Isı Bilimi ve Tekniği Dergisi, 32, 1, 101-107, 2012 J. of Thermal Science and Technology ©2012 TIBTD Printed in Turkey ISSN 1300-3615 TRANSIENT EFFECTS OF DIFFERENT HEATING MODES ON TEMPERATURE AND HUMIDITY INSIDE THE AUTOMOBILE CABIN DURING HEATING PERIOD M. Özgün KORUKÇU* and Muhsin KILIÇ Department of Mechanical Engineering, Uludag University, 16059 Bursa, Turkey * Corresponding author. Tel.: +90 224 2941927, fax: +90 224 2941903 E-mail: ozkorukcu@uludag.edu.tr (M. Özgün Korukçu), mkilic@uludag.edu.tr (Muhsin Kılıç) (Geliş Tarihi: 30. 11. 2010, Kabul Tarihi: 12. 01. 2011) Abstract: The aim of this study is to investigate the transient effects of heater on temperature and humidity in an automobile cabin under transient heating period. Interior volume of an automobile is relatively small to other indoor environments, so that temperature and humidity values can rapidly change under highly transient conditions. Studies that are investigating the effects of heater on automobile cabin environment in real car conditions are restricted. Experiments were carried out in a parked car inside a laboratory at nights to prevent the possible wind and solar irradiation effects. In the experiments only plane vents were operated with three different air velocity levels. Temperature and relative humidity differences between air velocity levels were obtained, relations between time, temperature and relative humidity were calculated. From this study it is understood that temperature and relative humidity values inside a car vary directly from air velocity values. The obtained results can be used to improve other thermal comfort studies inside automobiles and also CFD analyses can be validated under transient conditions. Keywords: Automobile, Heating period, Thermal comfort. ISITMA SÜRECİNDE FARKLI ISITMA MODLARININ OTOMOBİL KABİNİ İÇERİSİNDEKİ SICAKLIK VE BAĞIL NEME OLAN ANLIK ETKİLERİ Özet: Bu çalışmanın amacı ısıtıcının bir otomobil kabini içerisindeki sıcaklık ve bağıl neme olan anlık etkilerinin incelenmesidir. Otomobil kabini diğer iç ortamlara göre daha küçük olduğundan sıcaklık ve bağıl nem değerleri geçici rejim koşullarında çok hızlı bir biçimde değişmektedir. Isıtıcının otomobil kabini içerisindeki etkilerini gerçek kabin ortam koşullarında inceleyen çalışmalar oldukça sınırlıdır. Deneyler olası rüzgar ve güneş ışınımı etkilerini önlemek için laboratuarda park edilmiş bir otomobil içerisinde gerçekleştirilmiştir. Deneylerde üç ayrı hava hız düzeyi olan konsol menfezleri çalıştırılmıştır. Sıcaklık ve bağıl nem değerlerini hava hız düzeylerine göre farklılıkları ve zamana göre sıcaklık, bağıl nem değerleri arasındaki bağıntılar elde edilmiştir. Bu çalışmadan anlaşıldığı üzere araba kabini içerisindeki sıcaklık ve bağıl nem değerleri hava hızı değerlerinden doğrudan etkilenmektedir. Bu çalışmadan elde edilen sonuçların, otomobillerdeki ısıl konfor çalışmalarının geliştirilmesinde ve geçici rejim koşullarında gerçekleştirilen sayısal hesaplamalı akışkanlar dinamiği analizlerinin doğrulanmasında kullanılabilir. Anahtar Kelimeler: Otomobil, Isıtma süreci, Isıl konfor NOMENCLATURE spatial temperature gradients of over 10°C. For instance, obtained spatial temperature differences from 2 clo clothing insulation [0.155 m °C/W] 7 °C under an environmental of 26.7 °C (summer 2 met metabolic rate [60 W/m ] conditions) and increasing up to 13°C in winter Rh relative humidity [%] conditions while the environmental temperature became t time [s] as low as -20 °C (Zimney et. al, 1999). This heat stress T temperature [°C] not only influences the visibility (Nasr, 2000) but also V air velocity at vent outlet [m/s] affects the mental condition of the driver (Cisternino 1999). INTRODUCTION Aroussi and Aghil (2000), indicated that the need to Passenger and the driving thermal comfort has been improve the climatic comfort in passenger vehicles is always a concern since the development of modern crucial not only to passenger comfort but also to their cars, and thermal comfort inside the automobile cabin safety, and to make progress in this area, a good affects the driver’s awareness and ability to concentrate understanding of the flow behavior inside the passenger (Bhatti, 1999 a,b). Climate control systems in vehicle compartment is required. Daanen et al. (2003), compartments result in non-uniform temperature simulated the effects of warm, cold and thermoneutral distributions, with the occurrence of considerable ambient conditions on driving performance. They 101 obtained that driving performance was affected from glazing types. A linear relationship was found between cold and hot ambient conditions. Jones (2002), solar radiation and the thermal sensation. Korukçu and compared several thermal sensation model outputs with Kilic (2009), used IR-thermography to determine instant the measured data for a typical winter automobile surface temperature