Evaluation of a liquid-desiccant-enhanced heat-pipe air preconditioner

Recent increases in outside ventilation rates from 5 fr /min (cfm) per person to 15-20 cfm/person, in compliance with ASHRAE Standard 62-89, will impose additional sensible and latent loads on buildings. The concept of a desiccant-enhanc ed heat pipe discussed here has the potential to provide an efficient preconditioner for the ventilation air. This paper presents the results of an experimental evaluation of enhancing the dehumidification performance of a heat-pipe heat recovery unit by incorporating a liquid-desiccant dehumidification function. A commercial heat-pipe thermal recovery unit with an indirect evaporative-cool ing feature was modified by incorporating a liquid-desiccant contacting/recir culation loop on the supply-air side. Two liquid desiccants, lithium chloride (LiCl) and triethylene glycol (TEG) solutions, were tested in this device. The cooling capacity of the heat-pipe with desiccants increased 20%-40%. The cooling performance of the heat-pipe system using TEG was about 10% less than when using LiCl. The efficiency of the dehumidification operation was estimated to be only on the order of 40%-50% of the equilibrium dehumidification potential because of less than optimal gas/liquid contact. Further research and development work could improve this performance into the 80%-90% range. The outcome suggests that the liquid-desiccant ­ enhanced heat-pipe device could be a viable system for preconditioning ventilation air.