J. Cent. South Univ. (2012) 19: 764-769
DOI: 10.1007/s11771-012-1069-3
Pedestrian walking characteristics at stairs according to
width change for application of piezoelectric energy harvesting
YI Mi-hui1, NA Wook-jung1, HONG Won-hwa1, JEON Gyu-yeob2
1. School of Architecture and Civil Engineering, Kyungpook National University, Daegu 702-701, South Korea;
2. Department of Architecture, Jeju National University, Jeju 690-756, South Korea
? Central South University Press and Springer-Verlag Berlin Heidelberg 2012
Abstract: This work aims at finding pedestrian walking characteristics at U-type stairs according to the width change of stairs and appropriate spot for installing piezoelectric energy harvesting. The number of pedestrian at two kinds of stairs (one is stairs with 1.5 m in width and the other is stairs with 3 m in width) was estimated by calculating the number of steps on the stairs by a zone which is divided into 30 cm×30 cm. The result shows high density in the middle in the case of narrow stairs but traffic is concentrated on stair inside (pillar side) in stairs with large width. In conclusion, the location for installation of piezoelectric energy harvesting system should be considered differently on stairs width and the number of installation depends on total expected traffic and the expected traffic for a device.
Key words: piezoelectric energy harvesting; pedestrian walking; human power; traffic distribution
1 Introduction
Piezoelectric generation is one of the human-powered energy and the technology is developed rapidly. A Japanese corporation which leads piezoelectric technology showed outstanding growth because a generating plant invented in 2008 has 10 times efficiency than in 2006 [1]. A company in USA succeeded to generate 1 kW·h for 5 000 pedestrians [2]. In 2011, Korea Institute of Ceramic Engineering & Technology developed piezoelectric generator for Roadway and it showed 20.6 mW of power when vehicle speed is 30 km/h [3]. However, the generation of Korean piezoelectric elements shows 75% of that of USA according to KIST [4].
Notwithstanding the rapid development of piezo-electric generator, it has not used widely due to the low efficiency and high investment cost. The re-call period depends on the number of people who step on the installation spot. Now, it should be considered to analyze the pedestrian walking characteristics, and find areas where people walk a lot [5]. However, a study about analyzing density of pedestrians in a building to install the piezoelectric energy harvesting has not been made.
Therefore, this work tries to find pedestrian walking characteristics at common (U-type) stairs based on the fact that pedestrians’ ground reaction force gets stronger on stairs compared with level walking [6] and searches walking characteristics according to the width of stairs. This work analyzes the density of pedestrians, writes walk distribution chart, and provides a preferred spot for establishing piezoelectric energy harvesting system.
2 Case study of application experiments
Now, piezoelectric energy generating system has been invented worldwide and it has been grown quickly based on corporations in Israel, USA, Japan and so on. Especially, company S in Japan conducted three experiments at a subway station in 2000s and has verified it. Figure 1 shows the piezoelectric energy harvesting system established at stairs at Tokyo Station in 2008. The generating system was established on all surfaces of stairs in this experiment and pedestrian walking characteristic was not considered, which has bad influence in investment return period.
Table 1 gives the results of experiment of which corporations represent each country [1, 2, 7]. They did experiments for observing generation of piezoelectric energy harvesting systems with their own ways because the company I in Israel, P in USA, and S in Japan didn’t prepare an indicator for evaluating capacity of generating systems. The company in Israel focuses on products for establishing a generating system on the road or railroad but the companies in USA and Japan are inventing products used for interior material on the sidewalk or in a building. A company in England set a goal that they achieve $100-200/ft2 for early investment of piezoelectric generating floor. Wooden floor only costs $5-15/ft2 for establishing. So, it is quite expensive, but normal floor cannot produce electricity. Therefore, in the long term, to install piezoelectric generating floor has advantages.
Fig. 1 Experiment at Tokyo Station
Table 1 Results of piezoelectric energy harvesting
In Korea, company S1’s Energy Block using human power and company S2’s Eco Pass System which invented a generating system using cars are typical examples. Figure 2 shows S1’s energy block and Fig. 3 shows S2’s Eco Pass System [8]. S1 is trying to achieve 1 W·s generation efficiency through Ver. 3 product invention. S1’s product has not used widely so is under demonstration project on national projects. S2 revealed the fact that if it establishes 10 sets on the spot where 10 000 cars pass, they can generate 110 kW·h power a day. Now one set costs 40 million won but it is expected that it can be cut to (15-20)×106 won in mass production.
