On-site measurement and performance optimization of the air-conditioning system for a datacenter in Beijing

The sensible heat loads in datacenters are high-density, and improving the energy performance of heat extraction is an important aspect of the energy conservation of datacenters. This paper focuses on the heat extraction process of a datacenter in Beijing, in which a cooling tower is adopted for free cooling and water-cooled screw chillers are utilized for mechanical cooling. The tested coefficient of performance (COP) of this air-conditioning system approaches 9 in free cooling mode, but is lower than 3 in mechanical cooling mode; the PUE (power usage effectiveness) is lower than 1.2 for free cooling mode and is approximately 1.4-1.5 for mechanical cooling mode. The nonuniform temperature distribution of the exhaust air restricts the increase of the supply air temperature and the required temperature of chilled water. Accordingly, suggestions for improving the temperature distribution and increasing the temperature of the chilled water are proposed. An innovative LTD (large temperature difference) distribution system, increasing the chilled water temperature for heat extraction and utilizing a natural cooling source as much as possible, is introduced, and its operating modes are described in detail. It is easy to realize the changeover between natural and mechanical cooling sources in this new process, utilizing the natural cooling source more conveniently and efficiently.