Models of human thermoregulation and the prediction of local and overall thermal sensations

This study aims at comparing the predictions of skin temperature from different models of human thermoregulation and investigating the currently available methods for the prediction of the local and overall thermal sensations. In this paper, the Fiala model, the University of California, Berkeley (UCB) thermoregulation model and a multi-segmental (MS) Pierce model were tested against recently measured data from the literature. The local and overall thermal sensations were predicted for different room conditions, obtained from a recent experimental study, using the UCB comfort model coupled with the MS-Pierce model. The overall thermal sensation was further predicted using three other models. The predictions were then compared with the subjective votes obtained from that study. The equivalent temperature approach was also investigated based on the same experimental study. The results show comparisons of the predicted skin temperature by the thermoregulation models, under steady state and dynamic conditions, with the measured data as well as the predictions of the thermal sensations from the different models.     

Effects of temperature steps on human skin physiology and thermal sensation response

Air-conditioning is frequently used as a means of adjusting indoor thermal environment in hot-and-humid areas. However, when entering an air-conditioned building from outdoors people may experience thermal discomfort and risk health consequence if the instantaneous change of air temperature exceeds the thermoregulatory capacity. A study was conducted to investigate the alteration in thermal perception and in thermoregulation that simultaneously occurred in response to temperature step in a thermal transient. In this study, two temperature down-steps from 32/28 to 24 °C and an up-step from 20 to 24 °C were created in a climatic chamber consisting of two microclimate-controlled rooms, and subjects were evaluated for change in thermal sensation as well as in skin physiological properties, including skin capillary blood flow (SCBF), skin moisture, transepidermal water loss (TEWL), and skin temperature over the course of acclimation. As the results show, a cold sensation overshot occurred in thermal sensation vote (TSV), skin temperature, and SCBF in 1 min after the temperature dropped from 32 to 24 °C. TSV correlated the best with skin temperature (r = 0.60) and moderately with skin moisture and TEWL (r = 0.42–0.54) when the temperature down-step reached 8 °C. TEWL acclimated in a two-stage pattern, demonstrating a difference between the sensational change and thermoregulation. The gender-specific influence occurred in thermoregulation but not in subjective sensation. The findings of the study suggest that thermoregulatory burden might be adequately controlled when the temperature step in thermal transition zone is limited to 4 °C or lower.     

Overall thermal sensation,acceptability and comfort

The relationships between overall thermal sensation, acceptability and comfort were studied experimentally under uniform and non-uniform conditions separately. Thirty subjects participated in the experiment and reported their local thermal sensation of each body part, overall thermal sensation, acceptability and comfort simultaneously. Sensation, acceptability and comfort were found to be correlated closely under uniform conditions and acceptable range ran from neutral to 1.5 (midpoint between ‘Slightly Warm’ and ‘Warm’) on thermal sensation scale and contained all comfortable and slightly uncomfortable votes on thermal comfort scale. Under non-uniform conditions overall thermal acceptability and comfort were correlated closely. However, overall thermal sensation was apart from the other two responses and non-uniformity of thermal sensation was found to be the reason for the breakage. Combining the effects of overall thermal sensation and non-uniformity of thermal sensation, a new thermal acceptability model was proposed and the model was testified to be applicable to uniform and non-uniform conditions over a wide range of whole body thermal state from neutral to warm.     

Effects of radiant temperature on thermal comfort

The aim of this paper is to investigate the local differences between body segments caused by high radiant temperature, and to analyze the interior surface temperatures for different wall and ceiling constructions with their effect on thermal comfort. For the segment-wise thermal interactions between human body and its surrounding, simulations have been conducted by appropriately modifying Gagge 2-node model to multi-segment case to demonstrate the local differences. Simulation results are found to be in good agreement with experimental and simulation results reported in the literature. To calculate the interior surface temperatures of the wall and ceiling, the sol–air temperature approach is used for convenience. It is shown in the paper that the body segments close the relatively hot surfaces are more affected than others and interior surface temperatures of un-insulated walls and ceilings exposed to a strong solar radiation reach high levels, all of which cause thermal discomfort for the occupants in buildings.     

