Radiant Asymmetry Research Articles

Numerical and experimental study of the effect of solar radiation on thermal comfort in a radiant heating system

The study of the effect of solar radiation on the built environment is a significant subject especially in the radiant systems and it is increasingly important because large glazed envelopes are widely adopted in modern architecture. In this paper, a radiant heating system was analyzed the effect of solar radiation on indoor thermal comfort using CFD simulations and experiments.The results show that the existence of the sunspot on the floor and the heated window significantly affect the indoor thermal behaviors. Occupants could feel local discomfort near the superheated surfaces even if they can maintain global thermal comfort in most areas of the room in the presence of solar radiation. The local thermal comforts of three cases were studied and compared. Compared to the Case without solar radiation, the vertical air temperature difference (VATD) between the ankle and the head is smaller near the window. But the low-temperature fresh air from the air inlet may cause a high VATD and draught rate (DR), particularly in the cold season. When solar radiation was included, the radiant asymmetry at head level is about 4 °C higher than that of when solar radiation was not included. It is found that the interior shading can alter thermal behaviors in a radiant system. The important suggestions of this study are to reduce the difference between the radiant panels temperature and the supply air temperature while maintaining heat balance in a radiant heating system and properly controlling the temperature of the superheated surfaces in the presence of solar radiation.

Effects of external insulation component on thermal performance of a Trombe wall with phase change materials

A classical Trombe wall cannot satisfy the thermal comfort for the whole day due to the limited heat storage capacity and large heat loss at night. In present work, phase change materials and an external insulation component are used to improve thermal performance of a Trombe wall. The design approach of heat preservation at night is first obtained. An unsteady heat transfer model of a Trombe wall with phase change materials under heat preservation condition in the nighttime is established by MATLAB. The reliability of the mathematical model is validated by an experiment in Yuzhong (Gansu, China). With this model, the effects of the design parameters of the external insulation component on the thermal performance are analyzed. Finally, the indoor thermal comfort of a passive solar room is analyzed based on the experimental data. The results indicate that, it has a significant impact of the thermal conduction resistance of the insulation component and the thermal resistance of the closed air cavity. For closed air cavity, the internal surface emissivity of the insulation component plays an important role. The optimized additional thermal resistance for the external insulation component is 2 m2⋅°C⋅W−1, and the corresponding maximum thermal resistance of the closed air cavity is determined as about 0.5 m2⋅°C⋅W−1. Compared with no heat preservation at night, the operative temperature improves significantly, and the radiant temperature asymmetries of two massive walls are similar. The investigation can provide a design approach of heat preservation at night for a Trombe wall.

A new method for evaluating the joint effect of draught and the hot ceiling

For buildings with ceiling heating and mechanical ventilation, it is extremely important to know the combined effect of the draught and the radiant thermal asymmetry caused by a warm ceiling. There is plenty of literature offering separate descriptions of the dissatisfaction caused by draught and warm ceilings, but research on the combined effect of these two local discomfort factors is incomplete. In order to fill in this gap, human subject measurements were conducted involving 20 subjects, 10 men and 10 women, who were asked to complete questionnaires on thermal sensation, while being exposed to a random combination of 5 asymmetries and 2 draughts. Analyzing the results obtained this way made it possible to evaluate the combined effect of the draught and radiant thermal asymmetry on thermal comfort. The most important outcome of the research is the mathematical description of the expected dissatisfaction rate and the presentation of the differences depending on gender.

