Performance analysis of turbine ventilators for refugee camps usage

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The first part of the study was intended to select the best turbine ventilator design to test its performance while in the second part, simulation study was conducted on the selected design in comparison with the benchmarks (currently market-available turbine ventilators).

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 03, March 2019, pp. 1373-1383. Article ID: IJMET_10_03_138 Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed PERFORMANCE ANALYSIS OF TURBINE VENTILATORS FOR REFUGEE CAMPS USAGE M. I. N. Ma’arof Department of Mechanical Engineering, INTI International University, Persiaran Perdana BBN, Putra Nilai, 71800 Nilai, Negeri Sembilan, Malaysia Girma T. Chala Department of Mechanical (Well) Engineering, International College of Engineering and Management, P.O. Box 2511, C.P.O Seeb 111, Sultanate of Oman Shree R. Nair Department of Mechanical Engineering, INTI International University, Persiaran Perdana BBN, Putra Nilai, 71800 Nilai, Negeri Sembilan, Malaysia ABSTRACT A turbine ventilator is a promising technology used to achieve multiple cooling conditions. The present study proposed a method to improve the indoor air quality (IAQ) of refugee camps to overcome issues related to air borne diseases. A turbine ventilator was designed based on the ISO and ASHRAE standards. The effect of the turbine ventilation fan on the IAQ of a modelled refugee shelter was investigated via Computational Fluid Dynamics (CFD) simulation. The first part of the study was intended to select the best turbine ventilator design to test its performance while in the second part, simulation study was conducted on the selected design in comparison with the benchmarks (currently market-available turbine ventilators). It was observed that a 55° blade angle design performed best at 115 RPM and was tested for indoor air quality improvement for the transitional shelter found in the Dadaab region, Kenya. ISO 7730 (2005) standards were met with average internal air velocity of 0.25m/s. PMV and PPD for the whole space were at 0.452 and 9.938%, respectively, which are well within the recommended values. The results from this study would hopefully provide an insight into future developments of turbine ventilators not only for refugee camps, but also for other sectors requiring improvements to indoor air quality. Keywords: Turbine ventilator, Performance, Percentage of dissatisfied, Refugee camps. Cite this Article: M. I. N. Ma’arof, Girma T. Chala and Shree R. Nair, Performance Analysis of Turbine Ventilators for Refugee Camps Usage, International Journal of Mechanical Engineering and Technology, 10(3), 2019, pp. 1373-1383. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3 http://www.iaeme.com/IJMET/index.asp 1373 editor@iaeme.com
M. I. N. Ma’arof, Girma T. Chala and Shree R. Nair 1. INTRODUCTION Refugee camps in some places have not been getting sufficient attentions when it comes to indoor air quality and ventilation. The influx of refugees creates overpopulation and does not help reduce the spread of diseases, such as tuberculosis and influenza viruses. Over the years, the majority of refugee resides in the Dadaab region, Kenya where an estimate of 425,938 refugees are registered. The Kenya Ministry of health established nationwide facilities based on the spread of influenza pandemic in 2006, where the camps of Kakuma and Dadaab being the main targets [1]. Indoor air quality (IAQ) encompasses the structure and its surroundings and its assessment is based on the level of health and comfort of the occupants. Chianga and Laib [2] discussed that the indoor environment is complex and dependent on many factors. The main factors rely on identifying the air contaminant sources and proposing proper ventilation. Although not well documented, the effects of airborne contaminants towards deteriorating human health in the African region were brought to light in the studies conducted by [3]. Consequently, in tight and packed spaces like the refugee camps of Dadaab, Kenya, the chance of these contaminations spreading and affecting the rest of the camp is high, if proper care is not put in place. The main purpose of ventilation