Department of Architecture and Civil Engineering Graduate School of Science and Engineering, Saga University, Saga, Japan 2

Transcription

1 Proceedngs of Buldng Smulaton 011: 1th Conference of Internatonal Buldng Performance Smulaton Assocaton, Sydney, 14-1 ovember. DEVELOPMET OF PASSIVE DESIG TOOL USIG 3D-CAD COMPATIBLE THERMAL SIMULATIO -PREDICTIO OF IDOOR RADIATIO EVIROMET COSIDERIG SOLAR SHADIG BY SURROUDIG TREES AD BUILDIGS- Kazuak akaohkubo 1 and Akra Hoyano 1 Department of Archtecture and Cvl Engneerng Graduate School of Scence and Engneerng, Saga Unversty, Saga, Japan Department of Envronmental Scence and Technology, Interdscplnary Graduate Scence and Engneerng, Tokyo Insttute of Technology, Yokohama, Japan ABSTRACT In ths paper, a smulaton tool for passve desgn consderng ndoor and outdoor radaton envronment usng a three-dmensonal computeraded desgn (3D-CAD) system s developed. Ths tool predcts surface temperature dstrbuton on ndoor and outdoor surfaces of a buldng consderng the spatal geometry, materals used, and solar shadng. A radaton model algorthm wth a hghresoluton voxel model was developed to calculate surface temperature dstrbuton and mean radant temperature (MRT) dstrbuton whle consderng the detaled spatal desgn. The results of the applcaton of ths developed tool to a passve desgn housng usng drect heat gan and decduous tree cover confrmed that ths smulaton tool s useful for evaluatng the effect of passve desgn on the thermal envronment at the desgn stage. ITRODUCTIO In recent years, sustanable archtecture has ncreasngly attracted attenton because of global envronmental ssues. As a sustanable desgn method, passve desgn s an alternatve approach for ensurng thermal comfort condtonng nsde buldngs by takng advantage of local clmatc condtons, whle lowerng energy consumpton. To generate an effectve passve archtectural desgn, desgners should consder the effect of ther passve desgn on the thermal envronment of a buldng. To ths end, there are many buldng smulaton tools such as EnergyPlus, equest, and Energy-10 as well as studes on passve desgn support tools such as the one by Abraham (009). These buldng smulaton tools smulate room temperature, heat load, and energy consumpton of a buldng. However, most prevous studes have not focused on smulatng the nfluence of the desgn of outdoor and ndoor spaces on the thermal envronment of a buldng. We argue that t s mportant to predct the nfluence of the desgn of ndoor and outdoor surfaces on the surface temperature dstrbuton of a buldng. The surface temperature of a buldng nfluences the local radatve envronment and ar temperature. Furthermore, surface temperature has a drect relatonshp wth archtectural desgn parameters such as materal poston, materal types, and spatal geometry of a buldng. In other words, the detaled spatal geometry of a buldng decdes ts poston wth respect to the sun, and therefore, the amount of solar radaton n the room, and the buldng materal decdes the thermophyscal propertes such as heat capacty and coeffcent of thermal conductvty. Thus, t s mportant to create the passve solar desgn consderng not only the archtectural desgn but also the surface temperature dstrbuton. In ths paper, we developed a smulaton tool for passve desgn that takes nto account the ndoor and outdoor radaton envronments. Ths tool predcts surface temperature dstrbuton on ndoor and outdoor surfaces and the mean radant temperature (MRT) dstrbuton consderng spatal geometry, buldng materal, and solar shadng due to surroundng objects such as trees, other buldngs. Ths tool uses an all-purpose three-dmensonal computer-aded desgn (3D-CAD) software package as the pre-post processor because 3D-CAD would be qute useful to archtectural desgners and developers as practcal smulaton tools. PASSIVE DESIG TOOL COCEPT The followng three features are mportant consderatons n developng the passve desgn tool that allows archtects to numercally smulate the effects of ther passve desgns. (1) The passve tool should predct the thermal nfluence of passve desgn of a buldng The effects of passve desgn such as drect heat gan, Trombe's wall, solar shadng by decduous trees and so on, on ndoor thermal radatve envronment depend on spatal geometry, materal poston and materal types. Thus, t s mportant to evaluate the nfluence of dfference n these desgns on thermal radaton envronment. In ths tool, the heat balance on the surface s smulated usng hgh resoluton voxel mesh models. Ths tool evaluates the mpact of the desgn proposed buldng on thermal comfort wthn the buldng n terms of two ndces. The two ndces for evaluatng the thermal radant envronment are surface temperature dstrbuton and mean radant temperature dstrbuton (MRT). () Input and pre-processng method usng the

