Learning occupants’ indoor comfort temperature through a Bayesian inference approach for office buildings in United States

A carefully chosen indoor comfort temperature as the thermostat set-point is the key to optimizing building energy use and occupants’ comfort and well-being. ASHRAE Standard 55 or ISO Standard 7730 uses the PMV-PPD model or the adaptive comfort model that is based on small-sized or outdated sample data, which raises questions on whether and how ranges of occupant thermal comfort temperature should be revised using more recent larger-sized dataset. In this paper, a Bayesian inference approach has been used to derive new occupant comfort temperature ranges for U.S. office buildings using the ASHRAE Global Thermal Comfort Database. Bayesian inference can express uncertainty and incorporate prior knowledge. The comfort temperatures were found to be higher and less variable at cooling mode than at heating mode, and with significant overlapped variation ranges between the two modes. The comfort operative temperature of occupants varies between 21.9 and 25.4 °C for the cooling mode with a median of 23.7 °C, and between 20.5 and 24.9 °C for the heating mode with a median of 22.7 °C. These comfort temperature ranges are similar to the current ASHRAE standard 55 in the heating mode but 2–3 °C lower in the cooling mode. The results of this study could be adopted as more realistic thermostat set-points in building design, operation, control optimization, energy performance analysis, and policymaking

How subjective and non-physical parameters affect occupants’ environmental comfort perception

Employees’ wellbeing and comfort perception demonstrated to largely influence their productivity and tolerability of slight thermal discomfort conditions in the working spaces. Their whole comfort perception indeed depends on several parameters related to physical boundary conditions but also to the adaptation capability of occupants themselves and other personal, difficult to measure, variables. According to the available standards and regulations, only physical and measurable environmental parameters must be considered to evaluate occupants’ comfort conditions. Therefore, non-measurable factors such as socio-psychological, physiological, medical ones are currently not systematically considered. The present work aims to identify possible benefits in terms of occupants’ comfort perception due to non-physical strategies aimed at improving the work-environment quality and livability. To this aim, the environmental multi-physics and multi-domain performance of a mixed industry-office building is investigated through coupled in-field microclimate monitoring and questionnaires campaigns. The experimental microclimate monitoring and survey campaign were carried out to understand (i) the realistic indoor environmental conditions in terms of physical and measurable parameters and (ii) the personal perceptions and attitudes of the occupants with respect to those same ambient parameters, including also acoustic, lighting and medical investigation. Moreover, the collected experimental data were used to determine occupants’ comfort level through the classic comfort models, to be compared to the identified role of non-physical parameters on occupants’ final perception about the indoor environment. The main results show that non-measurable factors induced by virtuous company policy to improve employees’ working environment are effectively able to positively influence their whole-comfort perception even if the majority of workers do not have the opportunity to control their working environment. In fact, the consolidated comfort theories underestimate people satisfaction, as demonstrated by more than the 80% employees, who declared to be positively influenced by the pleasant aesthetics and livability of the workplace. The year-round experimental campaign demonstrated the need to further investigate the key role of non-physical parameters for possible incorporation into whole-comfort prediction models and standards. The role of such strategies could therefore be realistically considered as energy saving opportunities since they make building occupants much more open to tolerate slight uncomfortable conditions

Evaluation of Thermal Comfort Inside an Office Equipped with a Fan Coil HVAC System: A CFD Approach

An accurate assessment of thermal comfort inside a building is essential since it is associated to the human\u2019s perception of well-being and comfort. In the present study, a 3D computational fluid dynamic (CFD) code is employed to evaluate the indoor comfort indexes for a university office located in a historical building, built of thick masonry walls and of large single-glass windows, using fan coil as an air conditioning system. The experimental measurement has been carried out to validate the numerical model and to obtain the required initial and boundary conditions. The experimental set-up employs an innovative system for the sensor localization, based on acoustic sources, signal processing and trilateration algorithms. By means of finite volume method, the turbulent air flow, the local heat transfer characteristics and the operative temperature inside the room are obtained for a typical winter day. The results yielded by numerical simulations allow to evaluate thermal comfort condition at working places inside the office and to identify the best comfort areas. The results show that even when the air temperature is quite uniform inside the room, the operative temperature at the positions where occupants are placed is significantly affected by surface temperature of the windows, due to the large window to wall surface ratio and also by the position and operational condition of fan coil. It is concluded that 3D comfort map allows to optimize internal layout of the office room; furthermore, the possibility of thermal comfort optimization in specific workstation together with local control of heating system lead to gain remarkable energy saving results

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

Extending the applicability of the adaptive comfort model to the control of air-conditioning systems

Extensive studies have been done on adaptive thermal comfort for naturally ventilated buildings. However, further studies of the adaptive comfort model are needed to develop a control method for buildings with the air-conditioning systems. This study aims to extend the application of the adaptive comfort model by developing an adaptive comfort control (ACC) for air-conditioning systems. Special attention is given to testing the acceptability of the ACC to the occupants of the office buildings. Two extensive longitudinal field studies were carried out that involved 807 office workers and a total of 13,523 individual comfort votes were collected. This study reveals that it is possible to develop statistically and substantively significant adaptive comfort models for the cooling operation of air-conditioned buildings. This field study provides scientific evidence that the adaptive comfort model can be used to control an air-conditioning system without sacrificing occupants’ thermal comfort. Further field studies on air-conditioned buildings are warranted to quantify the energy use implications of the ACC.Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future Planning (Grant ID: 2014R1A1A2054494)This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.buildenv.2016.05.02

Stress intensity factors for surface cracks in round bar under single and combined loadings

This paper numerically discusses stress in-tensity factor (SIF) calculations for surface cracks in round bars subjected to single and combined loadings. Different crack aspect ratios, a/b, ranging from 0.0 to 1.2 and the relative crack depth, a/D, in the range of 0.1 to 0.6 are considered. Since the torsion loading is non-symmetrical, the whole finite element model has been constructed, and the loadings have been remotely applied to the model. The equivalent SIF, F∗EQ is then used to combine the individual SIF from the bending or tension with torsion loadings. Then, it is compared with the combined SIF, F∗FE obtained numerically using the finite element analysis under similar loadings. It is found that the equivalent SIF method successfully predicts the combined SIF, F∗EQ for Mode I when compared with F∗FE . However, some discrepancies between the results, determined from the two different approaches, occur when FIII is involved. Meanwhile, it is also noted that the F∗FE is higher than the F∗EQ due to the difference in crack face interactions and de-formations

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