The chisett was the traditional one room thatched house of the Ainu people in Hokkaido Japan. A primitive and traditional house, like the chisett, can be regarded as the origin of our present artificially produced spaces for human beings. It is important to know about the chisett in order to compare with the present state of artificially enclosed space as well as to understand Ainu culture deeply. A model house of the chisett (3.7×5.4m) was reconstructed in October 1986, and the heating environment was measured for 14 months until December 1987. It was heated by a hearth. In this paper, the fundamental characteristics of the air and globe temperatures in heating are presented. The globe temperature at the position of occupants by the hearth was around 20℃. The air and globe temperatures, in the center of the room 50cm above the floor, were about 10K and 15K higher than the outside air temperature of around -10℃ in the midwinter respectively. Gas and dust concentrations in the occupied space were 0.06% for CO_2, 20ppm for CO and 2mg/m^3 for dust respectively. These levels shows a 10〜14% of the regulation levels for the working place in Japan. Amount of flow rate of infiltrating air estimated was about 1.3×10^3m^3/h.

View full abstract

In the previous paper, it was proved that the cavitation in the confluent pipe occurred in two patterns, cavitation on the streamline separating from the down confluent point and that caused by vortices of confluence. In this paper, the attention was paid only to cavitation on the streamline, because the influence of the vortex cavitation on the flow is smaller than that of the cavitation on the streamline. Two dimensional potential flow analysis with free streamline was taken up as one of the methods to study the flow with separation, and cavitating flow in the confluent pipe with an arbitrary confluent angle was analyzed. The observation of cavitation shows that the cavitation incipience occurs on the separated streamline in the neighborhood of the down confluent point. With this result, it can be assumed that the velocity gets to the maximum at this point. Therefore, Roshko model of two dimensional potential flow theory was applied to analyze the flow in confluent pipe and obtain the shape of separated stremline, the contraction coefficient and the critical cavitation number. As the result, the following conclusions were obtained. 1) The shape of theoretical streamline obtained with Helmholtz-Kirchhoff model, agrees with the experimental data under supercavitation. 2) The contraction coefficient becomes smaller, and thickness of cavity becomes larger as the angle of confluence increases. 3) With large angle of confluence, the contraction coefficient becomes larger with decreasing area and velocity ratio of lateral to main pipe. However, with small angle of confluence, there is little change in the coefficient caused by the area and velocity ratio. 4) With increasing non-dimensional velocity, that is, with increasing ratio of velocity on the separated streamline near the confluent point to that at infinitely downstream point, the contraction coefficient becomes larger. 5) As the value of the velocity ratio of lateral to main pipe increases, the critical cavitation number becomes smaller, and it becomes more difficult for the cavitation to occur. 6) With small velocity ratio, measured critical cavitation number agrees with the theoretical value obtained on the assumption that the non-dimensional velocity is equal to 1.0. However, with increased velocity ratio of lateral to main pipe, a larger value of the non-dimensional velocity must be assumed to give a good agreement.

View full abstract

This paper introduces one of the many results of the questionnaire inquiry on building service systems and interior environment of office buildings which was conducted from 1983 through 1984 in Kyushu district. The actual conditions of thermal and hygienic environments in office rooms are described in this study, relating to the buildings mangement, the age of completion, the net area and so on. The statistically analyzed data of eighty buildings in Fukuoka, Kumamoto and Kagoshima City were measured from 1980 to 1982 according to "Law for Maintenance of Sanitation in Buildings". Those data are composed of six environmental variables such as air temperature and humidity, air flow speed, carbon mono- and dioxide concentration and dust concentration. The features of frequency distributions of six environmental variables were shown. The principal components of thermal environment and hygienic air quality were obtained by principal component analysis. Lastly, the relations between actual conditions of interior environment and "Building Sanitation Management Standards" were clarified.

View full abstract

In this study, it is investigated what effect the error in measured gas concentration and gas emission rate has on the ventilation rate when the tracer-gas method is applied to the estimation of the ventilation rate of a certain room. The appearance probability of the error of ventilation rate is calculated assuming that the appearance probabilities of the error of measured gas concentration and gas emission rate are normal probability density distribution. Following two conditions are set up. One is no gas emission (which is called decay method) and the other is constant gas emission (which is called increase method). In consequence, it is made clear that by the decay method, for the most accurate estimation of the ventilation rate, the gas concentration should be measured when the concentration decreases to 0.5〜0.3 times as much as the initial gas concentration. By the incease method, it is made evident that the longer the measuring time the higher the accuracy of ventilation rate, under any condition of ventilation rate, gas emission rate with the standard deviation of probability density of errors of gas concentration and gas emission rate.