2 Proceedngs of Buldng Smulaton 011: 1th Conference of Internatonal Buldng Performance Smulaton Assocaton, Sydney, 14-1 ovember. 3D-CAD system and the graphcal user nterface (GUI) To create passve desgn archtecture, desgners estmate the effects of a proposed desgn on the thermal envronment nsde the buldng at both the plannng and the desgn stages. Thus, pre- and post processng such as nputtng calculaton data, messng, and vsualzaton of calculaton result, obtaned from the 3D-CAD system. (3) Vsual expresson of the calculaton results Redesgnng a proposed buldngs desgn accordng to calculaton results leads to a more effectve passve desgn. Thus, t s mportant to express comprehensbly the calculaton results vsually n order to understand and evaluate the effects of spatal geometry and materals on the thermal radatve envronment around a buldng. Makng buldngs model usng 3D-CAD software Buldngs, room, trees and so on Spatal Component Datadatabes Buldng: structure, materal member and so on Tree:speces, solar transmttance and so on Ground: ground cover, materals and so on Materal Datadatabes Physcal propertes of materal: heat conductvty, volumetrc specfc heat, solara reflectance, longwave emttance Heat Transfer Calculaton Model Database rooftop lawn, vy covered wall, louver and so on Transformng 3D-CAD model nto Voxel model for calculaton Heat balance calculaton for each voxel Drect solar radaton Sky solar radaton consderng solar radance dstrbuton Reflected solar radaton (Specular, Dffused) [Multple reflecton] C A L C U L AT I O O F S U R F A C E TEMPERATURE DISTRIBUTIO O IDOOR SURFACES The developed tool allows desgners to evaluate the thermal radatve envronment by enablng them to vsualze surface temperature dstrbuton and MRT usng 3D-CAD. The sad tool bulds on the prevous outdoor thermal smulaton model (Takash A et al., 007) by predctng the ndoor surface temperature dstrbuton as well. The fundamental algorthm of ths smulaton model was constructed n a prevous study by the authors. The calculaton process and the algorthm used n the developed tool are descrbed n the followng paragraphs (Fgure. 1). Atmospherc radaton (outdoor) Convectve heat transfer ( the assumpton that there s no dstrbuton of ar temperature and wnd velocty) Claculaton of surface temperature (1-dmentonal heat conducton, the unsteady statc heat conducton) Input method of calculaton data from 3D-CAD Fgure. llustrates nput and pre-processng usng the 3D-CAD software nterface. A target buldng for calculaton, the buldngs and trees near the target, and ground geometry are generated usng 3D objects n 3D-CAD. Smultaneously, the room that s nvestgated to evaluate the effect of passve desgn on the thermal radatve envronment s drawn. Users can nput or select component materals and buldng members such as walls, roofs, and veranda from varous dalog boxes and databases. These materal nformaton lnk databases whch store the parameters for the heat transfer calculaton ncludng the physcal propertes of materals and the heat transfer calculaton models. Voxel mesh generaton method The 3D-CAD models generated by the above process are then transformed nto a 3D-voxel mesh model that ncludes the calculaton parameters requred for heat transfer analyss (Fgure 3) accordng to the procedure descrbed n the followng paragraph. The 3D-CAD model s sectoned horzontally at a certan heght, and a horzontal secton of the CAD model s then generated. The D fgure data of the secton s then transformed nto mesh data. Ths Dsplay of surface tempearuture dstrbuton on 3D-CAD Long wave radaton MRT dstrbuton at a heght of 1.5m Fgure 1 Flow of ths tool Renderng Wreframe Users nput buldng data, ncludng spatal geometry, materal poston and type, trees, and ground types,. In addton, they nput a smulaton target room, ncludng spatal geometry, materal poston and type usng 3D-CAD Fgure 3D-CAD model

