Semi-open absorption, heat pump, dehumidification, water heating
Water heating and dehumidification are major energy consumers in buildings. The novel semi-open absorption heat pump design utilizes the heat of absorption from the dehumidification of space for water heating. The architecture of the system consists of (1) a plate and frame membrane-based absorber, (2) a membrane-based desorber and condenser unit, (3) heat exchangers, (4) ionic liquid, and (5) a 189.3 L (50-gal) water tank. The membrane-based absorber enables heat and mass transfer between three streams: moist air, ionic liquid, and the heat transfer fluid. The heat of vapor absorption elevates the ionic liquid temperature and, in turn, heats the heat transfer fluid. In the desorber unit, the diluted ionic liquid after absorption is heated to above 150℃ and reconcentrated. The heat of condensation from the condensation of water vapor in the condenser is utilized for water heating. The dehumidification performance of the absorber directly affects the COP and heating capacity of the system. Understanding the absorber's performance at various operating conditions would allow one to optimize and design a better performing absorber. In this study, the absorber's water heating capacity and performance are evaluated for varying operating conditions. A maximum COP of 1.25 while water heating water from 18.6 to 60.2°C was achieved at a capacity of 1,010 Watts and an airflow rate of 47.19 L/s. Increasing the desorber oil mass flowrate had negligible effect on the COP. The average mass transfer resistance of the porous membrane absorber was 1.164 *107 m/s.