Reducing indoor air contaminants inside a bus passenger compartment

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:03 81 Reducing Indoor Air Contaminants Inside a Bus Passenger Compartment Noor Emilia Ahmad Shafie1, a, Haslinda Mohamed Kamar1, b* and Nazri Kamsah1, c 1 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia. a nemilia2@live.utm.my, b*haslinda@mail.fkm.utm.my, cnazrikh@fkm.utm.my Abstract-- Good ventilation system in a bus passenger compartment is important for providing clean, healthy air and comfortable micro-environment for passengers. Lack of fresh air inside the bus compartment could increase the contaminant concentration level and affect the passenger’s health. This research presents field measurement on contaminant concentration level of particulate matter and carbon monoxide inside the passenger compartment of a university’s shuttle bus. The field measurements were conducted at the front, middle and rear locations of the passenger compartment. Computational fluid dynamics software was used to develop a simplified three-dimensional model of the bus passenger compartment. Two cases of air return grilles location namely three air return grilles and four air return grilles were performed. The results show that four air return grilles could reduce the contaminant concentration levels of CO and PM1 inside the bus passenger compartment. Index Term-- Indoor Air Contaminant, Ventilation System, Air Return Grille, Bus Passenger Compartment. 1. INTRODUCTION Bus passenger compartment require good ventilation system for distribute a clean and healthy air in the occupied zone. In engineering approach, the efficiency of ventilation system is evaluated by the indoor air quality. Indoor Air Quality (IAQ) refers to the effect, good or bad of the contents of the air inside an enclosed environment. Good IAQ is the quality of air which has no unwanted contaminants. Poor of IAQ occurs when contaminants are present at an excessive concentration. In IAQ research two types of harmful contaminants were widely investigated namely particles and gaseous. Particulate matters (PM1) represent as particles whereas carbon monoxide (CO) represent as gaseous contaminants. Various diseases adversely affect the occupant health of these contaminants such as respiratory problem, cardiovascular and airborne transmission. Knowledge concerning the contaminants level is very important to prevent the harmful particles and gaseous inhaled by passengers when commuting in a bus. The ventilation system of the bus need to improve due to long time usages for business, shopping, campus, school, recreation or others activities. There were several factors that affect the design and performance of ventilation system such as size and type of bus, air supply velocity, air supply temperature, location of the air supply and location of the air return grille. The locations of air supply and air return grille are very important to reduce the contaminants concentration level especially in the occupied zone. At present, research works on reducing air contaminants inside the bus cabin is limited especially using computational fluid dynamics (CFD) approach. CFD tools offer an alternative platform which is more convenient than experimental practice to analyse the indoor air quality in various application. Hence, an investigation of ventilation system using CFD tools is necessity in which will improve the IAQ inside the bus cabin. Previous researchers were conducted the field measurement method to quantify the indoor air contaminant inside the bus passenger compartment. Chan, (2005) [1] was conducted the field measurement of indoor air contaminant inside the bus cabin. The measurements were performed in urban and rural areas in Hong Kong with twelve different short routes. The measurements were performed at the rear compartment and at the height of breathing level of passengers. Measurements were taken at peak hours (8.00 am to 9.30 am) and non-peak hours (10.30 am to 14.00 pm). Hsu et al., (2009) [2] were examined the contaminant concentration levels of CO and PM in the long distance buses. The measurements were performed in a highway road Taiwan. The total travelling distance was approximately 300 km, which normally took 4 hours to 5 hours, depending on traffic and weather condition. The sampling instruments were placed in the centre of the bus cabin and at the height of the breathing zone of seated passengers. Zhu et al., (2010) [3] were investigated the micro-environmental such as CO and PM in public transportation buses. The measurements were performed in a Harvard university shuttle bus. The measurement was conducted in an empty bus. The bus engine was kept in idle condition and the air-conditioning system was operated as usual. All the windows and doors were fully closed during the experimental. The measurements were performed at four bus locations (in the front and rear compartment at each side of the bus). The instruments were placed in two mesh boxes made by coarse wire, which were hanged at the shoulders of two of our field personnel at a height 