Development and verification of a new natural ventilation system for offices utilizing low-temperature outdoor

In recent years, due to seasonal changes in Japan, summers and winters have become longer and springs and autumns shorter. As a result, opportunities to utilize natural ventilation, one of the energy-saving methods for air conditioning, have decreased. In order to extend the available period of natural ventilation, the authors developed a natural ventilation system that can utilize low-temperature outdoor air. CFD analyses were performed by simulating one span in an office space of a standard floor where giving internal heat generation and natural ventilation inflow were given. By comparing three inflow patterns, i.e., the peri- counter method that supplies air from the foot of the window, wall slit method that supplies air from the top of the window, and ceiling perforated panel duct method, it was shows that the perforated panel duct method was the most comfortable of which ADPI was over 90%. The aperture ratio of perforated metal panels was also studied to supply low-temperature outdoor air evenly from the ceiling in an office with a depth of approximately 20 meters. Specifically, the flow network calculations were performed to find the difference between the indoor pressure and the duct pressure that finally determined the aperture ratio distribution between 3.0 to 12%. To confirm its effectiveness, full-scale measurements for both cases of calculated aperture ratio and a uniform aperture ratio were conducted. In addition, based on the on-site measurement, it was also confirmed that natural ventilation was promoted by exhausting waste heat from the cogeneration system through voids for buoyancy-induced ventilation, and natural ventilation rate increased. Finally, the actual operation was also analyzed and it was confirmed that by introducing low-temperature outdoor air, the effective time of natural ventilation system increased by 55 to 75%, and the amount of heat removed by natural ventilation increased by 104 to 170%.