NUMERICAL ANALISYS OF HUMAN THERMAL COMFORT INSIDE OCCUPIED SPACES. C. O. R. Negrão(*) C. O. Carvalho F o.() and C. Melo ()

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1 NUMERICAL ANALISYS OF HUMAN HERMAL COMFOR INSIDE OCCUPIED SPACES C. O. R. Negrão(*) C. O. Crvlho F o.(**) nd C. Melo (**) (*) Federl Centre of echnologicl Eduction of Prná Acdemic Deprtment of Mechnics Ru Sete de Setembro, 365 CEP Curitib/PR - Brzil (**) Federl University of Snt Ctrin Deprtment of Mechnicl Engineering Centre for Heting, Ventiltion nd Air Conditioning Reserch Cix Postl Florinópolis/SC Brzil ABSRAC In the present work, humn therml comfort is investigted within the built environment. he nlysis is bsed on two building therml simultion models. In the first one - Nodl Network the ir condition (such s, ir temperture nd velocity) within ech therml zone is ssumed uniform nd therefore, ll zone occupnts re exposed to the sme condition. In the second model Nodl Network- CFD coupling men rdint temperture, ir temperture nd velocity vritions re considered. his pproch llows the evlution of comfort conditions of ll individuls within the sme zone. Senstion of drught cn lso be computed from the distributed results. he ppliction of the developed pproch is demonstrted by test cses; window type ir-conditioning unit is employed to control the ir temperture of four-zone building in both cooling nd heting sesons. INRODUCION Buildings re usully constructed with the purpose of reducing the impct of severe climte chnges providing comfort nd sfety to the occupnts. In mny cses, however, the occupncy is fr from being dequte, s mn expresses stisfction with the mbient in smll rnge of climte conditions. herefore, rtificil mens of ir conditioning re necessry to imprt therml comfort. Severl works were conducted in order to quntify nd qulify the vribles tht ffects therml comfort (Fnger, 970, Ggge et l., 986, ASHRAE, 997). hey showed tht comfort cn be evluted from three different clsses of vribles: mbient vribles (men rdint temperture, humidity, ir temperture nd velocity), physicl ctivity nd clothing. he hypothesis of uniform indoor climte is usully employed on building design, ssuming tht ll occupnts re subjected to the sme condition within therml zone. However, in some situtions, significnt chnges of ir properties tke plce in the occupied spce, resulting in different perception of comfort t different loction. Usully, this is only verified fter the occuption of the building nd opertion of the plnt system. After the dvent of numericl techniques, the building therml behviour, s well s the possible ir property grdients within building zones, could be predicted (Clrke, 985 nd Chen nd Jing, 99). Consequently, this type of tool llows the evlution of therml comfort in different points of the sme enclosure. he nlysis of the simultion results my suggest modifictions on the building design nd/or plnt system, even before construction. he present work ims the evlution of therml comfort bsed on numericl simultion results. he ir condition is considered not only uniform (mixed ir) but lso distributed within n occupied spce. A technique, developed by Negrão (998), is employed on the evlution. his technique combines models of different resolution nd therefore complexity. MAHEMAICAL MODEL he building system is composed of severl components (constructions, plnt systems, lighting system, occupnts, etc.), ech one with its own therml chrcteristics. herefore, building modelling is complex mtter becuse of component interctions nd system size. Additionlly, the therml behviour of buildings is strongly dependent on the het nd mss trnsfer interction with the exterior environment.