in regard to air quality lies in its ability to transport out pollutants and contaminated air [4]. A review on different designs of wind driven natural and hybrid ventilation systems yielded that turbine ventilators are the best option when cost, performance and construction are concerned [5]. The same study also presented arguments supporting the fact that turbine ventilators are the ideal choice considering its size and its ability to maintain humidity and reduce the accumulation of contaminants and pollutants in the air. A turbine ventilator, also known as rotary ventilator, operates on the basic principles of buoyancy. As the air in the room of a structure rises, the stack effect allows the pressure differences between indoor and outdoor air to escape the structure into the surroundings. However, the fan in the turbine ventilator aids the process by utilizing a suction effect through the negative pressure that is created in the process of the spinning aero foil vanes, driving air out from the structure into the surrounding air [6]. The performance of the ventilators depends on the surrounding wind speed, the design of the vanes and also the way it is installed onto the roof, among other factors. Wang and Shen [7] concluded that the mass flow rates of the air are directly correlated with the pitch angle of the roof. Lien and Ahmed [8]; however, concluded that the rotational speed of a turbine can be increased by increasing the inclination of the roof. It was also observed that air change rate changes with the variation in wind direction. A change from 0° to 45° declined the air change rate by 10% [9]. Flynn and Ahmed [10] stated that larger diameter ventilators performed better with better extraction rates. This was backed by Lai [11], who discovered that smaller diameter turbine ventilators performed worst when compared to their larger counterparts. In terms of blade design, Revel [12] found that the straight vane turbine is more effective at air extraction as opposed to the curved vane turbine design. They also observed that the larger 300 mm diameter throat turbine ventilator outperformed the smaller 250 mm diameter throat. West [13] discussed that the flow rate of a straight vane turbine ventilator can be increased by 13.5% by increasing its blade or vane height by 50%. A CFD studies by Lien and Ahmed [8] showed that the performance metrics meet the general requirements and standards of indoor air quality for a modeled living room. Kuo and Lai [14] showed that the lower pressure caused by the turbine ventilator aids in reducing odor leakage to other parts in the building while maintaining sufficient air change rates. There seems to be little evidence to prove the effect of ventilations on reducing the spread of infections in a structure. Studies have been conducted to determine the cause and transmission of diseases; however, the impact of ventilation on reducing the transmission of airborne diseases remains to be properly researched. The objective of this study was, therefore, http://www.iaeme.com/IJMET/index.asp 1374 editor@iaeme.com
Performance Analysis of Turbine Ventilators for Refugee Camps Usage to test the different designs of turbine ventilator to improve the air indoor air quality (IAQ) of refugee camps in Africa to overcome issues related to air borne diseases. This would provide an insight towards the significance and viability of using wind turbine ventilator, and subsequently it can be implemented in more refugee camps. 2. MATERIALS AND METHODS The turbine ventilator was designed to meet the recommended ventilation rate standards for good indoor air quality. These standards are included in ventilation standards, such as American Society of Refrigerating and Air-Conditioning Engineers ANSI/ASHRAE standard 62 and ISO Standard 7730 [15, 16]. These standards for residential and public buildings do not particularly give a standard for refugee camps. Therefore, an estimation was taken into account based on the standard values of a recommended 4-8 air changes per hour (ACH) for different volumes of residential building and rooms. The mechanical ventilation rate required was then determined using the equation below: 𝑄𝑣𝑒𝑛𝑡 = 𝑛 × 𝑉𝑠ℎ𝑒𝑙𝑡𝑒𝑟 (1) Where: 𝑛 is the air change rate per hour (ACH) 𝑉𝑠ℎ𝑒𝑙𝑡𝑒𝑟 is