Effects of heated seats in vehicles on thermal comfort during the initial warm-up period

Eight subjects participated in a subjective experiment of eight conditions to investigate the effects of heated seats in vehicles on skin temperature, thermal sensation and thermal comfort during the initial warm-up period. The experimental conditions were designed as a combination of air temperature in the test room (5, 10, 15, or 20 °C) and heated seat (on/off). The heated seat was effective for improving thermal comfort during the initial warm-up period when air temperature was lower than 15 °C. Use of heated seats prevented decreases in or increased toe skin temperature. Heated seats also increased foot thermal sensation at 15 and 20 °C. Optimal thermal sensation in contact with the seat was higher when air temperature was lower. Optimal skin temperature in contact with the seat back was higher than that with the seat cushion. Moreover, these optimal skin temperatures were higher when air temperature was lower.     

Evaluation of an intelligent seat system

This study was conducted to evaluate the effect of an intelligent seat system, a microprocessor-based interactive seat that automatically adjusts itself to fit a seated individual by making pressure-sensitive adjustments on its own. First, a standard American automobile seat ('baseline' seat) was assessed for comfort. Subjective ratings of comfort, pressure distribution and seated anthropometric measurements were recorded for 20 test subjects. These measurements were recorded while the subjects maintained a simulated driving position in a seat buck. The comfort scale was based on a rating of 1 to 10, with 1 corresponding to 'very poor' and 10 corresponding to 'very good.' Based on a nonlinear, multiple regression model that had been previously developed, the comfort rating of the seat was predicted based on the subjective ratings and the recorded values of 450 pressure measurements from 20 subjects. The predicted comfort value was 7.46 for the baseline seat. Following the baseline assessment, the intelligent seat system was installed into the standard American automobile seat. The objective and subjective assessments were then repeated for 17 subjects and the new predicted comfort rating was 8.06. A t-test performed on the subjective and objective measures indicated that this was a significant improvement in seat comfort. Overall, subjects felt the self-adjusting seat was more customized and more comfortable, providing a better fit.     

An ergonomics investigation into human thermal comfort using an automobile seat heated with encapsulated carbonized fabric (ECF).

This report presents the results of an ergonomics investigation into human thermal comfort using an automobile seat heated with an encapsulated carbonized fabric (ECF). Subjective and objective thermal comfort data were recorded while participants sat for 90 min in a heated and a non-heated automobile seat in an environmental chamber. Eight male participants each completed eight experimental sessions in a balanced order repeated measures experimental design. The conditions in the chamber were representative of a range of cool vehicle thermal environments (5, 10, 15 and 20 degrees C; in the 20 degrees C trial participants sat beside a 5 degrees C 'cold wall'). Participants in the heated seat condition used the heating controller with separate temperature control over the back of the seat (squab) and bottom of the seat (cushion) in an effort to maintain their thermal comfort while wearing the provided clothing, which had an estimated insulation value of 0.9 Clo. The trials showed that participants' overall sensations remained higher than 'slightly cool' in the heated seat at all temperatures. Participants' overall discomfort remained lower (i.e. more comfortable) than 'slightly uncomfortable' at temperatures ranging down to nearly 5 degrees C in the heated seat. Hand and foot comfort, sensation and temperature were similar in both seats. Asymmetric torso and thigh skin temperatures were higher in the heated seat although no significant discomfort was found in the front and back of the torso and thigh in either seat. Participants reported no significant difference in alertness between the control and heated seat.     

Study of human–seat interface pressure distribution under vertical vibration

The influence of whole-body vertical vibration on the dynamic human–seat interface pressure is investigated using a flexible grid of pressure sensors. The ischium pressure and the overall pressure distribution at the human–seat interface are evaluated as functions of the magnitude and frequency of vibration excitation, and seated posture and height. The dynamic pressure at the seat surface is measured under sinusoidal vertical vibration of different magnitudes in the 1–10 Hz frequency range. Two methods based on ischium pressure and ischium force are proposed to study the influence of seat height, posture and characteristics of vibration. The results of the study reveal that the amplitude of dynamic pressure component increases with an increase in the excitation amplitude in almost entire frequency range considered in this study. The dynamic components of both the ischium pressure and the ischium force reveal peaks in the 4 to 5 Hz frequency band, the range of primary resonant frequency of the seated human body in the vertical mode. The mean values of the dynamic ischium pressure and the ischium force remain constant, irrespective of the excitation frequency and amplitude. The magnitudes of mean pressure and force at the human–seat interface, however, are dependent upon the seat height and the subject's posture. The inter-subject variability of the static ischium pressure and effective contact area are presented as functions of the subject weight and subject weight-to-height ratio. It was found that heavy subjects tend to induce low ischium pressure as a result of increased effective contact area.

