Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 135 (2016 ) 439 444 Study of Grid Ceiling on Parametric Optimization Design of Automatic Sprinkler System Xiang-yu Qu a,*, Hai-yan Wu b a Team One of Graduate Student, Chinese People Armed Police Force Academy, Langfang 065000, China b Fire Protection Bureau of Tongling City, Tongling 244000, China Abstract The parametric optimization design of automatic sprinkler system was studied experimentally with the grid ceiling installed below the sprinkler head. The experimental results indicated: the water distribution was affected by hollow rate of grid ceiling and installation height of sprinkler. In range of the decrease of the hollow rate and installation height of sprinkler, water distribution increased. When the hollow rate is high, the effect of water distribution will be greater by the change of the hollow rate. When the hollow rate is low, the effect of water distribution will be greater by the change of the installation height of sprinkler. 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 2016 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Peer-review under under responsibility of the of organizing School of committee Engineering of ICPFFPE of Sun 2015 Yat-sen University. Keywords: grid ceiling, automatic sprinkler system, hollow rate, installation height of sprinkler 1. Introduction In recent years, grid ceiling is used widely in large commercial building, hotel, office, waiting room, airport, exhibition center and other public places. Due to the particularity of the grid ceiling decoration, there are many irrational designs in the designing, construction and installation of automatic sprinkler system. The constructors often confuse the relationship between the position of sprinkler head and the ceiling. Two effects on design and selection of automatic sprinkler system by grid ceiling exist: One is the grid ceiling itself influencing on the water distribution as an obstacle. The other is the hollow part of the ceiling, which cause no smoke gathered under the ceiling, and influence the actuation time of sprinkler head. The principles of timely response, complete cover and effective spraying should be followed in the design of the sprinkler head. When the sprinkler head is on the grid ceiling, the smoke will penetrate through the hollow part of the ceiling and be gathered under the construction roof. It can make sure that the actuation time will be enough, but the water distribution will be influenced by grid ceiling certainly. When the sprinkler head is beneath the grid ceiling, the water flow will not be influenced, but the smoke cannot be gathered effectively around the sprinkler head and the actuation time cannot be enough. There are contradictions between the water distribution and the actuation time caused by the position of the sprinkler head, which is a difficult problem in designing and construction to be solved effectively. Developed countries have already carried out the study of grid ceiling on automatic sprinkler fire-extinguishing technology and defined it explicitly. The standard and specification related to the automatic sprinkler system in such places are NFPA13-2010 Standard for the Installation of Sprinkler Systems (American standard) and CEA4001 Sprinkler Systems: Planning and Installation (European standard). NFPA13-2010 [1] requires that: Open-grid ceilings shall only be installed beneath sprinklers when open-grid ceilings in which the openings are 1 4 in. (6.4 mm) or larger in the least dimension, * Corresponding author. Tel.: +86-15003267895 E-mail address: 1487804651@qq.com 1877-7058 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICPFFPE 2015 doi:10.1016/j.proeng.2016.01.153
440 Xiang-yu Qu and Hai-yan Wu / Procedia Engineering 135 ( 2016 ) 439 444 where the thickness or depth of the material does not exceed the least dimension of the opening, and where such openings constitute 70 percent of the area of the ceiling material. CEA4001 [2] requires that: Suspended open ceilings may be used beneath LH and OH sprinkler systems not involving storage areas where the following conditions are met: - The total plan open area of the suspended open ceiling, including light fittings, shall not be less than 70% of the ceiling plan area; - The minimum dimension of the ceiling openings shall be no less than 0,025m or no less than the vertical thickness of the suspended ceilings, whichever is the greater; - The structural integrity of the ceiling and any other equipment, such as light fittings within the volume above the suspended ceiling, shall not be affected by operation of the sprinkler system. At present, there are few rules for the automatic sprinkler system on the grid ceiling in our country. Current Code of Design for Sprinkler Systems GB50084-2001 (2005) [3] only Article 5.0.3 demands that: In the place installed with grid ceiling, the water spraying intensity of system should be determined as 1.3 times of specified value; Article 7.1.10 demands that: Sprinkler head should be installed beneath the roof where the grids or trays are used in the open ceiling. Bing Gao [4-5] studied the water distribution of automatic sprinkler system when the grid ceiling was installed and the effects of grid ceiling grid ceiling