Subzone control method of stratum ventilation for thermal comfort improvement

The conventional control method of a collective ventilation (e.g., stratum ventilation) controls the averaged thermal environment in the occupied zone to satisfy the averaged thermal preference of a group of occupants. However, the averaged thermal environment in the occupied zone is not the same as the microclimates of the occupants, because the thermal environment in the occupied zone is not absolutely uniform. Moreover, the averaged thermal preference of the occupants could deviate from the individual thermal preferences, because the occupants could have different individual thermal preferences. This study proposes a subzone control method for stratum ventilation to improve thermal comfort. The proposed method divides the occupied zone into subzones, and controls the microclimates of the subzones to satisfy the thermal preferences of the respective subzones. Experiments in a stratum-ventilated classroom are conducted to model and validate the Predicted Mean Votes (PMVs) of the subzones, with a mean absolute error between 0.05 scale and 0.14 scale. Using the PMV models, the supply air parameters are optimized to minimize the deviation between the PMVs of the subzones and the respective thermal preferences. Case studies show that the proposed method can fulfill the thermal constraints of all subzones for thermal comfort, while the conventional method fails. The proposed method further improves thermal comfort by reducing the deviation of the achieved PMVs of subzones from the preferred ones by 17.6%–41.5% as compared with the conventional method. The proposed method is also promising for other collective ventilations (e.g., mixing ventilation and displacement ventilation)

Thermal Perception in Mild Climate: Adaptive Thermal Models for Schools

A comprehensive assessment of indoor environmental conditions is performed on a representative sample of classrooms in schools across southern Spain (Mediterranean climate) to evaluate the thermal comfort level, thermal perception and preference, and the relationship with HVAC systems, with a comparison of seasons and personal clothing. Almost fifty classrooms were studied and around one thousand pool-surveys distributed among their occupants, aged 12 to 17. These measurements were performed during spring, autumn, and winter, considered the most representative periods of use for schools. A new proposed protocol has been developed for the collection and subsequent analysis of data, applying thermal comfort indicators and using the most frequent predictive models, rational (RTC) and adaptive (ATC), for comparison. Cooling is not provided in any of the rooms and natural ventilation is found in most of the spaces during midseasons. Despite the existence of a general heating service in almost all classrooms in the cold period, the use of mechanical ventilation is limited. Heating did not usually provide standard set-point temperatures. However, this did not lead to widespread complaints, as occupants perceive the thermal environment as neutral—varying greatly between users—and show a preference for slightly colder environments. Comparison of these thermal comfort votes and the thermal comfort indicators used showed a better fit of thermal preference over thermal sensation and more reliable results when using regional ATC indicators than the ASHRAE adaptive model. This highlights the significance of inhabitants’ actual thermal perception. These findings provide useful insight for a more accurate design of this type of building, as well as a suitable tool for the improvement of existing spaces, improving the conditions for both comfort and wellbeing in these spaces, as well as providing a better fit of energy use for actual comfort conditions

Experimental investigation on thermal comfort model between local thermal sensation and overall thermal sensation

To study the human local and overall thermal sensations, a series of experiments under various conditions were carried out in a climate control chamber. The adopted analysis method considered the effect of the weight coefficient of local average skin temperature and density of the cold receptors’ distribution in different local body areas. The results demonstrated that the thermal sensation of head, chest, back and hands is warmer than overall thermal sensation. The mean thermal sensation votes of those local areas were more densely distributed. In addition, the thermal sensation of arms, tight and calf was colder than the overall thermal sensation, which pronounced that thermal sensation votes were more dispersed. The thermal sensation of chest and back had a strong linear correlation with overall thermal sensation. Considering the actual scope of air-conditioning regulation, the human body was classified into three local parts: a) head, b) upper part of body and c) lower part of body. The prediction model of both the three-part thermal sensation and overall thermal sensation was developed. Weight coefficients were 0.21, 0.60 and 0.19 respectively. The model provides scientist basis for guiding the sage installation place of the personal ventilation system to achieve efficient energy use

Evaluating assumptions of scales for subjective assessment of thermal environments – Do laypersons perceive them the way, we researchers believe?