2 Air velocity nd temperture distribution, which chrcterise the ir flow nd het trnsfer within building, is determined by the solution of the conservtion equtions of mss, momentum nd energy. he conservtion eqution to be solved for ech vrible is expressed s: t φ + () x j x j x j ( ρφ) ( ρu jφ ) = Γ φ + Sφ where φ represents the vrible to be determined (velocity components nd temperture), Γ φ is the diffusion coefficient, S φ is the source term, ρ is the ir density nd U j is the velocity component in the x j direction. he terms of eqution () cn be found in ble. Eqution ble Governing equtions. Γφ Sφ Continuity - - Moment. µ ef P U i + µ ef x j x j x j Energy urbul. Energy Γ q c p, µ ef G C D ρε Gb σ ρg k Energy µ Dissipt. ef ε ε C G C ρ Gb σ ε k k Γ = µ µ t k + ; µ = µ ef t + µ ; ρ = ρ ( ) µ t = C Pr σ µ ρ ε µ G g t u u b G i j u = β ; = µ i x t + σ x i j x i x j u = U, V, W i C D =. 0 ; C =. 44 ; C =. 9 ; C 3 =. 44 x = x, y, z i σ =. 0 ; σ k ε =. 3 ; σ = 0. 9 ; C µ = k - turbulent kinetic energy ε - Dissiption of turbulent kinetic energy he equtions re discretized nd solved by the finite volume method (Ptnkr, 980). wo grids re considered: the first one (globl model) is less resolved the ir is considered mixed (only one cell represents the room ir condition nd only the energy eqution is solved) nd the second one (detiled model) is more refined the ir volume is divided in severl cells (ll conservtion equtions re solved for ech cell). In the detiled method, turbulence chrcteristic of indoor irflow is considered by the k-ε model (Rodi, 984). he het convection on internl nd externl surfces, het conduction through constructions, solr het gin, rdition between internl surfces, etc. re i lso modelled by the globl method. In the more refined model, only the irflow within zone is solved. wo possibilities re considered: i) solution of the globl domin nd ii) coupling between the more nd less resolved models. he coupling between domins tkes plce t internl surfces of wlls. his coupling llows evlution of not only globl (in some zones) but lso distributed comfort (in other zones). he detils bout this coupling cn be found in Negrão (998). HERMAL COMFOR By pplying het blnce to humn body s whole, Fnger (970) hs identified the following prmeters which ffects therml comfort: ir velocity, ir temperture, moisture content nd men rdint temperture (environment fctors), physicl ctivity nd clothing. Fnger correlted the body therml lod to n index, PMV (Predicted Men Vote). his index revels the therml senstion of group of individuls (cold, wrm or neutrlity) regrding n mbient condition. he PMV eqution cn be found in the literture (Fnger, 970) nd cn be genericlly written s: 0.036M PMV= ( 0.303e )L () where L is the body therml lod nd cn be expressed s L=L(M, I cl, mr, v,, w). M is the metbolic rte, I cl is the therml resistnce of clothing, mr is the men rdint temperture, v is the reltive ir velocity, is the ir temperture nd w is the moisture content. Fnger hs lso derived second index which quntify the percentge of disstisfied people with the mbient, the PPD (Predicted Percentge of Disstisfied). his index is obtined s function of PMV: 4 ( PMV PMV PPD = 00 95e ) (3) Men Rdint emperture he men rdint temperture ( mr ) is defined s the uniform temperture of blck enclosure tht results in the sme het trnsfer by rdition s the rel cse (rdition between the person nd the surrounding surfces). mr is function of person posture in the therml zone. he ccurte determintion of mr is however complicted becuse of the complex humn ntomy. In the present work, however, the mr is evluted for stnding mnnequin, plced in severl points within therml zone. his mnnequin (Figure ) is composed of seven cubic figures, which represents the different prts of the humn body (hed, trunk,

