Thermal Comfort Analysis of an Automobile Driver with Heated and Ventilated Seat

Transcription

1 -- Thermal Comfort Analyss of an Automoble Drver wth Heated and Ventlated Seat G. Karm, E.C. Chan, and J.R. Culham Department of Mechancal Engneerng, Unversty of Waterloo Waterloo, ON, Canada, NL G I. Lnjack and L. Brennan W.E.T. Automotve Systems Ltd., Wndsor, ON, Canada, N8N 5B8 Copyrght Socety of Automotve Engneers, Inc. ABSTRACT A thermal/physcal model of the dynamc nteracton between an automoble passenger, the cabn envronment, and a heated/ventlated seat s presented. The model consders the human body as beng made of dstnct segments and three-layers. Smple mathematcal models are presented to smulate heatng and ventlaton of cool ar through the seat. The model has the ablty to predct the transent response of a drver n a hghly non-unform thermal envronment n terms of local and overall thermal comfort levels. INTRODUCTION The cabn temperature of an automoble can exceed 8 C on a hot summer day due to ncdent solar radaton, whle durng harsh wnter condtons, ambent temperatures can drop below - C. Under ths extreme range of ambent condtons, automoble passengers can experence shockng localzed heatng or coolng as exposed body surfaces (5 to %) make contact wth the seat, back support and steerng wheel. Although the heatng and ar-condtonng systems wthn an automoble attempt to respond to the comfort needs of passengers, the thermal capacty of most cabn components lmts the tmely response of these heatng and ventlaton systems, resultng n passenger dscomfort for extended perods. Whle the ambent ar temperature s an mportant factor n determnng the level of thermal comfort, conductve heat transfer from the body due to contact wth a seat that s ntally very cold or very hot plays a sgnfcant role n nfluencng the thermal sensaton of an automoble passenger. The ablty to reach thermal neutralty over the contact area durng the cold season, can be expedted by ncorporatng resstve heatng elements nto the seat to augment the standard engne-coolant-based heatng system. A possble strategy to mprove the coolng process s to ventlate the seat wth ambent ar from the passenger compartment. Ths technque can substantally reduce the tme lag between heat transfer from the ambent ar to the seat contact area. Furthermore, t can enhance the comfort level n the mcroclmate n the contact area. Although automoble car seats wth heatng elements have been n the market for several years, ventlated seats are a more recent development, whch requre further attenton. In ths paper, physcal models are presented to smulate the thermal nteractons between a typcal drver, and a heated or ventlated seat. The effectveness of the seat for enhancng thermal comfort under severe wnter and summer condtons wll be examned. DRIVER S THERMAL RESPONSE MODEL There are two stages n thermal comfort modelng. The frst stage accounts for the heat exchange process between the body and the surroundng envronment n order to estmate the rate of heat storage and body temperature. The second stage uses the nformaton obtaned n the frst stage to predct the thermal sensaton (comfort) the person would experence. Several models that consder the thermal nteracton of the human body wth the envronment have been developed durng the past 5 years. Excellent revews and crtcal evaluatons of these models can be found n Dohetry and Arens (988), Haslam and Parsons (988), and Lotens (988).

