Field Study Of Thermal Comfort Research Articles

Quantification of thermal environments and comfort expectations of residents in hostel dormitories during hot and humid days in Indian composite climate

ABSTRACT Improved quality of the thermal environment in hostel buildings will have a constructive role in the health, learning and overall productivity of student’s activities. We, therefore, conducted a thermal comfort field study in two mid-rise naturally ventilated (NV) hostel buildings during rainy days (August–September, 2018). The field study conducted for three consecutive weeks collecting 642 valid subjective responses (out of 679 sample) with objective information of thermal environments in 253 rooms at different floor levels. Statistical analysis of measured thermal variables was performed for assessing the effects on student’s thermal perception considering inter buildings effects, different weather conditions and different daytime duration, respectively. The study reported higher comfort bandwidth of 25.2–33.3°C for the studied group. Results of present study are compared with Predicted Mean Vote (PMV), Predicted Mean Vote with expectancy factor (PMVe) and adaptive Predicted Mean Vote (aPMV). aPMV is observed to be more reliable than PMV and PMVe to estimate the actual thermal sensation of occupants. Further, field study results are showing good agreement with the adaptive comfort models for NV buildings in India. Highlights Study quantifies thermal environments of two multi-storey NV hostel buildings. About 76% responses voted comfortable (±1 TS scale). Comfort bandwidth for occupant's ranges between 25.2–33.3°C for the study period. aPMV model of thermal comfort predicts TS more closely than PMV or PMVe model. Indian composite climate-specific adaptive models fit better with present data base.

A field study of occupant thermal comfort with radiant ceiling cooling and overhead air distribution system

This paper presents the findings of a field research on occupant comfort with radiant ceiling cooling and overhead dedicated outdoor air system (RCF). This extends a previous thermal comfort study with radiant cooling and intended to investigate the actual occupant thermal comfort with radiant ceiling cooling and overhead air distribution system. The research is based on a revised ASHRAE RP-921 project protocol with a combination of field measurements and questionnaires. A total of 135 sets of data from 44 participants were collected in summer. The results show that occupant whole-body thermal sensations with the radiant ceiling and overhead air system had deviated from the PMV model at the 23.6~28.6 °C operative temperature (OPT) range in the summer. The main advantage of the RCF system for thermal comfort was found to be better comfort conditions than with conventional air conditioning at the same operative temperature range. The results of this study showed that the neutral temperature with the RCF is around 26 °C; the preferred temperature by occupants was around 25.3 °C with the RCF. The calculated Predicted Percentage Dissatisfied (PPD) rate is 13.9%, but the actual thermal environment dissatisfaction rate was 8.3% with an unacceptability rate of only 1.5%, which is substantially better than the calculated PPD rate. The study results were compared to earlier findings and validated against some important results, providing benchmarks for future work.

A field study of adaptive thermal comfort in primary and secondary school classrooms during winter season in Northwest China

Current thermal comfort evaluation models are based on the average level of an entire society, which is difficult to use as a direct guide for the design of classroom thermal environments in primary and secondary schools. Research was made on a group of pupils during winter in rural areas in Northwest China to analyze their thermal comfort level and regulation of their thermal adaptability under controlled and uncontrolled environments. Using questionnaire surveys and field measurements, 781 sets of valid data in controlled conditions and 345 sets in uncontrolled conditions were collected. Along with the measured air temperature, relative humidity, air velocity, globe temperature, and clothing level, a significant difference was observed between the thermal sensation vote and predicted mean vote. The preferred temperature and comfortable temperature range were obtained by analyzing the actual percentage of dissatisfied pupils and their thermal expectations. The result subsequently indicated that the comfortable temperature ranges for 90% of the pupils was 13.0–18.0 °C. The upper limit of comfortable temperature was 3.0 °C lower than the lower limit of the current recommended international standard in winter, and the clothing insulation was approximately 0.5 clo higher than the recommended value. By considering the influence of outdoor climate on the behavioral habits, psychological expectations, and physiological regulation, an adaptive thermal comfort model for primary and secondary school students in cold environments is proposed. The findings can serve as a guideline for the design and evaluation of heating systems in primary and secondary schools in rural areas.

