Investigation on humidification effect of desiccant coated heat exchanger for improving indoor humidity environment in winter

Abstract

In cold climates, keeping proper temperature and humidity level is essential to ensure a comfortable and healthy building environment. In this paper, a new method is developed to meet the demand for humidifying the indoor air in winter by using desiccant coated heat exchanger (DCHE) as a heating and humidifying unit during the regeneration process. The desiccant coating materials and configurations of DCHE are two main aspects affecting the humidification performance. With the same heat and mass transfer area but different structure sizes, PCHE (fin pitch 2 mm, fin depth 44 mm), SCHE A (fin pitch 2 mm, fin depth 44 mm), SCHE B (fin pitch 3 mm, fin depth 66 mm) and SCHE C (fin pitch 4 mm, fin depth 88 mm) are fabricated and tested. The heat and moisture transfer characteristics of four types of DCHE under various operation conditions are compared with test results. In one typical cycle, the average moisture added in winter of PCHE, SCHE A, SCHE B and SCHE C is 1.73 g/kg(DA), 1.53 g/kg(DA), 1.49 g/kg(DA) and 1.41 g/kg(DA), respectively. Compared with silica gel, potassium format compound desiccant helps improving humidification performance by 13%. Also performed is the dynamic analysis on moisture transfer mechanisms and mass transfer coefficient in a typical cycle, the results indicate that the potassium format compound desiccant coated heat exchanger performs the best. PCHE shows the highest humidification capacity, SCHE A shows the highest heating capacity, while SCHE C shows the highest heat recovery efficiency. With heating fluid temperature increasing from 40 °C to 60 °C, the humidification amount of four DCHEs increase by 30%. The optimal inlet air velocity is given as 1.60 m/s, considering humidification amount and heat recovery efficiency synthetically.