0.6 m and 1.1 m from floor. The field measurements were started early in the morning (9.00 am to 16.30 pm) with a lunch break around noon. Rim et al., (2008) [4] were investigated the characteristic of cabin air quality in a school buses in Central Texas. The measurement was performed using six school buses with different engine year in sub-urban Austin, Texas. The route was a typical 42.4 km suburban school bus route and required approximately 100 minutes to complete. Only research team members and driver were on-board buses during the tests. The air sampling was placed in the centre of bus cabin. Gomez et al., (2007) [5] were investigated the commuter’s exposure in the bus, minibus and metro bus. Commuters’ exposure measurements were taken for PM2.5 and CO in minibuses, buses and metro during morning and evening rush hours during January to March 2003 in Mexico City. The instrument was placed at a level of breathing zone. The measurements were taken in the morning (6.30 am to 9.00 am) and evening (17.30 pm to 20.30 pm). Wong et al., (2011) [6] were investigated in cabin exposure levels of CO 157003-6969-IJMME-IJENS © June 2015 IJENS IJENS International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:03 and PM10 for running buses in Hong Kong that equipped with Euro II, III and IV engines. Urban and sub-urban bus route were chosen in this research. Travelling distance between the two bus terminals is 32 km and it was monitored and recorded every one minute throughout the journey. All measurements were conducted on weekdays during bus service hours starting from 7.00 am to 10.00 am and 16.00 pm to 19.00 pm. Air samples were collected at the height of 1.45 m above the floor and kept away from the bus main entrances, air inlets, air outlets and passengers. This research presents field measurement on contaminant concentration levels of particulate matter and carbon monoxide inside the passenger compartment of a university’s shuttle bus. The field measurements were conducted at the front, middle and rear locations of the passenger compartment. CFD software was used to develop a simplified three-dimensional model of the bus passenger compartment. Two cases of air return grilles location namely three air return grilles and four air return grilles were performed. 2. RESEARCH METHODOLOGY 2.1. Field measurement of Air Contaminants Field measurements were conducted to quantify the contaminants concentration of PM1 and CO inside the passenger compartment of a university’s shuttle bus that ferries students from their hostels to the university’s campus. The total distance travelled by the bus was about 12 km. The in-campus route followed by the bus during the entire period of the field measurement is shown in Fig. 1. The field measurements were conducted in an empty bus and measured at the front, middle and rear locations of the passenger compartment. Also, the measurement was carried out at the door which the outside contaminant enters the bus during the trips. The contaminants concentrations of PM1 and CO were continuously monitored during the trips and data were recorded at several time intervals (1 minute), at the steady-state conditions. A handheld particle counter instrument (model HPC300) was used to measure the contaminant concentration of PM1 inside the bus passenger compartment. Indoor environmental quality (model IEQ Bacharach) instrument was used to monitor the contaminant concentration of CO. A digital anemometer (model V816B) was employed to measure the air velocity and temperature at the cool air supply diffusers. The particle counter and indoor environmental quality instruments were placed at the height of 1.1 m from the floor of the bus compartment, which is considered as the breathing level of the passengers [7]. The air velocity and temperature at the cool air supply diffuser were maintained as much as possible at 3 m/s and 23°C, respectively during the field measurement period. 82 Fig. 1. The in-campus route followed during the field measurement 2.2. Computational Domain Ansys Fluent (R-14) software was selected to simulate the problem, employing Reynolds-averaged Navier-Stokes (RANS) approach to solve the fluid flow. In particular, flow analysis was carried out using RNG k- turbulent model for air flow, discrete phase and species transport for contaminants. This study performed the field measurements in a real condition of the bus passenger compartment in order to validate the CFD simulation. A simplified threedimensional model of the bus passenger compartment is described in Fig. 2. There are fourteen four air supply diffusers located on the ceiling mounted duct work and two air return grilles located at the front and rear of the bus roof. The current locations of air supply diffuser and air return grille are known as mixing ventilation with two air return grilles (2RG). Fig. 2. A simplified three-dimensional model of the bus passenger compartment 2.3. Computational Mesh The computational mesh for the CFD simulations was created using the Ansys Mesh-R14 software. The mesh in the cabin space consists mostly of tetrahedron cells. Tetrahedron cell is suitable for three dimensional model, complex geometry and convergence will generally faster [8]. 