Tutorial Using Solar Load Model for Indoor Ventilation

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Introduction

The purpose of this tutorial is to provide guidelines and recommendations for setting up and The purpose of this tutorial is to provide guidelines and recommendations for setting up and solving an indoor ventilation problem of a building using solar load model. The problem is solving an indoor ventilation problem of a building using solar load model. The problem is initially solved excluding the radiation effects, and then radiation model is included in the initially solved excluding the radiation effects, and then radiation model is included in the calculation to study the effect of radiant heat exchange between the internal surfaces. calculation to study the effect of radiant heat exchange between the internal surfaces.

Pre-requisites

This tutorial assumes that you are familiar with the

This tutorial assumes that you are familiar with the FLUENTFLUENT interface and that you haveinterface and that you have good

good underunderstandistanding of ng of basic setup and solution procedbasic setup and solution proceduresures. . In this tutorial, you will useIn this tutorial, you will use solar load model and

solar load model and radiatradiation model, so ion model, so you shoulyou should have some experied have some experience with them. nce with them. ThisThis tutorial does not cover the mechanics of using these models, but focuses on the applications tutorial does not cover the mechanics of using these models, but focuses on the applications of this model to solve the indoor ventilation problem.

of this model to solve the indoor ventilation problem.

Problem Description

The problem considered is ventilation of the reception area of Fluent Europe’s office at The problem considered is ventilation of the reception area of Fluent Europe’s office at Sheffield, England (Figure

Sheﬃeld, England (Figure 11). The fron). The front t wawall ll of the of the recrecepteption is ion is almalmost fully glazost fully glazed fromed from the grou

the ground floor nd floor to the to the ceiceilinling g of the first floor of the first floor levlevel. el. TheThere is re is alsalso o a a smasmall glazed arell glazed area a onon the roof above the second floor landing.

the roof above the second ﬂoor landing.

This tutorial looks at the typical expected loads in the middle of summer on a normal This tutorial looks at the typical expected loads in the middle of summer on a normal da

dayy. . The adjoinThe adjoining rooms ing rooms and oﬃces and oﬃces are air-care air-condonditioitioned and ned and maimaintntainained ed at at a a conconstastantnt temperature of around 20

temperature of around 2000

C. So heat will be transferred through the internal walls to these C. So heat will be transferred through the internal walls to these rooms. Some heat will also be transferred to the floor. As the floor is a concrete base it is rooms. Some heat will also be transferred to the floor. As the floor is a concrete base it is assum

assumed to ed to havhave substane substantial thermal mass and tial thermal mass and a ﬁxed a ﬁxed temperatemperature. ture. OutsiOutside conditions arede conditions are considered to be pleasant and normal at 25

considered to be pleasant and normal at 25 00

C. An external heat transfer coeﬃcient of 4 C. An external heat transfer coeﬃcient of 4 W/m

W/m22

K

K is used to capture convective heat transfer from outside the building. There is anis used to capture convective heat transfer from outside the building. There is an air cooling unit located behind the receptionist’s desk.

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Figure 1: Problem Schematic—Reception Area Figure 1: Problem Schematic—Reception Area

Preparation

1. Copy the ﬁles

1. Copy the ﬁles fel atrium.mshfel atrium.msh to your working folder.to your working folder. 2. Start the 3D

2. Start the 3D (3d)(3d) version of version of FLUENTFLUENT..

Setup and Solution

Ste

Step 1: p 1: GriGridd

1. Read the mesh ﬁle

1. Read the mesh ﬁle fel atrium.mshfel atrium.msh.. File

File −−→→ReadRead −−→→Case...Case...

2. Check the grid. 2. Check the grid.

Grid

Grid−−→→CheckCheck

3.

3. DisplaDisplay the grid (Figurey the grid (Figure 22).). Display

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(a)

(a) SelSelectect FeatureFeature in thein the Edge TypeEdge Type group-box.group-box. (b)

(b) ClicClickk DisplayDisplay and close theand close the Grid DisplayGrid Display panel.panel.

Z Z Y Y X X Grid Grid FLUENT 6.3 (3d, pbns, lam) FLUENT 6.3 (3d, pbns, lam)

Figure 2: Graphics Display of the Grid (Features) Figure 2: Graphics Display of the Grid (Features)

We will follow a naming convention for labeling the grid. All the walls are prefixed We will follow a naming convention for labeling the grid. All the walls are prefixed with ‘w’ and all velocity inlets are prefixed with ‘v’.

with ‘w’ and all velocity inlets are preﬁxed with ‘v’.

Ste

Step 2: p 2: UnUnitsits

1.

1. Change the defauChange the default unit for temperature to centiglt unit for temperature to centigrade.rade. Deﬁne

Deﬁne −−→→Units...Units...

(a)

(a) SelSelectect temperaturetemperature from thefrom the QuantitiesQuantities list.list. (b)

(b) SelSelectect cc from thefrom the UnitsUnits list and close thelist and close the Set UnitsSet Units panel.panel.

Ste

Step 3: p 3: ModModelsels

1.

1. DefinDefine the solver sette the solver settings.ings. Define

Deﬁne −−→→ModelsModels −−→→Solver...Solver...

(a)

(a) SelSelectect Pressure BasedPressure Based in thein the SolverSolver group-box.group-box. (b)

(b) SelSelectect Green-Gauss Node BasedGreen-Gauss Node Based in thein the Gradient OptionGradient Option group-box.group-box.

This provides improved resolution of gradients, particularly with coarse or skewed This provides improved resolution of gradients, particularly with coarse or skewed cells.

cells. (c)

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2.