A new adaptive thermal comfort model for homes in temperate climates of Australia

The dominant models of adaptive thermal comfort are derived from observations largely drawn from commercial and non-residential buildings. The appropriateness of these models for application in the evaluation or specification of residential thermal performance, however, remains largely untested and emerging work suggests that people within their own homes—with more opportunities for adaptation—have markedly different comfort preferences. This study draws on a substantial database of observations from Australian residential thermal comfort field studies, comprising of over 50,000 observations contributed by occupants of over 300 houses and apartments. We develop a new analytical procedure for the derivation of adaptive thermal comfort models. This paper describes the methodological issues and presents the derived model.

KNN and adaptive comfort applied in decision making for HVAC systems

The decision making of a suitable heating, ventilating and air conditioning system’s set-point temperature is an energy and environmental challenge in our society. In the present paper, a general framework to define such temperature based on a dynamic adaptive comfort algorithm is proposed. Due to the fact that the thermal comfort of the occupants of a building has different ranges of acceptability, this method is applied to learn such comfort temperature with respect to the running mean temperature and therefore to decide the suitable range of indoor temperature. It is demonstrated that this solution allows to dynamically build an adaptive comfort algorithm, an algorithm based on the human being’s thermal adaptability, without applying the traditional theory. The proposed methodology based on the K-Nearest-Neighbour algorithm was tested and compared with data from an experimental thermal comfort field study carried out in a mixed mode building in the south-western area of Spain and with the Support Vector Machine method. The results show that K-Nearest-Neighbour algorithm represents the pattern of thermal comfort data better than the traditional solution and that it is a suitable method to learn the thermal comfort area of a building and to define the set-point temperature for a heating, ventilating and air-conditioning system.

Development of an adaptation table to enhance the accuracy of the predicted mean vote model

The Predicted Mean Vote (PMV) model is extensively used by current thermal comfort standards, such as ASHRAE 55 and ISO 7730, despite its discrepancy in predicting Thermal Sensation (TS). The implicit assumption is that PMV can be applied for predicting TS of a large population. Our statistical analysis of a subset of ASHRAE global database of thermal comfort field study shows that occupants’ expectations towards TS are affected by factors that are not accounted for in the classic PMV model, such as climate, building type, age group, season and gender. The influences of the climate and building type are more determinant. An adapted PMV (PMVa) model and an adaptation table were developed based on the selected samples to reduce this discrepancy. After adaptation, the medians of each category corresponding to the discrepancy are zero or near zero. The results also show that the adapted PMV outperforms the classic PMV in predicting TS, while increasing the overall accuracy from 36% to 39%.

Nudging the adaptive thermal comfort model

The recent release of the largest database of thermal comfort field studies (ASHRAE Global Thermal Comfort Database II) presents an opportunity to perform a quality assurance exercise on the first generation adaptive comfort standards (ASHRAE 55 and EN15251). The analytical procedure used to develop the ASHRAE 55 adaptive standard was replicated on 60,321 comfort questionnaire records with accompanying measurement data. Results validated the standard's current adaptive comfort model for naturally ventilated buildings, while suggesting several potential nudges relating to the adaptive comfort standards, adaptive comfort theory, and building operational strategies. Adaptive comfort effects were observed in all regions represented in the new global database, but the neutral (comfort) temperatures in the Asian subset trended 1–2 °C higher than in Western countries. Moreover, sufficient data allowed the development of an adaptive model for mixed-mode buildings that closely aligned to the naturally ventilated counterpart. We present evidence that adaptive comfort processes are relevant to the occupants of all buildings, including those that are air conditioned, as the thermal environmental exposures driving adaptation occur indoors where we spend most of our time. This suggests significant opportunity to transition air conditioning practice into the adaptive framework by programming synoptic- and seasonal-scale set-point nudging into building automation systems.