157003-6969-IJMME-IJENS © June 2015 IJENS IJENS International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:03 The total number of cells in the model was approximately 508057. The maximum and minimum sizes of the cells are 0.34 m and 0.002 m, respectively. Much finer surface was generated at the door, air supply diffuser and air return grille locations. This is to ensure the CFD simulation results more accurate. Fig. 3 shows the computational mesh of the bus passenger compartment. Tetrahedron cells 83 attach to or rebound from the object’s surface. It is therefore natural to terminate or trap a particle trajectory after hitting a rigid surface [10]. For gas simulation, non-reacting flow was applied due to the effects of contaminants concentration characteristic. The gas contaminant is assumed as a passive and low concentration in an enclosed environment [11]. The flow was assumed to be turbulent and the RNG k-ε turbulence model was applied. The discrete phase and species transport were applied for contaminants concentration analyses. The simulations were performed as steady state with pressure-based segregated solver with the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE), second order upwind discretization scheme and a convergence criterion for all equations is 10 -4 except energy 10-6 [12]. 2.5. CFD Validation Fig. 3. The computational mesh of the bus passenger compartment 2.3.1. Mesh Sensitivity Test Mesh sensitivity test was performed to ensure that meshing has no effects on the results of the CFD analysis. The meshes of 50000, 100000, 300000, 500000, 800000 and 1000000 of cells were generated and solved for contaminants concentration of CO and PM1 distributions. It was found that the mesh sensitivity test of contaminants concentration of CO and PM1 was constant at 500000 grid cells compared to 50000, 100000 and 300000, respectively. Thus, the numbers of elements of 508057 tetrahedral cells were employed throughout the CFD analysis. 2.4. Boundary Condition Temperature and velocity of the air supply diffuser was set to 23°C and 3 m/s based on the measured data. The wall of the bus was set to 26°C for the air temperature. The contaminants of CO and PM1 were applied at the bus door. The contaminants concentration of CO and PM1 were set to 7 ppm and 52 μg/m3, respectively. For all cases of air supply diffuser and air return grille locations the air temperature, air velocity and contaminant concentration were set to the same value. Turbulent intensity was set to 5% and turbulent parameter for the door, air supply diffuser and air return grille boundary conditions were hydraulic diameter. No slip condition was applied at the wall. When fluid in direct contact with a solid to the surface due to the viscous effects the velocity of the flow is zero and assumed no slip for the wall [9]. For particle simulation the door, air supply diffuser and air return grille were set to escape while the wall was set to trap boundary condition. When particles reach air supply diffuser, air return grille and door, the particles will escape and the trajectories terminate. This could be due to the effects of airflow against particle at each location. However, when reaching a rigid object such as wall, particle may either The CFD simulation procedure was validated by comparing the contaminant concentration level obtained from the CFD simulations at the front, middle and rear locations obtained from the field measurements. Following assumptions were made for the simulation setup:  The RNG k-ε turbulence model, Discrete phase model and Species transport model were applied for the airflow, particle and gas analyses.  The door was open and no passengers inside the bus.  No air contaminants inside the bus passenger compartment.  The source of contaminant concentrations of PM1 and CO were applied at the door due to the outside contaminant enters the bus during boarding and unboarding. 2.5.1. Results of CFD Validation The comparison of measured and predicted data of contaminants concentration is depicted in Table I and Table II for three different locations, namely front, middle and rear occupied zone. The contaminants concentration was high at the frontal location which is near to the bus door. This could be due to insufficient ventilation of fresh air supply inside the bus passenger compartment. The result shows that percentage differences of predicted data of PM1 and CO are below 20% which can be accepted for the complex flow for indoor environmental [13]. Table I Comparison of predicted and measured of PM1 concentration Particulate Matter, PM1 (μg/m3) Locations Front Middle Rear 157003-6969-IJMME-IJENS © June 2015 IJENS Max predicted ( ) 43 46 34 Max measured ( ) 52 ±9 43 ±3 40 ±6 Percentage difference ×100% -17.3 6.9 -15 IJENS International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:03 Table II Comparison of predicted and measured of CO concentration Carbon Monoxide, CO (ppm) Locations Front Middle Rear Max predicted ( ) 6.7 5.1 1.6 Max measured ( ) 7 ±0.3 5 ±0.1 2 ±0.4 Percentage difference ×100% -4.3 -2 -20 84 environment, the height of 1.1 m from the floor was chosen and represent as a breathing zone of the passengers [7]. This height is very suitable to measure the contaminants concentration in indoor environment that away from the airflow locations such as air supply diffusers, air return grilles and door. The CFD simulation results for all cases on contaminants concentration of PM1 and CO are presented at x-direction is 0.3 m, y-direction is 0.3 m (floor) to 1.45 m (air supply diffuser) and z-direction is 2.8 m as shown in Fig. 5. 