Thermal Comfort Of Occupants Research Articles

An IoT-Based Thermal Model Learning Framework for Smart Buildings

With the development of the Internet of Things (IoT) technologies, implementing intelligent controls in buildings to reduce energy consumption is becoming increasingly popular. Building climate control is of strong research interest due to high energy savings potentials associated with heating, ventilation, and air-conditioning (HVAC) controls. Because the operation of HVAC systems directly influences occupant thermal comfort, building-specific thermal models are needed for proper control. Such models describe how indoor temperature changes under different environmental conditions and HVAC status. Previous studies mainly developed thermal models for accurate building thermal simulation which are not practical for use in real-world applications as they require domain knowledge and lengthy building-by-building configuration. In this article, taking advantage of IoT technologies, a plug-and-play learning framework is proposed to automatically identify the thermal model of each thermal zone in a building without manual configuration. In contrast to the existing methods, a thermal model is learned using low-resolution temperature readings from IoT-based smart thermostats. The learning framework has been validated using the data collected from an IoT platform installed in a building over a summer. The performance of the learned model and the error of indoor temperature prediction based on this model have been evaluated and quantified. Findings demonstrate the learning process can be automated with either edge-computing or cloud-computing. This article shows the validity of the proposed IoT-based thermal model learning framework and offers a pragmatic solution for providing reliable thermal models to future smart building climate controls.

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Standard 55 or ISO Standard 7730 uses the PMV-PPD model or the adaptive comfort model that is based on small-sized or outdated sample data, which raises questions on whether and how ranges of occupant thermal comfort temperature should be revised using more recent larger-sized dataset.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.

The Potential of Smart Glazing for Occupant Well-Being and Reduced Energy Load in a Central-Mediterranean Climate

The ever-increasing aesthetically driven demand for fully glazed façades poses a design challenge; not least in controlling the cooling demand and occupant well-being of such buildings, especially in a central Mediterranean climate. This paper outlines the ever-important need to design for occupants and for designers to keep in mind, first and foremost, occupant well-being rather than aim solely to create energy-efficient buildings. The original objective of buildings was to provide shelter. Today however, the need for occupant comfort and its direct effect on productivity cannot be ignored. This need, therefore, ought to feature a central role in any building design. Studies show that occupant well-being is directly related to a range of environmental factors, particularly daylight distribution, glare and indoor air temperature. The use of external shading devices and more commonly, indoor blinds are often the adopted approaches to attempt to achieve indoor occupant comfort, often to the detriment of views. Adaptive facades seek to address the need to somehow strike a balance between occupant comfort and energy efficiency. These facades range from exterior and interior shading devices with varying control strategies, to the different forms of adaptive/switchable glazing technologies intended to control the visual light transmittance and solar radiation transmitted into a building’s interior. In the opinion of the authors, electrochromic glazing has a great potential in a cooling-dominated central Mediterranean climate, to achieve a compromise between occupant visual and thermal comfort whilst retaining unobstructed outdoor views at all times. Research shows that the potential benefits of electrochromic glazing have not yet been studied enough in real-life scenarios,and this paper further introduces the objectives for field study within two identical offices, having a South-South-East orientation, located in a central Mediterranean climate.

High-performance building: Sensitivity analysis for simulating different combinations of components of a two-sided windcatcher

Traditional windcatchers with massive structures were used to capture the local wind stream to improve occupant thermal comfort. To obtain smaller configurations with enhanced/similar performance metrics, the individual components of a conventional windcatcher, i.e. inlet opening, divider, outlet, and height are widely studied in the literature. This work aims to (1) use an in-house developed and verified numerical model to explore the impact of combinations of components of a windcatcher on its performance and (2) introduce the implementation of nozzles with different configurations in obtaining a flexible design for an extended range of applications. A 3-dimensional steady-state computational fluid dynamics simulation with a shear-stress-transport k-ω turbulence model is used to explore the flow characteristics. The airflow distribution throughout the system and mass flow rate at the outlet of a reference case, a well-studied two-sided windcatcher design, are validated with published wind tunnel experimental data. The verified model is then used for the following analyses. The results highlight the role of different windcatcher individual components and their combinations on the developed pressure gradients inside the windcatcher. A desired combination of components to improve the aerodynamic performance of the reference case is introduced: the integration of a convergent-divergent nozzle with finned-curved inlet openings along with the longest dividers increase the induced air mass flow rate up to 13%. The maximum flow velocity is increased by 45% at the nozzle throat area for the identified windcatcher configuration. The outcomes of this research can be used by engineers and researchers to enhance building-integrated windcatcher designs.

