Assessment of thermal environment using a thermal manikin in a field environment chamber served by displacement ventilation system

This paper presents a thermal comfort study using a thermal manikin in a field environment chamber served by the Displacement Ventilation (DV) system. The manikin has a female body with 26 individually heated and controlled body segments. The manikin together with subjects was exposed to 3 levels of vertical air temperature gradients, nominally 1, 3 & 5 K/m, between 0.1 and 1.1 m heights at 3 room air temperatures of 20, 23 and 26 °C at 0.6 m height. Relative humidity at 0.6 m height and air velocity near the manikin and the subjects were maintained at 50% and less than 0.2 m/s, respectively. The aims of this study are to assess thermally non-uniform environment served by DV system using the manikin and correlate the subjective responses with measurements from the manikin. The main findings indicate that room air temperature had greater influence on overall and local thermal sensations and comfort than temperature gradient. Local thermal discomfort decreased with increase of room air temperature at overall thermally neutral state. The local discomfort was affected by overall thermal sensation and was lower at overall thermally neutral state than at overall cold and cool sensations.     

Using a thermal manikin

There are reputed to be only ten examples of the thermal manikin (a computerized doll) in the world at present. Here, the author discusses their potential in microclimate research, and describes experiments with a thermal manikin at the Hungarian Institute for Building Science (ETI) to identify the quality of indoor comfort conditions. One study revealed that the correct heating system would yield better results than extra thermal insulation.     

国内外暖体假人的研究现状

迄今为止暖体假人的发展可分为三个阶段,即:单段暖体假人,多段可活动的暖体假人,出汗暖体假人。目前世界各国已研发了100多个暖体假人,包括:干态暖体假人、出汗暖体假人、呼吸暖体假人、浸水暖体假人、数值暖体假人、小型暖体假人、暖体假头和假手、假脚等。今后暖体假人的研究应侧重于:计算服装的局部热阻;模拟人体非均匀出汗的暖体假人;数值暖体假人的验证;出汗小型暖体假人;能活动的暖体假手;暖体假人和外部控制系统的无线数据传输。     

Experimental investigation into the interaction between the human body and room airflow and its effect on thermal comfort under stratum ventilation

Room occupants' comfort and health are affected by the airflow. Nevertheless, they themselves also play an important role in indoor air distribution. This study investigated the interaction between the human body and room airflow under stratum ventilation. Simplified thermal manikin was employed to effectively resemble the human body as a flow obstacle and/or free convective heat source. Unheated and heated manikins were designed to fully evaluate the impact of the manikin at various airflow rates. Additionally, subjective human tests were conducted to evaluate thermal comfort for the occupants in two rows. The findings show that the manikin formed a local blockage effect, but the supply airflow could flow over it. With the body heat from the manikin, the air jet penetrated farther compared with that for the unheated manikin. The temperature downstream of the manikin was also higher because of the convective effect. Elevating the supply airflow rate from 7 to 15 air changes per hour varied the downstream airflow pattern dramatically, from an uprising flow induced by body heat to a jet‐dominated flow. Subjective assessments indicated that stratum ventilation provided thermal comfort for the occupants in both rows. Therefore, stratum ventilation could be applied in rooms with occupants in multiple rows.     

Measurement and prediction of indoor air quality using a breathing thermal manikin

The analyses performed in this paper reveal that a breathing thermal manikin with realistic simulation of respiration including breathing cycle, pulmonary ventilation rate, frequency and breathing mode, gas concentration, humidity and temperature of exhaled air and human body shape and surface temperature is sensitive enough to perform reliable measurement of characteristics of air as inhaled by occupants. The temperature, humidity, and pollution concentration in the inhaled air can be measured accurately with a thermal manikin without breathing simulation if they are measured at the upper lip at a distance of <0.01 m from the face. Body surface temperature, shape and posture as well as clothing insulation have impact on the measured inhaled air parameters. Proper simulation of breathing, especially of exhalation, is needed for studying the transport of exhaled air between occupants. A method for predicting air acceptability based on inhaled air parameters and known exposure-response relationships established in experiments with human subjects is suggested. PRACTICAL IMPLICATIONS: Recommendations for optimal simulation of human breathing by means of a breathing thermal manikin when studying pollution concentration, temperature and humidity of the inhaled air as well as the transport of exhaled air (which may carry infectious agents) between occupants are outlined. In order to compare results obtained with breathing thermal manikins, their nose and mouth geometry should be standardized.     

