Demand for data centers has increased greatly with prevailing Internet and IT systems. Enormous heat generation of information handling requires reliable and high efficiency air-conditioning system. Recent high density servers are required to conserve more energy and have less running const than conventional ones. According to a previous study by Suwa et al., an air-conditioning system with both supplies and returns on the ceiling is the most effective air flow system; however, this study was done via computational fluid dynamics simulation and a shrink model experiment. In addition, Hayama et al. have proposed some important indexes for determining cooling characteristics of air flow systems; however, the indexes are difficult to utilize to control an air-conditioning system. In this study, the authors have performed actual model experiment for an air-conditioning system with supplies and returns on the ceiling. To determine cooling characteristics, the indexes were applied, and the authors compared the indexes of the actual model with those in the previous research. Furthermore, the authors applied RCI_<HI> to evaluate temperature distribution of the rack inlet in order to accumulate fundamental data for air-conditioning control of a data center. As a result, the following cooling characteristics of the air-conditioning system with supplies and returns on the ceiling were observed. ・Increases in supply flow decrease the normalized rack inlet temperature, but increase the exhaust efficiency. ・The supply temperature does not affect the cooling characteristics nor the exhaust efficiency. ・A hanged wall decreases the normalized rack inlet temperature on the center racks, but increases it on the edge racks. Further, it increases the exhaust efficiency on all the racks because it facilitates separation of air between hot aisles and cold aisles. The authors observed the following features by using RCI_<Hi>. ・All cases of all amounts of supply air under 20℃ without hanged wall result in over 0.93 RCI_<Hi>. ・If the supply air temperature is over 22℃ without hanged wall, RCI_<Hi> increases with an increase in the amount of supply air. ・All cases of all amounts of supply air under 20℃ result in an increase in RCI_<Hi> with an increase in the hanged wall ratio. ・Under the condition of 26℃ supply air and a hanged wall ratio of 0.8, the rack inlet temperature succeeds max allowable temperature. This is because the hanged wall prevents temperature increase on the center racks, but facilitates temperature increase on the edge racks.

View full abstract

The use of aquifer thermal energy storage (ATES) systems has spread widely in north Europe in recent years as a low-cost, high-capacity means to seasonal thermal storage. We intend to develop an ATES system for daily thermal storage cycles using a quantitative design approach. A model simulating the advection/diffusion of heat in an aquifer along with a model using a thermo-dispersivity constant was applied through parameter identification to reproduce the well temperature after warm water injection. Experiments were performed on two newly installed open wells, and the results from one well in a closed area were examined. The soil heat capacity, thermal conductivity, etc. were obtained from the literature. The regional groundwater flow speed and dispersion length were obtained from appropriate well pumping tests. In all cases, the well temperature could be accurately predicted.

View full abstract

This paper describes field measurements conducted in several households with different heat demands for performance evaluation of residential combined heat and power (CHP) systems, which are increasingly becoming efficient domestic hot water supply systems using a storage tank. The annual dependence rates of electric power measured in the three households stood comparison with an average value of 205 households by the New Energy and Industrial Technology Development Organization (NEDO) and the New Energy Foundation (NEF). In particular, the rates between 14:00 to 15:00 in summer were high, and this system contributes to the reduction in the electric power consumption in grid-connected network areas. The AC electrical efficiencies at rated output operation were approximately equal to values obtained by NEDO and NEF. The decrease in the efficiency in the lower load factor was small, and high energy saving characteristics were confirmed. The annual primary energy reduction was 6.6, 21.1, and 5.4 GJ in each household. The tendency that a reduction effect improved when a large amount of exhaust heat was used was shown quantitatively. A comparison between the measured values and the calculated values using a CHP optimization tool was performed. The calculated annual primary energy reduction exceeded the measured values in each household, and a further performance enhancement in future should be possible.

View full abstract

Breathing is one of the most essential activities in our lives and we might not realize the significance of these activities. The basic function of breathing is to supply oxygen from ambient air and remove carbon dioxide from the blood stream in our lungs. The air we breathe every moment comprises oxygen as well as a number of suspended particles. As a consequence, human beings experience lifelong exposure to billions of particles via inhalation. The health risk to humans is increasing owing to the amount of hazardous inhaled particles deposited in the respiratory tract. In this study, Computational Fluid Dynamic (CFD) technology has been applied as an alternative approach for providing an understanding of the air flow pattern as well as the aerodynamic deposition of particles in the human respiratory tract (human airway). The three-dimensional (3-D) respiratory tract model was created using computed tomography (CT) data of a healthy human male. Steady nasal inhalation (7.5 L/min) and aerosol (0.1-50 μm) behavior were computed using a low Reynolds number type k-ε turbulence model coupled with a Lagrangian discrete phase model. The flow patterns were obtained through the visualization of planes in complex flow areas that depicted formations of turbulent flow primarily from the nasal cavity to bifurcations. Beside the air supply function of the human airway, there is a condition function that regulates the inhaled air temperature to core body temperature to maintain the alveolar epithelium in the lungs under the stable condition. Room temperature (20 ℃) was assumed as the inhaled ambient air. The inner walls, which are covered by a mucus layer are assumed to be at a constant temperature of 37 ℃. The convective heat transfer coefficient (CHTC) was defined based on the heat flux and the temperature difference. The CHTC was determined at about 2.7 W/m^2/K in the airway model. 20,000 mono-dispersed particles were released uniformly in a direction normal to the inlet surface of each nostril. The total depositions in the airway model for particle sizes of 0.1 and 1 μm were about 19.9% and 20.1%, respectively. Large particles were mostly deposited in the nasal cavity at a rate of 99.4% whereas particles having a size of 10 μm were deposited at a rate of 42%. The vestibule region to the anterior turbinate area was recorded as being the region with the most number of airborne particles desposited.

View full abstract

This paper describes the development of a heat source characteristic model of an air conditioner during its cooling period, which is useful for saving energy when cooling is required while maintaining the comfort of residents in residential buildings. The major findings can be summarized as follows: 1) A heat source characteristic model of an air conditioner during cooling period was developed. This model aims to determine the ratio of the theoretical performance of the heat source to actual performance of the heat source of the appliance. The model does not depend on the characteristics of the specific appliance; therefore it is applicable to various appliances. 2) The cooling operation of an air conditioner under various conditions was investigated, and the precision of the model was evaluated. The monitored data and estimated data were almost equivalent. 3) The COP of a certain type of air conditioner under the different room temperatures or heat requirements was calculated based on the model.

View full abstract