• Energy Research

Abstract The indirect evaporative cooler (IEC), used as a novel energy recovery component for central air-conditioning (AC) systems, can cool and dehumidify the fresh air by capturing the waste thermal energy of exhaust air. To facilitate its implementation in hot and humid areas, the applicability of the hybrid AC system integrated with IEC needs to be addressed. This study quantitatively evaluated the cooling and energy-saving potentials of an IEC for energy recovery and compared it to a traditional hybrid AC system with a heat recovery wheel (HRW). On-site performance measurements were conducted in a wet market located in Hong Kong, where two air-handling units were integrated with a newly-designed IEC prototype and a commercial HRW respectively. Simulation models of the two hybrid AC systems were established based on TRNSYS platform by incorporating the numerical model of IEC and HRW respectively. The field-measurement data was used to validate the component models, and further calibrate the system models. To compare the regional adaptability of the two systems, annual simulations were conducted among 8 selected cities in southern China. Results showed that the total cooling capacities of IEC and HRW are closely related to local ambient relative humidity. Compared with the baseline AC system, the AC + IEC provides an annual energy saving intensity of 64.2–73.4 MJ/m2 for cities with hot and moderate humid climates, which is more competitive than the AC + HRW (45.5–51.8 MJ/m2). The annual energy saving ratios of the two types of hybrid systems range from 14.4% to 26.4%.

The rapid development of data centers (DCs) has led to a marked increase in energy consumption in recent years, which poses a direct challenge to global efforts aimed at reducing carbon emissions. In regions with hot and humid climates, the energy demand is largely driven by air conditioning systems necessarily to maintain appropriate operational temperatures. This study proposes a novel multi-stage indirect evaporative cooling (IEC) system, incorporating a liquid desiccant in the primary air channel to address the cooling demands of such DCs. Our approach involves a two-stage process where the first stage uses a liquid desiccant-based IEC (LD-IEC) for air dehumidification and the second stage utilizes the treated air from the first stage as the secondary air to enhance the cooling effect. A simulation model of the proposed system is established with validation, and the performance of the multi-stage system was also discussed based on different operation modes. Furthermore, a case study was conducted to investigate the feasibility of using this system in the DC under a typical hot and humid zone. The findings reveal that the first-stage LD-IEC is capable of diminishing the wet-bulb temperature of the ambient air. Furthermore, the case study demonstrates that the proposed system can greatly improve the temperature drop by 72.7% compared to the single IEC, which noticeably reduces the operation time of energy-intensive supplementary cooling equipment from 5092 h to 31 h given the supply air temperature threshold of 25 °C. In summary, the proposed system could substantially decrease reliance on traditional cooling systems, which demonstrates a promising avenue to fully use this passive cooling technology for cooling DCs.

Abstract Driven by the economic outbreak and the growing demand of thermal comfort, the energy consumption of air conditioning (AC) keeps increasing promptly. Indirect evaporative cooling, as an energy-efficient and eco-friendly AC approach, attracts attention in recent years. However, this traditional technology has some drawbacks associated with its working principles. For instance, the limited output temperature constrains its application scopes. Insufficient evaporation due to the poor wettability on the wet channel surface significantly affects the cooling performance. This study provides an updated review of the research progress for solving these problems. Specifically, lower-temperature air can be produced by dew-point evaporative coolers. Innovative wicks with different materials strengthen the surface wettability as well as promote evaporation. Besides, hybrid systems and system optimizations can ensure cooling performance under hot-arid and hot-humid weather conditions. With the recent developments and foreseeable future opportunities to cope with these problems, IEC is expected to make more contributions to reducing the energy consumption of AC in buildings.

202306 bcch ; Not applicable ; RGC ; Others ; Electrical and Mechanical Services Department of the Hong Kong SAR Government ; Published ; 24 months