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Heating and cooling in buildings accounts for over 20% of total energy consumption in China. Therefore, it is essential to understand the thermal requirements of building occupants when establishing building energy codes that would save energy while maintaining occupants thermal comfort. This paper introduces the Chinese thermal comfort dataset, established by seven participating institutions under the leadership of Xian University of Architecture and Technology. The dataset comprises 41,977 sets of data collected from 49 cities across five climate zones in China over the past two decades. The raw data underwent careful quality control procedure, including systematic organization, to ensure its reliability. Each dataset contains environmental parameters, occupants subjective responses, building information, and personal information. The dataset has been instrumental in the development of indoor thermal environment evaluation standards and energy codes in China. It can also have broader applications, such as contributing to the international thermal comfort dataset, modeling thermal comfort and adaptive behaviors, investigating regional differences in indoor thermal conditions, and examining occupants thermal comfort responses.

ASHRAE Standard 55 has been evolving in recent years to encourage more sustainable building designs and operational practices. A series of changes address issues for which past design practice has been deficient or overly constrained. Some of the changes were enabled by findings from field studies of comfort and energy-efficiency, and others by new developments in the design- and building-management professions.  The changes have been influencing practice and spurring follow-on research.The Standard now addresses effects of elevated air movement, solar gain on the occupant, and draft at the ankles, each with several impacts on energy-efficient design and operation. It also addresses the most important source of discomfort in modern buildings, the large inter- and intra-personal variability in thermal comfort requirements, by classifying the occupants’ personal control and adaptive options in a form that can be used in building rating systems. In order to facilitate design, new computer tools extend the use of the standard toward direct use in designers’ workflow. The standard also includes provisions for monitoring and evaluating buildings in operation. This paper summarizes these developments and their underlying research, and attempts to look ahead.

People's subjective response to any thermal environment is commonly investigated by using rating scales describing the degree of thermal sensation, comfort, and acceptability. Subsequent analyses of results collected in this way rely on the assumption that specific distances between verbal anchors placed on the scale exist and that relationships between verbal anchors from different dimensions that are assessed (e.g. thermal sensation and comfort) do not change. Another inherent assumption is that such scales are independent of the context in which they are used (climate zone, season, etc.). Despite their use worldwide, there is indication that contextual differences influence the way the scales are perceived and therefore question the reliability of the scales’ interpretation. To address this issue, a large international collaborative questionnaire study was conducted in 26 countries, using 21 different languages, which led to a dataset of 8225 questionnaires. Results, analysed by means of robust statistical techniques, revealed that only a subset of the responses are in accordance with the mentioned assumptions. Significant differences appeared between groups of participants in their perception of the scales, both in relation to distances of the anchors and relationships between scales. It was also found that respondents’ interpretations of scales changed with contextual factors, such as climate, season, and language. These findings highlight the need to carefully consider context-dependent factors in interpreting and reporting results from thermal comfort studies or post-occupancy evaluations, as well as to revisit the use of rating scales and the analysis methods used in thermal comfort studies to improve their reliability.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Thermal discomfort is one of the main triggers for occupants interactions with components of the built environment such as adjustments of thermostats and/or opening windows and strongly related to the energy use in buildings. Understanding causes for thermal (dis-)comfort is crucial for design and operation of any type of building. The assessment of human thermal perception through rating scales, for example in post-occupancy studies, has been applied for several decades; however, long-existing assumptions related to these rating scales had been questioned by several researchers. The aim of this study was to gain deeper knowledge on contextual influences on the interpretation of thermal perception scales and their verbal anchors by survey participants. A questionnaire was designed and consequently applied in 21 language versions. These surveys were conducted in 57 cities in 30 countries resulting in a dataset containing responses from 8225 participants. The database offers potential for further analysis in the areas of building design and operation, psycho-physical relationships between human perception and the built environment, and linguistic analyses.