distribution and facial skin warm-up conditions and showed that the models temperatures of the driver inside an automobile cabin differed widely in their predictions. during transient heating and cooling periods. They also investigated different air velocity levels that are Kaynakli et al. (2002), presented a computational model provided by the vents. Ambs (2002), analysed a car of heat and mass transfer between a human and the cabin during transient cooling period by using finite vehicle interior environment during heating and cooling element method. In his model thermal comfort level and periods. Their model was based on the heat balance local temperature values of virtual mannequins were equation for human body, combined with empirical obtained. From his study local discomfort regions and equations defining the sweat rate and mean skin thermal sensation for virtual passengers were also temperature. Kaynakli and Kilic (2005), also determined. investigated the thermal comfort inside an automobile during the heating period and compared their simulation Akyol and Kilic (2010), modeled thermal loads inside model and showed that the data obtained from their the automobile cabin. In their model they calculated the experimental studies were in good agreement with their interactions between the passenger and the ambient that simulation model. Guan et al. (2003a), presented an is affected by solar irradiation. They also investigated experimental study to examine human thermal comfort the effect of colours and windows’ optical properties under highly transient conditions inside an automobile. such as transmissivity, reflectivity and absorptivity In their study, they used a climatic chamber to simulate coefficients on thermal comfort. Mezrhab and Bouzidi 16 different winter and summer conditions and thermal (2005), developed a numerical model for thermal sensation modeling was investigated in their other paper comfort inside car compartment under transient (Guan et al., 2003b). In their mathematical model, conditions with combined conduction, convection and physiological and psychological factors were combined, radiation heat transfer. They also investigated effects of environmental and personal parameters used as inputs to solar radiation, different glazing types, car colours and determine the physiological responses. radiative properties of materials inside the compartment. Kilic and Sevilgen (2009), performed a three- Guan et al. (2003c), also presented a literature review dimensional transient numerical analysis inside an on current advances in thermal comfort modeling for automobile cabin during heating period. They added a both building and vehicle HVAC applications. virtual manikin with real dimensions and physiological Walgama et al. (2006), presented a wide review of shape into the vehicle cabin. The manikin surfaces were passenger thermal comfort in vehicles and they subjected to either constant heat flux or constant presented various empirical, thermal comfort and temperature. They calculated three-dimensional fluid computational models. Quanten et al. (2007), made a flow, temperature distribution, and heat transfer comparison of thermal comfort performance of two characteristics inside the cabin. different types of road vehicle climate systems, two cars which have an un-air-conditioned heating cooling In this study, the effects of different air velocity levels device and an air-conditioning climate control unit. on temperature and relative humidity inside the cabin They encountered temperature gradients in un-air- for 10°C outside temperature were obtained. The conditioned car up to 8-9°C, on the other hand air- correlations between temperature and relative humidity conditioned car had temperature gradients of 5-6°C for were calculated and the effects of air velocity levels the same condition. Yamashita et. al. (2007), were investigated. investigated summertime thermal conditions for cars in a climatic chamber. They reproduced the thermal METHODOLOGY conditions such ambient temperature, passenger seat The experiments were carried out in a parked FIAT temperature and radiation panels then they observed the Albea 2005 inside a laboratory to prevent the possible effects of these parameters. They concluded that interactions such wind, rain or other weather conditions ambient temperature is the only factor that influenced between the test car and the environment. All of the thermal acceptance. Cassetta and Musto (2006), experiments were done at nights to eliminate the assessed thermal comfort in a car cabin which has sky- possible effect of solar radiation. The vents were located roof. They made the first experimental study on this on the plane, which have 3 levels of air velocity. subject by using four different sky-roofs and compared the performances of them with on the road experiments. The data were collected during the February 2008 with 27 experiments, there is only one healthy male subject Hodder and Parsons (2007), determined the effects of chosen to omit the individual responses inside the solar radiation on thermal sensation in a test chamber. compartment. The characteristics of the subject were as They used metal halide compact source iodide lamps to follows: age = 28 yr, height = 183 cm, weight = 95 kg. create artificial sunlight during the experiments. In their The mean outside temperature of the car inside the study they performed three cases with different intensity laboratory was measured in every 10 seconds and the of solar radiation, spectral content of solar radiation and mean values were: 10.5°C (±0.8). 