Personalized Ventilation Research Articles

Simplified model for thermal comfort, IAQ and energy savings in rooms conditioned by displacement ventilation aided with transient personalized ventilation

The aim of this work is to evaluate the performance of an intermittent personalized ventilation (PV) system assisting a displacement ventilation (DV) system based on its ability in improving thermal comfort and protecting occupants from floor emitted passive contaminants. A simplified transient mathematical model was developed of heat and species transport to predict the temperature and concentration fields in the macroclimate room air, in the thermal plume induced by the occupant and internal heat sources and within the intermittent PV jet facing the occupant face at a fixed distance. The model’s predictions of temperature and concentration were experimentally validated for a PV frequency range [0.3–1 Hz] in a climatic chamber conditioned with a DV system assisted with an intermittent PV jet. Good agreement was found between the predicted and measured values of temperature and concentration of tracer gas in the different regions of macroclimate air, thermal plume, and PV jet.The validated model was used to conduct a case study where comfort and air quality were assessed and the energy consumption of the transient PV + DV system was compared to steady PV + DV and standalone DV systems. It was found that the intermittent PV range [0.3–1 Hz] was able to improve comfort compared to steady PV and provide acceptable air quality. Moreover, energy analysis showed that the intermittent PV + DV (40 L/s) was able to achieve maximum energy savings of 54.61% and 31.58% compared to a standalone DV and steady PV respectively for equivalent comfort.

Performance assessment of a ductless personalized ventilation system using a validated CFD model

The aim of this study is twofold: to validate a computational fluid dynamics (CFD) model, and then to use the validated model to evaluate the performance of a ductless personalized ventilation (DPV) system. To validate the numerical model, a series of measurements was conducted in a climate chamber equipped with a thermal manikin. Various turbulence models, settings, and options were tested; simulation results were compared to the measured data to determine the turbulence model and solver settings that achieve the best agreement between the measured and simulated values. Subsequently, the validated CFD model was then used to evaluate the thermal environment and indoor air quality in a room equipped with a DPV system combined with displacement ventilation. Results from the numerical model were then used to quantify thermal sensation and comfort using the UC Berkeley thermal comfort model.

A Numerical Analysis of the Air Distribution System for the Ventilation of the Crew Quarters on board of the International Space Station

Quality of life on the International Space Station (ISS) has become more and more important, since the time spent by astronauts outside the terrestrial atmosphere has increased in the last years. The actual concept for the Crew Quarters (CQ) have demonstrated the possibility of a personal space for sleep and free time activities in which the noise levels are lower, but not enough, compared to the noisy ISS isle way. However, there are several issues that needs to be improved to increase the performance of CQ. Our project QUEST is intended to propose a new concept of CQ in which we will correct these issues, like the noise levels will be lower, more space for astronaut, increased thermal comfort, reduce the CQ total weight, higher efficiency for the air distribution, personalized ventilation system in CQ for the crew members in order to remove CO2 from the breathing zone. This paper presents a CFD study in which we are comparing the actual and a proposed ventilation solution for introducing the air in CQ. A preliminary numerical model of the present configuration of the air distribution system of the Crew Quarters on board of the ISS, shows the need for an improved air distribution inside these enclosures. Lower velocity values at the inlet diffuser, distributed over a larger surface, as well as diffusers with improved induction would appear to be a better choice. This was confirmed through the development of a new model including linear diffusers with a larger discharge surface. In this new configuration, the regions of possible draught are dramatically reduced. The overall distributions of the velocity magnitudes displaying more uniform, lower values, in the same time with more uniform temperatures. All these observations allow us to consider a better mixing of the air inside the enclosure.