2. Enable the eﬀects of gravitEnable the eﬀects of gravityy..

This is because the bulk of the ﬂow is driven by natural convection. This is because the bulk of the ﬂow is driven by natural convection.

Deﬁne

Deﬁne−−→→Operating Conditions...Operating Conditions...

(a)

(a) EnaEnableble GravityGravity.. (b)

(b) EntEnterer -9.81-9.81 forfor YY in thein the Gravitational AccelerationGravitational Acceleration group-box.group-box. (c)

(c) ClicClickk OKOK to close theto close the Operating ConditionsOperating Conditions panel.panel. 3.

3. Enable k-eEnable k-epsilon turbpsilon turbulenculence model.e model. Deﬁne

Deﬁne−−→→ModelsModels −−→→Viscous...Viscous...

The ﬂow is expected to be turbulent, so an appropriate turbulence model is required. The ﬂow is expected to be turbulent, so an appropriate turbulence model is required.

(a)

(a) EnaEnableble k-epk-epsilon (2 silon (2 eqn)eqn) from thefrom the ModelModel list.list. (b) Enable

(b) Enable RNGRNG in thein the k-epsilon Modelk-epsilon Model group-box.group-box. (c)

(c) EnaEnableble Full Buoyancy EﬀectsFull Buoyancy Eﬀects in thein the OptionsOptions list.list. (d) Click

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4.

4. EnaEnable the solable the solar load model.r load model. Deﬁne

Deﬁne −−→→ModelsModels −−→→Radiation...Radiation...

(a)

(a) EnaEnableble Solar Ray TracingSolar Ray Tracing in thein the Solar LoadSolar Load group-box.group-box. (b)

(b) Retain thRetain the defaule default selectiot selection of n of Use Direction Computed from Solar CalculatorUse Direction Computed from Solar Calculator underunder Sun Direction Vector

Sun Direction Vector.. (c)

(c) SelSelectect solar-calculatorsolar-calculator from thefrom the Direct Solar IrradiationDirect Solar Irradiation andand Diﬀuse Solar IrradiationDiﬀuse Solar Irradiation drop-down lists.

drop-down lists. (d)

(d) Retain the defRetain the default vaault value of lue of 0.50.5 forfor Spectral Fraction [V/(V+IR)]Spectral Fraction [V/(V+IR)]..

A value of 0.5 speciﬁes 50% split between long (IR) and short (V) wave radiation. A value of 0.5 speciﬁes 50% split between long (IR) and short (V) wave radiation. (e)

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i. Enter

i. Enter -1.28-1.28 deg fordeg for LongitudeLongitude andand 53.2353.23 deg fordeg for LatitudeLatitude in thein the GlobalGlobal Position

Position group-box.group-box. ii. Enter

ii. Enter +1+1 forfor TimezoneTimezone in thein the Global PositionGlobal Position group-box.group-box. A value of 1 speciﬁes British summer time.

A value of 1 speciﬁes British summer time. iii.

iii. EnteEnterr0, 0, -10, 0, -1forfor NorthNorth andand1, 0, 01, 0, 0forfor EastEast in thein the Grid OrientationGrid Orientation group- group-box.

box. iv.

iv. Retain defRetain default valault values forues for Date and TimeDate and Time..

Default values are set to peak summer conditions. Default values are set to peak summer conditions. v.

v. Retain thRetain the defaule default selectit selection of on of Fair Weather ConditionsFair Weather Conditions in thein the Solar IrradiationSolar Irradiation Method

Method group-box.group-box.

These conditions are representative of a ﬁne day with little cloud cover. These conditions are representative of a ﬁne day with little cloud cover. vi.

vi. Retain the defRetain the default vault value of alue of 11 for thefor the Sunshine FactorSunshine Factor.. You can assume that there is no additional cloud cover. You can assume that there is no additional cloud cover. vii.

vii. ClicClickk ApplyApply and close theand close the Solar CalculatorSolar Calculator panel.panel. Information will be printed in the

Information will be printed in the FLUENTFLUENT console summarizing the diﬀuse console summarizing the diﬀuse and direct components that will be used to calculate the load.

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(f)

(f) Modify other model parameModify other model parameters that are avters that are available only throuailable only through the TUI.gh the TUI. i.

i. Retain defRetain default vault value foralue for ground-reﬂectivityground-reﬂectivity.. /define/model

/define/models/radiation/ss/radiation/solar-parameteolar-parameters> rs> ground-reflectground-reflectivityivity Grou

Ground nd ReflReflectiectivity vity [0.2[0.2]]

When the solar calculator option is selected for diffuse radiation, the When the solar calculator option is selected for diffuse radiation, the radia-tion reflected from the ground will be added to the total diffuse background tion reflected from the ground will be added to the total diffuse background radiation. The amount of radiation reflected from the ground depends on its radiation. The amount of radiation reflected from the ground depends on its reflectivity which can be set through this parameter. The default value of 0.2 reflectivity which can be set through this parameter. The default value of 0.2 is reasonable.

is reasonable. ii. Reduce the

ii. Reduce the scattering fractionscattering fraction to a value of to a value of 0.750.75.. /define/model

/define/models/radiation/ss/radiation/solar-parameteolar-parameters> rs> scattering fractioscattering fractionn Sca

Scattetterinring g FraFractiction on [1] [1] 0.70.755

The solar load ray trace model provides directional loading only to the ﬁrst The solar load ray trace model provides directional loading only to the ﬁrst op

opaque surfacaque surface e that it that it rereaches. aches. It does not It does not undertundertake further ray tracinake further ray tracing g toto account for reradiation due to reﬂection or emission. It does not discard the account for reradiation due to reﬂection or emission. It does not discard the re

reﬂeﬂectected d cocompmponent onent of of raradiatidiation, on, but but distridistributes butes it it acracross oss all all paparticirticipapating ting surfaces.

surfaces.