Thermal comfort under radiant asymmetries of floor cooling system in 2 h and 8 h exposure durations

Radiant heating and cooling systems inherently exhibit radiant asymmetries. Although many researchers have investigated the thermal comfort effects of asymmetric radiant environments, the exposure duration has not been emphasized, especially under floor heating and cooling scenarios. In this study, we conducted a series of tests in a climate chamber with floor cooling radiant asymmetries with human participants to investigate their thermal comfort effects from short-term (2 h) and long-term (8 h) exposure perspectives. The 2 h exposure test indicates that the floor cooling systems cause discomfort complaints more easily than other radiant systems such as ceiling heating/cooling because of its stronger cooling effects on the lower body parts. The cold floor resulted in significantly colder local thermal sensations and lower local skin temperatures in the foot, calf, and thigh areas. The comparison between the 2 h and 8 h exposures suggests that exposure duration affects both the subjective and physiological thermal comfort responses significantly. 2.5∼4 h are required for the foot and calf temperatures to stabilize in radiant floor cooling asymmetry cases. In accordance with these laboratory tests, we proposed two radiant asymmetry-satisfaction curves and equations for the floor cooling system with consideration of exposure duration. The calculated temperature limits for typical floor cooling room are >18.5 °C at a 2 h exposure and >20.5 °C at an 8 h exposure. These curves and temperature limits can serve as a reference for future guidelines for floor cooling system design and operation.

The influence of the combined effect of draught and radiant thermal asymmetry on human performance

Currently, there are studies which show the separate effect of the local discomfort parameters such as the draught and radiant thermal asymmetry. However, no studies have been conducted to find out the combined effect of the before mentioned two discomfort parameters on human performance. In order to fill this gap, a 17 months experiment was performed at the Budapest University of Technology and Economics. Throughout the experiment twenty human subjects (ten women and ten men) performed different cognitive tests and responded to questionnaires. Two different draught rates and five different radiant thermal asymmetry values were imposed in the Macskásy climate chamber, where the experiment took place. The results show the consequence of the combined effect of draught and radiant thermal asymmetry on the human performance.

Experimental and statistical survey on local thermal comfort impact on working productivity loss in university classrooms

The paper presents an experimental analysis of the relationship between local thermal comfort and productivity loss in classrooms. The experimental investigation was performed in a real university classroom during the winter semester in city of Belgrade. Measurements were taken for four scenarios, with different indoor comfort conditions. Variations were made by setting the central heating system on/off, adding an additional heat source to provoke higher indoor temperatures, and measuring the radiant asymmetry impact. Innovative questionnaires were developed especially for the research, in order to investigate students? subjective feelings about local thermal comfort and indoor environmental quality. Local predicted mean vote and predicted percentage dissatisfied indices were calculated using data measured in situ. The results were compared to existing models recommended in literature and European and ASHRAE standards. Student productivity was evaluated using novel tests, designed to fit the purposes of the research. Surveys were conducted for 19 days under different thermal conditions, during lectures in a real classroom, using a sample of 240 productivity test results in total. Using the measured data, new correlations between the predicted mean vote, CO2, personal factor and productivity loss were developed. The research findings imply that local thermal comfort is an important factor that can impact productivity, but the impact of the personal factor is of tremendous importance, together with CO2 concentration in the classroom.

Local effects on thermal comfort: Experimental investigation of small-area radiant cooling and low-speed draft caused by improperly retrofitted construction joints

Improper attention to construction joints in a building may lead to localized cold spots on the inside surfaces of the building and air leakage through the envelope. This in turn can affect the thermal comfort of residents due to small-area radiant asymmetry and low-speed draft.The effect of these two local discomfort events on thermal comfort were investigated in two sets of experiments. The test setting consisted of a cool-to-neutral environment, in which a custom-built arrangement replicated small-area radiant asymmetry and low-speed draft caused by improper retrofitting of construction joints. Participants rated their thermal sensation and comfort for three consecutive test conditions associated with radiant asymmetry or draft. Each radiant asymmetry condition consisted of a combination of the height and temperature of a small cold spot and the distance between the cold spot and the subject. The draft conditions comprised the height of the draft outlet and the speed and temperature of the airflow. The heights of the cold spot and draft outlet correspond to the feet, chest and head level of a seated person.Draft perception was found to not be linked to the experimental parameters of the draft conditions, and as such was not impacted by improperly retrofitted construction joints. However, several statistically significant relationships were found between the radiant asymmetry parameters and thermal sensation. Nonetheless, these effects were very small, and the variance explained by these parameters was very low. Therefore, small-area radiant asymmetry cannot be used to make practical decisions in retrofitting strategies for construction joints.

