A 3D CAD-Based Simulation Tool for Prediction and Evaluation

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www.elsevier.com/locate/solener

Solar Energy 83 (2009) 1064–1075

A 3D CAD-based simulation tool for prediction and evaluationof the thermal improvement effect of passive cooling walls in the

developed urban locations

Jiang He *, Akira Hoyano

Interdisciplinary Graduate School, Tokyo Institute of Technology, 4259-G5-2 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan

Received 2 July 2008; received in revised form 1 December 2008; accepted 14 January 2009Available online 24 February 2009

Communicated by Associate editor: Matheos Santamouris

Abstract

As a passive cooling strategy aimed at controlling increased surface temperatures and creating cooler urban environments, the authorshave developed a passive cooling wall (PCW) constructed of moist void bricks that are capable of absorbing water and which allow windpenetration, thus reducing their surface temperatures by means of water evaporation. Passive cooling effects, such as solar shading, radi-ation cooling and ventilation cooling can be enhanced by incorporating PCWs into the design of outdoor or semi-enclosed spaces inparks, pedestrian areas and residential courtyards. The purpose of the present paper is to detail the development of a 3D CAD-basedsimulation tool that can be used to predict and evaluate the thermal improvement effect in urban locations where PCW installation isunder consideration. Measurement results for the surface reduction effect of a PCW are introduced in the first part of the paper. Inthe second part, thermal modeling of a PCW is proposed based on analysis results of experimental data. Following that, a comparisonstudy that integrates the proposed thermal modeling was conducted to validate the simulation method. In order to demonstrate the appli-cability of the developed simulation tool, a case study was then performed to predict and evaluate the thermal improvement effect at anactual urban location where PCWs were installed. Simulations were performed by modeling the construction location in two scenarios;one where the PCWs were composed of dry bricks, and another where the bricks were wet. The results show that, in terms of surfacetemperature and mean radiant temperature (MRT), this simulation tool can provide quantitative predictions and evaluations of thermalimprovements resulting from the installation of PCWs.� 2009 Elsevier Ltd. All rights reserved.

Keywords: Passive cooling; Void brick; Evaporation; Thermal environment; Surface temperature; Simulation

1. Introduction

Summer thermal environments in urban areas have beendeteriorating as urbanization progresses. This can beunderstood by taking into consideration the environmentalproblems resulting from the urban heat island effect, whichin recent years has had a major impact on only large cities,but also on mid-sized cities and small towns as well. Addi-tionally, the number of very hot days and the number ofpeople suffering from heat stress have increased signifi-

0038-092X/$ - see front matter � 2009 Elsevier Ltd. All rights reserved.

doi:10.1016/j.solener.2009.01.006

* Corresponding author. Tel.: +81 459245510; fax: +81 459245553.E-mail address: [email protected] (J. He).

cantly in recent years. As pointed out in a number ofreports, the latter has something to do with the former. Itis well known that the worsening urban thermal environ-ment is primarily due to the massive amount of artifi-cially-generated heat from human activities as well asfrom the changes in land coverage that occur when naturalcover (such as trees and plants) are replaced by buildingsand pavement.

From the viewpoint of land-coverage changes, the heatingand heat storage effect of pavement and building surfacesresulting from sunlight have been recognized as a majorcause of urban heat island formation. This is because mosttypes of pavement and building exteriors are fabricated from

mailto:[email protected]

Nomenclature

a solar absorptancecp specific heat (J/(kg K))cm humid air specific heat (J/(kg K))D thickness of a brick (m)L latent heat (J/kg)RS solar insolation on the brick surface (W/m2)RL long-wave radiation from the surroundings (W/

m2)t time (h)T temperature (K)x distance in normal to an external surface (m)Xa absolute humidity mixing ratio at temperature

of Ta (kg/kg(DA))Xs absolute humidity mixing ratio at temperature

of Ts (kg/kg(DA))

v air velocity (m/s)