People often feel uncomfortably warm and sweaty in their workspace after commuting there by walking or cycling in summer. This is because body heat stored during the commute takes a substantial time to dissipate. People complaining about this uncomfortable transition may cause operators to lower the thermostat setpoint, causing long-term overcooling and wasting energy. In addition, space cooling is slow, requiring minutes to take effect. This study addresses how to improve comfort in the transition by increasing the availability of convective cooling, where the response time is in seconds. Thirty-five subjects (17 men and 18 women) dressed in 0.6 clo en-tered a test room after exercising at 4.4 met for 15 min in 30 ºC. The exercise emulates the commute activity in summer. The test room was controlled to 24, 26, and 28 ºC, with and without the option of cooling using fan-produced horizontal airflow. Subjects were sedentary for 60 minutes, during which subjective thermal responses and physiological responses were measured. The enhanced convective and evaporative heat loss caused by fans significantly shortened the time needed to reach thermal comfort after the exercise-induced thermal stress and improved the final comfort level. Compared to a typical indoor condition of 24 ºC and still air, 26 and 28 ºC with fans provided equal or better comfort more quickly, and inherently required much less energy to do so. Our study suggests that personally controlled air movement should be available in spaces where thermal and metabolic down-steps take place

Naturally ventilated buildings have been found to be comfortable over a wider range of indoor temperatures than in air-conditioned buildings, while using less energy. The mechanisms underlying this are not well understood. Through a longitudinal field study of a naturally ventilated office in Alameda, CA, we obtained insights into how occupants exercise various adaptive control opportunities to meet their comfort needs in the absence of a mechanical HVAC system. Continuous measurements were made of adaptive behaviors such as window state, ceiling fan usage, heater usage, and indoor and outdoor climate (dry-bulb air temperature, relative humidity, CO2, outdoor temperature). Over 1400 thermal comfort survey responses were collected, which showed that the building provided acceptable thermal conditions for 98% of the survey period, covering an indoor temperature range of 16–28°C. Occupants wore clothing between 0.5 and 0.6 clo in summer, and 0.7–0.8 in winter. Occupants opened windows when the outdoor temperature was above 15°C, with window opening often occurring at the occupant's arrival and proportional to outdoor temperature. Fan use was best explained by indoor temperature, typically being turned on during summer at indoor temperatures above 25°C. Heaters were turned on in winter more than an hour after arrival and commencement of sedentary activity. With these adaptive control behaviors, occupants were thermally neutral and satisfied from 18 to 27°C. Their satisfaction exceeded that predicted by ASHRAE Standard 55 or PMV-based ISO standards. Overall, our findings provide empirical support for adopting adaptive comfort model in office buildings.

The current study investigates the transient human physiological and comfort responses during sedentary activity following a period of elevated activity in a hot condition. Such metabolic and thermal down-steps are common in buildings as occupants arrive after commuting in summer. It creates a serious problem for thermostatic control, since arriving occupants find their transition uncomfortably warm at temperatures that resident occupants find comfortable. Fifty-nine participants (29 men, 30 women) dressed in 0.6 clo were tested while sedentary for 60 min in 26 °C, after having been exposed to 30 °C for 15min, during which they performed activities metabolically simulating commuting: sitting (SE- 1.2 met), or doing three levels of stair-step exercises: low (LEx- 2.2 met), medium (MEx - 3.0 met), and high (HEx - 4.4 met). Subjective comfort and physiological responses (metabolic rate, skin temperature, skin blood flow rate, heart rate, core temperature, and skin wettedness) were collected. Results show that sedentary conditions at 26°C became comfortable and acceptable within 2 min, but thermal sensation required much longer to change from ‘warm’ or ‘hot’ to ‘neutral’: 0, 8, 17, 30 min after SE, LEx, MEx, HEx respectively. Skin wettedness and core temperature did not recover within the60 min. The delays are mainly due to body heat stored during the exercise. A room temperature of 26°C may not provide sufficient cooling after summer commuting. Localized convective cooling of transitional spaces and work areas by ceiling or desk fans represent a way to enhance comfort recovery.