the volume of the shelter (𝑚3 ) 𝑄𝑣𝑒𝑛𝑡 is the ventilation rate (𝑚3 /ℎ) The maximum recorded extraction rate or ventilation rate is calculated as follows: 𝑄𝑣𝑒𝑛𝑡 = 𝐴𝑡ℎ𝑟𝑜𝑎𝑡 × 𝑉𝑝𝑜𝑖𝑛𝑡 × 3600 (2) Where: 𝐴𝑡ℎ𝑟𝑜𝑎𝑡 is the throat area of the turbine ventilator (𝑚2 ), 𝑉𝑝𝑜𝑖𝑛𝑡 is the velocity at the point (𝑚/𝑠) and 𝑄𝑣𝑒𝑛𝑡 is the ventilation rate (𝑚3 /ℎ) A target ventilation rate for the transitional shelter design with a volume of 83.64 m^3 and an air change rate of 8 ACH will have a value of 669.12 (m^3/h). However, the ASHRAE standards for recommended air changes per hour can be higher or lower depending on the occupancy. To categorize refugee camps under residential conditions is not the best solution but for the purpose of this study, the turbine ventilator was made to achieve a ventilation rates greater than 669.12 (m^3/h). Following suit, the ISO 7730 standards for indoor comfort relies on several aspects: temperature, indoor air velocity, humidity being the main parameters. To achieve a comfort level of 80% acceptance for the turbine ventilator, the results from the CFD simulation have to be within acceptable range of these comfort variable benchmarks: room temperature in the range of 24˚C - 26˚C, indoor air velocity < 0.25 m/s, Predicted Mean Vote (PMV) of -0.5 – 0.5 and Predicted Percentage of Dissatisfied (PPD) ≤ 10% 3. TRANSITIONAL SHELTER MODEL GEOMETRY The transitional shelter design selected for this study was the compact bamboo shelter design. The roof inclination and materials were not taken into account when modelling the shelter in SolidWorks. Figures 1 and 2 show the front elevation of compact bamboo T-shelter and the isometric view of the modeled T-shelter, respectively. Table 1 shows the dimensions of the modelled T-Shelter. http://www.iaeme.com/IJMET/index.asp 1375 editor@iaeme.com
M. I. N. Ma’arof, Girma T. Chala and Shree R. Nair Figure 1 Front elevation of compact bamboo T-Shelter (UNHCR Shelter Design Catalogue, 2016) [16]. Figure 2 Isometric view of the modeled T-Shelter (Dimensions in mm). Table 1 shows the dimensions of the modelled T-shelter. Shelter length (𝑚) 6.0 Shelter Width (𝑚) 4.1 Shelter Height (𝑚) 3.4 Shelter Volume (𝑚3 ) 83.64 Wall Thickness (𝑚) 0.15 Ceiling hole diameter (𝑚) 0.462 Window length (𝑚) 0.6 Window Height (𝑚) 0.6 4. TURBINE VENTILATOR DESIGN GEOMETRY The performance metrics of these ventilators are studied based on previous studies by Revel [12] and West [13]. The straight vane turbine ventilator design, shown in Figure 3, was chosen due its superior performance. The turbine ventilator design is inspired by the two models from http://www.iaeme.com/IJMET/index.asp 1376 editor@iaeme.com
Performance Analysis of Turbine Ventilators for Refugee Camps Usage Edmonds Hurricane line of products [18]. The dimensions of the turbine ventilator for the shelter are based on the H400 and H450 model. The number of blades were set to 24 to match the standard designs of the Edmonds ventilators. Three designs were tested with blade angles at 45˚, 55˚ and 65˚. Figure 3 Straight vane turbine ventilator design (Dimensions in mm). 5. WIND TUNNEL GEOMETRY A wind tunnel structure was designed in CAD to simulate the wind velocities. The wind tunnel aids in even distribution of uniform air flow to the ventilator at higher wind speeds. The wind tunnel is setup on top of the shelter model in the simulations, enclosing the turbine ventilator 6. NUMERICAL MODELLING SolidWorks flow simulation package was used for this study. Due to the dependency on mesh settings, boundary conditions and turbulence models of CFD testing, the settings used are detailed in this section. In SolidWorks Flow Simulation, the turbulence model used is the k- epsilon (k-ε) model. However, to calculate the transient flows, the local rotating regions (Averaging) option was used to select a rotating body. The meshing was done through a Cartesian meshing method. The mesh setting was done using the global automatic mesh method, maximum level 7 initial mesh level, with advance channel refinement option turned on. Figure 4 shows boundary conditions and set up of the turbine ventilator. To set up the internal flow analysis, first, the geometry must first be sealed to be “water-tight” for SolidWorks to define the boundary conditions. The conditions are then set accordingly. Inlet velocity was set as 7m/s according to the climate data of Dadaab, Kenya. Temperature was set as default at 20.5˚C as the temperature parameters are not of concern for the initial performance testing of the different blade angles of the turbine ventilator. Environment pressure of 101325 Pascals or 1 atmosphere is set as a boundary condition at the exit of the wind tunnel as well as the small window in the shelter model. http://www.iaeme.com/IJMET/index.asp 1377 editor@iaeme.com
