Modeling Thermal Comfort

You can model thermal comfort with different levels of complexity. The Equivalent Homogeneous Temperature model quickly provides a local thermal comfort index in the form of the equivalent homogeneous temperature (EHT). The Fiala Thermoregulation model provides more detail in that it incorporates thermophysiological responses of the body and assesses thermal comfort through skin temperature distributions and global thermal comfort metrics.

For both models, you must subdivide the manikin geometry into addressable parts. The manikin geometries are not meshed, but represent only the body surface. For the Fiala Thermoregulation model, the temperature inside the manikin is computed on a thermal network that does not require a volume mesh.

Currently, you can run thermal comfort simulations only in steady-state. In the cabin or room, you compute the flow and thermal solution, considering solar and thermal radiation, convection, and conjugate heat transfer between the manikin and solid parts.

If you combine the Equivalent Homogeneous Temperature model and the Fiala Thermoregulation model in one simulation, the skin temperature for the Equivalent Homogeneous Temperature model comes from the Fiala Thermoregulation model. If you run the Equivalent Homogeneous Temperature model on its own, you specify the skin temperature at the thermal network interface.

To model thermal comfort:
  1. Import and mesh the cabin geometry. The passengers within the cabin are not meshed. If you want to consider heat conduction in a seat or the steering wheel, create a solid mesh with interfaces for these geometry parts.
    Consider the boundary conditions that you require for the thermal comfort simulation, for example, the inflow and outflow boundary conditions for the heating or cooling vents, or separate wall boundary conditions for transparent windows.
  2. Define the physics continuum for the cabin air flow.
    1. Right-click the Continua node and create a physics continuum for the cabin air flow.
    2. Right-click the [cabin air physics continuum] > Models node and select the following models:
      Group Box Model
      Space Three Dimensional
      Time Steady—you can model thermal comfort only as a steady-state simulation.
      Material Gas
      Flow One of:
      • Coupled Flow
      • Segregated Flow
      Equation of State One of:
      • Contant Density
      • Ideal Gas
      Viscous Regime Any
      Optional Models
      • Coupled Energy (if you selected Coupled Flow)
      • One of Segregated Fluid Enthalpy, Segregated Temperature (if you selected Segregated Flow
      • Radiation
      Solar Radiation Solar Loads
  3. If you are accounting for heat conduction in seats and/or the steering wheel, create another physics continuum for the solids. Select the appropriate energy models and define the solid material(s).
  4. (Optional) Run a purely thermal simulation without any Thermal Comfort model to obtain a good starting solution.
  5. Split the manikin surfaces into the parts required for the chosen thermal comfort model. See Splitting the Manikin Geometry.
  6. Define the thermal network continuum. In this thermal network continuum, you specify which thermal comfort models to use and set properties for the manikin.
    1. Right-click the Continua node and create another physics continuum.
    2. Right-click the [thermal network physics continuum] > Models node and select the following models:
      Group Box Model
      Optional Models Thermal Comfort

      See Thermal Comfort Model Reference.
      One of:
      • Coupled Fiala Thermoregulation—select this model if you want to perform a detailed thermal comfort analysis and you selected Coupled Flow in the [cabin air physics continuum] previously.
      • Segregated Fiala Thermoregulation—select this model if you want to perform a detailed thermal comfort analysis and you selected Segregated Flow in the [cabin air physics continuum] previously.
      • Equivalent Homogeneous Temperature—select this model if you want to perform a quick thermal comfort analysis. You can select this model also as an addition to one of the Fiala models.

      See Coupled and Segregated Fiala Thermoregulation Model Reference and Equivalent Homogeneous Temperature Model Reference.

      Steady and Manikin are selected automatically.
    3. Expand the [thermal network physics continuum] > Models > Manikin > [manikin] > node and, depending on your thermal comfort model selection, do the following:
      Thermal Comfort Model Steps
      Segregated/Coupled Fiala Thermoregulation
      1. Select the Fiala Manikin Properties node and specify Activity Level (met) of the passenger for which you want to determine the thermal comfort. The activity level represents the metabolic rate of the manikin. The default value of 0.8 corresponds to a human at rest; higher values indicate physical activity of the manikin prior to getting into the vehicle cabin.

        The manikin is of pre-defined height (1.9096 m), weight (73.4 kg), and age (35 years).
      Equivalent Homogeneous Temperature
      1. Expand the EHT Segments node.

        There is a sub-node for each of the 17 body segments of the EHT manikin.

