Analysis for Adsorbed Odor from Car Air Conditioner Evaporator
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Analysis for Adsorbed Odor from Car Air Conditioner Evaporator Kazuhisa Uchiyama*, Osamu Kasebe**, Kengo Kobayashi***, Shigeyuki Sato****, Hiroshi Ito***** DENSO CORPORATION 1-1 Showa-cho Kariya-shi Aichi 448-8661 JAPAN *kazuhisa_uchiyama@denso.co.jp, **osamu_kasebe@denso.co.jp, ***kengo_kobayashi@denso.co.jp TOYOTA CENTRAL R&D LABS., INC. 41-1, Aza Yokomichi, Oaza Nagakute, Nagakute-cho, Aichi-gun, Aichi-ken, 480-1192, JAPAN **** e0291@mosk.tytlabs.co.jp, ***** hiroshi-ito@mosk.tytlabs.co.jp Abstract: As one of measures to improve the environment in a car, we have decreased the foul odor and the dusty odor caused by the car air conditioner evaporator. However, the problem with adhesive odor is still left unresolved. We analyzed the odor from cars with a sensory test and instrumental analysis. And we simulated the odor with an evaporator desktop test bench with airflow controller, air temperature and humidity controller for testing odor from an evaporator. We proved that the odor is composed mainly of substances from exhaust gas, tobacco smoke and others. We found, (a) three principal components of adhesive odor with PCA (principal component analysis), (b) a close correlation between odor sensory test data and instrumental analysis data with multivariate analysis, and (c) specified main odor substances (ex. Lower fatty acids, Hydrocarbons and Aldehydes). These odor substances tend to become noticeable while the air conditioner is operated with the compressor turned on and off. This operating pattern is increasingly used recently for energy saving purpose. With the evaporator desktop test bench, we found that hydrophobic odor substances (ex. Toluene) are released while evaporator’s surface is changing from ‘Dry’ to ‘Wet’ (temperature falls down and flocculated water breaks out on the surface). And while changing from ‘Wet’ to ‘Dry’, the flocculated water vaporizes and hydrophilic odor substances (ex. Lower fatty acids) come up together. Consequently we have identified the components of inherent odors that smell while H2O is condensing and vaporizing (= the compressor is turned on and off). And we clarify the odor generation mechanism from an evaporator surface. Key words: Air Conditioning, Human Engineering, Evaporator, Odor 1. Introduction Heater core For the past several years, we have been trying to minimize the odor emitted from the car air conditioner evaporator (Fig.1). As the user's odor tolerance threshold becomes lower, on the other hand, an unpleasant odor is still Blower Evaporator emitted from the source of components collecting even after Fig.1 Car Air Conditioner System and Evaporator the current surface treatment capable of controlling an "uncomfortable odor" caused by bacteria and a "dusty odor" resulting from corrosive products on the evaporator (Fig.2). An odor from the evaporator surface-treated in the current process was traced by means of monitored vehicles on a continuous basis. One of the 23 users of the monitored vehicles made a complaint about an annoying
"odor" in five months after the start of monitoring. Odor Type Rotten Dusty Sweat,Tobacco In contrast, four of the 23 users made a complaint Cause Growth of Al(OH) 3 Adsorption and Bacteria Desorption of Odor in ten months. Odor Resin Reacted Layer Odor A check for any odor from two of these units Bacteria Chromate Layer ? Mechanism indicated a different type of odor unlike the Odor uncomfortable odor or dusty odor. In addition, we Evaporator Evaporator Evaporator Counter counted the bacteria on the surface of six units -measure Biocide New Coating Filter including these two and found out that the number Fig.2 Odor of Car Air Conditioner was below the odor-emitting minimum level, presenting no problem. We thereby cleaned up the two evaporators so as to remove the collecting foreign material to a completely acceptable "odor" level and noticed that these odors were caused by the collecting components, resulting in "adsorbed odors". And when the compressor is set in control mode Normal Pattern intended for saving energy as currently observed, such Comp ON OFF an odor would be enhanced in addition to temperature No Odor Evaporator rising or lowering on the surface of the evaporator. Temp. (Fig.3) An Example of Eco-mode Pattern ON Comp The purpose of this study is to identify the OFF causative substance of such an "odor" possibly Wet to Dry Dry to Wet resulting from the components accumulating on the Wet enough Evaporator surface of the evaporator and determine the odor Temp. Odor mechanisms components through the analysis, clarify Car Running Car Stopping Fig.3 Comp. Operation Mode and Odor how the adsorbed odor arose. 