Energy impact of vacuum-based membrane dehumidification in building air-conditioning applications

Highlights: • The performance of a vacuum membrane dehumidification-based air-conditioning system were evaluated. • There described the method to decide vacuum pump working conditions and membrane module design. • The proposed system consumed 8.2% less energy than conventional system. • To achieve energy benefit, optimal membrane module design and vacuum pump operation are necessary. The energy and operating performances of a vacuum membrane dehumidification system were theoretically investigated for building air conditioning applications. The dehumidification effectiveness and coefficient of performance (COP) were adopted as performance indices. A one-dimensional mass-transfer model was derived to analyze the effect of each operating parameter on dehumidification performance. The data predicted by the model agreed well with measured results, with an error bound of 20%. Parametric analysis results indicated that the vacuum side pressure had the most significant impact on the energy and dehumidification performances. It was also observed that the membrane module length plays an important role in the module design. Based on the analysis results, a configuration and operating strategy of a vacuum membrane dehumidifier-assisted variable air volume air conditioning system were suggested. Subsequently, the proposed system was evaluated by comparing its energy and operating performances with those of the conventional variable air volume air system via energy simulations. The results indicated that the total primary energy consumption from the proposed system was 8.2% lower than that of the conventional system. However, the fan energy consumption in the proposed system was 2.5 times higher than that of the conventional system owing to the high pressure drop of membrane module. In addition, the proposed system consumed 7.7% more primary energy for dehumidification and sensible cooling process because of its lower COP. To achieve comparable energy performance, further research on the optimized design of a membrane module and optimized operation of a vacuum pump in the proposed system are necessary.