Greek symbols

ac convection coefficient (W/(m2 K))b evaporation efficiency (surface wet ratio)e emissivityk thermal conductivity (W/(m K))q density (kg/m3)r Stefan-Boltzmann constant (W/(m2K4))

Subscripts

a airi windward sideo leeward sides surface

J. He, A. Hoyano / Solar Energy 83 (2009) 1064–1075 1065

materials with low albedo and high thermal retention capac-ities, such as asphalt and concrete. As a result, they absorb agreat deal of solar heat during the day, and their surfacesremain warmer than the surrounding air at night due tothe retained solar energy. This indicates that reducing theheat absorbed by these surfaces, or otherwise lowering theirsurface temperatures, would be an effective method ofimproving outdoor urban thermal environments and miti-gating the urban heat island effect.

As a passive cooling strategy for controlling the increaseof urban surface temperatures and creating a comfortablethermal environment, the authors have developed a passivecooling wall (PCW) constructed of moist void bricks capa-ble of absorbing water (Shirai, Hoyano et al., 1995, Hoy-ano and Shirai, 1995, 1997). A PCW has features thatallow wind to pass through it, and thus reduce its temper-ature by facilitating the evaporation of water stored in thebricks. As shown in Fig. 1, the PCW provides a shadedarea free from direct solar radiation while the PCW surfaceitself can be cooled by evaporation. This results in coolersurfaces in outdoor locations on summer days. Further-more, the air passing through the PCW can be furthercooled when a breeze is blowing. As a result, the followingpassive cooling effects can be created: (1) solar shading, (2)

Fig. 1. Schematic description of a passive cooling wall constructed ofmoist void bricks.

radiation cooling and (3) ventilation cooling. It is expectedthat PCWs will be increasingly installed in outdoor loca-tions or semi-enclosed locations such as parks, pedestrianareas, patios and residential courtyards.

As described in literature (e.g. Givoni, 1994), porousmaterials such as unglazed pottery have long been used toimprove thermal comfort in residential spaces by assistingpassive evaporative cooling. However, previous studies onpassive cooling walls that allow wind penetration are scarce.

In order to investigate the cooling effects of the devel-oped PCW, experiments have been conducted in the labo-ratory and at outdoor locations using mock-ups andprototype walls. The experimental results were documentedin our previous papers (Shirai et al., 1997, 2000, 2002). Thispaper focuses on the development of a numerical simula-tion tool that can be used to predict and evaluate the ther-mal improvement effect in developed urban locations wherePCW installation is under consideration. The measuredresults of surface temperature reductions resulting from aPCW will be introduced in the first part of the paper. Inthe second part, we will describe thermal modeling for pre-dicting external surface temperatures of a PCW. A compar-ison study, in which the proposed thermal modeling wasintegrated, will then be conducted to validate the simula-tion method. In addition, in order to demonstrate theapplicability of the developed simulation tool, a case studywill be carried out to predict and evaluate temperature dis-tributions of all external surfaces in an actual outdoorspace where PCWs have been installed.

2. Description of the PCW

2.1. Void bricks

As shown in Fig. 2, we developed two types of water-permeable void bricks: (1) slit-type brick (Type 1) and (2)open-type brick (Type 2). A slit-type brick has 11 slit-

Fig. 2. Photos and diagrams of void bricks developed by the authors. Fig. 4. Experimental results of cooling effect of the developed bricks.

Table 1Specifications of the developed brick’s material.

Baking temperature 1000 �CDensity in dry condition 1750.55 kg/m3

Density in water-saturated condition 2012.60 kg/m3

Maximum absorbed water content in weight 14.9%

0

50

100

150

200

250

0 1 2 3 4 5 6 7 8 10

Wat

er p

enet

ratio

n he

ight

(mm

)

24 (hour)

Water penetrationheight

water

Brick

Fig. 5. Variation of water penetration height after soaking in water.

