USE OF MICROCLIMATE MODELS FOR EVALUATING THERMAL COMFORT: IDENTIFYING THE GAPS

USE OF MICROCLIMATE MODELS FOR EVALUATING THERMAL COMFORT: IDENTIFYING THE GAPS Tni Shrmin; Koen Steemers The Mrtin Centre for Architecturl nd Urn Studies, Deprtment of Architecture, University of Cmridge, - Scroope Terrce Cmridge, CB PX ABSTRACT The study identifies the gp etween ctul therml senstion nd theoreticl comfort clculted through simulted microclimte dt in different urn configurtions in tropicl, high-density, megcity: Dhk. The methodology stted here could e pplied for evluting outdoor comfort conditions for future urn res t n erly design stge. To pply the concept of theoreticl comfort it is importnt to understnd its limittions nd degree of devition from the ctul comfort conditions t rel scenrios. This study minly focuses on trditionl nd forml (contemporry) residentil settlements with different urn-geometry fetures. On-site climtic mesurements were crried out during the hot-humid months nd were compred with simultion results clculted through ENVI-met. Simultion results were found to hve good greement with ctul ir-temperture, men rdint temperture (Tmrt) nd reltive humidity. In terms of windspeed, the simulted model for complex trditionl settlement did not successfully mtch with the ctul scenrios. However, this does not ffect the model competency, ecuse, the re hs rther unusul wind pttern due to its loction nd current rrngements of uildings. The simulted results were susequently used to clculte outdoor therml comfort using the PET index in RAYMAN Pro. The clculted theoreticl comfort ws ssessed ginst Actul Therml Senstion Votes (ASV) otined through therml comfort survey in the cse-study res. Strong correltion (r=.8) ws found etween theoreticl nd ctul comfort in the forml settlements, while the comprison with the trditionl settlements produced rther wek results (r=.8). This leds to the understnding tht theoreticl comfort cn e useful tool for compring etween regulrly plnned sites; however, for complex urn geometry, theoreticl comfort cn devite from ctul comfort levels recorded, in prt due to dptive ehviour. Keywords: urn geometry, outdoor therml comfort, ctul senstion vote, PET, ENVI-met INTRODUCTION Unridled urnistion, unplnned growth of uilt environment, cute energy shortge nd elevted ir-pollution levels re common prolems in the high-density tropicl cities locted mostly in the developing countries. Such fctors hve dverse consequences on cities microclimte, consequently ffecting comfort levels in urn outdoor spces s well s energy performnce in urn uildings. Considering the socio-economic context of these cities, the most effective nswer to the deteriorting urn micro-climte cn e chieved mostly through proper urn plnning nd urn design. Especilly, modifiction of urn geometry, s n urn plnning tool, cn ply crucil role in meliorting the urn micro-climte. Urn micro-climte is lrgely determined y different components of urn geometry tht includes: configurtion of the streets, uilding heights, density nd seprtion, roughness length nd urn permeility. The effect of these components will vry ccording to the locl climte nd morphologicl context of the concerned re. The existing knowledge mostly concentrtes on the Western (usully colder) countries nd thus the strtegies pplied to improve their urn micro-climte re not suitle for use in tropicl cities. Studies concerning tropicl cities re still very limited. Therefore, insights from these cities could e CISBAT - Septemer 9-, - Lusnne, Switzerlnd 89

vlule towrds mking them more livele nd resilient, so tht they re le to ct ppropritely in response to potentil chllenges. The study summrises finding from therml comfort field-survey nd compres this with numericl nlysis. Numericl modelling nd computer simultion techniques re plying incresingly importnt roles in current studies for predicting urn microclimte. Urn microclimte is complex consequence of different prmeters which involves innumerle nturl nd urn processes. Due to the complexity of diverse processes involved ehind different microclimtes, numericl methods re ecoming more cceptle now--dys. However, the ppliction of physicl dt from the models for predicting pedestrin therml comfort conditions is rther new