A Comparative Study on Energy Efficiency and Indoor Thermal Comfort of DOAS Applied to Multi-zone Air-conditioning Systems

Conventional air conditioning systems are facing great challenges considering indoor relative humidity control, system safety and effective ventilation in an energy efficient way. The dedicated outdoor air system (DOAS) is widely believed to overcome these problems. A DOAS-integrated system, which combines a DOAS with dry fan-coil units, is presented in this study. Energy efficiency and indoor thermal comfort of this air-conditioning scheme is investigated and compared with two conventional systems, i.e. wet fan-coil units and variable air volume systems, serving the same multi-zone space of an office building in Hong Kong. Control strategies for the DOAS-integrated system are also presented. Tests on two typical operation conditions, i.e. summer day and spring day, are conducted on the simulation platform of TRNSYS. Simulation results show that the DOAS-integrated dry fan-coil unit system can achieve the best indoor relative humidity on two typical days, and it consumes almost the same amount of energy as the wet fan-coil unit system on the summer day and about 5% more energy on the spring day. In addition, the effect of total heat recovery exchanger on energy saving in hot and humid regions is obvious and demonstrated.