Development of an adaptive thermal comfort equation for naturally ventilated buildings in hot-humid climates using ASHRAE RP-884 database

The objective of this study was to develop an adaptive thermal comfort equation for naturally ventilated buildings in hot-humid climates. The study employed statistical meta-analysis of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) RP-884 database, which covered several climatic zones. The data were carefully sorted into three climate groups including hot-humid, hot-dry, and moderate and were analyzed separately. The results revealed that the adaptive equations for hot-humid and hot-dry climates were analogous with approximate regression coefficients of 0.6, which were nearly twice those of ASHRAE and European standards 55 and EN15251, respectively. The equation using the daily mean outdoor air temperature had the highest coefficient of determination for hot-humid climate, compared with other mean temperatures that considered acclimatization of previous days. Acceptable comfort ranges showed asymmetry and leaned toward operative temperatures below thermal neutrality for all climates. In the hot-humid climate, a lower comfort limit was not observed for naturally ventilated buildings, and the adaptive equation was influenced by indoor air speed rather than indoor relative humidity. The new equation developed in this study can be applied to tropical climates and hot-humid summer seasons of temperate climates.     

Thermal responses to different residential environments in Harbin

In China, adding space heating in residential buildings is normally scheduled at the end of October each year, with heat supplied by district heating systems. This paper describes a field study of thermal comfort conducted in Harbin during the winter from 2009 to 2010 before and after the space heating is added. The aim is to study human responses to thermal conditions in the two periods in cold climates. 23 buildings in six communities were investigated. 199 occupants from 135 families and 174 occupants from 104 families participated in the two surveys during the two periods, respectively. The neutral air temperature before adding the space heating is 25.1 °C, while during the space heating, it is 20.4 °C. The clothing insulation is 0.77 clo and 0.88 clo, respectively. If they were 0.88 clo instead of 0.77 clo before adding the space heating, the neutral air temperature should be 21.1 °C. Before and during space heating, more than 80% felt acceptable at the air temperature range between 17.5–24.0 °C and 19.0–26.5 °C for the two periods. The residents’ physiological acclimation may contribute to the differences. The preferred temperature is within the range of 23.0–24.0 °C and 21.5–24.0 °C, respectively. The preferred humidity is 47.7% and 40.5% during the two surveys. People felt cold generally before heating, while they felt comfortable at the same temperature range during space heating period. People often felt dry during heating when the relative humidity is lower than 30%, while they felt comfortable at the same relative humidity before heating.     

Thermal comfort for naturally ventilated residential buildings in Harbin

This field study was conducted during summer 2009 in Harbin, northeast of China in order to investigate human responses to the thermal conditions in naturally ventilated residential buildings in cold climate. We visited 257 families in six residential communities and collected 423 sets of physical data and subjective questionnaires. The neutral temperature is 23.7 °C, with the clothing insulation of 0.54 clo. The neutral temperature in Harbin is lower than neutral temperatures in warm climates by others, which is in accordance with the thermal adaptive model. 80% of the occupants can accept the air temperature range of 21.5-31.0 °C, which is wider than the summer comfort temperature limits by the adaptive model. The preferred temperature range fell between 24.0 °C and 28.0 °C. About 57.9% of the subjects voted “no change” with the humid range of 40% and 70%. 61.5% of the occupants voted “no change” with the air velocity within the range of 0.05-0.30 m/s. In summer, occupants preferred air velocity of lower than 0.25 m/s even at higher indoor temperature, which is different from the other field studies. The Harbin occupants in naturally ventilated dwellings can achieve thermal comfort by operable windows instead of running air-conditioners.     

Long-term field survey on thermal adaptation in office buildings in Japan

A long-term field survey was conducted with six buildings in order to investigate how the occupants adapt to the indoor climate in office buildings in Japan. More than 5000 questionnaires and corresponding indoor temperatures were collected. Clothing adjustment was observed to be related to outdoor temperature and indoor temperature, as well as dress codes. No considerable differences were found on the thermal perceptions between two groups of buildings, which provided different levels of opportunity for controlling indoor climate. With both groups, the preferred SET* was always close to 26 °C. The comfort temperature was estimated from the results of clothing adjustment and the preferred SET*. The gradient of the comfort temperature to outdoor temperature was found to be between the adaptive model for centralized HVAC and for natural ventilation. It could be caused by that the major part of the occupants in the present study had more opportunity to control their thermal conditions than in the centralized HVAC buildings (i.e. operable windows, controllable HVAC or personal fans).     