The scattering fraction, i.e., the amount of the reﬂected component which is The scattering fraction, i.e., the amount of the reﬂected component which is dis

distritributbuteed, d, is set is set to to a a defdefaulault t valvalue ue of 1. of 1. ThiThis s memeans that all ans that all the reflthe refleectected d rradiadiatiation on will be will be disdistritributbuteed d insinside the ide the domdomainain. . If If the buildthe building has ing has a a larlarge ge glazed surface area, a significant amount of the reflected component is glazed surface area, a significant amount of the reflected component is ex-pe

pectected d to to bbe e lost throulost through gh externexternal al glazinglazing. g. In In such cases, resuch cases, reducduce e scscatteriattering ng fraction

fraction accaccordingly.ordingly. iii.

iii. ActivActivate sourcing of energy into an adjacenate sourcing of energy into an adjacent ﬂuid t ﬂuid cell.cell. /define/model

/define/models/radiation/ss/radiation/solar-parameteolar-parameters> rs> sol-adjacent-fsol-adjacent-fluidcellsluidcells

sol-sol-adjacadjacent-ent-fluifluidcelldcells? s? [no] [no] yesyes

The solar load model calculates energy sources for every face subjected to The solar load model calculates energy sources for every face subjected to a

a solsolar ar loload. ad. By By defdefaulault, t, thithis s eneenerrgy gy will be will be sousourrcceed d intinto o an an adjadjacacent shell ent shell conduction cell, if available (if planar conduction is being used). Otherwise, conduction cell, if available (if planar conduction is being used). Otherwise, it will be put into an adjacent solid cell.

it will be put into an adjacent solid cell.

If neither conduction cell nor solid cell is adjacent, it will be sourced into the If neither conduction cell nor solid cell is adjacent, it will be sourced into the adjac

adjacent ﬂuid ent ﬂuid cecell. ll. HowevHowever, if er, if the mesh the mesh is too cois too coarse to arse to acaccurcurately resately resolve olve wall heat transfer (as is frequently the case with building studies), then it is wall heat transfer (as is frequently the case with building studies), then it is pr

prefereferable to able to put the heat straiput the heat straight into the ght into the ﬂuid cell every time. ﬂuid cell every time. This helps This helps reduce the likelihood of predicting unnaturally high wall temperatures while reduce the likelihood of predicting unnaturally high wall temperatures while still achieving the energy transfer into the room.

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Step 4:

Step 4: MateMaterialsrials

Deﬁne

Deﬁne−−→→Materials...Materials...

In this

In this step you step you will modify ﬂuid propwill modify ﬂuid propertieerties s for air for air and solid and solid prpropopertieerties s for steefor steel. l. YYou will ou will also create new materials (glass and a general insulating building material) in the setup. also create new materials (glass and a general insulating building material) in the setup.

1.

1. Modify the parModify the parameterameters for air.s for air. (a)

(a) SelSelectect boussinesqboussinesq from thefrom the DensityDensity drop-down list and enterdrop-down list and enter 1.181.18 as the value of as the value of density.

density.

A value of 1.18

A value of 1.18 kg/mkg/m33

speciﬁes the appropriate density of air at 25 speciﬁes the appropriate density of air at 25 00

C and 1 atm. C and 1 atm. This setting is more stable for problems with natural convection, and is valid over This setting is more stable for problems with natural convection, and is valid over relatively small variations in temperature. In general, if the temperature range is relatively small variations in temperature. In general, if the temperature range is more than 10-20% of the absolute temperature (in Kelvin) then another approach more than 10-20% of the absolute temperature (in Kelvin) then another approach should be considered.

should be considered. (b)

(b) EntEnterer0.003350.00335K K −−11for thefor the Thermal Expansion CoeﬃcientThermal Expansion Coeﬃcient and clickand click Change/CreateChange/Create..

Assuming an ideal gas relationship this is the inverse of the absolute temperature Assuming an ideal gas relationship this is the inverse of the absolute temperature (in Kelvin). For air at 25

(in Kelvin). For air at 25 00

C, it is 0.00335 C, it is 0.00335 K K −−11..

2. Copy the material 2. Copy the material steelsteel..

(a)

(a) ClicClick thek the Fluent Database...Fluent Database... button to open thebutton to open the Fluent Database materialsFluent Database materials panel.panel. (b) Select

(b) Select solidsolid from thefrom the Material TypeMaterial Type drop-down list and selectdrop-down list and select steelsteel from thefrom the FluentFluent Solid Materials

Solid Materials drop-down list.drop-down list.

Ensure that all other materials have been deselected from the list. Ensure that all other materials have been deselected from the list. (c)

(c) ClicClickk CopyCopy and close theand close the Fluent Database materialsFluent Database materials panel.panel. 3. Create a material called

3. Create a material called glassglass.. (a)

(a) SelSelectect steelsteel from thefrom the Fluent Solid MaterialsFluent Solid Materials drop-down list.drop-down list. Rename it as

Rename it as glassglass.. (b)

(b) EntEnterer glassglass as the materialas the material NameName in thein the MaterialsMaterials panel.panel. (c)

(c) Specify the followSpecify the following parameteing parameters:rs:

P Paarraammeetteer r VVaalluuee Density (kg/m3) Density (kg/m3) 22202220 Cp (j/kg-k) Cp (j/kg-k) 830830 Thermal Conductivity (w/m-k) Thermal Conductivity (w/m-k) 1.151.15 (d) Click

(d) Click Change/CreateChange/Create and clickand click NoNo in the question dialog box asking whether toin the question dialog box asking whether to overwrite existing materials.

overwrite existing materials. 4.