Thermal performance of a personalized ventilation air terminal device at two different turbulence intensities

The performance of a circular perforated panel (CPP) air terminal device for a personalized ventilation (PV) system operating under two levels of turbulent intensity (Tu) was examined. The impact of Tu on spatial distribution of the cooling effect on the facial region and whole body were studied through experiments carried out in an indoor environment chamber using a breathing thermal manikin and 24 tropically acclimatized subjects. The PV system was adjusted to deliver treated outdoor air over a range of conditions, which were presented blind to the subjects in a balanced order. Over a 15-min exposure, subjects voted their thermal sensation experienced at the facial region and whole body. At each of the conditions, the near body flow field characteristics and heat loss rate on each of the 26 body segments of the manikin were measured. The results indicate that over the range of PV air supply volume studied, by controlling the temperature and velocity of PV air supply at 15 cm from the face, PV air supplied at lower Tu, when compared against that supplied at higher Tu:

• Achieved a larger range of velocities at the face.

• Achieved a greater cooling effect on the head region.

• Achieved a lower facial thermal sensation, which has potential draft risks (when facial_thermal sensation vote <−1).

Computational analysis of reduced-mixing personal ventilation jets

In this paper we develop a detailed computational fluid dynamics (CFD) model of a personal ventilation (PV) setup comprising a PV nozzle, seated thermal manikin and floor diffuser, then use experimental velocity and tracer gas concentration data for the same setup to validate the CFD model. Specifically, we compare CFD results with the experimental results obtained with both a conventional round nozzle and a novel low-mixing co-flow nozzle directing a PV fresh air jet toward the breathing zone (BZ) of a seated thermal manikin in a thermally controlled chamber ventilated also by a floor diffuser behind the manikin. The CFD model shows excellent agreement with the experimental data. We then exercise the CFD model to study the effect of nozzle exit boundary conditions such as turbulence intensity and length scale, flow rate and temperature, and manikin temperature on the air quality in the BZ of the heated manikin. It is shown that the air quality of the novel PV system is sensitive to the nozzle exit turbulence intensity and flow rate, and insensitive to jet temperature within the 20–26 °C range, and to body temperature within a clo range of 0–1. A companion paper presents in detail the experimental set up and results used to validate the CFD model discussed in this paper.     

CFD simulation of naked flame manikin tests of fire proof garments

The overall performance of the thermal protective clothing can only be evaluated using an assessment based on an instrumented manikin under defined, close to real-life conditions in a laboratory. However, the manikin tests can only give a few of pointwise information. This paper presents a three-dimensional transient CFD simulation of heat and mass transfer in the flame manikin test of thermal protective clothing. The used grid model, simulated from Donghua Flame Manikin, have real dimensions and accurate shape of a typical Chinese man. The solver and physical models are defined in FLUENT system and the CFD simulation of a naked flame manikin test is accomplished. By means of CFD simulation, temperature and velocity fields on the manikin surface and of the whole chamber during the process of 4-second flash fire combustion are obtained, which give well predictions to the heat flux distribution in an average sense. The cumulative curve of heat fluxes in the CFD simulation is close to the curve measured by 135 sensors in the real manikin experiment. The study could be a foundation for further study on modeling heat and mass transfer in the clothed manikin experiment and predicting skin damage accurately.     