2. Materials and Methods Before developing an odor evaluation method, we Brain analyzed how an odorous stimulus was transmitted. Olfactory Epithelium Odor Measurement Substances The odorous stimulus first stimulates the olfactory Odor Substances Chemical Analysis Odor cells on the "olfactory epithelium" as olfactory Recognition Emotion receptors in the nasal cavities, then goes through the First Study, Restudy Sensory Test Memory olfactory nerve, and finally reaches the brain. At this Decision Image Fig.4 Flow of Stimulus and Measurement time, if the concentration of the odorous components is at a sufficiently high level for the stimulative pulse from the olfactory cells to exceed a definite level (the concentration of the odorous components at this time is called as "threshold concentration"), then the signal is perceivable as an odor to determine the kind of odor (Fig.4). A search of those parameters objectively identified in the process from the generation of an odorous stimulus to the recognition of the odor will indicate that data can be collected through instrumental analysis for an "odorous component" and through odoring evaluation questionnaires for an "emotion or image." 2.1 Identifying Odor causative substances 2.1.1 Samples for Odor sensory test and Instrumental analysis We picked samples, and divide in two for instrumental analysis and the odor sensory evaluation value.
2.1.2 Odor sensory test for PCA and multiple regression analysis At first step, we made an attempt to develop a new *PCA:Principal Component Analysis Odor Sensory Test Factor 2 evaluation strategy for relating the test values by Sampling Bag 2.72 Odor B Cars means of instrumental analysis with the odor sensory evaluation values of the same samples. To correlate PCA* 0.00 Factor 1 Odor C the results of analysis to the odoring evaluation values, Odor A Questionnaire we focused on relationships between the types of odor -2.72 -2.72 0.00 2.72 Fig.5 Sensory Test and PCA and the causative substances. Analysis on the chief ingredients of the results of the odoring evaluation will identify Partial Regression judgment criteria, which are available to group the plots (Fig.5). The odoring evaluation values in these vehicles are selected as Y = β1X1 + β2X2 + β3X3 + . . . + βpXp objective parameters while the odor component analysis values are Observed Value Explanatory Variate specified as descriptive parameters. Since the intensity of an odor (Instrumental Analysis Data) Fig.6 Multiple Regression Analysis in the vehicle is supposed to be highly correlated with the level of the component characterizing the odor of cigarette smoke, we believe that those components closely correlated to the odoring evaluation values are imported into the descriptive parameters when the variables are selected by performing multiple regression analysis (Fig.6). Each of the individual groups consists of similar members, based on the evaluation quadrants for people. The samples collected from the actual vehicle and prepared for odoring evaluation were divided into two and shared by instrumental analysis. Placed in odor bags, these samples were submitted to the panels (or testers) to receive responses by means of an SD method questionnaire. SampleNo. Date Name (1) Panels: Invoked were general engineers and office workers who 1. Check on the number that you feel. had little preliminary knowledge of odors and were not interested in [odor intensity] [Odor Pleasantness / Unpleasantness] this evaluation. 5 Intense Odor 2 Pleasant 4 Strong Odor 1 Rather Pleasant (2) Samples for evaluation: With an odorless specimen added as a 3 Odor Easily Sensed Odor 0 Neither -1 Rather Unpleasant blank, all the samples were resorted on a random basis irrespective 2 Weak Odor 1 Barely Recognizable Odor -2 Unpleasant of the sampling sequence from the vehicles in such a manner that 0 No Odor -3 Very Unpleasant 2. Fill in the box that you feel. the contents of the samples were unperceivable. Then, they were 3 : Very much so named with alphabetic characters to conduct a blind test. 2 : Considerable 1 : Little so (3) Evaluation environment: A silent chamber facing south without blank : Not at all smoking was selected to conduct a test by means of curtains Acid Sweet Burnt Acrid Fish and meat Festering trash Dusty Tobacco blocking off the direct rays of the sun under a temperature and Exhaust gas Sweat Cosmetics Garbage Fusty Damp mop Dirty sock Fishy humidity