Introduction
The COMFort formulA (COMFA) is a human energy-budget model that uses physically-based equations to describe the flows of heat to and from a person’s body. It is based on the principle that energy cannot be created or destroyed. It adds up all the heat energy a person receives and subtracts the heat energy that a person is able to give off. If the result is a positive amount of energy, the person will become warmer over time. And if the result is negative, the person will become cooler over time.
The main inputs of energy are:
Metabolism of the person. This is the amount of energy that a person is creating inside their body based on their activity level. The harder a person works, the more energy they produce. These values are typically derived from international standard tables.
Solar Radiation is absorbed by the person. COMFA uses equations to identify the location of the sun in the sky and uses three-dimensional geometry to determine how much solar radiation heats up the person.
Terrestrial radiation (AKA Longwave Radiation) is absorbed by the person. COMFA uses the well-known Stefan-Boltzman equation to model how much terrestrial radiation a person receives from their environment. The higher the temperature of nearby objects and/or the ground, the more terrestrial radiation a person will receive.
The main outputs of energy are:
Convection. The amount of energy convected away from (and in some cases towards) a person is calculated based on three values: the temperature difference between the air and the person’s skin temperature; the speed of the wind; and the level of clothing a person is wearing. The greater the temperature difference and the higher the wind speed the more convection. The more clothing a person is wearing the lower the convection.
Evaporation. The amount of energy that is carried away from a person through evaporation of sweat and respiration is calculated based on four things: the humidity of the air; the amount of sweat a person produces; the amount of respiration; and the level of clothing a person is wearing. The higher the air humidity, the lower the sweat and respiration levels, and the more clothing, the less cooling.
Terrestrial Radiation emitted. Everything on Earth emits terrestrial radiation as a function of its temperature and in some cases, as a function of the material, it’s made of. The amount of terrestrial radiation emitted by a person depends on their skin temperature and/or the temperature of the surface of their clothing.
Application of COMFA
When site conditions are input to COMFA each of the streams of energy is calculated and reported in Watts per square meter (Wm-2). By comparing the magnitude of the streams the most influential component can be identified. For example, in hot and sunny conditions, solar radiation might provide the largest stream of energy gain. In cold and cloudy conditions, convective cooling might be the largest stream of energy lost. Once the most important components are identified, the design can modify the elements in the landscape accordingly to reduce the stream.
COMFA Versions
COMFA
The basic COMFA model, appropriate for estimating the thermal comfort of adults, was developed by Dr. Terry Gillespie and Dr. Robert D. Brown who were both at the University of Guelph at the time. It is available in three programming languages: Excel; Matlab; and Python. The model is built in modules so it is easy for someone to modify the equations as their research or design project requires. In these versions, you input your own data.
COMFA-TD (COMFA Typical Days)
This version of COMFA has a complete set of microclimate data from cities around the world. It was developed by Dr. Jenni Vanos, now working at Arizona State University. All climate zones in the world have a representative city. Select the city in your Koppen-Geiger climate zone, and then simply input information about your site and your modeled person. COMFA-TD will generate thermal comfort estimates for typical conditions.
COMFA-K (COMFA-Kid)
This version of COMFA was developed by Dr. Wenwen Cheng from the University of Wisconsin-Madison. The equations have been revised to account for differences between children and adults. Please contact her if you are interested in details.
COMFA-Elderly
This version is currently developing by Dr. Zhixin Liu from the University of Sheffield and her colleagues at the Chinese University of Hong Kong as well as Xiaoyu Li from the Texas A&M University. This specific model is designed to be used in hot, humid climates to estimate the thermal comfort level of elderly people. Please contact them if you are interested in details.
COMFA-Courtyard
This version was developed by Dr. Renzhi Wu from the South China University of Technology, and can be used to estimate the thermal comfort conditions inside a courtyard.
Downloads:
We invite you to use COMFA in your research. It is in modular format and open architecture so each component can be readily adjusted. Please feel free to modify the components as necessary to meet the conditions of your study.
COMFA-K (not available for now)
COMFA-Elderly (not available for now)
Last update on Oct. 2023.