2 A more detaled thermal analyss can be obtaned by consderng the body to be made of dfferent layers and multple segments. The human thermal response model developed n ths work s based on the model of Burch et al. (99). The model consders the body to be made of three layers: core, skn and the clothng worn. The major dfference n the present study s n the number of human body segments, where the human body s dvded nto dstnct segments, as shown n Fg. and descrbed n Table-. 8 9, 4,5 6,7, 6,7 4,5 Table-: Body segments No. Descrpton Head face Head back Neck 4 Chest 5 Upper back 6 Stomach 7 Lower back 8 Rght upper arm 9 Rght lower arm Rght hand (back) Rght hand (palm) Left upper arm Left lower arm 4 Left hand (back) 5 Left hand (palm) 6 Upper leg (front) 7 Upper leg (back) 8 Rght lower leg 9 Rght foot Left lower leg Left foot 8 TAr TAr 9 Fg. : The human body segments The selecton of body segments, as shown n Fg., provdes local as well as overall thermal comfort estmaton of the human body for a wde range of clothng and envronmental condtons. For example, the subject can wear short sleeve shrts and shorts as well as regular clothng. In addton, the effect of heatng or ventlaton through the drver seat, the steerng wheel, and local ar velocty can be nvestgated. The thermal resstance network of a typcal clothed human body segment, as approxmated by ths model s llustrated n Fg.. As shown, heat (per unt area) s generated n the body by normal metabolc performance, q MT, and can be lost to the envronment by conducton, q CN, convecton, q CV, radaton, q RD, respraton, q RS, and evaporaton of sweat from the skn, q EP. The rate of heat storage n the body segment s the dfference between the rate of heat generaton and the rate of heat loss to the envronment. TCore Core q C-S R C-S q S-C Skn q EP TSkn RS-C q C-A TCloth Cloth R C-A R CV R RD q C-A q C-A Ar TAr Fg. : A typcal clothed body segments wth thermal resstances Fundamental heat transfer prncples can be used to evaluate the dry heat loss (conducton, convecton and radaton) n terms of skn temperature, T SK, the thermal resstances, R s, and envronmental condtons (T A, T RD, V A, and P A ). Skn temperature, T SK, and heat fluxes q EP, and q RS are dependent on complex thermo-regulatory functons of the body ncludng sweatng, shverng, and the control of the blood flow through vascular constrcton and dlaton. In general, these thermo-regulatory functons vary over the body n response to changng rates of heat loss due to thermal transents and nonunformty n clothng, temperature, and ar velocty.

3 The equatons for each of the heat gan/loss terms are presented and heat balances are made on each node n order to develop equatons for estmatng the temperature of the nodes as a functon of tme. BODY INTERNAL HEAT GENERATION Under normal condtons, heat s generated n the body core only from the metabolsm nherent to a gven physcal actvty. The amount of energy released by the metabolsm s dependent on the amount of muscular actvty. Accordng to Fanger (97), the average metabolc rate for an automoble drver vares between and.8 met ( met 58.5 W/m ) dependng on the traffc level. HUMAN BODY HEAT LOSS In ths secton the heat loss from body segments due to dfferent mechansms are presented. Heat Loss by Conducton Heat exchange between the core and the skn occurs by conducton and by advecton of blood. The heat transfer by advecton s dependent on the rate of blood flow between the core and skn layers. The combned thermal exchange between the core and skn can be wrtten as: {( h BL + ρ BL C P, BL BL ) A( T CR T SK } Q CS, υ ),,..., N () where h BL s the effectve conductance between the core and skn (5.8 W/(m.K), ASHRAE, 99). The specfc heat and densty of the blood are taken as 4,45 J/kg.K and, kg/m, respectvely, and A s the skn surface area. Equaton s used to calculate core-to-skn heat transfer for all body segments, N. The skn blood flow rate per unt of skn area, BL, whch s regulated by the thermo-regulatory system wll be dscussed later n ths secton. Transfer of dry heat between the skn and the outer surface of a clothed body s qute complcated, nvolvng nternal convecton and radaton processes n the clothng pores, and the conducton through the cloth tself. Generally, a heated mankn s used to accurately measure the effectve thermal conductvty of dfferent clothng ensemble. Heat loss from the skn to the clothng, Q SC, can be wrtten as T QSC, kcl f A,,..., N xcl () where k CL s the effectve thermal