Thermal comfort of people in the hot and humid area of China—impacts of season,climate, and thermal history

We conducted a climate chamber study on the thermal comfort of people in the hot and humid area of China. Sixty subjects from naturally ventilated buildings and buildings with split air conditioners participated in the study, and identical experiments were conducted in a climate chamber in both summer and winter. Psychological and physiological responses were observed over a wide range of conditions, and the impacts of season, climate, and thermal history on human thermal comfort were analyzed. Seasonal and climatic heat acclimatization was confirmed, but they were found to have no significant impacts on human thermal sensation and comfort. The outdoor thermal history was much less important than the indoor thermal history in regard to human thermal sensation, and the indoor thermal history in all seasons of a year played a key role in shaping the subjects' sensations in a wide range of thermal conditions. A warmer indoor thermal history in warm seasons produced a higher neutral temperature, a lower thermal sensitivity, and lower thermal sensations in warm conditions. The comfort and acceptable conditions were identified for people in the hot and humid area of China.     

Thermal comfort analysis of a low temperature waste energy recovery system: SIECHP

The use of a recovery device is justified in terms of energy savings and environmental concerns. But it is clear that the use of a recovery system also has to lead to controlling indoor environmental quality, nowadays a priority concern. In this article, experimental research has been carried out whose aim is to study the thermal comfort provided by a combined recovery equipment (SIECHP), consisting of a ceramic semi-indirect evaporative cooler (SIEC) and a heat pipe device (HP) to recover energy at low temperature in air-conditioning systems. To characterize this device empirically in terms of thermal comfort (TC), Fanger's predicted mean vote (PMV), draught rate, and vertical air temperature difference were used in this study as the TC criteria.     

Thermal Sensations Resulting From Sudden Ambient Temperature Changes

This paper investigates the conscious experience of thermal transients, both experimentally and by means of a model of dynamic thermoreception. The experiments involved a sample of twelve human subjects, each undergoing twelve different ambient temperature step-changes. The research design included both temperature up-steps and down-steps, clothed and naked subjects, and transients both away from, and towards, neutrality. Each experiment lasted three hours, with the step- change occurring after 1.5 h when the subjects crossed between the twin climate chambers. Immediate sensations resulting from the temperature up-steps closely resembled later steady-state responses to the warmer environment, while initial impressions of temperature down-steps were typically twice the magnitude of their up-step counterparts. These experimental findings were accurately simulated by a simple thermoreceptor model coupled to a numerical model of heat transfer through clothing and cutaneous tissue. This heightened subjective sensitivity to temperature down-steps was achieved with the model by taking the subcutaneous depth of cold thermoreceptors to be less than that of the warm units, as noted by Hensel in his review of this specialized field (1981).     

Thermal sensation and comfort models for non-uniform and transient environments, part III: Whole-body sensation and comfort

A three-part series presents the development of models for predicting the local thermal sensation (Part I) and local thermal comfort (Part II) of different parts of the human body, and also the whole-body sensation and comfort (Part III) that result from combinations of local sensation and comfort. The models apply to sedentary activities in a range of environments: uniform and non-uniform, stable and transient. They are based on diverse findings from the literature and from body-part-specific human subject tests in a climate chamber. They were validated against a test of automobile passengers. The series is intended to present the models’ rationale, structure, and coefficients, so that others can test them and develop them further as additional empirical data becomes available.A) The whole-body (overall) sensation model has two forms, depending on whether all of the body's segments have sensations effectively in the same direction (e.g warm or cool), or whether some segments have sensations opposite to those of the rest of the body. For each, individual body parts have different weights for warm versus cool sensations, and strong local sensations dominate the overall sensation. If all sensations are near neutral, the overall sensation is close to the average of all body sensations.B) The overall comfort model also has two forms. Under stable conditions, people evaluate their overall comfort by a complaint-driven process, meaning that when two body parts are strongly uncomfortable, no matter how comfortable the other body parts might be, the overall comfort will be near the discomfort level of the two most uncomfortable parts. When the environmental conditions are transient, or people have control over their environments, overall comfort is better than that of the two most uncomfortable body parts. This can be accounted for by adding the most comfortable vote to the two most uncomfortable ones.     

Evidence base prioritisation of indoor comfort perceptions in Malaysian typical multi-storey hostels

This study focuses on assessing the effects of the indoor climate in typical multi-storey hostels in Malaysia on student occupants through objective, subjective and evidence based prioritisation measurements. The objective measurements consisted of operative temperature; daylight ratio; luminance and indoor noise level. The subjective measurements were sampled from the student occupants' thermal, visual, acoustics and overall indoor comfort votes. The prioritisation measurement using Multiple Linear Regression and Friedman Tests assessed the relationship between physical indoor thermal, visual and acoustics conditions and students' overall indoor comfort perception vote. Findings suggest that subjective sensor ratings were significantly more reliable than objective measurements at predicting overall indoor comfort. Moreover, students living in hostel rooms with projected balconies voted that they were more satisfied with their indoor condition than the ones living in rooms without projected balconies. The results of this study also provide evidence that student occupants were more concerned with their rooms' thermal condition then followed by acoustics and finally visual conditions.     