Optimization of ventilation system in the open office space

The paper presents the results of study into the air parameters in open space offices. As office workers spend about 1/3 of the day in such spaces, it is important to provide them with the right climate comfort, and that is determined, most importantly, by: the temperature and humidity of the air, quality of the air, and the concentration of CO2. Two objects of study were selected - both of them open space facilities, each with a different intensity of use. In the course of study, measurements were taken on the basis of which the distributions of temperature, humidity, and concentrations of CO2 in the entire volume of the space were determined. Also the empirical coefficients of CO2 emission by the office workers were marked out, dependent on the volume of the working area and the number of people using it. The coefficients were developed at optimal working parameters of fans in the ventilation system; the criterion for optimization being heat loss in the office caused by discharge of the used heated air into the atmosphere. The results of the study have also shown that the use of personal ventilation (PV) with an installed recuperator for heat recovery from the used air discharged from the room significantly improves the energy efficiency of an open space office building.

Effectiveness of intermittent personalized ventilation in protecting occupant from indoor particles

In this study, the performance of an intermittent periodic personalized ventilation (PV) coupled with mixing ventilation (MV) was investigated with respect to its ability in protecting occupant from contaminants present in the space. To perform this study, a transient 3D computational fluid dynamics (CFD) model was used to assess the velocity, temperature and particle concentration fields in the space. Experiments were performed in a climatic chamber using a thermal manikin in order to validate the CFD model's predictions of the fluid flow and particle distribution in the space at supply MV flow rate of 63 L/s and room temperature of 28 °C and PV average flow rate of 3.5 L/s, supply temperature of 24 °C, and frequencies of 0.3 Hz and 1 Hz. Good agreement was found between the CFD model and experiments.The validated model was used to recommend PV operating parameters which would assure occupant protection from macroclimate contaminants' migration to the breathing zone and microclimate surrounding the occupant, and reduce particles' deposition on the surfaces in occupant proximity. It was found that an average flowrate of 7.5 L/s as well as an operating frequency of 0.86 Hz provided acceptable values of intake fractions in the breathing zone and the surrounding microclimate as well as acceptable values of deposition rates. These conditions provide good thermal comfort levels (0.87: comfortable), and good ventilation effectiveness (77.1%).

Impact of elevated air velocity on subjective thermal comfort sensation under asymmetric radiation and variable airflow direction

Buildings rarely have homogeneous thermal indoor environments. Transparent building elements are one of the sources of thermal asymmetry. Using advanced personalised ventilation systems, the discomfort caused by radiation asymmetry may be reduced. A series of measurements involving 20 subjects were carried out under controlled environmental conditions to investigate subjective thermal comfort in the case of asymmetric radiation combined with the personalised ventilation. Analysis showed that the subjective thermal comfort sensation without a personalised ventilation system is similar to the calculated predicted mean vote. However, there is a significant difference between the responses of female and male participants. The advanced personalised ventilation system lowers the subjective thermal comfort sensation, but does it differently for men and women. The skin temperatures of the hands of the women were significantly lower than that of the men. In the case of the men, radiation asymmetry led to significant differences in the facial skin temperature, while in the case of the women, the differences in the facial skin temperature were not significant.

Experimental investigation on thermal comfort model between local thermal sensation and overall thermal sensation

To study the human local and overall thermal sensations, a series of experiments under various conditions were carried out in a climate control chamber. The adopted analysis method considered the effect of the weight coefficient of local average skin temperature and density of the cold receptors’ distribution in different local body areas. The results demonstrated that the thermal sensation of head, chest, back and hands is warmer than overall thermal sensation. The mean thermal sensation votes of those local areas were more densely distributed. In addition, the thermal sensation of arms, tight and calf was colder than the overall thermal sensation, which pronounced that thermal sensation votes were more dispersed. The thermal sensation of chest and back had a strong linear correlation with overall thermal sensation. Considering the actual scope of air-conditioning regulation, the human body was classified into three local parts: a) head, b) upper part of body and c) lower part of body. The prediction model of both the three-part thermal sensation and overall thermal sensation was developed. Weight coefficients were 0.21, 0.60 and 0.19 respectively. The model provides scientist basis for guiding the sage installation place of the personal ventilation system to achieve efficient energy use.