Comparison of mean radiant and air temperatures in mechanically-conditioned commercial buildings from over 200,000 field and laboratory measurements

We assessed the difference between mean radiant temperature (tr¯) and air temperature (ta) in conditioned office buildings to provide guidance on whether practitioners should separately measure tr¯ or operative temperature to control heating and cooling systems. We used measurements from 48 office buildings in the ASHRAE Global Thermal Comfort Database, five field studies in radiant and all-air buildings, and five test conditions from a laboratory experiment that compared radiant and all-air cooling. The ASHRAE Global Thermal Comfort Database is the largest of these three datasets and most representative of typical thermal conditions in an office; in this dataset the median absolute difference between tr¯ and ta was 0.4 ∘C (with 5th, 25th, 75th, and 95th percentiles = 0.2, 0.2, 0.6, and 1.6 °C). More specifically, the median difference shows that tr¯ was 0.4 ∘C warmer than ta (with 5th, 25th, 75th, and 95th percentiles = −0.4 °C, 0.2 °C, 0.6 °C, and 1.6 °C). The laboratory experiments revealed that in a radiant cooled space tr¯ was significantly (p < 0.05) cooler than ta (average difference −0.1 ∘C), while in the all-air cooled space tr¯ was significantly (p < 0.05) warmer than ta (average difference +0.3 ∘C). These observations indicate that tr¯ and ta are typically closer in radiant cooled spaces than in all-air cooled spaces. Although the differences are significant, the effect sizes are negligible to small based on Cohen's d and Spearman's rho. Therefore, we conclude that measurement of ta is sufficient to estimate tr¯ under typical office conditions, and that separate measurement of tr¯ or operative temperature is not likely to have practical benefits to thermal comfort in most cases – this is especially true for buildings with radiant systems. Furthermore, spatial and temporal variations in ta can be greater than or equal to the difference between tr¯ and ta at any one location in a thermal zone, thus we expect that such variations typically have a greater impact on occupant thermal comfort than the differences between tr¯ and ta.

Retrofitting suspended timber ground-floors; comparing aggregated and disaggregated evaluation methods

ABSTRACT It is estimated that around 80% of UK dwellings have uninsulated ground floors, representing a significant heat loss mechanism in these buildings. In this research, an aggregated assessment of dwelling heat loss was made using the electric coheating test before and after a ground floor retrofit took place. Heat loss was reduced by 24% (43 ± 18 W/K) indicating that suspended timber ground floor retrofits could improve thermal comfort for occupants and contribute to government domestic energy efficiency policy targets. The findings indicate that disaggregated evaluation methods, such as spot heat flux density measurements, may overestimate the benefits of fabric retrofits. Aggregate methods may therefore be more appropriate tools with which to evaluate retrofits. The U-value improvement resulting from the suspended timber ground floor insulation retrofit, derived via aggregate measurement, was 0.55 W/m²K. Disaggregated spot heat flux density measurements indicated the improvement was 0.89 W/m2K. This research also indicates that Energy Performance Certificates, are unlikely to provide a reliable estimate of energy savings, because they rely on default assumptions for fabric U-Values and ventilation rates. This has implications for policy evaluations as well as householders, who may be excluded from financial support for retrofits.