Field study on occupants’ thermal comfort and residential thermal environment in a hot-humid climate of China

This paper discusses thermal comfort inside residences of three cities in the hot-humid climate of central southern China. Only a few thermal comfort studies have been performed in hot-humid climates and none in Central Southern China. Field sampling took place in the summers of 2003 and 2004 by obtaining 110 responses to a survey questionnaire and measuring environmental comfort variables in three rooms in each of 26 residences. The objectives are to measure and characterize occupant thermal perceptions in residences, compare observed and predicted percent of dissatisfied and discern differences between this study and similar studies performed in different climate zones. Average clothing insulation for seated subjects was 0.54 clo with 0.15 clo of chairs. Only 48.2% of the measured variables are within the ASHRAE Standard 55-1992 summer comfort zone, but approximately 87.3% of the occupants perceived their thermal conditions acceptable, for subjects adapt to prevailing conditions. The operative temperature denoting the thermal environment accepted by 90% of occupants is 22.0–25.9°. In the ASHRAE seven-point sensation scale, thermal neutral temperature occurs at 28.6°. Preferred temperature, mean temperature requested by respondents, is 22.8°. Results of this study can be used to design low energy consumption systems for occupant thermal comfort in central southern China.     

Thermal sensations of the whole body and head under local cooling and heating conditions during step-changes between workstation and ambient environment

This paper examines people’s thermal sensations during step-changes between ambient and workstation environments with a local ventilation device installed to supply-air motion around heads. We conducted human subject tests in a controlled environment chamber for summer and winter conditions. We performed 29 tests. The ambient air temperatures were 28 and 30 °C for summer conditions and 19 °C for winter conditions. The local supply-air temperatures were at 24, 28 and 30 °C for summer and 50 °C for winter. The supply-air velocities of the local ventilation device were at 3, 3.5, and 5 m/s for summer and 3.5 m/s for winter. The air temperatures near heads were 26–30 °C for summer and 32 °C for winter. The velocities along the jet-flow line at a distance of 10 cm from heads were 1.4–2.6 m/s for summer and 1.8 m/s for winter. In total, 23 subjects participated in the tests, and each subject participated in 1∼2 test conditions. Both the dynamic and stable thermal sensations of head and whole body were analyzed. When head is cooled by local ventilation, head thermal sensation has an effect on overall thermal sensation. When subjects moved from the workstation, where local devices were installed, to the ambient environment that was warmer in summer and colder in winter than the workstation, both overshooting and hysteresis were found. These thermal sensation changing trends in non-uniform step-change environments are helpful in personalizing environment control designs and exploring the possibilities of saving energy in buildings.     

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.     

我国湿热地区人群基础热舒适反应研究(3):冬夏对比分析

沿用经典热舒适研究方法,对我国湿热地区自然通风环境受试者分别进行夏季和冬季气候室实验,并对其心理反应与生理反应作冬夏季对比,得到其热反应的季节性变化特征为:与夏季相比,冬季的热感觉保持不变,但热舒适度与可接受度在低温环境显著降低,而在高温环境显著升高;心率显著增加,皮肤温度有所升高,在高温环境下的皮肤湿润度有所降低.季节性变化特征为湿热地区人群心理适应与生理习服提供了重要证据.     

Combined thermal acceptability and air movement assessments in a hot humid climate

In the ASHRAE comfort database [1], underpinning the North American naturally ventilated adaptive comfort standard [2], the mean indoor air velocity associated with 90% thermal acceptability was relatively low, rarely exceeding 0.3 m/s. Post hoc studies of this database showed that the main complaint related to air movement was a preference for ‘more air movement’ 3 and 4. These observations suggest the potential to shift thermal acceptability to even higher operative temperature values, if higher air speeds are available. If that were the case, would it be reasonable to expect temperature and air movement acceptability levels at 90%? This paper focuses on this question and combines thermal and air movement acceptability percentages in order to assess occupants. Two field experiments took place in naturally ventilated buildings located on Brazil’s North-East. The fundamental feature of this research design is the proximity of the indoor climate observations with corresponding comfort questionnaire responses from the occupants. Almost 90% thermal acceptability was found within the predictions of the ASHRAE adaptive comfort standard and yet occupants required ‘more air velocity’. Minimum air velocity values were found in order to achieve 90% of thermal and air movement acceptability. From 24 to 27 °C the minimum air velocity for thermal and air movement acceptability is 0.4 m/s; from 27 to 29 °C is 0.41–0.8 m/s, and from 29 to 31 °C is >0.81 m/s. These results highlight the necessity of combining thermal and air movement acceptability in order to assess occupants’ perception of their indoor thermal environment in hot humid climates.     