3 Proceedngs of Buldng Smulaton 011: 1th Conference of Internatonal Buldng Performance Smulaton Assocaton, Sydney, 14-1 ovember. process s repeated automatcally from the bottom to the top of the CAD model; the step nterval for ths process s the mesh sze. Thus, the 3D-voxel mesh model s generated. The calculaton pont s set for all of meshes, and the calculaton parameters (component materals, normal to the mesh surface, etc.) nput durng the aforementoned process are automatcally stored n the 3D-mesh model. Tree mesh models are also generated by the same process. Heat balance calculaton Fgure 4 shows the heat balance calculaton (1) Solar radaton calculaton () Drect solar radaton The amount of drect solar radaton receved by a voxel s smulated usng the ray-tracng method. The ray-tracng s carred out toward the solar poston from a voxel. If ray tracng s nterrupted by other voxels that have no transmssve attrbute, the ray tracng s stopped. However, f the ray tracng nterrupted s by a voxel that has the transmssve attrbute, such as a glass wndow and tree crown, the ray-tracng contnues after takng nto account the nfluence of the transmttance of materals on solar radaton. The ray-tracng contnues untl the ray extends outsde the calculaton area. If the ray extends outsde a calculaton area, the amount of solar radaton s calculated usng the relatonshp between the solar poston and the normal drecton of the voxel. () Sky solar radaton The amount of sky solar radaton s calculated by consderng sky solar radance dstrbuton. In the developed smulaton tool, the sky solar radance dstrbuton s expressed by means of the all-sky model-r, whch was developed by IGAWA (oro I et al. 004). The followng steps are nvolved n the process of determnng the amount of sky solar radaton by runnng a mult-tracng smulaton orgnatng from the voxel n multple drectons bound wthn a hemsphere. Frst, the tracng drecton s establshed such that the tracng densty (nterval) comes to have the same form (fgure 5). Then, ray tracng s carred out along the tracng drecton. The ray-tracng s performed usng the same algorthm as that used for drect solar radaton. If the ray extends outsde the calculaton area, the sky radance s calculated usng the all sky model-r. Fnally, the sky solar radaton s calculated by summng up the sky radance along each tracng drecton. () Reflected solar radaton The reflected solar radaton calculated by our tool ncludes both specular reflecton and sotropc dffuse reflecton. Specular reflectve radaton s calculated such that the tracng smulaton toward the drecton of the specular reflecton s mplemented, and the amount Data stored 3D-Voxel a)ormal drecton b)materal property Optcal reflectance Optcal transmttance Solar reflectance Solar transmttance Heat conducton Volumetrc specfc heat Fgure 3 3D-voxel model Sky solar radaton (consderng solar radance dstrbtuon ) Heat balance on a surface asu (cosθ IDR + IΦSR ISR +)IRR ) q = aqsu=(cosθ IDR + Φsky IRR sky+ n +s Φsky σta4 a + b e + s Φ σt4 s σts4 +αc (Ta Ts ) Drect solar radaton Convectve heat transfer Transmtted solar radaton Reflected Solar radaton (Dffused,Multple) Buldng o dstrbuton of room temp. and wnd heat conducton velocty transfer Buldng o dstrbuton of ar temp. and wnd velocty Reflected Solar radaton (Dffused, Multple) Long wave radaton Reflected Solar radaton (Specular) Long wave radaton q T asu : Amount of heat conducton nto surface [W/m ] : Temperature [K] : Solar absorptvty θ : Incdence angle of drect solar radaton [rad] IDR : Amount of drect solar radaton [W/m ] : Shap modulus [sky : sky factor] Φ ISR : Amount of sky solar radaton [W/m ] IRR : Amount of reflected solar radaton [W/m ] : Longwave emttance ε 4 : Stefan Boltzmann constant [W/m K ] cσ a,b : Constant on Brunt's formula : Water vapor pressure near the ground [Pa] e α : Convectve heat transfer coeffcent [W/m K] s(subscrpt) : Surface a(subscrpt) : Atmosphere n(subscrpt) : The total number of objects whch emt long wave radaton Ground Fgure 4. Heat balance calculaton =1

