Comfort In Non-uniform Environments Research Articles

Calculating the local and overall view factors of a multi-segment human model

In non-uniform environments, such as spaces with radiant ceilings or floors, or with hot or cold windows, view factors (VFs) of a person towards these surfaces are needed for calculating the heat exchanges between the person and the surroundings. Multi-body segmented human models can simulate the heat exchanges of individual body parts with the environment. Simulating heat transfer at the local body parts is important for assessing comfort in non-uniform environments. These models require VFs for each individual body part. Accurately determining these VFs is time-consuming, often requiring methods such as ray-tracing techniques. A fast calculation method to accurately determine the view factor (VF) for each segment has yet to be investigated. This study employed a 16-segment human model into various architectural radiation scenarios. The surface-to-surface model in computational fluid dynamics was utilized to simulate VFs for the 16 body segments in relation to radiant surfaces at different locations. Through a series of simulations, comprehensive formulas for VFs were derived for each individual at various positions within a room, encompassing 16 body segments and computing parameters for 24 building surfaces. The accuracy of these general formulas was validated by comparing the whole-body VF with results from several available studies. Additionally, this study developed a visualization tool for calculating VF and mean radiant temperatures with different room space dimension and embedded radiant surfaces. The users can use this online tool to easily calculate VFs and mean radiant temperatures for each body parts, and for the whole-body. The tool offers valuable insights for predicting thermal comfort in asymmetric radiant environments and facilitating control over building environments.

Physiological responses and data-driven thermal comfort models with personal conditioning devices (PCD)

Thermal comfort in uniform environments created by HVAC systems have been investigated for decades. However, the case in nonuniform microenvironments created by the personal conditioning device (PCD) is different because of the local thermal stimuli on occupants. This study used PCD to provide localized cooling for users based on their individual thermal preferences. We collected PCD users' wrist temperatures and heart rate variabilities (HRV), as well as thermal sensation/comfort questionnaires. Because of the nonuniform thermal stimuli, the physiological responses triggered by the PCD show unclear patterns, which are incompatible with traditional thermal comfort models developed for the uniform environment. Therefore, we utilized machine learning methods to model PCD users’ thermal comfort. By using SVM with RBF kernel based on multiple HRV indices in addition to wrist temperatures, the F1 score is improved by more than four times when compared to the model only based on wrist temperatures. This indicates the importance of HRV as physiological indices for the thermal comfort with nonuniform thermal stimuli. The best performances of our models are higher than 0.90 for both thermal sensation and comfort, which can provide a reliable solution in predicting the thermal sensation and comfort in nonuniform environments with the PCD.

The correlation between the overall thermal comfort, the overall thermal sensation and the local thermal comfort in non-uniform environments with local cooling

The evaluation of overall thermal comfort in non-uniform thermal environments has not been fully clarified; it was therefore studied in this paper. For this aim, a series of experiments were conducted under non-uniform thermal environments with local cooling, where subjects’ thermal responses were surveyed by questionnaires. The correlations between the overall thermal comfort, the overall thermal sensation and the local thermal comfort were explored under both steady and unsteady states. As well, the relationship between the overall thermal comfort and the local thermal comfort was examined under steady-state conditions. The results indicated that the overall thermal comfort was dependent on the overall thermal sensation and also on the local thermal comfort at the body parts exposed to local cooling, whether in steady or transient states. Considering the two factors, the overall thermal comfort models were proposed for steady and unsteady states. Also, the overall thermal comfort was approximated by the average of the maximum and minimum local thermal comfort under steady states. Another overall thermal comfort model was therefore proposed. The two overall thermal comfort models for the steady state were verified by experimental results.

