Adaptive Comfort Standards Research Articles

Influence of outdoor temperature on thermal adaptation: Annual neutral temperature and thermal sensitivity

Building evaluation and guidance for naturally ventilated buildings rely on adaptive comfort models and standards. This study aims to establish an analytical and predictive thermal sensation and adaptation method. The proposed approach is based on the Griffiths method, which reveals a sinusoidal pattern in the neutral temperature and Griffiths coefficient throughout the year. Calculating the daily neutral temperature and evaluating thermal sensitivity through the Griffiths method highlight the delayed response of neutral temperature to outdoor temperature. With the input of operative and outdoor temperature, the Griffiths method predicts adaptive thermal sensation better than the PMV model. The regular fluctuations of neutral temperatures and Griffiths coefficients provide new research ideas and references for designing naturally ventilated buildings. Further research works are still required to check the method’s applicability in the presence of various climate characteristics.

The impact of occupant's thermal sensitivity on adaptive thermal comfort model

Occupants' thermal sensitivity influences comfort temperature, thermal comfort models, and building energy simulation. To date, a universal thermal sensitivity estimate (i.e. 0.5/°C), the so-called Griffiths Constant, has been widely used to estimate comfort temperatures. However, recent field evidence indicates that the constant is actually a variable that changes according to context. The objective of this study is to explore the impact of different thermal sensitivity values on adaptive comfort models using the ASHRAE Global Thermal Comfort Database II. The method followed five main steps: i) subset Database II to include entries with the requisite parameters; ii) estimate neutral temperature using the standard Griffiths method; iii) iterate step “ii” using different thermal sensitivity values; iv) derive adaptive comfort models for air-conditioned and naturally ventilated office buildings considering global and European datasets; v) compare resulting models. The results highlight that occupants’ thermal sensitivity varies according to building ventilation type. Occupants in naturally ventilated offices were about half as sensitive to temperature changes as occupants in air-conditioned buildings. The most important outcome of this study is that thermal sensitivity and geographic region significantly affect the adaptive model relationship between outdoor temperature and indoor neutral temperature for occupants of naturally ventilated buildings; Occupants of European buildings are more sensitive to temperature changes than counterparts in other regions. The significance of this finding is that the adaptive model relationship forms the basis of the adaptive comfort standards, and so it has implications for both the design and operation of naturally ventilated and mixed-mode buildings.

Indoor Thermal Comfort Analysis: A Case Study of Modern and Traditional Buildings in Hot-Arid Climatic Region of Ethiopia

Indoor thermal comfort is an essential aspect of sustainable architecture and it is critical in maintaining a safe indoor environment. Expectations, acceptability, and preferences of traditional and modern buildings are different in terms of thermal comfort. This study, therefore, attempts to evaluate the indoor thermal comforts of modern and traditional buildings and identify the contributing factors that impede or facilitate indoor thermal comfort in Semera city, Ethiopia. This study employed subjective and objective measurements. The subjective measurement is based on the ASHRAE seven-point thermal sensation scale. An adaptive comfort model was employed according to the ASHRAE standard to evaluate indoor thermal comfort. The results revealed that with regards to thermal sensational votes between −1 and +1, 88% of the respondents are satisfied with the indoor environment in traditional houses, while in modern houses this figure is 22%. Likewise, 83% of occupants in traditional houses expressed a preference for their homes to remain the same or be only slightly cooler or warmer. Traditional houses were, on average, in compliance with the 80% acceptability band of the adaptive comfort standard. The study investigated that traditional building techniques and materials, in combination with consideration of microclimate, were found to play a significant role in regulating the indoor environment.

