Evaluation of a Liquid Desiccant-Enhanced Heat Pipe Air Preconditioner

Recent increases in outside ventilation rates from 5 cfm per person to 15 to 20 cfm/person, per ASHRAE Standard 62-1989, will impose additional sensible and latent loads on buildings. The concept of a desiccant-enhanced heat pipe 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 cooling feature was modified by incorporating a liquid desiccant contacting/recirculation 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% to 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% to 50% of the equilibrium dehumidification potential because of less-than-optimal gas/liquid contact. Further research and development could improve this performance into the 80% to 90% range. The outcome suggests that the liquid-desiccant-enhanced heat pipe device could be a viable system for preconditioning ventilation air.