1066 J. He, A. Hoyano / Solar Energy 83 (2009) 1064–1075

shaped ventilation channels while an open-type brick hasthree square-shaped channels. The temperature reductioneffect of air passing through a PCW constructed of slit-typebricks is greater than that of the open-type bricks. On theother hand, the volume of air passing through a slit-typePCW is smaller than that for an open-type PCW underthe same inflow condition. To examine the difference ofcooling effect between slit-type and open-type bricks,experiments were conducted in the laboratory using anexperimental setup illustrated in Fig. 3. Fig. 4 shows exper-imental results under the experimental conditions that airtemperature and relative humidity of inflow were kept tobe 32 �C and 40%, respectively. As seen in Fig. 4, the airtemperature were reduced by 3 and 1 �C after passingthrough the slit-type and open-type bricks, respectively.From this result, it can be understood that the temperaturereduction effect for a slit-type PCW is greater than that foran open-type PCW.

Specifications for the developed brick’s material arelisted in Table 1. Fig. 5 shows the variations of water pen-etration height for a brick material sample over a period ofseveral hours. After soaking the bottom of the brick inwater, it took about 3 h for water penetration to reach alevel equal to the height of a standard brick (84 mm).

2.2. Water supply method

A U-shaped steel liner (tray) is sandwiched betweenupper and lower bricks as shown in Fig. 6. The ends of

Fig. 3. Section of experimental setup and locations of measurementpoints.

Fig. 6. Schematic description of water supply method for a PCW.

these liners are connected to a vertical rectangular duct ateach corner of a PCW. Water is supplied into one edge,flows along the liner tray where some of it is absorbed intothe brick bottoms, then out from the other edge. A sponge


is sandwiched between the bricks and the tray. This watersupply method ensures that each brick can be indepen-dently water-supplied, and that the surface of the supplywater will remain stable and at a certain level.

Fig. 8. Diurnal variations of brick surface temperature, ambient dry-bulbtemperature (DBT), wet-bulb temperature (WBT) on a sunny day (Sep. 7).

2.3. Characteristics of surface temperature distribution

Prototype PCWs were constructed on the roof of a two-story building. A thermograph for the PCWs is shown atthe right of Fig. 7. The thermograph was taken at a timewhen the PCWs were completely wet. It can be seen thatthe surface temperature for the south-facing PCW was29–30 �C, which is lower than the dry-bulb temperature(DBT) by 3–4 �C and higher than the wet-bulb temperature(WBT) by 2–3 �C. The surface temperature for the east-fac-ing PCW, which was not exposed to direct solar radiation,was approximately 25 �C, nearly equal to the wet-bulb tem-perature. Fig. 8 shows the diurnal variations of the surfacetemperature on the windward and leeward sides of thesouth-facing PCW on a sunny day. The temperatures indi-cated in Fig. 8 were the results measured by thermocouplesthat provide an accuracy of 0.1 �C. It is obvious that thesurface temperature on the leeward side, which was notexposed to direct solar radiation, was equal to the WBTthroughout the day. The interior surface temperature ofthe brick was also equal to the WBT.

2.4. Water consumption of a PCW

Two slit-type PCWs and one open-type PCW wereused to measure water consumption. These test PCWswere facing south during measurements. Measurementresults of water consumption for a period of four sum-mer sunny days were presented in Fig. 9. From the fig-ure, it can be seen that the maximum of waterconsumption was approximately 35 g/(m2 min). The max-imum of diurnal water consumption was 15 kg/(m2 day)during the measurement period. A significant difference

Fig. 7. The left and right are a photo of PCWs and thermograph

of water consumption between slit-type and open-typePCWs was not found.

3. Numerical simulation

3.1. Methodology

As can be understood from the measurement resultsdescribed above, PCW surface temperatures can bereduced below ambient air temperature by water evapora-tion. In order to predict and evaluate the expected thermalimprovement of a PCW in a developed urban environmentduring design stages, numerical simulations are a necessaryand practical alternative to physical experiments. As adesign tool for supporting the prediction and evaluation

taken at noon on a sunny summer day (Aug. 11), respectively.