M. I. N. Ma’arof, Girma T. Chala and Shree R. Nair Figure 4 Boundary conditions and setup of the turbine ventilator test. The boundary conditions for the second part of the simulations remains the same except the temperature is set at 26˚C to simulate the indoor temperatures in the shelters of Dadaab, Kenya. The heat sources in this simulation are the human models and since this test does not utilize the heat conduction in solids method in the simulation, the models are set as fixed surface heat sources. For this simulation, the metabolic rate of these models were set based on ISO 7730 (2005) where the metabolic rate of an adult at rest without much physical activity is 70 "W/" "m" ^"2" . Part 2 of the simulation utilizes 18 points arranged throughout the shelter geometry, as shown in Figure 5. This technique in testing indoor air quality parameters was discussed in a study conducted by Lien and Ahmed (2012) [8]. The points are spaced 2.0 m apart in the Z axis, 2.0 m apart in the X axis and 1.0 m apart in the Y axis Figure 5 Numbered point parameter locations from point 1 to 18. 7. RESULTS AND DISCUSSION Figure 6 shows the maximum recorded extraction rate or ventilation rate of all the designs at different RPMs. The cut plots used in all the results are selected to be in the center of the turbine ventilator, following the point parameters. This would provide the best representation of the pressure and velocities of the point parameters. The values obtained from the simulation suggests that at 90RPM, the 45° angle blade outperforms the other two. However, this is not the case at higher RPMs. The 65° blade angle performed the best at the highest RPM while http://www.iaeme.com/IJMET/index.asp 1378 editor@iaeme.com
Performance Analysis of Turbine Ventilators for Refugee Camps Usage falling behind in lower RPMs. The highest velocities are recorded to be in point 4 which lies in the middle of the throat of the turbine ventilator. 1600 1400 VENTILATION RATE (M3/H) 45 55 65 1200 1000 800 600 400 200 0 90 100 115 TURBINE VENTILATOR SPEED (RPM) Figure 6 Performance of different blade angle designs at point parameter 4. Cut plot region from the right is shown in Figure 7. These values seem to correlate with the testing results from the Edmonds H400 and H450 series of turbine ventilators. However, the Edmonds ventilator was only tested under 6 m/s maximum wind speeds. Realistically, the wind speeds in Dadaab averages at 7-7.5 m/s. At these speeds, based on other tests, the turbine ventilator would be running at the 100-120RPM range. Therefore, it can be stated that the best performing in all situations is the 55° blade angle design with maximum extraction rates slightly under 1400 m^3/h. This simulated performance outperforms the expected target extraction rate of 669.12 (m^3/h) needed for shelter design with a volume of 83.64 m^3 and an air change rate of 8 ACH. The simulated maximum air change rate in this case is above double the target at 16.6 ACH. Part 2 of the simulation is done using the ideal values where the maximum performance is observed, which is 55° blade at 115RPM. Figure 7 Cut plot regions 1,2 and 3 from the right. Figure 8 shows the temperature contour plot with velocity vector of region 2. Based on the results of the simulation in part 2, the temperature contour cut plots show the minor changes to air temperature from the turbine ventilator. The highest temperatures are accumulated around http://www.iaeme.com/IJMET/index.asp 1379 editor@iaeme.com