Field investigation on occupant's thermal comfort and preferences in naturally ventilated multi-storey hostel buildings over two seasons in India

In India, there is a scarcity of field data reported on occupant's comfort preferences and expectations in multi-storey naturally ventilated (NV) hostel buildings over the last three decades. To fill the research gap, a field study of adaptive thermal comfort was carried out in twelve NV hostel buildings in a composite climate of India, six from each of the two case cities, Jalandhar and Jaipur, respectively. The study is spread over rainy (July–September) and autumn season (October). 1516 valid responses from hostel occupants were collected and were further analyzed statistically to determine comfort temperature and thermal comfort zone for hostel buildings operated under NV mode. Mean Griffiths comfort temperature (Tc) of 29.7 °C and 30.4 °C was observed for Jalandhar and Jaipur city, respectively. Preferred temperature of hostel occupants was about 3 °C lower than mean Tc obtained for both cities. The comfort temperature found in present study were well within the thermal acceptability limits defined in adaptive models EN 16798 (formerly 15251) and NBC-2016 except ASHRAE standard 55–2017. Analysis of the data showed that at elevated air speed (using ceiling fans) the comfort boundary extends by 1.8 °C.

Thermal sensitivity of occupants in different building typologies: The Griffiths Constant is a Variable

The Griffiths method is widely used in thermal comfort studies to derive building users’ comfort temperature, or thermal neutrality as it is sometimes known. A single value (so called the Griffiths Constant, typically 0.5/°C) is prescribed as a representation of thermal sensitivity of building occupants to indoor temperature variations, which in turn is used to estimate indoor thermal neutrality from a subject's actual thermal sensation vote at a measured room temperature. Despite the Griffiths Constant of 0.5/°C having been used widely across the thermal comfort research literature and in some generic standards, the constant was derived exclusively from office building data and its applicability across different typologies is yet to be rigorously validated. The objective of this study is to quantify how sensitive people are to temperature variations inside a building, and to investigate if thermal sensitivity differs between different contexts (including building typologies, modes of ventilation, outdoor climatic types, and genders). A collection of thermal comfort field studies in different building typologies containing around 11,500 datasets was used to statistically derive building users’ thermal sensitivity, i.e. the rate of change in thermal sensation per unit change in indoor temperature within a day. Our results suggest that occupant thermal sensitivity does vary depending on building typologies and building ventilation mode. In naturally ventilated spaces users are about half as sensitive to temperature variations as in air-conditioned spaces. Age, gender and climate are found to be factors that can also influence thermal sensitivity of building occupants. Our findings imply that reliance on a universal thermal sensitivity value, the Griffiths Constant, in comfort temperature (neutrality) calculations should be avoided because it is in fact a variable.

Field study on indoor thermal comfort of office buildings using evaporative cooling in the composite climate of India

Thermal adaptation can play a significant role in defining thermal comfort levels for evaporatively cooled office buildings commonly found in India. However, there are no dedicated studies to record the occupant perception and indoor thermal comfort in these buildings. The contribution of adaptive thermal comfort theory on occupant perception remains unclear for accurate design and operation of evaporatively cooled office buildings in India. Therefore, a multi-year field study of thermal comfort was conducted in ten office buildings operated under evaporative cooling systems in the composite climate of Jaipur, India. Transverse type questionnaire following Class II measurement protocols was carried out for recording office occupant's sensation and preferences for different indoor variables using ASHRAE 55 seven point and five-point scales, respectively. A total of 1554 datasets were collected spread over a total period of eighteen months, covering the entire summer season which includes very hot and dry days as well as few rainy days. Comfort temperature calculated using the Griffiths method was found 28.8 °C (SD=±1.9 °C). Results from the field study showed acceptable indoor humidity and airspeed range of 35–85% and 0.75–1.5 m/s for office subjects. Furthermore, 80% and 90% acceptability limits based on operative temperature and SET* were determined for present field surveys and results were compared with the existing adaptive models in National Building Code of India for different building types. This work is the first step towards the formation of an adaptive comfort model for evaporatively cooled buildings in the composite climate of India.