Thermal comfort perception in naturally ventilated affordable housing of India

ABSTRACT Indoor thermal comfort is critical to building sustainability besides improving occupants’ health, well-being and productivity. However, the applicability of the existing comfort standards within different climatic conditions and contextual settings is often in question. This study presents the findings from a longitudinal thermal comfort study conducted in low-income affordable housing in Mumbai, India. Surveys were conducted in three distinct seasons within a warm–humid climate. The linear regression method yielded a mean neutral temperature of 28.3°C and a wide comfort band ranging from 24.6°C to 32.2°C indicating high thermal adaptation among the occupants. The preferred temperature was found to be 26.3°C. Adaptive comfort standards, ASHRAE and the National Building Code of India prescribed a narrow range of comfort and were ineffective in predicting comfort conditions within affordable housing units. The role of income in shaping comfort expectations was established, lending support to the economic dimension of comfort. The results would be helpful in providing design recommendations for the future affordable housing stock and the development of an adaptive comfort model for vulnerable low-income communities.

Summer thermal discomfort in substandard housing with openable windows in Hong Kong

The sub-divided unit (SDU) is the major type of substandard housing in Hong Kong. This study monitored the microclimatic conditions in eight SDUs for 24 h in summer. The mean CO2 concentration (1012 mg/m3) under natural ventilation was much higher than the outdoor level (∼410 mg/m3), suggesting that ventilation was ineffective in most SDUs. The mean predicted mean vote (PMV) was 1.7 (warm), corresponding to 75% predicted percentage dissatisfied (PPD). None of the SDUs was thermally acceptable (PPD < 20%) at any time in the monitoring period. If the adaptive thermal comfort standard was considered, the acceptable temperature range would be between 23.4 °C and 30.4 °C in operative temperature and the thermally acceptable time would be 47%. Larger openable window size, larger external wall area and poor ventilation significantly contributed to higher maximum indoor air temperature.

Influence of the Improvement in Thermal Expectation Levels with Adaptive Setpoint Temperatures on Energy Consumption

A sustainable use of active heating, ventilation, and air conditioning (HVAC) systems is crucial for minimum energy consumption. Currently, research studies are increasingly applying adaptive setpoint temperatures, thus reducing considerably the energy consumption without influencing comfort levels excessively. Most of them, however, are focused on the limit values of adaptive comfort standards without considering the tolerance in users’ adaptation capacity. This research study analyzed various tolerance ranges in the recent adaptive thermal comfort model from EN 16798-1:2019 used in setpoint temperatures. The study focused on the south of Europe, considering 47 cities in Spain, 18 cities in Portugal, 13 cities in Greece, and 20 cities in Italy. In addition, such cities were analyzed in three climate scenarios: present time, 2050, and 2100. The results showed that values prefixed by EN 16798-1:2019 for new buildings (tolerance of 0.00 °C) produced significant savings with respect to the static model and that each progressive improvement in users’ thermal expectations in 0.25 °C increased the energy consumption between 6.57 and 9.31% in all scenarios analyzed. Even applying a thermal tolerance of 1.50 °C, energy savings are currently produced with respect to the static model. This tendency increases in future scenarios until a thermal tolerance of 1.75 °C. The results of this paper provide greater knowledge about the possible energy increase that the improvement in users’ expectations would produce.

A field investigation on indoor thermal environment and its associated energy use in three climatic regions in Nepal

Nepal is a mountainous country with low energy use so far and its climatic patterns remarkably differ from one place to another due to its geographical variation. In the north, summer is cool and winter is severe, while in the south, summer is tropical and winter is mild. Each year, harsh thermal environment creates serious health problems ranging from discomfort to illness and even to death. Household energy availability is one of the important ingredients required to provide the occupants with adequate indoor thermal environments, with which they can minimize thermal dissatisfaction. In order to get quantitative information on this issue, a series of survey on household energy-use patterns and the indoor thermal environmental characteristics in three different climatic regions was carried out in winter season of 2018. The survey results showed that most of the indoor air temperature of investigated houses in three climatic regions were lower than the values given as adaptive comfort standard. Average measured indoor air temperature was 8.0 °C, 13.9 °C and 12.8 °C, respectively, and per-capita daily energy use was 37, 30 and 20 MJ/(person · day) in cold, temperate and sub-tropical regions, respectively. Firewood, electricity and liquefied petroleum gas (LPG) were found as the major energy carriers used in the studied households. The present finding suggests that a substantial improvements of the indoor thermal environment by improving thermal insulation of building envelopes together with rationally small energy use must be required for the well-being of the people in all three regions. This survey results are hopefully useful to understand the current energy-use situation and thermal environment of existing residential buildings in Nepal and thereby to assist the policy formulation for better indoor thermal environment of existing buildings with low energy use.

