Zhiwei Lian

Effects of thermal discomfort in an office on perceived air quality, SBS symptoms, physiological responses, and human performance

UNLABELLED The effects of thermal discomfort on health and human performance were investigated in an office, in an attempt to elucidate the physiological mechanisms involved. Twelve subjects (six men and six women) performed neurobehavioral tests and tasks typical of office work while thermally neutral (at 22°C) and while warm (at 30°C). Multiple physiological measurements and subjective assessment were made. The results show that when the subjects felt warm, they assessed the air quality to be worse, reported increased intensity of many sick building syndrome symptoms, expressed more negative mood, and were less willing to exert effort. Task performance decreased when the subjects felt warm. Their heart rate, respiratory ventilation, and end-tidal partial pressure of carbon dioxide increased significantly, and their arterial oxygen saturation decreased. Tear film quality was found to be significantly reduced at the higher temperature when they felt warm. No effects were observed on salivary biomarkers (alpha-amylase and cortisol). The present results imply that the negative effects on health and performance that occur when people feel thermally warm at raised temperatures are caused by physiological mechanisms. PRACTICAL IMPLICATIONS This study indicates to what extent elevated temperatures and thermal discomfort because of warmth result in negative effects on health and performance and shows that these could be caused by physiological responses to warmth, not by the distraction of subjective discomfort. This implies that they will occur independently of discomfort, i.e. even if subjects have become adaptively habituated to subjective discomfort. The findings make it possible to estimate the negative economic consequences of reducing energy use in buildings in cases where this results in elevated indoor temperatures. They show clearly that thermal discomfort because of raised temperatures should be avoided in workplaces.

Investigation of gender difference in thermal comfort for Chinese people

Gender difference in thermal comfort for Chinese people was investigated through two laboratory experiments. Both subjective assessment and objective measurement were taken during the experiment. Skin temperature (17 points) and heart rate variability (HRV) were measured in one of the experiment. Our results show that there are gender differences in thermal comfort for Chinese people. Correlation of thermal sensation votes and air temperature and vapor pressure shows that females are more sensitive to temperature and less sensitive to humidity than males. Subjective assessment, skin temperature and HRV analysis suggest that females prefer neutral or slightly warmer condition, due to their constantly lower skin temperature and the fact that mean skin temperature is a good predictor of sensation and discomfort below neutrality. Female comfortable operative temperature (26.3°C) is higher than male comfortable operative temperature (25.3°C), although males and females have almost the same neutral temperature and that there is no gender difference in thermal sensation near neutral conditions.

Experimental study on physiological responses and thermal comfort under various ambient temperatures.

This study mainly explored the thermal comfort from the perspective of physiology. Three physiological parameters, including skin temperature (local and mean), electrocardiograph (ECG) and electroencephalogram (EEG), were investigated to see how they responded to the ambient temperature and how they were related to the thermal comfort sensation. A total of four ambient temperatures (21 degrees C, 24 degrees C, 26 degrees C and 29 degrees C) were created, while the other thermal conditions including the air velocity (about 0.05+/-0.01 m/s) and the air humidity (about 60+/-5 m/s) were kept as stable as possible throughout the experiments. Twenty healthy students were tested with questionnaire investigation under those thermal environments. The statistical analysis shows that the skin temperature (local and mean), the ratio of LF(norm) to HF(norm) of ECG and the global relative power of the different EEG frequency bands will be sensitive to the ambient temperatures and the thermal sensations of the subjects. It is suggested that the three physiological parameters should be considered all together in the future study of thermal comfort.

Energy consumption analysis on a dedicated outdoor air system with rotary desiccant wheel

Abstract A dedicated outdoor air system (DOAS) with rotary desiccant wheel is the combination of a desiccant dehumidification system and a vapor compression refrigeration system. An energy consumption model of this hybrid DOAS is established for its analysis. Coefficient of performance, COP, is appropriately defined for evaluation on performance of the hybrid DOAS. The results indicate that, compared with a conventional DOAS, energy savings are possible for the suggested DOAS, when solar energy or natural gas is used for regeneration. Ventilation air flow rate, temperature or humidity of outdoor air, as well as regeneration-to-process air ratio, influence the energy consumption and the COP of the hybrid DOAS, greatly.

Experimental Study on Skin Temperature and Thermal Comfort of the Human Body in a Recumbent Posture under Uniform Thermal Environments

Experiments are conducted on human subjects to study the overall and the local thermal sensation and thermal comfort as well as the skin temperature distribution of the body in a recumbent posture under different environmental temperatures (21, 24, 26, and 29°C). Local skin temperatures are measured and 14 methods for the mean skin temperature overall are investigated. Statistical analysis showed that the Burton (3 points) method wiu obtain similar results for mean skin temperature compared with the other methods, e.g., Colin/Houdas (10 points), Hardy/DuBois (12 points), Stolwijk/Hardy (unweighted 10 points), and Mitchell/ Wyndham (unweighted 15 points), and is employed in this study due to its simplicity and convenience. Meanwhile, the relationship between skin temperature and thermal comfort and sensation is investigated and overall/local thermal sensation models based on the skin temperature are established according to the experimental data in this study.