for fire control capability of sprinkler system in small-scale experiment. And the completed burning time was used to calculate the effective fire control factor in order to quantify this factor. Nan Chen [6] used 16 photoelectrical and smoke detector above and below the grid ceiling to studied the influence of detector response in different hollow rate of grid ceilings, which used pyrolysis and smoldering wood as combustible. The influence of the safety height and the grid thickness to the detector response is studied by added FDS simulation to the experiment. For the current code, the influence of the grid ceiling is considered, which requires the automatic sprinkler system to increase the water spraying intensity and use the vertical type of the sprinkler head. But it doesn t demand the proportion of the projected area of grid ceiling. As for engineering design, the design of automatic sprinkler system is selected according to the regulation of smoke spread and the proportion of the projected area of grid ceiling. This paper studies the setting of the sprinkler head in different hollow rate of grid ceiling and different installation height of sprinkler experimentally, which is instructive in design and construction. 2. Experiments In this study, the experiments were performed using a ZSTX-15 open-type sprinkler installed in the exact middle of the area of experimental roof. The area of experiment was 2.0m 2.0m, and the area of the grid ceiling was 2.0m 1.0m, which was half of the experimental area and symmetrical distribution in length. Three different installation height of sprinkler as 300mm, 600mm, and 900mm were used to text the water distribution. The hydraulic pressure was 0.33MP. The water collectors were placed radially in the experimental area, shown in Fig. 1. Line1, 2, 3 water collectors were in the Area B without grid ceiling, Line 5, 6, 7 in the Area A with grid ceiling, and Line 4, 8 just on the boundary. The water collectors were 10cm diameter and 20cm high. After 4 min water spraying, the weight of the water collectors was measured by an electronic balance (accuracy: 1g). The effect of grid ceiling on automatic sprinkler system was studied in this paper. (a) (b) Fig. 1 Experimental equipment for (a) grid ceiling and (b) water collectors. The experiment was used the square grid ceiling of aluminum, whose hollow size was 10cm 10cm. Table 1 presents different hollow rate made by tapes of different widths and different stickup methods.
Xiang-yu Qu and Hai-yan Wu / Procedia Engineering 135 ( 2016 ) 439 444 441 Table 1 Method of changing the hollow rate Hollow rate Method 25% 45mm tapes, stickup along long& short side 45% 45mm tapes, stickup along long side 75% No tapes 100% No grid ceiling 3. Results and discussion The weight of the water collectors is measured and part of results is as follow: Table 2 Water distribution with 75% hollow rate and 300mm installation height of sprinkler Distance from the center of the water collectors (cm) 0 1524 Weight of the water collectors (g) Line 1 Line 2 Line 3 Line 4 Line 5 Line 6 Line 7 Line 8 20 898 556 982 1487 1184 893 1116 1953 40 967 330 497 1332 918 841 1434 826 60 879 351 318 862 704 479 442 854 80 899 260 251 551 321 349 277 824 100 598 236 234 273 202 287 165 1055 Table 3 presents the arrangement of the experimental data. Table 3 Effect of hollow rate and installation height of sprinkler on water distribution Installation height of sprinkler (mm) Hollow rate 100% 75% 45% 25% 300 715.25 756.2 924.96 808.4 600 600.4 627.5 711.7 698.95 900 559.85 540.25 745.85 627.25 Table 4 presents the arrangement of the increment of water distribution in different installation height of sprinkler when changing the hollow rate. It can be seen that the effect of hollow rate and installation height of sprinkler on water distribution exists indeed. (1) The water distribution is effected by hollow rate seriously. When changing the hollow rate, an extreme value will get the maximum water distribution. Fig. 2 presents that the hollow rate decreases while the water distribution increases with the overall trend. In addition to the height of 900mm, the minimum water distribution gets with no grid ceiling, while the maximum gets with 45% hollow rate. This is because large droplets impact on the grid ceiling and change the moving trace, while small droplets absorbed on the grid ceiling, aggregated into the larger drops and dripping. Therefore, the grid ceiling has an effect on atomization degree and spraying range of the sprinkler head, which lead to the water distribution increased but the coverage become smaller with the grid ceiling. This phenomenon is also indicated in the experiment. When no grid ceiling installed, the sprinkler sprays around as cone-shaped normally. While installing the grid ceiling, the spraying range is reduced with the droplets vertical fell and atomization degree decreased. The grid ceiling is from sparse to dense that the phenomenon becomes more obvious. Thus as the result of the experiment, the hollow rate decreases while the water distribution increases. However, when the hollow rate decreases further, the grid ceiling hinders the droplets and part of the water gathers on the ceiling, which cause a decrease of the water distribution.