4. SimilarSimilarlyly, , creatcreate e anotheanother material calledr material calledbuilding-insulationbuilding-insulation with following prop-with following prop-erties: erties: P Paarraammeetteer r VVaalluuee Density (kg/m3) Density (kg/m3) 1010 Cp (j/kg-k) Cp (j/kg-k) 830830 Thermal Conductivity (w/m-k) Thermal Conductivity (w/m-k) 0.10.1

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Step 5:

Step 5: BounBoundary Conditdary Conditionsions

Deﬁne

Deﬁne−−→→Boundary Conditions...Boundary Conditions...

By default, all the internal and external boundaries participate in the solar ray tracing and By default, all the internal and external boundaries participate in the solar ray tracing and are opaque. All the wall in this model participate in solar ray tracing.

are opaque. All the wall in this model participate in solar ray tracing. 1.

1. Set the boundary conSet the boundary conditions forditions for solid-steel-framesolid-steel-frame.. (a)

(a) SelSelectect SteelSteel as theas the Material NameMaterial Name.. The stee

The steel frame is actually l frame is actually a hola hollow seclow section. tion. In this In this cacase, it se, it is repris representesented as a ed as a solid section. The properties of steel have been retained only for simplicity. solid section. The properties of steel have been retained only for simplicity. (b)

(b) ClicClickk OKOK to close theto close the SolidSolid panel.panel. 2.

2. Set the boundary conSet the boundary conditions forditions for w ﬂoorw ﬂoor.. (a)

(a) ClicClick thek the ThermalThermal tab and enabletab and enable TemperatureTemperature in thein the Thermal ConditionsThermal Conditions group- group-box.

box. (b)

(b) ClicClick thek the RadiationRadiation tab and entertab and enter 0.810.81 forfor Direct Direct VisibVisiblele andand 0.920.92 forfor Direct IRDirect IR in the

in the AbsorptivityAbsorptivity group-box.group-box. (c)

(c) ClicClickk OKOK to close theto close the WallWall panel.panel. 3.

3. Set the boundary condiSet the boundary conditions for externtions for external gazed wall (al gazed wall (w south-glassw south-glass).). (a)

(a) ClicClick thek the ThermalThermal tab and enabletab and enable MixedMixed in thein the Thermal ConditionsThermal Conditions group-box.group-box. The thermal condition is set to

The thermal condition is set to MixedMixed to to acaccocount unt for for externexternal al coconvenvective heat ctive heat transfer and external radiant losses from the glazing unit.

transfer and external radiant losses from the glazing unit. (b)

(b) Specify folloSpecify following parametewing parameters:rs:

P

Paarraammeetteer r VVaalluuee

Heat Transfer Coeﬃcient (w/m2-k)

Heat Transfer Coeﬃcient (w/m2-k) 44

Free Stream Temperature (c)

Free Stream Temperature (c) 2222

External Emissivity

External Emissivity 0.490.49

External Radiation Temperature (c)

External Radiation Temperature (c) -273-273

The value of

The value of External Radiation TemperatureExternal Radiation Temperature is not set to the outside background is not set to the outside background temperature value because the incoming radiation is already being supplied by the temperature value because the incoming radiation is already being supplied by the solar load model.

solar load model. (c)

(c) SelSelectect glassglass from thefrom the Material NameMaterial Name drop-down list and enterdrop-down list and enter 0.010.01 m form for WallWall Thickness

Thickness..

This is a double-glazed wall and should have material properties which account This is a double-glazed wall and should have material properties which account for

for the the gas gas spacspace e betwebetween en the the two two panes. panes. But But you you can can ignore ignore this this in in the the ﬁrst ﬁrst instance.

instance. (d)

(d) ClicClick thek the RadiationRadiation tab and selecttab and select semi-transparentsemi-transparent from thefrom the BC TypeBC Type drop-downdrop-down list.

list.

i. Enter

i. Enter 0.490.49 forfor Direct VisibleDirect Visible,, Direct IRDirect IR andand Diﬀuse HemisphericalDiﬀuse Hemispherical in thein the Ab- Ab-sorptivity

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ii. Enter

ii. Enter 0.30.3 forfor Direct VisibleDirect Visible andand Direct IRDirect IR andand0.320.32 forfor Diﬀuse HemisphericalDiﬀuse Hemispherical in the

in the TransmissitivityTransmissitivity group-box.group-box. (e)

(e) ClicClickk OKOK to close theto close the WallWall panel.panel. 4.

4. SimilarSimilarly set the ly set the boundarboundary conditiony conditions fors for w doors-glassw doors-glass andand w w roof-roof-glassglass.. 5.

5. Set the boundary conSet the boundary conditionditions fors for w roof solidw roof solid..

The roof is an opaque external surface that receives a solar load from the outside. As The roof is an opaque external surface that receives a solar load from the outside. As it is

it is well insulwell insulateated, d, we can assume that therwe can assume that there e is is litlittle heatle heat t trtransansfer acrfer across it. oss it. The The default thermal condition of zero heat ﬂux can be used.

default thermal condition of zero heat ﬂux can be used. (a)

(a) Retain the defRetain the default settinault settings for thegs for the ThermalThermal tab.tab. (b) Click the

(b) Click the RadiationRadiation tab.tab.