conductvty of the clothng ensemble and T/ x CL s the temperature gradent across the clothng. f s a factor ( ) to correct for the heat transfer area from the skn to the external surface of the clothng. υ Heat Loss by Convecton The heat loss by convecton from the drectly exposed skn and the outer surfaces of the clothed body can be expressed by the followng equaton: { h f A T} N QCV, CV,,..., () Here, T s the dfference between the skn temperature (or the clothng temperature) and the ambent ar. f s the rato of the effectve surface areas of the clothed body and the nude body. The convectve heat transfer coeffcent, h CV, s gven by (ISO 77).5 h CV,. VA, f.8 T <. VA, h CV,. 8 T.5 Otherwse,,..., N (4) Heat transfer between the clothng and the seat n the contact areas s governed by conducton and s calculated usng Eq.. Heat Loss by Radaton Heat loss by radaton s gven by 4 4 { σ F f A ( T T )}, N QRD, ε G RD,..., where σ s the Stefan-Boltzmann constant, W/(m.K 4 ). ε s the average emssvty of clothng or body surface (about.9 for most cotton clothng and about. for the skn) and F G s the vew factor, or the fracton of the skn or clothed area that radates to the envronment. Body segments are consdered as smple planar elements parallel to the plane of surroundng surfaces and vew factors are approxmated based on the area fracton exposed to the surroundng surfaces (e.g. vew factors are estmated at. for the head face, and head back, and. for the upper leg back, respectvely). Heat Loss by Evaporaton of the Sweat The total latent heat loss from the skn due to evaporaton, Q EP, s gven by PSK P A QEP, ω AEff,,..., N (6) RM, SA where ω s the total skn wetness (percentage of the exposed area whch s most), and R M,SA s the total vapor dffuson resstance due to the clothng and the surroundng ar. P SK and P A are water vapor pressures at the skn and ambent temperatures, respectvely. Respraton Heat Loss Heat and water vapor are transferred to nhaled ar by convecton and evaporaton durng respraton. Assumng the ar s exhaled at saturated condtons, the total sensble and latent heat due to respraton s equal to (5)

4 Q RS ( PCR PA ) m A[ CP, A ( TCR TA) + h fg ] (7) P Here, P CR and P t are the water partal pressure at the core temperature and the ambent pressure, respectvely. h fg s the water latent heat of vaporzaton. It s assumed that the respraton heat loss affects only the frst fve body segments hence; Q RS s dvded among these segments proportonal to ther surface area. The mass flow rate of ar nhaled s estmated as a lnear functon of total metabolsm (Burch et al. 99): D (8) 6 m A. Q MT Human Thermo-regulatory System The human body has a very effectve temperature regulatory system, whch ensures that the body s core temperature s kept at approxmately 7 C. When the body becomes too warm, two processes are ntated: frst the blood vessels dlate, ncreasng the blood flow through the skn and subsequently one begns to sweat. If the body s gettng too cold, the frst reacton s for the blood vessels to constrct, reducng the blood flow through the skn. The second reacton s to ncrease the nternal heat producton by stmulatng the muscles, whch cause shverng. The control sgnal equatons used n the present work are taken from Dohetry and Arens (988). The parameters used n the control sgnals are the core, skn, and mean body temperatures. The mean body temperature, T B, s a mass weghted average of the skn and the core temperatures. The ncrease n the metabolsm due to shverng s estmated by { 4.9(.7 T )(6.8 T )}, N QSH, SK CR,..., (9) The blood flow between the core and the skn per unt of skn area s expressed as υ BL, 6 (.75 )( +.7( T +.(.7 T CR SK t 6.8)) ),,..., N () The rate of sweat producton per unt skn area, estmated by m SW, s 5 {(4.7 ) f ( T 6.5) }, N md SW, SW B,..., () SW, (( T SK,.7) /.7) f e () In the foregong equatons, a control sgnal, such as (.7-T SK ) s set equal to zero, f negatve. HEAT BALANCE By performng heat balances on the segmental core, skn, and the clothng layers, the change n these temperatures wth tme can be predcted. The heat balance equatons for segments,,,n are: ( Q + Q Q Q MT, RS, CS, ) ST, CR, ( m. C) Q CS, ( QEP, + QCL, ) QST, SK, dt dt CR, CR, () ( m. C) Q SC, ( QCV, + QRD, ) QST, CL, dt dt SK, SK, (4) ( m. C) dt dt CL, CL, (5) In these equatons Q ST represents the total heat ganed or lost. For small tme ntervals, t, the rate of change of core temperature, T CR, skn temperature, T SK, and clothng temperature, T