Indoor comfort conditions assessment in educational buildings with respect to adaptive comfort standards in European climate zones

Educational buildings across Europe refer to a large amount of structures for which critical interventions are necessary. Particularly, for old buildings, comprehensive refurbishment efforts are essential, in order to enhance the indoor comfort conditions and establish the best possible settings for students and users. Evidently, the above issue is decisive to stimulate and support students with reference to the learning process and aims of the educational system (superior learning performance); this has also a positive effect on users’ interaction with the nearby environment, in terms of social adaptability and health for children and adults. In this context, the main goal is to transform entirely the design of educational building spaces with respect to the initial conditions. To this end, governments often set targets on upgrading and utilizing school infrastructure in the urban district (mostly, for school classes situated in the urban core of the social and local communities). As is well known, the improvement of a building from a building physics point of view is fundamentally related to the attainment of acceptable hygro-thermal, visual and acoustic comfort conditions. On the other hand, limiting the heat flux through the buildings’ envelope and restricting CO2 emissions, is of great importance, from an environmental point of view. However, the complexity and significance to assess educational facilities mostly relies on the use of heating in winter and the absence of cooling systems during summer. In addition, climate change, which results into growing values of the air temperature, makes it difficult to attain acceptable indoor comfort conditions with natural ventilation. To reduce this effect, especially in the southern part of Europe, shading devices, as well as ventilation and cooling systems offer rational approaches to scrutinize the indoor environment. The central points of the present investigation, with respect to the indoor comfort conditions of educational buildings in different climate zones, during the cooling season, are as follows: (a) the retrofit measures to improve the thermal performance during heat waves; (b) how to gain tolerable indoor comfort conditions with or without a cooling; (c) the implementation of adaptive thermal comfort models. A dynamic thermal simulation on three levels (envelope, classroom, school building) has been carried out in order to assess the school building stock and investigate possibilities of improvements . For three different locations several retrofit scenarios have been evaluated by considering adaptive comfort standards (for typical users, as well as for children). Furthermore, to stretch the impact of this investigation, the analysis has been extended for a real case study: the “Modulo Didattico” building in the Smart Campus of the University of Brescia. At last, the integrated workflow of the design process is presented, considering both BIM and BEM data, and demonstrating an interesting application of visualization techniques for assessment of the comfort conditions in the different thermal zones. The study is the outcome of a collaborative workplan between the University of Brescia (unibs, Italy) and the Aristotle University of Thessaloniki (A.U.Th., Greece).

Development and application of future design weather data for evaluating the building thermal-energy performance in subtropical Hong Kong

To better understand the impacts of the warming caused by global climate change on building performance, future hourly weather data that account for climate change are crucial to building simulation studies. Downscaling from general circulation models (GCMs) by the morphing method has been adopted by researchers worldwide. Using this method, we developed six sets of future hourly weather data for Hong Kong, taking the typical meteorological year (TMY) as the baseline climate. The ensemble mean from 24 general circulation models (GCMs) in the Coupled Model Intercomparison Project Phase 5 (CMIP5) has also been incorporated to take into account the uncertainties and biases between different models. These newly developed future weather data were then employed in the building energy simulation to evaluate the impacts of future climate change. Moreover, this study used the adaptive comfort standard (ACS) from ASHRAE Standard 55 in a mixed-mode residential building to consider the acclimatization effects of occupants in the changing climate. Results indicate that by the end of this century, the indoor discomfort percentage in the cooling seasons are expected to increase from 21.9% for TMY to 36.0% and 50.4% under RCP4.5 and RCP8.5 scenarios, respectively, while the annual cooling load is expected to increase up to 278.80%.

