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Physiological Model

The Vehicle Ancillary Loads Reduction team developed a three-dimensional model to simulate human internal thermal physiological systems (muscle, blood, etc.) and thermoregulatory responses such as metabolic heat generation. The model was developed with ANSYS, a finite element software which computes heat flow by conduction, convection, and mass transport of the blood.

A human tissue system model represents the human body, including the physiological and thermal properties of the tissues. The arms and legs consist of bone, muscle, fat, and skin. There are additional lung, abdominal, and brain tissues in the torso and head zones. The model calculates the conduction heat transfer based on the temperature gradients between the tissue nodes. Blood flow is modeled with a network of supply and return pipe elements within each body zone.

Schematic of physiological model in the thermal manikin.

The physiological model was generated in sections, consisting of hand, lower arm, upper arm, foot, lower leg, and thigh, one each for the left and right sides. The body is developed as a torso together with neck and head. Each part is generated individually and populated with arteries and veins. The primary blood vessels join via capillaries placed adjacent to the skin layer.

The thermoregulatory system in the model controls physiological responses such as vasomotor control, sweating, shivering, and metabolic changes. Blood vessels constrict and dilate at differing rates in different body zones, according to changes in skin and core temperatures. Equations controlling constriction and dilation are based on medical experiments. The sweating response also is a function of skin and core temperatures, and the number of sweat glands in each zone. With approximately 40,000 nodes and elements, this complex model provides a very detailed picture of temperature distribution in the body.

The physiological model sends and receives data to/from the thermal manikin and sends the data to the thermal comfort model.