Over-cooling happens commonly in air-conditioned buildings that costs energy and results in discomfort complaints. There are many reasons causing overcooling, and HVAC engineers and researchers have proposed several approaches to prevent it from happening. In this paper, we describe a field study to show how the overcooling and energy use were significantly reduced by lowering maximum and minimum supply air flowrate setpoints, while providing personal comfort systems for occupants. The study was conducted over 16 months in two office spaces of a campus building with high HVAC energy expenditure and frequent cold complaints. The initial visit and measurements showed that the spaces were over-ventilated, causing cold discomfort in several workstations. We provided personal comfort systems to 26 occupants (heated/cooled chair, footwarmer, legwarmer based on occupants’ own choices) to maintain comfort, and gradually reduced the maximum and minimum supply air volume setpoints, to reduce the air-conditioning intensity and to let the office ambient temperature float. We increased occupants’ satisfaction rate from 56% to over 80%, meanwhile lowered HVAC zone energy use by 60% in heating and 40% in cooling.

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.

Prolonged sedentary behavior has been shown to increase chronic diseases. Using standing and treadmill desk reduces sitting time, increases metabolic rate and thus has potential to improve health. There is little existing guidance on how to keep thermal comfort when using standing and treadmill desk. It is unknown what are the suitable ambient temperatures for occupants at elevated office activity levels. This experiment investigated thermal sensation and preferred temperature at elevated office activity levels, including sitting (SED), standing (STD), and two slow-walk speeds: walking at 1.2 km/h (TRD1) and walking at 2.4 km/h (TRD2). Comfort votes were obtained from 20 subjects under personal controlled ambient temperature. The active workstation significantly increased human metabolic level and reduced preferred temperature. The measured metabolic rates were 1.0, 1.1, 1.9 and 2.5 met for SED, STD, TRD 1 and TRD 2. The preferred ambient temperature reduced from 25.85 °C for SED, to 25.0, 24.1 and 23.2 °C for STD, TRD 1 and TRD 2 respectively. All subjects were comfortable at their preferred temperatures. PMV model was found to predict too cool temperature than needed for higher metabolic rates.

Of the six fundamental parameters in the classic heat balance model of human thermal comfort, metabolic rate is probably the most important and yet it is the most crudely assessed in both research and practice. Most studies in thermal comfort domain to date have relied on simple activity diaries to estimate metabolic rate. To better understand the pros and cons of this convenient approach, a literature review of cognate disciplines was conducted with the aim of transferring developments in human metabolic science to the built environmental context. This review leads to the conclusion that the dairy methods prevalent in thermal comfort research and practice are probably not accurate enough to sustain common thermal comfort modeling with any semblance of precision. Additional research effort is needed to develop better metabolic rate estimation methods for building occupants, especially accommodating individual differences in BMI, sex, age, pregnancy and menopause status, and non-steady state scenarios. In particular, three avenues of future research topics hold promise for improving practical metabolic estimation and thermal comfort in buildings were discussed:1) development and validation of new metabolic rate instrumentation, 2) field measurement of human metabolic rate characteristics, 3) determine comfort zones for buildings with specific metabolic rate features.

Ceiling fans may cool room occupants very efficiently, but the air speeds experienced in the occupied zone are inherently non-uniform. Designers should be aware of several generic flow patterns when positioning ceiling fans in a room. Key to these are the fan jet itself and lateral spreading near the floor. Adding workstation furniture redirects the jet’s airflow laterally in a deeper spreading zone, making room air flows more complex but potentially increasing the cooling experienced by the occupants.This paper presents the first evaluation of the effects of tables and workstation partitions on a room’s generic air flow and comfort profiles. In a test room with a ceiling fan, we moved five anemometers mounted in a “tree” at heights of 0.1, 0.6, 0.75, 1.1, and 1.7 m to sample a dense measurement grid of 7 rows and 6 columns.  We tested five different table and partition configurations and compared them to the empty room base case. From the results we propose a simplified model of room airflow under ceiling fans, useful for positioning fans and workstation furniture.  We also present comfort contours measured in two ways that have comfort standards implications.  The measured data are publicly available on the internet.

