Solar Load Modelin FLUENT 6.2

23 Nov 2005 UGM, Melbourne

Outline

Solar Load Model Solar Ray Tracing (Method 1) Discrete Ordinates Irradiation (Method 2) Both methods have the option of using the

Solar Calculator in Fluent-6

Examples Solar Load Model for Outdoor Solar Load Model for Indoor

Demonstration

Solar Load Model Calculates the radiation intensity from the sun's rays

which enter the domain. Both direct and diffuse solar radiation components are

accounted for. Treats the two important bands of radiation (visible and

infra-red) separately. Provides a wide range of user choices in terms of

computing or specifying solar radiation components: Directly: constant, profiles, user-defined

Automatically: computed by the Solar Calculator utility

Visualisation of illuminated and shadow areas.

Solar Load Model

Two options are available using the solar load model: Solar ray tracing Discrete ordinates (DO) irradiation

Solar ray tracing can be applied as a stand alone solar loading model, or it can be used in conjunction with one of the FLUENT radiation models (P1, Rosseland, Discrete Transfer, Surface-to-Surface, Discrete Ordinates).

DO Irradiation is available only when the Discrete Ordinates (DO) radiation model is enabled.

Solar Load Model

Radiation Models

Solar Load Model

Solar Ray Tracing Solar ray tracing is an efficient and practical way to apply

solar loads as heat sources in the energy equation.

Solar ray tracing algorithm: Predicts the illumination energy source from incident solar radiation. It tracks a beam using the sun position vector and illumination values to

selected wall, inlet and outlet boundaries that you specify. It performs a face-by-face shading analysis to determine well-defined

shadows on all boundary faces and interior walls It then computes the heat flux on each boundary face. The resulting heat flux is coupled to the FLUENT analysis using a

source term in the energy equation.

Solar Ray Tracing

Inputs required for the solar ray tracing algorithm: Sun direction vector Direct solar irradiation Diffuse solar irradiation Spectral fraction Direct Visible and Direct IR absorptivity (opaque wall) Direct Visible and Direct IR absorptivity and transmissivity (semi-

transparent wall) Diffuse absorptivity and Diffuse transmissivity (semi-transparent

wall) Scattering fraction (semi-transparent wall) Ground reflectivity

Solar Ray Tracing

DO Irradiation

Applies solar loads directly to the DO model.

The irradiation flux is applied directly to semi-transparent walls as a boundary condition.

And the radiative heat transfer is derived from the solution of the DO radiative transport equation.

Inputs for DO irradiation at semi-transparent walls: Total irradiation (direct and diffuse) Beam direction Beam width Diffuse fraction

DO Irradiation

Solar Calculator For a given time, date, and position the solar calculator

computes the solar beam direction and irradiation.

These values are used as inputs to both the solar ray tracing and DO Irradiation methods.

Inputs required for the solar calculator are: Global position (latitude, longitude, time zone) Starting date and time Grid orientation Solar irradiation method (Theoretical Maximum or Fair Weather

Condition) Sunshine factor

Solar Calculator

Solar Calculator Outputs are displayed on the console window whenever

the solar calculator is used: Sun direction vector Direct normal solar irradiation at earth's surface Diffuse solar irradiation - vertical and horizontal surfaces Ground reflected (diffuse) solar irradiation - vertical surface

Fair Weather Conditions:Sun Direction Vector: X: -0.836605, Y: 0.42895, Z: -0.340725Sunshine Fraction: 1Direct Normal Solar Irradiation (at Earth's surface) [W/m^2]: 783.099Diffuse Solar Irradiation - vertical surface: [W/m^2]: 52.9415Diffuse Solar Irradiation - horizontal surface [W/m^2]: 66.5895Ground Reflected Solar Irradiation - vertical surface [W/m^2]: 40.25

Examples

Solar Load Model for Outdoor Solar Load Model for Indoor (two cases)

Example: Outdoor Domain

20m radius hemisphere around an object of 2m height

Prediction of: Solar heat flux on object walls

located in Melbourne (22th of Sept. 2004: 9am, 12pm & 4pm)

Boundary Conditions: Ground & object: fixed

temperature of 15C Surrounding: 15C still air No flow-field calculation

N

S

E

W

sky

ground

Example: Outdoor9am

12pm

4pm

Example: Indoor

Domain 2m x 2m x 2m room interior

Simulation Solar heat flux into a room

located in Melbourne (22th of Sept. 2004: 9am, 12pm & 4pm)

Boundary Conditions Vent-in: air 2m/s, 15C ground: 15C Roof & side-walls: h=10W/m2K,

15C, opaque wall Window: h=10W/m2K, 15C,

semi-transparent wall Flow-field & thermal calculation

vent-in

vent-out

floor

roof

window

north-wall

south-wall

west-wall

east-wall

9am

12pm

4pm

9am

12pm

4pm

9am

12pm

4pm

Example: Indoor

Solar Load Model: Building Services

Contours of Total Solar Heat Flux (W/m2)

Solar Load Model Ray tracing algorithm

to solve solar radiant energy transport

Solar calculator computes position and intensity of sun

FLUENT 6.2

Solar Load Model: Cabin Interior

Solid ZonesOpaque

Semi-Transparent

Solar Heat Flux (w/m2)

Temperature (Celsius)

Geometry

West

South

East

North

9:30 AM

9:15 AM

Courtesy of National Renewable Energy Laboratory

DO Model used for internal re-radiation of the solar energy. Natural convection also simulated

Demonstration