2020 Volume 45 Issue 282 Pages 27-35
Because businesses are required to save energy in accordance with the Strategic Energy Plan proposed by the Agency for Natural Resources and Energy of Japan, it is necessary to reduce the energy utilized for building operation as much as possible. Therefore, a new rousing system using lighting that conveys to occupants the suitability of the present state of the outer air for natural ventilation and operates the mechanical air conditioning system has been developed and introduced in a new office building at Takamatsu. In this paper, the actual energy consumption report and the indoor environment survey conducted in this building for a floor with a total of 23 windows on all four sides, are discussed. First, the rousing system was turned on frequently from March to June and from September to December. Energy consumption for air conditioning was reduced by 50 - 70 % in these periods, and particularly in May, June and October in the second year. In other words, the rousing system helped this building become net zero energy building (ZEB) ready. Second, the natural ventilation efficiency of this building was investigated. Fresh air was found to enter through the north window and exit through the south window, when all the windows were open. Furthermore, at this time, the ambient air velocity was under 0.5 m/s and the ventilation volume was such that the indoor air was replaced 5 to 15 times per hour. Third, the survey on indoor environment during natural ventilation indicated that the carbon dioxide concentration was 400 to 600 ppm. Although only half the number (10 - 12) of windows were opened, this value was lower by 150 to 200 ppm than that during mechanical air conditioning. Lastly, the results of the occupant questionnaire indicate that there was no significant difference in thermal sensation, thermal comfort, and overall satisfaction between natural ventilation in autumn or spring and mechanical cooling in summer. However, the air flow sensation exhibited a significant difference between spring and summer, and the average of the subjective intellectual productivity in autumn was slightly lower than that in summer. In summary, this report suggests that it is possible for manually operated natural ventilation to not only enable energy saving but also maintain the same levels of indoor thermal sensation, thermal comfort, and satisfaction as those during mechanical air conditioning. However, further studies must be conducted so as to not reduce intellectual productivity.