Evaluation of calculation methods of mean skin temperature for use in thermal comfort study

A method was established to evaluate calculation methods of mean skin temperature, in order to find appropriate ones for use in human thermal comfort study. In this method three indexes, including reliability, sensitivity and number of measurement sites, were proposed. Under air temperatures of 21 °C, 24 °C, 26 °C, and 29 °C, 22 subjects’ local skin temperatures (21 sites) and electrocardiograms were measured, and their thermal sensation and thermal comfort were inquired. Human heart rate variability indicated the physiological relation between mean skin temperature and ambient temperature for the sensitivity evaluation. Adopting the evaluation method, 26 types of mean skin temperature calculation methods were evaluated based on the experimental data. The results indicate that a calculation method of mean skin temperature with 10 sites is the most appropriate one, due to its high reliability, excellent sensitivity and fewer measuring sites. When it was applied to reflect thermal comfort, the performance was good.     

Thermal comfort and workplace occupant satisfaction—Results of field studies in German low energy office buildings

The issues of comfort and workspace quality in buildings have gained much importance with the European “Energy Performance of Buildings Directive” of 2001. New energy efficient building concepts and technologies require a revision of comfort standards, which were developed for air-conditioned buildings only. Particularly, the question of recommendable upper indoor temperature limits needs further investigation. In addition, a broader approach to occupant satisfaction in buildings is necessary with respect to overall building performance.     

Relationship between thermal sensation and comfort in non-uniform and dynamic environments

The relationship between thermal sensation and thermal comfort was studied experimentally under uniform and non-uniform, steady and dynamic conditions separately. Thirty subjects participated in all the experiment and reported their thermal sensation and thermal comfort simultaneously. Thermal sensation and comfort are found to be correlated closely under steady and uniform conditions and the comfort zone of thermal sensation vote in warm side is (0, 1.25). Under steady and non-uniform conditions thermal sensation change with space is found to be an important factor determining thermal comfort. Combining the effects of overall thermal sensation and thermal sensation change with space, a thermal comfort model for steady conditions is proposed. Under dynamic conditions, thermal sensation change with time affects thermal comfort significantly.     

Adaptive use of natural ventilation for thermal comfort in Indian apartments

Thermal comfort research in India is in its nascent stage. Indian codes specify uniform comfort temperatures between 23 and 26 °C for all types of buildings. About 73% of energy in Indian residences is consumed for ventilation and lighting controls. Therefore, a thermal comfort field survey was conducted in apartment buildings in Hyderabad, which included information on the use of building controls. The present analysis is based on this database. Due to the poor availability of adaptive opportunities, 60% of the occupants were uncomfortable in summer. The comfort range obtained (26.0–32.5 °C) was way above the standard.     

Using the adaptive model of thermal comfort for obtaining indoor neutral temperature: Findings from a field study in Hyderabad,India

There is a dearth of thermal comfort studies in India. It is aimed to investigate into the aspects of thermal comfort in Hyderabad and to identify the neutral temperature in residential environments. This was achieved through a thermal comfort field study in naturally ventilated apartment buildings conducted during summer and monsoon involving over 100 subjects. A total of 3962 datasets were collected covering their thermal responses and the measurement of the thermal environment. The comfort band (voting within –1 and +1), based on the field study, was found to be 26–32.45°C, with the neutral temperature at 29.23°C. This is way above the indoor temperature standards specified in Indian Codes. It was found that the regression neutral temperature and the globe temperature recorded when voting neutral converged when mean thermal sensation of the subjects was close to 0. This happened during the period of moderate temperature when the adaptive measures were adequate. The indoor temperatures recorded in roof-exposed (top floor) flats were higher than the lower floors. The thermal sensation and preference votes of subjects living in top floors were always higher. Consequently, their acceptance vote was also lower. It was found that the subjects living in top floor flats had a higher neutral temperature when the available adaptive opportunities were sufficient. This was due to their continuous exposure to a higher thermal regime due to much higher solar exposure. This study calls for special adaptive measures for roof-exposed flats to achieve neutrality at higher temperature.     

