Local Thermal Discomfort Research Articles

Numerical Simulation of the Application of Solar Radiant Systems, Internal Airflow and Occupants’ Presence in the Improvement of Comfort in Winter Conditions

In this work, the use of numerical simulation in the application of solar radiant systems, internal airflow and occupants’ presence in the improvement of comfort in winter conditions is made. The thermal comfort, the local thermal discomfort and the air quality in an occupied chamber space are evaluated. In the experimental measurements, a wood chamber, a desk, two seats, two seated hygro-thermal manikins, a warm radiant floor, a solar radiation simulator and a water solar collector are used. The air velocity and the air temperature fluctuation are experimentally evaluated around 15 human body sections. The chamber surface temperature is experimentally measured. In the numerical simulation, a coupling human thermal comfort (HTC) integral model, a computational fluids dynamics (CFD) differential model and a building thermal response (BTR) integral model are applied. The human thermal comfort level is evaluated by the HTC numerical model. The airflow inside the virtual chamber, using the k-epsilon and RNG turbulence models, is evaluated by the CFD numerical model. The chamber surface and the collector temperatures are evaluated by the BTR numerical model. In the human thermal comfort level, in non-uniform environments, the predicted mean vote (PMV) and the predicted percentage of dissatisfied (PPD) people are numerically evaluated; in the local thermal discomfort level the draught risk (DR) is experimentally and numerically analyzed; and in the air quality, the carbon dioxide CO2 concentration is numerically calculated. In the validation tests, the experimental and numerical values of the chamber surface temperature, the air temperature, the air velocity, the air turbulence intensity and the DR are presented.

Beyond nearly-zero energy buildings: Experimental investigation of the thermal indoor environment and energy performance of a single-family house designed for plus-energy targets

A detached, one-story, single-family house in Denmark was operated with different heating and cooling strategies for 1 year. The strategies compared during the heating season were floor heating without ventilation, floor heating supplemented by warm air heating (ventilation system), and floor heating with heat recovery from exhaust air. During the cooling season, the house was cooled by floor cooling and was ventilated mechanically. Air and globe (operative, when applicable) temperatures at different heights at a central location were recorded. The thermal indoor environment, local thermal discomfort and overheating were evaluated based on EN 15251 (2007), EN ISO 7730 (2005), and DS 469 (2013), respectively. Energy performance was evaluated based on the energy production and HVAC system energy use. The thermal indoor environment during the heating season was satisfactory but it was not possible to reach the intended operative temperature when the outside temperatures were very low. During the cooling season, the cooling demand was high and overheating was a problem. Although the house was designed as a plus-energy house, it did not perform as one under the Danish climate conditions. It would be possible to decrease the heating and cooling demand during the design phase through careful consideration of parameters such as the orientation, glazing area, solar shading, and thermal mass. With a lower demand, plus-energy levels can be achieved even with the minimum contribution from the energy producing components.

Numerical study of different ceiling-mounted air distribution systems for a virtual classroom environment

This paper presents a comparative numerical study of different ceiling-mounted-localized air distribution systems placed above students in a virtual classroom in summer conditions. The influence of four different ceiling-mounted-localized air distribution systems, using vertical descendent jets, on the thermal comfort, local thermal discomfort, and air quality levels was numerically evaluated. The air distribution index, developed previously, was used for non-uniform environment. This index considers the thermal comfort level, air quality level, effectiveness for heat removal, and effectiveness for contaminant removal. Numerical simulations were conducted for a virtual classroom equipped with one of four different ceiling-mounted-localized air distribution systems and with 6 desks, 6 or 12 students, and 2 upper airflow outlets. Inlet air supply temperature of 20 and 24℃ and an outdoor air temperature of 28℃ were used. The simulation results show that the air supply system having a vertical air jet placed at 1.8 m above the floor level (Case III), and with an inlet area of 0.01 m2 and a supply air velocity of 3 m/s would represent the best option in comparison with other air supply methods. In general, the air distribution index value decreases with an increase in inlet air temperature and the number of occupants. The air distribution index values are highest for Case III representing a classroom with 6 or 12 occupants with an inlet air temperature of 20 or 24℃.

Can radiant floor heating systems be used in removable glazed enclosed patios meeting thermal comfort standards?

