Diffuse Ceiling Ventilation: design guide

Diffuse ceiling ventilation is an innovative ventilation concept where the suspended ceiling serves as an air diffuser to supply fresh air into the room. Due to the large opening area, air is delivered to the room with very low velocity and no fixed direction, therefore the name ‘diffuse’. Compared with conventional ventilation systems (mixing or displacement ventilation), diffuse ceiling ventilation can significantly reduce or even eliminate draught risk in the occupied zone. Moreover, this ventilation system presents a promising opportunity for energy saving, because of the low pressure loss, extended free-cooling period and night cooling potential. The investment cost of this ventilation system is about 5-10% lower than the conventional ones, because the acoustic ceiling could be directly applied as air diffuser and the use of plenum to distribute air reduces the cost of ductwork. There is a growing interest in applying diffuse ceiling ventilation in offices and other commercial buildings because of the benefits from both thermal comfort and energy efficiency aspects.
Although the interest in the diffuse ceiling ventilation is growing recently, the practical experiences are quite limited and the knowledge is not well structured with this system. These become the motivations in developing the design guide. This design guide aims to establish a systematic understanding of diffuse ceiling ventilation and provide assistance in designing of such a system. The guide is targeted at design engineers, architects and manufacturers and the users of diffuse ceiling technology.
The design guide introduces the principle and key characteristics of room air distribution with diffuse ceiling ventilation. It provides an overview of potential benefit and limitations of this technology. The benefits include high thermal comfort, high cooling capacity, energy saving, low investment cost and low noise level; while the limitations include condensation risk and the limit on the room geometry. Furthermore, the crucial design parameters are summarized and their effects on the system performance are discussed. In addition to the stand-alone ventilation system, the integrations of diffuse ceiling ventilation with other HVAC systems are also discussed. Especially, the coupling with the thermally activated building system (TABS) is addressed and the control strategies for optimal operation is proposed. Finally, two case studies demonstrated the application and the deign procedure of the ventilation concept are presented.