With the improvement of people’s living standard, the requirements of indoor air environment are also increased correspondingly. Trombe wall can not only improve the natural ventilation of buildings ...but also play an important role in cooling and heat storage of indoor temperature. The study of air flow velocity in Trombe Wall is critical for the improvement of Trombe wall performance. In this study, the regular patterns of air velocity is derived and analyzed by combining mathematics and simulation. And the changing rules of air velocity under different conditions are obtained. These research results can provide reliable basis and good reference for Trombe wall design and natural ventilation analysis.
•Trombe wall should be the same width as the boundary line.•The air velocity can be controlled by changing of the wall height.•The air velocity also increases with the increase of temperature difference.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Relative humidity could be a predominant parameter for thermal comfort. The existing ventilation performance index regarding thermal comfort, i.e., the Effective Draft Temperature (EDT), does not ...account for the effect of relative humidity on thermal comfort. This study proposes a novel ventilation performance index, i.e., the Effective Moisture Temperature (EMT), to account for the effects of air temperature and relative humidity on thermal comfort. The proposed EMT is defined as an analogy of the EDT and is quantified by the theoretical analysis of the thermal neutrality, boundaries of thermal comfort zone, and equivalent transfer between the relative humidity and air temperature. The proposed EMT is tabulated for practical convenience under cooling and heating scenarios with different thermal comfort requirements. The results based on Monte Carlo simulations and ASHRAE Global Thermal Comfort Database II show that for the low air movement conditions, the accuracy of the original EDT is 23.8%–88.0%, while the accuracy of the proposed EMT is 98.6%–99.5%. This study further develops the Effective Draft and Moisture Temperature (EDMT) for elevated air movement by integrating the EMT and the cooling effect of air movement. For the elevated air movement conditions, the accuracy of the extended EDT is 84.1%–95.5%, while the accuracy of the proposed EDMT is 96.7%–99.2%. The proposed EMT and EDMT contribute to developing thermally comfortable built environments.
•EMT considers effects of air temperature and relative humidity on thermal comfort.•EMT is tabulated for cooling/heating with different thermal comfort requirements.•EDMT is developed from EMT for elevated air movement.•EMT largely improves thermal comfort evaluation with accuracy of 98.6%–99.5%.•EDMT largely improves thermal comfort evaluation with accuracy of 96.7%–99.2%.
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The cooling effect of air movement is widely recognized as an energy-efficient measure for thermal environment management under the cooling mode, but it is generally neglected under the heating mode. ...This study proposes that the cooling effect of air movement negatively impacts the energy efficiency of advanced air distribution and should be considered when modulating advanced air distribution under the heating mode. Advanced air distribution like stratum ventilation and wall attachment ventilation supplies warm and clean air into the occupied zone by employing supply air momentum to suppress thermal buoyancy. However, the supply air momentum elevates the air movement in the occupied zone and the cooling effect of air movement negatively impacts the energy efficiency of advanced air distribution under the heating mode. Based on numerical simulations validated by the experiments, the results show the cooling effect of air movement significantly impacts the optimal operation, particularly the optimal supply airflow rate of stratum ventilation and the optimal supply air temperature of wall attachment ventilation. Accounting for the cooling effect of air movement can improve the optimal overall performance of advanced air distribution, particularly when the preference for energy efficiency increases. Compared with the optimization ignoring the cooling effect of air movement, the optimization considering the cooling effect of air movement improves the overall performance by up to 38.7% for stratum ventilation and up to 67.6% for wall attachment ventilation. Therefore, the cooling effect of air movement should be considered for modulating advanced air distribution under the heating mode.
•CE (Cooling effect) of air movement negatively impacts energy efficiency under heating mode.•CE of air movement significantly impacts optimal supply airflow rate of stratum ventilation.•CE of air movement significantly impacts optimal supply air temperature of wall attachment ventilation.•Optimization considering CE of air movement improves overall performance by up to 38.7% for stratum ventilation.•Optimization considering CE of air movement improves overall performance by up to 67.6% for wall attachment ventilation.
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This study managed to create thermal comfort conditions at three temperatures (24°C‐T24, 26°C‐T26, and 28°C‐T28) by adjusting clothing and air velocity. Thirty‐six subjects (18 males and 18 females) ...were exposed to each of the three conditions for 4.5 h in a design balanced for order of presentation of conditions. During each exposure, they rated the physical environment, their comfort, the intensity of acute subclinical health symptoms, and their mental load, and they performed a number of cognitive tasks. Their physiological reactions were monitored. The subjects rated T24 to be comfortably cool, T26 to be comfortably neutral, and T28 to be comfortably warm. Their self‐estimated performance did not differ between conditions but 12 of 14 objective metrics of cognitive performance decreased significantly at the elevated temperatures: compared with T24, their average cognitive performance decreased by 10% at T26 and by 6% at T28. At the elevated temperatures, their parasympathetic nervous system activity (as indicated by PNN50) and their arterial blood oxygen saturation level (SpO2) were both lower, which would be expected to result in reduced cognitive performance. The subjects also rated their acute subclinical health symptoms as more intense and their workload as higher at the elevated temperatures. These results suggest that where cognitive performance is the priority, it is wise to ensure a comfortably cool environment. The present study also supports the use of fans or natural ventilation to reduce the need for mechanical cooling.