CL, wll be approxmately constant, so that T T T CR, SK, CL, QST, CR,. t ( t) TCR, ( t t) + (6) ( mc) CR, QST, SK,. t ( t) TSK, ( t t) + (7) ( mc) SK, QST, CL,. t ( t) TCL, ( t t) + (8) ( mc) CL, Thus, f ntal values of T CR, T SK, and T CL are gven, subsequent values can be calculated from the heat rate terms and heat capactes. HEATED/VENTILATED SEAT THERMAL MODEL The schematc of the all-purpose drver seat s shown n Fg.. The seat s desgned to augment the standard engne-coolant-based heatng system n wnter and to provde ventlated cold ar to the contact surfaces durng the summer to acheve a hgher level of comfort. Heat s produced by passng electrc current through a heatng pad made of carbon fbers placed beneath the leather coverng. Ambent ar s drawn n usng a bult-n fan and then flows through spacer materal, a heatng mat, and the porous leather cover before comng n contact wth the drver s body. where

5 T T o t T T e β t () Human Body where Leather Cover Heatng Pad Spacer Fabrc Sponge x β ( mc P ) ( mc ) P Ar Materal x Fan Here, T t s the ntal seat temperature, m s mass of the seat materal n the control volume, mc s mass flow rate of ventlated ar, and C P s the specfc heat of the ar or the seat materal. Fg. : Schematc of the heated/ventlated seat Although heat transfer n the seat s a three-dmensonal phenomenon, smple transent one-dmensonal thermal models are used to predct the tme varaton of temperature n the seat durng the heatng and ventlaton processes. The assumpton of -D heat transfer can be justfed by consderng relatvely large thermal resstances n other drectons compared to the prmary flow drecton (x-drecton). The governng equaton for the heated seat s T QD + k x T α t,,..., No. of seat layers (9) Equaton 9 shows the tme varaton of temperature across the seat materals. Q D s the heat generaton per unt volume of the heatng pad and s zero for other seat materals. k and α are thermal conductvty and thermal dffusvty (k/ρc P ) of the seat materals. The governng equaton for ventlaton s obtaned by wrtng an energy balance over a small control volume as shown n Fg. 4. Tout. m Ar, T n dx Fg. 4: Energy balance over an element of the seat Ar enters the control volume at T, exchanges heat wth the seat materal and leaves the control volume at T o. The change n temperature wth tme can be estmated usng a lumped heat capacty approach as follows x Equaton s derved based on the followng assumptons: (a) heat transfer occurs only n the x- drecton, (b) the conducton term s neglgble compared to convecton, (c) the mass of ar trapped n the materal s neglgble n comparson to the mass of the materal, and (d) a thermal equlbrum s reached between the ar and the materal when ar leaves the control volume. Wnter smulatons are obtaned by applyng ntal and boundary condtons. Equaton 9 s dscretzed mplctly usng a fnte dfference technque. The resultng set of algebrac equatons forms a tr-dagonal matrx, whch s solved usng a Thomas Algorthm. The temperature dstrbutons are updated wth tme. Transent temperature profles due to ventlaton are obtaned by dvdng the seat layers nto small control volumes. Calculatons are started from the begnnng of the spacer materal where ar s ntroduced and contnued upward to the leather cover. The temperature profles n the sponge and the leather on the seat back are stll governed by conducton and obtaned by solvng Eq. 9. THERMAL COMFORT The second stage of the thermal comfort modelng s to use the heat transfer data found n the frst stage to predct the thermal sensaton (comfort) the person would experence. The physologcal comfort a person perceves n a car s the result of hs or her subjectve thermal and mosture sensaton. The thermal sensaton s created partly due to the drver contact wth the seat, and partly due to hs/her exposure to the ambent ar. The thermal sensaton values can be computed by comparng the rate of heat generaton by the body (due to metabolsm and a possble shverng) wth the rate of heat dsspaton that a person would requre to mantan thermal neutralty under the specfed level of actvty, clothng and ambent condtons. The present model uses Fanger s emprcal correlaton to estmate the local as well as the overall thermal sensaton of a drver. The correlaton s