This research program investigated the potential energy savings to be gained by retrofitting non-domestic buildings in California with natural ventilation for cooling. The simplest and most cost effective retrofit is to open windows on the façade and turn off any mechanical ventilation. To make the problem tractable attention was restricted to wind-driven natural ventilation. Stack-driven ventilation is likely to also be present in practice, and usually improves the cooling potential.The program was split into three major projects. Project 1 assessed the potential of and the barriers to the implementation of natural ventilation. Project 2 examined induced air movement and the possible ingress of outdoor pollutants. Project 3 produced new tools for predicting the energy performance of naturally ventilated buildings, and provided training in their use.The major barriers to the introduction are the lack of specific design guidance and a lack to easy-to-use modeling tools. These are compounded by a lack of design experience and case studies and the mandatory requirements for the amount and location of openable area specified in Title 24.Research on wind-driven natural ventilation using computational fluid dynamics and wind tunnel tests provided new algorithms for cross ventilation, single-sided ventilation and corner ventilation, accounting for opening size, location and number, and the effects of sheltering by neighboring buildings. These algorithms were implemented in EnergyPlus, and the new version of the code was used in three training sessions to provide the design and engineering community with some familiarity in the new modules that calculate natural ventilation.The overall outcome of this program is a comprehensive study of the current issues concerning retrofitting commercial buildings in California and an assessment of the potential risks and benefits. It has also significantly extended the capabilities for modeling, design, and operation of naturally ventilated buildings in California.

Fitness centers are energy-intensive in warm climates, cooling the interior to low temperatures that are comfortable for exercise. There is little existing guidance on how to do this efficiently. However it is well-known that significant energy can be saved by cooling sedentary occupants with air movement at elevated setpoint temperatures. This experiment investigated thermal comfort and air movement at elevated activity levels. Comfort votes were obtained from 20 subjects pedaling a bicycle ergometer at 2, 4, and 6 MET exercise intensities in four temperatures (20, 22, 24, 26 °C, RH 50%) under personal controlled ceiling fan airflow, as well as in a 20 °C still-air reference condition. An additional test of frontal airflow was conducted at 26 °C. The hypothesis, that air movement together with higher temperatures would produce equal or better comfort and perceived air quality below the reference condition, Center for the Built Environment (CBE) University of California, Berkeley was confirmed for every temperature up to 26 °C. Subjects preferred air speeds up to 2.3 m/s to maintain acceptable thermal environment at 6 MET. The small frontal fan affecting the facial area was effective but the ceiling fan affecting the whole body provided greater comfort. Fitness centers should operate with elevated air movement to improve both comfort and efficiency.

This paper discusses a spectrum of systems that cool or heat occupants personally, termed ‘personal comfort systems’ (PCS), in order to quantify their ability to produce comfort in ambient temperatures that are above or below the subjects’ neutral temperatures.The comfort-producing effectiveness may be quantified in terms of a temperature difference, coining the index ‘corrective power’ (CP). CP is defined as difference between two ambient temperatures at which equal thermal sensation is achieved - one with no PCS (the reference condition), and one with PCS in use.  CP represents the degree to which a PCS system may “correct” the ambient temperature toward neutrality. CP can alternatively be expressed in terms of thermal sensation and comfort survey scale units.Published studies of PCS are reviewed to extract their CP values. Cooling CP ranges from -1 to -6K, and heating CP from 2K to 10K.  The physical characteristics of the particular PCS systems are not reported in detail here, but are presented as prototypes of what is possible.  Deeper understanding of PCS will require new physiological and psychological information about comfort in local body segments and subsegments, and about spatial and temporal alliesthesia.  These topics present many opportunities for productive future research.