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DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
15.
Evolving opportunities for providing thermal comfort Brager, Gail; Zhang, Hui; Arens, Edward
Building research and information : the international journal of research, development and demonstration,
05/2015, Volume:
43, Issue:
3
Journal Article
Peer reviewed
Open access
The building industry needs a fundamental paradigm shift in its notion of comfort, to find low-energy ways of creating more thermally dynamic and non-uniform environments that bring inhabitants ...pleasure. Strategies for providing enriched thermal environments must be conjoined with reducing energy; these are inseparable for any building striving for high performance. The objective of current comfort standards is to have no more than 20% of occupants dissatisfied, yet buildings are not reaching even that scant goal. A significant energy cost is incurred by the current practice of controlling buildings within a narrow range of temperatures (often over-cooling in the summer). If building designers and operators can find efficient ways to allow building temperatures to float over a wider range, while affording occupants individual control of comfort, the potential for energy savings is enormous. Five new ways of thinking, or paradigm shifts, are presented for designing or operating buildings to provide enhanced thermal experiences. They are supported by examples of research conducted by the Center for the Built Environment, and include shifts from centralized to personal control, from still to breezy air movement, from thermal neutrality to delight, from active to passive design, and from system disengagement to improved feedback loops.
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BFBNIB, IZUM, KILJ, NUK, PILJ, SAZU, UL, UM, UPUK
The cooling effect of air movement significantly affects the energy-efficient provision of thermal comfort with advanced air distribution. Existing studies merely focus on the cooling effect of air ...movement under cooling mode. However, the cooling effect of air movement under heating mode can be different from that under cooling mode. This is because the cooling effect of air movement negatively and positively affects thermal comfort under heating and cooling modes respectively. This study experimentally investigates the cooling effect of air movement of stratum ventilation under heating mode. Stratum ventilation is representative of advanced air distribution with significant air movement for a proper airflow pattern under heating mode. A wide range of thermal conditions are tested with the air temperature of 19 °C–25 °C and air velocity of 0.1 m/s – 1.2 m/s. The thermal sensation votes and percentages of dissatisfied are simultaneously surveyed. Based on the experimental data, the cooling effect of air movement under heating mode is quantified, which is higher and lower than that under cooling mode in the cool and warm thermal environments respectively. Moreover, based on the upper and lower boundaries determined according to the percentage of dissatisfied of 10% predicted by an optimized model, the thermal comfort zone is prescribed under heating mode. For the thermal comfort zone, the cooling effect of air movement is compensated by the enhanced air temperature. This study contributes to improving the heating performances of advanced air distribution with the cooling effect of air movement.
•CEAM under heating mode is different from that under cooling mode.•CEAM is significantly affected by both air velocity and thermal sensation.•Minimal PPD is reduced to 1.5%.•Lower thermal comfort boundary is extended to air temperature of 17.5 °C.
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As an energy-efficient and high-comfort indoor environment control method, the rational application of airflow in modern buildings has brought renewed attention, especially in hot and humid areas. ...Chamber experiments were conducted to examine occupants’ preferred air speed and its effects on thermal comfort in hot-humid climate, and the extended thermal comfort zone limit was obtained. Three temperature levels (26 °C, 29 °C, and 32 °C) and two relative humidity levels (40%–60% and 70%–90%) were set, achieving six experimental conditions. During each condition, thirty-six participants were sequentially exposed to two stages with still air and personal controlled stable mechanical airflow produced by electric fans, each lasting 30 min. Their subjective perceptions were collected repeatedly, and skin temperature was measured continuously. For the six conditions, the average preferred air speeds were estimated to be 0.53 m/s, 0.62 m/s, 1.06 m/s, 1.31 m/s, 1.28 m/s, and 1.48 m/s respectively. The preferred air speed at high humidity (70%–90%) was approximately 0.15 m/s-0.3 m/s higher than that at moderate humidity (40%–60%), and such difference increased with air temperature. Elevated air speeds may be used to offset thermal discomfort, as indicated by a 0.2°C–0.5 °C significant decrease in the mean skin temperature and improvements in subjective perceptions. However, for extremely hot and humid conditions including 29 °C/85%, 32 °C/55%, and 32 °C/85%, the discomfort cannot be completely eliminated. When local control of airflow is provided to occupants, the acceptable operative temperature range could be extended by approximately 1 °C regardless of humidity, compared with that under near still air speed below 0.1 m/s.
•The preferred air speeds in hot-humid climate up to 32 °C and 85% were determined.•Quantitative effects of self-controlled airflow on thermal comfort were examined.•Preferred air speed at high humidity was 0.15 m/s-0.3 m/s above that at moderate.•The upper acceptable temperature could be increased by 1 °C under preferred airflow.•Preferred airflow has a limit to offset thermal discomfort in hot-humid climate.