6 TS.6Q A + n. exp. 8,,..., Q N n Q A out () where Q n ad Q out are the rate of heat generaton and heat loss from the body segment, respectvely. The overall thermal sensaton, TS, s calculated by averagng local thermal sensatons, TS, proportonal to the surface areas. The thermal sensaton values obtaned by the foregong equaton are nterpreted aganst the thermal sensaton scale n Table-. RESULTS Table-: Scale of thermal sensatons Scale Thermal Sensaton 5 Panfully hot 4 Very hot Hot Warm Slghtly Warm Thermally neutral - Slghtly cool - Cool - Cold -4 Very cold -5 Panfully cold In ths secton transent thermal nteractons of a typcal drver wth the heated/ventlated seat and the ambent ar s smulated for severe wnter and summer condtons. Throughout the smulatons, an average drver of 75 kg, 75 cm hgh s consdered under moderate traffc condtons. The drver s body s dvded nto segments, and physcal parameters such as mass fracton and skn thckness are assgned for each segment. The drver s wearng a busness sut wth up to three layers of clothng allowed for every segment. The drver s ntal skn and core temperatures are consdered to be at 4 and 7 C, respectvely. The ntal clothng temperature s taken as a proportonal average of the skn and the ambent temperatures. Ar movement s consdered to be constant at. m/s all around the drver. All smulatons are performed over a perod of mnutes wth a tme nterval of second. WINTER SIMULATIONS Intal cabn temperature and relatve humdty are consdered to be C and 5%, respectvely. It s assumed that the seat ntally comes to a thermal equlbrum wth the ambent ar. Although the cabn ar temperature s usually changng exponentally durng the warm up perod, the ar temperature s consdered to ncrease lnearly to the comfort level of C over a perod of mnutes for smplcty. Fgures 5a-, show varatons of seat cushon and back surface (leather cover) temperatures as a functon of tme for dfferent heat settngs. Varaton of the cabn ar temperature s also shown n the fgures. It takes about mnutes for the unheated seat to reach the steady state temperature, whch s stll well below an acceptable comfortable level. When the heatng pad s actvated, heat s produced n the resstve carbon fbers at a rate of,745, W/m and transferred to the leather cover and eventually to the drver s skn. The rate of heat transfer s so fast that the seat surface temperature exceeds C n less than 5 mnutes. The electrcal heater s shut down once ts temperature rses above a predefned value (eg. 7, 45, and 55 C for the heatng, low, medum and hgh, respectvely) and reactvated f ts temperature drops more than C. Fgures 5b-, show varatons of skn temperatures n contact wth the seat cushon and the seat back, respectvely. As shown n the fgures, the skn temperatures decrease contnuously wth the unheated seat, however; the rate of skn temperature drop would decrease wth tme due to shverng stmulated n the correspondng body segments. When the heatng system s actvated, the skn temperatures drop for the frst few mnutes due to the seat, clothng and skn s heat capactes. However, the seat heat dsspaton can ncrease skn temperature above 4 C very quckly, dependng on the seat settngs. Fgures 5c-, show local heat loss/gan for the body segments n contact wth the cushon and back, respectvely. As ndcated, both segments loose heat quckly at the begnnng for all settngs however, the rate of heat loss decreases wth tme due to the body thermoregulatory system and/or the heat transfer from the seat. Wth the heated seat actvated, heat s eventually transferred from the seat to the skn n both regons. Fgures 5d-, show local thermal sensatons as a functon of tme. It s clearly shown n these fgures that when the seat s unheated the drver wll feel very cold at the contact areas for the frst few mnutes. Even the thermo-regulatory system s unable to brng thermal comfort n a reasonable tme perod. When the heatng system s actvated, local thermal sensatons ncrease quckly and the drver wll feel warm after about mnutes. If the heatng system s not shut down after ths perod the drver wll feel localzed heatng at the contact areas wth the seat. At ths tme the body thermoregulatory system wll lower the hgh thermal sensatons to reasonable values through vascular constrcton and by producng more evaporaton of sweat. The fluctuatons n the thermal sensaton values are due to the seat bult-n on/off controller as descrbed before. SUMMER SIMULATIONS Intal cabn and seat temperatures are consdered to be 5 C. The relatve humdty s 5%, and t s assumed that the cabn ar condtonng system reduces the ar temperature lnearly to C n mnutes. The bult-n fans are able to take up to 4 CFM of ambent ar and delver t to the seat cushon and back.

