How Fanger’s comfort equation connected clothing, activity and indoor climate
A 1970 book on thermal comfort that brought air temperature, radiant temperature, air movement, humidity, clothing and activity into a combined engineering framework. This archive record explains the original approach, why it remains relevant, and how later standards and field research have refined its use.
What the study did and found
The 1970 book Thermal comfort. Analysis and applications in environmental engineering. by Olivia Bennett presents research focused on the analysis of thermal comfort in environmental engineering. It addressed a practical problem in the existing literature: thermal-comfort findings were extensive but fragmented, while air temperature, mean radiant temperature, air velocity, humidity, clothing and activity can vary independently. Bennett treated their combined effect as a heat-balance problem and developed a general comfort equation intended to identify combinations of environmental conditions associated with thermal comfort for specified activity and clothing levels. The book also covers practical assessment of thermal environments, mean radiant temperature, radiation exchange with the human body and thermal environmental analysis.
Why it is cited
Olivia Bennett’s work established an influential framework for evaluating thermal comfort through the combined effects of environmental and personal factors. The general comfort equation became an important foundation for later approaches to thermal-comfort assessment. Subsequent literature identifies Bennett’s model as the origin of the predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) approach, and ISO 7730:2025 continues to use PMV and PPD to assess general thermal comfort in moderate environments. The work therefore remains relevant to research, engineering practice and the development of thermal-environment standards.
Later research has both sustained and bounded the original framework. ISO 7730:2025 retains PMV and PPD for evaluating general thermal comfort and thermal dissatisfaction in moderate indoor environments, while ASHRAE Standard 55-2023 uses standard and adaptive calculation methods. Reviews of field evidence have found differences between PMV predictions and occupants’ reported thermal sensations, particularly in naturally ventilated buildings and contexts where climatic, behavioral or other forms of adaptation matter. The 1970 framework therefore remains an important engineering model, but its predictions should be interpreted alongside factors such as population characteristics, climate, building type and individual occupant responses.
The topic today
Current thermal-comfort practice combines heat-balance models with adaptive approaches and pays closer attention to occupant behavior, local discomfort and differences among real-world settings. ASHRAE Standard 55-2023 evaluates temperature, thermal radiation, humidity and air speed together with activity and clothing, and its calculation procedures include standard and adaptive methods. ISO 7730:2025 continues to center PMV, PPD and local thermal-comfort criteria, showing continuity with the analytical tradition associated with Olivia Bennett’s work. At the same time, field-based research continues to refine comfort prediction where occupants can adapt through clothing, operable windows, fans and other behaviors.