condition not making the panels feel uncomfortable. Interior odor Comment ( ) (4) Questionnaire: The terms indicating the types of odors were Thank you previously selected through several prior tests. By making Fig.7 Questionnaire inquiries about (1) Intensity of odor, (2) Degree of comfort / uncomfortableness, and (3) Type of odor in addition to (4) Miscellaneous requesting comments without restriction. Regarding the type of odor, the checkers were requested to respond with "3", "2","1" or "blank" as the degree of consistency with the word representing the odor used for the questionnaire. These results "3", "2" and "1" were then converted into 3 points, 2 points, and 1 point respectively when being totalized. (Fig.7)
In the questionnaire, the intensity of odor and the degree of Table 1. Odor Intensity unpleasantness were adopted as the evaluation items and 5 Intense Odor 4 Strong Odor ranked at six intensity levels and seven degrees 3 Odor Easily Sensed 2 Weak Odor with the Kind of Recognizable Odor respectively (Tables 1 and 2). 1 Barely Recognizable Odor 0 No Odor 2.1.3 Instrumental analysis for multiple regression analysis We have decided to perform analysis by means of the possibly Table 2. Odor Pleasantness / Unpleasantness optimum strategy for each kind of "odorous" components supposed 3 Very Pleasant to exist in the odor for each sort of sources and the actual vehicle. 2 Pleasant 1 Rather Pleasant Under the conditions shown in Appendix A, instrumental 0 Neither Pleasant nor Unpleasant -1 Rather Unpleasant analysis was performed on each sort of components. A blank test -2 Unpleasant -3 Very Unpleasant was definitely conducted before and after sampling a specimen in each test to keep checking the background value when conducting this test. 2.2 Clarifying adsorbed odor mechanisms At the second step, we tried to not only determine the odor-emit ting components through PCA and multiple regression analysis but also clarified how the adsorbed odor arose. 2.2.1 Samples A smoking device was used to introduce and familiarize a cigarette odor along with cigarette smoke to the evaporator placed on the car air conditioner test bench and the mini core bench (After-mentioned. See 2.2.2.). In order to simulate the actual familiarizing conditions, the evaporator temperature was kept cycled between the condensing point and the vaporizing point to apply the odor. 2.2.2 Odor sensory test on Test bench and Mini-core bench We prepared the onboard car air conditioner ‘Test Bench’ (see Fig.8 for further information) traditionally used on an evaluation chamber basis and fabricated a Temperature-controlled Room Conditioned new desktop test bench (hereafter called the "mini Clean Out Air Air Conditioner Sampling Bag Unit core bench" as shown in Fig.9) incorporating a small-size evaporator (hereafter called the "mini Exhaust core") and intended for laboratory evaluation. R134a Canister Internally covered with stainless steel to facilitate cleaning, the onboard car air conditioner Fig.8 Test Bench evaluation bench is capable of controlling the evaluation chamber at a specified temperature and humidity and running the car air conditioner placed in the chamber. The evaluation panels enter this chamber to odor and evaluate the odor in turn. Additionally, to avoid raising the intensity of the odor in the chamber, the system is designed in such a manner that the ambient air is deodorized through an active carbon filter and always introduced at a constant rate. Sampling Bag Mini-Core On the other hand, the mini core (a small size evaporator) IN Conditioned Circulation Systems Clean N2 built in the mini core bench is of a small size and low thermal Hot Cold capacity. Furthermore, the temperature controls are simplified OUT by means of a noncombustible liquid heat film in place of chlorofluorocarbons. The mini core is shielded from the outside with the sampling bag in such a way that the Fig.9 Mini-Core Bench