Revisiting the use of globe thermometers to estimate radiant temperature in studies of heating and ventilation

The globe thermometer has been considered a reliable instrument to quantify mean radiant temperature (MRT) since Bedford & Warner isolated its readings from air movement in their 1934 paper so that radiation could be quantified. Recent expanded use of radiant heating and cooling systems has presented new challenges for the usage of globe thermometers in the built environment by causing additional radiant asymmetries and performance expectations. Therefore, we replicate the original Bedford & Warner work to reconsider and develop a more holistic understanding of black globe performance and the determination of MRT in buildings. We recreate the MRT and air temperature separation to investigate the accuracy of globe thermometers on measuring MRTs. A radiantly heated open-plan laboratory and a radiantly cooled conference room were selected and measured with multiple globe thermometers and non-contacting infrared sensors. The globe temperature results were then corrected with air movement to produce MRTs and compared against MRTs simulated from measured surface temperatures. We demonstrate a significant impact of air speed on the MRTs obtained from globe thermometers. We also illustrate a less-investigated non-graybody emissivity variation and spatial variation of MRTs of up to 5 °C at the same height. We believe the increasing temporal and spatial resolution of digital sensors may create new challenges for using globe thermometers to measure MRTs, since fluctuating readings may camouflage potential MRT changes. Through a validation of our spatial MRT distribution with experimental results, we believe there is a need for better sensors that could spatially resolve MRTs, and recognize issues with both air speed and emissivity.

The effect of the climatic condition on the radiant asymmetry

The effect of the climatic condition on the radiant asymmetry

Thermal environment in a simulated double office room with convective and radiant cooling systems

The thermal environment in a double office room obtained with chilled beam (CB), chilled beam with radiant panel (CBR), chilled ceiling with ceiling installed mixing ventilation (CCMV) and overhead mixing total volume ventilation (MTVV) under summer (cooling) condition was compared. Design (peak) and usual (average) heat load from solar radiation, office equipment, lighting and occupants was simulated, respectively at 62 W/m2 and 38 W/m2 under four different workstation layouts. Air temperature, globe (operative) temperature, radiant asymmetry, air velocity and turbulent intensity were measured and draught rate was calculated. Manikin-based equivalent temperature (MBET) was determined by using two thermal manikins. CCMV provided slightly more uniform thermal environment and the least sensitive to different workstation layouts than the other systems. CB provided a bit higher draught rate levels than CCMV especially in the design heat load cases. With CBR, the thermal environment was found to be between CB and CCMV. MTVV generated high draught level under the tested design heat load cases. All cooling systems generated similar thermal environment in the usual heat load cases. It would be recommended to include the measurement height of 0.05 m in indoor climate testing standards for obtaining more generic view of the draught risk.

Thermal comfort in indoor environment: Effect of the solar radiation on the radiant temperature asymmetry

This paper analyzes the influence of solar radiation, considering both its direct and diffuse component, on the local thermal comfort of subjects in indoor environments. More precisely, an original equation for the assessment of the plane radiant temperature in presence of solar radiation is proposed. It can be used to evaluate the correspondent radiant asymmetry and therefore allows detailed analysis of local thermal discomfort conditions. Its reliability and feasibility have been tried out by means of an application to a simple case study and the obtained results proved that, in the studied environment, solar radiation affects the symmetry of the radiant field to a considerable extent, being the main cause of local discomfort due to not acceptable values of the radiant asymmetry. Therefore, the method can be used to verify the presence of zones not suited to human activities inside rooms and, in addition, it can be exploited by the procedures aimed at the classification of the comfort quality of indoor environments.