(a) Weather conditions

Total horizontal solar radiation

Wind speed Wind direction

Slit-type Slit-type Open-type

(b) Water consumption

1200

1000

800

600

400

200

0

3.0

2.5

2.0

1.5

1.0

0.5

0

45

35

25

15

5

-5

N

E

W

S

N

35

30

20

25

15

10

5

Aug. 9 Aug. 10 Aug. 11 Aug. 12 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00

Wet-bulb temp.Dry-bulb temp.

Fig. 9. Measurement results of water consumption of test PCWs on summer sunny days.


of thermal improvements resulting from the installation ofPCWs, we adapted a numerical simulation method usingthe 3D CAD-based simulation tool that was previouslydeveloped by our research group. A PCW was modeledand a calculation algorithm for its surface temperaturewas integrated into the simulation tool. The simulationmethodology is described below.

3.2. Description of the developed simulation tool

The simulation process is outlined in Fig. 10. The sim-ulation is performed using 3D CAD models for build-ings, trees and other structures in the area beinganalyzed. Three-dimensional spatial forms of the build-ings, trees, etc., and two-dimensional ground surfacesare divided into mesh grids, and thermophysical dataof construction materials, such as albedo and conductiv-ity and solar transmittance, are assigned to the grids. Anautomatic mesh-dividing process has been integrated andonly uniform mesh can be used in the present version ofthe tool. A uniform mesh size of 0.2 m was used in thesimulation.

The external surface temperature for each mesh can becalculated by solving a non-steady-state one-dimensionalheat balance equation in normal to the surface. In the heatbalance equation, three-dimensional radiation irradiatedon the surface is taken into account. The short-wavelengthradiation on the surface is direct solar insolation, sky solarradiation and reflected solar radiation. Reflected solar radi-ation includes both specular reflection and isotropic diffusereflection. Only the first reflected solar radiation is consid-ered in the present study. Atmospheric radiation and long-wavelength radiation from the surroundings are consideredin the long-wavelength radiation irradiated on the surface.Sky solar radiation and atmospheric radiation are calcu-lated from the sky view factor for each mesh.

The sky view factor is calculated by the multi-tracingsimulation from the mesh toward multiple hemisphericaldirections. The tracing direction is established so that thetracing density (interval) comes to have the same shape fac-tor. The sky view factor is estimated by counting the num-ber of tracers reaching the boundary surfaces. The shapefactor for calculating the reflected solar radiation andlong-wavelength radiation from the surroundings is deter-

Fig. 11. Energy flowpaths at the PCW surface.

Fig. 10. Description of the simulation tool.


mined by the same method used in the estimation of the skyview factor.

Convective heat transfer is calculated on the assumptionthat ambient air temperature and wind velocity are uni-formly distributed in the outdoor spaces at the time ofanalysis. This assumption is valid under weather conditionswith low wind velocity. The surface convection coefficientis considered to be a function of air velocity and is givenby Jurges’ equation.

The non-steady-state one-dimensional heat conductionequation for each mesh is solved using the above-men-tioned heat balance data as boundary conditions for exter-nal surfaces. Boundary conditions for internal surfaces arethe indoor air temperature for the buildings and the under-ground temperature for the ground. Rooms on the samefloor of a building are considered to be a single room,and the indoor air temperature is uniformly distributed atthe time of analysis.

The tree shape is modeled as a 3D CAD model and thecrown is composed of meshes containing solar transmit-tance data. Solar transmission radiation decreases as itpasses through the tree mesh model. This mesh modelmakes it possible to quantify the influence of the positionand distance of sunlight passage within the crown on solartransmission. The surface temperature of a tree’s crown iscalculated by empirical formulas derived from the experi-mental data, and can be expressed as a function of the solarradiation incident on the surface, ambient air temperature,and wind velocity (Shimokawa et al., 1996).

The backward-difference method is used for solving thenon-steady-state heat balance equation. One simulation isrun using 5-day weather data in 5-min time steps in orderto obtain a periodic steady-state solution. The simulatedresults of surface temperatures for the 5th day are outputand used for analysis.

