Katsunori Nagano

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 thermal-photovoltaic hybrid exterior wallboards incorporating PV cells in and their winter performances

The authors have developed experimental thermal-photovoltaic (PV) hybrid exterior wallboards that incorporate of PV cells. The clapboard-shaped hybrid wallboards permit modular assembly that can be more easily adapted for building applications than previous PV systems. Solar heat is collected in the form of heated air circulating in the air gap between the hybrid wallboard and the thermal insulation of the exterior walls. This paper presents an evaluation of both the electrical power generating ability and the solar heat collection capacity during winter of six variations of the experimental thermal-PV hybrid wallboard. In addition, exergy analyses were conducted.

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.

Influence of natural convection on forced horizontal flow in saturated porous media for aquifer thermal energy storage

Abstract Estimation of the heat recovery rate in high-temperature underground storage (>50 °C) is required before such a system can be built. However, if high-temperature water is injected into and stored in the aquifer, large-scale natural convection could occur that might reduce the heat recovery rate. This study aims to clarify the universal quantitative condition under which natural convection appears and exerts an observable influence for a system with forced horizontal flow in the saturated porous medium. The authors investigated this using both experiments and computer simulations. A test section simulating an aquifer was made. Warm water was injected into the test section, which was filled with glass beads. The temperature distribution and the flow rate profile at the outlet were measured. The authors found that the limit condition at which natural convection influences the forced horizontal flow can be determined from the velocity profile and modified Rayleigh number Ra*. In addition, the heat transfer coefficients of the upper and the lower side of walls were estimated. A computer simulation was made for calculation of the temperature field and the velocity vector in the porous medium under natural convection and under forced convection. As calculated temperature fields and flow rate distributions at the outlet were similar to the experimental results, it is thought that this program can be applied to evaluation of the temperature and the velocity of aquifer thermal energy storage. In addition, an index expressing the degree of influence of natural convection on forced convection was proposed.

DEVELOPMENT OF THE PCM FLOOR SUPPLY AIR-CONDITIONING SYSTEM

Floor supply air-conditioning system using PCM can enhance the building mass storage. In this study, diurnal cooling load is aimed to be covered by stored cold energy in PCM and building during night. Results from actual scale experiments and performance predictions are given.

Experiments to determine the convective heat transfer coefficient of a thermal manikin

Abstract In order to determine an equation for calculating the convective heat transfer coefficient in humans, that can be used in an outdoor environment, experiments using a thermal manikin were carried out at an air velocity in the range of 0.7–4.7 m/s. The convective heat transfer coefficient of the naked human body almost agreed with that of the clothed human body with two clothing ensembles. Empirical formulae of the convective heat transfer coefficient for the whole and 10 parts of the body were calculated using experimental data at an air velocity in the range of 0.1–1.0 m/s, which are applicable formulae at an air velocity in the range of 0.1–4.7 m/s. The thermal insulation of the two clothing ensembles decreased with increasing air velocity.

Effective radiant temperature including solar radiation

An evaluation method for thermal sensations of the human body in an outdoor thermal environment was developed. Effective radiant temperature was proposed as the mean radiant temperature in an outdoor environment. The operative temperature and standard new effective temperature, SET*, in outdoor environments could be calculated using the effective radiant temperature. In order to examine the operative temperature and SET* based on the effective radiant temperature, experiments using subjects were carried out in an outdoor environment at Sapporo city. The SET* calculated from experimental data correlated well with the thermal sensation votes of the subjects. It was shown that a SET* based on the effective radiant temperature can evaluate the thermal sensation of the human body in an outdoor environment.

Energy Balance of Low Energy House with Ground Source Heat Pump in Hokkaido

This study describes the construction and evaluation of a low energy house which should be in harmony with the environment, assisted by hybrid natural energy resources as well as supplied by unused energy. An experimental house with ground source heat pump (GSHP) was built at Hokkaido University, Japan in March, 1997. As a result of experiments, it was shown that approximately 80% of the total energy was provided from photovoltaic (PV) modules, solar collectors, underground and exhaust heat. The annual energy consumption was 12.5% of a typical house in Hokkaido.

Energy saving effect of desiccant ventilation system using Wakkanai siliceous shale

The nuclear power station accident resulting from the Great East Japan Earthquake disaster has resulted in a constrained electricity supply. However, in this Asian region there is high temperature and high humidity and consequently dehumidification process requires a huge amount of energy. This is the reason for the increasing energy consumption in the residential and commercial sectors. Accordingly, a high efficiency air-conditioning system is needed to be developed. The desiccant ventilation system is effective to reduce energy consumption for the dehumidification process. This system is capable of dehumidifying without dew condensing unlike a conventional air-conditioning system. Then we focused on Wakkanai Siliceous Shale (WSS) as a desiccant material to develop a new desiccant ventilation system. This is low priced, high performance, new type of thing. The aim of this study is to develop a desiccant ventilation unit using the WSS rotor which can be regenerated with low-temperature by numerical calcul...

Field measurement of indoor air quality and airborne microbes in a near-zero energy house with an earth tube in the cold region of Japan

This study was conducted to evaluate the level of microbial contamination of indoor air during 3 years for two residences in one building equipped with heat recovery ventilation devices and located in Kimobetsu town of Hokkaido, Japan. This article documents a case study aimed at monitoring the microbes contaminations indoors for a safe use of energy saving ventilation devices and sanitary indoor air. This articles describes an investigative approach with three components. First, the authors evaluated the indoor air quality and microbial concentration by comparing the concentrations of particulate matter (PM10 and PM2.5), carbon dioxide, and airborne bacteria and fungi of indoor air and outdoor air during spring, summer and winter. Second, the microbial concentration inside an earth tube and a fixed sensible heat exchanger was evaluated by measuring the airborne microbial concentration of the supply air. Third, the authors assessed the possibility of microbial contamination inside the earth tube using the fungal index and by measuring temperature and relative humidity at the tubes outlet airflow. The results showed that the total concentration of airborne fungi was higher in summer than in spring or winter and that the fungal genera Cladosporium sp. and Penicillium sp. were dominant in the samples. Additionally, it was found that the environment inside the earth tube allowed easy growth of fungi from May to September with the highest fungal index measured in August. It was also confirmed that the earth tube did not affect the supply air for a building constructed 4 years ago.