Human thermal sensation and comfort in a non-uniform environment with personalized heating

BackgroundThermal comfort in traditionally uniform environment is apparent and can be improved by increasing energy expenses. To save energy, non-uniform environment implemented by personalized conditioning system attracts considerable attention, but human response in such environment is unclear. ObjectivesTo investigate regional- and whole-body thermal sensation and comfort in a cool environment with personalized heating. MethodsIn total 36 subjects (17 males and 19 females) including children, adults and the elderly, were involved in our experiment. Each subject was first asked to sit on a seat in an 18°C chamber (uniform environment) for 40min and then sit on a heating seat in a 16°C chamber (non-uniform environment) for another 40min after 10min break. Subjects' regional- and whole-body thermal sensation and comfort were surveyed by questionnaire and their skin temperatures were measured by wireless sensors. We statistically analyzed subjects' thermal sensation and comfort and their skin temperatures in different age and gender groups and compared them between the uniform and non-uniform environments. ResultsOverall thermal sensation and comfort votes were respectively neutral and just comfortable in 16°C chamber with personalized heating, which were significantly higher than those in 18°C chamber without heating (p<0.01). The effect of personalized heating on improving thermal sensation and comfort was consistent in subjects of different age and gender. However, adults and the females were more sensitive to the effect of personalized heating and felt cooler and less comfort than children/elderly and the males respectively. Variations of the regional thermal sensation/comfort across human body were consistent with those of skin temperature. ConclusionsPersonalized heating significantly improved human thermal sensation and comfort in non-uniform cooler environment, probably due to the fact that it increased skin temperature. However, the link between thermal sensation/comfort and variations of skin temperature is rather complex and warrant further investigation.

Investigation on temperature range for thermal comfort in nonuniform environment

This study uses the previously adopted local ventilation air-conditioning mode to study the effect of temperature on thermal comfort for subjects. Three room temperatures (26, 28, 30°C (78.8, 82.4, 86°F)) and three local ventilation temperatures (20, 26, 28°C (68, 78.8, 82.4°F)) were used for the study. The air velocity was purposely set low for the local ventilation tests, in order to focus on the temperature combinations between the ambient and local air temperature from the local ventilation device. Eighteen subjects participated in the experiment, using the within-subjects design method. During exposure in the room, the subjects reported thermal sensation and thermal comfort accompanied by the skin temperature measurement of the subjects. The room temperature of 28°C (82.4°F) combined with the local ventilation temperature of 26°C (78.8°F) (28°Crt and 26°Clv (82.4°Frt and 78.8°Flv)) was assessed to be the most comfortable environment. Through the experiments, the neutral room temperature of 26°C (78.8°F) combined with the local ventilation temperature of 20°C (68°F) as well as the warm room temperature of 30°C (86°F) combined with 26°C (78.8°F) was found to be within the comfortable range. The results imply that compared with the traditional air conditioning mode, which creates a uniform comfortable environment by setting the air temperature to be 26°C (78.8°F), the adoption of local ventilation could improve the thermal comfort while consuming less energy.

Thermal comfort, skin temperature distribution, and sensible heat loss distribution in the sitting posture in various asymmetric radiant fields

This study aimed at investigating the thermal comfort for the whole body as well as for certain local areas, skin temperatures, and sensible heat losses in various asymmetric radiant fields. Human subject experiments were conducted to assess the overall comfort sensation and local discomfort, and local skin temperatures were measured. Through thermal manikin experiments, we discovered a new method for the precise measurement of the local sensible heat loss in nonuniform thermal environments. The local sensible heat losses were measured by the use of a thermal manikin that had the same local skin temperatures as the human subjects. The experimental conditions consisted of the anterior–posterior, right–left, and up–down asymmetric thermal environments created by radiation panels. A total of 35 thermal environmental conditions were created ranging from 25.5 to 30.5 °C for air temperature, from 11.5 to 44.5 °C for surface temperature of radiation panels, from 40% RH to 50% RH for humidity, and less than 0.05 m/s for inlet air velocity to the climatic chamber. The local skin temperature changed depending on the environmental thermal nonuniformity, even if the mean skin temperature remained almost the same. It is essential to use the skin temperature distribution as well as mean skin temperature for expressing thermal comfort in nonuniform environments. The local sensible heat loss changed depending on the environmental thermal nonuniformity, even if the mean sensible heat loss remained almost the same. The relationship between the local skin temperature and local sensible heat loss cannot be depicted by a simple line; instead, it varies depending on the environmental thermal nonuniformity. The local heat discomfort in the head area was dependent on both the local skin temperature and local sensible heat loss. However, the local cold discomfort in the foot area was related only to the local skin temperature.