re of reserch nd could e useful tool for compring etween different sites which hve vrile urn morphology. Therefore, in this study theoreticl comfort model hs een compred ginst ctul therml comfort level. Previous studies in this field hve compred theoreticl comfort index (PMV, PET) with ctul comfort, ut using on-site microclimte dt insted of simulted dt [,]. The methodology followed in this study could e pplicle for understnding outdoor comfort conditions for virtul environments for still unuilt res t the design phse. SITE SELECTION AND METHOD The study focuses on the tropicl megcity Dhk. The city flls under tropicl Monsoon climte with distinct wrm-humid riny seson, hot-dry summer nd short cool-dry or winter seson. The men nnul temperture is.8 C with n nnul rnge etween 8. C to 9. C. The men nnul reltive humidity is 7%. Figure. Typicl forml res: )FRA EW, ) FRA EW, c) FRA NS Figure. Typicl trditionl res: )TRA EW, ) TRA NS, c) TRA NS Two sets of residentil settlements: trditionl nd forml, were selected for the study. Tle lists the site nmes, revitions nd their common geometric chrcters. In generl, forml residentil res, which evolved from urn plnning regultions, re chrcterised with uildings of equl height nd width, with rods lid out in grid-iron pttern (Fig ). Trditionl residentil res on the other hnd, mostly resulted from spontneous developments under loose plnning controls; hve vrile uilding forms, heights, plot sizes nd even different uilding usge (Fig ). While oth settlements hve compct design, high H/W rtio (uilding height/ street width) nd lck of vegettion, the former (forml) is mostly uniform nd the ltter is quite diverse nd vrile. Mesurements were crried out in north-south (NS) nd est-west (EW) oriented streets in two trditionl nd two forml sites during the hot-humid month in Septemer. These included ir-temperture (T ), humidity (RH), gloe temperture (T g ), men rdint temperture (Tmrt) nd windspeed c c 896 CISBAT - Septemer 9-, - Lusnne, Switzerlnd

(V). Instruments used in the study were: tiny-tg ir-temperture nd humidity dt loggers nd OM-CP-WINDA dt logger with -cup nemometer. Gloe temperture ws mesured using Tiny-tg dt-loggers with thermo-couple thermistor proe inserted inside mm (D= di=.m) gloe pinted in Humrol mtte grey (ε = emissivity =.97). Susequently, Tmrt ws mesured using the following formul: Tmrt = A questionnire survey ws crried out long with physicl mesurements mong 9 people. Pedestrins were sked out their therml senstion. The ctul therml senstion vote ws nlysed ccording to ASHRAE seven point therml senstion scles []. Typicl vlues from site mesurements were used to set up the oundry conditions for the micro-climte simultion tool ENVI-met. ENVI-met is numericl microclimtic tool with high temporl nd sptil resolution tht is le to recrete the mjor microclimtic processes inside complex urn rrngements []. In order to exmine comfort conditions in outdoor spces, this study dopted PET (Physiologiclly Equivlent Temperture) []; widely used therml comfort index sed on the Munich Energy-lnce Model for Individuls (MEMI). The simulted climtic dt clculted y Envi-met tht included T, RH, Tmrt nd V ws used s n input for PET clcultions in Rymn Pro [6]. 8 6 9 8 7 6 Air-temperture FRA EW FRA NS TRA EW TRA NS FRA EW TRA NS Simulted mesurement :: :: :: Figure : Simulted versus on-site mesurements of ) ir-temperture, ) humidity :: :: :: :: 6:: 6:: 7:: 7:: 7:9:9 Humidity FRA EW FRA NS TRA EW 9 8 7 6 8:: 8:: 9:: 9:: :: :: :: :: TRA NS FRA EW TRA NS 9 8 7 6 Simulted mesurement :: :: :: :: :: :: :: :: 9 8 7 6 9 8 7 6 RESULTS Micro-climtic simultions using ENVI-met for the hot-humid climte of Dhk is vlidted through the current study y compring ctul on-site mesurements with the simulted mesurements of the climtic vriles. Comprison of irtemperture, humidity nd Tmrt led to the conclusion tht simultion results were in good greement with ctul mesurements (Fig., Fig ). Only exception ws FRA NS where humidity nd Tmrt ws over estimted y simultion. This cn explined y the fct tht simultion models were kept s simple s possile due to their long running time. Therefore, due to their simplicity, the exct chrcter, numer nd position of plnts re not identicl to the ctul sites. Plnt sizes nd their positions seem to hve ffected the humidity nd Tmrt levels. Another nomly ws identified regrding windspeed in trditionl res tht re more diverse in chrcter (TRA EW, TRA NS). Simulted results, in this cse, devited quite CISBAT - Septemer 9-, - Lusnne, Switzerlnd 897