Many systems are used for heating glazed enclosed patios of restaurants, pubs or other restaurant businesses. This paper explores the possibilities of use radiant floor heating systems (RFHS) in removable glazed enclosed patios maintaining thermal comfort in terms of predicted percentage of dissatisfied (PPD) and predicted mean vote (PMV) optimal ranges. The effects of different envelope structures of glazed enclosed patios on floor surface temperature using a radiant floor heating system have been analyzed. In addition, considering the use of removable and modular radiant floor heating panels, delivery and return pipes layouts from a heat power generator to each single radiant floor heating panel have been analyzed assessing flow velocity and pressure drops in order to pinpoint the best layout for optimizing heat transfer efficiency and energy saving. The findings showed at assumed outdoor and indoor temperatures what are the considered glazed enclosed patio envelopes that allow the use of a RFHS maintaining the floor surface temperature within thermal comfort ranges and avoiding local thermal discomfort due to floor temperature and vertical radiation asymmetry. Moreover, the flow velocity and concentrated/distributed pressure drops analysis pinpointed optimal pipe layouts for connecting heat power generator to each underfloor heating panel. concluding, the paper highlighted that, up to meet thermal comfort standards, under floor heating systems could be used for heating glazed enclosed patios only for certain envelope structures. Additionally, a delivery and return pipe layout should be properly designed for minimizing pressure drops and optimize heat transfer efficiency.

Producing a better performance for the under floor air distribution system in a dense occupancy space

This study deals with the possibility of the under floor air distribution system usage in a dense occupied space (80 occupants) regarding to the general thermal comfort conditions of occupants, local thermal discomfort, and indoor air quality. Computational fluid dynamics methods are used to predict general thermal comfort conditions of occupants, local thermal discomfort, and indoor air quality in this space. Different locations for the diffusers and velocities of the supply air are varied to determine what produces a better performance for the under floor air distribution system. It is found that when the diffusers are installed under seats, higher temperatures are measured at relatively lower heights due to the impedance in the injection of the fresh air supply. Moreover, the mean local age of air, as indoor air quality index, is increased by reducing the supply air velocity, which means that there is a less fresh air in the breathing zone of occupants. However, general thermal comfort conditions and local thermal discomfort should be considered as determining factors in each study. Based on the overall results of the study, under floor air distribution system is capable of creating a comfortable indoor environment in a dense occupied space.

Thermal pleasure in built environments: spatial alliesthesia from air movement

ABSTRACTIn recent years there has been a shift in research focus away from the negative effects of draught towards the positive benefits of air movement, particularly in the context of personal environmental control (PEC) systems. Thermal perception under targeted air movement is different from exposures in airflow uniformly distributed across the body, but is less well understood. Specification of performance criteria for PEC systems remains unresolved, as there are no clear conclusions regarding optimum target area, velocity ranges or patterns of velocity dynamics. This paper examines the effects of different local air-velocity profiles on thermal sensation and thermal pleasure experienced by human subjects near the upper boundary of the comfort zone, and interprets the findings within the theoretical framework of spatial alliesthesia. It was found that positive thermal pleasure can be achieved when contrasting relationships between local and global skin temperatures trends are established. The substantial body of research literature on local thermal discomfort can be coherently interpreted within the theoretical framework of spatial alliesthesia; local discomfort represents thermal alliesthesia with the incorrect polarity between local and global thermal states. Spatial alliesthesia therefore provides a conceptual framework to understand PEC systems and their potential to minimize occupant thermal dissatisfaction.

Thermal comfort and ventilation effectiveness in an office room with radiant floor cooling and displacement ventilation

The influence of displacement ventilation and a cooled floor on indoor climate in the cooling season were experimentally studied in a room representing an office with a shaded window, occupied by two simulated employees. The aim was to investigate whether the combination of these two systems can retain the favorable air and temperature distribution patterns and high ventilation effectiveness that are typically attained by displacement ventilation, while exploiting the energy conservation advantages of a high temperature cooling system. The tests were performed under a range of boundary conditions, varying the nominal air change rate from 4.5 h−1 down to 1.5 h−1. Contaminant removal and mean-age-of-air measurements were performed to characterize the ventilation effectiveness and air velocity; air and operative temperature profiles were measured, together with thermal manikin equivalent temperatures, to evaluate the thermal environment. The combined system was able to achieve good ventilation effectiveness close to a heat source, so that in the occupant's breathing zone the ventilation effectiveness was significantly better than for ideal mixing, even at a nominal air change rate as low as 1.5 h−1. However, for a broad range of boundary conditions, decreasing the floor temperature resulted in vertical air temperature differences of up to 6 K and vertical equivalent temperature differences of up to 8 K for a seated person. Thus although the maximum draught rating at ankle level was 21% at the highest nominal air change rate of 4.5 h−1, even for an occupant sitting 1 meter in front of the supply diffuser, the local thermal discomfort occasioned by the excessive vertical temperature differences gives chilled ceilings the advantage over chilled floors for use with displacement ventilation.

