Performance analysis of desiccant wheels assisted fresh air humidifiers in winter using natural gas boilers: Applied in cold and dry climate regions

Abstract

A fresh air handling unit is proposed for space humidification in winter for buildings located in cold and dry climate regions. The air handling unit has three-stage desiccant wheels to transfer moisture from dehumidification air (A deh ) to humidification air (A hum ), both of which are from outdoor, and heat from boilers is used to drive this process. Humidification performances of this device were discussed when ambient humidity ratio was from 1 to 4.5 g kg −1 and corresponding operating strategies under different ambient conditions were proposed to keep the supply humidity ratio in the range of 5.1–5.5 g kg −1 . Then, effective heating systems, including air side heat recovery and step utilization of heat from low-grade waste heat, were investigated. Humidification efficiency ( η sys ) of systems without heat recovery ranges from 0.24 to 0.9. With heat recovery at the air side, which is called improved system I, η sys was enhanced to 0.4–1.2. Water circulation layout was redesigned to realize step utilization of heat. Return water temperature from humidification devices could be reduced, and η sys can be obviously enhanced when low-grade waste heat sources are available. When air source heat pumps are used to preheat the return water, from Case A to Case H, primary energy efficiency can be improved by 5.8–26.1% as compared with the improved system I.