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How Users Perceive tHe climate comfort of veHicle seats Using a portable, thermo-hygrographic measuring system which can record microclimatic conditions over certain areas, Munich University of Applied Sciences intends to simplify the development of vehicle seats. The system allows two and three-dimensional temperature and humidity distributions to be measured over time.
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AUThorS
Dipl.-Wirtsch.-ing. maria rosaria morena is a project engineer at Faculty 09 of the Munich University of Applied Sciences (Germany).
robert Krah is General Manager of Krah & Grote Messtechnik in otterfing (Germany).
prof. Dr.-ing. bernharD Kurz is a lecturer and laboratory manager at Faculty 09 of the Munich University of Applied Sciences (Germany).
motivation
A study conducted by the German Federal Statistical Office shows that 67 % of all occupational commuters cannot do without their passenger cars [1]. Also, the Federal Republic of Germany is one of the leading countries in the export business. This causes lively transport traffic which will go on increasing in the future, too. Thus, in particular commuters and occupational motorists will be spending more and more time in their vehicles. In view of the considerable increase in the demands made on drivers with regard to the safe driving of their vehicles, the best possible working conditions must be available to them. Besides vehicle steering providing good assistance and the optimisation of interactive ergonomics, seat comfort in the form of individual setting possibilities as well as climate management are of particular importance. Though the latest technologies are available for achieving a high degree of climate comfort in the vehicle interior, the feeling of well-being in the car can be impaired in spite of the presence of an air-conditioning system. Over longer distances, the heat as well and the humidity produced by the driver accumulate in the seat and lead to negative sensations, impairment of concentra-
tion, tiredness and reduced performance. Consequently, the vehicle seat itself is challenging enough for the automobile industry in terms of ergonomics and safety, but when hygro-thermal functions are taken into account too it is probably one of the most complicated tasks arising in car development. methoDs
Against the background of long years of experience collected via studies on the climatic wearing comfort of clothing and as a result of numerous cooperation projects with well-known seat manufacturers, the laboratory for applied ergonomics of Munich University of Applied Sciences has developed a measuring technique with which microclimatic conditions can be captured over a wide area and turned it into an industrial product. The portable, thermo-hygrographic measuring system THG-SeatView allows two and threedimensional temperature and humidity distributions to be measured over time in optically invisible layers such as in the contact area of human and seat and/or backrest in particular. The results are not adversely affected by the measuring technique and are displayed graphically in compressed form, 1.
1 Test seat with THG SeatView 0 6 i 2 012
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With the goal of specifying the climatic comfort of vehicle seats by measuring the contact climate and by asking the user to express his perceptions, the first step was to develop suitable test setup under standardised conditions, that means in a climate chamber. In particular a data processing method (clustering) has been established which was then applied under real-life conditions, that means in vehicles on differing seats. The climate chamber tests were carried out under specified climatic conditions (28 °C and 60 % relative humidity) with a selected series-produced seat of the BMW 3-Series. A driving simulator ensured the reproduction of the movements and stress situations occurring in a real driving situation. The previously selected and instructed test persons (n=15) wore underwear as well as cotton trousers, cotton shirts and sports shoes. After a short preconditioning period, the test person sat down on the equipped seat with the THG SeatView measuring mats and the three-hour driving and measuring program was initiated. Every 30 min, the person had to express their subjective perceptions. Five-step scales were used for humidity (1: pleasant to 5: humid), comfort (1: comfortable to 5: uncomfortable) and for the perceived temperature (1: pleasant to 5: warm). As a result of the experimental climate selected, a cold sensation did not occur. In the real-life tests (n=5), the drivers were instructed to wear the same specified test clothes, to adjust the vehicle climate control to 26 – 28 °C, not to use a seat/armrest climate control until after 2 h and to as far as possible achieve an interrupted test period of 3 h without drinking. The special test conditions were included in an extended questionnaire including information on type of car and seat, basic conditions on the day of the test, settings relevant for the climate as well as the additional specification of body regions showing aboveaverage perspiration.
2 Measurement patterns with clustering
results
In addition to the large data quantities produced by the THG SeatView system, individual factors such as body height and contact area as well as sitting position and posture complicate the automated extraction of valid indicators reflecting the climate and its perception.