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.

Thermal comfort in a mixed-mode building: Are occupants more adaptive?

Mixed-mode (MM) ventilation approaches are becoming increasingly popular as a more energy efficient alternative to conventional HVAC solutions. By integrating both natural ventilation and mechanical cooling strategies, mixed-mode (or hybrid) building operation is able to achieve comfortable indoor environments whilst minimising reliance on energy intensive HVAC systems. This study investigated how different modes of operation in a mixed-mode building - air-conditioning (AC) and natural ventilation (NV) - affect indoor thermal environmental conditions and occupant perceptions of thermal comfort. Longitudinal field observations were made in a mixed-mode building located in subtropical climate area of Australia. Continuous indoor environmental quality (IEQ) data and building operational data such as HVAC system and windows states were collected, alongside right-here-right-now occupant comfort surveys. Time-and-place matching of these objective and subjective data streams enabled analysis of the relationships between building operational modes, indoor thermal environments, and occupant perception of comfort. The results indicate that the mode of ventilation influenced comfort responses of occupants beyond the direct effects of different thermal conditions. Occupants of the mixed mode building were more tolerant of, or adaptive to, the indoor thermal conditions when the building was in the NV mode of operation compared to the AC operational mode. Participants more actively thermoregulated their clothing insulation (clo) than what was predicted by the ASHRAE Standard 55′s dynamic clothing model. These findings support the call for extending the scope of applicability of adaptive comfort standards to include mixed-mode buildings.

Comfort temperature and occupant adaptive behavior in offices in Qatar during summer

Qatar tops the world in per capita CO2 emissions and per capita total primary energy supply. Adaptive comfort standards and thermal comfort field survey data are not available for Qatar. We conducted a thermal comfort survey in Doha, Qatar, for five summer months in 2016. In nine typical randomly selected air-conditioned office buildings, 828 subjects returned 1926 questionnaires. We found 24.1°C as Griffiths comfort temperature. Subjects mostly felt cooler sensation (mean: −0.23). Fanger’s Predicted Mean Vote always overestimated the actual sensation. We recorded very low to near still air conditions in all the indoors (mean speed: 0.04m/s.) While 39.1% occupants felt neutral, 72.1% voted in the central band of the sensation scale and 85% accepted the environments. The occupants adapted through clothing. Clothing insulation significantly varied with air temperature. Public buildings are significantly cooler than the private buildings, and yet are less acceptable throughout the survey.

Thermal adaptive models in the residential buildings in different climate zones of Eastern China

Adaptive comfort standards have become the main stream comfort research and are now considered an optional choice of natural ventilated buildings in the international thermal comfort standards. However, the international adaptive models were not suitable to evaluate the thermal adaptation level of all the climates. To explore thermal adaptive ability and develop thermal comfort models in different climate zones, field studies on thermal comfort in 120 residential buildings in summer and winter have been conducted in 12 cities, representative of four climate zones in eastern China. Those data were gathered using instantaneous subjective questionnaire surveys and objective on–site measurements. The results showed that the predicted neutral temperatures based on MTS in winter in four climate zones were all lower than the predicted neutral temperatures based on PMV, and vice versa in summer. The clothing was mainly affected by the indoor temperature in the severe cold climate; however, it was affected by the outdoor temperature in the warmer climates. Clothing adjustment was more obvious in the warmer climate than in the colder climate. The warmer the climate, the smaller the yearly temperature difference, and the higher a sensitivity of the neutral temperature to outdoor temperature. The adaptive models in the hot summer and cold winter zone (HSCW) and hot summer and warmer winter zone (HSWW) can be used to predict the comfort temperatures of the natural ventilated buildings in the above two climate zones. Different climate zones should develop their own thermal adaptive models. These findings provide support to the climate adaptation theory and can serve as reference for the design of natural ventilated buildings.