Specify the values as per the radiant properties for walls mentioned in the table Specify the values as per the radiant properties for walls mentioned in the table in Appendix.

in Appendix. i. Ensure that

i. Ensure that BC TypeBC Type is set tois set to opaqueopaque andand Participates in Solar Ray TracingParticipates in Solar Ray Tracing isis enabled.

enabled. ii. Enter

ii. Enter 0.260.26 for guiDirect Visible andfor guiDirect Visible and 0.90.9 forfor Direct IRDirect IR in thein the AbsorptivityAbsorptivity group-box.

group-box. (c)

6. Set the boundary conSet the boundary conditionditions fors for w steel-frame-outw steel-frame-out.. (a)

(a) ClicClick thek the ThermalThermal tab and enabletab and enable MixedMixed in thein the Thermal ConditionsThermal Conditions group-box.group-box. Y

You ou neeneed d to to acaccocount for unt for externexternal al solar loadisolar loading ng and and cconveonvectionction. . The computeThe computed d solar loads are not applied to the outside surface of any opaque surfaces located solar loads are not applied to the outside surface of any opaque surfaces located at the boundary of the domain. Instead, they need to be imposed using the thermal at the boundary of the domain. Instead, they need to be imposed using the thermal conditions.

conditions.

The direct solar load calculated by the solar calculator is 857.5

The direct solar load calculated by the solar calculator is 857.5 w/mw/m22

at a at a di-rection vector of (0.0275, 0.867, 0.496). The direct south-facing vertical surface rection vector of (0.0275, 0.867, 0.496). The direct south-facing vertical surface loading comes out to be 425

loading comes out to be 425 w/mw/m22

. Add to this the diﬀuse vertical surface loading . Add to this the diﬀuse vertical surface loading of 134.5

of 134.5 w/mw/m22

and ground reﬂected radiation of 86

and ground reﬂected radiation of 86 w/mw/m22

to get a total vertical to get a total vertical surface loading of 645.5

surface loading of 645.5 w/mw/m22

. This equates to an eﬀective radiation temperature . This equates to an eﬀective radiation temperature of 326.65 K or 53.5

of 326.65 K or 53.5 00_C._C.

You can ignore the material name and wall thickness as the wall thickness is You can ignore the material name and wall thickness as the wall thickness is repr

represented esented explicitly.explicitly. i.

i. Specify the vSpecify the values for the parametalues for the parameters as per ers as per the follothe following table:wing table:

P

External Emissivity

External Emissivity 0.910.91

External Radiation Temperature (c)

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(b)

(b) Retain the defauRetain the default settings underlt settings under RadiationRadiation tab.tab.

This wall boundary will not face any incident radiation as is not adjacent to air. This wall boundary will not face any incident radiation as is not adjacent to air. (c)

7. Set the boundary conSet the boundary conditions forditions for w steel-frame-inw steel-frame-in.. (a)

(a) Retain the defRetain the default settingault settings in thes in the ThermalThermal tab.tab. (b)

(b) ClicClick thek the RadiationRadiation tab.tab.

Specify the values as per the radiant properties for dark grey gloss material Specify the values as per the radiant properties for dark grey gloss material men-tioned in the table in Appendix.

tioned in the table in Appendix. i. Ensure that

enabled. ii. Enter

ii. Enter0.780.78 forfor Direct VisibleDirect Visible andand0.910.91 forfor Direct IRDirect IR in thein the AbsorptivityAbsorptivity group- group-box.

box. (c)

8. Set the boundary conSet the boundary conditions forditions for w north-wallw north-wall.. (a)

(a) ClicClick thek the ThermalThermal tab and enabletab and enable ConvectionConvection in thein the Thermal ConditionsThermal Conditions group- group-box.

box. i.

i. Specify the vSpecify the values for the parametalues for the parameters as per ers as per the followthe following table:ing table:

P

M

Maatteerriiaal l NNaamme e bbuuiillddiinngg--iinnssuullaattiioonn Wall Thickness (m)

Wall Thickness (m) 0.10.1

(b)

(b) ClicClick thek the RadiationRadiation tab.tab.

Specify the values as per the radiant properties for walls mentioned in the table Specify the values as per the radiant properties for walls mentioned in the table in Appendix.

in Appendix. i. Ensure that

enabled. ii. Enter

ii. Enter 0.260.26 forfor Direct VisibleDirect Visible andand 0.90.9 forfor Direct IRDirect IR in thein the AbsorptivityAbsorptivity group- group-box.

box. (c)

9. SimSimilarilarly ly set set the the bounboundardary y conconditditions ions for for othother er ininterternal nal wawalls lls namnamelyely w east-wallw east-wall,, w west-wall

w west-wall,, w room-wallsw room-walls, and, and w pillarsw pillars.. 10.

10. Set the boundary condiSet the boundary conditions for the remainintions for the remaining walls.g walls. The

The rremaemainiining ng wall wall arare e w ac-unitw ac-unit,, w door-topw door-top,, w door-top-shadoww door-top-shadow,, w glass-barriersw glass-barriers,, w glass-barriers-shadow

w glass-barriers-shadow,, w landingsw landings,, w plants-and furniturew plants-and furniture,, w south-wallw south-wall,, w steel-frame-w steel-frame-in-shadow

in-shadow,, w steel-frame-out-endsw steel-frame-out-ends,, w stepsw steps,, w steps-shadoww steps-shadow. . All theAll these wallse walls will have s will have default thermal conditions (coupled or zero heat ﬂux).