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•Quantified relations between mechanical airflow and thermal comfort were studied.•The upper limit of air speeds that did not cause draught feelings were examined.•Mean skin temperatures decreased ...0.2 °C-0.6 °C for increasing the air speed by 1 m/s.•Cooling effect of mechanical airflow was restricted under humidity up to 85%.•Acceptable operative temperature range in 40%-60% humidity was extended by 1.3 °C.
Indoor air movement is beneficial for building energy conservation and human thermal comfort. Chamber experiments were conducted to evaluate the cooling effect of elevated air speeds on thermal comfort. Three temperature (26, 29, and 32 °C) and two relative humidity (40%–60% and 70%–90%) levels were selected for a total of six experimental conditions. Thirty-six subjects in summer clothes (0.5 clo) were exposed to mechanical airflow produced by electric fans and experienced four 30-min exposures at various air speeds (0.01–2.0 m/s), and subjective perceptions and skin temperature were collected. Results showed that mean skin temperatures decreased by 0.2 °C–0.6 °C for every 1 m/s increase in air speed. Airflow may alleviate thermal dissatisfaction, but air speeds up to 2.0 m/s cannot eliminate discomfort in extremely hot-humid environments (29 °C/85%, 32 °C/55%, and 32 °C/85%). In the experimental conditions of 26 °C/45%, 26 °C/75%, 29 °C/55%, 32 °C/55%, and 32 °C/85%, the upper air speed limits were 1.2, 1.2, 1.6, 2.0, and 2.0 m/s, respectively. Based on experimental data, comfort zones with elevated air speed for both moderate (40%–60%) and high humidity (70%–90%) were obtained. The maximum acceptable operative temperatures in two humidity conditions were 31.3 and 28.6 °C, extending the ASHRAE 55 values by 1.3 and 0.1 °C, respectively.
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Subjects were tested under a set of air speed setpoints as might be used in automated control of ceiling fans. At lower temperatures the fan speeds were slightly higher than needed for thermal ...neutrality, to account for occasional non-sedentary metabolic rates associated with getting up, standing, or moving about. At higher temperatures the air speed supplied was conservative, to minimize mechanical wind disruption, while allowing thermal sensations above neutral.
Twenty-three subjects in summer clothing experienced a matrix of four temperatures (24 °C, 26 °C, 28 °C and 30 °C), two levels of humidity (RH 40% and 60%), and two metabolic rate (1.0, 1.4 met). Each test condition was 2 h in length, made up of four 30-min sessions following the same pattern: sedentary without fan; sedentary under a fixed fan speed chosen by experimenters to be appropriate for the temperature; exercising at 1.4 met under personally adjusted fan speed; and sedentary under personally adjusted fan speed. Throughout, the subjects rated their thermal sensation, thermal comfort, perceived air quality, and air-movement acceptability and preference.
The air speeds personally chosen by test subjects in the 24 °C and 26 °C conditions differed little from the experiment's fixed air speeds. Subjects chose significantly greater air speeds in the 28 °C and 30 °C conditions. The elevated 1.4 metabolic rate slightly increased subjects' thermal sensation, but caused no significant difference in the air speeds they chose for sedentary activity. Personal control over air movement had no significant effect on comfort in the conditions tested.
•A range of air movement improves thermal comfort and PAQ in warm environments.•A single set of air speeds can provide comfort for both 1.0 and 1.4 met levels.•Availability of air movement is more important than providing control over it in warm temperatures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Providing an appropriate thermal comfort level is crucial for the technical feasibility of stratum ventilation at elevated room temperatures. This paper presents a subjective study of thermal comfort ...in a stratum-ventilated environmental chamber. Overall thermal sensation (OTS), local thermal sensation (LTS) of body segments, overall thermal comfort (OTC) and draft were investigated. The objectives of this study were twofold: to evaluate the effect of room temperature on thermal comfort (Test Series 1) and to assess the effect of supply airflow rate and supply air temperature on thermal comfort (Test Series 2). Test Series 1 revealed that the room temperature had a great impact on the OTS, LTS, OTC and draft. Under 10 air change per hour (ACH), a room temperature of 27 °C provided neutral OTS, satisfactory OTC and low draft risk. However, at room temperatures of 24 and 29 °C, the percentages of subjects feeling comfortable were obviously less than 80%. Test Series 2 showed that at the room temperature of 27 °C, increasing the supply airflow rate from 7 ACH to 17 ACH only exhibited a small influence on the thermal sensation and draft, indicating a preference for air movement. More than 80% subjects felt comfortable at 27 °C. However, to minimize draft complaints, the supply air temperature should not be below 20 °C. These results show that stratum ventilation provides a thermally comfortable environment, so that people can have the feeling of “cool head and warm feet”, with low draft risk at a room temperature up to 27 °C.
•Room temperature, supply air temperature and flow rate affected thermal comfort.•Room temperature had a great impact on thermal comfort.•Supply airflow rate had little influence on comfort at a room temperature of 27 °C.•More than 80% subjects felt comfortable at the neutral temperature of 27 °C.•Supply air temperature should not be below 20 °C to minimize draft risk.
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