2.6. Parametric Analysis Two cases of air return grilles location inside the bus passenger compartment were performed. The parametric analysis was prescribed in Fig. 4. Case 1 (3RG); Three air return grilles are placed in a one row on the roof and Case 2 (4RG); Four air return grilles are placed in a one row on the roof. Fig. 5. The reference line 1 of the CFD simulation results 3.1. Field Measurement of PM1 and CO Concentrations Fig. 6 shows the contaminant concentration of PM1 in the bus as a function of time. The result shows that the PM1 was high in the morning, afternoon and evening at the front location of the bus passenger compartment. This is due to the outside contaminant enters the bus when the door is open. Insufficient ventilation of the bus is the factor that increases the contaminant concentration level of PM1 at the front location of the bus passenger compartment. However, the CO concentration was slightly lower in the morning, afternoon and evening at the middle and rear locations. The maximum and minimum concentrations of PM1 were 52 μg/m3 and 1 μg/m3, respectively. In particular, the contaminant of PM1 is originates from the vehicular exhaust, ambient air and dust. It was observed that the contaminant concentration of PM1 was exceeding the acceptable level by the World Health Organization [14]. The acceptable level of PM1 in an enclosed environment should be below 25 μg/m3. (a) (b) Fig. 4. Parametric analysis: (a) 3RG and (b) 4RG 3. RESULTS AND DISCUSSIONS Results of the field measurements are presented at the front, middle and rear locations as a function of time in the morning, afternoon and evening. Height of measurement is 1.1 m from the floor for all contaminants. In an enclosed 157003-6969-IJMME-IJENS © June 2015 IJENS IJENS International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:03 85 60 Concentration (μg/m3) 3.2. CFD Simulation of PM1 and CO Concentrations 50 40 30 20 10 PM1 (Front) PM1 (Rear) 5:00 4:00 2:30 1:30 8:30 7:30 0 PM1 (Middle) Time (hr) Fig. 8 shows the comparison of contaminant concentration of CO with different cases of air return grille locations. The modified of air return grille locations namely 3RG and 4RG. The current location of air return grilles namely 2RG generally had the highest contaminant concentration of CO at 0.3 m to 1.45 m height, respectively. It was observed that the 4RG could reduce the contaminant concentration of CO at 0.3 m to 1.45 m height, respectively. The 4RG could reduce the CO concentration that accumulated in the occupied zone compared to the 2RG and 3RG. This could be due to the locations of air return grille which was placed along the bus roof. The 4RG of air return grille location is suitable to remove all the contaminant of CO which was trapped inside the bus passenger compartment. 1.5 Fig. 7 shows the contaminant concentration of CO in the bus as a function of time. The result shows that the contaminant concentration of CO was high in the afternoon and evening at the front location of the bus passenger compartment. However, the contaminant concentration of CO was also high in the morning at the middle location of the bus passenger compartment. This is due to the outside contaminant enters the bus when the door is open. Insufficient ventilation of the bus and heavy traffic condition are the factor that increases the contaminant concentration level of CO at the front and middle locations of the bus passenger compartment. Based on the measured data the heavy traffic condition occurs in the morning, afternoon and evening in a university’s campus. In particular, the contaminant of CO is originates from the vehicular exhaust. It was observed that the maximum and minimum concentrations of CO were 7 ppm and 1 ppm, respectively. The CO concentration levels was below 7 ppm, much lower than the average limit of 10 ppm, which was recommended by the World Health Organization [14]. 