Thermal performance of courtyard buildings

In this analysis, the energy performance of a courtyard in buildings is investigated under conditions of different factors of climate, height, glazing type, and glazing percentage. The courtyard design used for the analysis was square in plan and surrounded by the building on all four sides. The glazing type and percentage for the courtyard walls were varied in the analysis. Weather data from four cities representative of climatic conditions of cold, temperate, hot-humid, and hot-dry were used. The computer energy simulation program DOE2.1E was used in this analysis as a tool to evaluate the impact of these factors on the energy consumption of the buildings. The results of the parametric simulation showed that the courtyard building thermal performance differed from climate to climate and even the impact of the measures or the variables on cooling, heating, and the total annual energy consumption differed with different variables’ configuration. In general, the open courtyard building exhibits a better energy performance in hot-dry and hot-humid climates.     

Thermal comfort in air-conditioned mosques in the dry desert climate

In Kuwait, as in most countries with a typical dry desert climate, the summer season is long with a mean daily maximum temperature of 45 °C. Centralized air-conditioning, which is generally deployed from the beginning of April to the end of October, can have tremendous impact on the amount of electrical energy utilized to mechanically control the internal environment in mosque buildings. The indoor air temperature settings for all types of air-conditioned buildings and mosque buildings in particular, are often calculated based on the analytical model of ASHRAE 55-2004 and ISO 7730. However, a field study was conducted in six air-conditioned mosque buildings during the summers of 2007 to investigate indoor climate and prayers thermal comfort in state of Kuwait. The paper presents statistical data about the indoor environmental conditions in Kuwait mosque buildings, together with an analysis of prayer thermal comfort sensations for a total of 140 subjects providing 140 sets of physical measurements and subjective questionnaires were used to collect data. Results show that the neutral temperature (T_n) of the prayers is found to be 26.1 °C, while that for PMV is 23.3 °C. Discrepancy of these values is in fact about 2.8 °C higher than those predicted by PMV model. Therefore, thermal comfort temperature in Kuwait cannot directly correlate with ISO 7730 and ASHRAE 55-2004 standards. Findings from this study should be considered when designing air conditioning for mosque buildings. This knowledge can contribute towards the development of future energy-related design codes for Kuwait.     

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.     

Assessing thermal comfort of active people in transitional spaces in presence of air movement

The aim of this study is to develop a modeling methodology to assess thermal comfort and sensation of active people in transitional spaces and consider how comfort can be achieved by air movement while changing upper body clothing properties. The modeling is based on a bioheat model, capable of predicting segmental skin and core temperature from locally ventilated clothed body parts. The bioheat model is integrated with thermal comfort and sensation models to predict comfort in presence of air movement.The model accuracy in predicting comfort was validated by and agreed with the results of a survey administered to subjects wearing typical clothing at different activity levels to record their overall and local thermal sensation and comfort in a transitional space at Beirut summer climate. The transitional space temperature monitored during the experiments ranged between 27 °C and 30 °C.A parametric study is performed to assess thermal comfort in transitional spaces for different air movement levels and for three clothing designs. The high permeable clothing at 1.5 m/s and indoor temperature of 30 °C improved the Predicted Mean Vote to values less than 0.5 compared to 1.01 attained with typical low permeable clothing.     