7 Fgures 6a-, show varatons of seat surface temperatures at dfferent ventlaton settngs as a functon of tme. Varatons of the cabn ar temperature wth tme are also shown n the fgures. As ndcated, the surface temperature of a non-ventlated seat decreases very slowly and stays well above local skn temperatures for more than mnutes of smulatons. As a result, the heat s contnuously transferred from the seat to the skn and the local skn temperatures rse above the comfort level. Wth the ventlaton system on, local seat surface temperatures drop almost at the same rate as the ar temperature and eventually stay a couple of degrees above the steady-state ambent temperature. Ventlaton of warm ar through the seat durng the frst few mnutes wll ncrease local skn temperatures however, as soon as the car s A/C reduces the ar temperature the seat cools down quckly and ensures a hgher level of comfort at the contacted areas. Ths s clearly shown n Fgs. 6b-, where the local skn temperatures drop more than C. Fgures 6c-, ndcate rates of heat transfer at the contacted areas as a functon of tme. As seen from the fgures, when the body comes n contact wth the seat, the rate of heat transfer s very hgh due to the large temperature gradents at the contact areas. The rate of heat transfer wll decrease wth tme due to the lower temperature gradent and body thermo-regulatory actvtes. The ntal heat flux on the seat s affected by the heat capacty manly, of the coverng materal, e.g. leather n ths case study. Ventlaton of the cabn ar through the seat causes the rate of local heat transfer to lnearly decrease and ts drecton to be reversed n 6 mnutes of operaton. The heat transfer rate approaches a steady-state value soon after the ambent temperature becomes constant. The steady-state heat flux on the seat s affected on one hand by the seat s thermal nsulaton, manly created by the nner components of the seat cushon and the backrest and on the other hand by the rate of ventlaton. The present study shows lttle dfference between low and medum ventlatons rates and almost no dfference between the medum and hgh rates. Local thermal sensaton values at dfferent ventlaton settngs are shown n Fgs. 6d,. As seen from the fgures, ventlaton of ar wll reduce thermal sensatons quckly to the negatve terrtores and a thermally uncomfortable stuaton wll be reached f ventlaton contnues. Agan numercal results show no dfference between the medum and hgh rates of ventlatons. OVERALL THERMAL SENSATION The body transent overall thermal sensatons were calculated usng Eq.. Local thermal sensatons are combned and an average value obtaned based on body segmental areas. n a shorter perod of tme, typcally between to mnutes dependng on the settng on the seat. Ths fgure also shows that t s more comfortable to deactvate the heatng system after the thermal comfort level s approached. Fgure 7b dsplays transent overall thermal sensatons for summer condtons. As seen from the fgure, thermal comfort wll be acheved at a shorter tme wth a ventlated seat. CONCLUSIONS A transent physcal model s developed to smulate the thermal nteractons between an automoble passenger, the cabn envronment, and a heated/ventlated seat. The model takes nto account the effect of heatng and ventlaton through the seat on the local and overall thermal sensatons. Smulaton results ndcate that a heated seat wll brng thermal comfort to the passenger very quckly n the contact areas whch n turn enhance overall thermal sensatons. On the other hand, ventlaton wll brng the seat temperature to that of the ambent ar and ncrease thermal comfort of the passenger. ACKNOWLEDGMENTS The authors would lke to acknowledge