Fig. 2 S1’s Energy Block
Fig. 3 S2’s Eco Pass System
3 Methodology
3.1 Investigated buildings
The investigation was made at the central library at Kyungpook National University. 1 864 880 people use here for a year. This accounts for the half of 3 751 772 users at 13 university libraries in Daegu.
There are 4 stairs between 1st floor and 2nd floor in this building and all of them are U shaped. Among 4 stairs, 2 stairs was made for research subjects. One is 1.5 m wide and another is 3 m wide. The reason why subjects are two is to make walk distribution chart of two different width stairs and to analyze influence on pedestrian walking characteristics. Figure 4 shows 1st floor plan at the central library at Kyungpook National University. On this plan, we can notice two subject stairs.
Fig. 4 Floor plan of investigated building
The construction outline of two stairs is listed in Table 2. The narrow stair A consists of 23 steps and wider stair B has 24 steps and other characters are similar except the fact that the stair A has 2 middle landings.
Table 2 Construction outline of subjects
3.2 Methodology of investigation
This work used CCTV and DVR (UDR-416C) to observe and analyze the walk character of pedestrians passing stairs. Cameras for observing were attached on the ceiling and wall like Fig. 5 so as to minimize effects on pedestrians during survey. For analyzing pedestrians’ walk character, the scene which shows walking on the stairs was recorded for a week and shooting time was set at service hour of the building in Table 2.
Fig. 5 Attached cameras on wall for observing
To analyze walk character of pedestrians through writing walk distribution chart, for each step we divided into several zones sized by 30 cm×30 cm which is common size for piezoelectric generating system and counted the number of people who stepped on the zone. The zones were divided on the screen which recorded the pedestrians passing stairs like Figure 6. The zone where pedestrians stepped on heels is recorded.
In this work, walk distribution chart means walk traffic for an hour. To exclude the effect of walk density, we recorded traffic and zones which the pedestrians stepped on for three hours: an hour for the lowest density, an hour for the middle density, and an hour for the highest density in a day. Traffic distribution chart averages traffic on each zone for three hours and it makes an average traffic for an hour.
Fig. 6 Stair B (1st-12nd steps) divided into 10 zones
4 Results
In this work, traffic distribution chart for walking characteristics of stairs shows the proportion of traffic of each zone to whole traffic and it is calculated as
(1)
where DT is the traffic distribution for each zone; TZ is the traffic for each zone; TS is the sum of traffic.
4.1 Traffic distribution on stairs with narrow width
Stairs A with 1.5 m in width was divided into 5 zones at each step. Zone 1 is outer zone of the step (wall side) and zone 5 is at the center where the step is curved (pillar side). There are 23 steps and the traffic distribution of whole 115 zones is shown in Fig. 7. In Fig. 7, the 1st step is started at the 1st floor and the 23rd step is the last step before the 2nd floor. Stair landings stay between the 10th and 11th step and the 14th and 15th. Usually, traffic is concentrated in middle 2, 3, and 4 zones. It is outstanding that between a stair landing zone 4 takes 40% traffic. This is considered because pedestrians prefer short distance walking.
Fig. 7 Traffic distribution on stairs with narrow width
Table 3 gives average traffic distribution for each zone of narrow stairs. Figure 7 shows slightly different aspects of traffic at each step. However, average traffic distribution shows that 2, 3, and 4 zones take up similarly about 30%.
Table 3 Average traffic distribution on stairs with narrow width
4.2 Traffic distribution on stairs with large width
Stair B with 3 m in width was divided into 10 zones at each step. Zone 1 is outer zone of the step (wall side) and zone 10 is at the center where the step is curved (pillar side). Whole steps are 24 so we can record traffic and location for 240 zones and the traffic distribution is shown in Fig. 8. The shape of stairs is U and a stair landing is between the 12th and 13th step. A different character was spotted which was not shown in narrow stairs. That is, except zone 10, the traffic was concentrated in the inside of stairs (pillar side). However, in the wide stairs between the stair landings, a specific zone takes up more than 25%. Two phenomena are similar because pedestrians prefer short cut.
Fig. 8 Traffic distribution on stairs with large width
Table 4 represents average traffic distribution for each zone of wide stairs. From Fig. 8, unlike the narrow stairs except the last step before a stair landing it doesn’t show large difference of traffic distribution for each step. Average 20% people step on zone 9 and zones 7 and 8 take up more than 15% preference.
