Energy performance evaluation of liquid desiccant and evaporative cooling-assisted 100% outdoor air system

Abstract

The indirect and direct evaporative cooling-assisted 100% outdoor air system is known as an environmental-friendly air conditioning system that uses the latent heat of water vaporization to cool the supply air. Through the pilot system operation, the proposed system could save significant operating energy in intermediate and heating season comparing with the conventional variable-air-volume (VAV) system; however, it was observed that over 36% of operating energy was more consumed in cooling season. It was mainly caused by the limitation of cooling capacity of indirect and direct evaporative cooler in cooling season. In this research, the enhanced evaporative cooling system integrated with desiccant system was proposed and developed, and applicability of two types of desiccant system (i.e., solid desiccant and liquid desiccant system) was investigated and energy saving potentials were also analyzed through the detailed simulation. Based on this simulation results, the prototype of a desiccant and evaporative cooling-assisted 100% outdoor air system was proposed and operation sequence depends on the outdoor and indoor air condition was developed. Through the integration of water-side free cooling and solar thermal system for liquid desiccant system, operating energy saving potential via conventional VAV system was investigated through the simulation. It was found that about 51% of cooling season operating energy savings comparing with the conventional VAV system were obtained. In order to validate the simulation results, 42-m2 floor area served pilot systems of proposed system was installed. A conventional VAV system was also installed for comparison with the proposed system. The outlet air conditions and effectiveness of the system were monitored by measuring the variation of air condition at each measurement location. The proposed system was integrated with water-side free cooling in the desiccant solution and process air cooling to enhance its energy performance. The energy coefficient of performance (COP) of water-side free cooling applied to cool the desiccant solution was 8-17, whereas that of the conventional air-cooled chiller was 1-3. The operating energy of the systems were compared under identical indoor air and outdoor air conditions. It was found that the operating energy of the proposed system in heating season can save 73.2% comparing with the conventional VAV system. However, in cooling season, it was observed that the proposed system consumed 9-27% more operating energy. It was mainly caused by the undesirable regenerator fan operating energy consumption. The simulated operating energy consumption of major components of the proposed system was well matched with the experimental data using pilot system. When the unexpected regenerator fan energy consumption was modified, it could be expected that the 57% of annual operating energy saving potential can be achieved via detailed simulation.