Air movement acceptability limits and thermal comfort in Brazil's hot humid climate zone

In hot humid climates, natural ventilation is an essential passive strategy in order to maintain thermal comfort inside buildings and it can be also used as an energy-conserving design strategy to reduce building cooling loads by removing heat stored in the buildings thermal mass. In this context, many previous studies have focused on thermal comfort and air velocity ranges. However, whether this air movement is desirable or not remains an open area. This paper aims to identify air movement acceptability levels inside naturally ventilated buildings in Brazil. Minimal air velocity values corresponding to 80% and 90% (V80 and V90) air movement acceptability inside these buildings. Field experiments were performed during hot and cool seasons when 2075 questionnaires were filled for the subjects while simultaneous microclimatic observations were made with laboratory precision. Main results indicated that the minimal air velocity required were at least 0.4 m/s for 26 °C reaching 0.9 m/s for operative temperatures up to 30 °C. Subjects are not only preferring more air speed but also demanding air velocities closer or higher than 0.8 m/s ASHRAE limit. This dispels the notion of draft in hot humid climates and reinforce the broader theory of alliesthesia and the physiological role of pleasure due to air movement increment.     

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.     

我国湿热地区自然通风建筑热舒适与热适应现场研究

在2008—2009年为期1年的广州某高校自然通风建筑现场调研的基础上,对23周共计921人次的调研数据在热环境、人体热反应及适应行为等方面进行了分析,得到了我国湿热地区典型自然通风建筑的室内热环境全年变化特征,获取了热感觉与标准有效温度的确定关系,验证了修正的PMV模型的适用性,分析得到我国湿热地区自然通风建筑的期望因子为0.8,同时获得了调整服装、开窗与使用风扇等适应行为的变化规律。     

Selection of window sizes for optimizing occupational comfort and hygiene based on computational fluid dynamics and neural networks

The present paper presents a novel computational method to optimize window sizes for thermal comfort and indoor air quality in naturally ventilated buildings. The methodology is demonstrated by means of a prototype case, which corresponds to a single-sided naturally ventilated apartment. Initially, the airflow in and around the building is simulated using a Computational Fluid Dynamics model. Local prevailing weather conditions are imposed in the CFD model as inlet boundary conditions. The produced airflow patterns are utilized to predict thermal comfort indices, i.e. the PMV and its modifications for non-air-conditioned buildings, as well as indoor air quality indices, such as ventilation effectiveness based on carbon dioxide and volatile organic compounds removal. Mean values of these indices (output/objective variables) within the occupied zone are calculated for different window sizes (input/design variables), to generate a database of input–output data pairs. The database is then used to train and validate Radial Basis Function Artificial Neural Network input–output “meta-models”. The produced meta-models are used to formulate an optimization problem, which takes into account special constraints recommended by design guidelines. It is concluded that the proposed methodology determines appropriate windows architectural designs for pleasant and healthy indoor environments.     

Thermal sensation of Hong Kong people with increased air speed,temperature and humidity in air-conditioned environment

In the warm and humid climate zone, air-conditioning (AC) is usually provided at working places to enhance human thermal comfort and work productivity. From the building sustainability point of view, to achieve acceptable thermal sensation with the minimum use of energy can be desirable. A new AC design tactic is then to increase the air movement so that the summer temperature setting can be raised. A laboratory-based thermal comfort survey was conducted in Hong Kong with around 300 educated Chinese subjects. Their thermal sensation votes were gathered for a range of controlled thermal environment. The result analysis shows that, like in many other Asian cities, the thermal sensation of the Hong Kong people is sensitive to air temperature and speed, but not much to humidity. With bodily air speed at 0.1–0.2 m/s, clothing level 0.55 clo and metabolic rate 1 met, the neutral temperature was found around 25.4 °C for sedentary working environment. Then recommendations are given to the appropriate controlled AC environment in Hong Kong with higher airflow speeds.     

Improving energy performance of school buildings while ensuring indoor air quality ventilation

Energy conscious design of school buildings, as well as deemed-to-satisfy provisions in a Performance Based Energy Code, should address the problem known as the energy efficiency—thermal comfort—indoor air quality dilemma (EE-TC-IAQ Dilemma). In warm and moderate climates, the large internal heat sources usually found in school buildings prevent achieving thermal comfort without active cooling in summer, but are not sufficient to eliminate the need for heating in winter. Commonly used air-conditioners do not improve air quality, while natural ventilation induces uncontrolled energy losses. In this study, a step by step process was used for the development of deemed-to-satisfy design solutions, which cope with the EE-TC-IAQ Dilemma, for a performance based code. A distinction is made between improving building design variables and improving ventilation schemes. Results indicate that implementation of improved ventilation schemes in an otherwise well designed energy-conscious building result in savings of 28–30% and 17–18% for northern and southern classroom orientations, respectively.