Thermal comfort in environments with different vertical air temperature gradients

The use of displacement ventilation for cooling environments is limited by the vertical temperature gradient. Current standards recommend a temperature difference of up to 3 K/m between the head and the feet. This paper reviews the scientific literature on the effect of vertical temperature gradients on thermal comfort and compares this to the results of our own experiments. Early experiments have demonstrated a high sensitivity of dissatisfied test subjects to changes in the temperature gradient between head and foot level. Recent studies have indicated that temperature gradients of 4‐5 K/m are likely to be acceptable, and the mean room temperature may have a greater sensitivity on the percentage of dissatisfied (PD). In new experiments, test subjects have evaluated the thermal comfort of different vertical air temperature gradients in a modular test chamber, the Aachen comfort cube (ACCu), where they have assessed vertical temperature gradients of ΔT/Δy = 1, 4.5, 6, 8, and 12 K/m at a constant mean room temperature of 23°C. The results of the different temperature gradients are in contrast to ANSI/ASHRAE Standard 55 (Thermal Environmental Conditions for Human Occupancy, Atlanta GA, American Society of Heating, Refrigerating and Air Conditioning Engineers, 2013) as the PD increases almost constantly with higher vertical air temperature gradients. The PD for the overall sensation increases by approximately 7% between gradients of 1 and 8 K/m. The evaluation of our own tests has revealed that vertical temperature gradients of up to 8 K/m or higher are likely to be acceptable for test subjects.     

A comparative analysis of urban and rural residential thermal comfort under natural ventilation environment

The paper presents a field study of occupants’ thermal comfort and residential thermal environment conducted in an urban and a rural area in Hunan province, which is located in central southern China. The study was performed during the cold winter 2006. Twenty-eight naturally ventilated urban residences and 30 also naturally ventilated rural residences were investigated. A comparative analysis was performed on results from urban and rural residences. The mean thermal sensation vote of rural residences is approximately 0.4 higher than that of urban residences at the same operative temperature. Thermal sensation votes calculated by Fanger’s PMV model did not agree with these obtained directly from the questionnaire data. The neutral operative temperature of urban and rural residences is 14.0 and 11.5 °C, respectively. Percentage of acceptable votes of rural occupants is higher than that of urban occupants at the same operative temperature. It suggests that rural occupants may have higher cold tolerance than urban occupants for their physiological acclimatization, or have relative lower thermal expectation than urban occupants because of few air-conditioners used in the rural area. The research will be instrumental to researchers to formulate thermal standards for naturally ventilated buildings in rural areas.     

A field study of the thermal comfort in residential buildings in Harbin

This field study was performed during the winter of 2000–2001 in order to investigate the thermal environment and thermal comfort in residential buildings in Harbin, northeast of China. A total of 120 participants provided 120 sets of physical data and subjective questionnaires. An indoor climate analyzer and a thermal comfort meter made in Denmark were used to collect the measured parameters of the indoor environment, the predicted mean vote (PMV), and predicted percentage of dissatisfied (PPD). The conclusions are as follows: males are less sensitive to temperature variations than females; the neutral operative temperature of males is 1 °C lower than that of females; Harbin subjects are as sensitive to temperature variations as the Beijing and Tianjin subjects; the minimum value of PPD (7.5%) is similar to the Tianjin occupants; both the sensitivity and the minimum value of PPD are lower than those of the foreign field studies.     

Behavioural adaptation and the use of environmental controls in summer for thermal comfort in apartments in India

Building energy use in India is rising phenomenally. Indian codes prescribe a very narrow comfort temperature range (23-26 °C) for summer. Ventilation controls alone consume 47% of total energy in residences. Thermal comfort field studies in Indian residences were not attempted. The author conducted a field study in apartments in Hyderabad, in summer and monsoon seasons in 2008. This paper presents the occupants’ methods of environmental and behavioural adaptation and impediments in using controls.Only about 40% of the occupants were comfortable in summer due to inadequate adaptive opportunities. The comfort range obtained in this study (26.0-32.5 °C), was way above the standard. Fanger's PMV always overestimated the actual sensation.The occupants used many adaptation methods: the environmental controls, clothing, metabolism and many behavioural actions. Use of fans, air coolers and A/cs increased with temperature, and was impeded by their poor efficacy and noise, occupant's attitudes and economic affordability. A/c and air cooler usage was higher in top floors. Behavioural adaptation was better in summer and was restricted in higher economic groups always. Thermal tolerance was limited in subjects using A/cs and resulted in “thermal indulgence”. This study calls for special adaptation methods for top-floor flats.     