A data-driven approach to defining acceptable temperature ranges in buildings

Current thermal comfort standards use Predicted Mean Vote (PMV) classes as the compliance criteria despite previous critiques. The implicit assumption is that a narrower PMV range ensures higher thermal acceptability among building occupants. However, our analysis of a global database of thermal comfort field studies demonstrates that PMV classes are not appropriate design compliance criteria, and reinforces the need for a new and robust approach to thermal comfort compliance assessment. We compared two statistical methods to derive acceptable temperature ranges from occupant responses applied one to the ASHRAE Global Thermal Comfort Database II. Derived acceptable temperature ranges in real buildings (7.4K-12.2 K) using this new method are wider than the current standards mandate (2 K-6K). Our findings support the call for a relaxation of suggested temperature ranges in thermal comfort standards so as to minimize unnecessary space conditioning. The proposed data-driven statistical methods to determine temperature design compliance criteria are viewed as an important step forward in the age of continuous and pervasive monitoring and the associated large databases of building comfort measurements.

The time-scale of thermal comfort adaptation in heated and unheated buildings

Air conditioning technologies (HVAC) have dramatically shaped today's building environment. However, the mutually dependent relationship between the indoor climate experience and occupants' thermal comfort adaptation rarely been given attention. To investigate the dynamic processes of adapting to different indoor climates, two comparative thermal comfort field studies were conducted in China, where the northern cities such as Beijing (with district heating) have much warmer indoor temperatures than the southern cities such as Shanghai (without district heating) during the winter. The results indicate that occupants' thermal comfort adaptation exhibits asymmetric trajectories. Building occupants can raise their expectations much faster to accept a neutral indoor climate than they can lower their expectations and acclimate to underconditioned environments. The northern groups took 3 years to adapt to cold indoor temperatures while the southern groups accepted neutral and warm indoor temperatures in less than 1 year. These dynamic processes are well reflected by the ‘demand factor’ metrics. Furthermore, we discussed the practical implications of the asymmetric nature of building occupants' thermal adaptation. It can not only help elucidate the underlying principles behind adaptive comfort phenomena but also help guide building design and operation.

Adaptive thermal comfort model for educational buildings in a hot-humid climate

In this work, we show a thermal comfort field study and adaptive thermal comfort model in educational buildings under tropical Aw climate, considering air conditioning systems (AC) and natural ventilation (NV). The thermal comfort field study and the adaptive thermal comfort model considers 496 collected datasets, in 27 buildings in Tuxtla Gutiérrez-México, in warm season. In AC mode, the 48.1% of occupants surveyed felt comfort, the 44.0% felt cold and the 7.9% felt warmth. In NV mode, the 59.7% felt comfort, the 11.0% felt cold and the 29.3% felt warmth. In AC mode, the neutral preferences, the temperature, the relative humidity and the air velocity were 24.7 ± 1.6 °C, 52.1 ± 5.2% and 0.14 ± 0.05 m/s, respectively; in NV mode were 26.9 ± 1.3 °C, 54.4 ± 5.6% and 0.13 ± 0.04 m/s. The effect of the comfort temperature on the air movement was noticed, the Va was directly proportional to Tcomf. In AC mode, the Tcomf increase up to 27.4 ± 1.9 °C with a Va of 0.17 ± 0.06 m/s, which can be supplied at 0.17 ± 0.03, for cold conditioned supply air. In NV mode, the Tcomf can rise up to 29.3 ± 2.6 °C with a Va of 0.14 ± 0.03 m/s, for fresh air. As seen in AC Mode under tropical Aw climate, the surveyed in educational building prefer higher comfort temperatures up to 1.0 °C in reference to current standards, and this temperature can rise as the air movement increase. Thus, the increase of comfort temperature allows save energy and increase the percentage of satisfied people at the same time, if the thermal adaptability of occupants is considered.