Full-scale test and CFD-simulation of radiant panel integrated with exposed chilled beam in heating mode

Thermal conditions in an office room with a chilled beam having integrated radiant panel (CBRP) were analysed in the full-scale laboratory test and using computational fluid dynamic (CFD) simulation. Thermal conditions in the office room were measured in six heating cases under steady state conditions that had different window surface temperatures and internal heat gain conditions. CFD simulations of two measured cases were done in order to investigate indoor climate conditions in more detail and comparing CFD results to measured results. An additional CFD simulation was done with office desk location to near to window to study thermal conditions below the desk. Ventilation efficiency was studied with CFD-simulation. Indoor climate conditions with all measured cases were at good level. Radiant asymmetry and vertical temperature stratification fulfil the requirements of category A in ISO-7730. The highest room air velocities and draught rate readings were 0.16 m/s and 17% respectively. The results indicate that radiant panel heating is applicable solution also in cold climate. Good thermal conditions could be ensured when the temperature of window surface is at least 14–15 °C. At the same time, vertical temperature stratification is acceptable and thus maintains high energy efficiency. Results indicate also that when room is occupied and ventilation is introduced, the temperature gradient is much smaller compared to unoccupied room space.

Thermal environment in simulated offices with convective and radiant cooling systems under cooling (summer) mode of operation

The thermal environment in a double office room and in a six-person meeting room obtained with chilled beam (CB), chilled beam with radiant panel (CBR), chilled ceiling with ceiling installed mixing ventilation (CCMV) and four desk partition-mounted local radiant cooling panels with mixing ventilation (MVRC) under summer (cooling) condition was compared. MVRC system was measured only for the office room case. CB provided convective cooling while the remaining three systems (CBR, CCMV and MVRC) provided combined radiant and convective cooling. Solar radiation, office equipment, lighting and occupants were simulated to obtain two different heat load conditions: 38 W/m2 and 64 W/m2 in the case of office room, and 71 W/m2 and 86 W/m2 in the case of meeting room. Air temperature, globe (operative) temperature, radiant asymmetry, air velocity and turbulent intensity were measured and draught rate calculated. Manikin-based equivalent temperature (MBET) was determined by using two thermal manikins to identify the impact of the local thermal conditions generated by the studied systems on occupants' thermal perception. The results revealed that the differences in the thermal conditions achieved with the four systems were not significant. CB and CBR provided slightly higher velocity level in the occupied zone. The operative temperature in the studied cases with chilled ceiling in operation with mixing ventilation was almost the same as the operative temperature obtained with the active chilled beam (i.e. only convective cooling). The heat load distribution played major role for the airflow pattern in all studied systems.

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.

Predictive Models for Evaluating Mobility Buses Thermal Performance

Every day, in every city, many buses are moving, carrying a lot of citizens. During the year, especially during the summer, buses become uncomfortable places because of both environmental and internal conditions. Due to the rising of the mobility needs, time that people spend in vehicles has strongly grown. Moreover, also the thermal environment in urban buses changes greatly, in fact passengers onboard are exposed to local heating and/or cooling due to vertical temperature gradients, radiant asymmetry and local unexpected airflow. This study aims to optimize the energy performance of a bus envelope, identifying practical solutions. The analysis was carried out numerically, considering a hot day during July and passengers on board during the 24 hours per day.

Environmental monitoring of a Sardinian earthen dwelling during the summer season