As outputs of the simulation, temperatures of all exter-nal surfaces can be predicted and visualized on the 3Dmodels (see the lower left corner of Fig. 10). From the cal-culated results of surface temperatures, mean radiant tem-perature (MRT) at a point can be estimated. The meanradiant temperature at a point is the measure of the com-bined effects of the temperatures of all surfaces that sur-round the point. The larger the surface area is and thecloser one is to it, the more effect the surface temperatureof that surface has on the individual. The MRT at a heightof 1 m above the ground was used to evaluate thermal com-fort in outdoor human activity

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spaces in the present study. A detailed description of thesimulation methodology can be found in Asawa et al.(2008).

3.3. Energy balance equation on the PCW surface

Fig. 11 shows the energy flow on a PCW surface. Non-steady-state one-dimensional heat balance equations forexternal surfaces of a PCW can be expressed by Eqs. 1and 2. The heat balance equation inside the brick is writtenby Eq. 3. In Eq. 1, the left term is the conduction heattransferred into the brick. At the right of Eq. 1, the firstterm is the solar insolation, the second term is the netlong-wave radiation, the third term is the convective heatflux and the fourth term is the latent heat by evaporation.In the latent heat term, evaporation efficiency (b) was usedto express the wetting condition of the brick surface. This isbecause part of the brick surface may become dry due toactive evaporation when exposed to direct solar radiation,causing the surface temperature to rise, as can be seen inFig. 12. The shaded brick surfaces, such as the internal sur-faces in the ventilation channels, can be kept completely

The PCW (Type2,Ratio of openings=48%) Visualization of surface temperature 20cm

openingsBrick

20cm

20cm

Fig. 13. Description of surface temperature calculation method.


wetted. As understood from the above-mentioned measure-ment results, the surface temperature for the shaded bricksurface can be considered to be equal to the wet-bulbtemperature.

Because the simulation methodology is valid under lowwind velocity weather conditions (wind speed less than3 m/s), the wind velocity on the windward and leewardsides of a PCW is assumed to be the same as the inputweather data. The PCW surface temperature is calculatedby solving Eq. 3, using Eqs. 1 and 2 as boundary condi-tions. The brick openings are composed of quadrangle sur-faces as shown in Fig. 13. Each square is 20 � 20 cm andequal to the size of the minimum mesh used in the calcula-tion. Temperatures of the quadrangle surfaces are consid-ered to be equal to the wet-bulb temperature. Thenumber of the squares is determined by the ratio of open-ings to the sectional area of a brick. The ratio of openingsis 34% and 48% for a slip-type and open-type brick,respectively.

3.4. Validation of the simulation method

In order to validate the proposed simulation method, wecarried out a comparison study of the simulated and mea-

Difference between surface temperature and ambient air temperature

420-2-4

68

1012

420-2

-4

6

8

Fig. 12. The top photo shows the test PCWs. The middle and bottom arethermographs of the PCWs that were exposed to direct daytime solarradiation.

sured surface temperatures. Measurements were conductedusing the experimental PCW shown in Fig. 14. A compar-ison study was carried out to determine the evaporationefficiency. Surface temperatures of the experimental PCWwere calculated using the proposed simulation methodunder calculation conditions in which the evaporation effi-ciency was assumed to be a value between 0.0 and 1.0. Theresults of the comparison study showed that strong agree-ment was found between the simulated and measured sur-face temperatures when the value of evaporation efficiencywas between 0.4 and 0.6. As an example, Fig. 15 showsdiurnal variations of simulated and measured surface tem-peratures on a sunny day. The evaporation efficiency wasassumed to be 0.5 in the simulation of surface temperature.Weather conditions for the day are indicated in Fig. 16.Wind speeds were measured below 2 m/s throughout theday.

As shown in Fig. 15, the measured surface temperaturewas slightly different at different measurement points andthe maximum temperature difference was approximately5 �C. The average values of the measured surface tempera-ture for three measurement points ((S1–S3) provided inFig. 14) were compared with the simulated results. The cor-relation between the simulated surface temperature and theaverage measured surface temperature is presented inFig. 17. From an examination of this figure, it can be deter-mined that the simulated surface temperature agreed within

100100

Watertank

660

1008

S1S2S3

588

Measurementpoints

M1M5

M2M3M4

Water supply

Fig. 14. An experimental PCW and locations of measurement points.