Influence of air stability and metabolic rate on exhaled flow

The characteristics of contaminant transport and dispersion of exhaled flow from a manikin are thoroughly studied in this article with respect to the influence of two important factors: air stability conditions and metabolic rates. Four cases with the combinations of stable and neutral conditions as well as lower (1.2 met) and higher (2 met) metabolic rates for a breathing thermal manikin are employed. The exhaled contaminant is simulated by smoke and N₂O to visualize and measure the contaminant distribution both around and in front of the manikin. The results show that the microenvironment around the manikin body can be affected by different air distribution patterns and metabolic heating. Under stable conditions, the exhaled contaminant from mouth or nose is locked and stratified at certain heights, causing potentially high contaminant exposure to others. In addition, velocity profiles of the pulsating exhaled flow, which are normalized by mean peak velocities, present similar shapes to a steady jet. The outlet velocity close to the mouth shows decrement with both exhalation temperature and body plume. The velocity decay and concentration decay also show significant dependence on air stability and metabolic level.     

Numerical investigations of the effects of manikin simplifications on the thermal flow field in indoor spaces

As one of the most basic parameters, manikin body feature could be an important factor influencing the airflow and temperature fields in indoor environments. This study aims to improve the computational efficiency by optimising and simplifying manikin body features. A 3D scanned computer-simulated person (CSP) with extremely detailed body features was employed, followed by two simplified CSP models with different approaches. One of the simplified models was rebuilt based on the skeleton of the 3D scanned model with very limited body features, while the other model was simplified by removing some of the features from the 3D scanned model. All CSPs were tested under quiescent condition, followed by further comparisons under displacement and mixed ventilations. The outcomes indicated that the geometric difference of manikin body would have significant impact on the airflow patterns near manikin bodies, whilst it has very limited influence on the temperature field. The difference of body features could significantly affect the development of thermal plume, which mainly reflected above the manikin head. Also, change of CSP body features due to simplifications may become more sensitive to the predicted results under mixed ventilation, as a result of fewer interactions between the thermal plume and injected airflow.     

Measuring the human body's microclimate using a thermal manikin

The human body is surrounded by a microclimate, which results from its convective release of heat. In this study, the air temperature and flow velocity of this microclimate were measured in a climate chamber at various room temperatures, using a thermal manikin simulating the heat release of the human being. Different techniques (Particle Streak Tracking, thermography, anemometry, and thermistors) were used for measurement and visualization. The manikin surface temperature was adjusted to the particular indoor climate based on simulations with a thermoregulation model (UCBerkeley Thermal Comfort Model). We found that generally, the microclimate is thinner at the lower part of the torso, but expands going up. At the head, there is a relatively thick thermal layer, which results in an ascending plume above the head. However, the microclimate shape strongly depends not only on the body segment, but also on boundary conditions: The higher the temperature difference between the surface temperature of the manikin and the air temperature, the faster the airflow in the microclimate. Finally, convective heat transfer coefficients strongly increase with falling room temperature, while radiative heat transfer coefficients decrease. The type of body segment strongly influences the convective heat transfer coefficient, while only minimally influencing the radiative heat transfer coefficient.     

Evaluation of thermal comfort using combined multi-node thermoregulation (65MN) and radiation models and computational fluid dynamics (CFD)

The 65-node thermoregulation model was developed, based on the Stolwijk model. The model has 16 body segments corresponding to the thermal manikin, each consisting of four layers for core, muscle, fat and skin. The 65th node in the model is the central blood compartment, which exchanges convective heat with all other nodes via the blood flow. Convective and radiant heat transfer coefficients and clothing insulation were derived from the thermal manikin experiments. A thermoregulation model combined with radiation exchange model and computational fluid dynamics (CFD) is proposed. The comprehensive simulation method is described.     

