To make an evaluation of ventilation systems, numerical computation was carried out for three dimensional, isothermal, and turbulent flow schemes. It was found that there exists an optimum position for an inlet in relation to an outlet whereby the most effective ventilation can be attained. In addition, similar to the results for the two dimensional computation, the slope of the concentration decay is virtually constant and independent of the position in the room, so the mixing factor derived from this slope can be used as an index of the ventilation efficiency. Further, three dimensional computation seems to be necessary for a quantitative estimation of the mixing factor.

View full abstract

Studies on effects of geometric condition and variable input condition were carried out in order to prepare a model enabling to simulate thermal responses of a stratified-type heat storage water tank in heat storage system. A model which was proposed in Part 1 to explain mixing process in the tank is presently modified. The tank is divided into three parts; a perfect mixing region whose depth grows in proportion to inflow water volume, a one-dimension diffusion region and a dead water region. The initial depth of the perfect mixing region has relation to Archimedean number which is induced from the input condition. Geometric condition as the relation between inlet and outlet and the aspect ratio of tank little change the characteristic number defined as R_0 value. The regression equation for pipe inlet and full slot inlet, however, are presented differently. The model is extended to variable input conditions, both for the input temperature and flow rate, after the experiments, in which the new depth of the perfect mixing region is recalculated with new condition at the time the inlet condition varies.

View full abstract

Evaporative cooling is noteworthy as one technique of passive cooling on the ground that use of natural energy in buildings has become a matter of interest. This paper takes up evaporative cooling by means of roof spraying and examines the dynamic calculation method of room temperature and heat extraction of the building roof sprayed, to show the thermal effect of roof spraying. As far as the thermal effect of roof spraying is concerned, the preceding studies were considered in the previous paper, where the prediction method of heat gain using Wet Sol-Air Temperature, as an extension of the idea so-called Sol-Air Temperature including mass transfer mechanism on the wet building surface, was also described to obtain the thermal design data of roof spraying. Also the other previous paper described the combined passive cooling effect of roof spraying and natural ventilation. In order to grasp the seasonal thermal effect and energy saving by means of roof spraying according to areas and buildings, it is necessary to calculate accurately room temperature and heat extraction in roof spraying. For this, unsteady-state calculation method of room temperature and heat extraction which takes account of heat transfer related to mass transfer phenomenon on the roof surface is indispensable in addition to the one as ever. Mass transfer between water and vapor on the wet surface occures in relation to the surface temperature, and for its non-linearity against the temperature of the surface convergency-process is involved in the calculation of room temperature and heat extraction at every calculation time step. Availability of this convergency-process to the unsteady-state calculation method has its own problems in practical use and, therefore, it is necessary to devise some technique of linearization. From this point of view, this study shows the unsteady-state calculation method of room temperature and heat extraction in the multi-room building roof-sprayed, which takes account of radiant heat exchange between room surfaces and air movement through each room, and examines the thermal effect of passive cooling and energy saving related to heat extraction decrease by roof spraying in a model house. Further the simplified calculation method is proposed, which excludes convergency-process by linearizing mass transfer against the temperature approximately and its effectiveness is proved by estimating accuracy and CPU time required. In the report Part 1 of this study, outline of the above-mentioned calculation method is described and in the following report Part 2, the thermal effect of roof spraying is described, followed by a discussion on the evaluation of the simplified calculation method, simulating room temperature and heat extraction of the model house roof sprayed.