View full abstract

Natural convection flows in thermosyphon have been utilized in many technological applications in the past. Even in the field of building equipment, a closed-loop two-phase thermosyphon system, incorporating an evaporator and condenser, is a particularly attractive way to recover heat from such heat sources as solar energy and waste heat and to convey heat without any external power in the air conditioning system. The purpose of this paper is to present a simulation model to predict operating and heat transfer characteristics of a closed-loop two-phase thermosyphon system from air heat source with temperature less than 100 degree Celsius to water. The two-phase thermosyphon system consists of an evaporator (two plate finned coils), a condenser (shell and coil heat exchanger) located above the evaporator and connecting tubes (riser tube and down comer). Freon R-113 is used as the working fluid. Experiments are conducted by changing such operating parameters as a heat source temperature and Freon charge level keeping cooling water flow rate, temperature and air flow rate constant. The simulation model to predict operating and heat transfer characteristics of this closed-loop two-phase thermosyphon system was proposed and simulation results were compared with experimental results. Fairly good agreements were obtained between simulation and experimental results and it was found that this simulation model is useful for the design and the prediction of the optimum operating conditions of the closed-loop two-phase thermosyphon system.

View full abstract

Energy loss has been increased from the mixing of heated air jet and cooled air jet in an air-conditioned office room where the perimeter heating and interior cooling are applied simultaneously. It has become the serious problem due to an increase in heat generation along with the development of automation functions in the office room. The purposes of the present study are to disclose the mechanism of the energy loss and to establish the optimum design methods of air-diffusion devices and the control devices in the simultaneous heating and cooling system. In the present paper, the effects of type of interior outlet and heat storage load produced due to the intermittent air-conditioning on the energy loss were mainly analyzed through two series of experiments using a simulated full-scale office room. Furthermore, the air temperature distribution were analyzed and evaluated. The standards of designs for the air-diffusion device and the control method were given based on the series of experimental results including the previous study. The results are summarized as follows: 1) The types of interior outlets investigated in the present study are the anemostat diffuser, radial-flow outlet and rectangular grille. The grille mounted on the high sidewall brought the largest amount of the energy loss. 2) It was confirmed that the control temperature difference between the perimeter and the interior had the greatest influence on the energy loss. 3) The heat storage load in the floor slab had almost no effect on the energy loss. However, it seems to have great influence on the thermal comfort of occupants because of the considerable lowering of air temperature above the floor. 4) Among locations of the perimeter thermostat, the front position of the fan-coil unit brought the most desirable effects and the inlet position of the fan-coil unit brought the most disadvantageous effects on both the energy loss and the room air temperature distribution.

View full abstract

Natural ventilation of an air cavity in a building wall has long been practiced as measures for internal condensation prevention in a cold district, and for radiative heat dissipation in a hot district. But this technic has been developed empirically, and its scientific base has not yet been known sufficiently. A building wall is exposed to a daily change of weather, especially of solar radiation. So the thermal response of a naturally ventilated cavity wall must be examined under an unsteady heat transfer condition. For this purpose, a simple method is required to simulate the thermal effect of natural ventilation in a cavity. Natural ventilation in a wall cavity changes from laminar flow, when solar radiation is scarce, to turbulent flow, when a wall exterior recieves strong solar radiation. There exists abundant experimental and theoretical research results on the heat transfer of a heated internal surface of a duct or a pipe, which is ventilated naturally. But most of them belong to either one of the regions of laminar and turbulent flow. Natural convection heat transfer is not yet thoroughly studied for the transition region between them, where the natural ventilation of a cavity performs for a long duration. So the mass and heat transfer in wall cavities was examined with full scale thermal models of wall cavities. The thickness of the cavities, the contraction at the entrances and exits of the air passages and the heat flux of the walls were changed in ranges. An experimental equation was induced from the results of the heat transfer experiment. The applicable region of this equations is limited in the area, where natural ventilation in a wall cavity may experience. A numerical analysis computer program was made to simulate the response of a naturally ventilated cavity wall under a daily change of outdoor and indoor conditions. This program consists of two parts. In one of the parts, the horizontal heat transfer across the cavity and the vertical air flow and its heat transportation effect is processed. The proposed equation for the heat transfer in a cavity is adopted in this process. In the other part, the heat transfer through the solid part of the wall is treated as transient and two dimensional heat flow. The simulation results of this computer program was examined by comparing it with the experimental results of the two typical wall models, which were exposed to the weather of a typical Japanese country side. This comparison indicated that the numerical analysis program simulated the temperature variation in the walls, and the heat flux on the external and internal surfaces of the wall main bodies reasonablly well. This numerical analysis program may be used effectively for performance examination of natural cooling of cavity ventilated walls, which may have various configurations and various thermal characteristics, and may be exposed to various climates.

