Journal of Environmental Engineering (Transactions of AIJ)
Online ISSN : 1881-817X
Print ISSN : 1348-0685
ISSN-L : 1348-0685
Volume 86 , Issue 790
Showing 1-6 articles out of 6 articles from the selected issue
  • Yukiko CHATANI, Kazunori HARADA
    2021 Volume 86 Issue 790 Pages 863-872
    Published: December 01, 2021
    Released: December 01, 2021
    JOURNAL FREE ACCESS

     To construct large-scale buildings, principal construction elements such as beams and columns shall be fire resistant. In case of timber structures, fire resistance is needed so that construction element shall withstand the standard fire for a specified time and so that the self-burning shall be stopped until the elements are cooled down to normal ambient temperature. Self-extinguishment is a complex phenomenon that involves various external factors and the properties of wood. Self-extinguishment is confirmed by experiments in practice. However, it is expected to predict the occurrence of self-extinguishment by analytical methods for use in design and development of wide varieties of wooden members.

     Based on the two-dimensional unsteady heat conduction equation, Harada et al. have created a model that incorporates the effects of reactions peculiar to wood combustion: moisture evaporation, pyrolysis of volatile components, glowing combustion (char oxidation), shrinkage and cracking.

     In this paper, the rate of decrease in the residual ratio due to glowing combustion was derived from the results of experiments on glulam heated by constant radiant heat flux using a cone calorimeter. The derived rate equation was applied to the heat conduction model to reproduce the cone calorimeter experiments. The calculated values showed that the samples burned more violently than the experimental value. The reason is that the analysis did not consider the oxygen concentration distribution within the char layer.

     The glowing reaction rate equation was modified in consideration of the influence of the oxygen concentration distribution within the char layer, based on the following assumptions. (1) The oxygen concentration distribution decays exponentially with depth from surface. (2) The effect of shape changes due to shrinkage and cracking of the char layer is ignored. (3) The change in the surface position of the sample is ignored.

     As a result of calculation using the modified glowing reaction rate equation, the maximum value of the surface temperature and the maximum value of the mass loss rate were in good agreement between the calculated value and the experimental value. On the other hand, the values of charred depth and burnout depth were smaller in the calculations than in the experiments in case of low heating intensity. When the heating intensity was 30kW/m2, the calculation value and the experimental value of charred depth and burnout depth agreed very well. Further verification is required for the cause of the difference between the calculated value and the experimental value at low heating intensity.

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  • Ryuta TOMITA, Kyoko ABE
    2021 Volume 86 Issue 790 Pages 873-882
    Published: December 01, 2021
    Released: December 01, 2021
    JOURNAL FREE ACCESS

     The "floor" that is in constant contact with people is important for users to spend comfortably and safely in the architectural space. Improving floor performance (safety and comfort) is considered to be an important issue for all generations, including children, adults and the elderly.

     The purpose of this study is to be safe and comfortable for children and the elderly, and to solve the problem of floor impact sound. It is "Development of tatami with consideration for sound insulation performance and safety and formulation of design guidelines".

     In this paper, we first focused on tatami as a basic study. We examined heavy-weight floor impact sound, the hardness at the time of a fall collision, and the hardness at the time of walking. In addition to commercially available straw tatami and building material tatami, five types of tatami mats focusing on vibration isolation were prototyped and experimentally examined. For reference, we also examined light-weight floor impact sound.

     As a result of this paper, the following findings were obtained.

     1) Straw tatami and building material tatami had no effect on the heavy-weight floor impact sound level reduction in the 63 Hz band, and were about 0 to -1 dB. In tatami mats that was prototyped in this paper, considering the vibration isolation, we were able to achieve a performance improvement of 3 dB by reducing the heavy-weight floor impact sound level in the 63 Hz band.

     2) Regarding the hardness at the time of a fall collision, straw tatami and building material tatami were 50 to 53 G. The prototype tatami mats had a large impact mitigation effect of 20 to 31 G.

     3) Of the prototype tatami mats that were able to realize (1) and (2), T4 and T5 were also good for walking.

     4) Regarding the four types of performance related to floor hardness, the relationship of quantitative evaluation of each performance was clarified. It turns out that none of the performances correspond linearly. It was suggested that it is necessary to examine each layer in the floor cross section and the combination of each layer for each performance.

     As described above, in this paper, it was found that the prototype tatami mat does not impair the walking feeling, and the effect can be obtained by the amount of reduction in heavy-weight floor impact sound level and the hardness at the time of a fall collision. In addition, the effectiveness of introducing such a vibration-proof structure into tatami mats was suggested.

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  • Mika KATO, Nozomu YOSHIZAWA, Hideki YAMAGUCHI, Yasuhiro MIKI
    2021 Volume 86 Issue 790 Pages 883-891
    Published: December 01, 2021
    Released: December 01, 2021
    JOURNAL FREE ACCESS

     This study proposes clues to control the luminance contrast between windows and the walls around them.