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3 Climate (red: seat, blue: backrest) and perception (black)
The analysis of the climate chamber measurements first required the test subjects to be classified as small and tall persons, strong and weak perspirers and men and women. The temperature and humidity distributions of these test subjects were then evaluated statistically in order to specify the sensors or sensor areas which reproduce, in a representative way, the microclimate with the maximum values occurring while using averages to minimise the impact of non-marked climatic conditions. The result was a cluster technique for the measuring sensors which allowed the definition of areas on the seat and the backrest area in which the climatic interactions can be reproduced adequately for all test subjects and all test conditions. By way of an example, ❷ shows humidity distributions on the seat and the backrest area as well as the sensor clustering developed including
the clusters S2 and L2 on which the evaluation of the climatic interactions is based. Only the test results occurring at the end of a 30-min interval in each case were used for assessing the climatic perception and its effects on the feeling of comfort experienced by the test subjects. This allows a considerable reduction in the data volume while still reproducing the test dynamics adequately. By way of an example, 3 shows, for one test group, the averaged climate values temperature as well as relative and absolute humidity with the corresponding perception values. The dependencies between subjective and objective indicators are clearly recognisable and are statistically significant, but they appear on different levels for the other test groups, for example strong/weak perspirers or men/women. In the real-life tests, test subjects were permitted to activate any seat or backrest
4 Climate (red: seat, blue: backrest) and perception (black) with ventilation of the seat after the 120th minute of the test (4th point in time) 0 6 i 2 012
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ventilation systems after a test period of 2 h. 4 shows selected results. Use and effects of the ventilation as well as their positive effects on subjective perception are clearly visible. With respect to the central issue “comfortable or uncomfortable”, most of the test subjects specified the medium perception value, that means grade 3 for humidity, temperature and comfort. These perception limits now also allow conclusions to be drawn as to relevant temperature limits and relative and/or absolute humidity limits. However, what would be desirable is a specification, regardless of individual perceptual variance, of climatic limits and their bandwidths which lead to a reproducible change in perception. perceptual sensitivit y
In spite of individual differences in thermal regulation and climatic perception, the evaluations of all the test results show a consistent dependence between measured values and perceptual values. This opens up the possibility of a global correlation with the option of determining perceptual sensitivities for temperature and humidity and/or comfort and to derive relevant limits from the correlation, at least for the test conditions described. 5 presents the correlations involved. When the perceptual limits (grade 3) above which discomfort is felt are taken as a basis, the resulting climatic limits are as follows: : temperature: 35.5°C : relative humidity: 60% rh : absolute humidity: 23 g/kg. These limit values prove to be in good correspondence with the comfort limits revealed by various scientific investigations of other body regions or clothing components [2, 3]. Finally, one question of special interest is that as to ”which change of measured climatic values leads to a valid change in perception,” that means the question as to the perceptual sensitivity. Preliminary studies preceding the one described provided the result that the individual differentiation of perceptions correlates well with a change of 0.5 steps. This in turn allows the following resolution ranges to be determined from the correlations: : discernable temperature change in the range 30 to 35°C: 0.4 to 0.5°C : discernable change of the relative humidity: 5% rh
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vant subjective perception of comfort. However, these still remain to be verified for other climatic areas and/or seat designs. This study provides an evaluation and assessment automatism which also allows comparable correlation results from various analyses while complying with less standards and is thus suitable for building up a continually extendable comfort database. references [1] Statistisches Bundesamt: Pressemitteilung no. 138 from 22 March 2005 [2] Kuklane, K.; holmer, i.; Anttonen, h.; Burke, r.; Doughty, P.; Endrusick, T.; et al.: interlaboratory Tests on Thermal Foot Models. in: Tochihara, Y.; ohnaka, T.: Environmental Ergonomics. The Ergonomics of human Comfort, health and Performance in the Thermal Environment. Elsevier, pp. 449 – 457, 2005 [3] Zimmermann, C.; Uedelhoven, W.; Kurz, B.; Grellmann, S.; rottenfusser, M.; langenmeir, S.: Correlation Between Different Thermophysiological Simulation Methods and the Self Perceived Wearing Comfort of Military Footwear. Presented at 14 th international Conference of Environmental Ergonomics (iCEE), nafplia, Greece, 10 – 15 July 2011
5 Correlations between measured valued and perceptual values
: discernable change of the absolute humidity: 2 to 3 g/kg. The developer thus has climatic limits at his disposal which determine the transition to discomfort in the case of normal perspiration behaviour under the test conditions described. summary
With the goal of specifying limit ranges or transitional ranges for good climatic comfort on vehicle seats, climate measurement values were correlated with subjective perceptual statements with regard to warmth, humidity and comfort in selected test series. To compress the extensive measuring data, a suitable evaluation procedure in the form of clus-
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tering was developed, so that further evaluations only include sectorial indicators but no longer individual measured values or global averages. The results demonstrate a good intraindividual correlation between measured values and perception values, in particular with regard to temperature and heat perception and/or absolute humidity and the perception of comfort. In addition, the relevant analysis of the whole group even allows comfort limits to be established, at least for the test conditions on which the tests are based. Finally, it was possible to develop evaluation standards for climatic comfort on vehicle seats with the help of the objective measured data on the transmission of heat and humidity by the test subject and the rele-