The relation between thermal comfort and human-body exergy consumption in a temperate climate zone

Human body exergy balance calculation method gives minimum human body exergy consumption rates at thermal neutrality (TSV = 0) providing more information on human thermal responses than other methods. The literature is lacking the verification of this method in various climatic zones. The aim of this study is to investigate the relationship between thermal comfort and human body exergy consumption in a temperate climate zone. A small office building in Izmir Institute of Technology campus, Izmir/Turkey, was chosen as a case building and equipped with measurement devices. The occupant was subjected to a survey via a mobile application to obtain his Thermal Sensation Votes. Objective data were collected via sensors and used for predicting occupant thermal comfort and for exergy balance calculations. Under given conditions, the results show that Thermal Sensation Votes are generally zero at a Ti range of 21–23 °C and, are mostly lower than Predicted Mean Votes in summer while the opposite is observed in winter. Predicted Mean Votes at minimum Human Body Exergy Consumption rates were on slightly warm side while Thermal Sensation Votes are zero. It means that for given case, the HBexC rate calculation gave a better prediction of the environmental parameters for the best thermal comfort.

The Cooling Effect of Large-Scale Urban Parks on Surrounding Area Thermal Comfort

This empirical study investigates large urban park cooling effects on the thermal comfort of occupants in the vicinity of the main central park, located in Madrid, Spain. Data were gathered during hot summer days, using mobile observations and a questionnaire. The results showed that the cooling effect of this urban park of 125 ha area at a distance of 150 m could reduce air temperatures by an average of 0.63 °C and 1.28 °C for distances of 380 m and 665 meters from the park. Moreover, the degree of the physiological equivalent temperature (PET) index at a distance of 150 meters from the park is on average 2 °C PET and 2.3 °C PET less compared to distances of 380 m and 665 m, respectively. Considering the distance from the park, the correlation between occupant perceived thermal comfort (PTC) and PET is inverse. That is, augmenting the distance from the park increases PET, while the extent of PTC reduces accordingly. The correlation between these two factors at the nearest and furthest distances from the park is meaningful (p-value &lt; 0.05). The results also showed that large-scale urban parks generally play a significant part in creating a cognitive state of high-perceived thermal comfort spaces for residents.

Patterns of thermal preference and Visual Thermal Landscaping model in the workplace

The main purpose of research on occupant behaviour is to enhance building energy performance. However, it is difficult to reduce the energy use without understanding the occupant, their needs and preferences. Individual differences and preferences for the thermal environment in relation to the spatial context are overlooked in the main stream of research. This study investigates the patterns of occupant thermal preference based on individual differences in perceiving the thermal environment to enhance user comfort and energy performance. A novel method of Visual Thermal Landscaping is used, which is a qualitative method to analyse occupant comfort and user behaviour according to the spatial context. This method drives away from the notion of ‘thermal neutrality’ and generic results, rather it opens to details and meaning through a qualitative analysis of personal-comfort, based on individual differences and spatial context information. Field test studies of thermal comfort were applied in five office buildings in the UK, Sweden and Japan with overall 2313 data sets. The primary contribution of the study was the recognition of four patterns of thermal preference, including consistent directional preference; fluctuating preference; high tolerance and sensitive to thermal changes; and high tolerance and not-sensitive to thermal changes. The results were further examined in a longitudinal field test study of thermal comfort. In several cases, occupant thermal comfort and preferences were observed to be influenced by the impact of outdoor conditions, when the windows were fixed. Practical solutions for research, practice and building design were recommended with direct implications on occupant comfort and energy use.

Evaluation of the thermal comfort for its occupants inside a vehicle during summer

Thermal comfort of occupants from the vehicle environment has gained more importance in the last decades because time spent by people in the vehicles is increasing. During each trip, driver’s thermal comfort must to be ensured to reduce both thermal stress (thus reduces the risk of accidents) and for a healthy state of the occupants. Given the fact that the vehicle environment is non-uniform and fast transient, and because the actual standard (ISO 14505) proposes comfort evaluation methods developed for the steady state conditions in buildings, the purpose of the study is to evaluate a vehicle environment using the three standardised method presented in the above standard. All the three standardized evaluation indices were achieved through standardised methods. The equivalent temperature (teq) index was assessed with an advanced thermal manikin and its values were compared with the survey answers given by people in questionnaires (TSV Thermal Sensation Vote index) and with Predicted Mean Vote (PMV) index values calculated with Comfort Sense standardized evaluation equipment. A first conclusion is that the results of the three evaluation indices are different. Air temperature is different from a zone of the car to another and the thermal evaluation must be done in the place of each passenger.