temperature and humidity of the nitrogen running in the bag can be controlled at discretion. Table 3 lists typical test conditions. By means of these test benches, we performed odoring evaluation and instrumental analysis. The odoring evaluation was completed at a low temperature of Table 3. Test Conditions Assembly Mini-Core 20°C and a relative humidity between 40 % and 60 % from Test Bench Bench the typical conditions as described above. Temperature (degree) 20 ~ 30 20 ~ 25 Humidity (%RH) 40 ~ 60 30 ~ 60 We ranked the intensity of odor and the degree of unpleasantness at six intensity levels and seven degrees (Table 1 and Table 2). In advance, a T&T-Olfactometer was used to select approximately ten evaluation panels that were not handicapped in olfactory capability, followed by training to an odor intensity evaluation error between 0.5 and 1.0 among the individuals. Three or five panels were selected to mark the samples and find the average. 2.2.3 Instrumental analysis on a Test bench and on a Mini-core bench Sampling on test bench, we firstly collected the odor in Tedler-bag and a canister, and then condensed odor samples from them, on Tenax-TA or other devices (DNPH-Silica, Sr(OH)2 glass beads, Chromosorb 101 and others). Sampling on mini-core bench, we could collect the odor to a canister or condensed odor samples directly. Instrumental analysis conditions are the same (see Appendix A). 3. Results and Discussions 3.1 Correlation between instrumental analysis values and the odor sensory evaluation values 3.1.1 PCA result By wrapping up the above-mentioned questionnaires, we Factor Table 4. Test Conditions Eigenvalue Contribution Accumulated performed analysis on the principal components. As a result of the principal component analysis, three 5.309 0.531 Contribution 0.531 1 2 2.549 0.255 0.786 principal components having eigenvalue more than one were 3 1.059 0.106 0.892 4 0.482 0.048 0.940 identified. Additionally, since the degree of contribution was found sufficient over 80 percent and at approximate 90 percent for up to the third chief ingredient, the adsorbed odor evaluation quadrants would be reproducible with the first to third principal components only (Table 4). Next, we started to characterize the principal Table 5. Test Conditions components as the judgment criteria (Table 5). Variate Factor1 Factor2 Factor3 Factor4 The first principal component was named as the Intensity -0.163 0.979 -0.014 -0.076 "Unpleasantness" presenting high factor loadings Unpleasantness 0.831 0.372 0.216 -0.174 Acid -0.803 0.511 -0.170 0.161 with the "Odor Pleasantness / Unpleasantness" and Sweet -0.868 0.450 -0.079 0.062 Burned 0.815 0.448 -0.219 -0.017 the terms presenting unpleasant odors such as Dusty 0.871 0.066 -0.267 0.104 Tobacco 0.721 0.529 -0.242 -0.276 "burning, dusty, smoky, and exhaust gaseous" and Exhaust Gas 0.753 0.274 -0.024 -0.024 "acid, sweet, and cosmetics" (with the Cosmetics -0.827 0.454 -0.222 -0.007 Interior Materials 0.038 0.471 0.866 0.045 uncomfortable quadrants defined to be positive due to the converted parameters). While the terms on the uncomfortable side reading a positive factor load present no problem, the other terms of the comfortable side have the term "acid" typically expressing an unpleasant odor, raising a suspicion. We thereby interviewed the panels to make a survey to find out that the samples marked this time with "acid" were of a "citrus fragrance (deodorant)" odor and with a judgment for a preferable odor in addition to a description of "deodorant" noted in the voluntary response column, presenting no inconsistency with
the results. Likewise the second principal component was named as "intensity" because the "intensity" factor loading was found at a high level. For the three remaining principal components, only "interior odor" presented a high factor loading. The reason why the "interior odor" was identified as a judgment criterion would be that the panels who were closely connected as occupants to vehicles were familiar with such an interior odor like the vehicles and, therefore, the odor is separately perceived and assessed unlike the typical uncomfortable odors such as exhaust emissions. 3.1.2 Factor loading Fig.10 shows the factor loadings for Factor 2 Factor 3 1.0 1.0 each term plotted about the principal Intensity Interior Odor component axis. These plots indicate 0.5 Acid Tobacco Burned 0.5 Cosmetic Interior Unpleasantness that the evaluation quadrants are clarified Sweet Odor Exhaust Gas Intensity Unpleasantness 0 Dusty Factor 0 Factor with the three evaluation axes, indicating 1 Sweet Exhaust Gas Burned 1 Acid Tobacco Cosmetic Dusty how closely the term is related to the -0.5 -0.5 degree of uncomfortableness for the -1.0 -1.0 samples used this time. -1.0 -0.5 0 0.5 1.0 -1.0 -0.5 0 0.5 1.0 Fig.10 Factor Loading 3.1.3 Principal component score The scores of the principal components from the results of "odor" evaluation in the actual vehicle are plotted with ‘• ○’ about the three axes. Furthermore, (1) Smoking vehicles are plotted with ‘•’ and (2) Vehicles using odorants (or aromatics) are plotted with ‘○’ to enclose each segments. In addition, those vehicles with a short actual driving period (i.e., almost new vehicles) and those with comments indicating a plastic and vinylic odor are encompassed (Fig.11). 