442 Xiang-yu Qu and Hai-yan Wu / Procedia Engineering 135 ( 2016 ) 439 444 Fig. 2 Effect of hollow rate and installation height of sprinkler on water distribution Table 4 Effect of hollow rate and installation height of sprinkler on increment of water distribution Installation height of sprinkler (mm) Hollow rate 75% 45% Increment 1 % 45% 25% Increment 2 % 300 756.2 924.96 22.32 924.96 808.4-12.6 600 627.5 711.7 13.42 711.7 698.95-1.79 900 540.25 745.85 38.06 745.85 627.25-15.9 (2) The water distribution is also influenced by the installation height of sprinkler. From Fig. 2, the height is reduced with the water distribution decreased. The maximum water distribution is at 300mm height, the minimum is at 900mm, and the average is at 600mm. But when the hollow rate is 45%, the water distribution at 900mm is more than the one at 600mm, which is indicated that the effect of the hollow rate and the installation height is interaction, rather than individual factors. (3) Fig. 3 presents that the hollow rate decreases from 75% to 45%, causing all of the water distribution increased at different installation height. The increment of water distribution is more than 10%. The minimum increment is 13.42% at 600mm, and the maximum is 38.06% at 900mm. When the hollow rate decreases from 45% to 25%, all of the water distribution reduced less than 20%. The minimum increment is 1.79% at 600mm, and the maximum is 15.9% at 900mm. The maximum of the water distribution is at 45% hollow rate, 900mm installation height. Though large water distribution doesn t mean a good fire control capability. The experiment illustrates that a large water distribution is usually accompanied by a decreased atomization degree and reduced spraying range. Consequently, the change of hollow rate and installation height of sprinkler on fire control capability of automatic sprinkler system remains to be further studied.
Xiang-yu Qu and Hai-yan Wu / Procedia Engineering 135 ( 2016 ) 439 444 443 Fig 3 Effect of hollow rate and installation height of sprinkler on increment of water distribution (4) Based on the second and third points, when the hollow rate is more than 45%, the water distribution is effected significantly by the hollow rate rather than the installation height. On the contrary, when the hollow rate is less than 45%, the water distribution is more effected by the installation height, and the effect of the hollow rate is weakened. This is because when the hollow rate is more than 45%, the change of the hollow rate that has a larger influence of the moving trace of droplets. The hollow rate is smaller with the trend of the droplets vertical fell more obviously. The atomization degree decreases while the water distribution increases. While the hollow rate is less than 45%, the grid ceiling hinders the water droplets that parts of the water gather on the ceiling. At this time, changing the installation height is better than the hollow rate influencing the water distribution. 4. Conclusion In this paper, the influencing factors of automatic sprinkler system were studied experimentally with the grid ceiling installed. The experimental results indicated: the uniformity of the sprinkler will be effected by the grid ceiling, which further impacts on fire control capability of automatic sprinkler system. (1) Under the certain grid ceiling and hydraulic pressure, the major factors influencing the water distribution are hollow rate of grid ceiling and installation height of sprinkler and they are interaction. The minimum value of water distribution exists on certain hollow rate and installation height. (2) In range of the decrease of the hollow rate and installation height of sprinkler, water distribution increased. (3) When there is a larger hollow rate, the water distribution is influenced more by changing the hollow rate. While there is a smaller rate, the water distribution is influenced more by changing the installation height. (4) In practical engineering, the installation height should be designed reasonable according to the specific characteristics of grid ceiling. That can reduce the disadvantage of installing the grid ceiling, and the fire suppression effectiveness of automatic sprinkler system can be ensured. References [1] An International Codes and Standards Organization, 2010. NFPA 13 Standard for the Installation of Sprinkler Systems 2010 Edition, Chapter 8 Installation Requirements, p. 13-84.
444 Xiang-yu Qu and Hai-yan Wu / Procedia Engineering 135 ( 2016 ) 439 444 [2] CEA 4001, 2009. Sprinkler Systems: Planning and Installation, 11 Space and location of sprinklers, p. 81. [3] Ministry of Public Security of the People's Republic of China, 2005.Code of Design for Sprinkler systems. [4] Bing Gao, Ying Li, Bin Yao, Zhen-kun Wu, Ping Huang, 2006. Experimental Study of Grid Ceiling Effect on Fire Extinguishment Efficiency of Automatic Sprinkler, Fire Safety Science 15, pp. 184-188. [5] Bing Gao, Bin Yao, 2008. Experimental Study of Grid Ceiling Effect on Fire Control Efficiency of Automatic Sprinkler, Fire Safety Science 17, pp. 244-249 [6] Nan Chen, 2012. Experimental Study on the Response Performance of Smoke Fire Detectors in Grid Suspended Ceilng, Fire Safety Science 21, pp. 216-224.