3 legs nd rms). he cubic shpes re sized (ble ) ccording to the dimensions of thin dult person. Its dimensions re obtined s function of the mnnequin height, H M, nd the dimension P M is the only one chosen independently from the others. Additionlly, these cubes cn be rerrnged to model other postures (e.g. sitting, lying, etc.). For ech visible fce of the cube, plne rdint temperture ( rp ) is determined s function of view fctors, F p-i, (between fce p nd n internl surfce i of zone) nd of surfce tempertures ( i ): / 4 n 4 rp = Fp ii (4) i= he view fctors F p-i re obtined from the combintion of view fctors of prllel or perpendiculr rectngulr plnes. hese expressions cn be found in the literture (Clrke, 985). ble Mnnequin dimensions. l M,c h M,c /H 0.5 h M,t /H h M,p /H 0.53 l M,c /H 0.88 l M,t /H 0.63 l M,p /H P M 0 cm h M,c where m is the number of the mnnequin exposed res (in this cse, m=7). A j corresponds to the fce re nd A is the mnnequin totl surfce re. Crvlho F o (998) presents the determintion of equtions (4) nd (5) in detil. Risk of Drught he therml neutrlity (PMV=0) is necessry condition but not sufficient to estblish comfort. Although the whole body therml lod cn be zero, the individul my feel uncomfortble if one prt of his body is cold nd the other is wrm. Fnger et l. (988) estblished complementry index, PD (Percentge of Disstisfied), in order to quntify the risk of drught. his index is ssocited to locl climte prmeters nd to turbulence intensity of the irflow. he uthors emphsised tht this risk exists prticulrly in sedentry nd rrely in high intensity ctivity. he percentge of disstisfied due to drught is obtined s function of ir temperture ( ), men ir speed ( v ) nd the ir turbulence intensity ( u ): v ( 34 ) ( v ,05) + ( 34 ) ( v 0,05) PD = 3.43 (6) u urbulence intensity, u, is computed s function of turbulence energy nd ir velocity ( k / u 00 3 % ). In study of displcement ventiltion system, Melikov et l. (990) estblished tht PD should be less thn 5% for comfortble environment. here re little informtion regrding other type of system, nd this limit is usully ccepted in such cses. l M,t h M,t h M,p H Evlution of the Comfort Indices he indices proposed by Fnger (PMV nd PPD) re computed in severl points in horizontl plne within zone. As the het blnce is considered for the body s whole, PMV nd PPD re bsed on men vlues of ir temperture nd velocity. he verges re computed from vlues under.80m high. l M,p Figure Mnnequin. Once the plne rdint tempertures of ll visible fces re known, the mr is then clculted s n verge of the rp weighed by their respective res: 4 4 rp, j A P M m mr = Aj (5) j = RESULS he building under nlysis, locted in Florinópolis- SC (Ltitude = 7 o South), is composed of three occupied zones nd one ttic (Figure ). he ir volume is considered mixed in ll zones but zone. In zone, window type ir-conditioner is employed nd the zone ir temperture nd velocity distributions re computed. he room depth, width nd height re, respectively, 8.0m, 4.0m nd.85m, s shown in Figure 3. he building wlls re mde of perforted bricks. In the north wll, there is het source under the window, which dissipte 500 W (the 3

dissiption is by convection nd rdition). he irconditioner ws originlly locted in the room west wll,.4 m from the floor nd equidistnt from north nd south wll.

4 dissiption is by convection nd rdition). he irconditioner ws originlly locted in the room west wll,.4 m from the floor nd equidistnt from north nd south wll. he totl cooling cpcity of the equipment is 635 W (0 000 BU/h). he occupnts perform sedentry ctivities (met). Simultions were performed for typicl summer nd winter dys. For ech dy, two simultions were considered: ) globl simultion nd b) combined simultion in only one simultion time-step in zone (in the other zones, the ir is ssumed mixed). In the summer time, the combined pproch ws performed t 3pm nd in the winter t m zone (3 m ) Entrnce door.0 of the cooling coil is equl to 0.76). During the room occuption period (8:00 to 8:00 h, the unit my cool nd ventilte (on) or only ventilte (off) the mbient, since the cooling cpcity is lrger thn the mbient cooling lod. he zone return temperture is controlled within 3 to 5 o C. he simultion results of the globl model (ir completely mixed) cn be observed in Figure 4. Note tht, during the first hours of occuption, the unit opertion time is shorter thn the time it is not in opertion. At bout middy, the on nd off periods re bout the sme order of mgnitude. On the other hnd, the opposite tkes plce during the fternoon; the opertion time is much lrger thn the off period. he reson is tht the cooling lod increses during the dy. In the morning, the cooling lod is smll nd progressively increses until the mximum is reched t 4:00pm. his is lso justified by the cooling cpcity vrition, seen in Figure 4. Figure Building geometry. 4.0 zone (6 m ) hll (5 m ) Bsed on the simultion results, the comfort indices cn be evluted, s cn be seen in Figure 5. Although the PMV fluctute s fst s the ir temperture, its verge vlue increses during the dy. At the beginning of opertion, the verge PMV is pproximtely 0.5 nd close to 4:00pm, this vlue reches his chnge is relted to the vrition of the men rdint temperture, s shown in Figure 5. Despite the PMV vrition, the percentge of disstisfied people (PPD) chnges from 5 to 5%, which cn be considered cceptble. Figure 3 Zone geometry. Fnger s model ws developed for stedy stte situtions, nd therefore the chnges of PMV nd PPD t the sme frequency of the ir temperture my not be representtive. herml comfort under trnsient regime should be investigted in order to verify how dequte is the model on the tretment of such cses. Additionl informtion bout problem configurtion nd climte dt cn be found in Crvlho F o (998). Although the ir-conditioner performnce is dependent on the return ir nd outside conditions, the cooling cpcity ws considered constnt during opertion. he ir flows perpendiculr to the unit frontl plne, nd therefore the louver deflexion ngle is zero. Summer Cse In this cse, the occupnts wer typicl summer clothes (0.6 clo). he sensible cooling cpcity of the ir conditioning unit is 000W (sensible het fctor A five seconds time-step ws employed bove this vlue, the results re sensitive to the time-step. he men ir temperture within zone, observed during the combined simultion, is presented in Figure 6. he blue colour t middle of the room indictes the lower temperture t tht region. he temperture vrition within the zone is pproximtely o C. he higher temperture tkes plce close to the west wll nd the lower temperture t the region where the ir jet flls. he PMV distribution is shown in Figure 7. his distribution indictes the people locted under the fll of the cold ir jet my feel cold while those close to the het source re slightly wrmer. his vrition is relted not only to the ir temperture but lso to two other fctors: i) Adjcent to the jet, people feel reltively high ir speed, ii) while close to the het source, the effect of men rdint temperture is more pronounced (see Figure 8). 4