4 Proceedngs of Buldng Smulaton 011: 1th Conference of Internatonal Buldng Performance Smulaton Assocaton, Sydney, 14-1 ovember. of reflected solar radaton s allotted to the voxel at =1 whch the tracng termnates. The specular reflecton consders the frst reflecton. The dffuse reflectve radaton s estmated under the assumpton of sotropc dffuse reflecton, followng Lambert s cosne law, and the amount of dffuse reflectve radaton ncdent on a voxel s calculated by performng mult-tracng smulatons drected toward surroundng voxels. The method used for [] performng the mult-tracng smulaton s the same as that used for estmatng the sky solar radaton. In ths tracng process, f trace hts a voxel wth a dffuse =m reflecton surface, then the amount of radaton reflected by that voxel s obtaned. Ths tracng s mplemented along multple drectons to estmate Fg.3Establshment of tracng drectons the total amount of radaton receved from the m= π+1 surroundngs. Dffuse reflecton consders multple reflecton untl the amount of reflected solar radaton n[] = π ( 1) by a voxel s less than 10W/m n each reflecton. 1 ()Long-wave radaton calculaton φ[] = cos 1 ( ) m The amount of long-wave radaton s calculated π accordng to the followng steps. Frst, the heat θ[] = n[] balance of each voxel s smulated by assumng that the surface temperature of the surroundngs s : Total number of tracer equal to the room temperature. Secondly, long-wave m : Dvson number for elevaton angle (round off) n[] : Dvson number for horzontal angle (round off) radaton receved from the surroundngs s smulated φ[] : Elevaton of the tracng for dvson (rad) based on surface temperature approxmated n the : Horzontal dvson angle for tracng (rad) Δθ[] frst step. Fnally, the heat balance of each voxel s Fgure.5 Establshment of tracng drectons calculated agan by usng the results obtaned n the second step, and the corrected surface temperature, whch accounts for the effect of long-wave radaton, s then obtaned. In the developed tool, the mult-tracng smulaton Surface weghtng factor Long wave on the mcro-cube [5] radaton The human drected toward the surroundng voxels s body s weghtng mplemented to determne the voxels that are used to expressed by drecton factor mcro-cube estmate the radant flux from the surroundngs. The front surface 0.9 method used for the tracng smulaton s the same as back surface 0.8 Ap Ap rght sde surface Lsky ) Rhuman = asolar Ib + W (IdR+ Ir )} = + a1{ W (L object ) the method used for the estmatng sky radaton Ib + + LW + I )} + a W (L 1{ sky human (I d r object Shuman Shuman left sde=1 surface 0.15 =1 =1 =1 and dffuse reflectve radaton. Ths calculaton upper surface Rhuman assumes all surroundng subjects to be perfect black under surface M RT = σ bodes wth respect to long-wave radaton. (3) Method for calculatng surface temperature Fgure. Caluculaton of MRT dstrbuton One-dmensonal heat conducton n each spatal component s smulated usng the above-mentoned heat balance data as the boundary condton for both nternal and external surfaces. In ths calculaton, convectve heat transfer (sensble heat flux) s calculated under the assumpton that there s no Weather Wnter clear dstrbuton of ar/room temperature and wnd condton sky day, Tokyo velocty n the target urban canopy and room. The depth of 0m ~ 1.0m eaves backward-dfference method s used for calculatng Floor area 5m the unsteady statc heat conducton. A smulaton wndow sze.0m.0m s run for fve days to obtan a perodc steady-state soluton wth ntal condtons of perodc weather Target Room data. The surface temperature obtaned on the ffth day s used as the output. Fgure.7 House model φ[] θ