Development of metabolic rate prediction model using deep learning via Kinect camera in an indoor environment

Currently, there are only a few conventional methods to measure individual factors affecting metabolic rate (MET) based on the thermal comfort of occupants in residential buildings. In this work, a deep learning based MET prediction using a Kinect camera, which is a non-contact sensor, was developed. The root mean squared error (RMSE) and the coefficient of variation (CV) of the RMSE were used as indicators to predict MET accuracy. A total of 31 subjects participated in the experiment (16 men and 15 women). The METs of eight representative activities in the ASHRAE Standard 55 were measured (lying down, sitting, cooking, walking, eating, house cleaning, folding clothes, and handling 50 kg of books). The predicted results for all eight activities were significantly high. (RMSE: 0.26, CV: 13%). Further, METs were analyzed according to the gender and body mass index (BMI). Results of the analysis based on gender reveal that METs of men are higher than those of women. Analysis based on BMI showed that MET increased with higher BMI. However, with respect to sitting and eating food, the higher the BMI, the lower is the MET. This paper suggest that, a creative method was developed herein for predicting MET in an indoor environment with fairly high accuracy. Moreover, the difference in MET considering behavior as a factor was analyzed according to gender and BMI; these results can be used to develop guidelines for more accurate thermal comfort control.

Numerical investigation on the impact of different supply air terminal devices on the performance of the newly combined ventilation and heating system

An increased focus on energy saving has led to a rapid development of energy-efficient buildings. In the residential buildings, space heating, ventilation and air conditioning (HVAC) have the highest energy use. The ventilation system is the main tool to provide acceptable indoor air quality and thermal comfort for occupants. This study presents an investigation of the thermal environment in a room served by new developed, combined ventilation and heating system. The focus is on different configurations of the supply air terminal device in the studied system. The main goal is to investigate the influence of different supply air parameters, which in this study are flowrate and temperature, on the airflow behaviour and performance of the mixing ventilation. In this regards, three different supply air conditions with two inlet configurations were considered. This work has been carried out numerically and validated with the laboratory measurements. Computational Fluid Dynamics (CFD) simulation was applied in this study to map the airflow patterns and air temperature distribution. The results showed that decreasing supply air temperature and increasing the flowrate provided a uniform temperature distribution for both inlet configurations. Inlet configuration investigated in case1 has lower vertical temperature differences in comparison with case 2.

Ventilation mode effect on thermal comfort in a mixed mode building

Between 2017 and 2018, we conducted a longitudinal field experiment in a mixed-mode ventilation building located in Wollongong Australia, with a particular focus on occupant thermal comfort and adaptive behaviour. This study investigated how different building operation modes i.e. air-conditioning (AC) and natural ventilation (NV), can have an impact on occupant perception of thermal comfort. Time-and-place matching of objective (physically measured indoor climate parameters, outdoor meteorological data, and building operational information) and subjective data (i.e. occupant survey questionnaires) enabled empirical investigation of the relationships between those parameters. The result of the analysis revealed that subjective perception of indoor thermal environment can be affected by different modes of building operation. Occupants were found to be more tolerant of, or adaptive to, the indoor thermal conditions when the building was in the NV mode of operation compared to the AC operational mode. The applicability of the adaptive comfort standard to the mixed-mode ventilation context was also discussed.

Evaluation of the occupants’ exposition to the indoor environment.