Indoor Environment Influenced by Radiant Effect of Floor Heating

The paper is oriented on the indoor environment influenced by radiant effect of floor heating. Questionnaire survey has showed problems with providing quality of indoor climate in new office building in Bratislava. The cause of problems was formation of local thermal discomfort, in particular mainly radiant asymmetry. To clarify the radiant asymmetry, there were carried out experimental measurements with thermal manikin in a special microclimatic laboratory for the radiant floor heating. The scientific analysis and the outputs from measurements are presented in this paper. In the conclusion of this paper are introduced principals for designing the offices’ interiors without local thermal discomfort.

Experimental Research of Thermal Comfort Conditions in Small Test Buildings with Different Types of Heating

The aim of this study is detailed analysis of long-term monitoring data of thermal comfort conditions and energy efficiency in small test buildings equipped with different heating systems. Calculations of PPD index and local thermal discomfort factors are provided for the test buildings during three weeks of heating season. It is shown that the type of heating system has influence not only on heating energy need, but also on thermal comfort conditions in the room.

Retrofit Strategies for the Improvement of Visual Comfort and Energy Performance of Classrooms with Large Windows Exposed to East

The typical orientation of the facades of school buildings, along with the presence of large windows and permanent position of the students, can create uncomfortable environmental conditions caused by eye strain due to glare and local thermal discomfort due to asymmetrical thermal radiation. In this work, the effectiveness of various types of high performance glazing and external shading is evaluated, by means of simulations of visual comfort and energy efficiency. Simulations were carried out for a case study which is representative of a typical classroom of a school, located in a town of Tuscany, where instrumental monitoring of existing thermal and lighting conditions was conducted. The case study was selected through an analysis of energy consumption of the whole school building stock of the city, over a period of five years. The analysis has allowed to select the most critical one in terms of energy consumption and the most representative one regarding the Italian school building stock. The selected building has been analyzed by means of building performance simulation software. A survey about the school users’ perception of comfort levels was also carried out by means of questionnaires.

Thermal pleasure in built environments: spatial alliesthesia from contact heating

The comfort zone is bounded by thermal environmental conditions that may be described as acceptably cool or acceptably warm, and engineering out of existence these innocuous thermal conditions on the fringes of the adaptive comfort range may not be necessary. In contrast to the conventional understanding of local discomfort, spatial alliesthesia exploits corrective differences in the rate of change in skin temperature between individual body segments to elicit positive affective sensations. This paper examines reverse instances of local discomfort, or spatial alliesthesia, from warm contact stimuli applied to hand and feet when exposed to ambient conditions towards the lower margin of the comfort zone. It was found that subjects with moderate feelings of displeasure or even indifference were still capable of experiencing a pleasant response to localized thermal stimuli. Brief whole-body thermal pleasure was observed from in-situ skin temperature changes at a single distal body site. These effects were subtle and not universally experienced, so the success of their deliberate implementation in built environments depends heavily on some form of individual control. Spatial alliesthesia therefore complements the body of literature investigating personal environmental control and local thermal discomfort by providing a theoretical framework of thermal perception in non-neutral environments.

The impact of environmental and human factors on urban heat and microclimate variability

Urbanization is known to cause noticeable changes in the properties of local climate. Studies have shown that urban areas, compared to rural areas with less artificial surfaces, register higher local temperatures as a result of Urban Heat Islands (UHIs). Hong Kong is one of the most densely populated cities in the world and a high proportion of its population residing in densely built high-rise buildings are experiencing some degrees of thermal discomfort. This study selected Mong Kok and Causeway Bay, two typical urban communities in Hong Kong, to gather evidence of microclimate variation and sources of thermal discomfort. UHIs were estimated from 58 logging sensors placed at strategic locations to take temperature and humidity measurements over 17 consecutive days each in the summer/hot and winter/cool periods. By employing geographic information and global positioning systems, these measurements were geocoded and plotted over the built landscape to convey microclimate variation. The empirical data were further aligned with distinct environmental settings to associate possible factors contributing to UHIs. This study established the existence and extent of microclimate variation of UHI within urban communities of different environmental configuration and functional uses. The findings provided essential groundwork for further studies of UHI effects to inform sources of local thermal discomfort and better planning design to safeguard environmental health in public areas.