5 Proceedngs of Buldng Smulaton 011: 1th Conference of Internatonal Buldng Performance Smulaton Assocaton, Sydney, 14-1 ovember. Post-processng method usng 3D-CAD The voxel data from the surface temperature calculaton results are converted nto surface texture data, and the textures are vsually projected onto the 3D-CAD model generated durng pre-processng. Ths allows the user to understand and evaluate the effects of spatal geometry and materals on the outdoor surface temperature from almost any vewpont. resoluton and the amount of drect solar radaton. It can be nferred from the fgure that a voxel resoluton of less than 5 cm does not sgnfcantly nfluence the smulaton result. Thus, the optmum voxel resoluton s 5 cm, as mentoned above. Identcal results were obtaned n examnatons conducted on other buldngs. Optmum number of tracers n mult-tracng smulaton The ncrease n the number of tracers n the multtracng smulaton used for estmatng the sky vew factor and radatve heat transfer ncreases the calculaton load; therefore, the optmum number of tracers should be determned for practcal use. To ths end, we examne the relatonshp between the number Defference of budget of drect solar radaton [W] Mean radant temperature (MRT) calculaton In the developed tool, the effect of passve desgn on the thermal radaton envronment s evaluated by usng the MRT (Fgure ). The human body s represented by a mcro-cube. The relatonshp of the form factors between a human body and other objects s expressed by the surface-weghtng factor on the mcro-cube accordng to the process developed n a prevous study (Yoshch O et al., 003). The MRT s calculated as per the followng steps. The surface temperature dstrbuton s calculated by above processes. A mult-tracng smulaton drected toward the surroundng walls, celng, and floor surface voxel, s performed to determne the radant flux from the surroundngs to the mcro-cube. The tracng smulaton s performed usng the method used for estmatng long-wave radaton. The radaton ncdent on the human body was calculated; thereafter, the MRT was smulated. In ths paper, the long-wave emttance was set to mm-0mm mm-0mm 30mm-0mm Tme [hour] Fgure.8 Dfference of budget of drect solar radaton for each voxel sze RM SE = n 5984 =1 (Etotal 149 Etotal m) Etotal_5984 : Sky solar radaton[w/m] RMSE : Calculaton error ndex (Root Mean Square Error) : The number of Voxel Etotal_m : Sky solar radaton usng the each tracer number 0 The number of tracer RMSE of Sky solar radaton [W/m] Investgaton of spatal geometry reproducton In ths tool, radatve analyss s carred out by ray-tracng n the voxel space. Consequently, the accuracy of ths radatve analyss depends on the spatal resoluton of the voxel space. Therefore, the relatonshp between the accuracy of the radatve analyss and the reproducton of the spatal geometry s examned. In ths study, a room wth south-facng wndows and leaf cover was chosen as the buldng model (Fgure 7). Usng the method descrbed above, the amount of drect solar radaton transmtted through the glass wndows was calculated for several dfferent spatal resolutons n the voxel space. The voxel resoluton was vared between and 50 cm, and the -cm voxel resoluton was used for the comparson. Fgure 8 shows the relatonshp between the voxel 500mm-0mm 00mm-0mm 100mm-0mm V E R I F I C AT I O O F R A D I AT I V E CALCULATIO PARAMETERS In ths tool, calculaton errors manly occur whle smulatng the amount of solar radaton. The accurate determnaton of the amount of solar radaton depends on the voxel spatal resoluton and the number of tracers n the mult-tracng smulaton. Therefore, n ths secton, we descrbe the optmzaton of the spatal resoluton and number of tracers Calculaton tme [mn] Fgure.9 Relaton between the number of tracer and RMSE of sky solar radaton

6 Proceedngs of Buldng Smulaton 011: 1th Conference of Internatonal Buldng Performance Smulaton Assocaton, Sydney, 14-1 ovember. (1) Summer Fgure 10. 3D-CAD model () Wnter Ar temp.: Ar temp.: () Surface temperature dstrbuton n wnter (1:00) (1) Surface temperature dstrbuton n summer (1:00) Fgure 11. Surface temperatrue dstrbuton at outdoor space (1:00) Room temp.: Room temp.:0.0 () Surface temperature dstrbuton n wnter (0:00) (1) Surface temperature dstrbuton n summer (0:00) Fgure 1. Surface temperatrue dstrbuton at lvng room(0:00) Lvng MRT[ ] MRT[ ] Room temp. :.0 1 Room temp. : 0.0 Plan (1) In summer (0:00) () In wnter (0:00) Fgure 13. Mean radant temperature dstrbuton at lvng room(0:00)