Investigation of thermal comfort and the nozzle usage behaviour in aircraft cabins

In order to understand passengers’ demand for thermal comfort in aircraft cabins, we carried out a measurement of thermal environment parameters and thermal comfort field survey in an aircraft cabin under cruising at altitude in both summer and winter. The results showed that the air temperature studied was always kept within the range of 25℃ to 28℃ and the relative humidity was maintained within the range of 20% to 35%. The Mean Thermal Sensation Vote (MTSV) of passengers’ back and feet was higher than other local body parts, with lower air movement sensation. The MTSV of passengers in winter was higher than that in summer. Due to the muggy thermal environment, more than 60% of passengers advocated that it was necessary to utilize the personal ventilation system. In their usage of the personal ventilation nozzle, more than half of these passengers chose to cool upper body parts, only a minimum number of passengers opened the nozzle to direct airflow to their head. Therefore, we concluded that the position of the personal ventilation nozzle should be as close to the upper body part of a passenger’s body as possible, making it more convenient and effective to regulate passengers’ thermal comfort.

Numerical and experimental study of personalized ventilation installed in a double occupation desk placed nearby a window subjected to solar radiation

ABSTRACTIn this study the thermal comfort, the local thermal discomfort and the air quality levels, experienced by two occupants seated at a classroom desk are analysed. The desk is equipped with personalized ventilation systems and is positioned nearby a window subjected to solar radiation. Experimental observations are based on a manikin study and results are compared with CFD analysis using the k-epson and the RNG turbulent models. In the experimental tests the air velocity and temperature were measured in the air terminal devices and around the human body. Relative humidity was measured inside the space, solar radiation was evaluated in the window glass and the Mean Radiant Temperature was numerically evaluated.In the numerical methodology, the thermal comfort level in a non-uniform environment was evaluated using the developed multi-nodal human thermal comfort numerical model, the local thermal discomfort level is evaluated through empirical models, while the air quality level and the detailed airflow around the occupants were evaluated using CFD analysis.

Mixing ventilation coupled with personalized sinusoidal ventilation: Optimal frequency and flow rate for acceptable air quality

This study investigates and optimizes the performance of a localized dynamic personalized ventilation (PV) coupled with a mixing ventilation system (MV). A transient computational fluid dynamics model (CFD) was used to assess the velocity, temperature and CO2 fields around the occupant microclimate. The CFD model was also coupled with a transient bio-heat model to compute the segmental skin temperatures, overall thermal sensation and comfort. The model was then validated experimentally by using a thermal manikin in a climatic chamber representing an occupant in a typical office space. There was a good agreement between experimental and predicted values. The model was then used to optimize the operating frequency and average flowrate for the best thermal comfort and ventilation effectiveness. The optimal operating conditions of the localized dynamic airflow for a background temperature of 26°C and a PV temperature of 22°C, were for an average supply flowrate of 7.5L/s and a frequency of 0.94Hz providing an overall comfort of 0.95 (comfortable) on a comfort scale from very uncomfortable at −4 to very comfortable at +4 and a ventilation effectiveness of 77%. These conditions were able to provide the best compromise between comfort and air quality. They were also able to reduce energy costs by 21.34% compared to a constant personalized ventilation system providing the same levels of comfort.

Numerical Simulation of Energy Utilization Coefficient Influenced by Desktop Personalized Ventilation Modes