Smart heating sleeping bags for improving wearers' thermal comfort at the feet

Sleeping bags are portable products, which are essential for sleeping outdoors. Generally, a sleeping bag is comprised of an outer layer, an inner lining layer and the filler. The EN 13537 (2012) and ASTM F1720 (2014) standards are widely used to determine the thermal insulation of sleeping bags by means of thermal manikin. Previous studies have found that local thermal discomfort at feet was often seen despite the mean skin temperature was well within thermoneutral range under the defined comfort and limit temperature [1]. Thus, it is meaningful to design smart heating sleeping bags to improve the local thermal comfort of the users. In this study, a novel smart sleeping bag was developed by incorporating heating fabrics into the feet region of the bag. The physiological and psychological responses when using traditional sleeping bag and the smart sleeping bag were investigated and compared.

Effects of return air vent height on energy consumption, thermal comfort conditions and indoor air quality in an under floor air distribution system

In this article, an under floor air distribution (UFAD) system with separate return and exhaust air vents is investigated. The proper angle of the swirl inlet diffuser is selected by comparing the general thermal comfort conditions obtained from three different inlet angles. At this proper inlet angle, the effects of return air vent height on energy consumption, thermal comfort conditions, and indoor air quality (IAQ) are investigated. To this end, thermal comfort indices (PMV–PPD), local thermal discomfort index (temperature gradient in vertical direction), and IAQ index (mean local age of air) are probed by CFD methods. Energy consumption reduction in an UFAD system equipped with a return air vent compared to MV system is 10.9, 15.3, 18.9, and 25.7% when the return air vent height is set at 2.0, 1.3, 0.65, and 0.3m, respectively. Reducing the height of return air vent from ceiling to floor leads to an increase in exhaust air temperature and temperature gradient at the vertical direction. It is found that selection of the 1.3m height from floor (upper boundary of occupied zone in seated mode) for return air vent height will cause a 15.3% reduction in energy consumption and would maintain the thermal comfort and IAQ in the specified range.

Indoor Climate of Residential Interiors and Asymmetry of Radiation

The paper is oriented on the indoor climate of residential interiors. Questionnaire survey in new residential building has showed problems with securing quality of indoor climate. In smaller residential interiors with large glazed surface was this problem bigger. Cause of problems was formation of local thermal discomfort. One of the most serious area of local thermal discomfort is asymmetry of radiation. To clarify asymmetry of radiation, there were carried out experimental measurements in a special microclimatic laboratory for convective heating. In this paper, there is presented the scientific analysis and the outputs from measurements. In the conclusion of this paper are introduced principals for designing the residential interiors without local thermal discomfort.

Web application for thermal comfort visualization and calculation according to ASHRAE Standard 55

Thermal comfort is one of the fundamental aspects of indoor environmental quality and it is strongly related to occupant satisfaction and energy use in buildings. This paper describes a new web application for thermal comfort visualization and calculation according to ASHRAE Standard 55-2013. Compared to existing software, the web application is free, cross-platform, and provides a visual and highly interactive accurate representation of the comfort zone. Its main features are: dynamic visualization of the comfort zone on psychrometric, temperature-relative humidity, and adaptive charts; new implementation of the Elevated Air Speed model; local thermal discomfort assessment; compliance document automation for LEED thermal comfort credits; metabolic activity and clothing insulation tables and dynamic models; and compliance with the standard. The tool can be used by architects, engineers, building operators, educators, and students.

Computational investigation on the factors influencing thermal comfort for impinging jet ventilation

Impinging jet ventilation (IJV) has been proposed to achieve an effective ventilation of an occupied zone in office and industrial buildings. For IJV systems, draught discomfort is the issue of most concern since it supplies cooled air directly to the occupied zone. This study investigated a number of factors influencing draught discomfort and temperature stratification in an office environment equipped with IJV. The factors considered were: shape of air supply device, discharge height, supply airflow rate and supply air temperature. The Response Surface Methodology (RSM) was used to identify the level of the significance of the parameters studied, as well as to develop the predictive models for the local thermal discomfort. Computational fluid dynamics (CFD) was employed to perform a set of required studies, and each simulation condition was determined by the Box–Behnken design (BBD) method. The results indicated that at a low discharge height, the shape of air supply device had a major impact on the flow pattern in the vicinity of the supply device because of the footprint from impinging jet, which consequently affected the draught risk level in the occupied zone. A square-shaped air supply device was found to result in lower overall draught discomfort than rectangular and semi-elliptic shapes. The RSM analysis revealed that the supply airflow rate had a significant impact on the draught discomfort, while the shape of air supply device and discharge height had moderate effects. The temperature stratification in the occupied zone was mostly influenced by the supply air temperature within the range studied.