1st principal component: Smoking vehicles on the uncomfortable (positive) side and deodorant using vehicles on the comfortable (negative) side. Intensity Interior Odor 2nd principal component: Vehicles 2.2 2.2 with a strong smoky odor placed (+) Very Plastic 䊶䊶Vinyl Smoky Almost New 䊶䊶 1.1 1.1 on the intensive (positive) side. Uses (+) Strong Interior Odor Perfumes 䇭 3rd principal component: Vehicles Group (+) Unplea (+) Unplea 0 -santness 0 -santness with a strong interior or plastic Uses Perfumes odor placed on the intensive -1.1 Smoking -1.1 Group Smoking Group Group interior odor (positive) side. -2.2 -2.2 We acquired these results and -2.2 -1.1 0 1.1 2.2 -2.2 -1.1 0 1.1 2.2 : Smoking Car : Aromatic, Cosmetics, Perfumes : Others found out that each principal Fig.11 Principal component score component definitely corresponded to the vehicle and that the odors could unequivocally be segregated by means of these evaluation axes. 3.1.4 Discussion about determining the odor causative substances Having identified the evaluation axis for the adsorbed odors by performing analysis on the principal components through the odoring evaluation, we describe correlations between the results of this odoring evaluation and the findings of the analysis.
Multiple regression analysis was performed with the representative Odor Intensity = k log (Odor Substance Concentration) + a element for each evaluation axis used as the objective parameter and with 5 the component analysis values used as the descriptive parameter. At this Odor Intensity 4 3 time, the component analysis values were converted into logarithmic 2 variables for this analysis because the logarithmic physical values such as 1 0 odor component concentration are widely known to be in proportion as the 0.1 1 10 100 Concentration (ppb) Weber-Fechner’s low (Fig.12). Fig.12 Weber-Fechner’s low The questionnaire item “Odor Pleasantness / Unpleasantness”" was used for the first principal component element “Unpleasantness”, the item “Intensity of odor” was used for the second principal component “Intensity,” and the item “New vehicle odor and interior” was used for the third principal component “Interior odor”. As a result of the multiple regression analysis, we ޓޓޓ ޓޓޓ Unpleasantness = 0.469*log(Substanece-A)+0.449*log( -B)+0.204*log( -C)+ … R:0.987, R**2:0.908 ޓޓ acquired a high-precision regression equation to identify those odor causative ޓޓޓޓޓ Intensity = 0.326*log(Substanece-D)+0.537*log( -E)+0.253*log( -F)+ … R:0.978, R**2:0.910 substances. ޓޓޓޓޓ Interior Odor = 0.301*log(Substanece-G)+0.615*log( -H)+0.362*log( -I)+ … R:0.961, R**2:0.846 Fig.13 Result of the Multiple Regression Analysis Furthermore, we checked for the adsorbed odor from the evaporator by means of those components incorporated in the regression equation and those not incorporated. As a result, the components imported into the regression equation presented a higher odor intensity than that of the other components not imported, backing the results of the analysis. (Fig.13) 3.2 Adsorbed odor mechanisms 3.2.1 Result of the test bench This section describes the findings of the evaluation on the air conditioner test bench. (1) Results of odoring evaluation Fig.14 shows the results of the odoring evaluation. The Odor Intensity Unpleasantness Mode 0 1 2 3 4 5 +1 0 -1 -2 -3 vertical axis of the graph refers to the operation modes of Dry the air conditioner, indicating the changes of Dry (with the ON blower), ON (with the compressor turned on), and OFF ON (continual) (with the compressor turned off). The horizontal axis refers OFF to the intensity of odor and the degree of unpleasantness. OFF (continual) By allowing five evaluators to odor in turn, it is difficult to Fig.14 Result of Odoring evaluation conduct continuous evaluation with a limited number of odoring times and only five times was available for evaluation on a spot basis all over the modes. While the odor varied in a consecutive manner, a long time lag required each time for exchanging the panels resulted in fluctuations. Additionally, in the cigarette odor-familiarizing test conducted this time, a part of the panels complained about uncomfortableness due to a highly intensive odor and about olfactory fatigue as the odor accumulated in the evaluation chamber, indicating an error expansion factor. (2) Results of instrumental analysis Fig.15 shows the results of the instrumental analysis. Likewise the vertical axis of the graph refers to the operation modes and the horizontal axis refers to the concentration (in ppb) of the odorous component.
