Comparison of Behaviour and Energy Performance of Desiccant Air Handling Unit under Various Control Method

Desiccant air handling unit (DAHU) dehumidifies moisture in the air with adsorbent or sorbent. Hot water is necessary to regenerate them. In many buildings, for regeneration of the dehumidifier, hot water from combined heat and power (CHP) is used because it can supply hot water at stable temperature. When using fluctuating energy such as hot water from solar thermal collector, it is mixed with hot water from CHP in order to compensate the fluctuation, and supplied. In order to use renewable energy including solar thermal energy efficiently, we propose flexible control compared to ordinary fixed control. The ordinary fixed control controls outlet air temperature of pre-cooling coil at fixed temperature, for example 19°C, and the relative humidity is 100%. Therefore, dehumidification amount at dehumidification wheel as well as regeneration coil demand does not fluctuate very much. On the other hand, flexible control controls outlet condition of pre-cooling coil with absolute humidity of supply air and hot water temperature to regenerating coil. When hot water temperature is enough hot, absolute humidity of supply air fulfills set point, therefore pre-cooling coil demand decreases. When hot water temperature is not hot enough, supply absolute humidity does not fulfill the set point. In this case, outlet temperature of pre-cooling coil will get lower in accordance with hot water temperature. This study investigates the behavior and performance of DAHU under different control methods through energy simulation. Simulation results show that when installing flexible control, outlet air state of pre-cooling coil is determined depending on the hot water temperature to regenerating coil. It proves that it is possible to handle required latent heat load even when hot water temperature is low around 45°C. DAHU with flexible control can contribute the effective use of solar thermal heat.]