102 The initial temperature and the relative humidity inside Vent outlet temperatures the compartment were adjusted to 14°C and %45 respectively for the heating period at the beginning of The measured air temperature values in the car at the all experiments. The indoor conditions such outlet of the vents for the heating period were presented temperature, relative humidity and the air velocity in Figure 2. measurements were made by a Testo 350 M/XL 454 probe in every 10 seconds. Accuracy, and the measuring range of the equipments were presented in Table 1. Table 1. Accuracy of the equipments. Parameter Interval Tolerance Air velocity 0 m/s – 10 m/s ± 0.04 m/s Relative Humidity 0 % – 100 % ± 0.1 % Temperature - 20°C – 70°C ± 0.4 °C Figure 2. Measured air temperature values at the vent outlet The subject wore casual clothes, which is approximately for the heating period. 1 clo for winter conditions. Level of metabolic activity was taken 1 met for a sedentary person (ISO 9920). The As seen on from the Figure 2 outlet air temperature for subject stayed 15 min in the car. Experimental setup is the third air velocity level is lower than that of other illustrated in Figure 1. velocity levels. The capacity of the heater is same for all air velocity levels, therefore outlet air temperature values are lower for the high air velocity levels. Vents and indoor air temperature differences The measured air temperature difference values between vent outlet and the indoor for the heating period were presented in Figure 3. Figure 1. Experimental setup inside the cabin, 1-Temperature, Rh probe, 2-Air velocity, 3-Data logger. To determine the effects of air velocity inside the Figure 3. Air temperature difference values between vent passenger compartment, subject sat 15 minutes inside the outlet and the indoor for the heating period. car sedentary and measurements were taken both from In the Figure 3 temperature difference between vent inside and outside simultaneously. The differences of both outlet and the indoor air temperature were calculated temperature and humidity between air velocity values were during the heating period. With the increasing air presented via multiple analyses of variance (MANOVA). velocity level, indoor air was also heated. Hence the RESULTS third air velocity level has the lowest outlet temperature and the highest indoor temperature, lower air Air velocity temperature differences were obtained than that of for the other air velocity levels. The measured air velocity values for the velocity levels Effect of air velocity from the vent outlets were presented in Table 2. Mean (and standard error) plots of temperature for air Table 2. Air velocity values. velocity values at 10°C outside temperature are given in Symbol Air velocity (m/s) Figure 4. V1 0.78 V2 1.65 Mean (and standard error) plots of relative humidity for V3 2.66 air velocity values at 10°C outside temperature are given in Figure 5. From the multiple analysis of variance (MANOVA), the effects of air velocity and time factors on temperature 103 interaction of air velocity and time factors was found less effective on temperature and humidity. Table 3. MANOVA test statistics for air velocity at 10°C outside temperature. 95% Air- Std. Confidence Velocity Mean Error Interval Lower Upper Bound Bound V1 22.62 .20 22.23 23.02 Temp. V2 26.79 .20 26.40 27.18 (°C) V3 27.74 .20 27.35 28.13 Rel. V1 34.06 .32 33.42 34.71 Figure 4. Mean temperatures for air velocity values at 10°C Hum. V2 26.66 .32 26.01 27.30 outside temperature. (%) V3 25.42 .32 24.78 26.06 Table 4. Partial eta squared results at 10°C outside temperature. Dependent Partial Eta Source Variable Squared Temp. 0.80 Air-Velocity Rel. Hum. 0.81 Temp. 0.96 Time Rel. Hum. 0.95 Air-Velocity x Temp. 0.26 Time Rel. Hum. 0.31 In Table 5, the results of Student-Newman Keul’s Test Figure 5. Mean humidity values for air velocity values at were presented of temperature for air velocity values at 10°C outside temperature. 