The development of building energy saving technology makes the personalized air supply mode as a new energy saving way to be applied to achieve the required cooling and energy saving purposes. This topic in the summary of personalized ventilation research results based on, the numerical simulation is used to study various personalized send wind end and air supply conditions on the effect of task ambient airflow energy utilization coefficient, in order to explore in different working conditions and a variety of desktop personalized send wind end of energy-saving effect. Research results show that the personalized mobile (MP) send wind end, in m3 under the condition of energy utilization coefficient are the highest, indicating that the mobile type tuyere this personalized send wind of indoor airflow energy using coefficient was the highest, and the energy-saving effect is the best.Numerical simulation method was used to study the effect of air supply temperature and air supply angle on thermal comfort of air conditioning room in an office and the indoor thermal environment is evaluated by using the energy utilization coefficient index. The research results show that, with the increase of the air supply angle, the PPD value indoor increased at first and then decreased, and the maximum value is reached when the air supply angle is 90 degrees; under the condition of stratum ventilation, the effect of air supply angle and air supply temperature on energy utilization was small, and the energy utilization coefficient in different working conditions is more than 1, which has a certain energy saving effect.

An indoor environment evaluation by gender and age using an advanced personalized ventilation system

In a closed space, appropriate thermal comfort and proper indoor air quality are extremely important in order to obtain the optimal work performance and to avoid health problems of the occupants. Using advanced personalized ventilation systems, different comfort needs can be locally satisfied even in case of warm environments. Thermal sensation and the subjective evaluation of indoor air quality of young and elderly people, men and women respectively, were studied in warm environment using advanced personalized ventilation system combined with total volume ventilation system. Using an advanced personalized ventilation system, 20 m3 h−1 air flow was alternately introduced by three air terminal devices built-in the desk and placed on a horizontal plane at the head level of the sitting subject. Thermal sensation was significantly cooler in case of young women in comparison with the other groups. Odor intensity was evaluated to be significantly lower in case of elderly women in comparison with the other groups. Evaluation of air freshness is in correlation with the general thermal sensation. Variation of the direction of the air velocity vector has a cooling side-effect, which, in warm environments, might be useful in order to improve the thermal comfort sensation. Practical application: From the basic factors that influence the thermal comfort sensation, air velocity is the one and only parameter that must be treated as a vector. The air flow velocity has an important effect on the convective heat quantity released by the human body, but the changes in the air velocity direction have a cooling side-effect. This cooling side-effect should be exploited properly in warm environments by advanced personalized ventilation systems to improve the thermal comfort sensation of the occupants without supplementary energy use.

Sensitivity of personalized ventilation air terminal device geometry with regard to a human thermal sensation

Thermal comfort of people using personalized ventilation system is affected by the amount of air and the air terminal devices. However impact of small changes in air terminal device's geometry alone has not been examined and assessed. The aim of the current article was to compare thermal sensations and productivity of users who used three kinds of personalized ventilation air terminal devices with similar construction (the same size of a box, the same perforated surface used inside) and differs in spacing of blinds used at the outlet of the device. During the measurement volunteers were asked to complete a questionnaire survey containing questions about: local and general thermal comfort, air movement, expectations for thermal environment, dryness of the eye, and their mood and fatigue. Statistical analysis were conducted to examine whether significant differences in volunteers responses among air terminal devices occur. The results showed the significance of the geometry and design of air terminal device on user’ thermal sensations. Changes in the perception of thermal environment were mostly felt after 2 and 3 h of exposure to the microenvironment shaped by personalized ventilation. The changes concerned mainly the perception of thermal environment, which also translated into respondents' self-assessment and, in the long-term, into their productivity.

Numerical Simulation of Air Terminal Type on Thermal Environment of Occupied Zone under Desktop Personalized Ventilation

With the development of the energy-saving building technology, the personalized air supply mode has been applied to achieve the purposes of the required cooling and energy-saving as a new energy-efficient method. This study was based on the study of domestic and foreign research results and the numerical simulation method was used to investigate the temperature distribution, velocity distribution and energy utilization coefficient of the human body in the desktop personalized air supply systems of the desktop, finally, a reasonable method of terminal air supply and air supply parameters were given.