Relevance to industry

Pressure distribution at the human–seat interface has been found to be an important factor affecting the seating comfort and work efficiency of various workers. The study of human–seat interface pressure distribution under vibration is specifically critical to the comfort, work efficiency and health of vehicle drivers, who are regularly exposed to vibration. The results reported in this paper will be useful to study dynamic response of the interface pressure and design vehicle seats.     

An evaluation of comfort of a bus seat

The aim of this research was to evaluate the comfort of a passenger seat for a new type of bus. A fuzzy set model of a multistage comfort scale (MCS) was adopted for the assessment of comfort, together with the techniques of human back shape and EMG measurements as well as posture analysis. The subjects were 30 university students. It is concluded that MCS is a rapid but comprehensive evaluation method for single chair evaluation. The overall rating of MCS is 0.532, which is acceptable under the conditions of the prototype evaluation. The seat profile fits better with the back curve of subjects who had higher comfort rating in the way that the upper profile of the seat coincides with the human back curve and the lower part of the profile intersects the human back curve in the lumbar region; here the human back curves were measured in the slumped sitting posture. There was a significant difference in the EMGs of back muscles between the two sitting postures (sitting upright and the slumped sitting posture) at all the seat heights.     

The influence of heated or cooled seats on the acceptable ambient temperature range

In 11 climate chamber experiments at air temperatures ranging from 15 to 45°C, a total of 24 subjects, dressed in appropriate clothing for entering a vehicle at these temperatures, were each exposed to four different seat temperatures, ranging from cool to warm. In one simulated summer series, subjects were preconditioned to be too hot, while in other series they were preconditioned to be thermally neutral. They reported their thermal sensations, overall thermal acceptability and comfort on visual analogue scales at regular intervals. Instantaneous heat flow to the seat was measured continuously. At each ambient room temperature, the percentage dissatisfied was found to be a second-order polynomial function of local heat flow. Zero heat flow was preferred at an air temperature of 22°C and the heat flow that minimized the percentage dissatisfied was found to be a single linear function of air temperature in all conditions. The analysis indicates that providing optimal seat temperature would extend the conventional 80% acceptable range of air temperature for drivers and passengers in vehicle cabins by 9.3°C downwards and by 6.4°C upwards.     

Age-related difference in perceptual responses and interface pressure requirements for driver seat design

Due to typical physiological changes with age, older individuals are likely to have different perceptual responses to and different needs for driver–seat interface design. To assess this, a study was conducted in which a total of 22 younger and older participants completed six short-term driving sessions. Three subjective ratings (comfort, discomfort and overall) were obtained, along with 36 driver–seat interface pressure measures, and were used to assess differences and similarities between the two age groups. For both age groups, localised comfort ratings were more effective at distinguishing between driver seats and workspaces. Older individuals appeared to be less sensitive to discomfort than younger individuals. Across age groups, two distinct processes were used in determining whole-body comfort and discomfort perceptions based on localised comfort/discomfort perceptions. Whole-body discomfort levels were largely affected by lower back discomfort in the younger group versus upper back discomfort in the older group. Four specific pressure measures at several body regions differed between the age groups, suggesting distinct contract pressure requirements and loading patterns among these groups.     

An on-the-road experiment into the thermal comfort of car seats

This paper presents an evaluation of thermal comfort in an extended road trial study. Automobile seats play an important role in improving the thermal comfort. In the assessment of thermal comfort in autos, in general subjective and objective measurements are used. Testing on the road is very difficult but real traffic conditions affect the comfort level directly, as well as the driver's experience to real conditions. Thus, for such cases real traffic situations should not be neglected in the evaluation of comfort. The aim of this study was to carry out, on an extended road trial study, an evaluation of thermal comfort using human subjects. In the experiments used, the 100% polyester seat cover had three different cover materials, which were velvet, jacquard and micro fiber. All experiments were carried out on a sunny day with ten participants over 1h. They were carried out at air temperatures of 25 degrees C in a Fiat Marea 2004, which had an automatic climate function. Skin temperature at eight points and skin wettedness at two points on the human body were measured during the trials. Participants were required to complete a questionnaire of 15 questions, every 5 min. It can be concluded that there was negligible difference in participants' reported thermal sensation between the three seats. According to objective measurement results, all seat cover materials have the same degree of thermal comfort. On the road the participants feel warmer around their waist than any other area of the body. It was suggested that the effects of real traffic conditions must be accounted for in comfort predictions.     