Local thermal sensation and comfort study in a field environment chamber served by displacement ventilation system in the tropics

This paper presents a study of local thermal sensation (LTS) and comfort in a field environmental chamber (FEC) served by displacement ventilation (DV) system. The FEC, 11.12 m (L)×7.53 m (W)×2.60 m (H), simulates a typical office layout. A total of 60 tropically acclimatized subjects, 30 male and 30 female, were engaged in sedentary office work for 3 h. Subjects were exposed to three vertical air temperature gradients, nominally 1, 3 and 5 K/m, between 0.1 and 1.1 m heights and three room air temperatures of 20, 23 and 26 °C at 0.6 m height. The objective of this study is to investigate the mutual effect of local and overall thermal sensation (OTS) and comfort in DV environment. The results show that in a space served by DV system, at OTS close to neutral, local thermal discomfort decreased with the increase of room air temperature. The OTS of occupants was mainly affected by LTS at the arm, calf, foot, back and hand. Local thermal discomfort was affected by both LTS and OTS. At overall cold thermal sensation, all body segments prefer slightly warm sensation. At overall slightly warm thermal sensation, all body segments prefer slightly cool sensation.     

Experimental study of the influence of anticipated control on human thermal sensation and thermal comfort

To investigate whether occupants’ anticipated control of their thermal environment can influence their thermal comfort and to explain why the acceptable temperature range in naturally ventilated environments is greater than that in air‐conditioned environments, a series of experiments were conducted in a climate chamber in which the thermal environment remained the same but the psychological environment varied. The results of the experiments show that the ability to control the environment can improve occupants’ thermal sensation and thermal comfort. Specifically, occupants’ anticipated control decreased their thermal sensation vote (TSV) by 0.4–0.5 and improved their thermal comfort vote (TCV) by 0.3–0.4 in neutral‐warm environment. This improvement was due exclusively to psychological factors. In addition, having to pay the cost of cooling had no significant influence on the occupants’ thermal sensation and thermal comfort in this experiment. Thus, having the ability to control the thermal environment can improve occupants’ comfort even if there is a monetary cost involved.     

Gender differences in thermal comfort and use of thermostats in everyday thermal environments

Differences in thermal comfort between male and female subjects are generally considered to be small. In this study gender differences in thermal comfort and use of thermostats were examined by a quantitative interview survey with a total of 3094 respondents, and by controlled experiments. The studies were carried out in Finland and considered everyday thermal environments: homes, offices and a university. The results show significant gender differences in thermal comfort, temperature preference, and use of thermostats. Females are less satisfied with room temperatures than males, prefer higher room temperatures than males, and feel both uncomfortably cold and uncomfortably hot more often than males. Although females are more critical of their thermal environments, males use thermostats in households more often than females.     

现场研究中热舒适指标的选取问题

对热舒适现场研究结果进行了总结,并对热舒适指标的选取、有效温度的计算、热感觉的表述方式等问题进行了讨论分析。认为当相对湿度在热舒适范围内时,采用有效温度作为热舒适指标并采用平均热感觉值,能更好地预测人体热感觉。     

A field study of occupant thermal comfort and thermal environments with radiant slab cooling

This paper presents the findings of a field study of occupant thermal comfort and thermal environments with a radiant slab cooling system. The study combined field measurements and questionnaires based on the ASHRAE RP-921 project protocol. A total of 116 sets of data from 82 participants were collected in summer and winter. The results reveal that occupant whole-body thermal sensations with radiant cooling were consistent with the PMV model. The main advantage of radiant cooling for thermal comfort was found to be reduced local thermal discomfort with reduced vertical air temperature difference as well as reduced draft rate. The survey results revealed that 14–22% of participants in the study reported local cold discomfort in the arm–hand and the leg–foot regions. The results indicated that there may be lower limits on air speeds acceptable to occupants. Statistical analysis indicated that occupant thermal votes were free of significant correlation with personal, contextual and psychological factors. Suggestions to improve the questionnaire and the field survey process are offered.     

Effect of transient temperature on thermoreceptor response and thermal sensation

This work investigates the dynamic response of cutaneous thermoreceptors (TRs) under various environmental conditions. The model consists of an electrical submodel and a Pennes bioheat transfer submodel. The electrical submodel assumes that the response of the cutaneous TRs has a static and dynamic part, in which the static one is proportional to the temperature and the dynamic part proportional to the temperature change rate. A one-dimensional multi-layer model is presented to model the heat exchange between the skin and the ambient medium. Then the temperature of the TRs and the necessary parameters of the electrical submodel are predicted using a finite difference method. Approaches proposed in this paper can help identify the difference of the warm and cold TRs under the same environmental conditions. This difference may be the real mechanism that people are more sensitive to cold stimuli than warm stimuli.