     Until now, the idea of incorporating daylight to save energy has been the mainstream, but in recent years the "right to receive daylight" has been reviewed in light of the impact on circadian rhythm. However, as has been conventionally recognized, taking direct sunlight directly into the room produces extremely bright areas. Even if the window is not exposed to direct sunlight, the brightness of the sky and surrounding buildings may cause glare, which reduces visual comfort. In addition, even if glare does not occur, if the contrast between the outdoor and indoor brightness seen through the window is large, the impression of the room will be darkened. It is not desirable to have too much or too little daylight. Especially in the visual environment, it is very difficult to adjust it, and appropriate control is required.

     There are daylight factor and glare index (eg PGSV) as clues for daylight control. However, the former is only a guideline for the amount of light that should be guaranteed in daylight, and it cannot be said that visual comfort can be guaranteed. The latter can predict the degree of glare, but it is not clear how much glare is acceptable. Previous studies by the authors have shown that interior reflectance changes the required level of spatial brightness. As with spatial brightness, glare may have different tendencies in perception and demand, so this study examined the effect of interior reflectance.

     Experiments are conducted in full-scale space, and the main variables are interior reflectance, blind slat width and angle. The size of the window is strictly different because the space used for each experiment is different, but it is about 1m x 2m and is installed at waist height. Windows were prepared both artificial uniform luminance and natural sky. Subjects are men and women in their 20s.

     From the experimental results, the following became clear. First, glare standards are set according to visual task, but this study shows that the degree of glare tolerance tends to differ depending on the interior reflectance. This does not mean that the perception of glare is different, but that the permissible degree depends on the interior reflectance. Next, when calculating the luminance contrast between the window and the surrounding walls, the conditions for windows with blinds were also examined. It was thought that the maximum luminance and the non-uniformity of luminance had an effect, but these effects were not detected, and it became clear that the average luminance in the window area could be sufficiently explained. On the other hand, in the case where the high-luminance part such as the sky and the low-luminance part such as planting are clearly separated in the window area, the average value of only the high-luminance part is better than the entire window area.

     Based on the experimental results, the formula "75% AIL " was proposed. The equation includes the brightness of the window and the internal reflectance. The correlation coefficient is R = 0.98.

     By using this relationship, it is possible to control the window luminance and the output of artificial lighting, but the size of the window and other factors are limited in experimental conditions, so further studies are required.

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  • Jun MUNAKATA, Saya KUBOTA, Naoko SANO
    2021 Volume 86 Issue 790 Pages 892-898
    Published: December 01, 2021
    Released: December 01, 2021
    JOURNAL FREE ACCESS

    The performance of daylighting as the cause of glare is important for the residents' comfort. Today evaluation item on daylighting of interior environment were adopted by international certification system such as LEED or WELL. In order to disseminate these systems in Japan, it is required to use them with evaluation items in line with Japan's situation such as climate, density of city and residents' value. Therefore, it is necessary to continue to study the effect of daylighting on residents' subjective response. In such studies, experiments are often conducted in the laboratory. It is common in laboratory experiment to set several physical conditions and get subjects evaluate them. Previous studies suggests that the range of stimulus affects the result of evaluation. For example, the borderline between comfort and discomfort depend on the maximum luminance presented to the subjects. In this study, the effect of range width on psychological evaluation is named as range bias, and the tendency of the effect of range bias during glare evaluation experiment was examined.

    The experiment was conducted in a laboratory room with a pseudo window. We prepared three sets of setting, each of which have four luminance of the pseudo window. The minimum luminance of each set is the same as 2000 cd/m2, but the maximum luminance vary as 8000, 14000 and 20000 cd/m2. Subjects evaluated each set at intervals of about one week. The order of the three sets and the four luminance levels within each set was completely randomized for each subject. 12 subjects evaluated the environment by the usual GSV scale. They also evaluated the degree of glaring and discomfort with stepless scale like GSV scale. Additionally subjects evaluated the impression of the room with SD scale and the acceptability as an office.

    Data by the stepless scales and the SD scales was analyzed by two-way ANOVA with the presented 12 levels of luminance and subjects as factors. As a result, the main effect of luminance was observed on all scales but one. There was no significant difference among the three maximum luminance, and it was confirmed that range bias existed as the effect that subjects judge the maximum luminance in comparison to other luminance presented in one experiment, rather than the absolute judgement. On the other hand, there was a difference in the evaluation tendency between the case where the contents of the scale directly evaluated the physical conditions such as brightness and the case where the atmosphere of the room was evaluated. When directly evaluating physical conditions, the tendency of range bias may be small. Finally, the data of acceptability was analyzed by logistic regression analysis for each set. There was a big difference between the set with the highest maximum brightness and the other two sets. It is also suggested that there is a threshold at which range bias occurs.