extensively from the ctul vlues. It is one of the model limittions tht the windspeed nd direction t the model oundry remins constnt throughout the simultion period lthough this is modified inside the model depending on the presence of dimensionl ojects. This indictes the clcultion of windspeed using ENVI-met cn e somewht compromised for very complex urn geometry. It is lso importnt to rememer tht simultions tools re minly for understnding the trend of microclimte, rther thn generting ctul numers. However, the model is not solely ccountle for the devition. Most other micro-climtic sites in the city were found to hve very low windspeed, while, the site in question ws reported with high turulence during the survey. Therefore, none of the other sites were ffected y the fct. The reson why windspeed ws higher in the prticulr site is due to the fct tht the site is locted next to n ndoned irport, mking the north-west side of the re totlly open. This mkes the wind-pttern in the re rther unpredictle. Accurte windspeed prediction of the re will men modelling of entire the urn district in very high resolution. The necessry modelling time nd computer power is eyond the scope of this reserch. 6 6...... 6..... TMRT FRA EW FRA NS TRA EW 6 TRA NS FRA EW TRA NS 6 Simulted mesurement Figure : Simulted versus on-site mesurements of ) Tmrt, ) windspeed 6 6 Windspeed FRA EW FRA NS TRA EW..... 8:: 8:: 9:: 9:: :: :: :: :: TRA NS FRA EW TRA NS. 6..... Simulted mesurement :: :: :: :: :: :: :: ::.......... PET ws compred with ASV for ll cse-study res nd moderte (spermn s rho =.8) ut significnt correltion (p-vlue =.88e-) ws found. This finding suggest theoreticl comfort clcultion will follow the similr trend s the ctul comfort senstion of the pedestrins, ut the ltter my not e fully explined y physicl conditions only. Afterwrds, PET ws clculted seprtely for the trditionl nd forml res. For forml res stronger (spermn s rho =.8) nd significnt (p-vlue <.e-6) correltion ws seen etween PET nd ASV. This is due to good greement etween micro-climte vriles in simulted models nd ctul mesurements. Also, the comprtively simpler geometry in the forml res ided nlysis nd understnding of the outdoor comfort conditions through theoreticl clcultions. Within trditionl res, especilly in TRA EW, TRA NS, simultion model ws still le to predict the micro-climtic vriles quite competently except for the windspeed, s discussed previously. Windspeed is n importnt prmeter for outdoor therml comfort nd ws somewht compromised in the micro-climtic simultions. Since, simulted windspeed ws lower in cse of TRA EW nd TRA NS nd higher in TRA NS thn the ctul vlues (Fig. ) PET ws slightly overestimted in the first two cses nd under-estimted in the third cse respectively. 898 CISBAT - Septemer 9-, - Lusnne, Switzerlnd

MICRO-CLIMATE SITE NAME ABBREVIATE D NAME H/W RATIO TRADITIONAL RESIDENTAL AREA EAST-WEST_ SOUTH KAFRUL TRA EW.6.77 TRADITIONAL RESIDENTAL AREA NORTH-SOUTH_ SOUTH KAFRUL TRA NS.. TRADITIONAL RESIDENTAL AREA NORTH-SOUTH _ MID KAFRUL TRA NS..9 FORMAL RESIDENTIAL AREA EAST-WEST_MAHAKHALI DOHS FRA EW.. FORMAL RESIDENTIAL AREA EAST-WEST_BARIDHARA DOHS FRA EW.8.9 FORMAL RESIDENTIAL AREA NORTH-SOUTH _BARIDHARA DOHS FRA NS..9 Tle. Site nmes, revitions nd urn geometry chrcters Susequently, sttisticl nlysis in the trditionl sites etween PET nd ASV produced wek (spermn s rho =.8) ut significnt (p vlue =.) correltions. Aprt from the physicl microclimte, ASV seems to e devited from PET for the effect from therml dpttion s well. The rods in these res eing quite nrrow nd deep were le to cut down lrge mount of solr rdition. However, other fctors like higher trffic nd sence of pvements my hve ffected the ASV in TRA NS, while the other two streets (TRA EW, TRA NS) were not ffected due to lower trffic. Therml senstion PET rnge Cold -8 Cool 8- Slightly cool -6 Neutrl 6- Slightly wrm - Wrm -8 Hot 8- Very hot < Tle. PET rnge for Tiwn SVF PET ll site ASV_ll site 6 8 Cold Cool Slightly Neutrl