Investigation on thermal comfort of air carrying energy radiant air-conditioning system in south-central China

A field study of thermal environment and thermal comfort under air carrying energy radiant air-conditioning system (ACERS) and split air conditioner was conducted in south-central China. The results reveals that the ACERS can create a comfortable thermal environment with small vertical temperature gradient. Based on the regression equation of thermal sensation vote and operative temperature, it is found that the neutral temperature in ACERS is about 28 °C in summer and 18 °C in winter, while in split air conditioner, the temperature is about 26.1 °C and 19.3 °C. Besides, the comfortable temperature range for 80% acceptability in ACERS is 25.5–30.7 °C in summer and 13.8–22.2 °C in winter, and the corresponding range of split air conditioner is 23.9–28.3 °C and 16.7–21.8 °C. The results show that the ACERS has a larger temperature adjustment range compared to the split air conditioner and the thermal comfort stability of ACERS is better. The actual comfortable temperature range is wider than the theoretical value calculated by PMV-PPD equation, and the reason may be that people in their long-term life have been adaptable to the environment. This research is helpful for the design and operation of air-conditioning system in future and provides the theoretical basis for indoor temperature setting in this area.

Evaluation of comfort preferences and insights into behavioural adaptation of students in naturally ventilated classrooms in a tropical country, India

A transverse questionnaire based thermal comfort field study was conducted in 30 naturally ventilated university classrooms during peak summer months in composite climate of India. A detailed statistical analysis was carried out on 900 thermal comfort surveys database containing information about sensation and preference for different indoor environmental variables. Neutral temperature predicted through linear regression method varied more than 3 °C for different surveyed buildings. More than 90% comfortable votes (±1 votes) of the present database do fit within adaptive comfort boundaries for this climatic zone of India. Additionally, the study estimated a preferred temperature of 26.4 °C using probit analysis. During the field study, personal and global adaptive actions (adaptive actions that tend to modify the indoor environment of classroom) of students during regular classes were recorded and analyzed. Analysis concluded that students preferred high air speed ranges for restoring comfort either by opening windows and doors as or by operating ceiling fans. Logistic regression model predicts more than 80% ceiling fan usage at indoor air temperature 29 °C.

Development of the ASHRAE Global Thermal Comfort Database II

Recognizing the value of open-source research databases in advancing the art and science of HVAC, in 2014 the ASHRAE Global Thermal Comfort Database II project was launched under the leadership of University of California at Berkeley's Center for the Built Environment and The University of Sydney's Indoor Environmental Quality (IEQ) Laboratory. The exercise began with a systematic collection and harmonization of raw data from the last two decades of thermal comfort field studies around the world. The ASHRAE Global Thermal Comfort Database II (Comfort Database), now an online, open-source database, includes approximately 81,846 complete sets of objective indoor climatic observations with accompanying “right-here-right-now” subjective evaluations by the building occupants who were exposed to them. The database is intended to support diverse inquiries about thermal comfort in field settings. A simple web-based interface to the database enables filtering on multiple criteria, including building typology, occupancy type, subjects' demographic variables, subjective thermal comfort states, indoor thermal environmental criteria, calculated comfort indices, environmental control criteria and outdoor meteorological information. Furthermore, a web-based interactive thermal comfort visualization tool has been developed that allows end-users to quickly and interactively explore the data.

Thermal comfort and thermal adaptive behaviours in traditional dwellings: A case study in Nanjing, China

Adaptive thermal comfort is the predominant model used for studying thermal comfort in naturally ventilated buildings. However, current international thermal comfort standards do not represent the people living in all the different types of Chinese buildings, especially in old and traditional dwellings. Much of China's urban and rural populations live in traditional dwellings; their indoor thermal comfort and characteristics differ from those of people who reside in modern dwellings because of their unique thermal experiences and adaptive behaviours. To improve upon the thermal comfort database for energy-saving transformation of traditional dwellings, such as installation of heating or cooling devices and systems for residents, we conducted a field study of thermal comfort and thermal adaptive behaviours of residents in a traditional residential settlement in Nanjing in summer and winter. The results show that traditional dwellers are more tolerant to harsh environments, and their thermal neutral temperature and thermal sensitivity are lower in winter and higher in summer, than those of the people that reside in modern dwellings. Residents of traditional homes employ a series of thermal adaptive behaviours to expand their thermal comfort zone. We demonstrate a significant difference in human thermal comfort, which provides a basis for heating systems design for traditional dwellings and for further research on thermal comfort in different kinds of dwellings and regions.