Experimental study on a bedside personalized ventilation system for improving sleep comfort and quality

A bedside personalized ventilation (PV) system was investigated by experiments on human subjects including children, adults and elderly. Short-term exposure experiment was first carried out to find out the subjects’ perception of air movement and temperature and the effect on falling asleep. Through the comparative analysis of subjective questionnaires returned from participants and objective physiological tests in all-night sleep experiments, the influence of this system on sleep comfort and quality was obtained as well as the optimal system operation parameters. For conditions with bedside PV system, the returned questionnaires from participants reflected the thermal comfort level and subjective sleep quality were relatively higher than condition without the PV system. Physiological tests results like heart rate and heart rate variability also indicated that a calmer and more comfortable sleep could be obtained with this system. Bedside, PV system could provide a more obvious positive impact on children than adults in sleep quality, and the impact on elderly subjects was not significant. Optimal conditions for improving sleep comfort and quality are to keep the room ambient temperature at 22℃, PV outlet air temperature at 21℃ and air velocity of breathing zone at 0.1 m/s. Through this study, potential applications of bedside PV system could benefit human sleep comfort and quality, particularly in summer which could also be of benefit to hospital care of patients.

Thermal effects on human performance in office environment measured by integrating task speed and accuracy.

We have proposed a method in which the speed and accuracy can be integrated into one metric of human performance. This was achieved by designing a performance task in which the subjects receive feedback on their performance by informing them whether they have committed errors, and if did, they can only proceed when the errors are corrected. Traditionally, the tasks are presented without giving this feedback and thus the speed and accuracy are treated separately. The method was examined in a subjective experiment with thermal environment as the prototypical example. During exposure in an office, 12 subjects performed tasks under two thermal conditions (neutral & warm) repeatedly. The tasks were presented with and without feedback on errors committed, as outlined above. The results indicate that there was a greater decrease in task performance due to thermal discomfort when feedback was given, compared to the performance of tasks presented without feedback.

Investigation of sleep quality under different temperatures based on subjective and physiological measurements

This study investigated sleep quality at different indoor temperatures (17°C, 20°C, and 23°C [62.6°F, 68.0°F, and 73.4°F]) via subjective and physiological methods by evaluating the thermal comfort and sleep quality before and after sleep. Electroencephalograms were also obtained, and skin temperatures were measured throughout the entire sleep cycle. The quantitative powers of each electroencephalogram frequency rhythm were calculated, and the duration of every sleep stage was determined. Both results show that the ambient temperature has a significant effect on sleep quality. The subjective results show that 20°C (68.0°F) was the most comfortable temperature for the waking state and 23°C (73.4°F) was the most satisfactory temperature for sleeping. The objective results show that at 23°C (73.4°F), the relative power of the sleep δ band was the highest, the duration of sleep onset latency was the shortest, and the slow-wave sleep was the longest. All these results were highly consistent, indicating that sleep quality was highest at 23°C (73.4°F). The higher thermal comfort temperature in sleep compared with that in the waking time may be due to the lower mean skin temperature during sleep.

Investigation of Gender Differences in Sleeping Comfort at Different Environmental Temperatures

The purpose of this investigation was to determine whether there is gender difference in sleep comfort of healthy individuals at various temperatures. During winter, sleep quality was examined under different indoor temperatures (17, 20 and 23°C) using questionnaires and electroencephalogram (EEG). To explore the mechanism responsible for gender differences in comfortable sleeping temperatures, mean skin temperature, finger temperature and finger blood flow were measured. The results showed that females would prefer a higher ambient temperature during sleep than the men. The mean skin temperature for females was higher than that of males, whereas finger skin temperature and finger blood flow were significantly lower in females than in males. Furthermore, skin temperature and finger blood flow were more sensitive to ambient temperature with females than in males. The gender differences in preferred sleeping temperature could therefore be related to these physiological characteristics. Both subjective evaluations and EEG found better sleep quality in males under the same temperatures compared to females. Skin temperature changes over the course of the night also demonstrated longer periods of deep sleep in males compared to females.

The effect of indoor plants on human comfort

There is growing evidence to support the notion that plants can play an important role in providing a higher quality living environment. This study conducted a series of experiments to investigate the effects of characteristics, such as colour, odour and size of plants on human comfort, which was evaluated by a satisfaction survey and physiological measurements. Different kinds of plants with different levels of colour (green, tint and multicolour), odour (no odour, slight scent and strong scent) and size (small, medium and large) were chosen for the experiment design. A survey of participants’ satisfaction degree as well as measurements from electroencephalogram (EEG), electrocardiogram (ECG), oxyhaemoglobin saturation, fingertip blood flow, skin resistance and respiration rate were utilized to illustrate the response of participants to the environments either with different plants or without plants. The results demonstrated that an interior office with plants was preferred over an office without plants. The environments with green, slightly scented and small plants were reported as the most favourite conditions. The EEG and oxyhaemoglobin saturation showed significant changes when plant conditions varied. These outcomes provided design strategies for incorporating the plants into the interior office spaces and also provided the physiological variables to evaluate human comfort in the outside environment.