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•A literature review to occupant-centric thermal comfort studies was performed.•Many variables and data-collecting sensors were utilized to support the approach.•Data-driven thermal ...comfort models got a median predicting accuracy of 84%•Occupant-centric thermal comfort control could save 22% energy and improve 29.1% thermal comfort.•Challenges and opportunities in the field were discussed.
Ensuring occupants’ thermal comfort and work performance is one of the primary objectives for building environment conditioning systems. In recent years, there emerged many occupant-orientated technologies aiming to optimize thermal comfort while saving energy. These attempts offered opportunities to move the indoor thermal environment control from the one-fits-all approach toward a new paradigm with occupant-centric merits. A timely review of this emerging field would help to fill the knowledge gap and provide new insights for future research and practice. This study performed a literature review to summarize recent occupant-centric thermal comfort practices following a framework with three themes: sensing, predicting, and controlling. The results show that occupant-centric thermal comfort control has become a hot research topic in recent years. A wide range of variables and data-collecting sensors were utilized to support the concept. Among all the potential variables, occupants’ comfort feedback, skin temperature, and air temperature are the top three popular input features for thermal comfort prediction. Using different machine learning algorithms, data-driven thermal comfort models were reported to have a median predicting accuracy of 84% and some of them can predict thermal comfort at a personal level. Cases implementing occupant-centric thermal comfort control strategy were reported to save air-conditioning energy by 22% and improve thermal comfort by 29.1%. These observations from the literature support the prospects of the new thermal comfort paradigm. Additionally, the challenges and opportunities in this emerging field were discussed.
Advances in heating, ventilation and air conditioning (HVAC) technologies have dramatically improved the indoor thermal environment, but attention should be paid on how this would affect building ...occupants' thermal comfort perception. In this paper, we studied the mutually dependent relationship between indoor climate experience and occupants' comfort expectation. An intriguing experiment was conducted in China where wintertime indoor thermal environments in northern cities (with district heating) are much warmer than in southern region (without district heating). By analyzing the 4411 responses from four college-aged subject groups with different indoor thermal history, two interesting findings emerged. Firstly, people's understandings of thermal comfort change with their indoor thermal experiences. Those permanently live in lower-grade non-neutral thermal environment can achieve similar thermal comfort perception as those who live in long-term comfortable thermal conditions. Secondly, the dynamics of building occupants' thermal comfort adaptation project asymmetric trajectories. It is much quicker for occupants to accept neutral indoor climate than to lower their expectation and adapt to under-conditioned environments. These two phenomena can be well described by the index “demand factor”, which can serve as a reference for future thermal comfort study.
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•This study explores indoor climate experience and thermal comfort expectation.•4411 responses from subject groups with different indoor thermal history were collected.•The results show that people's understandings of thermal comfort are malleable.•The dynamics of building thermal comfort adaptation exhibit asymmetric trajectories.•The index “demand factor” was adopted to describe expectation dynamics.
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.
‘Personal comfort systems’ and thermally active clothing are able to warm and cool individual building occupants by transferring heat directly to and from their body surfaces. Such systems would ...ideally target local body surfaces with high temperature sensitivities. Such sensitivities have not been quantified in detail before. Here we report local thermal sensations and sensitivities for 318 local skin spots distributed over one side of the body, measured on a large number of subjects. Skin temperature changes were induced with a thermal probe 14 mm in diameter, and subjective thermal sensations were surveyed after 10 s. Our neutral base temperature was 31 °C and the spot stimulus was ±5 °C. Cool and warm sensitivities are seen to vary widely by body part. The foot, lower leg and upper chest are much less sensitive than average; in comparison, the cheek, neck back, and seat area are 2–3 times as sensitive to both cooling and warming stimuli. Every body part exhibits stronger sensitivity to cooling (1.3–1.6 times stronger) than to warming. Inter-personal differences and regional variance within body parts were observed to be 2–3 times greater than potential sex differences. These high-density thermal sensitivity maps with appended dataset provide the most comprehensive distributions of cold and warm sensitivity across the human body.
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•Detailed thermal sensitivity maps have been created for the entire body.•Thermal sensitivity varies 3-fold across different body parts.•Human body shows 30–60% stronger cooling sensitivity than warming.•Large interpersonal sensitivity difference (50%) and within-region variance (20%).•Differences between males and females are small.
The personal comfort system (PCS) aims to meet individual thermal comfort demands efficiently to achieve higher thermal comfort satisfaction while reducing air conditioning energy consumption. To ...date, many PCS devices have been developed and evaluated from the perspective of thermal comfort. It will be useful for future PCS development if an approach to quantify the thermal comfort and energy performance of certain PCS devices and their combinations with consideration of user behaviors can be established. This study attempted to fill this gap by integrating thermal comfort experiments, occupancy simulations, usage behavior modeling, and building energy simulation technologies. First, human subject experiments were conducted to quantify the thermal comfort effects of the PCS. Then, the Markov chain model and conditional probability model were employed to describe the room occupancy and PCS usage behaviors. Finally, the extended comfort temperature range and user behavior models were imported into the building energy simulation tool to analyze the energy-saving potential of the PCS. The results show that the use of PCS can significantly improve occupants’ thermal comfort and satisfaction rate under both warm and cool conditions. Using a cooling cushion and desktop fan can lift the upper limit of the comfortable temperature to 29.5 °C while the heated cushion can extend the lower limit to 15 °C. By increasing the air conditioning temperature setpoint by 2 °C in summer and reducing by 2.5 °C the heating temperature setpoint in winter, PCS devices can reduce heating and air conditioning energy consumption by 25%–40% while maintaining occupants’ thermal comfort.
