Periodic Reporting for period 2 - comfortA (A better understanding of thermal Alliesthesia and thermal Adaptation for correctly predicting dynamic thermal comfort)
Période du rapport: 2022-09-01 au 2023-08-31
As humans, we are frequently exposed to transient thermal conditions during our daily lives. These exposures can be the results of our actions such as changes in clothing, body posture, and activity. They can be also encountered in free-running buildings due to fluctuating temperatures and air velocities, or in any building when transitioning between different building thermal zones, or between a building and the outdoors. Lately, ways forward for actively implementing heating and cooling set-point temperature modulations are being explored to promote building energy savings and boost their energy flexibility as part of demand-management electricity programs.
Despite transient thermal states being widespread in the built environment and in spite of their potential to create thermal delight and enhance building occupants’ well-being and health, a quantitative model to describe dynamic thermal sensation and comfort does not yet exist. Much of the effort in thermal comfort research has been dedicated to understanding which set of environmental and personal steady-state conditions leads to thermal comfort. As a consequence, the psycho-physiology of thermal perception under transient conditions remains relatively poorly understood and we are still far from being able to design and control dynamic modulations of indoor set-point temperatures that would be acceptable, let alone comfortable for occupants.
The proposed research project aims to address this knowledge gap by shedding new light on the psycho-physiological mechanisms driving the dynamic thermal perception, with a particular focus on the phenomena of thermal alliesthesia and thermal adaptation, and by creating a more accurate physiological-based thermal comfort model, which can better account for these two phenomena. This project will provide the research community with a new robust set of empirical data, novel knowledge and a novel thermal comfort model, which has the potential to revolutionize the way professionals design and operate indoor comfort systems: not just aiming for thermal neutrality but striving for thermal delight.
Despite transient thermal states being widespread in the built environment and in spite of their potential to create thermal delight and enhance building occupants’ well-being and health, a quantitative model to describe dynamic thermal sensation and comfort does not yet exist. Much of the effort in thermal comfort research has been dedicated to understanding which set of environmental and personal steady-state conditions leads to thermal comfort. As a consequence, the psycho-physiology of thermal perception under transient conditions remains relatively poorly understood and we are still far from being able to design and control dynamic modulations of indoor set-point temperatures that would be acceptable, let alone comfortable for occupants.
The proposed research project aims to address this knowledge gap by shedding new light on the psycho-physiological mechanisms driving the dynamic thermal perception, with a particular focus on the phenomena of thermal alliesthesia and thermal adaptation, and by creating a more accurate physiological-based thermal comfort model, which can better account for these two phenomena. This project will provide the research community with a new robust set of empirical data, novel knowledge and a novel thermal comfort model, which has the potential to revolutionize the way professionals design and operate indoor comfort systems: not just aiming for thermal neutrality but striving for thermal delight.
Three thermal comfort experiments with human participants in climate chambers were designed, prepared and run. These experiments were dedicated to studying warm and cold cyclical temperature variations at different times of the day during both summer and winter. These studies included over 200 participants (about half females and half males) aged between 20 and 60 years old. The experiments aimed to better understand how the psycho-physiological phenomena of thermal alliesthesia and thermal habituation affect human thermal perception under dynamic cyclical variations of indoor air temperature. They also aimed to quantify the impact of interindividual and, in particular, sex differences in the unfolding of these two phenomena. During the experiments, the environmental conditions in the test rooms were finely controlled and monitored, including air temperature, mean radiant temperature, relative humidity, air velocity, light (spectrum and illuminance), and CO2 concentration. Skin temperature was measured with both thermocouples and a thermal camera. Participants were asked to repeatedly fill out a questionnaire to assess their thermal sensation, thermal comfort/pleasure and thermal preference.
The analysis of the collected experimental data revealed interesting insights into the impact of interindividual differences on human dynamic thermal perception. In particular, females were found to have greater skin temperature variations during cooling transients than males and, correspondingly, experienced stronger thermal sensation overshoot responses. These differences in perceptual responses could be fully explained in terms of skin temperature differences since the relationship between the thermal sensation vote and the skin temperature was found to be independent of sex. We tested whether other factors influence the interindividual variability of the dynamic sensory response and found that the participant's Body Mass Index (BMI) and age affect the thermal sensation overshoot response to cutaneous thermal transients by diminishing it as the BMI increases and the age decreases. We hypothesize that the decrease in thermal sensitivity with the BMI could be due to a higher thickness of subcutaneous fat associated with a higher BMI. While the observed increase of thermal sensitivity with age up to 50-60 years old could be explained in terms of menopausal hormonal changes. These experimental results suggest that we need to account for interindividual differences not only in thermophysiological models but also in physiological-based thermal perception models.