Modelling the effect of an occupant on displacement ventilation with computational fluid dynamics

Displacement ventilation of a room with an occupant is modelled using computational fluid dynamics (CFD) and compared against experimental data. The geometry of the experimental manikin is accurately represented in the CFD model to minimise potential errors from using a simplified form. Modelling thermal radiation from the manikin is found to be important and calculations using a radiation model show good agreement with experimental data. The influence of turbulence modelling is considered and a comparative study is made between an unsteady Reynolds-averaged approach (URANS) and detached-eddy simulation (DES). The results show that the URANS and DES give similar predictions with the DES results in slightly better agreement with the experimental data. The realistic manikin geometry is required to give accurate heat transfer and contaminant exposure predictions; such geometries can be handled with relative ease using current grid generation tools and CFD solvers.     

Person to person droplets transmission characteristics in unidirectional ventilated protective isolation room: The impact of initial droplet size

Person to person droplets/particles or contaminant cross transmission is an important issue in ventilated environment, especially in the unidirectional ventilated protective isolation room (UVPIR) where the patient’s immune system is extremely low and easily infected. We simulated the dispersion process of the droplets with initial diameter of 100 μm, 10 μm and gaseous contaminant in unidirectional ventilated protective isolation room and studied the droplets dispersion and cross transmission with different sizes. The droplets with initial size of 100 μm settle out of the coughing jet quickly after coming out from mouth and cannot be carried by the coughing jet to the human thermal plume affecting (HTPA) zone of the susceptible manikin. Hence, the larger droplets disperse mainly in the HTPA zone of the source manikin, and the droplets cross transmission between source manikin and susceptible manikin is very small. The droplets with initial size of 10 μm and gaseous contaminant have similar dispersion but different removal process in the UVPIR. Part of the droplets with initial size of 10 μm and gaseous contaminant that are carried by the higher velocity coughing airflow can enter the HTPA zone of the susceptible manikin and disperse around it. The other part cannot spread to the susceptible manikin’s HTPA zone and mainly spread in the source manikin’s HTPA zone. The results from this study would be useful for UVPIR usage and operation in order to minimize the risk of cross infection.     

Thermal comfort evaluation with virtual manikin methods

Computational fluid dynamics has become an important tool in the prediction of thermal comfort in occupied spaces. Despite its ability to predict temperature and velocity fields, it is more difficult to evaluate the degree of thermal comfort experienced by an occupant. This article describes the construction of a new numerical thermal manikin, with new comfort evaluation methods based on data from thermal manikin measurements as well as subjective results from several hundred experiments. The level of thermal comfort is highly dependent on the local environment. Human beings respond differently to local heat transfer in different parts of their bodies. It is suggested for that reason that local results from manikins should be presented in new clothing independent comfort zone diagrams. The research presented in here is intended to be used to evaluate system solutions that provide improved thermal climate in many different everyday situations, e.g. all types of buildings and vehicles.     

Effectiveness of a personalized ventilation system in reducing personal exposure against directly released simulated cough droplets

The inhalation intake fraction was used as an indicator to compare effects of desktop personalized ventilation and mixing ventilation on personal exposure to directly released simulated cough droplets. A cough machine was used to simulate cough release from the front, back, and side of a thermal manikin at distances between 1 and 4 m. Cough droplet concentration was measured with an aerosol spectrometer in the breathing zone of a thermal manikin. Particle image velocimetry was used to characterize the velocity field in the breathing zone. Desktop personalized ventilation substantially reduced the inhalation intake fraction compared to mixing ventilation for all investigated distances and orientations of the cough release. The results point out that the orientation between the cough source and the breathing zone of the exposed occupant is an important factor that substantially influences exposure. Exposure to cough droplets was reduced with increasing distance between cough source and exposed occupant.     