the fnancal support of Materals and Manufacturng Ontaro (MMO) and the Natural Scences and Engneerng Research Councl of Canada (NSERC) REFERENCES ASHRAE. Fundamentals Handbook, 99. p. 8.6 S. D. Burch, S. Ramadhyan and J.T., Pearson, Analyss of Passenger Thermal Comfort n an Automoble Under Severe Wnter Condtons, ASHRAE Transactons T. J. Dohetry, and E. Arens, Evaluaton of the Physologcal Bases of Thermal Comfort Models, ASHRAE Transactons, 988, Vol. 94, Part I, P. O. Fanger, Thermal Comfort: Analyss and Applcatons n Envronmental Engneerng, McGraw Hll Co., 97. R. A. Haslam, and K.C. Parsons, An Evaluaton of Computer-based Models That Predct Human Responses to the Thermal Envronment, ASHRAE Transactons, 988. Vol. 94, Part, 4-6. W. A. Lotens, Comparson of Thermal Predctve Models for Clothed Humans, ASHRAE Transactons, 988, Vol. 94, Part, -4. Fgure 7a shows overall thermal sensatons as a functon of tme for wnter smulaton. It s clear from the fgure that a heated seat wll brng thermal comfort to the drver

8 CONTACT Gholamreza Karm, Mcroelectroncs Heat Transfer Laboratory, Department of Mechancal Engneerng, Unversty of Waterloo, Waterloo, ON, NL G, Canada RS respraton SC,S-C skn-to-cloth SH shverng SK skn ST storage SW sweatng Phone: (59) , Ext. 56 E-Mal: NOMENCLATURE A surface area, m C P specfc heat, J/kg.K f dmensonless correcton factor F G geometrc functon, dmensonless h heat transfer coeffcent/conductance, W/m.K h fg heat of vaporzaton, J/kg k thermal conductvty, W/m.K m mass, kg mc mass flow rate, kg/s N number of body segments P pressure, Pa q heat flux, W/m Q total heat flow rate, W Q heat generaton per unt volume, W/m R thermal resstance, m.k/w R M,SA mass transfer resstance, m.pa/w t tme, s T temperature, C TS thermal sensaton V velocty, m/s υd volumetrc flow rate per unt of skn area, m /m.s x thckness/dstance, m Greek Symbols α thermal dffusvty, m /s ε emssvty ω wetness ρ densty, kg/m σ Stefan-Boltzmann constant dfference Subscrpts A ambent ar B body BL blood CA,C-A cloth-to-ar CL cloth CN conducton CR core CS,C-S core-to-skn CV convecton EP evaporaton Eff effectve nlet/body segment number MT metabolsm O outlet RD radaton

9 6 5 (a-) Seat Cushon 6 5 (a-) Back Support Cushon Temperature [C] t[mn] 8 7 (b-) OFF Heatng, Low Heatng, Medum Heatng, Hgh Ambent Temperature Back Temperature [C] t[mn] 8 7 (b-) Local Skn Temperature [C] Local Skn Temperature [C] t[mn] (c-) 7 6 t[mn] (c-) Local Heat Loss/Gan [W] Local Heat Loss/Gan [W] t[mn] 5 4 (d-) -4 t[mn] 5 4 (d-) Local TS - Local TS t[mn] -5 t[mn] Fg. 5: Tme varaton of seat temperature, local skn temperatures, local heat losses/gans, and local thermal sensatons (TS) as a functon of heat settngs durng wnter condtons. (Cushon: LHS fgures, Backrest: RHS fgures)

10 Cushon Surface Temperature [C] Local Skn Temperature [C] (a-) (b-) Seat Cushon OFF Ventlaton, Low ( CFM) Ventlaton, Medum (8 CFM) Ventlaton, Hgh (4 CFM) Ambent Temperature t[mn] 7 Back Surface Temperature [C] Local Skn Temperature [C] (a-) Back Support t[mn] 7 (b-) t[mn] (c-) 4 t[mn] (c-) Local Heat Loss/Gan [W] - Local Heat Loss/Gan [W] t[mn] 5 - t[mn] Local TS Local TS (d-) - t[mn] - (d-) - t[mn] Fg. 6: Tme varaton of seat temperature, local skn temperatures, local heat losses/gans, and local thermal sensatons (TS) as a functon of heat settngs durng summer condtons. (Cushon: LHS fgures, Backrest: RHS fgures)

11 (a) 5 4 (b) OFF Ventlaton, Low ( CFM) Ventlaton, Medum (8 CFM) Ventlaton, Hgh (4 CFM) Overall TS - - Overall TS - -4 OFF Heatng, Low Heatng, Medum Heatng, Hgh - -5 t[mn] - t[mn] Fg. 7: Drver overall thermal sensatons as a functon of tme. (a) Wnter smulaton, and (b) Summer smulaton