When studying the thermal adaptation of building occupants, understanding the effects of different thermal experiences on adaptation is necessary, particularly for moderate and severe heat exposure. ...However, this area has seen limited research. Further, skin temperature, a common parameter for quantifying thermal sensation, may insufficiently reflect the automatic thermoregulation of the human body. This study investigates the effects of long-term heat exposure on the human body using multiple physiological and subjective indexes. Two heat exposure experiments were conducted on healthy male participants from northern and southern China. Participant responses, including skin temperature, heart rate, heart rate variability, blood volume pulse (BVP), subjective thermal comfort, thermal sensation, thermal acceptability, and normalized high and low frequency values were collected and compared. The results indicated that the subjective responses of northern and southern participants were not significantly different; however, the subjective physiological symptoms and self-reported discomfort of the latter were less than those of the former, indicating that the southern participants had superior heat tolerance. Additionally, the physiological responses of all the participants were largely similar. However, southern participants showed slightly higher normalized high frequency and BVP values, indicating that they have more active vagus nerves and better vasodilation. They also showed a wider acceptable temperature range and better acclimation to heat exposure. Notably, the mean skin temperature could not effectively predict thermal sensation during heat exposure; this was more accurately achieved using the rate of change of skin temperature. These findings suggest that long-term thermal experiences can affect building occupants’ thermal adaptability.
Older people are very likely to experience transitions among spaces with different temperatures in daily life. But little has been known about their thermal comfort and physiological responses to ...these temperature steps. This study investigated 18 healthy older people's thermal perceptions and physiological parameters under cold and warm exposures with 3/5/6 °C temperature steps. The results showed that subjects' thermal sensation was sensitive to all moderate temperature steps, but their thermal comfort perception could only distinguish temperature changes greater than 5 °C. Thermal unacceptability was only observed when subjects' tympanic temperature reached at 37.08 °C. Also, we found older people need more than 50 min time to get their mean skin temperature steady after cold stimuli, while they only need <24 min after warm ones. Cold stimuli could significantly boost subjects' blood pressure, respiratory rate, blood oxygen saturation, and depress heart rate. To predict older people's transient thermal sensation after temperature steps, we proposed two regression models for cold and warm exposures respectively. Based on the above observations, we suggest older people should try their best to avoid large step temperature changes, especially for cold side steps.
•The effects of four temperature steps on older people’s thermal perceptions and physiological parameters were tested.•Overshooting phenomenon on thermal sensation was not observed in this study.•Two regression models were proposed to predict older people’s cold or warm thermal sensation after a temperature step.•A cold temperature step can markedly affect older people’s cardiovascular system and respiratory system.
•An experiment for metabolic rate measurement by CO2 variation in an airtight chamber have been carried out, and it has been confirmed to be feasible and accurate approach.•The laws of metabolic rate ...changes at different exercise intensity have been observed, and the time lengths required to get to steady conditions both in exercise state and after exercise have been found.•The effects of metabolic rate variation on human thermal sensation and thermal comfort have been described.
The human metabolic rate is probably the most fundamental but least accurately assessed parameter in thermal comfort research and practice. This study aims to test the dynamic changes of the metabolic rate and its effects on thermal comfort perception. An airtight chamber (2 × 2 × 2 m3) was utilized to measure subjects’ accumulated CO2 production, and metabolic values then were calculated based on indirect calorimetry theory. During the test, 31 subjects were first asked to ride a spinning bike for 8 min at different intensities, and then asked to remain sitting for 22 min. The results showed how the human metabolic rate changed during different exercise periods. It took the human body 5–6 min to reach a new exercising metabolic level while the human body needed 7–9 min to recover from exercise to a normal sedentary state. The dramatic changes in metabolic rate markedly influenced subjects’ thermal sensation and thermal comfort perception. These findings provide a general principle of metabolic rate changes and could serve as a reference for future thermal comfort research.
•We examine whether personal control can influence human thermal comfort.•Occupants with personal control had lower neutral temperature.•Occupants should be offered opportunities to interact with ...thermal environment.
Due to the impetus of climate change and the consequential need to conserve energy, the adaptive comfort model has gradually become a popular focus of thermal comfort research, representing one of the most sweeping changes across the field in the past few decades. However, the mechanism behind the adaptive model, especially with regard to certain key hypotheses, still requires further clarification. To offer more solid support for the hypothesis that people with greater personal control tend to accept wider ranges of indoor thermal environments, we designed an investigational study in which occupants in residential apartments had different degrees of personal control over their space heating systems. Through statistical analysis of the thermal responses of each group, considerable differences in thermal comfort were observed, although occupants in the experimental groups experienced quite similar comfort-related thermal parameters. The results show that occupants with personal control had 2.6°C lower neutral Top and expressed lower expectation to change their current thermal conditions than those without the capability of personal control. These findings provide support for the adaptive model and can serve as a valuable reference for the design of more efficient space heating systems.
Abstract
Thermal desalination evaporation of high-salt wastewater has been widely used in industry because of the proposed concept of ‘zero liquid discharge’. However, due to the high content of Ca2+ ...and Mg2+ in high-salt wastewater, the heat exchanger, as the main treatment equipment, suffers from serious scaling problems. This review presents descaling and scale inhibition technologies of high-salt wastewater. The advantages and disadvantages of various technologies are summarized and analyzed to provide theoretical support for the research of descaling and anti-scaling of heat exchangers with high-salt wastewater. In future industrial development, the synergistic application of electromagnetic water treatment technology and scale inhibitors can significantly improve the anti-scaling effect, which can reach over 95% stably. Furthermore, the addition of a physical field can also expand the application range of scale inhibitors.
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