10°C outside temperature. were found significant (FVELOCITY =190.164, p < 0.05) and In Table 6, the results of Student-Newman Keul’s Test (FTIME =161.828, p < 0.05). On the other hand, the effect of were presented of relative humidity for air velocity the interaction of air velocity and time factors on values at 10°C outside temperature. temperature was not found significant (FVELOCITYxTIME =1.145, p >0.05). From the Tables 5 and 6, it can be seen that there are three subgroups occurred both in temperature and Multiple analysis of variance (MANOVA) results for the humidity parameters, because V1, V2 and V3 values are relative humidity showed that the effects of air velocity and different from each other. time on humidity were found significant (FVELOCITY =208.813, p < 0.05), (FTIME =138.797, p < 0.05), but the Table 5. Student-Newman Keul’s Test of temperature for air interaction of air velocity and time factors were not found velocity values at 10°C outside temperature. significant (FVELOCITYxTIME =1.411, p >0.05). Air-Velocity Subset 1 2 3 As seen from the Figure 4 and Figure 5, temperature and V the humidity values differ with V1 , V and V 1 22.62 2 3 air velocity values. V2 26.79 V3 27.74 The test statistics for air velocity values after multiple analysis of variance (MANOVA) are presented in Table 3. Table 6. Student-Newman Keul’s of relative humidity for air velocity values at 10°C outside temperature. From the partial eta squared values of the multiple Air-Velocity Subset analysis of variance (MANOVA) results which were presented in Table 4, both air velocity and time factors 1 2 3 were found significant on temperature and humidity V3 25.42 parameter at the same level. On the other hand, V2 26.66 V1 34.06 104 The relations between time and temperature, and (3) With increasing air velocity values, inside humidity with time and temperature were obtained from temperature also increases during the heating periods. the linear regression analysis. From the Equation (1), relation between time (t) and temperature (T) is (4) For the third air velocity level lower air temperature presented for the first air velocity value (R²=0.933). differences between vent outlet and the indoor air temperature were obtained than that of for the other air T=14.713+1.055t (1) velocity levels during the heating period. In Equation (2), relative humidity (Rh) is obtained in (5) Low air velocity values have more relative humidity terms of time and temperature for the first air velocity values during the heating period. value, (R²=0.952). (6) From this study it is understood that temperature and Rh= 69.282-0.0073t-1.533T (2) humidity inside a car varies directly from air velocity values. For the second air velocity value, the relationship between time and temperature is presented in Equation (7) Equations for predicting the temperature and relative (3), (R²=0.952). humidity values respect to time and air velocity levels were obtained. T=17.507+1.237t (3) (8) The obtained results from this study will lead further The relative humidity value for the second air velocity studies in automobile thermal comfort studies and with value is presented in Equation (4) in terms of time and this research; CFD studies and thermal comfort models temperature, (R²=0.957). with regard to thermophysical interactions between subjects and the ambient can be validated for transient Rh=73.76+0.54t-1.911T (4) conditions. In Equation (5), the variation between temperature and (9) There are many studies for building HVAC systems time is presented for the third air velocity value, but the investigations for automobile HVAC systems (R²=0.897). are restricted. Results from this study will be useful for automobile manufacturers for designing and improving T=17.981+1.302t (5) HVAC systems. The relative humidity value for the third air velocity (10) We recommend that more experiment time with value is presented in Equation (6) in terms of time and more cars, in a climatic chamber or wind tunnel at temperature, (R²=0.914). determined conditions will be better for thermal comfort researches inside a car. Rh=59.839-0.314t-1.146T (6) ACKNOWLEDG EMENT S CONCLUSION The authors would like to acknowledge to the Scientific The driver vigilance and the concentration are vital for and Technological Research Council of Turkey driving safety. The ambient conditions inside an (TUBITAK) for supporting this research under the automobile directly affect both the driver and also the project number of 105M262 and also to FIAT-TOFAS passengers. 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He has several international and national publications. M. Özgün KORUKÇU He took his B.Sc. degree from Mechanical Engineering Department of Uludag University in 2002. He started to work as research assistant in the same department in 2004. he got M. Sc. in 2005 and in 2010 he gained Ph. D. degrees from Uludag University. Since 2004 he has been working in the same department. He is interested in Heat and Mass Transfer, Renewable Energy Systems, Thermal Comfort and Infrared Thermography subjects. 107