10

15

20

25

30

0 2 4 6 8 10 12 14 16 18 20 22 24

Tem

pera

ture

()

Time (hour)

Average of (S1+S2+S3)

Ambient air

S2 (measured)

S3 (measured)

S1 (measured)

Simulated sureface temp.

Fig. 15. Comparison between simulated and measured surfacetemperature.

0

200

400

600

800

10

15

20

25

30

0 2 4 6 8 10 12 14 16 18 20 22 24Time(hour)

Air t

empe

ratu

re (

)

Rel

ativ

e hu

mid

ity (%

)

90

80

70

60

50

4

3

2

1

0

Sola

r rad

iatio

n (W

/m2 )

Win

d sp

eed

(m/s

)

Total horizontal solar radiation

Air temperature

Wind speed

Relative humidity

Fig. 16. Weather data used in the comparison study.

Table 2Thermal properties of the void brick.

Solar reflectance Thermal conductivity(W/m K)

Specific heat(kJ/(kg K))

0.3 0.8 840


2 �C of the actual measured data. The thermal properties ofthe brick used in the simulation are provided in Table 2.

4. Case study

4.1. Description of the analysis object

An actual urban location where PCWs could be installedwas selected for analysis. As shown in Fig. 18, a one-story

10

15

20

25

30

Sim

ulat

ed s

urfa

ce te

mpe

rare

(ºC

)

Measured surface temperature (ºC)

Fig. 17. Correlation between simulated and measured surfacetemperature.

building with a meeting room is located at the North end ofthe location. A tree with a height of 7 m was growing at thecenter of the developed urban location. A roof covered reststation with walls composed of PCWs was constructed atthe South end of the location. Illustrations showing the

Fig. 18. Photos of the actual developed location where PCWs wereinstalled. The top photo is a view from Northwest. The middle photo is abirds-eye view from Southwest. The bottom shows an internal view of therest station from the Southeast.

Fig. 19. Plan (left) and section (right) of the developed location with incorporated PCWs.

Fig. 20. Birds-eye views of 3D CAD models for the developed location with incorporated PCWs.

40

60

80

100

25

30

35

40

Rel

ativ

e hu

mid

ity Absolute humidity

Air temperature

Relative humidity

Abso

lute

hum

idity

g/kg

(DA)

)

0.0 0.5 1.0 1.5 2.0 2.5

0200400600800

1000

0 2 4 6 8 10 12 14 16 18 20 22 24Time hour)

Wind speed

Global solar radiation incident upon a horizontal surface

Win

d sp

eed

m/s

)

Sola

r rad

iatio

n W

/Te

mpe

ratu

re

Fig. 21. Weather conditions for a sunny summer day (Aug. 5) in Tokyo.


design and layout of the rest station are provided inFig. 19. 3D CAD models for the location are shown inFig. 20.

4.2. Simulation results

The developed location was modeled in two scenarios:(1) Case 1 stipulates that the PCW was composed of drybricks (without the evaporative cooling effect) and (2) Case2 stipulates that the PCW was composed of wet bricks.Simulations were performed using hourly weather datafor a typical sunny summer day (August 5) in Tokyo.

The input weather data is for a reference weather year,and was prepared based on data provided by the Transac-tions of the Society of Heating, Air-Conditioning and San-itary Engineers of Japan. The reasons for choosing this dayare as follows: (1) high air temperature, (2) low wind speedthroughout the day, (3) high solar radiation intensity (clearsky) during the daytime, and (4) cloudy sky at night (cool-ing by nocturnal radiation is reduced). Urban heat islandsform easily during the day. Diurnal variations of air tem-perature, relative humidity, wind speed and solar radiationare shown in Fig. 21.