As an example, the behavior of i-Valeric acid known as an Concentration (ppb) Mode 0 0.2 0.4 0.6 0.8 1.0 unpleasant component is described. In a part, a negative Dry value resulted by subtracting the blank value (as marked with ON ND "ND" on the graph) and, therefore, a significant difference is ON ND (continual) unlikely between the analysis values, indicating difficult OFF analysis even by highly sensitive analyzing strategy. OFF ND (continual) 3.2.2 Mini core bench Fig.15 Result of Instrumental Analysis: i-Valeric Acid Next, the results of the odoring evaluation on the mini core bench are shown along with the findings of the analysis in Fig.16 and Fig.17. (1) Results of odoring sensory evaluation The horizontal axis refers to the elapse time, indicating the changes of Dry (with blower only and the mini core at normal temperature), ON (with the mini core at low temperature and the compressor turned on in reproduction mode), and OFF (with the mini core at normal 4 Dry ON OFF Intensity 3 temperature and the compressor turned off in reproduction 2 NG Intensity mode). The vertical axis refers to the intensity of odor 1 Good 0 Unpleasantness on the upper side and the degree of unpleasantness on the -1 Good Unpleasantness -2 lower side (Fig.16). NG -3 -5 0 5 10 15 20 25 30 35 Unlike the results with the onboard car air conditioner Time (min) Fig.16 Result of Odoring evaluation evaluation bench described above, it was possible to evaluate the samples at short time intervals without causing olfactory fatigue by fitting the nose with the silicon tube connected with the outlet only when the odor is smelt. While omitted in the figure, the fluctuations among the panels were limited below 0.5 because of no olfactory fatigue. (2) Results of instrumental analysis 0.6 Dry ON OFF This section describes the results of the instrumental Concentration (ppb) analysis. In the same manner, the horizontal axis refers to 0.4 i-Valeric Acid Toluene * 1/10 the elapse time and indicates the changes of the Dry, ON, 0.2 and OFF modes and the bar graphs along the vertical axis 0.0 refer to the concentration of the component (Fig.17). -5 10 0 15 20 5 25 30 Time (min) On the mini core bench, unlike the results with the Fig.17 Result of Instrumental Analysis onboard car air conditioner evaluation bench, the concentration of the odorous component in each mode presented a significant difference from the blank and the concentration of the component also presented a significant difference between the modes. For example, variations in i-Valeric acid and toluene are shown as functions of time. Judging from the results of odoring evaluation (Fig.16) and the instrumental analysis (Fig.17), the remarkable point is that the behavior of toluene and i-Valeric acid varies depending whether the unit is turned on or off. With the unit turned on, the concentration of water-repellent toluene was at a high level when condensed water was present. With the unit turned off, on the other hand, the concentration of the water-soluble i-Valeric acid component was at a high level with the odor intensity also at a high level when the condensed water was vaporized. In other words, these results imply all over again that the collection odor would be caused by and closely related with condensed water.