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(a)

(a) Retain the thermRetain the thermal condition for all the walls as default.al condition for all the walls as default. (b)

(b) Set the radiant properSet the radiant properties accordties according to ing to the valthe values provues provided in the table ided in the table in Ap-in Ap-pendix.

pendix.

The boundaries

The boundaries w ac-unitw ac-unit and and w plants-and furniturew plants-and furniture will have radiant properties will have radiant properties of

of FurnishingsFurnishings. The boundaries . The boundaries w door-topw door-top,, w door-top-shadoww door-top-shadow, and , and w south-wallw south-wall will have radiant properties of

will have radiant properties of WallsWalls. . ThThe be bououndandary ry w glass-barriersw glass-barriers will have will have radiant properties of

radiant properties of Internal GlassInternal Glass. The boundaries . The boundaries w landingsw landings,, w stepsw steps,, w steps-w steps-shadow

shadow will have radiant properties of will have radiant properties of FlooringFlooring. . KeKeep ep defauldefault t raradiant propdiant propertieerties s for

for the the rest.rest. 11.

11. Set the bSet the boundaoundary conditionry conditions for s for the air conditioninthe air conditioning equipmeng equipments.ts. (a)

(a) SelSelectect Magnitude and DirectionMagnitude and Direction from thefrom the Velocity Speciﬁcation MethodVelocity Speciﬁcation Method drop-downdrop-down list.

list. (b)

(b) EntEnterer 1010 m/s for them/s for the Velocity MagnitudeVelocity Magnitude.. (c)

(c) EntEnterer 0.1, 1, 00.1, 1, 0 forfor X-Component of Flow DirectionX-Component of Flow Direction,, Y-Component of Flow Di-Y-Component of Flow Di-rection

rection andand Z-Component of Flow DirectionZ-Component of Flow Direction.. (d) Select

(d) Select Intensity and Length ScaleIntensity and Length Scale from thefrom the Speciﬁcation MethodSpeciﬁcation Method drop-down list indrop-down list in the

the TurbulenceTurbulence group-box.group-box. (e)

(e) EntEnterer 1010 % for% for TTurbulent urbulent IntensityIntensity andand 0.020.02 m form for Turbulent Length ScaleTurbulent Length Scale.. (f)

(f) ClicClick thek the ThermalThermal tab and entertab and enter 1515 c for thec for the TemperatureTemperature.. (g)

(g) ClicClickk OKOK to close theto close the Velocity InletVelocity Inlet panel.panel. 12. Close the

12. Close the Boundary ConditionsBoundary Conditions panel.panel.

Step 6:

Step 6: SoluSolutiontion

1.

1. Deﬁne the solution conDeﬁne the solution control parametetrol parameters.rs. Solve

Solve −−→→ControlsControls −−→→Solution...Solution...

(a)

(a) EntEnterer 0.30.3 forfor PressurePressure,, 0.20.2 forfor MomentumMomentum andand 0.90.9 forfor EnergyEnergy in thein the Under- Under-Relaxation Factors

Relaxation Factors group-box.group-box.

You can also solve this problem with the default relaxation factors initially. This You can also solve this problem with the default relaxation factors initially. This will

will prprovide optimum convovide optimum converergencgence e rarates if tes if they are suitably stable. they are suitably stable. If larger re-If larger re-laxation is required then the suggested values for momentum and energy are 0.3 laxation is required then the suggested values for momentum and energy are 0.3 to 0.5 and 0.8 to 0.9 respectively.

to 0.5 and 0.8 to 0.9 respectively. (b) Select

(b) Select Body Force WeightedBody Force Weighted as a discretization scheme foras a discretization scheme for PressurePressure and retainand retain default

default First Order UpwindFirst Order Upwind discretization scheme for other parameters.discretization scheme for other parameters.

Natural convection problems are inherently unstable and it is better to solve them Natural convection problems are inherently unstable and it is better to solve them using

using First Order UpwindFirst Order Upwind discrdiscretizaetization scheme tion scheme in in the begthe beginninginning. . When converWhen conver--gence is achieved, higher order schemes can be used.

gence is achieved, higher order schemes can be used. (c)

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2.

2. DeﬁnDeﬁne surface monie surface monitor.tor. Solve

Solve −−→→MonitorsMonitors −−→→Surface...Surface...

Due to high transience it may be diﬃcult to achieve good convergence in this case, it Due to high transience it may be diﬃcult to achieve good convergence in this case, it is useful to

is useful to obserobserve the ve the solutsolution proion progrgress by ess by monitmonitoring some useful surfacoring some useful surfaces. es. HerHere,e, you will monitor the heat transfer across the glass.

you will monitor the heat transfer across the glass. (a)

(a) EntEnterer 11 for thefor the Surface MonitorsSurface Monitors.. (b)

(b) EnaEnableble PlotPlot,, PrintPrint, and, and WriteWrite options foroptions for monitor-1monitor-1 .. (c)

(c) ClicClick thek the Define...Define... button to open thebutton to open the Define Surface MonitorDefine Surface Monitor panel.panel.

i. Select

i. Select Wall Fluxes...Wall Fluxes... andand Total Surface Heat FluxTotal Surface Heat Flux from thefrom the Report of Report of drop- drop-down lists.

down lists. ii. Select

ii. Select w southglassw southglass from thefrom the SurfacesSurfaces list.list. iii. Set

iii. Set 11 for thefor the Plot WindowPlot Window.. iv. Click

iv. Click OKOK to close theto close the Deﬁne Surface MonitorDeﬁne Surface Monitor panel.panel. (d)

(d) ClicClickk OKOK to close theto close the Surface MonitorsSurface Monitors panel.panel. 3.