International audienc

Thermal comfort guidelines for production spaces within multi-storey garment factories located in Bangladesh

This research presents extensive field data on indoor thermal conditions along with workers' comfort votes taken at their workstations within three existing multi-storied garment factories during the three seasons (cool-dry, hot-dry and warm-humid) of Bangladesh. The main objective of the study was to observe the impact of thermal conditions on workers’ indoor thermal perception during each season of a year and from this identify thermal comfort guidelines (e.g. neutral temperatures, comfort ranges, preferred airspeeds and directions) to execute their production work comfortably. Subjective votes were collected from a total of 908 workers with the thermal data, physiological data and adaptive measures recorded simultaneously. Statistical analyses revealed that workers can accept a wider and relatively higher comfort range than the predicted band during cool-dry and hot-dry seasons, for instance, 22.7–29.1 °C and 22.3–30.4 °C respectively. A narrower comfort band (e.g. 28.7–30.9 °C), close to the predicted range, was found during the warm-humid season, which can be maintained by reducing radiant temperature and elevating airspeed. Further analyses indicated that workers prefer a mean airspeed of 0.3  m/s and comfort range of 0–3.0  m/s specific to their activities preferably from inlets located on south, north and east facades while upward and downward air movement, from for example ceiling fans, causes a rise of air temperature in the occupational zone and thermal discomfort. This research also suggested that the maximum distances of workstations from the ventilation inlets (windows) should be maintained at 12–18 m for sufficient cross ventilation, personal controls and adaptive opportunities to help maintain preferred thermal condition

Field study on adaptive thermal comfort in typical air conditioned classrooms

This study investigates adaptive thermal comfort in air conditioned classrooms in Hong Kong. A field survey was conducted in several typical classrooms at the City University of Hong Kong. This survey covered objective measurement of thermal environment parameters and subjective human thermal responses. A total of 982 student volunteers participated in the investigation. The results indicate that students in light clothing (0.42 clo) have adapted to the cooler classroom environments. The neutral temperature is very close to the preferred temperature of approximately 24 °C. Based on the MTSV ranging between −0.5 and + 0.5, the comfort range is between 21.56 °C and 26.75 °C. The lower limit is below that of the ASHRAE standard. Of the predicted mean vote (PMV) and the University of California, Berkeley (UCB) model, the UCB model predictions agree better with the mean thermal sensation vote (MTSV). Also, the respective fit regression models of the MTSV versus each of the following: operative temperature (Top), PMV, and UCB were obtained. This study provides a better understanding of acceptable classroom temperatures

Thermal comfort prediction, conditions and air quality for younger and older children in Kuwait schools