Design and validation of a low cost indoor environment quality data logger

The appraisal of indoor environment quality in residential dwellings presents a range of technical challenges. Indoor environment quality (IEQ) is often described as having thermal, visual, aural and olfactory dimensions, each of which is assessed subjectively by the resident. While it is possible to objectively assess physical parameters relating to these aspects of IEQ, either directly or indirectly, resident satisfaction with the environment is determined subjectively so must be inferred. In the field study of thermal comfort (FSTC) approach, objective physical measurements are collected simultaneously with resident preference and sensation information, usually via a diary or written survey. This research paper explores a new approach to residential IEQ appraisal which extends the FSTC approach to the visual, aural and olfactory dimensions using a low-cost data collection system based upon the Arduino microcontroller platform. The paper describes the design developed, presents early validation results and draws preliminary conclusions.

Neutral thermal sensation or dynamic thermal comfort? Numerical and field test analysis of a thermal chair

Neutral thermal sensation is considered as the measure of thermal comfort in research, as when participants report feeling neutral regarding the thermal environment, they are considered as thermally comfortable. This is taken for granted, and although a few researchers have criticised the matter, still researchers use thermal sensation and the neutral point to assess the thermal conditions in their studies. This study questions the application of thermal neutrality and consequently poses a question on the findings of all the studies that only rely on it. Field studies of thermal comfort were applied in an open plan office in the UK in the winter of 2014. Participants were provided with a thermal chair and before and after using the chair, their views of comfort were recorded, including the ASHRAE seven point scale of thermal sensation, thermal preference, comfort, and satisfaction. The thermal environment was measured and compared against the ASHRAE Standard 55-2013. In addition, numerical modelling was also conducted to investigated the airflow and thermal distribution around the proposed thermal chair with a seated occupant. The results indicated that overall, 72% of the respondents, who did not feel neutral (thermal sensation) before or after using the thermal chair reported to feel comfortable and 65% reported to be satisfied. The results indicated that a neutral thermal sensation does not guarantee thermal comfort of the occupants and that thermal comfort is dynamic and other thermal sensations need to be considered. This study recommends the use of multiple methods (e.g. thermal, preference, decision, comfort, and satisfaction) to assess thermal comfort more accurately. Also, it questions the findings of any research that solely relies on thermal sensation and particularly on the neutral thermal sensation to assess thermal comfort of the occupants. The results also emphasised the importance of the application of numerical modelling in evaluating the thermal performance of the chair.

An adaptive relationship of thermal comfort for the Gulf Cooperation Council (GCC) Countries: The case of offices in Qatar

Escalating building energy expenditure encourages rethinking on thermal comfort delivery in the Gulf Cooperation Council (GCC) countries in warm desert climate. The GCC states do not have an adaptive comfort standard, or its precursor long term field surveys. Therefore, we carried out thermal comfort field studies in Qatar for thirteen months. In ten typical air-conditioned office buildings, 1174 voluntary subjects have completed 3742 questionnaires, while their thermal environments were simultaneously being measured. We found the mean Griffiths comfort temperature to be 24.0°C. It varied seasonally and also with the indoor temperature. Indoor Griffiths comfort temperature adaptively related with the outdoor temperature. This relationship can be used in buildings of similar nature in the GCC region. The subjects mostly felt cooler sensations. Thermal acceptance was high (82.7%). The offices had very low indoor air movement (median air speed 0.02m/s), while 80% recorded less than 0.05m/s. This is below the average air speed of 0.28m/s, American Society of Heating, Refrigerating and Air-conditioning Engineers permitted. Increased air movement can effectually facilitate an elevated thermal regime, more in sync with outdoor conditions. Adopting variable comfort standards may be made mandatory to achieve the building sustainability goals of the GCC nations.