M. I. N. Ma’arof, Girma T. Chala and Shree R. Nair the inlet window as well as the human models. However, the stack and buoyancy effect can be observed as well. The temperature is higher near the ceiling when compared to the floor area. The turbine ventilator reduces the temperature around it and can be seen in the temperature cut plot of region 1. The simulation points results are shown in Table 2 and shows the maximum temperature drop from the points is 0.3717 °C. The results are in line with Lien (2012) [8] where the conducted simulations only resulted in a maximum temperature drop of 0.55°C. The velocity vectors show the direction of air flow in the shelter. There appears to be sucked in to the turbine ventilator and this can be seen clearly in regions 1 and 2. The highest velocities as indicated from Table 2 are at points number 5 and 6 near the opening of the turbine ventilator as it is sucking the air in. However, the other points are well within the ISO 7730 (2005) standard that recommends a benchmark under 0.25m/s. Figure 8 Temperature contour plot with velocity vectors of region 2. Table 2 IAQ Performance metrics for 55° blade angle turbine at 115RPM Point Velocity [m/s] Temperature [°C] PMV PPD [%] 1 0.12953259 25.6661008 0.546798257 11.28404416 2 0.13687088 25.65793133 0.5286013 10.92242539 3 0.332186014 25.62823111 0.281984381 6.688873996 4 0.228939508 25.74670195 0.415874547 8.622382354 5 0.397011296 25.78933994 0.276159709 6.615470338 6 1.353907615 25.67868481 -0.124996532 5.429010368 7 0.101183111 25.98876467 0.679150351 14.70571346 8 0.200103504 25.99473304 0.52354704 10.73639305 9 0.249815623 25.75246178 0.392960419 8.261901853 10 0.157429244 26.03567814 0.590599072 12.31202201 11 0.230928401 26.05904447 0.501226958 10.28587898 12 0.187851585 25.83345231 0.482613607 9.962618019 13 0.188876045 26.05451479 0.550843944 11.39545969 14 0.18827564 26.04620685 0.551806386 11.4046623 15 0.18172908 25.96780292 0.536012899 11.02928139 16 0.226904225 26.06028774 0.507113833 10.38702794 17 0.202013413 26.0574051 0.53420937 11.00192121 18 0.339916563 25.95680671 0.368496914 7.851772372 Predicted Mean Vote (PMV) performance and Predicted Percentage Dissatisfied (PPD) performance are depicted in Figures 9 and 10 respectively. The PMV and PPD standards for http://www.iaeme.com/IJMET/index.asp 1380 editor@iaeme.com
Performance Analysis of Turbine Ventilators for Refugee Camps Usage this study are based on the ISO 7730 (2005) standard. The standard uses the steady state heat balance for the human body and is related to the 7 thermal sensations of the human. These values are recommended to be in the +0.5 to -0.5 PMV range with a PPD of less than 10% granted that the metabolic rate of the human is between 1-1.3 met. The rate used in part 2 of the simulation is 70 "W/" "m" ^"2" which is 1.2 met. The data from the simulation show promising results for PMV values, where the points near the turbine ventilator having the maximum values of 0.28 to a high of 0.68 which slightly exceeds the standard. The corresponding range for PPD is between a low of 5.43% and a maximum of 14.71%. However, these maximum and minimum values are only in hot spots and the average for PMV and PPD for the whole space are at 0.452 PMV and 9.938% PPD and these are well within the recommended values from the standards. The relationship between PMV and temperature is also observed. The trend of PMV being higher in the regions of higher temperature is apparent. Figure 9 Predicted Mean Vote (PMV) contour plot of region 2. Figure 10 Predicted Percentage Dissatisfied (PPD) contour plot. 8. CONCLUSION In the present study, a turbine ventilator was designed with the aim to improve indoor air quality for the shelters in refugee camps. In the process, different factors that affect the performance of the turbine, including wind speed, design, installation practices and the physical characteristics are investigated. The turbine design process involved testing several blade angle designs while keeping the main design parameters of the turbine ventilator similar to the current market leading products. The 55° blade angle design performed best and was tested for its improvement http://www.iaeme.com/IJMET/index.asp 1381 editor@iaeme.com