The collected experimental data were also used to build a novel model that can predict the Whole-Body Dynamic Thermal Sensation and Thermal Comfort under uniform and transient thermal conditions. The model is based on physiological signals (body core temperature, mean skin temperature and its rate of change, skin wetness) simulated with Gagge’s two-node thermophysiological model. The model has three specific features:
• It correctly accounts for the impact of high relative humidity at high air temperatures by including skin wettedness as an input.
• It correctly accounts for the effect of exercise. The relation between thermal sensation and mean skin temperature when exercising is not the same as that observed during rest since exercise reduces thermal sensitivity.
• It correctly models the dynamic sensory phenomena of “thermal overshoot” and “thermal alliesthesia” a function of both the rate of change in the skin temperature and the mean skin temperature.
The validation is performed against more than 60 thermal exposures to steady-state and transient conditions and shows that the novel model has better predictive performances than the classical Fanger’s PMV/PPD model, especially for dynamic conditions far from neutrality.
The analysis of the collected experimental data revealed interesting insights into the impact of interindividual differences on human dynamic thermal perception. In particular, females were found to have greater skin temperature variations during cooling transients than males and, correspondingly, experienced stronger thermal sensation overshoot responses. These differences in perceptual responses could be fully explained in terms of skin temperature differences since the relationship between the thermal sensation vote and the skin temperature was found to be independent of sex. We tested whether other factors influence the interindividual variability of the dynamic sensory response and found that the participant's Body Mass Index (BMI) and age affect the thermal sensation overshoot response to cutaneous thermal transients by diminishing it as the BMI increases and the age decreases. We hypothesize that the decrease in thermal sensitivity with the BMI could be due to a higher thickness of subcutaneous fat associated with a higher BMI. While the observed increase of thermal sensitivity with age up to 50-60 years old could be explained in terms of menopausal hormonal changes. These experimental results suggest that we need to account for interindividual differences not only in thermophysiological models but also in physiological-based thermal perception models.
The collected experimental data were also used to build a novel model that can predict the Whole-Body Dynamic Thermal Sensation and Thermal Comfort under uniform and transient thermal conditions. The model is based on physiological signals (body core temperature, mean skin temperature and its rate of change, skin wetness) simulated with Gagge’s two-node thermophysiological model. The model has three specific features:
• It correctly accounts for the impact of high relative humidity at high air temperatures by including skin wettedness as an input.
• It correctly accounts for the effect of exercise. The relation between thermal sensation and mean skin temperature when exercising is not the same as that observed during rest since exercise reduces thermal sensitivity.
• It correctly models the dynamic sensory phenomena of “thermal overshoot” and “thermal alliesthesia” a function of both the rate of change in the skin temperature and the mean skin temperature.
The validation is performed against more than 60 thermal exposures to steady-state and transient conditions and shows that the novel model has better predictive performances than the classical Fanger’s PMV/PPD model, especially for dynamic conditions far from neutrality.
Given that the rates of change in the air temperatures studied in the experiments are those that can be typically found in buildings during demand-response events, our results can contribute to the design and control of comfortable temperature fluctuations during these events. In particular, these results point to the importance of using Personal Comfort Systems as a further means of accommodating individuals’ thermal needs, in particular females’ ones, while at the same time being able to operate on batteries and, therefore, independently of the grid during demand-management events.
The novel Whole-Body Dynamic Thermal Sensation and Thermal Comfort Models have the potential to be used in the design and control of comfortable temperature fluctuations. Their simplicity and low computational cost are important advantages over more complex and computationally expensive thermal perception models based on multi-segment and multi-node thermo-physiological models.
The novel Whole-Body Dynamic Thermal Sensation and Thermal Comfort Models have the potential to be used in the design and control of comfortable temperature fluctuations. Their simplicity and low computational cost are important advantages over more complex and computationally expensive thermal perception models based on multi-segment and multi-node thermo-physiological models.