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    • Documentation

    SimScale DocumentationValidation CasesValidation case: Mean Radiant Temperature

    Validation case: Mean Radiant Temperature

    This validation case belongs to fluid dynamics and heat transfer with radiation. The aim of this test case is to validate the following parameters:

    • Mean Radiant Temperature at various locations within the domain.

    The simulation results from SimScale were compared to an online Web tool from ASHRAE for MRT & Thermal comfort: CBE MRT Calculator

    View Project

    Geometry

    The geometry is a simple cuboidal room:

    Mrt room geometry
    Figure 1: Geometry is a simple cuboidal domain representing the walls of the room.

    All faces represent walls. The dimensions of the room are 10 \(m\) x 5 \(m\) x 2.6 \(m\).

    Analysis Type and Mesh

    Tool Type: OpenFOAM®

    Analysis Type: Conjugate Heat Transfer v2.0. Steady-state analysis with Radiation, using the  k-omega SST turbulence model.

    Mesh and Element Types:

    The Standard mesher algorithm with hexahedral cells was used to generate the mesh. The sizing was set to automatic with a fineness of 5 and 3 boundary layers were generated next to the walls.

    Additionally, a thin-section mesh refinement was also performed.

    Mesh TypeNumber of cells/nodesElement Type
    Standard mesh106176 cells, 113715 nodes3D Hexahedral
    Table 1: Standard mesh algorithm was used to generate the mesh.
    mrt mesh
    Figure 2: Final mesh generated for the room domain consisting of 3D hexahedral elements

    Simulation Setup

    Material:

    • Air
      • \((\nu)\) Kinematic viscosity: 1.529 \(e5\ m^2/s\)
      • \((\rho)\) Density: 1.196 \(kg/ m^3\)
      • \((C_p)\) Specific heat: 1004 \(J/kg K\)

    Boundary Conditions:

    • There are two wall-type boundary conditions applied to the North side wall and the remaining walls.
    FaceVelocityTemperature Radiative BehaviorEmissivity
    North wallNo-slipFixed value of 35 \(°C\)Opaque0.9
    Remaining wallsNo-slipFixed value of 21 \(°C\)Opaque0.9
    Table 1: Boundary conditions on all the wall faces include a fixed value temperature with an emissivity of 0.9.
    probe points and boundary conditions for mean radiant temperature
    Figure 3: No slip wall boundary condition with opaque radiative behavior is applied on all walls.

    Result Comparison

    The mean radiant temperature value, in degrees Celcius, was computed at 14 different locations within the room (see Figure 3). These computed values were compared against the CBE tool from ASHRAE for MRT and Thermal comfort.

    The plot shows great agreement between the simulated values from SimScale and the CBE MRT calculator.

    mean radiant temperature cbe vs simscale line chart
    Figure 4: Line chart comparison of mean radiant temperature in degrees Celsius between the CBE tool and Simscale results for the 14 probe points

    The mean radiant temperature distribution on the north wall from SimScale and the CBE tool can be further observed in Figure 5:

    mean radiant temperature cbe tool vs simscale
    Figure 5: Mean radiant temperature contour comparison between the CBE MRT calculator and SimScale integrated online post-processor (north wall on the right)

    References

    • Modeling the comfort effects of short-wave solar radiation indoors 2015 Arens, Edward; Hoyt, Tyler; Zhou, Xin; Huang, Li; Zhang, Hui; Schiavon, Stefano

    Note

    If you still encounter problems validating you simulation, then please post the issue on our forum or contact us.

    Last updated: May 8th, 2024

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