View full abstract

In temperature stratified water thermal storage, the vertical allocation of inlets and outlets gravely affects the storage performance. Authors are convinced that a recommended standard allocation is available in newly constructed buildings. Sometimes, however, in the retrofits or other particular case, it may be unavoidable to adopt any other allocation. A study on these cases will give us more universal design data as well as much more understandings on the mechanism of the mathematical model of temperature stratified tanks. With the premise of the knowledge on R-value model which were already reported in five series, authors summarized the mixing properties of the temperature stratified tanks. After introducing the relation between the concept of effective volume ratio and the vertical allocation of the inlets and outlets, authors presented the regressive equations to predict the mixing depths in case of vertical input and in the combination of various aspect ratios of inlets and tanks. The mixing depth increases when the inlets sinks deeply below the water surface and the dead space appears when the outlets are highly put over the bottom in case of the hot water storage, and vice versa in case of the chilled water storage. The method of modification of R-value model for these particular cases were shown and the calculation ways of storage performance either by hand or by computer simulation were presented.

View full abstract

In order to estimate the thermal environment of underground spaces or heat loss from buried pipes, it is essential to develop an efficient simulation model of underground temperature profiles beneath different surfaces. In this study, first of all, long-term measurements of underground temperature profiles beneath grass covered and asphalt pavement surfaces are performed. Underground temperature profiles beneath the asphalt pavement surface were considerably higher than beneath the grass covered surface; the difference attained a maximum of 9.0℃ at 0.5m depth in summer and the difference between two annual average temperatures was about 4.0℃. Using these data, a least squares analysis was performed to obtain the thermal diffusivities of the soils. After the measurements, numerical simulation of underground temperature was performed. Several parameters in the simulation model were optimized so that simulation results using the weather data at the same time as the measurement agree of with the measured temperature most exactly. After that, use of the standard weather data and simplification of boundary condition at the surface were examined.

View full abstract

Understanding of the thermal characteristic of a building is essential for engineers to design the building. This paper describes a simplified procedure, applicable for education of students and practical engineers, to predict heating load for the given room air temperature in a dynamic situation. In a case of intermittent heating, the accuracy of the predicted heating load and room temperature greatly depends both on the calculating time interval (normally one hour) in computer program and the appropriate modelling of the mutural radiant heat exchanges between internal surfaces. The Successive Integration Method has an advantage to shorten the calculating time interval without a substantial increase of calculation time. Thus shortening the calculating time interval from one hour to 0.5 hour provides an acceptable prediction of the room temperature drop, followed heater shut-down. Another advantage of this procedure is to predict the approximate pre-heating load by replacing temperature rise curve with the hypothetical linear rise. By applying the environmental temperature, which combines the effect of the air temperature and radiation, instead of the room air temperature, more accurate results can be obtained on all aspect of thermal behavior in buildings.

View full abstract

At the author's laboratory, the Tokyo area weather observed by the Tokyo district meteorological observatory at Otemachi has been edited for file every year. This time, we have completed the hourly weather data for 16 years from 1972 to 1987. Based upon the data, outdoor design conditions for heating and cooling loads calculation have been compiled. The data were arranged for TAC 2.5, 5.0, 7.5, 10.0, 50.0% with the minimum and maximum values to help decide on system capacities and seasonal heat loads as well. The new weather data, compared to the conventional TAC outdoor design conditions, show a drop in humidity at both heating and cooling seasons and a rise in temperature at night. From this observation, it is evident the Tokyo metropolitan area weather is changing to that of the deserts.

View full abstract