7 Proceedngs of Buldng Smulaton 011: 1th Conference of Internatonal Buldng Performance Smulaton Assocaton, Sydney, 14-1 ovember. of tracers n the mult-tracng smulaton and the calculaton accuracy, usng the sky solar radaton. The buldng model used for ths examnaton s the same as that shown n Fgure 7. The root mean square error (RMSE) ndex s used for determnng the calculaton accuracy. The standard maxmum number of tracers for calculatng the RMSE s more 50,000. The relatonshp between the number of tracers and the RMSE ndex of the sky solar radaton for the entre floor voxel s shown n Fgure 9. The dfference n the RMSE s small when more than 3000 tracers are used. Ths fndng confrms that for the multtracng smulaton, the optmum number of tracers s more than SIMULATIO TOOL APPLICATIO The effectveness of the developed tool n evaluatng the effects of passve desgn on a thermal radatve envronment of a buldng was determned by applyng the tool to a purpose-bult passve solar house. Fgure 10 shows the target passve desgn house. The house has large wndows drected toward the south and a large decduous tree on the wooden deck n front of the wndows. Durng summer, the large tree shades the house from drect solar radaton. In wnter, the leafless huge tree transmts drect solar radaton nto the house. The concrete floor of the aforementoned room has huge heat capacty and can therefore store heat from the ncdent solar radaton durng wnter. The summer and wnter weather condtons used for calculaton were representatve of days wth clear skes n the respectve seasons. Fgure 11 shows the surface temperature dstrbuton n outdoor space durng both summer and wnter (1:00). In summer, the surface temperature of the wooden deck s low because t s shaded by the large tree. However, the surface temperature of the wooden deck durng wnter s the same as that of the ground because the lealfess tree drects the solar radaton to the wooden deck. Fgure 1 shows the surface temperature dstrbuton n the ndoor lvng space durng both summer and wnter (0:00). The surface temperature of the floor n summer s low because the large tree prevents the drect ncdence of solar radaton nto the room durng daytme. However, surface temperature n wnter s hgh because the floor, whch s made of a hgh heat capacty materal, stores the heat from the solar radaton ncdent durng the day. Fgure 13 depcts the MRT dstrbuton at a heght of 1.5 m n the lvng room durng summer and wnter (0:00). In summer, at 0:00, there s no dstrbuton of MRT. In wnter, the value of MRT n the space near the wndow, whch was exposed to solar radaton, s C hgher than that n other spaces because of the heat stage. Ths fndng shows that passve desgn ensures a comfortable radatve envronment durng both summer and wnter. These results reveal that the developed tool s able to smulate the effects of solar shadng by a large tree and drect heat gan on the surface temperature dstrbuton and the MRT. Therefore, ths tool can be used to evaluate the effects of passve desgn on thermal radatve envronment around a buldng. COCLUSIOS In ths paper, we descrbed a passve desgn tool that s capable of predctng the surface temperature dstrbuton and the MRT for both outdoor and ndoor surfaces. To allow for the consderaton of detaled spatal geometry as well as materal postons, materal types, and trees, a radaton analyss algorthm wth a hgh-resoluton voxel model was developed. Then, the smulaton parameters,.e., optmum voxel sze and the number of tracers n the mult-tracng smulaton, were establshed. The results of applyng ths tool for creatng passve desgn archtecture revealed that t was capable of smulatng the effects of passve desgn such as solar shadng of tree, buldng spatal geometry, and materals on the surface temperature and MRT dstrbuton, and that t could be used to study the passve desgn at the desgn stage. In future work, ths system wll be combned wth buldng heat load smulaton for the comprehensve evaluaton of a passve desgn. ACKOWLEDGEMET Ths work was supported by Grants-n-Ad for Young Scentsts (B)(17044). REFERECES Abraham Yezoro, 009. Renewable Energy, Volume 34, pp EnergyPlus, Web homepage ( gov/ buldngs/energyplus) equest, Web homepage ( com) Energy-10, Web homepage ( org/energy10-soft) oro Igawa, Yasuko Koga, Tomoko Matsuzawa, Hrosh akamura, 004. Solar Energy, o. 77, pp Takash Asawa, Akra Hoyano, Kazuak akaohkubo, 008. Buldng and Envronment, Volume 43, Issue 1, pp Yoshch Ozek, Tetsuya Hramatsu, Shn-ch Tanabe, 003. J. Envron. Eng., AIJ, o. 5, pp