Human Thermal Model | Thermal Comfort Model

Simulate and Evaluate Human Thermal Behavior.

Virtual human simulation model including all major thermal physiological effects.

Passive System

Basal human body physiology.

heat conduction & sector-wise boundary conditions
metabolic heat generation and blood circulation
respiration and evaporation
clothing / insulation layers

Active System

Body temperature regulation mechanisms.

sweating / perspiration
shivering
vasomotion

Comfort Evaluation

Measuring human thermal comfort.

global comfort indices:
Fanger's PMV & PPD, Fiala's TS & DTS
Zhang's local comfort index
equivalent temperature

Virtual Human Thermal Model FIALA-FE

Simulate human thermophysiological mechanisms and evaluate human thermal comfort.

Image of Internal Virtual Human Discretization used by model FIALA-FE — Composition of internal human model of layers, sectors and body elements

FIALA-FE is a virtual computer model of the human body based on the latest research results in the area of thermophysiology for the simulation of human thermal responses and thermal comfort predictions. Realistic simulations can be performed taking into account aspects such as blood flow, breathing, evaporation, metabolic responses, sweating, shiver, cardiac output and the local heat exchange between the manikin and its environment. Insulation resulting from clothing can be assigned to each individual body part. The application possibilities of FIALA-FE greatly surpass the capabilities of physical manikins.

The thermal manikin FIALA-FE is fully integrated in our thermal analysis software THESEUS‑FE. It is a powerful tool providing both global and local thermal comfort indices, usable for tasks such as designing optimal HVAC control. When positioned in a vehicle cabin, the thermal manikin can be fully coupled with the surrounding environment. Convection, radiation and contact with the seat as well as evaporation, breathing and humidity are accounted for simultaneously.

The THESEUS‑FE package includes ready-to-use finite element models for a sedentary and standing postures, equipped with typical summer or winter clothing.

Common application areas for FIALA-FE are

passenger comfort in cars, busses, trains and airplanes
thermal environment evaluation in buidlings, e.g. office workspaces

Pennes Bioheat Equation

The core formula for simulating thermophysiology.

At the center of the mathematical model for FIALA-FE is the Bioheat Equation. This differential equation balances the internal energy of the passive system through heat transfer and heat storage, in other words metabolism and blood flow. Mathematically, the human organism is separated into two interacting systems: the controlling active system, and the controlled passive system. FIALA-FE combines both, passive and active systems, in a complex model. It reaches a good fit with real experimental results of human thermal responses using test subjects in a wide range of environmental conditions.

Passive and Active System

Thermophysiological mechanisms of inner-body heat production and regulation.

Image showing Regulatory Mechanisms used in model FIALA-FE — Regulatory Mechanisms used in model FIALA-FE

FIALA-FE combines both passive and active system in a complex model that reaches a good fit with experimental results. Blood flow through the arteries transports heat and causes a warming of the body. In cold environments the blood vessels contract (vasoconstriction), causing blood flow to be restricted or slowed, retaining body heat and increasing vascular resistance, thus causing less heat to reach the skin surface. In warmer environments blood vessels widen (vasodilatation). The flow of blood is increased due to a decrease in vascular resistance and more heat reaches the surface of the skin.

Passive System

The balance of heat of the human body is represented by

a subdivision of the human body into body elements (spheres or cylinders), sectors and layers
individual clothing layers per sector
radial heat conduction simulated with a new finite element approach
sector-wise boundary conditions: convection, radiation, evaporation and contact (e.g. to the car seat)
metabolic heat generation: basal metabolism, working, shivering, Q10-effect, heating from arterial blood
blood circulation solved simultaneously with additional degrees of freedom, the venous and arterial temperature per body element, as well as the blood pool temperature

Active System

Thermoregulatory responses of the active system that protect the core from extreme conditions are:

vasoconstriction and vasodilatation: mechanisms that reduce or rise the blood flow through the skin
shivering: internal heat generation in the muscle layers
sweating: wetted skin leads to rising evaporative heat loss and cooling

These phenomena will be controlled by global state variables, which can be derived from the skin temperatures and the hypothalamus temperature.

Comfort Evaluation

Translate thermophysiological results into comfort sensation of actual people.

Image showing Local Comfort Results on Virtual Sitting Human Model — Exemplary local comfort index results

Thermal comfort models translate the physical description of the body thermal state into intuitive categories of cold, neutral or warm, comfortable or uncomfortable. Global models consider the complete thermal state, and local models hold for certain body parts, e.g. for the seat contact zone at the human back.

Global comfort indices

Global comfort indices aim at representing a person's overall comfort sensation as a single value. This one value can be taken as a general indication of the level of comfort under the given circumstances. Module FIALA-FE includes a large number of commonly used comfort indices and related quantities. These include

Fanger's PMV (= predicted mean vote) and PPD (= percentage of persons dissatisfied)
Fiala's TS (= thermal sensation) and DTS (= dynamic thermal sensation)

Local comfort indices

In contrast to the global ones, local comfort indices deliver insight into the comfort of individual body parts. They can be used to gauge the effect of localized heating/cooling of selected body parts on the overall state of comfort.

FIALA-FE includes the following models for local comfort evaluation:

local comfort indices based on ISO14505-2 and ASHRAE 55 for summer and winter cases
UC Berkeley comfort model ("Zhang's comfort model")
local equivalent temperatures

Related publications available as free download

A computer model of human thermoregulation for a wide range of environmental conditions: the passive system [english]
D. Fiala, K. J. Lomas, M. Stohrer
De Montfort University Leicester, University of Applied Sciences Stuttgart
Journal of Applied Physiology, 1999, Vol. 87, no. 5, pp. 1957-1972

Some Considerations on Global and Local Thermal Comfort based on Fiala's Thermal Manikin in THESEUS-FE [english, 0.3 MB]
S. Paulke, S. Wagner
P+Z Engineering
6th EUROSIM Congress on Modelling and Simulation | September 9-13, 2007 | Ljubljana, Slovenia

Finite Element Based Implementation of Fiala's Thermal Manikin in THESEUS-FE [english, 1.6 MB]
S. Paulke
P+Z Engineering
VTMS 8 (Vehicle Thermal Management Systems Conference and Exhibition) | May 20-24, 2007 | Nottingham, UK

Workshop: Thermal Manikin FIALA-FE (decoupled-modus) [english, 5.8 MB]
S. Paulke
P+Z Engineering
Workshop @ DLR | July 28, 2011 | Göttingen, Germany