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  • Yuta TANAKA, Yasushi KONDO
    2021 Volume 86 Issue 790 Pages 899-908
    Published: December 01, 2021
    Released: December 01, 2021
    JOURNAL FREE ACCESS

     The energy consumed by air-conditioning is large in convenience stores that are open 24 h. This is because the air-conditioning load caused by the infiltration of outdoor air through the entrances is particularly large. This study investigates the sealing efficiency of air curtains in reducing the air that infiltrates through doorways in stores by using CFD simulations and experiments. In particular, this study focuses on double air curtains in which two air curtains are installed on both the outdoor and indoor sides, and the sealing efficiency of the double air curtains is compared with that of normal single air curtains.

     If the air curtain is installed at the top of the door, the airflow from the air curtain to the floor affects the efficiency of the air curtain. When the air curtain is installed on the outside, the outdoor air from the air curtain reaches the floor and partially enters the interior. When the air curtain is installed on the inside, the indoor air from the air curtain reaches the floor and partially exits. When air curtains are installed on both sides, the infiltration of outdoor air and the exfiltration of indoor air can be small. The results of this study are as follows:

    (1) CFD simulations were conducted using a model comprising an experimental room and its surrounding large space. Summer or winter conditions were set as the initial temperature condition of the experimental room and the surrounding space, and the temperature variation was simulated. Under both summer and winter conditions, the sealing efficiency of the double air curtain was higher than that of the single air curtains.

    (2) CFD simulations were performed under various supply air velocity conditions of the double air curtain. The results showed that a high-velocity supply air generated an imping jet in the vicinity of the floor under the air curtain, and the indoor and outdoor air were mixed by turbulence. In contrast, when the supply air velocity was low, the supply air did not reach the floor, and the sealing efficiency was low.

    (3) The experiments were conducted under conditions similar to those of the CFD simulations, and the sealing efficiency was calculated using the measured temperature of several points. Under the summer conditions, the sealing efficiency of the double air curtain and the single outside air curtain was high, and the efficiency of the single inside air curtain was low. However, under the winter conditions, the efficiency of the double air curtain and the single inside air curtain was high, and the efficiency of the single outside air curtain was low. The double air curtain had a high efficiency under both summer and winter conditions.

    (4) When the human body moves through the entrance, it causes an air disturbance and may decrease the sealing efficiency of the air curtain. In this study, the influence of air disturbance on the air curtain efficiency was investigated using a moving body CFD simulation. The infiltration of outdoor air increased when the panel entered the interior. The exfiltration of indoor air increased when the panel moved outward. In the case of the double air curtain, both the infiltration and exfiltration air volumes were smaller than those in the single air curtain cases.

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  • Daisuke KUBOI, Hisaaki SATO, Ryuta TSURUMI, Masashi KAWANO, Masayuki I ...
    2021 Volume 86 Issue 790 Pages 909-919
    Published: December 01, 2021
    Released: December 01, 2021
    JOURNAL FREE ACCESS

    This study proposes a maintenance plan for air-conditioning system using the repairable system model in reliability analysis. The Weibull process model, which is one of the repairable system models, is applied to clarify the trend of deterioration and failure for the latest periodic inspection data of 5 types air-conditioning equipment (AHP, PUMP, AHU, FCU and HEX). In addition, the cost optimization model for calculating the proper renewal cycle of air-conditioning equipment presented in the previous paper is extended to a model that can take into account the cost of energy and inspection, and an air-conditioning system consisting of multiple equipment, and its theoretical equations are derived. As a result, the proper renewal cycle of air-conditioning equipment and system with the latest data is evaluated by the extended cost optimization model.

     

    The followings are main points of this study:

    (1) Repairable system data is created from the periodic inspection data of air-conditioning equipment (AHP, PUMP, AHU, FCU and HEX). The Weibull process model is applied to the repairable system data to obtain the parameter values that indicate the failure tendency of the equipment.

    (2) Two extended theoretical model are proposed based on the cost optimization model with equipment cost 𝐾 and repair cost 𝑟(𝑡) presented in the previous paper: the model that takes into account the operating cost 𝑒(𝑡) and the inspection cost 𝐼, and the model that can be applied to air-conditioning system consisting of multiple equipment.

    (3) The operating cost 𝑒(𝑡) is a model that can take into account the effect of performance degradation due to equipment aging.

    (4) Proper renewal cycles for five types of air-conditioning equipment (AHP, PUMP, AHU, FCU and HEX) and their combined system are clarified by an extended cost optimization model using failure trends obtained from repairable system data based on actual field data.

    (5) The proper renewal cycle of air-conditioning equipment and system varies greatly depending on the value of the performance degradation factor 𝜖. Therefore, it is important to minimize the performance degradation due to aging that affects the operating cost of the equipment. In addition, repairing and continuing to use equipment for which the proper renewal cycle exceeds 30 years contributes to an economically rational maintenance plan for air-conditioning system.

    (6) As a future development of this study, the maintenance planning of air-conditioning equipment by the repairable system model can be used to rationalize and save labor in maintenance work, such as reducing the timing of inspections and inspection items. The approach of this study is also useful for the maintenance planning of building materials and other equipment or devices to be inspected and repaired.

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