5 Although the vrition of PMV between 0.55 nd shows tht 90% of people re stisfied with the condition, the sme chnge ( 0.9) my indicte disstisfction of 5% to 0% for different clothing or physicl ctivity. Figure 4 Air temperture nd cooling cpcity for the summer cse. Figure 5 Chnges of men rdint temperture, PMV nd PPD for the summer cse. Figure 6 Distributed men ir temperture ( o C) in zone (summer). Figure 7 PMV distribution in zone. Summer cse. 5

6 Although the individul globl discomfort is smll in the ir jet region, the percentge of disstisfied due to drught is significntly high. Figure 9 shows the PD distribution inside zone in the middle verticl plne. At the height of the hed (,75m), eighty to ninety percent of people under the ir jet will be uncomfortble. he only region where the risk of drught is not significnt is tht between the west wll nd the fll of the ir jet. tkes plce within the first operting hours of the unit, showing tht the on nd off periods re pproximtely the sme. As the hours pss, the operting periods decreses until pm when the equipment does not work ny more. Even though, the ir temperture is kept within the control limit (3 to 5 o C). Different from summer, the on nd off times re pproximtely the sme. his indictes tht the unit cpcity is much higher thn the heting lod. In the winter, the equipment works s het pump with heting cpcity of 500W. Figure 8 Men rdint temperture ( o C) distribution. Summer cse. Winter cse A typicl winter dy ws lso simulted nd the mixed ir temperture is shown in Figure 0. Unlike the summer sitution, the mximum heting lod Figure 9 PD distribution (%) in verticl plne. Summer cse. Figure 0 Air temperture nd heting cpcity of zone. Winter cse. On the other hnd, Figure shows tht the verge therml comfort chnges within wider rnge when compred to the summer cse. he reson is tht the internl surfce tempertures re much lower in the morning, resulting in lower men rdint temperture during tht period. For the clothing type (0.8 clo), the percentge of disstisfied (people feeling cold) my rech 30%. he ir temperture distribution within zone for the combined simultion is shown in Figure. Once more, the temperture vrition is smll inside the zone (mximum chnge is.3 o C). Unlike summer, men rdint temperture vries.5 o C inside the zone, s cn be seen in Figure 3. Figure 4 shows tht the PMV chnges from 0.3 to 0.73, indicting tht the percentge of disstisfied re within the limit of 8 to 8% (ll feeling cold). Note 6