There is great energy-saving potential in reducing variable air volume (VAV) box minimum airflow setpoints to about 10% of maximum.  Typical savings are on the order of 10-30% of total HVAC energy, remarkable for an inexpensive controls setpoint change that properly maintains outside air ventilation. However, there has long been concern whether comfort and room air mixing are maintained under low flows through diffusers, and this concern has prompted VAV minima to be typically set at 20-50% of maximum.RP 1515 evaluated occupants’ thermal comfort and air quality satisfaction in operating buildings under both conventional and reduced minimum VAV flow setpoints, and measured the air diffusion performance index and air change effectiveness for typical diffuser types in the laboratory.  The hypotheses were that lowered flow operation would not significantly reduce comfort or air quality, and that HVAC energy savings would be substantial. The hypotheses were almost entirely confirmed for both warm and cool seasons.  But beyond this, the reduction of excess airflow during low-load periods caused occupants’ cold discomfort in the warm season to be halved, a surprising improvement.  It appears that today’s widespread overcooling of buildings can be corrected without risk of discomfort by lowering conventional VAV minimum flow setpoints.

An office equipped with personal footwarmers was maintained at cooler-than-normal indoor temperatures in the winter, producing great energy savings.  The occupants’ thermal comfort was not affected.  The footwarmers provide individual heating control over a segment of the body that most strongly influences comfort perception when one is cool overall.  If cooler ambient indoor temperatures could be made comfortable, savings in central heating energy would be possible.  During a six-month winter period in Berkeley California, knowledge workers with low-energy footwarmers experienced a lowering of room heating set point from 21.1ºC (70ºF) to 18.9ºC (66ºF). Surveys showed equal thermal comfort in the original ‘higher heating setpoint no-footwarmer’ condition and the ‘lower heating set point plus occupant-controllable footwarmer’ condition.  Heating energy was closely monitored throughout.  It dropped 38% to 75% depending on the setpoint reduction and outdoor conditions. The added plug load energy from the low-energy footwarmers was much less than the central heating energy saved by lowering the heating set point (3-21W vs 500-700W average power per occupant during occupied hours).  A few subjects had ergonomic issues with the particular footwarmers used, so usage was not universal.  Additional foot- and leg-warmer design options would help.

To achieve the radical improvements in building energy efficiency being called for by the State of California, it will be necessary to apply an integrated approach involving new designs, new technologies, new ways of operating buildings, new tools for design, commissioning and monitoring, and new understanding of what comprises a comfortable and productive indoor environment. This project, which is an amendment to CEC Contract 500-08-044, has focused on two space conditioning technologies that were part of the original project and showed significant potential to dramatically improve traditional levels of energy efficiency while also increasing occupant satisfaction and thermal comfort. The amendment allowed us to extend our ongoing research on these two promising technologies: personal comfort systems , and radiant heating and cooling systems.The work done under this project has advanced the understanding of personal comfort systems and radiant heating and cooling systems, and has generated the following findings and recommendations: (1) four field demonstration studies with personal comfort systems technologies showed evidence of reduced zone heating energy use (as much as 46-75 percent for one study) while also dramatically improving occupant comfort under a variety of challenging thermal situations; (2) the personal comfort systems components tested in the four demonstration field studies included foot warming devices, leg warming devices, chairs that provide both heating and cooling, and small desk fans for cooling; (3) the results of the personal comfort systems field studies demonstrated that personal comfort systems have reached a level of performance that supports commercial market introduction; (4) building energy performance data, occupant satisfaction assessments, and valuable lessons learned from two successful and well-performing radiant slab office buildings; (5) development of an online map of buildings using radiant technologies to provide resources to building stakeholders who are interested in their implementation; (6) laboratory experiments comparing zone-level sensible cooling loads between radiant chilled ceiling and overhead air distribution systems confirmed the fundamental differences and implications for cooling load calculation methods; (7) two energy simulation studies showed that the David Brower Center design and heating, ventilating and air conditioning strategy present a viable design option in terms of predicted energy use and thermal comfort over a range of California climates, and demonstrated the potential impact of more accurately specifying furniture and contents (i.e., internal mass) on predicted zone peak cooling loads.