      2. Select each of the [EHT body segments] nodes and specify x0 and x1. These properties are the linearization coefficients of the EHT algorithm. Typically, you leave them at their default values. For more information, see EHT Manikin Segment Properties.
  7. Define the thermal network region for the manikin.
    1. Right-click the Regions node and select New > Network Region.
    2. Select the Regions > [thermal network region] node and set the following properties:
      Property Setting
      Physics Continuum By default, this property is automatically assigned to the [thermal network continuum].
      Parts Select the segmented Fiala or EHT manikin geometry part.
      If you want to determine thermal comfort for several manikins, you can either assign multiple manikin geometry parts to Parts for one network region or you can create a thermal network region for each manikin geometry part.
    3. Select the [thermal network region] > Physics Values > Manikin Part Groups > [manikin] node and set Parts to the manikin geometry part.
      This selection associates the part surfaces of the mankin geometry part to the network links of the Fiala Thermoregulation model.
    4. Expand the [manikin] node and do the following:
      • If you selected one of the Fiala Thermoregulation models, select each Network Links > [network link node] node and set Part Surfaces to the corresponding part surface of the manikin geometry part.
      • If you selected the Equivalent Homogeneous Temperature model, select each EHT Segments > [EHT segment node] node and set Part Surfaces to the corresponding part surface of the manikin geometry part.
      NoteIf you follow the naming convention for naming the part surfaces of the manikin geometry, Part Surfaces is associated automatically to the correct part surface of the manikin geometry for each [network link node] or [EHT segment node]. If you use one of the Fiala Thermoregulation models together with the Equivalent Homegeneous Temperature model in one thermal comfort simulation, it is sufficient to have one Fiala segmented manikin for both models, provided that you follow the naming convention. In that case, Simcenter STAR-CCM+ recognizes the body part segment strings in the Fiala names and maps them automatically onto the EHT segments. For more information, see Manikin Segmentation Naming Convention Reference.
      If you do not follow the naming convention for naming the part surfaces of the manikin geomery, use dynamic queries to find the correct surfaces or select them manually. If you have multiple manikins in your thermal network region, these manikins appear as individual [manikin] nodes.
    5. For the Fiala Thermoregulation models only, select the [thermal network region] > Physics Values > Ambient Relative Humidity node and specify a relative humidity percentage for the air in the cabin.
  8. Create interfaces between the thermal network region for the manikin and the other fluid and solid regions.
    1. Multi-select the Regions > [thermal network region] and [cabin air region] nodes and select Create Interface.
      The Interfaces > [thermal network region]/[cabin air region] interface is created. This interface is of type Thermal Network Interface.
    2. Select the Interfaces > [thermal network region]/[cabin air region] node and set Contacts to all contacts between the manikin and air that have been created previously during the geometry preparation and meshing process, (for example, by imprinting).
    3. If you are considering heat conduction in a solid seat or steering wheel and the manikin is in contact with it, multi-select the Regions > [thermal network region] and [solid seat region] nodes and select Create Interface.
      The Interfaces > [thermal network region]/[solid seat region] interface is created. This interface is of type Thermal Network Interface.
    4. Select the Interfaces > [thermal network region]/[solid seat region] node and set Contacts to all contacts between the manikin and the solids (seats or steering wheel) that have been created previously during the geometry preparation and meshing process, (for example, by imprinting).
  9. Specify the evaporative resistance and the contact resistance of clothing.
    1. Expand the Interfaces > [thermal network region/[cabin air region]/[solid seat region] > Physics Values node and select the following nodes:
      Node Setting
      Clothing Evaporative Resistance—represents to what extent the clothes pose a resistance to the sweat that is evaporating from the body of the manikin to the environment. Specify a constant value for the entire manikin body in Pa-m2/W. A low value for the evaporative resistance corresponds to high evaporation.
      Contact Resistance—represents the thermal insulation effect of clothes. Specify a constant value for the entire manikin body in m2K/W. Another unit that is used in industry is clo. 1 clo = 0.155 m2K/W. A value of clo = 0 corresponds to bare skin, a value of clo = 1 corresponds to the amount of clothing that is needed to keep a person comfortably at rest at room temperature of 21 ℃ with relative humidity of 50%. Such clothing can be, for example, a business suit.
    2. If you want to specify Clothing Evaporative Resistance and Contact Resistance locally for each body part surface, repeat Step 8 and create interfaces for each body part surface that you require. Set Contacts for each of these interfaces to the local contacts. For example, if you want to specify a local clothing evaporative resistance for the head, you select all contacts belonging to the head. Following the naming convention, these contacts contain the names Face_L, Face_R, Head_Back, and Head_Top.
  10. If you are using the Equivalent Homogeneous Temperature model without the Fiala Thermoregulation model, select the Interfaces > [thermal network region interface] > Physics Values > Static Temperature node and specify the skin temperature.
    The thermal specification condition under Physics Conditions is set to Specified Temperature.
  11. To assess thermal comfort, create dedicated reports for the Fiala and the Equivalent Homogeneous Temperature models.
    1. Right-click the Reports node and select New > Flow / Energy, then choose the following reports:
      Thermal Comfort Model Report
      Segregated/Coupled Fiala Thermoregulation
      Equivalent Homogeneous Temperature Equivalent Homogeneous Temperature

      For more information, see Equivalent Homogeneous Temperature.
    2. Select each [thermal comfort report] that you require and set Parts to the manikin geometry part.
    3. Create monitors and plots for each of these reports.
  12. Visualize the manikin temperatures:
    1. Create a scalar scene and set Parts to Regions > [cabin air region] > [interface boundaries of interfaces between manikin and cabin air].
      Since the thermal network region for the manikin is not meshed, you cannot visualize any quantities directly on the thermal network region boundaries. Instead, you use the interface boundaries on the [cabin air region] side to display the values.
    2. If you want to visualize the passenger clothing temperature, set Scalar Field to Temperature.
    3. If you want to visualize the skin temperature of the passenger, set Scalar Field to Temperature on External Side.
  13. Run the simulation.