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.     

Thermal comfort evaluation of naturally ventilated public housing in Singapore

Field survey was conducted to evaluate thermal comfort perception of the occupants in naturally ventilated public housing in Singapore. Thermal acceptability assessment was performed to find out whether the naturally ventilated indoor environment meets the ASHRAE Standard-55's 80% acceptability criteria. The study investigated whether thermal perception was influenced by different sessions of the day, building height, and flat types. Comparative analysis of thermal sensation and thermal comfort votes revealed that a high proportion of people experiencing sensations of +2,+3 still found the conditions to be comfortable. The survey also examined the adaptive behavior of the occupants in the usage of climatic control such as windows, fans and air-conditioning to modify the indoor environment.     

Addressing climate change in comfort standards

According to the Buildings Energy Data Book published by the U.S. Department of Energy, in 2006 the building sector consumed 38.9% of the total primary energy used in the United States. Of this energy, 34.8% is used by buildings for space heating, ventilation, and air conditioning. This energy often involves the combustion of fossil fuels, contributing to carbon dioxide emissions and climate change. Even if greenhouse gas concentrations are stabilized in the atmosphere, extreme climate events and sea level rise will continue for several centuries due to inertia of the atmosphere. Therefore, adaptation will be a necessary compliment to carbon dioxide mitigation efforts. This paper argues that both mitigation of greenhouse gases and adaptation to climate change should be added to our building codes and standards. Since space heating, ventilation, and air-conditioning utilize a large amount of energy in buildings, we should begin by redefining our thermal comfort standards and add strategies that mitigate carbon dioxide emissions and adapt to predicted climate variability.     

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.     

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.     

Observations of upper-extremity skin temperature and corresponding overall-body thermal sensations and comfort

This paper explores how upper extremity skin temperatures correlate with overall-body thermal sensation. Skin temperature measurements of the finger, hand, and forearm might be useful in monitoring and predicting people's thermal state. Subjective perceptions of overall thermal sensation and comfort were collected by repeated surveys, for subjects in a range of test chamber temperatures. A positive temperature gradient (finger warmer than the forearm) of as much as 2 K was seen when subjects felt warm and hot, while a negative temperature gradient (finger colder than the forearm) as much as 8.5 K was seen for cool and cold subjects. A useful warm/cold boundary of 30 °C was found in finger temperature, for both steady state and transient conditions. When finger temperature was above 30 °C, or finger-forearm skin temperature gradient above 0 K, there was no cool discomfort. When finger temperature was below 30 °C, or the finger-forearm skin temperature gradient less than 0 K, cool discomfort was a possibility. Finger temperature and finger-forearm temperature gradient are very similar in their correlation to overall sensation. We also examine how overall sensation is affected by actively manipulating the hand's temperature.     

Thermal comfort in naturally ventilated buildings in hot-humid area of China

Human responses to thermal environments in naturally ventilated (NV) buildings in hot-humid area of China were systematically investigated in the present study. Thirty local inhabitants long-time living in NV buildings participated in the study and reported their thermal sensations and perceptions and adaptive behaviors while all physical and personal variables were collected. Based on a year-long survey, a close match of indoor physical variables and occupants’ clothing insulation with outdoor climate was found as an important feature of NV buildings. Integrated indices can capture more thermal contexts in the NV buildings in hot-humid area of China than simple indices. Thermal sensation was found to be a good linear function of SET* with the thermal neutrality of 25.4 °C and the 90% (80%) acceptable range of 23.5–27.4 °C (22.1–28.7 °C) in SET*. The adaptive evidences were obtained for clothing adjustment, window opening and using fan respectively and the modified PMV model was validated to be applicable in NV buildings in hot-humid area of China with an expectancy factor of 0.822. Comparisons with other field studies indicate that people can develop various human-environment relationships through thermal adaptation to local climate, resulting in different thermal neutral temperatures in various climates. The subjects in hot-humid area of China are more acclimated and tolerable with hot and humid environments and more uncomfortable and intolerable with cold environments while compared with those in temperate climates.     

Discomfort due to Vertical Thermal Gradients

Abstract Abstract When 207 subjects wearing their own clothing were randomly assigned to 9 conditions, consisting of 3 levels of vertical thermal gradient (nominally 0, 2 & 4 K/m), and 3 levels of estimated whole-body heat loss (40, 48 & 56 W/m² as measured on a similarly-clothed and seated thermal manikin, corresponding to warm, neutral and cool conditions respectively, “warm” being 1.4 K above neutral in terms of operative temperature, and “cool” being 1.4 K below) and exposed for 1 hour, local thermal discomfort was reported by 45% of the group. Local and whole-body discomfort sensations were unaffected by thermal gradient (P>0.30), but were strongly affected by operative temperature (P<0.001). Discomfort due to dry air was unaffected by thermal gradient (P>0.30), but increased significantly with operative temperature (P<0.001). Discomfort due to dry eyes increased significantly above 2 K/m (P<0.01), but was unaffected by operative temperature (P>0.80). Individual differences in thermal and air quality requirements are shown to be sufficient to cause the thermal discomfort associated with thermal gradients up to 4 K/m.     