Fig. 22 shows the simulated surface temperature distri-bution for both cases at three different times (09:00, 12:00and 15:00). At 09:00, the surface temperature of the drybrick wall that was not exposed to direct solar radiationwas nearly equal to the ambient air temperature, whereasthe surface temperature of the wet brick wall was severaldegrees lower than the ambient air temperature. At 12:00and 15:00, the surface temperatures of the dry brick wallexposed to direct solar radiation rose above 40 �C and werehigher than the ambient air temperature by 5–10 �C. Thesurface temperature of the wet brick wall, on the otherhand, remained below the ambient air temperature. Ascan be seen at the lower right corner of Fig. 22, the groundsurface in the rest station with a roof was also kept at alower temperature by the surrounding PCWs.

Fig. 23 shows diurnal variations of the brick surfacetemperature for points P1 and P2 indicated in Fig. 19. P1and P2 were set at a height of 1 m above the ground. Asseen in Fig. 23, in Case 2 (with wet brick walls) the surface

Fig. 22. Simulation results of surface temperature distribution for the dry (left) and wet (right) brick walls.


20

25

30

35

40

45

50

0 2 4 6 8 10 12 14 16 18 20 22 24

Tem

pera

ture

(ºC

)

Time (hour)

P1 (wet brick surface)

Ambient air

P2 (dry brick surface)

P2 (wet brick surface)

P1 (dry brick surface)

Fig. 23. Diurnal variations of dry and wet brick surface temperature.

Fig. 24. Comparison of MRT at 1 m above ground for the cases with dry(top) and wet (bottom) brick walls.


temperature (P1) of the Southeast-facing brick remainedlower than the ambient air temperature throughout theday. Furthermore, the former was 5 �C lower than the lat-ter during the daytime. The surface temperature (P2) of thesouthwest-facing wet brick wall was about 1 �C lower thanthe ambient air temperature, except during the period of13:00–17:00. During the period of 13:00–17:00, the surfacetemperature (P2) of the wet brick went higher than theambient air temperature because the brick surface wasexposed to direct solar radiation.

In order to thoroughly comprehend the thermalimprovement of the PCWs on thermal comfort in thedeveloped location, the mean radiant temperature (MRT)at a height of 1 m above the ground was used as an evalu-ation index. The simulated results of the MRT distributionfor Case 1 and Case 2 at 12:00 are shown in Fig. 24. TheMRT for Case 2, (wet brick walls), was 2–3 �C lower thanthat for Case 1 (dry brick walls). Furthermore, from thelower thermal image seen in Fig. 24, it can also be statedthat the MRT near the wet brick walls was the lowestand measured 2–4 �C less than the ambient airtemperature.

5. Conclusions

In order to predict and evaluate the thermal improve-ment effect in a developed urban location where applica-tion of a passive cooling wall (PCW) is under designstage consideration, a numerical simulation method wasdeveloped and presented in this paper.

A PCW was constructed of moist void bricks and wasfound to be capable of providing the following passivecooling effects: solar shading, evaporative cooling and ven-tilation cooling. Our measured results show that the day-time surface temperature of the PCW that was exposedto direct solar radiation was lower or slightly higher thanthe dry-bulb temperature, and that the surface temperaturefor the PCW that was not exposed to direct solar radiationwas nearly equal to the wet-bulb temperature when thePCW was completely wet.

Based on the above-mentioned measurement results, athermal model for calculating the surface temperature ofa PCW was proposed. The calculation algorithm basedon the proposed thermal model was integrated into a 3DCAD-based simulation tool previously developed by theauthors’ group. An examination of a comparison betweenthe simulated and measured results for a test PCW deter-mined that the simulated surface temperature of thePCW agreed with the actual measured data within a rangeof 2 �C.

Furthermore, a case study was conducted to predict andevaluate the thermal improvement of PCWs on the envi-ronment of an actual developed location. Simulations wereperformed by modeling the developed location in both wetand dry scenarios. The surface temperature reductionscaused by the PCWs and the places where a cooler radiantenvironment was formed in the examined installation loca-

tion can be visually understood by comparing the simula-tion results of the two cases.