3. InitialInitialize the solutize the solution.ion. Solve

Solve −−→→InitializeInitialize −−→→Initialize...Initialize...

(a)

(a) SelSelectect all-zonesall-zones from thefrom the Compute FromCompute From drop-down list.drop-down list. (b)

(b) EntEnterer 2222 forfor TemperatureTemperature andand 00 for all the remaining parameters in thefor all the remaining parameters in the InitialInitial Values

Values group-box.group-box. (c)

(c) ClicClickk InitInit and close theand close the Solution InitializationSolution Initialization panel.panel.

Initialization may take a little more time than usual as the solar load model Initialization may take a little more time than usual as the solar load model calculates the loads to be applied to all surfaces.

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4. Save the case and data ﬁles (

4. Save the case and data ﬁles (fel atrium.casfel atrium.cas andand fel atrium.datfel atrium.dat).). File

File −−→→WriteWrite −−→→Case & Data...Case & Data...

The postprocessing tools can be used at this stage to review the solar load that each The postprocessing tools can be used at this stage to review the solar load that each surface will be subject to. This can easily be done by plotting contours of selecting any surface will be subject to. This can easily be done by plotting contours of selecting any of the following wall ﬂuxes:

of the following wall ﬂuxes:

•

• Solar Heat FluxSolar Heat Flux •

• Absorbed Visible Solar FluxAbsorbed Visible Solar Flux •

• Absorbed IR Solar FluxAbsorbed IR Solar Flux •

• Reﬂected Visible Solar FluxReﬂected Visible Solar Flux •

• Reﬂected IR Solar FluxReﬂected IR Solar Flux •

• Transmitted Visible Solar FluxTransmitted Visible Solar Flux •

• Transmitted IR Solar FluxTransmitted IR Solar Flux

5.

5. IteratIterate the solution foe the solution forr10001000 iterations.iterations. Solve

Solve −−→→Iterate...Iterate...

6. Save the case and data ﬁles (

6. Save the case and data ﬁles (fel atrium-1.casfel atrium-1.casandand fel atrium-1.datfel atrium-1.dat).). File

File −−→→WriteWrite −−→→Case & Data...Case & Data...

Step 7:

Step 7: IncluInclude Radiatiode Radiation Modeln Model

Activate a radiation model to include the radiant heat exchange between the internal surfaces. Activate a radiation model to include the radiant heat exchange between the internal surfaces. This

This is is neneededed beed becacause use after inspeafter inspecting the cting the initiinitial al reresults you sults you will will sesee e high high temptempereraturatures,es, particularly on the second ﬂoor.

particularly on the second ﬂoor. 1.

1. ActivActivateate P1P1 oror S2SS2S radiatradiation ion model.model.

Both models will run with a comparable speed, but the S2S model will take several hours Both models will run with a comparable speed, but the S2S model will take several hours to establish the view factors. The results from the S2S model will be more accurate. to establish the view factors. The results from the S2S model will be more accurate.

Deﬁne

Deﬁne−−→→ModelsModels −−→→Radiation...Radiation...

2. In the

2. In the BoundarBoundary y ConditionsConditions panel, set thepanel, set the Internal EmissivityInternal Emissivity for all thefor all the WallWall boundariesboundaries to the value same as that of

to the value same as that of Direct IR absorptivityDirect IR absorptivity ((ααIRIR).).

Deﬁne

Deﬁne−−→→Boundary Conditions...Boundary Conditions...

3. If you are using S2S model, do the following settings in the

3. If you are using S2S model, do the following settings in the Radiation ModelRadiation Model panel.panel. Deﬁne

Deﬁne−−→→ModelsModels −−→→Radiation...Radiation...

(a)

(a) UndUnderer Iteration ParametersIteration Parameters, reduce the value of , reduce the value of Flow Iterations per Radiation Iter-Flow Iterations per Radiation Iter-ation

ation toto 55.. (b)

(b) UndeUnder Parameter Parameters, clickrs, click Set...Set... i. Set

i. Set Faces per Surface Cluster for Flow Boundary ZonesFaces per Surface Cluster for Flow Boundary Zones toto 1010.. ii. Click

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4.

4. IteratIterate the solution foe the solution forr10001000 more iterations.more iterations. Solve

Solve −−→→Iterate...Iterate...

5.

5. SaSave thve the case and date case and data ﬁles (a ﬁles (fel atrium-p1.casfel atrium-p1.cas andand fel atrium-p1.datfel atrium-p1.dat).). File

File −−→→ WriteWrite−−→→Case & Data...Case & Data...

Step 8:

Step 8: PoPostprocstprocessiessingng

1.

1. Create isCreate isosurfosurfaces ataces at x=3.5x=3.5 andand y=1y=1.. Surface

Surface −−→→Iso-Surface...Iso-Surface...

2.

2. DisplDisplay conay contours of tours of Static TemperatureStatic Temperature on the ground ﬂoor at y=1 (Figureon the ground ﬂoor at y=1 (Figure 33).). Display

Display −−→→Contours...Contours...

3.

3. DisplDisplay conay contours of tours of Static TemperatureStatic Temperature atat x=3.5x=3.5 (Figure(Figure 44).). 4.

4. DisplDisplay conay contours of tours of Solar Heat FluxSolar Heat Flux onon w south-glassw south-glass (Figure(Figure 55).). 5.