M. I. N. Ma’arof, Girma T. Chala and Shree R. Nair in indoor air quality for the transitional shelter found in the Dadaab region, Kenya. The comfort levels were observed to have a direct correlation with the extraction of air in the space by the turbine ventilator. The CFD analysis showed that the turbine ventilator improves the indoor air quality in the shelters and subsequently improves the lives of many refugees. It can be concluded that the results from this study are promising and the prospects of implementing turbine ventilators for refugee camps appear to be suitable. The results from this study would hopefully provide an insight into future developments of turbine ventilators not only for refugee camps, but also for other sectors that require improvements to indoor air quality. Moreover, temperature reduction through the higher exhaust rate could be achieved through a hybrid turbine ventilator which utilizes solar energy to power a secondary fan to improve overall exhaust rates REFERENCES [1] Kim, C., Nyoka, R., Ahmed, JA., Winchell, JM., Mitchell, SL., Kariuki Njenga, M., Auko, E., Burton, W., Breiman, RF., Eidex, RB. (2012). Epidemiology of respiratory infections caused by atypical bacteria in two Kenyan refugee camps. Journal of Immigrant and Minor Health.; 14 (1): 140-145. [2] Chianga C., Laib C., 2002, A study on the comprehensive indicator of indoor environment assessment for occupants' health in Taiwan, Building and Environment, vol.37, P 387-392. [3] Tanimowo, MO (2000) Air pollution and respiratory health in Africa: a review. East African 898 Medical Journal, 77:71-75. [4] Muhammad Izzat Nor Ma‟arof, Hazran Husain, Amir Ashraf Abd Rahman and Girma T. Chala, Smart Metering Device for Hvac System, International Journal of Mechanical Engineering and Technology, 9(8), 2018, pp. 397–403. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=8 [5] Khan, N., Su, Y., & Riffat, S. B. (2008). A review on wind driven ventilation techniques. Energy and Buildings, 40. [6] Battle McCarthy (1999) Consulting Engineers, Wind Towers: Detail in Building, Wiley, New York. [7] Wang, S., & Shen, Z. (2012). Effects of roof pitch on air flow and heating load of sealed and vented attics for gable-roof residential buildings. 4,1999–2021. [8] Lien, J., & Ahmed, N. (2012). Numerical evaluation of wind driven ventilator for enhanced indoor air quality, 49(0), 124–134. [9] Li, J. Q., & Ward, I. C. (2006). Investigation of roof pitch and wind induced ventilation by computational fluid dynamics. In PLEA2006 – The 23rd Conference on Passive and Low Energy Architecture Geneva, Switzerland. [10] Flynn, T. G., & Ahmed, N. A. (2005). Investigation of rotating ventilator using smoke flow visualisation and hot-wire anemometer. In Proc. of 5th Pacific Symposium on Flow Visualisation and Image Processing Whitsundays, Australia, Paper No. PSFVIP-5-214. [11] C.M. Lai, Experiments on the ventilation efficiency of turbine ventilator used for building and factory ventilation, Energy and Buildings 35 (9) (2003) 927–932 [12] Revel, A., & Huynh, B. P. (2004). Characterizing roof ventilators. The 15th Australasian Fluid Mechanics Conference, The University of Sydney, Australia. [13] West, S. (2001). Improving the sustainable development of building stock by the implementation of energy efficient, climate control technologies. Building and Environment, 36, 281-289. [14] Kuo, I. S., & Lai, C. M. (2005). Assessment of the potential of roof turbine ventilators for bathroom ventilation. Building Services Engineering Research and Technology, 26(2), 173- 179. http://www.iaeme.com/IJMET/index.asp 1382 editor@iaeme.com
Performance Analysis of Turbine Ventilators for Refugee Camps Usage [15] American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc, (2009). ASHRAE Handbook – Fundamentals. [16] International Standards Organization, (2005). Ergonomics of Thermal environment analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. ISO 7730. [17] United Nations Refugee Agency, Shelter Design Catalogue 2016. [Online] available from:https://cms.emergency.unhcr.org/documents/11982/57181/Shelter+Design+C atalogue+January+2016/a891fdb2-4ef9-42d9-bf0f-c12002b3652e [accessed 13.02.18]. [18] Edmonds Hurricane Technical Data Sheet. [Online] Available from: https://www.edmonds.com.au/-/media/edmonds/files/hurricane-technical-data.pdf (Accessed 6 September 2018) [19] WHO (2009) Guidelines for Natural Ventilation for Infection Control in Health-Care Settings. Geneva, World Health Organization. http://www.iaeme.com/IJMET/index.asp 1383 editor@iaeme.com