User behaviour has a significant contribution to the final energy consumption figures of buildings. As indicated in finding from the IEA EBC Annex 66 project, proper and continuous monitoring of occupant behaviour inside buildings can support reaching of the zero energy-building standard (ZEB). The collected data, however, must be gathered via in situ methodology to avoid potential influences on data quality. Commonly used measurement techniques such as plug-load monitoring, CO2 level sensing or PIR, are sufficient to describe energy-related occupant behaviour at the zone/room level. However, this resolution of description can only be treated as an energy consumption overview as it cannot guarantee an identification of individual indoor environment quality preferences. Development of a solution that can grant access to an individual description of occupant needs requires direct monitoring of their inside building activity. Herein, access to necessary input data can be provided with the use of the depth registration camera because the suggested measuring technique can deliver information about routine occupant positioning inside each zone/room. Additionally, it provides data about the position of the observed occupants’ body limbs. If information about the distribution of the occupants is delivered, it is possible to couple such with a result matrix obtained via CFD studies. Moreover, the coordinates of occupant limb positions can be used as a data-probing device in simulation studies. With such a tool, it will be possible to monitor the exposure of each limb to the thermal properties of indoor air. Collecting data through this methodology can grant access to a more profound understanding of the occupant thermal comfort sensation and the habits that influence building energy use.

Prediction of indoor clothing insulation levels: A deep learning approach

Clothing insulation is a key variable in the prediction of occupant thermal comfort. Consequently, the aim of the current study was to develop predictive models that forecast clothing insulation levels of building occupants. Using field measurements, we investigated the influence of outdoor environment factors and mode of transport on clothing insulation levels of university students. Our results showed that both the mode of transport and weather variables influenced the clothing insulation levels of the students. We then developed a deep neural network model that forecasts mean daily clothing insulation levels using outdoor air temperature at 6 am, dew point temperature at 6 am, gender, season and mode of transport in the based on the collected data from 1316 questionnaire surveys. In addition, we revealed that outdoor environment factors had stronger associations with clothing insulation levels than indoor environment elements. The developed deep neural network model indicated a high R² value of 0.90. In comparison to the deep neural network model, a developed linear model using the same data indicated a lower R² value of 0.698, which implies that the proposed deep neural network model provides an efficient method to forecast clothing insulation levels.

Evaluation of environmental design strategies for university buildings

ABSTRACTThis paper examines the performance of environmental strategies in seven recently constructed or refurbished university buildings in the UK. These buildings contain a range of administrative spaces, classrooms, libraries and studios, reflecting their often complex, multi-use, heterogeneous nature. The key features of each environmental strategy are described (including passive, mixed-mode or active systems), in the context of the occupants and spaces they serve and the level of interaction that they afford. Energy performance and occupant thermal comfort (assessed by user surveys) are analysed and compared with studies of other non-domestic buildings, which have typically focused on more predictable single administrative uses (e.g. government offices), and unusually effective operation scenarios (e.g. continuous monitoring by expert building managers). The paper concludes by examining two of the case studies that reflect an increasingly common model of ‘flexible’ environmental design in more detail, identifying key features of the strategies for each building that have had a significant impact on their performance. The design assumptions leading to these features will be explored, and key lessons identified, contributing towards the development of a more robust evidential basis for choosing appropriate environmental strategies for university and other non-domestic buildings in the UK.

Field investigation on occupant's thermal comfort and preferences in naturally ventilated multi-storey hostel buildings over two seasons in India

In India, there is a scarcity of field data reported on occupant's comfort preferences and expectations in multi-storey naturally ventilated (NV) hostel buildings over the last three decades. To fill the research gap, a field study of adaptive thermal comfort was carried out in twelve NV hostel buildings in a composite climate of India, six from each of the two case cities, Jalandhar and Jaipur, respectively. The study is spread over rainy (July–September) and autumn season (October). 1516 valid responses from hostel occupants were collected and were further analyzed statistically to determine comfort temperature and thermal comfort zone for hostel buildings operated under NV mode. Mean Griffiths comfort temperature (Tc) of 29.7 °C and 30.4 °C was observed for Jalandhar and Jaipur city, respectively. Preferred temperature of hostel occupants was about 3 °C lower than mean Tc obtained for both cities. The comfort temperature found in present study were well within the thermal acceptability limits defined in adaptive models EN 16798 (formerly 15251) and NBC-2016 except ASHRAE standard 55–2017. Analysis of the data showed that at elevated air speed (using ceiling fans) the comfort boundary extends by 1.8 °C.