Energy Saving Potential of Personalized Ventilation Applied in an Open Space Office under Winter Conditions

Mixing and displacement air distribution are the main ventilation principles applied in both residential and non-residential buildings. Recently, personalized ventilation when the fresh air is delivered directly to the occupants at a high ventilation effectiveness has become an alternative. Despite of this fact, little research has been carried out to quantify the energy saving potential of personalized ventilation. This study aimed to quantify the effect of ventilation effectiveness and control strategy on the energy performance and thermal comfort for an open plan office equipped by different types of ventilation systems, including mixing ventilation with constant air volume, demand control ventilation and personalized ventilation. A model was created in a program for dynamic energy simulations TRNSYS, representing one floor of a typical office building divided into four zones with different orientations and a core. Space heating and cooling were provided by ceiling fancoil units recirculating the room air, thus the tasks of ventilation and air conditioning were provided by two separate systems. The potential of personalized ventilation to save energy for fans and for the heating coil of the ventilation system presented about 70% compared to constant air volume mixing ventilation, however, the overall saving was only 20% when also the energy demand for space heating was considered. The energy benefit of demand control ventilation and personalized ventilation depends on the energy need for space heating and cooling, system configuration and operation, and occupancy.

Influence of sinusoidal airflow and airflow distance on human thermal response to a personalized ventilation system

Since the concept of personalized ventilation was introduced in the late 1990s, many studies on thermal comfort have been conducted and a number of parameters identified. In this research, the influence of three parameters, the airflow speed, airflow fluctuating period and a parameter which has drawn less attention in previous studies – the airflow distance between the human subject and the nozzle of the personalized ventilation device on air movement perception, thermal sensation and thermal comfort – are studied. The combinations of fluctuating period and airflow amplitude were selected based on the Power Spectrum Density method. Then 25 human subjects participated in the thermal comfort experiment, each of them underwent 54 tests of different experimental conditions and expressed their thermal feelings by completing the survey questionnaire. Our findings showed that a longer airflow distance could lead to cooler thermal sensation, but not cause any difference in thermal comfort. Changing the fluctuating period of the sinusoidal airflow from 10 s to 60 s did not cause an influence on thermal sensation, but a shorter fluctuating period could result in a higher air movement perception. When dealing with thermal comfort issues, a joint effect with airflow speed and fluctuating period occurs and this should also be considered.

Control of sleep environment of an infant by wide-cover type personalized ventilation

With a validated computational fluid dynamics (CFD) program, we investigated the potential for a wide-cover type personalized ventilation (WCPV) system to reduce the risk of Sudden Infant Death Syndrome (SIDS) due to thermal stress, rebreathing of expired carbon dioxide and exposure to airborne pathogens for a sleep infant. The WCPV system was intended to minimize draft discomfort by blowing cooled air upward and then descending uniformly and slowly over a sleep infant's head. Two settings for personalized airflow were simulated: a spreading angle of 75° (WCPV-75°) and 35° (WCPV-35°) above the horizontal plane. Simulations demonstrated that a well ventilated comfort microenvironment could be maintained around the infant's head with air temperature varying between 19 and 22°C and draft rate kept under 15%. For the infant with supine position, the average time for the air from both ambient and personalized ventilations to reach the infant's inhalation decreased by 29.3% with WCPV-75° and 89.0% with WCPV-35°. Moreover, the infant's exposure to the infectious influenza quanta from an adult standing aside the bed decreased by 54.3% with WCPV-75° and 80.4% with WCPV-35°. On the other hand, WCPV-35° could take 90.3% less time to deliver 26.6% more personalized air to the infant. For the infant with face-to-side sleep position, the WCPV would also improve the infant's microenvironment. A smaller spreading angle resulted in a much better performance, while a bigger spreading angle led to a better “wide-cover” effect.