View full abstract

According to the unsteady-state calculation method of room temperature and heat extraction in the multi-room building, whose roof surface is wet by roof spraying, which was described in the report Part 1 of this study, simulation has been made in a model house roof sprayed in Tokyo and the thermal effect of roof spraying is examined, compared with the one without roof spraying. As the result of the simulation, with the use of thermal cooling storage of building structure by roof spraying, thermal environment of the room is clearly improved and natural cooling hours are lengthened. Also in the air-conditioned room, related to decrease of transmission heat gain from the roof, rate of heat extraction is lowered and cooling operation hours shortened. Further effectiveness of the simplified calculation method, which includes approximate linearization of heat transfer related to mass transfer phenomenon from the roof surface in roof spraying operation, is proved by analyzing accuracy of the result and CPU time required in the calculation of room temperature and heat extraction. Estimating the result obtained from the simplified calculation method based on calculation time interval of 1 hour in Tokyo, which approximates the curve of enthalpy of saturated air by fold line, it is clear that the fold line by every 5 degree C enables to maintain accuracy required in the calculation of room temperature and heat extraction.

View full abstract

To extend the authors' previous experimental study on the thermal storage efficiency of the first vessel of a hot water storage tank compartmented with submerged weirs, an additional experimental study was made on the thermal storage efficiency at the outlets of the second and third vessels, by measuring transient liquid temperature responses for the case in which hot water was discharged into the tank filled with cold water, under various hot-cold water temperature differences, flow rates, and tank configurations. From the experimental results and theoretical consideration, a semi-empirical equation suitable for predicting the thermal storage efficiency at the outlet of the n-th vessel, η_<nV>, was deduced as a function of the Archimedes number based on inflow conditions, Ar_0, the Peclet number, Pe, and three geometric parameters, φ_1, φ_2, and τV_1.

View full abstract

In planning a solar heating/cooling system, the direction, tilt angle and interval of arrays should be evaluated in order to achieve the maximum performance of the system. Including the contribution by applying additional reflecting mirrors, the effect of these factors on the collector efficiencies when CPC collectors are applied is considered different from when the conventional flat-plate or non-concentrating vacuum tube collectors are used. In the present study, calculation algorithm is explained at first, and then calculation results are illustrated for Sapporo, Tokyo, Nagoya and Kagoshima using the program and HASP standard weather data. The collector efficiency and mirror contribution are shown separately both based on the total collector area and roof area. The method of illustration may be quite useful for cost and/or performance evaluation. Lots of interesting guidelines for planning and designing have been figured out, with a conclusion that the reflecting mirrors were not so effective in CPC arrays.

View full abstract

This report analyzes a capillarity effect which influences on the water seal loss in the trap of sanitary fixtures. The experimental and the theoretical analyzes were carried on the thread which is adhered to the S trap. The experiments have been conducted for five kinds of threads and mainly measuring the changes of the water seal loss in relation to variations of the length of adherence and the number of the thread at the outlet leg of the trap. The results of experiments make it clear that the water seal loss is influenced by the length of the adherence, number and thickness of the thread. And also it is largely affected by the water seal level from the trap wear. By the theoretical examination, the increase of the capillary's radius which is produced between the glass surface of the trap and the thread is closely related to the changes of the water seal level in the trap.

View full abstract

The air layer in a rectangular cavity having isothermal vertical walls of different temperatures is widely used in thermal insulating walls. The authors had guessed that the heat flow should be impeded by setting appropriate partition plates in the rectangular air cavity in such a way that the hot wall was positioned upper than the cold wall in each separate air cavity. The numerical computations and experiments were carried out for a case that the partition plates were flat plates. The authors reported in the previous paper, that the air cavity which was partitioned by the flat plates showed good heat transfer characteristics as an insulating wall under a certain kind of conditions. After the examinations of these results, the authors reached to a conclusion that the air cavity which was partitioned by corrugated plates, should show better heat transfer characteristics than by flat plates. Free convection and heat transfer in the air cavity which was partitioned by the corrugated plates has been analyzed by the Finite Element Method to investigate the heat transfer responses. The radiation heat transfer was taken into the computations. The computations were carried out for the Prandtl number of 0.72, in the Rayleigh number range from 10^3 to 10^6, for two aspect ratios of the cavity, and for various radiation parameters under assumptions that the same air cavities were stacked infinitely in the vertical direction and the partition plate has no thickness. The rate of the heat transfer by convection, Nu_<mH>, takes a value below 2 under the all combinations of the wall emissivities. The rate of the heat transfer by radiation, Nu_<mHr>, decreases with decreasing the emissivities ε_H and/or ε_U. The effect of ε_H on Nu_<mHr> is larger than that of ε_U. The wall which has small emissivity ε_H, should be chosen for the hot wall to minimize the rate of the heat transfer by radiation. In this case, a small value of ε_U is also required. In this report, the comparisons were also made with the results under the flat plates. Both heat transfer rates by convection and radiation under the corrugated partition plates are less than the rates under the flat plates. Air cavity which is partitioned by the corrugated plates shows extremely good heat transfer characteristics as an insulating wall.