In conclusion, in terms of surface temperature and meanradiant temperature (MRT) distribution, the authorsfound that the developed simulation tool can be used dur-ing design stages to evaluate the thermal improvementsthat might result from installation of PCWs in developedurban environments.

6. Final remarks

The main goal of the study presented in this paper is todescribe a simulation tool for quantifying the improvementeffect of the PCW on the thermal radiation environmentfrom surface temperature reductions. Except the radiationcooling effect, the PCW can also provide air temperaturereduction effect and ventilation cooling effect as well. In


order to evaluate these effects, a coupled simulationmethod is being developed (Kakuya et al., 2007). This cou-pled simulation method makes it possible to predict solarand thermal radiation, airflow and humidity distribution.However, the calculation load is too great (the computingtime is too long) to carry out the coupled simulation on aPC at the present time. It still requires a lot of researchand development efforts to integrate the coupled simula-tion method into a design tool that can be used by a generaldesigner. In such situation, the simulation tool proposed inthis paper is very useful for the designers who require aquick analysis of the improvement effect by the differenceof surrounding materials and spatial forms on the thermalradiation environment during the design phase.

Acknowledgement

This work was in part supported by the New Energy andIndustrial Technology Development Organization of Japan(NEDO) under Contract No. 0827001.

References

Shirai, K., Hoyano, A., Horiguchi, T. 1995. Development of water-permeable ventilable bricks as the basis for a new evaporative coolingtechnique, the International Solar Energy Society 1995 Solar WorldCongress, Harare, Zimbabwe.

Hoyano, A., Shirai, K., 1995. Design and development of an evaporative-cooling prototype wall made of water-permeable ventilable bricks, theInternational Solar Energy Society 1995 Solar World Congress,Harare, Zimbabwe.

Hoyano, A., Shirai, K., et al., 1997. Experimental evaluation of theevaporative cooling effect produced by practical application of a feedwater-supplied passive cooling wall made of water-permeable ventila-ble bricks, Proceedings of ISES 1997 Solar World Congress, Taejon,Korea, 310–316.

Shirai, K., Hoyano, A., et al., 1997. Investigation of thermal comfort in anoutdoor space partly enclose by a passive cooling wall made of water-permeable ventilable bricks, Proceedings of ISES 1997 Solar WorldCongress, Taejon, Korea, 233–238.

Shirai, K., Hoyano, A., et al., 2000. Effect of a passive cooling wall to formmicro-climate in a semi-outdoor space (Formation of outdoor andsemi-outdoor comfortable space through evaporative cooling bywater-permeable perforated wall, Part 1). Journal of Architecture,Planning and Environmental Engineering (Transactions of AIJ) 527,21–27, in Japanese.

Shirai, K., Hoyano, A., Oguri, K., 2002. Evaluations of coolness at aspace constructed with passive cooling walls (Formation of outdoorand semi-outdoor comfortable space through evaporative cooling bywater-permeable perforated wall, Part 3). Journal of Architecture,Planning and Environmental Engineering (Transactions of AIJ) 552,15–20, in Japanese.

Givoni, B., 1994. Passive and Low Energy Cooling of Buildings, AnInternational Thomson Publishing Company.

Asawa, T., Hoyano, A., Nakaohkubo, K., 2008. Thermal design tool foroutdoor spaces based on heat balance simulation using a 3D-CADsystem. Building and Environment 43, 2112–2123.

Shimokawa, K. et al., 1996. Prediction of thermal environment on streetswith roadside trees part 5 –A study on thermal characteristics of thefoliage crown by measurements–, Summaries of Technical Papers ofAnnual Meeting (Environmental Engineering). Architectural Instituteof Japan 8, 131–132, in Japanese.

Kakuya, A., He, J., Hoyano, A., 2007. Numerical analysis of the microclimaticeffect of bioclimatic design using a combination of CFD and outdoorthermal simulation, Proceedings of the 24th International Conference onPassive and Low Energy Architecture, Singapore, pp. 641–648.

A 3D CAD-Based Simulation Tool for Prediction and Evaluation

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