Shintaro Yokoyama

Field experiments and analyses on a hybrid solar collector

Abstract This paper describes the effectiveness of a hybrid solar collector that generates both electric power and heat. Experiments and analyses were conducted on power and heat generation characteristics of the hybrid solar collector. First, experiments under constant supply temperature of brine were made and it was found that conversion efficiency ranged from 10% to 13%, and that collector efficiencies at 20 and 40 °C brine temperature were from 40% to 50% and approximately 20%, respectively. Second, the efficiency of the hybrid solar collector was compared to those of a photovoltaic and a solar collector and it was clarified that the hybrid collector had an advantage in terms of exergy efficiency, though there is some lowering of collector efficiency. Evaluation of annual energy balance of hybrid solar collectors installed on a low energy house at Hokkaido University proved the hybrid solar collectors to have a high degree of feasibility.

Development of a database of low energy homes around the world and analyses of their trends

This study aims to develop a database of low energy techniques for homes around the world, for use in systematically evaluating the low energy home in each region, where climate, culture and policy differ. First, a database was made for the purpose of the systemizing passive and active techniques. Data were input according to seven chapters and 155 items, and 66 homes in 17 nations have been recorded. Homes adopting super insulation, high airtightness and solar energy utilization are common in the each country. The thermal insulation performance of wall and window of the housing in Japan is somewhat inferior to that overseas. It was shown that exhaust heat recovery is rarely adopted in Japan and that the underground thermal energy utilization was seen in less than 10% of recorded homes. Second, recorded homes were categorized according to characteristics of adopted strategies, and the reduction rate of purchased energy versus the purchased energy for a typical home was calculated. This revealed the purchased energy reduction rate of homes with both solar heat utilization and photovoltaic power generation to be very high.

An electrostatic integrating 222Rn monitor with cellulose nitrate film for environmental monitoring.

This paper describes a new type of electrostatic integrating 222Rn monitor designed for the environmental 222Rn monitoring. The window area of the monitor was selected to make the exchange rate optimal. The collecting electrode was positioned on the basis of calculating the internal electric field. A drying agent, P2O5, was placed in the bottom of the monitor, since the collection efficiency of 218Po+ atoms depends on the humidity of the air. The monitors have been calibrated against known 222Rn exposures. The detection limit is 1.2 Bq m-3 for an exposure time of 2 mo. In a small survey, annual mean 222Rn concentrations between 3.7 and 9.5 Bq m-3 in outdoor air and between 6.4 and 11.9 Bq m-3 in indoor air were measured.

Human thermal models for evaluating infrared images

Discusses comparing infrared images under various thermal environmental conditions through normalization of skin surface temperature. To evaluate IR images obtained under various thermal environmental conditions, we proposed a human thermal model with which IR images obtained under certain thermal environmental conditions can be converted into images under other conditions. The model was based on a numerical calculation of the bio-heat transfer equations that express heat transfer phenomena within the human body. A 16-cylinder-segment model was used as the geometry of the human body. Comparisons of IR images with their converted images indicate that this method is effective in eliminating the influence of the thermal environmental conditions. However, the difference between the converted images and the original ones varies among segments. In future work, we will use this method to investigate the IR images of several subjects under various thermal environments.

Estimation of radiative heat transfer using a geometric human model

In order to provide a detailed estimate of radiative heat transfer between a human body and its surrounding environment, the authors have developed a geometric model of a human form and an algorithm. The model closely resembles the actual shape of a human body and is composed of small quadrilateral surfaces. Dealing with an object or a space with an arbitrary shape, the developed algorithm can judge efficiently whether there is an obstruction between a pair of surfaces. As a result, the angle factors between a pair of surfaces that only occur during radiative heat transfer can be defined. The distribution of the radiative heat transfer rates shows the characteristics of body shape and variations in posture.

Study on underground thermal characteristics by using digital national land information, and its application for energy utilization

This paper describes a method for evaluating characteristics of underground thermal properties and groundwater, whose evaluation is essential for designing systems of underground thermal energy utilization. First, the systems using underground thermal energy are classified into two categories: borehole system with indirect heat exchange, and aquifer system with direct use of underground water. These systems are also divided into thermal storage systems and heat source/sink systems. Second, the characteristics of the underground in Japan are analyzed by using a geographical information system (GIS) and hydrogeological information. Regulations on environmental protection, such as those relating to national parks for instance, and the distribution of thermal energy demand eliminate 77% of Japan from consideration for underground thermal energy utilization. Areas limited to borehole thermal energy utilization account for 17% of areas where underground thermal energy can be used, with the remaining 74% suitable for both boreholes and aquifers. Finally, we estimate the thickness of aquifer and groundwater velocity in Sapporo. We find that most parts of Sapporo are suitable for aquifer thermal energy storage (ATES).

Cockpit thermal conditions and physiological reactions in flight: effects of mental workload on thermal regulation of aircrew while flying tasks⋆

Thermal conditions in aircraft cockpits may affect aircrew performance, yet few in-flight measurements are available for the Japan Air Self-Defense Force (JASDF). This survey investigated the thermal environment in both the front and rear seats of the cockpit, as well as thermal strain on each of the pilots during flight, with the focus on the differences between the front and rear, using data collected during ten normal sorties by F-4EJ (kai) and T-4 aircraft based at Naha AFB, Okinawa. Environmental and physiological data were recorded in both the front and rear cockpits at 1-min intervals throughout each mission. Cockpit temperatures at shoulder level in the F-4EJ (kai) and T-4 exceeded 40°C during flights in summer, and there were no significant differences between front and rear cockpit thermal conditions in either type of aircraft. However, increases in rectal temperature and heart rates of the front pilots during flight were greater than those of the rear pilots in both types. The total sweat rate of the F-4EJ (kai) pilots was 153±40 and 125±37 g/m2 h in the front and rear, respectively. Further, thermal comfort sensations reported by the front pilots were more uncomfortable than those by the rear pilots in both types of aircraft. Although there were no significant differences between front and rear cockpit thermal conditions and flying experience of each pilot, physiological strain experienced by the front pilots during flight was greater than by the rear pilots. Peripheral skin temperature of the front-seat pilots decreased gradually during flight. Since the mental workload imposed by the flying tasks contracted the peripheral blood vessels of the front-seat pilots, the prevention of heat loss from peripheral portions induced an increase in rectal temperature. It is suggested that thermal regulation is influenced by mental workload when performing flying tasks.