View full abstract

In order to achieve the correct heat balance equations for the walls of an air-conditioned space, the simultaneous quartic equations are generally required to be set up due to existence of radiant heat exchange between the interior surfaces. However, strict solving of the set of simultaneous quartic equations does not seem to be quite easy. In this regard, linearization process is generally applied to convert the quartic equations into the linear ones and the resultant set of simultaneous linear equations can be finally solved by matrix method. However, finding of the coefficient matrix in the matrix method seems to be troublesome. On the other hand, if the error arising from the linearization in matrix method, exceeds the limitation, the iteration process has to be performed in order to proceed the solution. In this paper, iteration process is proposed as a method through which the accurate heat balance equations can be directly solved. This method, so far called MRT-iteration method by the authors, is supposed to contain few advantages comparing with the abovementioned matrix method. In other words, as the algorithm being applied in the procedure of computer programing is simple above all, an accurate solution without any error arising from the linearization process can be directly obtained. Also, in this method the surface temperatures can be considered as effective factors in determining the convective heat transfer coefficients in the vicinity of the walls. In addition, a solution with sufficient accuracy can be practically reached within few times of iterations in the calculation, and this helps curtail the computation cost. In this study, iteration method has been employed in solving the heat balance equations of the space for two cases, that is, when the space is heated seperately, by warm air heating system and or radiant heating system. Meanwhile, for either case two different conditions of operation are assumed; first, if the space temperature is regulated by means of room temperature control, and second, if the space temperature is regualted by means of operative temperature control. Moreover, although Gebhart absorption-factor method has been applied in the calculation of radiant heat exchange, computations of the absorption factors have been proceeded, not by means of matrix method, but through simple algorithm by using the iteration method.

View full abstract

Ventilation of an air cavity in a building envelope by natural force is expected to be an effective measure to release solar irradiation in a hot or arid district. An external surface of a wall absorbs solar irradiation, and transfers it to the air in the cavity. The warmed air gets buoyant force. So when openings are provided at the top and bottom of the cavity, the warmed air is released through the top opening and cooler outside air replaces the space in the cavity. This reduces the further heat transmission into the built environment. This natural ventilation effect seems to be steady and strong. So if the width of a cavity and the openings are properly designed, the cooling load reduction by natural ventilation is believed to be considerable. An experimental model of an air cavity was constructed to examine the natural ventilation effect. The model has height 2.4m, width 70mm and depth 0.45m. Electric heating panels were hurried in the both sides of the cavity. Slit shaped openings were provided at the top and bottom of the cavity. Temperature and velocity measuring facilities were prepared in the experimental model. A number of measurements were carried out by changing the combinations of heat production and slit width. When heat production on the both sides were 78W/sq.m, and slits were set to 40mm, the average air velocity was 0.28m/s. The average convective heat transfer coefficient was 2.4W/sq.m K. It was affected by the surface heat production rate, but it was little affected by the slit size and the air velocity. When slit width was gradualy reduced the air temperature rose, and the air velocity fell suddenly between slit widths 10 and 20mm. The influence of dynamic loss seemed to become critical between these slit widths. When heat was produced on one of the two surfaces, a strong upward air stream was caused at the near region to the heated surface. The velocity fell steeply in the central region, and the velocity was nearly null at the unheated surface. The velocity boundary layer was much thinner than the half of the cavity width. When the both sides were heated symmetrically, the air temperature was highest at the directly attached regions to the surfaces, and the lowest temperature was observed at the center. The buoyant force was strongest at the attached regions to the surfaces, and it was weakest at the center. The buoyant force, frictional resistance and velocity pressure loss influence each other, and they form the velocity distribution. The peaks of the velocity distribution were observed in the regions 5 to 10mm from the two surfaces. The velocity distribution showed a trough at the center. The effect of momentum difused and disappeared in a relatively short distance from the entrance, it was shorter than 550mm. In the longer distance, the two thin velocity boundary layers were formed along the two sides, and the air in the center was induced by the air movement of the velocity boundary layers. This experiment indicated that if a cavity width and opening size are appropriately arranged, the natural ventilation performs effectively to release solar irradiation to the outside.

