A direct expansion air handling unit assisted by liquid desiccant for different sensible and latent heat ratios

Abstract

Reheating is needed in the traditional cooling and dehumidification system, which results in the offset of cooling and heating. There is no reheating in the liquid desiccant system, but equipment for latent heat and sensible heat are both necessary. This paper proposes a direct expansion air handling unit assisted by liquid desiccant (LDAHU) for adapting to various sensible and latent heat ratios using only one set of equipment. Numerical models were developed for calculating the system performance under various load demands of an office building in Nanjing, China. A comparison of the energy performance and economy between the LDAHU system and two conventional systems, i.e., an electric chiller and boiler (ECB) system and an air source heat pump (ASHP) system, was performed. The results indicated that the LDAHU system can treat the mixed air for achieving the required state of the supply air directly by controlling the temperature and concentration of the sprayed solution and can operate efficiently in both summer and winter. Compared with the ECB system and the ASHP system, the coefficient of performance of the LDAHU system is 13.2% and 30.4% larger, respectively, in summer, and 37.0% and 6.2% larger, respectively, in winter. The total cost savings for the LDAHU system over 15 years of life-cycle operation are 11.6% and 6.8%, respectively, although the initial costs are 5.1% and 31.2% higher, respectively, resulting in the dynamic payback periods as 0.9 and 5.3 years, respectively.