The thesis presents the field and laboratory work conducted to investigate the applicability of different thermal comfort indices and equations to assess the thermal sensation of very young children (6-10 years) and older children (11-17 years) in Kuwait classrooms under different ventilation modes (hybrid, natural and air-conditioned), in addition to investigating the quality of the air inside the classrooms. Few thermal comfort and indoor air quality studies have been conducted to determine the thermal comfort and indoor air quality situation inside the classrooms (especially where the young children are presents) in comparison to that for adults in other building environments such as offices or vehicles. The aim of this thesis was to provide baseline data and expand the knowledge for young children s thermal comfort (as well as older children) and the effects of the indoor air quality inside classrooms on them throughout different ventilation modes (hybrid, natural and air-conditioned). The work was achieved by conducting both laboratory and field experiments, as follows: Laboratory tests were conducted to measure the insulation value of the different schoolwear ensembles used in Kuwait classrooms. Three methods were used to indicate and compare the thermal insulation values of different schoolwear ensembles worn by girls and boys in Kuwait classrooms during summer and winter seasons. Results suggest that the clothing insulation values found from the measured and adapted data were similar to the adult s data in standards tables for the same summer and winter seasons ensembles. In addition, the temperature ratings of the clothing are close to, and in agreement with, the scholars comfort temperature. A new thermal comfort questionnaire has been designed for gathering thermal sensation and reflected data from younger children. The questionnaire has been designed employing learning and educational techniques for very young people, and was statistically tested against the standard questionnaire and with old age groups to ensure no bias was introduced. The results show that the new designed thermal comfort questionnaire can help children to assess their sensation in a better manner than that of the standard questionnaire, and that it can be considered as a new subjective assessment tool that can support the thermal comfort standard by investigating the thermal comfort sensations of younger children age groups. A large scale field study was then conducted to investigate the applicability of different thermal comfort indices for Kuwait classrooms along the academic year and under different ventilation modes to assess the thermal sensations for younger (6-10 years) and older (11-17 years) students age group during the school day. The newly designed thermal comfort questionnaire and the clothing insulation values mentioned previously were used to collect the subjects responses for comparison with a range of thermal comfort indices (PMV, ePMV, PMV10 and adaptive, and various comfort equations). Results show that no difference in the neutral temperature between both age groups during the different ventilation modes and the PMV model is the most appropriate model to predict the thermal sensations of the younger subjects during the different ventilation modes, including the natural ventilation mode, since Kuwait classrooms largely considered as air-conditioned spaces. This work provides knowledge of thermal comfort and comfort conditions in Kuwait classrooms. The final part of the field study was conducted to investigate the adequacy of the ventilation rates during naturally and air-conditioned ventilation modes inside 10 elementary classrooms in Kuwait occupied by 6-10 year old children by measuring the CO2 concentration levels inside these classrooms. The findings showed that naturally ventilated classrooms have lower average CO2 concentration levels (708 ppm) than air-conditioned classrooms (1596 ppm). The main reason for the high CO2 concentration in air-conditioned classrooms is attributed to the possibly inappropriate selection of ventilation system type (wall-mounted split units) inside the classrooms. This type of ventilation system cools recirculated room air provides no outside air (fresh air), which is may not be appreciated for high occupancy zones like classrooms. Suitable means for fresh air provision must be made for this mode of operation. Some remedial solutions are theoretically suggested to reduce the high CO2 levels in air-conditioned classrooms which may enhance the students and staffs performance. The latter data on CO2 levels being above recommended values have been communicated to Kuwaiti government

The impact of indoor environment quality (IEQ) on school children's overall comfort in the UK; a regression approach

Indoor Environment Quality (IEQ) is grouped into four main categories: thermal comfort, indoor air quality (IAQ), visual and acoustic comfort. Individual aspects of IEQ are investigated to examine their impact on children's overall comfort in primary schools in the UK. This study has surveyed 805 children in 32 naturally ventilated classrooms during non-heating and heating seasons. This study has calculated the proportion of comfort votes by individual aspects of IEQ, predicted comfort votes by multilinear regression model and estimated the probability of having uncomfortable votes by binary logistic regression. Results of this study highlight that the proportion of uncomfortable votes should be kept below 10%. The developed multilinear model suggests that for a unit change in Air Sensation Votes (ASVs) and operative temperatures (Top), comfort votes change by 0.28 and 0.12, respectively. Developed multilinear and logistic regression models show that ASVs have a more significant impact on overall comfort than Top. To achieve acceptable comfortable votes and keep the probability of having uncomfortable votes below 10%, ASVs and Top should be kept within these limits: [ASV = very fresh and Top = 19–27 °C], [ASV = fresh and Top = 19–24 °C], and [ASV = OK and Top = 19–22 °C]. The ranges suggest that better perception of IAQ makes up for higher temperatures. It is advised to maintain individual aspects of IEQ, however, dissatisfaction with one aspect of IEQ does not necessarily result in overall discomfort unless that aspect is extremely unacceptable. Investigating the most influential factors on occupants’ comfort suggests which building controls should be prioritized for designers