An innovative fault impact analysis framework for enhancing building operations

The primary objective of this paper is to rank building faults based on their impacts on the building energy penalty and occupant thermal comfort penalty considering multiple faults and fault occurrence rates. A fault impact analysis framework is created by incorporating the fault model library with the whole building energy performance simulation (e.g., EnergyPlus used in this study). The fault occurrence rate is introduced as a “meta” parameter in the simulation. This framework involves three essential aspects of conducting a fault impact analysis: fault constructing, fault simulation, and fault impact analysis.A parametric sensitivity analysis was used to determine and rank the criticality of the faults considering the fault concurrence frequency, by using the deep-learning based response surface model (i.e., the multi-layer perceptron regression). The proposed fault analysis framework with ranking was tested and demonstrated for the DOE's prototype medium-sized office in four different climate zones (i.e., Atlanta, Chicago, Miami, and San Francisco) with 12,000 EnergyPlus fault simulations. A total of 129 fault modes from 41 groups of fault models were simulated for the medium-sized office case.The results demonstrate the proposed framework is robust and scalable for the fault impact analysis. The top critical fault for the medium-sized office is the fault of HVAC-Left-ON for the packaged rooftop unit, regarding the site energy, source energy, and HVAC energy. Excluding the fault of HVAC-Left-ON, the top critical faults vary significantly among the four climate zones.

Application of the thermal comfort index as a control logic of VRF system and analysis of its performance by field measurement

Variable refrigerant flow (VRF) systems are known for their high energy performance and the installation of VRF systems in buildings is increasing. However, most studies have focused on improving the mechanical efficiency of VRF systems and there has been little research on energy efficient control strategies considering the thermal comfort of occupants. In this study, the application of the thermal comfort index as a control logic of VRF system was analyzed by field measurement. Indoor thermal environment and energy consumption characteristics according to control strategies such as set-point temperature and thermal comfort range in VRF system were analyzed. In this paper, the system configuration and the measurement results will be described.

Evaluation of vernacular and new housing indoor comfort conditions in cold climate – a field survey in eastern Turkey

PurposeThe purpose of this study is to compare vernacular and new houses in terms of indoor occupant satisfaction and thermal and visual comfort in a region with cold climatic conditions. In line with the data obtained, the contribution of passive design techniques to comfort in housing indoor will be revealed.Design/methodology/approachIn this study, the comfort conditions to be provided in a residence were determined and evaluated in Bingol with the help of questionnaires applied on vernacular and new houses. The information gathered from the occupants and the survey study was mainly designed for three purposes: (i) acquiring general information about houses; (ii) acquiring general information about occupants; and (iii) inquiring about the physical comfort satisfaction of the occupants (thermal comfort and visual comfort).FindingsAlthough the average occupant satisfaction in terms of thermal performance in vernacular houses in summer and winter is 3.91, this average is 2.01 for new houses. The average of the general visual comfort of occupants in vernacular houses is 3.59, whereas this rate is 2.63 in new houses. According to the data obtained, occupant satisfaction was higher in vernacular houses than in new houses. In general, the new settlement area is designed and positioned independently of climate and environmental conditions. This situation increases the need to use mechanical systems to provide indoor thermal comfort conditions. The increase in the need for mechanical systems leads to a significant increase in energy expenditures, as well as deterioration of health conditions in places.Research limitations/implicationsTo ensure occupant satisfaction, indoor thermal comfort conditions and healthy environments, vernacular houses should be an example for the design and building of new houses in terms of orientation, environment relations, space dimensions and space usage in accordance with the character of the region and material selection.Originality/valueThere has not been a serious research on bioclimatic, socioeconomic and cultural sustainability of the vernacular architecture of Bingol. Therefore, this region has been preferred as the study area.