An exergy analysis and parameter optimization of solid desiccant heat pumps recovering the condensation heat for desiccant regeneration and heat transfer enhancement

Solid desiccant is subjected to remove extra humidity from unsaturated air once thermally regenerated and then sufficiently cooled down. Therefore, it can be incorporated into the traditional vapor compression (VC) systems to handle the latent heat load with elevated evaporation temperature. The condensation heat can be recovered to regenerate the desiccant periodically, with an extra bonus of overall heat transfer enhancement. Such system is named after solid desiccant heat pumps (SDHP), expectedly to deliver higher evaporation temperature and lower pressure ratio at the expenses of the periodical switchover, increased wind friction and slightly impaired sensible heat transfer performance due to the desiccant thermal resistance. To verify the feasibility and superiority of SDHPs, this article proposes a robust thermodynamic model to calculate the operational parameters in SDHPs, such as evaporation temperature, condensation temperature and electricity consumption, corresponding to specific application scenarios. An exergy analysis based on the calculated parameters then followed to identity the origin and destination of the exergy. It concludes that, SDHPs can recover the dehumidification capacity of desiccant by low-grade condensation heat (∼50 °C), with the transfer enhancement up to 120%. Meanwhile, the introduction of the solid desiccant will contribute to a 11%–169% improvement in coefficient of performance (COP) and a 52%–207% improvement in exergy efficiency, in spite of the exergy destruction by air-side friction (<5%) and switchover offset (<10%). Last but not least, for normally encountered latent heat ratio (0.2–0.5), desiccant with linear isotherms or with moderate stepwise position (35–45%) will surpass materials with earlier or later stepwise position.