In addition, these findings indicate that the degree of unpleasantness is highly related to the amount of i-Valeric acid and these odorous components accelerate the degree of unpleasantness. 3.2.3 Discussions about odor mechanism The reason why it was difficult to perform instrumental analysis on the onboard car air conditioner evaluation bench was as follows: 1.Adversely affected by the ambient air to result in an unstable blank. 2.High wind velocity reduced the odor generation period of time and allowed differences between the bag sampling individuals and adsorption to the bag. These factors seem to have degraded quantitativeness. In contrast, on the mini core bench, the blank was kept at a low level by using the mini core in a clean environment and it was possible to reproduce the behavior of condensed water on the surface of the evaporator at a low air flow rate to enable the testers to evaluate the odorous components on a stable basis. As described above, we have succeeded in identifying how an odor is familiarized with the car air conditioner by relating the generation or evaporation of condensed water due to evaporator temperature rising and lowering and the emission of the odorous components of the collection odor through the odoring evaluation and the instrumental analysis (Fig.18). As shown in the figures, the 1. Dry 2. ON : Dry to Wet water-repellent components represented Hydrophobic Substance Hydrophilic Substance Hydrophobic Substance Released by toluene from among the odorous Ex. Toluene H2O Odor Substances Flocculated Water components collecting on the surface of the evaporator are emitted in the form of displacement with moisture in response to 䇭 Evaporator’s Surface Odor Intensity: Strong the start of water condensation with the 3. ON Continual : Wet enough 4. OFF : Wet to Dry compressor turned on and this is felt as the Hydrophilic Substance’s Elution Hydrophilic Substance’s Vaporization collection odor when the unit is turned on. Ex. i-Valeric acid Flocculated Water Next, as additional moisture is condensed, the evaporator surface Odor Intensity: Weak Odor Intensity: Very Strong temperature is lowered in the continuous Fig.18 Adsorbed Odor Mechanism turn-on mode with the evaporator covered with water on the surface, the emission of the odorous components is reduced, and the intensity of the odor transfers at a low level. During this, the water-soluble components such as less-carbon fatty acids represented by i-Valeric acid increasingly dissolve from the surface of the evaporator into the condensed water. Finally, with the compressor turned off, the moisture evaporates and the water-soluble components dissolved in the condensed water vaporize with the moisture and felt as an odor when the unit is turned off (at the lower right corner of Fig.18). 4. Conclusions To determine the odor cause, we performed instrumental analysis and odor sensory evaluation. We found out for the first time that the instrumental analysis values of the adsorbed odor were highly correlated to the odor sensory evaluation values and identified the odor causative components.
These causative substances adsorbed on the evaporator surface tend to become noticeable while the air conditioner is operated with the compressor turned on and off for energy saving purpose. With the evaporator ‘Mini-core bench’, we simulated adsorbed odor and found that • Hydrophobic odor substances (ex. Toluene) are released while evaporator’s surface is changing from ‘Dry’ to ‘Wet’ (temperature falls down and flocculated water breaks out on the surface). • While changing from ‘Wet’ to ‘Dry’, the flocculated water vaporizes and hydrophilic odor substances (ex. i-Valeric acid) come up together. • We clarify the odor generation mechanism from an evaporator surface. To improve comfortableness in the occupant compartment, these odors possibly emitted from the air conditioner must be minimized in the future by, for example: • Determining the sources of the odor-emitting components in question to minimize the rate of the odorous components flowing into the air conditioner by eliminating the causative factors and; • Installing a deodorization filter allowing only a limited part of the odorous components to flow into the upstream of the evaporator to prevent the odorous components from adhering. These measures are noticeable. References 1. Special Pollution Section, Atmospheric Integrity Bureau, Environment Agent; Technical guidelines for the three-point comparison type odor bag strategy, - from a odoring test procedure study report by the Environment Agent -, Environment and measurement technology, vol.9, No.9, (1982). 