Forward Osmosis Absorption Heat Pumps for Space Conditioning and Graywater Purification: Cycle Development and Working Fluids Selection

Abstract

A thermodynamic model is developed for a forward osmosis (FO) absorption heat pump capable of purifying graywater and providing year-round space conditioning with low-temperature heat as the primary energy input. The model is applied to 16 potential absorbents, and six are selected for parametric studies on desorber temperature, absorber temperature, condenser temperature, and heat sink temperature to determine the effects on the energy ratio (defined as the ratio of total useful output to total power input) of the cycle and the required graywater flowrate. Experiments are conducted to test the water flux and reverse solute flux in FO for the most promising absorbents. Of the six selected absorbents, four to two salt-organic mixtures and two pure salts appear to have the most promising thermodynamic behavior, while an ionic liquid demonstrates the best FO behavior.