) technologies have been proposed. This paper presents an extensive overview of the research advances and the applications of TES technologies in data centers. Operating conditions, energy mismatch and requirement of high security in data center were overviewed. Principles and characteristics of TES technologies were discussed. Applications of passive TES coupled air flow and applications of active TES integrated cooling system are summarizes, and the design and performance of these TES integrated thermal systems are analyzed, with a focus on energy saving, cost savings and high security. [ABSTRACT FROM AUTHOR]