Economizers play an important role in reducing the cooling energy in data centers. They are generally combined with chillers since it is difficult for economizers to meet the cooling demand throughout a year. To achieve energy-efficient operation in such hybrid systems, it is crucial to switch between operational modes and allocate the proper cooling load to the subsystems according to the outdoor conditions and cooling demand. This study aims to optimize the operation of a water-side economizer system functioning in a cold climate. A simple semi-optimal control was realized by adjusting the control setpoints using polynomial regression equations that represent the relationship between boundary conditions and optimal setpoints based on simulation-based optimization results. The operational data showed that the use of the semi-optimal control resulted in an increase in the system efficiency from 7.5 to 13.2. Additionally, the results suggest the importance of optimizing the cooling load allocation to the subsystems by leveraging the cooling potential of outdoor air while avoiding inefficient operation.

In recent years, as the demand for a decarbonized society has intensified, building clients have become increasingly concerned about the environmental performance of their buildings. In Japan, there have been many efforts and discussions concerning energy conservation in buildings. These have focused on design and construction, with few studies addressing the operational phase. The application of commissioning as a method of realizing substantial energy savings throughout a building's life cycle has become the standard worldwide. However, it has not yet become widespread on a business basis in Japan. One reason is that the non-energy benefit (NEB) generated by commissioning has not been sufficiently evaluated in Japan. In this study, NEB items arising when commissioning is introduced were comprehensively organized. The actual conditions were investigated in domestic cases. Based on the survey results, attempts were made to quantify each NEB. Simultaneously, the possibility that NEBs that did not occur or were negative may occur in the future were considered. The analysis indicated that some of the NEB items that may have arisen have not realized their value due to the current challenges of the Japanese construction industry, such as labor shortages and the use of multiple subcontractors. Future aims include the improvement of the NEB evaluation method proposed in this paper and the development of a tool that can estimate NEB according to project information by investigating the actual status of NEB in many cases and considering the relationship between project characteristics and the existence and size of NEB.

The objectives of this study are to clarify the path to create carbon-neutral for office buildings and to examine policy scenarios through a multi-agent simulation consisting of building owners and tenants. Based on previous studies, this study established and evaluated policies from a backcasting perspective, and examines their combination and timing of implementation in detail to achieve the new goal of achieving a carbon-neutral society. For this purpose, various parameters of the existing simulation program were readjusted, and some additions and modifications were made and reconstructed, such as incorporating new CO₂ emission coefficients for electricity and gas. The findings imply that it will be difficult to achieve a 51% reduction in CO₂ emissions by FY2030 with current policies. On the other hand, the findings indicate that continuous revision of policies could reduce CO₂ emissions by 70~90% by FY2050. In the future, this simulation model is expected to be useful for long-term policy design for office buildings.

In an open air system where outside air is supplied and room air is exhausted, methods to measure the age of air distribution using tracer gas have been established. However, in air recirculating systems where exhausted air is re-supplied back into the room, no tracer gas technique for evaluating fresh air distribution effectiveness and contaminated air removal efficiency has been developed. Here, we carried out a theoretical study on the tracer gas experimental method for measuring the age of air distribution in an air recirculating system by applying the concept of dynamic steady-state concentration. Furthermore, in order to determine key issues faced when applying this theoretical method to perform accurate measurements of the ventilation efficiency of air recirculating systems, case studies were carried out using CFD. In this paper, we theoretically considered the relationship between the concept of dynamic steady-state concentration in the air recirculation system and the age of air distribution and studied the effect of leakage when measuring the age of air distribution in an actual space. When the source was located in contact with the supply outlet, the concentration increase rate at each point in the air recirculation system without air leakage was constant, which was consistent with the increase rate of the average concentration. On the other hand, the ratio of the concentration increase rate at each point to the average concentration increase rate when there was air leakage became constant after 2 to 3 times the nominal time constant of the recirculating ventilation rate to the room volume. The results confirmed that the smaller the leakage is, the closer the value of the rate at each point is to 1.

The amount of air leakage from duct flanges is relatively large in duct systems. In this study, experiments were conducted to investigate effective sealing methods that can reduce air leakage from the flanges. The air leakage rate was measured when a duct sealer or an aluminum tape was used as the sealing material in both angle flanges and TDC flanges. In angle flanges, the effective sealing method was unclear because the amount of air leakage was small in all experiments. In TDC flanges, the effective sealing method was to cover the duct flange corners on the longitudinal seams from the outside with the duct sealer.