Adaptive thermal comfort in the two college campuses of Salesian College, Darjeeling – Effect of difference in altitude

Thermal comfort standards help building designers to provide good indoor climate as well as optimization of energy consumption in a building. Usually, Predicted Mean Vote (PMV) model which had its basis on the extensive climate chamber experiments is utilized to estimate the comfort condition for a building. However, the recent studies in the field of thermal comfort shows that the commonly used PMV model frequently underestimates and overestimates the thermal sensation in cooler and warmer condition in the real conditions leading to a more extreme set point temperature than required thus with higher energy consumption. This discrepancy in predicted and actual sensation was explained by the adaptive theory researches where the subjects have various adaptive opportunities to make themselves more comfortable than as predicted. However, the field survey based adaptive comfort standards depend upon several factors like the local climatic condition, ethnicity, etc. In this paper, we present the results of adaptive thermal comfort based field study conducted on two campuses of the same institution separated by altitude. A total of 1147 datasets were collected from 356 subjects with age group 18–29 years, most of whom were college students. We have discussed the variation of clothing insulation and thermal neutrality both with the altitude and with outdoor conditions. A wider range of indoor temperature for which the subjects voted neutral was seen especially on the lower side (12.5°–32.3 °C) in comparison to previous studies.

An Exhaustive Parametric Study on Major Passive Design Strategies of a Typical High-rise Residential Building in Hong Kong

This paper presents a comprehensive sensitivity analysis (SA) of the typical High-rise residential building in Hong Kong. A generic building model is constructed with proposed natural ventilation strategies subject to the examination of thermal comfort criteria. The numerical modelling exhaustively investigate the thermal and energy responses based on the variation of different passive design parameters. The parametric studies with respect to multiple output indices are able to prove that the window solar heat gain coefficient is the most influential architectural design factor. Different thermal comfort models including the Adaptive Comfort Standard (ACS) and Predicted Mean Vote (PMV) are compared in estimating the indoor environmental quality (IEQ) for the generic building. It is believed that sensitivity analysis benefit the identification of important inputs to facilitate further optimization of the building performance in initial plan stages.

Comparison of the Efficiency of Building Hybrid Ventilation Systems with Different Thermal Comfort Models

Building hybrid ventilation integrates the advantages of both natural ventilation and mechanic ventilation. Ventilation efficiencies and system costs are found to be associated with different control strategies. Two indoor thermal comfort indices, which are predicted mean vote (PMV) model and adaptive comfort standard (ACS) model, are chosen as the control objective in this paper. A hybrid ventilation system with these thermal models was developed. Experimental tests were conducted to compare the time percentage of thermal comfort in summer, and the running time of the exhaust fan between the two systems. The results show that the percentage of the interior thermal comfort time is between 64.5% and 86.4% when the outside air temperature is between 10°C and 25°C (the average temperature is about 17.5°C, Period 1). The percentage is 45.2∼60.7% when the outside air temperature was 13∼32°C (the average temperature is about 22.7°C, Period 2), and 29.4∼49.3% when the outside air temperature was 18∼34°C (the average temperature is about 26.5°C, Period 3). The comfort time percentage is always higher with ACS model than that with PMV model in these three test periods. The results also indicate that the ventilation efficiency, which is defined as ratio of window opening time to the fan's running time, is higher with the ACS model than that with the PMV model in the period 2 and 3. The ACS model could be considered as the prior control objective for the hybrid ventilation system.