Experimental investigation on the airflow characteristics of an attachment-based personalized ventilation method

An attachment-based personalized ventilation method, different from the traditional personalized ventilation methods in mechanisms, is presented in this study to improve the micro-environment surrounding a human body. To identify the airflow characteristics of this personalized ventilation method, field measurements were performed to examine the air distribution via the airflow fields near the body. Three factors on the airflow fields under the personalized ventilation method were analyzed in this study, including the supplied air velocity, the horizontal distance between the air outlet and the human body, the vertical distance between the air outlet and the head of the man. According to the measurements in this study, the results show that the higher the supplied air velocity, the more easily the air attachment is formed. For a certain horizontal distance and a certain vertical distance, air attachment is formed only when the supplied air velocity is greater than a critical supplied air velocity. That critical supplied air velocity is an increasing function of the horizontal distance. When the horizontal distance reaches 0.3 m and regardless of the value of the supplied air velocity, air attachment cannot be formed. In addition, the critical supplied air velocity decreases with the vertical distance. Based on the field measurements, design parameters of the personalized ventilation method are analyzed to achieve optimization. Practical application: A novel personalized ventilation method, which is based on air attachment, is introduced in this paper. Such a personalized ventilation method can be applied to the worktable in factory, office, kitchen, and so on. The experimental results indicate that the novel personalized ventilation method can meet the requirements of fresh air in the breathing zone and provide an acceptable thermal comfort for occupants under certain conditions.

Optimizing performance of ceiling-mounted personalized ventilation system assisted by chair fans: Assessment of thermal comfort and indoor air quality

This study investigates and optimizes the performance of ceiling-mounted personalized ventilation system when assisted with chair-mounted fans. Detailed computational fluid dynamics simulations were performed to study the velocity, temperature, and CO2 fields around the microclimate of the occupant. The computational fluid dynamics model was integrated with a bio-heat model to determine the corresponding segmental skin temperature and local and overall comfort and sensation. The computational fluid dynamics model was validated experimentally using a thermal manikin in a climatic chamber. The segmental skin temperature, velocity field, and CO2 field were validated experimentally. The predicted values and the measured values showed good agreement. The validated computational fluid dynamics model was used to optimize the height of the chair fan and the fan flow rate for the best combination of indoor air quality and thermal comfort. The chair fan's configuration to achieve the best thermal comfort and the best indoor air quality occurred at different fan heights. The optimal fan height and flow rate for best thermal comfort were 40 cm (15.75 in.) above floor level and 10 L/s (0.35 ft3/s), respectively. However, the optimal fan height and flow rate for best air quality were found to be 50 cm (19.69 in.) above the floor level and 10 L/s (0.35 ft3/s), respectively. At this configuration, the chair-mounted fans were able to reduce the thermal plumes and improve the performance of the personalized ventilation system by nearly doubling thermal comfort and ventilation effectiveness. The use of chair-mounted fans allowed for the achievement of energy savings up to 17% when compared with conventional mixing ventilation system.

Effect of shifts from occupant design position on performance of ceiling personalized ventilation assisted with desk fan or chair fans

Recently, personalized ventilation systems have gained popularity since they consist on localizing the occupant needs in terms of thermal comfort and indoor air quality (IAQ). Localized ventilation systems are designed on the basis of fixed occupant position. Since people move and do not remain in same position, it is of interest to study personalized ventilation system performance with respect to shifts from occupant design position. The aim of this work is to study and compare the performance of ceiling personalized ventilation (CPV) when aided with desk fans (DF) versus chair fans (CF) in crowded office spaces for shifts from seated occupant chair position with respect to the CPV jet. A computational fluid dynamics (CFD) model for particle transport and deposition was developed to simulate a two-station office ventilated by CPV system to predict particle transport and to assess ventilation effectiveness. The CFD model was coupled with a bio-heat model to predict segmental and overall sensation and comfort in addition to segmental skin temperatures. In this work, experiments were conducted to validate the CFD model accuracy in capturing the effect of the CF on particle transport.The use of CF allowed the reduction of CPV flow rate by 22.72% resulting in energy savings of 14.87% for the case where the occupant was beneath the jet. Installing CFs allowed maintaining good performance of the system when chair shift due to movement of person occurred while installing DFs resulted in largely degrading the system performance at equal chair shift from the CPV center.