The influence of clothing distribution and local discomfort on the assessment of global thermal comfort

A field study was carried out in a hypermarket located in Southern Italy in order to evaluate the environmental comfort in large-scale retail trade buildings. Global and local thermal comfort conditions were studied by collecting exposure data and subjective responses of employees using both questionnaires and simultaneous physical measurements. In a few cases discrepancies appeared between subjective ratings and the corresponding PMV-index, suggesting that the latter could be unable to reliably estimate thermal comfort when clothing insulation is unevenly distributed on human body. Analysis of collected data confirmed this, with particular reference to female workers wearing skirts. In addition, such effects may be further emphasized by local thermal discomfort, which may finally influence global thermal perception. Analysis of the results showed that cold floor and radiant temperature asymmetry caused by warm ceiling played a major role in emphasizing the negative effects due to uneven clothing distribution, confirming that this particular combination of events may bias PMV model accuracy.

Analysis of Thermal Emissions from Radiators in Classrooms in Mediterranean Climates

Using computational fluid dynamics (CFD), this study focuses on the analysis of the thermal emissions of a typical classroom in an educational establishment in the south of Spain, and heated by radiators situated under the windows. It aims to study the way to exchange energy within the venue with this system. In order to do so a work methodology is developed which applies the Fanger method (PMV and PPD indicators) and the local thermal discomfort method to the isothermal curve sections generated by the CFD calculations, drawing up a series of lineal variation graphs on the temperature. This allows us to not only evaluate the degree of thermal comfort of the occupants in accordance with ASHRAE standards but also to carry out future comparisons between different thermal exchange system variants arising from the HVAC system. Following the application of this analysis the paper concludes that efficiency of the traditional radiator system to cope with the energy demand of the location is limited, given its incapacity to carry out a uniform exchange of energy between itself, the convective phenomena it generates, and the low relation between air volume/emitting surface, which translates into a lack of energy efficiency in the system, an aspect which is not usually contemplated in traditional analysis methods.

Evaluation of comfort level in desks equipped with two personalized ventilation systems in slightly warm environments

In this work the comfort level, namely the thermal comfort, local thermal discomfort and air quality levels, in a classroom with desks equipped with two personalized ventilation systems, in slightly warm environments, is evaluated. A manikin, a ventilated classroom desk, two indoor climate analyzers, a multi-nodal human thermal comfort numerical model and a computational fluid dynamic numerical model, are used. The classroom desk, with double occupation capacity, is used by a student, located in the right side seat. Each personalized ventilation system is equipped with one air terminal device located above the desk writing area, in front to the trunk area, and an other located below the desk writing area, in front to the legs area. The thermal comfort level is evaluated by the developed multi-nodal human thermal comfort numerical model, using a PMV value, the local thermal discomfort level, namely the draught risk and the air velocity fluctuation equivalent frequencies, is evaluated by empirical models, while the air quality level and the detailed airflow around the manikin are evaluated by the computational fluid dynamic numerical model. In the experimental tests the mean air velocity and the turbulence intensity in the upper air terminal device are 3.5 m/s and 9.7%, while in the lower air terminal device are 2.6 m/s and 15.2%. The mean air temperature in the air terminal devices is around 28 °C, while the mean radiant temperature in the occupation area, the mean air temperature far from the occupation area and the internal mean air relative humidity were, respectively, 28 °C, 28 °C and 50%. The air velocity and temperature around the occupant are measured around 15 human body sections. The actual personalized ventilation system, which promotes an ascendant airflow around the occupant with highest air renovation rate in the respiration area, promotes acceptable thermal comfort conditions and air quality in the respiration area in accord to the present standards. The draught risk is verified in the head and left leg and the uncomfortable air velocity equivalent frequency is verified in the left arm. The left human body sections present higher local thermal discomfort levels than the right human body sections, because they are also influenced by the left air terminal device. In accord to the obtained results, the classroom desk design, equipped with two personalized ventilation systems, guarantees acceptable thermal comfort conditions and promotes good air quality conditions, with acceptable local thermal discomfort conditions and with low energy consumption level.