View full abstract

Heat gain reduction by ventilating a building envelope cavity should be examined under natural conditions of weather. The behavior of the air in a cavity is not so well understood as the heat flow in a solid wall is. Firstly, a method was developed to simulate the air and heat flows in a cavity by applying a finite difference method. Then the correction of the viscosity and heat conductivity of the air were examined to adjust the simulation results to the experimental results. Air flow in a cavity was considered to be one dimensional. A cavity was considered to consist of many vertical thin layers. The buoyancy, which is caused by the absorbed heat from the sides, frictional resistances between the layers, and dynamic losses at the entrance and exit of the cavity are the forces which were considered to decide the velocities of the layers. The velocity distribution in a cavity were sought by balancing all the forces over the layers. The air temperature distribution in the cavity were treated by considering two dimensional heat flow, and the heat transportation by the vertical air flow were also considered in it. A relaxation method was applied to balance the air flow and heat flow simultaneously. A computer program was written to treat the relaxation calculation. The theory of turbulent mixing length was applied to take into account the horizontal component of the air movement in a cavity. In the same manner, the eddy heat conductivity of the air was applied to cover the horizontal heat transportation by the horizontal air movement. These two concepts were adopted into the simulation program, then the constants in the eddy viscosity and the eddy heat conductivity were adjusted by comparing the calculated results with the corresponding experimental results. The performance of this calculation method was examined by changing heat production of the sides and restriction of entrance and exit in ranges. The strongest heat production was set to be the value, which may rise when strong solar radiation hits the exterior surface of a cavity wall. When this heat production was assumed, the Reynold's number of the air flow in a cavity were between 1500 and 2500, according to the restriction of the top and bottom openings. This range belongs to the transition region of laminar and turbulent flows. When heat transfer of the both sides of a cavity is strong, and also when openings on top and bottom of a cavity are larger than 30 percents of the section, this calculation method simulates reasonably well the heat and air transfers in a cavity. For the smaller heat production and stronger air flow restriction, carefull adjustment of the properties of the air was required. The eddy viscosity appeared to be different between the stronger and the weaker heat production sides. The strength of turbulency seemed to vary with the restriction of the openings. By these modifications, the heat and air transfer in a cavity wall seemed to be well included in the total thermal performance analysis of a cavity ventilated building envelope under natural weather.

View full abstract

This research estimates the amount of heat which can be recovered and utilized from Incineration Plants which have many examples already and further prospect in future in the field of waste heat recovery. We analyzed the available using amount of waste heat based on the data obtained through the investigation on the actual condition among Incineration Plants having continual incinerators in Japan. The available using amount from Incineration Plants equipped with continual incinerators in Japan is about 7600Tcal per year. This is proportionated to an amount of 800000kl per year in oil conversion, so that it's effective to use them. Only 24 percent of Incineration Plants have waste heat boiler that is indispensable in order to use waste heat.

View full abstract