Table 4 Average traffic distribution on stairs with large width
5 Comparison and discussion
As a result of this experiment, appropriate zone for installing is given in Table 5 when stairs with 1.5 m and 3 m in width show the highest density. Stair A is 1.5 m so the maximum installation number of 30 cm×30 cm piezoelectric energy harvesting system is five. Therefore, we calculated the sum of expected traffic distribution of stairs A and B according to the number of installation up to five. When three equipments are installed, the difference of total distribution is the highest. Stairs with 1.5 m in width is 89.4%; stairs with 3 m in width is 53.4% so the difference is 36%. When installing three equipments, stairs with 3 m in width need 36% more traffic than those with 1.5 m do to produce power that stairs with 1.5 m generate. Looking through the order of installation number, stairs with 3 m need 10.1%, 23.1%, 36%, 28.1%, 21.5% more traffic to generate the same power that stairs with 1.5 m produce.
Table 5 Appropriate zones for installing and sum of expected traffic distribution according to number of installation
Power generation that piezoelectric generating system produces is proportional to the passing traffic, so we try to contrast the efficiency compared to expected traffic. To do so, we suppose the situation that passing traffic is 500, 1 000, and 1 500 people per hour and count the number of pedestrians who stepped on the equipments. Traffic was calculated by multiplying the sum of distribution by passing traffic according to the number of installation in Table 6.
When the number of installation is identical, the more the sum of traffic is, the more the expected traffic is. When the passing traffic is the same, the more the installations are, the more the traffic is. Therefore, if five equipments were established at stairs A where 1 500 people pass, it is expected to produce the maximum power. However, five equipments where 1000 people pass are expected to have more expected traffic than two equipments where 1500 people pass, which means total traffic and the number of installation should be considered simultaneously.
For considering the re-call period of equipment, expected traffic for a device should be considered. The period for re-call is also shortened when there is a lot of expected traffic for a device. Therefore, Table 7 gives the expected traffic for a device. The expected traffic for a device gets more if total passing traffic becomes more, but if the number of installation gets fewer, it becomes fewer as well. According to Table 7, when establishing a device at stairs A where 1500 people pass, the expected traffic is the most, so it makes the period for re-call shorten.
As the total passing traffic changes, we looked through the expected traffic for the number of installation and average traffic rank for a device. The expected traffic for the number of installation and average traffic for a device should be considered at the same time. Power demand and installation cost should be considered while establishing actual piezoelectric energy harvesting system. For proper installation, installation should be done by considering re-call period compared to investment, after observing traffic at the place to be installed.
The study on how traffic distribution changes in other parts of buildings with various widths should be conducted later.
Table 6 Sum of expected traffic (people) according to passing traffic of stairs A and B, and ranking
Table 7 Sum of expected traffic (people/device) according to passing traffic of stairs A and B, and ranking
6 Conclusions
1) The stairs with 1.5 m in width shows 30% similar traffic distribution on three zones (2, 3 and 4) and zone 1 and 5 show 5.9% and 4.9% traffic distribution, respectively.
2) In the case of the stairs with 3 m in width, traffic is concentrated on stair inside (pillar side). The traffic on zones 7, 8, and 9 show high rates more than 15%.
3) If we differentiate the number of piezoelectric energy harvesting system installation from 1 to 5, recommended place for installation is changed and the total distribution is 30.3%, 60.3%, 89.4%, 95.2% and 100 % for stairs with 1.5 m width and 20.2%, 37.2%, 53.4%, 67.1% and 78.5% for stairs with 3 m width.
4) As changing the number of installation from 1 to 5, stairs with 3 m width needs 10.1%, 23.1%, 36%, 28.1%, 21.5% more traffic than that of the stairs with 1.5 in width to produce the same power that stairs with 1.5 m make.
5) We supposed the traffic inflow is 500, 1 000 and 1 500 people and examined the expected traffic. As a result, the expected traffic for the number of installation shows the highest when installing five equipments at stair A with 1 500 pedestrians, and the expected traffic for a device shows the highest when establishing one device where traffic is 1 500 people. But as the passing inflow and the number of installation change, the total expected traffic and the expected traffic for a tool change, both should be considered simultaneously.
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(Edited by YANG Bing)
Foundation item: Project(NRF-2011-0000868) supported by the National Research Foundation of Korea (NRF) funded by the Korea government (MEST); Project(2011-0003968) supported by Basic Science Research Program through the National Research Foundation of Korea (NRF)
Received date: 2011-07-26; Accepted date: 2011-11-14
Corresponding author: JEON Gyu-yeob, PhD; Tel: +82-64-754-3703; E-mail: hi.gyuyeob@jejunu.ac.kr