7 tht the lrger number of disstisfied re plced in the lower mr regions. However, the vrition ( PMV=0,39) is not s lrge s in the summer cse, showing much more uniform conditions. his mens tht n increse of clothing therml resistnce my keep the percentge of disstisfied fewer thn 5%. his smll chnge of PMV is minly relted to the fct the men ir velocity chnges little in the occuption re (0.07 to 0.5m/s). Even in the heting seson, the risk of drught is still possible, s cn be seen in Figure 5. he distribution of PD in horizontl plne (,0m high) shows tht close to the est wll, where the ir jet flls, 3% of people expresses disstisfction with drught. In other loction, the percentge of disstisfied is kept under 5%. DISCUSSION AND CONCLUSIONS In the present work, n nlysis of therml comfort within occupied spces ws conducted bsed on numericl simultion of buildings. wo simultion models re considered: globl nd combined model (the globl model coupled to distributed one). he simultion ws performed for typicl winter nd summer dys. In the globl nlysis, despite the ir temperture being controlled between 3 to 5 o C, the level of comfort chnges considerbly during the occuption period. his chnge tkes plce becuse of men rdint temperture vrition during the dy. he effect of the men rdint temperture is more pronounced in the winter since the surfce tempertures re much colder in the morning. Figure Men rdint temperture, PMV nd PPD for winter. Figure Men ir temperture ( o C) distribution in zone (winter). Figure 3 Men rdint temperture ( o C) distribution in zone (winter). he results show tht the comfort indices oscillte s fst s the temperture of the ir. he ir temperture my vry between 3 to 5 o C during period of 3 minutes, s in the winter period. Nevertheless, Fnger s indices were developed for conditions of 7

8 therml equilibrium of the humn body. rnsient nlysis is necessry to verify the influence of the oscilltion of temperture in therml comfort. he ir tempertures of the other occupied zones were mintined rtificilly fixed. he indices of comfort nd men rdint tempertures for such zones, not shown becuse of spce constrin, my be obtined from Crvlho F o (998). In the summer, the risk of drught is quite high for those locted under the fll of the ir jet. Deflection of the inlet irflow cn reduce this. Although this risk is still present in the winter, it is much reduced even becuse the ir velocity is smller. Figure 4 Distribution of PMV in zone (winter). Figure 5 PD distribution (%) in horizontl plne. Winter cse. he winter sitution presents higher distribution of ir velocity inside the zone thn the summer cse. his is justified by the fct tht buoyncy effect produces fster fll of the ir jet in the summer. In the winter, the ir is mintined in higher regions of the room until it is cooled off close to the ceiling. After tht, the ir flls. his fct decelertes the irflow resulting in more uniform velocity distribution. On the other hnd, the ir temperture vrition is higher in the winter thn in the summer, just becuse of ir strtifiction. Although the ir temperture vrition is not so lrge (bout.0 o C in the summer nd.3 o C in the winter), the temperture distribution ffects nturl convection which consequently chnges the velocity field. As seen, these chnges hve strong influence in comfort. REFERENCES Crvlho F o, C. O., 998, Numericl Anlysis of herml Comfort in Conditioned Room (in Portuguese), MSc. hesis, Federl University of Snt Ctrin, Florinópolis, Brzil. Chen, Q. nd Jing, Z., 99, Significnt Questions in Predicting Room Air Motion, ASHRAE rnsctions, Vol. 98, Prt, pp Clrke, J. A., 985, Energy Simultion in Building Design, Adm Hilger Fnger, P., 970, herml Comfort. Anlysis nd Appliction in Environmentl Engineering, McGrw-Hill. Fnger, P. O., Melikov, A. K., Hnzw, H. nd Ring, J., 988, Air urbulence nd Senstion of Drught, Energy nd Buildings No., pp Ggge, A. P., Forbelets, A. P., Berglund, P. E., 986, A Stndrd Predictive Index of Humn Response to herml Environment, ASHRAE rnsctions, pp , Prt, Vol. 9. ISSO 7730, 984, Moderte herml Environments. Determintion of the PMV nd PPD Indices nd Specifiction of the Conditions for herml Comfort. Interntionl Stndrds Orgnistion. Negrão, C. O. R., 998, Integrtion of Computtionl Fluid Dynmics with Building herml nd Mss Flow Simultion, Energy nd Buildings, pp , Vol 7-. Melikov, A. K., Lngkilde, G. nd Derbiszewski, B., 990, Chrcteristics in the Occupied Zone of Rooms with Displcement Ventiltion, ASHRAE rnsction, Vol. 96, Prt I, pp Ptnkr, S. V., 980, Numericl Het rnsfer nd Fluid Flow, ylor nd Frncis. Rodi, W. 984, urbulence Models nd heir Applictions in Hydrulics A Stte of he Art Review, University of Krlsruhe, Krlsruhe, Germny. 8

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