Increasing interest in earth architecture has led to the development of new international norms regarding these structures. Although Italy has no specific legislation for this building type, both national laws for the safeguard of rural architecture and regional norms regarding the conservation of historical centers have considerably slowed down the pace of their destruction. This is particularly true for Sardinia, which maintains a conspicuous heritage of "raw earth" architecture, mostly in the old town centers of the Campidano plain and in its adjacent valley. Due to the current legislation on energy efficiency in buildings, it has become essential – particularly for the Sardinian region – to define guidelines for the improvement of energy efficiency for this existing building heritage and identify the best parameters for their energetic classification. Currently, these constructions are heavily penalized by the gap that persists between the requirements of current energy balance evaluations, calculated upon heating and domestic hot water energy demands, and the actual year-round energy performance, which also includes the summer season. Moreover, this building type has a low lifecycle environmental impact, but this aspect is not properly "rewarded" by Italian regulations. The study proposed herein firstly took into account the simulation of the thermal transient characteristics of the adobe wall (brick made of clay, earth and straw, forged with wooden molds and sun dried). Analytical calculations were performed using a transient model, assuming sinusoidal behavior of all the parameters acting on the system. The results showed a high thermal inertia of the material and a good ability in dampening the external thermal wave. Next, we conducted an internal and external environmental monitoring of an existing earthen residential building in Sardinia ("Casa Mancosu", Serramanna, VS), which provided the experimental data for the evaluation of the whole building thermo-physical behavior. The measurements were taken during the 2010 summer season; the dwelling was not cooled by an air conditioning system. Thermal comfort analyses based on these experimental data indicate that the roof is the "weak" component, creating local discomfort due to radiant asymmetry. The described methodology is expected to be applicable also to the many buildings of this geographical area similar to the examined one.

Thermal comfort and local discomfort in an operating room ventilated with spiral diffuser jet

Operating rooms often exhibit vertical temperature gradient, radiant asymmetry, local airflows, and local body cooling. The impact of these parameters on the thermal comfort of the occupants can be greatly affected by the type of air-conditioning system used in the room. This work evaluated thermal comfort conditions in an operating room ventilated with a spiral diffuser jet using an instrumented thermal manikin with heated sensors. The objective is to assess the conditions of thermal comfort and local discomfort of the patient and surgical team in this kind of environment using the concept of equivalent temperatures and a manikin with heated sensors. Additionally, the method proposed by Fanger was used to evaluate the thermal sensation. The results showed a very small change in the equivalent temperatures in different parts of the body for the surgeon and nurse. The thermal sensation for the surgeon and nurse simulated by the manikin and using a thermal comfort diagram for equivalent temperature was neutral in the whole body. However, higher equivalent temperatures were found on the heads of the surgeon and nurse because of the heat exchange by radiation from the surgical lights. The local thermal sensation for the patient varied from too cold, cold, and neutral, depending on the body part. Finally, the methodology proposed showed to be very effective for evaluating the thermal comfort conditions in operating rooms when compared to the method proposed by Fanger.

Indoor Climate Analysis for Urban Mobility Buses: a CFD Model for the Evaluation of thermal Comfort

The aim of this work is to analyze the indoor climate in city buses; the study was developed by numerical simulation and experimental validation carried out on the urban mobility buses of the city of Rome (Italy). Several factors have contributed to increase the concern about the comfort evaluation in vehicles and particularly in city buses. Due to the rising of the mobility needs, time that people spend in vehicles has grown substantially. The thermal environment in urban buses also varies greatly: passengers are exposed to local heating and/or cooling due to vertical temperature gradients, radiant asymmetry and local unexpected airflow. The interaction of the cabin thermal environment, created by the HVAC-system, the outdoor conditions as well as the occupants is rather complex. At the moment no standards exist for assessment and classification of the thermal environment quality in vehicles. To obtain some evidences, in order to enhance the indoor climate for a city bus and to improve occupants’ comfort monitoring local temperature and air distribution around passengers, we have developed a mathematical model. The numerical model was implemented with Computational Fluid Dynamic software (CFD, Fluent Inc.): it permits the evaluation of the thermal and fluid-dynamic performances of the air conditioning system and diffusers’ distribution. To gain a deeper understanding of the local climate comfort, the numerical simulation results were experimentally validated by several measurements inside the urban buses performed under real operative conditions during the summer season.The experimental results are in good agreement with the CFD evidences. This shows that the model developed can give reliable results to optimize and locally modify the air diffusers distribution inside cabin spaces. These evidences can help to improve the air conditioning distribution as a function of the obstructions’ typical for a city bus vehicle and to reduce the draught risk related to the bus stop door apertures. One of the most important reasons of local temperature differences and unexpected air velocity gradients is due to the multi-door system apertures at each bus stop. This situation is particularly recurrent in a city area where an urban bus can afford several stops during his programmed route. For this reason it’s important to get more information about this transient localized load for the climate conditions and about the time needed to reach again the steady conditions. To avoid or, at least, reduce this kind of problem it is proposed an air knife screened doors system bus. The thermo fluid dynamic results obtained show a significant improvement in the indoor climate comfort.