Personalized ventilation: evaluation of different air terminal devices

Personalized ventilation (PV) aims to provide clean air to the breathing zone of occupants. Its performance depends to a large extent on the supply air terminal device (ATD). Five different ATDs were developed, tested and compared. A typical office workplace consisting of a desk with mounted ATDs was simulated in a climate chamber. A breathing thermal manikin was used to simulate a human being. Experiments at room air temperatures of 26 and 20 °C and personalized air temperatures of 20 °C supplied from the ATDs were performed. The flow rate of personalized air was changed from less than 5 up to 23 l/s. Tracer gas was used to identify the amount of personalized air inhaled by the manikin as well as the amount of exhaled air re-inhaled. The heat loss from the body segments of the thermal manikin was measured and used to calculate the equivalent temperature for the whole body as well as segments of the body. An index, personal exposure effectiveness, was used to assess the performance of ATDs in regard to quality of the air inhaled by the manikin. The personal exposure effectiveness increased with the increase of the airflow rate from the ATD to a constant maximum value. A further increase of the airflow rate had no impact on the personal exposure effectiveness. Under both isothermal and non-isothermal conditions the highest personal exposure effectiveness of 0.6 was achieved by a vertical desk grill followed by an ATD designed as a movable panel. The ATDs tested performed differently in regard to the inhaled air temperature used as another air quality indicator, as well as in regard to the equivalent temperature. The results suggest that PV may decrease significantly the number of occupants dissatisfied with the air quality. However, an ATD that will ensure more efficient distribution and less mixing of the personalized air with the polluted room air needs to be developed.     

Numerical analysis of air flow, heat transfer, moisture transport and thermal comfort in a room heated by two-panel radiators

A three-dimensional steady-state numerical analysis was performed in a room heated by two-panel radiators. A virtual sitting manikin with real dimensions and physiological shape was added to the model of the room, and it was assumed that the manikin surfaces were subjected to constant temperature. Two different heat transfer coefficients for the outer wall and for the window were considered. Heat interactions between the human body surfaces and the room environment, the air flow, the temperature, the humidity, and the local heat transfer characteristics of the manikin and the room surfaces were computed numerically under different environmental conditions. Comparisons of the results are presented and discussed. The results show that energy consumption can be significantly reduced while increasing the thermal comfort by using better-insulated outer wall materials and windows.     

Performance of “ductless” personalized ventilation in conjunction with displacement ventilation: Impact of intake height

The importance of the intake positioning height above the floor level on the performance of “ductless” personalized ventilation (“ductless” PV) in conjunction with displacement ventilation (DV) was examined with regard to the quality of inhaled air and of the thermal comfort provided. A typical office room with two workstations positioned one behind the other was arranged in a full-scale room. Each workstation consisted of a table with an installed “ductless” PV system, PC, desk lamp and seated breathing thermal manikin. The “ductless” PV system sucked the clean and cool displacement air supplied over the floor at four different heights, i.e. 2, 5, 10 and 20 cm and transported it direct to the breathing level. Moreover, two displacement airflow rates were used with a supply temperature adjusted in order to maintain an exhaust air temperature of 26 °C. Two pollution sources, namely air exhaled by one of the manikins and passive pollution on the table in front of the same manikin were simulated by constant dosing of tracer gases. The results show that the positioning of a “ductless” PV intake height up to 0.2 m above the floor will not significantly influence the quality of inhaled air and thermal comfort.     

A comparison between tracer gas and aerosol particles distribution indoors: The impact of ventilation rate,interaction of airflows,and presence of objects

The study investigated the separate and combined effects of ventilation rate, free convection flow produced by a thermal manikin, and the presence of objects on the distribution of tracer gas and particles in indoor air. The concentration of aerosol particles and tracer gas was measured in a test room with mixing ventilation. Three layouts were arranged: an empty room, an office room with an occupant sitting in front of a table, and a single‐bed hospital room. The room occupant was simulated by a thermal manikin. Monodisperse particles of three sizes (0.07, 0.7, and 3.5 μm) and nitrous oxide tracer gas were generated simultaneously at the same location in the room. The particles and gas concentrations were measured in the bulk room air, in the breathing zone of the manikin, and in the exhaust air. Within the breathing zone of the sitting occupant, the tracer gas emerged as reliable predictor for the exposure to all different‐sized test particles. A change in the ventilation rate did not affect the difference in concentration distribution between tracer gas and larger particle sizes. Increasing the room surface area did not influence the similarity in the dispersion of the aerosol particles and the tracer gas.