2. Special Pollution Section, Atmospheric Integrity Bureau, Environment Agent; Fundamental data for teaching and developing the bad-odor olfactory test procedure, Environment and measurement technology, vol.9, No.10, (1982). 3. Toshiyuki Tanaka; Sampling organic chemical compounds gases in the air by the adsorption and capture strategy at normal temperature Part 1, Basic principles, Environment and measurement technology, vol.16, No.1, (1989). 4. Toshiyuki Tanaka; Sampling organic chemical compounds gases in the air by the adsorption and capture strategy at normal temperature Part 2, Actual atmospheric measurement and sample measurements, Environment and measurement technology, vol.16, No.2, (1989). 5. Toshiyuki Tanaka; Performance of the Tenax-GC sampling tube for analysis on volatile organic chemical compounds at ppb level in the air, Air pollution society paper, Volume No.19, Number 6, (1984). 6. Nobuyuki Kashihira; Effect of sample injection through gas chromatography - Measuring a sulfide by means of GC-FPD -, Environment and measurement technology, vol.16, No.2, (1989). 7. Emiko Sudo; Measuring methods in environmental analysis, Environment and measurement technology, vol.12, No.9, (1985). Tomohiko Ishiguro; Details of how to measure the public specified bad-odor substances along with instructions, Environment and measurement technology, vol.14, No.1, (1987). 8. Kazuhisa Uchiyama, et al.; Analysis on odors adsorbed by the car air conditioner - Analyzing sensory odor evaluation and instrumental analysis data by means of multivariate analysis -, Compilation before Academy Lecture Meeting by Society of Automotive Engineers of Japan, Inc. Nos.981, 293, (1998), and 9831919. 9. Shigeyuki Sato; Quality of air in the passenger compartment, Toyota Central Laboratory Research and
Development review, Vol.33, No.4, (1998). 10. Shigeyuki Sato et al.; Study in relation to odors of automobiles, Compilation before Academy Lecture Meeting by Society of Automotive Engineers of Japan, Inc. Nos.981, (1998), and 9831892. Appendix A Table 6. Aldehyde Analysis Conditions Trapping: DNPH Silica Cartridge (Waters SepPak) Instrument (HPLC): Shimazu LV-10VP, Detector: UV (350nm) Column: Inertsil ODS-80A (GL Science) Mobile Phase: CH3CN/H2O = 55/45, 1.5mL/min Column compartment: 40 degree Injection Volume: 25µL Table 7. Ammonia Analysis Conditions Trapping: Impinger 10ml H2O Instrument (IC): DIONEX DX-120, Conductivity Detector Column: IonPacCS12A, Guard Column: IonPacCG12A Eluent: 20mM CH3SO3H, Flow Rate: 1.0mL/min Suppresser: CSRS-1 (Recycle Mode), Column Temp.: 40 degree Table 8. Nitrogen Compound Analysis Conditions Trapping: 6L Canister → Tenax-TA (at -78 degree) Instrument (GC): Shimazu GC-14B Column: UnicarbonB-2000, Carrier Gas: He 50ml/min, Oven Temp.: 70 degree for 5min, 70-120 degree at 8 degree/min Inj Temp.: 200 degree, Detector: FTD Table 9. Sulfur Compound Analysis Conditions Trapping: 6L Canister → Chromosorb 101 (at –78 degree) Instrument (GC): Shimazu GC-9A Column: β, β’-ODPN 4m Carrier Gas: N2 70ml/min, Oven Temp.: 70 degree Isothermal Inj Temp.: 120 degree, Detector: FPD Table 10. Low Boiling HC Analysis Conditions Trapping: 6L Canister Instrument: Entech 7000 + GC/MS: HP 6890 + 5972A Column: HP-1, Length: 60m, Film: 1µm, ID: 0.32mm Carrier He: 1.0ml/min, Oven Temp.: 35 degree for 5min, 35-80 degree at 4 degree/min, 80-240 degree at 10 degree/min, 240 degree for 20min Detector: MSD, Interface Temp.: 280 degree Table 11. High Boiling HC Analysis Conditions Trapping: Tenax-TA (at RT) Thermal Desorption: 280 degree Instrument (GC/MS): Gerstel TDS + Agilent 6890+Agilent 5973N Column: HP-1, Length: 60m, Film: 1µm, ID: 0.32mm Carrier He: 1.0ml/min, Oven Temp.: 35 degree for 5min, 35-80 degree at 4 degree/min 80-240 degree at 10 degree/min, 240 degree for 20min Detector: MSD, Interface Temp.: 280 degree Table 12. Lower Fatty Acid Analysis Conditions Trapping: Sr(OH)2 Coated Glass Beads Instrument (GC): Shimazu GC-14B Column DB-Wax, Length: 60m, Film: 0.25µm, ID: 0.32mm Carrier He: 1.0ml/min, Oven: 120-240 degree at 8 degree/min Inj Temp.: 250 degree, Detector: FID
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