Thermal sensation and comfort with different task conditioning systems

Subjective experiments with task conditioning systems, 3DU⁺, PEM, TU, and RCU were conducted to investigate the effect of three different types of Task air-conditioning systems on thermal comfort in a climate chamber. The chamber was conditioned at 28 °C/50%RH with task systems and 26 °C/50%RH without them. Under the condition with the task conditioning systems, the average rating of comfort sensation was between comfortable (0) and slightly uncomfortable (−1). For males it was between −0.5 and −0.7 and for females between −0.3 and −0.4. This was equal to or even better than that in condition without task system. It was found that these systems were effective in providing thermal comfort. The parts to which subjects wanted to diffuse air were different for each system. However, the individual control of task conditioning system contributed to create the preferred environment.     

Thermal environment characterisation of a glass-covered semi-outdoor space subjected to natural climate mitigation

The human thermal sensation inside a semi-outdoor space enclosed by a semi-transparent pitched roof, located in Parma, north of Italy, is compared with the outdoor sensation under the same climate conditions. The assessment of the semi-outdoor setting was performed using the Physiological Effective Temperature (PET) thermal sensation index. With the aim of mitigating the semi-outdoor climate, some natural means were considered at the design stage, namely, the solar radiation absorptivity of the glass sheet roof, natural airflow, space thermal capacity and roof evaporative cooling. The dynamic thermal simulation of the semi-outdoor space was performed for three representative weeks of the months of January, March and July by accounting for the actual climate of the location. The results show that the semi-transparent roof can improve the human thermal sensation inside the semi-outdoor space with respect to that of the outdoor space. The results also demonstrate the effect of each design parameter on the PET index.     

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.     

Thermal comfort in office buildings: Two case studies commented

Air conditioning in offices has become a current practice in North Western Europe. The main reasons for that are high internal loads, solar gains and increased comfort expectations. Hence, the move away from the naturally ventilated cellular office increased thermal comfort complaints.     

Thermal comfort in Italian classrooms under free running conditions during mid seasons: Assessment through objective and subjective approaches

This work shows the results of a field study about indoor thermal comfort, based on investigations in Italian classrooms. The surveys were carried out in Turin, in the North–West of Italy. The monitoring campaigns were performed during the mid season, in free running conditions. This study follows a previous one based on a monitoring campaign performed during the heating season. The responses from these two different configurations were integrated, analyzed and compared.     

Thermal comfort assessment and application of radiant cooling: A case study

A field assessment of thermal comfort was conducted at Mehran University of Engineering and Technology, situated in the subtropical region of Pakistan. The results show that people of the area were feeling thermally comfortable at effective temperature of 29.85 °C (operative temperature 29.3 °C). A comparison of this neutral effective temperature was made with the neutral effective temperature determined from adaptive models. It is found that the neutral effective temperature determined during this study closely match that of the adaptive model based on either indoor temperature or both indoor and outdoor temperatures. The results of thermal acceptability assessment show that more than 80% of occupants were satisfied at an effective temperature of 32.5 °C, which is 6.5 °C above the upper boundary of ASHRAE thermal comfort zone. Naturally ventilated classrooms and air-conditioned offices of the University were simulated using TRNSYS system simulation program for two cases, once when conventional air-conditioning is used for providing thermal comfort, and when comfort is achieved through radiant cooling. In the simulation, cooling tower was used to regenerate cooling water for the radiant cooling system. Energy consumption was estimated from simulation of both cases. The results show that it is possible to achieve thermal comfort for most of the time of the year through the use of radiant cooling without a risk of condensation of moisture from air on the radiant cooling surfaces. A comparison of the energy consumption estimates show that savings of 80% is possible in case thermal comfort is achieved through radiant cooling instead of conventional air-conditioning.     

Climate change,thermal comfort and energy: Meeting the design challenges of the 21st century

This paper addresses the dual challenge of designing sustainable low-energy buildings while still providing thermal comfort under warmer summer conditions produced by anthropogenic climate change—a key challenge for building designers in the 21st century. The main focus is towards buildings that are ‘free running’ for some part of the summer, either being entirely naturally ventilated or mixed-mode (where mechanical cooling is only used when thought to be essential). Because the conditions in these buildings will vary from day to day it is important to understand how people react and adapt to their environment. A summary is made of recent developments in this area and of the climate data required to assess building performance. Temperatures in free running buildings are necessarily closely linked to those outside. Because the climate is changing and outside summer temperatures are expected to increase, the future will offer greater challenges to the designers of sustainable buildings aiming to provide either entirely passive or low-energy comfort cooling. These issues are demonstrated by predictions of the performance of some case study buildings under a climate change scenario. The examples also demonstrate some of the important principles associated with climate-sensitive low-energy design.