Vibration and comfort HI. Translational vibration of the feet and back

The effects on discomfort of the frequency and direction of the translational vibration of a footrest and flat firm backrest have been studied in two experiments. At frequencies in the range 2.5-63 Hz, the first experiment determined the levels of fore-and-aft, lateral and vertical vibration of the feet of seated subjects which caused them discomfort equivalent to that from 0.8 m/s² r.m.s. 10 Hz vertical vibration of a firm flat seat. The levels of fore-and-aft, lateral and vertical vibration at the back of a seat which were equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined in the second experiment. The vibration of the feet or back occurred without simultaneous vibration at the seat.

Individual and group equivalent comfort contours are presented. It is concluded that the data provide a useful initial indication of the relative contribution of foot and back vibration to discomfort. Equivalent comfort contours for foot vibration were similar for all three directions of vibration. The contours for vibration of the back show a high sensitivity to fore-and-aft vibration. The results obtained from two additional studies show that vibration from a backrest and other variations in seating conditions can influence subject comfort.     

Thermal comfort of aeroplane seats: influence of different seat materials and the use of laboratory test methods

This study determined the influence of different cover and cushion materials on the thermal comfort of aeroplane seats. Different materials as well as ready made seats were investigated by the physiological laboratory test methods Skin Model and seat comfort tester. Additionally, seat trials with human test subjects were performed in a climatic chamber. Results show that a fabric cover produces a considerably higher sweat transport than leather. A three-dimensional knitted spacer fabric turns out to be the better cushion alternative in comparison to a moulded foam pad. Results from the physiological laboratory test methods nicely correspond to the seat trials with human test subjects.     

Comparisons of apparent mass responses of human subjects seated on rigid and elastic seats under vertical vibration

The apparent mass (AM) responses of human body seated on elastic seat, without and with a vertical back support, are measured using a seat pressure sensing mat under three levels of vertical vibration (0.25, 0.50 and 0.75 m/s² rms acceleration) in 0.50–20 Hz frequency range. The responses were also measured with a rigid seat using the pressure mat and a force plate in order to examine the validity of the pressure mat. The pressure mat resulted in considerably lower AM magnitudes compared to the force plate. A correction function was proposed and applied, which resulted in comparable AM from both measurement systems for the rigid seat. The correction function was subsequently applied to derive AM of subjects seated on elastic seat. The responses revealed lower peak magnitude and corresponding frequency compared to those measured with rigid seat, irrespective of back support and excitation considered.     

Driver sitting comfort and discomfort (part II): Relationships with and prediction from interface pressure

Pressure at the driver–seat interface has been used as an objective method to assess seat design, yet existing evidence regarding its efficacy is mixed. The current study examined associations between three subjective ratings (overall, comfort, and discomfort) and 36 measures describing driver–seat interface pressure, and identified pressure level, contact area, and ratio (local to global) variables that could be effectively used to improve subjective responses. Each of 27 participants was involved in six separate driving sessions which included combinations of two seats (from vehicles ranked high and low on overall comfort), two vehicle classes (sedan and SUV), and two driving venues (lab-based and field). Several pressure variables were identified as more effective for assessing sitting comfort and discomfort across a range of individual statures. Based on the results, specific approaches are recommended to improve the sitting experience: (1) lower pressure ratios at the buttocks and higher pressure ratios at the upper and lower back; and (2) balanced pressure between the bilateral buttocks, and between the lower and upper body. Finally, separate analyses supported that human–seat interface pressure was more strongly related with overall and comfort ratings than with discomfort ratings.

Relevance to industry

Several interface pressure variables were identified that showed associations with subjective responses during sitting. Use of these measures is suggested to improve the quality of car seats.     

