Air conditioning system with dual-temperature chilled water for air grading treatment in data centers.

• Circulating air is treated with dual-temperature chilled water in two stages. • Multiple natural energies are used to produce dual-temperature chilled water. • Longer free cooling duration and lower energy consumption are realized. • Dual-temperature chilled water system has very short payback period. Indoor high-temperature circulating air is only treated with one type of low-temperature chilled water in a conventional waterside free cooling system, resulting in a short free cooling duration and high energy consumption in a data center. This study develops an air conditioning system using dual-temperature chilled water for a two-stage treatment of air. Mathematical models are developed to calculate the system performance throughout the year. A data center located in Hohhot, China is taken as a case, and the energy consumption, energy efficiency, and economics of the grading treatment system are analyzed and compared with those of two conventional systems (i.e., waterside economizer and air-cooled heat exchanger systems). The results show that the grading treatment system achieves increased free cooling duration and energy efficiency in the data center compared with the conventional systems. Compared with the conventional waterside economizer and air-cooled heat exchanger systems, the grading treatment system realizes annual energy-saving rates of 27.4% and 25.4%, energy efficiency increments of 37.8% and 34.0%, and payback periods of 2.55 and 2.59 years, respectively. [ABSTRACT FROM AUTHOR]