An adaptive thermal comfort model for the tropical climatic regions of India (Köppen climate type A)

Adaptive comfort standards have been gaining wider acceptance and are now considered an integral part of main stream comfort research. Several adaptive comfort equations have been developed, some as part of international comfort standards and some for specific climatic regions. In the current work, an attempt was made to find a best fit among available comfort equations for predicting occupant comfort in the tropical climatic regions of India. Comfort temperatures found in surveys done across tropical India were compared to comfort temperatures computed from five different adaptive comfort equations. Additionally, to estimate energy savings possible through implementation of adaptive comfort standards, adaptive comfort degree days (ACDD) were calculated across seven Indian cities using comfort temperature predictions from the five equations. Put together, results from these two analyses showed that the comfort equation from EN15251 may be used as a reasonable predictor of comfort in naturally ventilated buildings of hot–humid Indian regions and such use would also result in major energy savings. It is proposed that till further studies in India provide more detailed results, the EN15251's standard for naturally ventilated buildings may be used as a suitable option for Indian conditions. Formalisation of appropriate adaptive comfort standards for India would be a significant asset to the sustainable development of this country.

A new hybrid thermal comfort guideline for the Netherlands: background and development

In 2004, the first adaptive thermal comfort guideline was introduced in the Netherlands. Recently, a new, upgraded version of this ISSO 74 (ATG) guideline has been developed. The new requirements are hybrid in nature as the 2014 version of the guideline combines elements of traditional non-adaptive comfort standards with elements of adaptive standards. This paper describes the new guideline and explains the rationale behind it. Also changes in comparison with the original 2004 version and (some) issues related to performance verification are discussed. The information presented in this paper can be used by others (other countries) as inspiration material for new adaptive comfort guidelines and standards.

Using the central ventilation shaft design within public buildings for natural aeration enhancement

The natural ventilation of buildings can be closely related to building design. The object of this investigation is to conduct computational fluid dynamic (CFD) simulations and field measurements for studying the natural ventilation effectiveness of office space in a common public building with a built-in central ventilation shaft (CVS). The aeration flow behavior was predicted and compared with the measured air velocity and temperature data at 16 monitoring positions over three different floors inside the main building to validate the computer software as well as attain a better understanding of the natural ventilation mechanism associated with the interaction of the wind with the building. CFD simulations were also extended to examine the design impacts of removing the CVS and reducing the cross-sectional area to a half-sized CVS on the building aeration performance in terms of the air exchange rate per hour (ACH) and the adaptive comfort standard (ACS) and predicted mean vote (PMV) results. This CFD simulation procedure can serve as a useful analysis tool to facilitate architects for improving the natural ventilation design of buildings during their decision-making process.

Thermal comfort in offices in summer: Findings from a field study under the ‘setsuden’ conditions in Tokyo, Japan

Post Fukushima disaster, the energy consumption perspective in Japan has changed. It initiated unprecedented exercises towards energy saving and produced interesting results. These included the ‘setsuden (energy saving)’ campaigns, which promoted the minimum indoor temperature setting of 28 °C in summer. However, there is no scientific basis for this recommendation. Japan does not have adaptive comfort standards and the ASHRAE standard-55 does not include the data from the land of the rising sun. In this context, we conducted a thermal comfort field study in four office buildings in Tokyo for three months in summer 2012. We measured all the four environmental and the two personal variables. Through a paper based field survey, we interviewed 435 occupants who returned 2402 questionnaires.The occupants' comfort temperature was found to be 27.2 °C. Thermal acceptability was very high at 89% even when 26% of the environments were outside the three central categories of the thermal sensation scale. PMV always significantly overestimated the sensation owing to a wide range of adaptations by the subjects. The indoor air speeds were low, indicating a need for ceiling fans. In 50% of the environments the indoor temperature was more than the 28 °C limit. As the buildings were designed for AC mode, running them in NV mode posed challenges. This study calls for elaborate field studies in offices in Japan for the development of custom made adaptive comfort standards.