Benchmarking thermoception in virtual environments to physical environments for understanding human-building interactions

Thermal comfort influences occupant satisfaction, well-being and productivity in built environments. Several decisions during the design stage (e.g., heating, ventilation, air conditioning design, color and placement of furniture, etc.) impact the building occupants’ thermoception (i.e., the sense by which animals perceive the temperature of the environment and their body). However, understanding the influence of design decisions on occupant behavior is not always feasible due to the resources needed for creating physical testbeds and the need for controlling several contributing factors to comfort and satisfaction. Virtual environments (environments created with virtual reality technology) are novel venues for studying human behavior. However, in order to use virtual environments in the thermoception domain, validation of these environments as adequate representations of physical environments (built environments) is imperative. As the first step towards this goal, we benchmarked virtual environments to physical environments under different thermal stimuli (i.e., hot and cold indoor air temperature). We identified perceived thermal comfort and satisfaction, perceived indoor air temperature, number and type of interactions as markers for the thermoceptive comparison of virtual and physical offices. We conducted an experiment with 56 participants and pursued a systematic statistical analysis. The results show that virtual environments are adequate representations of physical environments in the thermoception domain, especially for subjective perceived thermal comfort and satisfaction assessment. We also found that the type of first adaptive interactions could be used as the markers of thermoception in virtual environments.     

Effects of heated seat and foot heater on thermal comfort and heater energy consumption in vehicle

Subjective experiments involving 12 different conditions were conducted to investigate the effects of heated seats and foot heaters in vehicles on thermal sensation and thermal comfort. The experimental conditions involved various combinations of the operative temperature in the test room (10 or 20°C), a heated seat (on/off) and a foot heater (room operative temperature +10 or +20°C). The heated seat and foot heater improved the occupant's thermal sensation and comfort in cool environments. The room operative temperature at which the occupants felt a ‘neutral’ overall thermal sensation was decreased by about 3°C by using the heated seat or foot heater and by about 6°C when both devices were used. Moreover, the effects of these devices on vehicle heater energy consumption were investigated using simulations. As a result, it was revealed that heated seats and foot heaters can reduce the total heater energy consumption of vehicles.

Statement of Relevance: Subjective experiments were conducted to investigate the effects of heated seats and foot heaters in vehicles on thermal comfort. The heated seat and foot heater improved the occupant's thermal sensation and comfort in cool environments. These devices can reduce the total heater energy consumption in vehicles.     

The effect of an adjustable sitting angle on the perceived discomfort from the back and neck-shoulder regions in building crane operators

In a previous working environment study of building crane operators, it has been found that approximately 70% experienced discomfort from the locomotor system. Comments by the interviewed crane operators indicated that it is, among other things, the forward flexed sitting position during lifts close to the crane that causes discomfort. This investigation sought to apply knowledge from the forestry industry concerning the beneficial effects of improved operator's seats to the work situation of crane operators.

On a construction site with three cranes, an operator's seat with adjustable sitting angle was installed in one of the cranes. Estimation of perceived strain-discomfort in the lumbar region of the back as well as in the neck-shoulder region was assessed according to Borg's scale. Data were collected from the crane operators seated in their ordinary operator's seat, seated in the test seat, and seated in another crane with an ordinary type of seat. The results showed that in 1/3 rd of all lifts, the crane operator was sitting bent-forward with little opportunity for relief via a backrest or armrests. The highest estimated discomfort values in the study were also obtained in an ordinary operator's seat on days with a high proportion of lifts close to the crane. When working in the test seat, none of the subjects gave an estimate higher than 0·5 (discomfort equivalent to very, very weak). An adjustable operator's seat could be a good alternative to a fixed seat, and more tests would be desirable.     

Technical note: spine loading in automotive seating

For car manufacturers, seat comfort is becoming more important in distinguishing themselves from their competitors. Therefore, many studies on participative seat comfort are carried out. In this paper, an objective assessment approach is reported which evaluates the concept of "optimal load distribution", based on the identification of a close relationship between the pressure on the seat and the discomfort felt by the person sitting. An in vivo measurement of the pressure in the spinal disc, which is an indicator of the load in the spine, was performed. For this research, a pressure sensor was implanted with a canula in the middle of the disc intervertebralis of a participant. The local pressure on the disc was established for the participant in an automobile seat set in various seat positions. The results indicate that in the seat position with the pressure distribution corresponding to the most comfortable posture the pressure in the intervertebral disc is lowest. The pressure in this position is 0.5 bar, while in the upright seated position the pressure is 1.6 bar.     