Slightly Wrm Hot Very cool wrm hot Figure : Comprison of ASV nd PET (percentge) ll sites () Figure 6: Compre pek therml senstion in ech site for PET() nd ASV() nlysis For the hot-humid climte of Dhk, comfortle tempertures for outdoor conditions rnges from 8. C to C t n verge reltive humidity of 7% under still ir conditions for people wering typicl summer clothes (. to. Clo) nd involved in sedentry ctivities [7]. This comfort rnge is not ctegorised for PET index. In the sence of PET rnge for Dhk, the scle developed for Tiwn (wrm-humid su-tropicl region) hs een used in this study [8]. The PET dt ws rrnged ccording to the PET rnge nd ASHRAE seven point therml comfort scle nd then compred with the ASV dt collected through the questionnire survey. The comprison of shows tht in oth nlyses most people were found to e feeling slightly wrm : % for ASV nd % for PET nlysis (Fig ). However, the PET nlysis slightly overestimtes people feeling wrm nd hot nd highly overestimtes 8 7 6 Neutrl Slightly wrm Wrm Hot Very hot () CISBAT - Septemer 9-, - Lusnne, Switzerlnd 899

people feeling very hot. In the ctul survey, none of the sujects reported feeling very hot. The pek therml senstion for oth ASV nd PET nlysis on site y sis re lso compred to ech other (Fig 6). Therml senstion ws over estimted for ech of the sites y PET nlysis, except TRA NS. For exmple, the pek therml senstion for TRA EW, TRA NS nd FRA EW were neutrl. But this hs een replced y wrm, slightly wrm nd slightly wrm respectively. It is nticipted tht the rod conditions, pvements nd trffic, s mentioned efore, hve further modified the therml comfort levels prt from the micro-climte. The other forml res FRA EW nd FRA NS were highly overestimted y PET, especilly, for the est-west streets, lthough the micro-climte ws quite ccurtely predicted in the simulted model. The use of PET rnge from different city my hve ffected the results to some extent. This still indictes, theoreticl comfort lrgely ignores the therml dpttion level of the pedestrins in tropicl climte. CONCLUSION Numericl simultions in this study were found to e in good greement with ctul microclimte mesurements. Theoreticl comfort clculted using simulted dt, on the other hnd produced mixed results depending on the site geometry. For simple urn geometry in the forml res, the results were strongly ligned with ctul mesurements, lthough overestimted. For complex geometry in the trditionl res, poor correltion ws reported nd the results devited significntly. This indictes, s long s microclimtic simultions re closely correlted with ctul mesurements, theoreticl comfort (PET) will follow similr pttern s the ctul comfort (ASV). However, this does not men PET vlues will e identicl to the ASV vlues. In fct, for most of the microclimtes sites PET ws overestimted in reltion to ASV. Previous studies hve lso demonstrted tht solely physiologicl pproch is insufficient to understnd comfort conditions outdoors []. This suggests tht theoreticl comfort models cn e pplicle for otining reltive understnding of comfort situtions t urn outdoors; however, they cn vry considerly from ctul therml senstions due to the role of therml dpttion. REFERENCES. Mrilen, N.: Therml comfort in outdoor urn spces (Doctorl disserttion, University of Cmridge), 998.. Rjpksh, I. nd Rthnyk, C. T.: Therml cceptility for urn prks in tropics: Evluting the effects of environmentl ttriutes on user perceived controls. Proc. of the 8th Windsor Conference, London,.. ASHRAE Stndrd :therml environmentl conditions for humn occupncy, ASHRAE Inc., Atlnt, 99.. Ali-Toudert, F.: Dependence of outdoor therml comfort on street design in hot nd dry climte (Doctorl disserttion, Universitätsiliothek Freiurg),.. Höppe, P.: Het lnce modelling. Experienti, Vol 9, pp 7-76, 99 Mtzrkis nd Rutz 6 6. Mtzrkis, A. nd Rutz, F.: Modelling the therml ioclimte in urn res with the RyMn Model. Interntionl Conference on Pssive nd Low Energy Architecture, 6. 7. Ahmed, K. S.: Comfort in urn spces: defining the oundries of outdoor therml comfort for the tropicl urn environments. Energy nd Buildings, Vol (), pp -,. 8. Lin, T, et l.: Shding effect on long-term outdoor therml comfort, Building nd Environment, Vol (), pp -,. 9 CISBAT - Septemer 9-, - Lusnne, Switzerlnd