An experimental study of air flow and temperature distribution in a room with displacement ventilation and a chilled ceiling

Displacement ventilation and chilled ceiling panel systems are potentially more energy efficient than conventional air conditioning systems and are characterized by the presence of vertical temperature gradients and significant radiant asymmetry. The characteristics of this type of system have been studied by making temperature and air flow measurements in a test chamber over a range of operating parameters typical of office applications. Results from the displacement ventilation study are consistent with other studies and show that normalized temperature profiles are independent of internal heat gain. Linear temperature gradients in the lower part of the room were found, in all cases, to be driven by convection from the adjacent walls. Significant mixing, indicated by reduced temperature gradients, was evident in the upper part of the room in the chilled ceiling results at higher levels of heat gain. Visualization experiments, velocity measurements and related numerical studies indicated that with greater heat gains the plumes have sufficient momentum to drive flow across the ceiling surface and down the walls. The significance of forced, as opposed to natural convection, is also suggested by relatively low Richardson Number (Ri) values found near the ceiling. Furthermore, in cases with moderately high internal gains, comparison of the temperature gradients indicated that the effect of ceiling surface temperature on the degree of mixing and the magnitude of the temperature gradient were of secondary importance. These findings are in contrast to the view that it is natural convection at the ceiling that causes enhanced mixing.

Effect of stove asymmetric radiation field on thermal comfort using a multisegmented bioheat model

The multinode multisegment bioheat model of Salloum et al. [Salloum M, Ghaddar N, Ghali K. A new transient bio-heat model of the human body. In: Proceedings of the ASME 2005 summer heat transfer conference, 17–22 July 2005, San Francisco, Paper no. HT2005-72303] is integrated with a space heat model to study human thermal response when subjected to radiant asymmetry in stove-heated domestic spaces in Lebanon. For any given person position, the overall comfort level is based on Frank et al. model correlations [Frank SM, Srinivasa NR, Bulcao CF, Goldstein DS. Relative contribution of core and cutaneous temperatures to thermal comfort and autonomic responses in humans. Journal of Applied physiology 1999;86(5):1588–93]. The assessment of local comfort level is based on the maximum deviation of the clothed segments skin temperature from the mean skin temperature and its relation to the radiant temperature asymmetry. Experiments were run on human subjects at steady-state conditions to measure the variation of the skin temperature at different locations of the human body segments while standing in an asymmetric thermal radiation field generated by a stove-heating unit. The experiments were conducted to validate the applicability of the bioheat model in predicting skin temperature in asymmetric conditions. The measured skin temperature of various body segments and the radiative asymmetry agreed within ±5% of values predicted by the bioheat model [Salloum M, Ghaddar N, Ghali K. A new transient bio-heat model of the human body. In: Proceedings of the ASME 2005 summer heat transfer conference, 17–22 July 2005, San Francisco, Paper no. HT2005-72303]. The space heat model and the bioheat model are applied to a case study to predict both overall thermal comfort and local thermal discomfort in a typical radiant heat space at different standing positions of the person. Strong thermal discomfort exists within the vicinity of the stove high-temperature surface. The local discomfort is considered at values of maximum SD>1.1 °C derived from consideration of Fanger et al. [Fanger PO, Ipsen BM, Langkilde G, Olesen BW. Comfort limits for asymmetric thermal radiation. Energy and Buildings 1985;8(3):225–36] data of comfort limits and skin temperature measurements for asymmetric thermal radiation.