Effects of differences in office chair controls, seat and backrest angle design in relation to tasks

In this study the influence of chair characteristics on comfort, discomfort, adjustment time and seat interface pressure is investigated during VDU and non-VDU tasks: The two investigated office chairs, both designed according to European and Dutch standards are different regarding: 1) seat cushioning and shape, 2) backrest angle and 3) controls. Thirty subjects in total, both male and female, participated in two experiments: twenty in the first and ten in the second.Significant differences are found for ease of adjustment and adjustment time of controls, independent of the tasks. Related to tasks, a significant difference was found for the backrest range of motion. For non-VDU tasks a larger range of backrest motion was preferred by 70% of the subjects. The chair design differences were most clear for comfort and adjustment time of controls, followed by comfort of backrest angle. No differences are found between seat pan comfort and discomfort, first impressions and peak interface pressure.     

Environmental and human factors influencing thermal comfort of office occupants in hot—humid and hot—arid climates

The effects of environmental and individual factors on thermal sensation in air-conditioned office environments were analysed for two large, fully compatible thermal comfort field studies in contrasting Australian climates. In the hot—humid location of Townsville, 836 office workers were surveyed; 935 workers participated in hot—arid Kalgoorlie-Boulder. Overall perceived work area temperature and measured indoor operative temperature correlated moderately with thermal sensation for Townsville (T) subjects but only perceived temperature correlated with Kalgoorlie-Boulder (KB) sensation. Multiple regression analyses confirmed that indoor climatic variables (including Predicted Mean Vote) contributed to actual thermal sensation vote (24% T; 15% KB), with operative temperature having more of an effect in T than in KB. Subsequent analyses of individual characteristics showed no linear contributions to thermal sensation. The remaining variances were significantly related to perceived work area temperature (7% additional explained variance in T; 12% in KB). Mann Whitney analyses (after correction for climatic variables) showed that T subjects with higher job satisfaction had thermal sensations closer to ‘neutral’. Males, healthier subjects, non-smokers, respondents with earlier survey times and underweight occupants had lower median thermal sensations in KB. Townsville occupants appeared more adapted to their outdoor climatic conditions than Kalgoorlie-Boulder respondents, perhaps due to limited home air-conditioning. Further research into non-thermal impacts on gender-related thermal acceptability is suggested.     

Vibration and comfort I. Translational seat vibration

A series of studies of discomfort caused by multi-axis vibration at the seat, feet and back of seated persons is described. This first paper reports on studies with translational seat vibration. Two experiments concerned with the effects of level, frequency and direction of the translational vibration of a firm flat seat are reported.

At octave centre frequencies from 1 to 63 Hz the first experiment determined the levels of fore-and-aft, lateral and vertical seat vibration which caused discomfort equivalent to 0.5 and l.25m/s²r.m.s. 10 Hz vertical seat vibration. In the second experiment, comfort contours equivalent to 0.8m/s²r.m.s. 10 Hz vertical seat vibration and subject transmissibilities were determined from 18 males and 18 females at preferred third-octave centre frequencies from 1 to 100 Hz. In both studies the feet of subjects were not vibrated and there was no backrest.

It was concluded that the shapes of equivalent comfort contours need not normally depend on vibration level. The forms of both individual and group equivalent comfort contours and seat-to-head transmissibilities are presented. Significant correlations were found between subject characteristics (size and transmissibility) and subject relative discomfort. The males and females produced similar equivalent comfort contours.

Information on the computerized application of the method of constant stimuli which was developed for the series of experiments is presented together with a consideration of alternative methods of determining the central tendency of the data. A method of assessing the effect of vibrator distortion on judgements of equivalent discomfort is also defined.     

The postural support of seats: a study of driver preferences during simulated tractor operation

The overall comfort of four current production tractor seats and some individual features of seat design have been assessed by a method of paired comparisons. The experiment was carried out under both static and dynamic conditions and subjects had to adopt natural postures similar to those adopted when ploughing. The results suggest that operators can differentiate seat comfort differences reliably. Subjects' posture has proved important particularly when assessing the height of the back rest. On the other hand most appraisals were not significantly affected by the conditions (dynamic or static) of the simulation. An exception to this was the cushion length. This experiment has finally produced enough information on the relative importance of various aspects to enable us to design an experimental seat to be used in a series of experiments to assess specific features of seat aspects. The ultimate objectives of this investigation are to determine what aspects of seat and workplace design affect the comfort of the operator and how these can be altered to improve the tractor driver's posture.