8 Concentration (ppm) 7 6 5 4 3 2 1 Height above floor (m) Fig. 6. Contaminant concentration of PM1 in the bus as a function of time 1.3 1.1 0.9 0.7 0.5 0.3 0 2 4 2RG 6 3RG 8 4RG Concentration (ppm) Fig. 8. Comparison of contaminant concentration of CO with different cases of air return grille locations Fig. 9 shows the comparison of contaminant concentration of PM1 with different cases of air return grille locations. The current location of air return grilles namely 2RG generally had the highest contaminant concentration of PM1 at 0.3 m to 1.45 m height inside the bus passenger compartment. The result shows that the 4RG of air return grilles location could reduce the contaminant concentration of PM1 at 0.3 m to 1.45 m height, respectively. However, the 3RG could reduce the PM1 concentration inside the bus passenger compartment. The accumulated concentration of PM1 in the occupied zone could be removed effectively when four of air return grilles (4RG) were located at the bus roof compared to 2RG and 3RG. Fig. 10 and Fig. 11 show the contaminant concentrations of CO and PM1 on a vertical symmetrical plane of the bus passenger compartment of various cases of air return grilles locations. CO (Front) CO (Rear) 5:00 4:00 2:30 1:30 8:30 7:30 0 CO (Middle) Time (hr) Fig. 7. Contaminant concentration of CO in the bus as a function of time 157003-6969-IJMME-IJENS © June 2015 IJENS IJENS International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:03 86 Height above floor (m) 1.5 1.3 1.1 0.9 0.7 0.5 0.3 0 10 20 2RG 30 40 3RG 50 4RG Concentration (μg/m3) (c) Fig. 10. Contaminant concentration of CO on a vertical symmetrical plane of the bus passenger. Air return grille locations: (a) 2RG, (b) 3RG and (c) 4RG Fig. 9. Comparison of contaminant concentration of PM1 with different cases of air return grille locations (a) (a) (b) (b) 157003-6969-IJMME-IJENS © June 2015 IJENS IJENS International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:03 [4] [5] [6] [7] [8] (c) [9] Fig. 11. Contaminant concentration of PM1 on a vertical symmetrical plane of the bus passenger. Air return grille locations: (a) 2RG, (b) 3RG and (c) 4RG [10] [11] 4. CONCLUSIONS Field measurements were conducted to quantify the contaminants concentration of PM1 and CO at the front, middle and rear locations of a university’s shuttle bus. The CFD simulation was carried out to simulate the contaminant concentration levels of PM1 and CO on a various cases of air return grille locations inside the bus passenger compartment. The followings are major findings of this study:    [12] [13] [14] 87 Rim, D., Siegel, J., Spinhirne, J., Webb, A., & McDonald-Buller, E. (2008). Characteristics of cabin air quality in school buses in Central Texas.Atmospheric Environment, 42(26), 6453-6464. Gómez-Perales, J. E., Colvile, R. N., Fernández-Bremauntz, A. A., Gutiérrez-Avedoy, V., Páramo-Figueroa, V. H., Blanco-Jiménez, S., ... & Nieuwenhuijsen, M. J. (2007). Bus, minibus, metro intercomparison of commuters’ exposure to air pollution in Mexico City. Atmospheric Environment,41(4), 890-901. Wong, L. T., Mui, K. W., Cheung, C. T., Chan, W. Y., Lee, Y. H., & Cheung, C. L. (2011). In-cabin exposure levels of carbon monoxide, carbon dioxide and airborne particulate matter in airconditioned buses of Hong Kong. Indoor and Built Environment, 1420326X11409450. Chan, A. T. (2003). Commuter exposure and indoor–outdoor relationships of carbon oxides in buses in Hong Kong. Atmospheric Environment, 37(27), 3809-3815. Fluent, I. (2012). ANSYS FLUENT 14: theory guide. USA: Fluent Inc. Cengel, Y. A., & Cimbala, J. M. (2006). Fluid mechanics (Vol. 1). Tata McGraw-Hill Education. Shek, K. W. (2010). Thermal & indoor air quality environment on air-conditioned buses (Doctoral dissertation, The Hong Kong Polytechnic University). Zhang, T., & Chen, Q. Y. (2007). Novel air distribution systems for commercial aircraft cabins. Building and Environment, 42(4), 1675-1684. Bari, S., & Naser, J. (2010). Simulation of airflow and pollution levels caused by severe traffic jam in a road tunnel. Tunnelling and Underground Space Technology, 25(1), 70-77. ASHRAE Standard Committee. (2013). ASHRAE HANDBOOK: Fundamentals 2013. World Health Organization. (2000). Guidelines for air quality. The contaminant concentration levels of PM1 and CO were high at the front location of the bus passenger compartment. The contaminant concentration level of PM1 was exceeding the acceptable level of indoor air quality by the World Health Organization. The air return grille location namely 4RG could reduce the contaminant concentration level of PM1 and CO inside the bus passenger compartment. It can be concluded that new location of air return grilles namely 4RG created the best cabin environment and it is therefore recommended for possible use in commercial bus compartment. ACKNOWLEDGEMENTS The authors are grateful to the Universiti Teknologi Malaysia for providing the funding on this study, under the vot number of 06H75. REFERENCES [1] [2] [3] Chan, M. Y. (2005). Commuters' exposure to carbon monoxide and carbon dioxide in air-conditioned buses in Hong Kong. Indoor and Built Environment,14(5), 397-403. Hsu, D. J., & Huang, H. L. (2009). Concentrations of volatile organic compounds, carbon monoxide, carbon dioxide and particulate matter in buses on highways in Taiwan. Atmospheric Environment, 43(36), 5723-5730. Zhu, S., Demokritou, P., & Spengler, J. (2010). Experimental and numerical investigation of micro-environmental conditions in public transportation buses.Building and Environment, 45(10), 2077-2088. 157003-6969-IJMME-IJENS © June 2015 IJENS IJENS