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Contours of Static Temperature (c) Contours of Static Temperature (c)

FLUENT 6.3 (3d, pbns, rngke) FLUENT 6.3 (3d, pbns, rngke) 4.86e+01 4.86e+01 4.69e+01 4.69e+01 4.53e+01 4.53e+01 4.36e+01 4.36e+01 4.19e+01 4.19e+01 4.02e+01 4.02e+01 3.85e+01 3.85e+01 3.68e+01 3.68e+01 3.52e+01 3.52e+01 3.35e+01 3.35e+01 3.18e+01 3.18e+01 3.01e+01 3.01e+01 2.84e+01 2.84e+01 2.68e+01 2.68e+01 2.51e+01 2.51e+01 2.34e+01 2.34e+01 2.17e+01 2.17e+01 2.00e+01 2.00e+01 1.84e+01 1.84e+01 1.67e+01 1.67e+01 1.50e+01 1.50e+01ZZ Y Y X X

Figure 3: Contours of Static Temperature at y=1 Figure 3: Contours of Static Temperature at y=1

Contours of Static Temperature (c) Contours of Static Temperature (c)

Figure 4: Contours of Static Temperature at x=3.5 Figure 4: Contours of Static Temperature at x=3.5

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Contours of Solar Heat Flux (w/m2) Contours of Solar Heat Flux (w/m2)

FLUENT 6.3 (3d, pbns, rngke) FLUENT 6.3 (3d, pbns, rngke) 4.36e+02 4.36e+02 4.14e+02 4.14e+02 3.92e+02 3.92e+02 3.70e+02 3.70e+02 3.49e+02 3.49e+02 3.27e+02 3.27e+02 3.05e+02 3.05e+02 2.83e+02 2.83e+02 2.62e+02 2.62e+02 2.40e+02 2.40e+02 2.18e+02 2.18e+02 1.96e+02 1.96e+02 1.74e+02 1.74e+02 1.53e+02 1.53e+02 1.31e+02 1.31e+02 1.09e+02 1.09e+02 8.72e+01 8.72e+01 6.54e+01 6.54e+01 4.36e+01 4.36e+01 2.18e+01 2.18e+01 0.00e+00 0.00e+00 ZZ Y Y X X

Figure 5: Contours of

Figure 5: Contours of Solar Heat FluxSolar Heat Flux onon w south-glassw south-glass

Contours of Transmitted Visible Solar Flux (w/m2) Contours of Transmitted Visible Solar Flux (w/m2)

Figure 6: Contours of

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Appendix Appendix

For all opaque materials, you need to know the absorptivity for the infrared (long wave) and For all opaque materials, you need to know the absorptivity for the infrared (long wave) and visible (short wave) bands. Generally, absorptivity is higher in the infrared band. Reliable visible (short wave) bands. Generally, absorptivity is higher in the infrared band. Reliable inp

inputs for uts for thithis s datdata a mamay y be be diﬃdiﬃculcult t to to obtobtain from ain from manmanufaufactucturerrers s andand/or supp/or supplierliers. s. SoSo some estimation may be required, based on the data provided in standard heat transfer some estimation may be required, based on the data provided in standard heat transfer textbooks.

textbooks.

For transparent surfaces you need to provide the absorptivity and transmissivity for For transparent surfaces you need to provide the absorptivity and transmissivity for infra-red and visible components of direct radiation. The value you specify should be for normal red and visible components of direct radiation. The value you specify should be for normal incident radiation.

incident radiation. FLUENTFLUENT will automatically adjust for the actual angle of incidence. Youwill automatically adjust for the actual angle of incidence. You also need to provide the overall absorptivity and transmissivity for diﬀuse (mainly infra-red) also need to provide the overall absorptivity and transmissivity for diﬀuse (mainly infra-red) radiation. This will be the hemispherically averaged value.

radiation. This will be the hemispherically averaged value.

If you have diﬃculty obtaining values for glass, refer to following table (

If you have diﬃculty obtaining values for glass, refer to following table (Table 13 in Chapter Table 13 in Chapter 30 of the 2001 ASHRAE Fundamentals Handbook

30 of the 2001 ASHRAE Fundamentals Handbook ):):

S

Suurrffaacce e MMaatteerriiaal l RRaaddiiaannt t PPrrooppeerrttiieess

W

Waalllls s MMaattt t WWhhiitte e PPaaiinntt ααV V = = 00..26,26, ααIRIR = 0= 0..99

F

Flloooorriinng g DDaarrk k GGrreey y CCaarrppeett ααV V = = 00..81,81, ααIRIR = 0= 0..9292

F

Fuurrnniisshhiinnggs s VVaarriioouuss, , ggeenneerraalllly y mmiidd colour

coloured ed mattmatt

α

αV V = = 00..75,75, ααIRIR = 0= 0..9090

St

Steeeel l FFrarame me DaDark rk grgraay y glglososss ααV V = = 00..78,78, ααIRIR = 0= 0..9191

Ext

Externernal Glaal Glass ss DouDouble gble glazelazed coatd coated glaed glassss ααV V = = 00..49,49, ααIRIR = = 00..49,49, ααDD = = 00..49,49,

τ

τ V V = = 00..3,3, τ τ IRIR = = 00..3,3, τ τ DD = = 00..3232

In

Interternal nal GlaGlass ss SinSingle gle lalayeyer clr clear ear ﬂoaﬂoat glt glassass ααV V = = 00..09,09, ααIRIR = = 00..09,09, ααDD = = 00..1,1,

τ