Thermal Comfort: Analysis and Applications in Environmental Engineering
About this book
Thermal Comfort: Analysis and Applications in Environmental Engineering P.O. Fanger McGraw-Hill (US edition); Danish Technical Press (original 1970) Summary based on: Wikipedia article on Thermal Comfort and Povl Ole Fanger; National Research Council Canada report IRC-RR-162 by K.E. Charles on Fanger's models; Van Hoof (2008) 'Forty years of Fanger's model of thermal comfort' in Indoor Air journal; ScienceDirect Comfort Equation overview; ASHRAE and ISO 7730 standard references; Scribd document of the 1972 edition; Cornell University Thermal Comfort lecture notes.
Poul Ole Fanger's 'Thermal Comfort: Analysis and Applications in Environmental Engineering' is one of the most consequential scientific works ever produced in the field of building environmental science. First published in 1970 by the Danish Technical Press and subsequently issued by McGraw-Hill, the book introduced a rigorous, quantitative framework for defining and predicting thermal comfort that has shaped building codes, HVAC engineering standards, and indoor environment research for more than half a century. Fanger's central intellectual contribution was transforming thermal comfort from a vague, subjective notion into a precise, measurable phenomenon amenable to engineering analysis.
Prior to his work, comfort was addressed largely through empirical rules of thumb and comfort zones defined by simple temperature ranges. Fanger's achievement was to root the analysis in the thermophysiology of the human body — specifically, in the conditions under which the body achieves a steady-state heat balance — and to translate that physiological foundation into a predictive mathematical model. The book's analytical framework begins with the heat balance of the human body.
The body generates heat through metabolic activity and must continuously exchange that heat with its surroundings through a combination of radiation, convection, conduction, and evaporation. Thermal comfort arises when the body can maintain thermal equilibrium without resorting to excessive thermoregulatory effort — without significant sweating, shivering, or altered peripheral blood flow. Fanger derived a 'comfort equation' that specifies the precise combination of environmental and personal variables under which this equilibrium is achieved at a state of minimal physiological strain.
The six input variables of Fanger's model fall into two categories. The four environmental variables are: air temperature, mean radiant temperature (the weighted average temperature of the surrounding surfaces with which the body exchanges radiant heat), relative air velocity, and relative humidity (expressed as partial water vapor pressure). The two personal variables are: metabolic rate, reflecting the level of physical activity, and clothing insulation, expressed in 'clo' units — a measure of the thermal resistance of the garments worn.
The systematic identification and simultaneous treatment of all six variables was itself a major advance, demonstrating that comfort cannot be adequately characterized by air temperature alone. Fanger's empirical validation of his model drew on carefully controlled experiments involving approximately 1,300 subjects at Kansas State University in the United States and at the Technical University of Denmark. Subjects were exposed to systematically varied combinations of the six comfort variables and asked to rate their thermal sensation on a seven-point scale running from cold (-3) to hot (+3), with 'neutral' (0) at the center.
Statistical analysis of this large dataset yielded the Predicted Mean Vote (PMV) index, which estimates the average thermal sensation vote of a large group of people in a given environment. A companion index, the Predicted Percentage Dissatisfied (PPD), was derived from PMV to estimate the proportion of occupants who would report dissatisfaction — either feeling too warm or too cool — under given conditions. The mathematical relationship between PMV and PPD shows that even at a perfectly neutral PMV of zero, approximately 5% of occupants will still express dissatisfaction, establishing a practical lower bound on achievable comfort.
Beyond the global PMV/PPD framework for overall thermal sensation, the book also addresses local thermal discomfort — the ways in which non-uniform thermal environments can cause discomfort even when the overall heat balance is satisfied. Fanger identified four principal sources of local discomfort: draught (unwanted air movement across exposed skin, particularly the neck and ankles), radiant temperature asymmetry (unequal radiant heat exchange between the body and different parts of its surroundings, as from a cold window or a hot ceiling), vertical air temperature gradients, and floor surface temperatures that are too cold or too warm for the feet. Each of these local effects was analyzed with the same quantitative discipline applied to the global model, yielding design criteria that could be directly incorporated into building specifications.
The book also presents practical applications of the theoretical framework to environmental engineering, demonstrating how the comfort equation can be used to specify acceptable indoor climate conditions for different building types and occupancy patterns. Fanger showed how the model could be inverted — used not just to evaluate existing conditions but to set design targets for heating, ventilating, and air-conditioning (HVAC) systems. This application-oriented dimension made the work directly useful to engineers and architects, extending its reach far beyond the academic literature.
The international influence of Fanger's model has been profound. The PMV/PPD framework was adopted as the basis of ISO Standard 7730, first published in 1984 and revised multiple times since, as well as ASHRAE Standard 55, the primary North American standard for thermal environmental conditions for human occupancy. These standards govern the design of virtually every mechanically conditioned building in the world.
The model has also been incorporated into building simulation software, energy performance standards, and certification systems including those used in green building assessment. Subsequent decades have seen both the validation and the critique of Fanger's approach. Researchers have noted that the PMV model was calibrated primarily on young, healthy, sedentary populations in controlled laboratory conditions and that its predictive accuracy varies for older individuals, for people in naturally ventilated buildings, and for populations in climates very different from those of Denmark and Kansas.
The adaptive comfort model, developed in the 1990s, emerged partly in response to these limitations, offering a complementary approach for naturally ventilated contexts. Nevertheless, Fanger's PMV/PPD model remains the dominant framework in the field, particularly for mechanically conditioned buildings, and his 1970 book remains the foundational reference upon which all subsequent thermal comfort research is built. For green building professionals, the significance of Fanger's work is twofold.
First, it provides the scientific basis for evaluating whether a proposed building design — envelope, HVAC system, fenestration — will deliver acceptable thermal conditions for occupants. Second, it highlights the degree to which thermal comfort drives energy consumption: the pursuit of PMV values near zero across all climate conditions is a major driver of heating and cooling loads, making the comfort model central to any serious analysis of building energy performance and the trade-offs between occupant well-being and environmental impact.