Personalized Ventilation Research Articles

Performance of Ductless Personalized Ventilation in Conjunction with Displacement Ventilation: Impact of Workstations Layout and Partitions

The performance of a new personalized ventilation system, referred to as ductless personalized ventilation (DPV), was studied in full-scale room experiments in conjunction with displacement ventilation (DV). The idea behind DPV is to utilize clean and cool air supplied via DV. In the experiment, the DPV, consisting of an air supply terminal device, a small fan, and a short duct, sucked clean air from floor level near the desk. The performance of the DPV system was evaluated under various arrangements of two identical workstations. Two breathing thermal manikins were used to simulate seated occupants. Two tracer gases, one mixed with the air exhaled by one of the manikins and the other generated on the table in front of the same manikin, were used to simulate pollution. When the DPV system was operational, the inhaled air was as clean as the air inhaled using only the DV alone and even cleaner for some of the layouts studied. The use of DPV in conjunction with DV substantially decreased the temperature of the inhaled air and increased the body cooling in comparison with use of DV alone, i.e., DPV also had potential for improving occupants' perceived air quality and thermal comfort.

Energy analysis of the personalized ventilation system in hot and humid climates

Personalized ventilation (PV) is an individually controlled air distribution system aimed at improving the quality of inhaled air and the thermal comfort of each occupant. Numerous studies have shown that PV in comparison with traditional mechanical ventilation systems may improve occupants’ health, inhaled air quality, thermal comfort, and self-estimated productivity. Little is known about its energy performance. In this study, the energy consumption of a personalized ventilation system introduced in an office building located in a hot and humid climate (Singapore) has been investigated by means of simulations with the empirically tested IDA-ICE software. The results reveal that the use of PV may reduce the energy consumption substantially (up to 51%) compared to mixing ventilation when the following control strategies are applied: (a) reducing the airflow rate due to the higher ventilation effectiveness of PV; (b) increasing the maximum allowed room air temperature due to PV capacity to control the microclimate; (c) supplying the outdoor air only when the occupant is at the desk. The strategy to control the supply air temperature does not affect the energy consumption in a hot and humid climate.

On the Control of Environmental Conditions Using Personal Ventilation Systems

The concept of personal control is examined as this relates to the conceptual design of personal ventilation systems based upon the body's physiological and psychological homeostatic requirements. Literature on the effects of personal control of environmental conditions is reviewed. The concept of a “just noticeable difference in discomfort” that underpins the desire to initiate some personal control action is discussed. The concept of personal control is symmetrical for thermal conditions (hot or cold) but, apart from some pleasant fragrances, is asymmetric for indoor air quality (where less pollution is better). Factors that may influence the exercise of personal control will be summarized. Finally, important information for the design of PVS systems that are both energy efficient and effective in optimizing the micro-environmental conditions for workplace employees will be presented.

Personalized ventilation as a control measure for airborne transmissible disease spread.

The protective role of personalized ventilation (PV) against plausible airborne transmissible disease was investigated using cough droplets released from a 'coughing machine' simulating the human cough at different distances (1, 1.75 and 3 m) from the PV user. Particle image velocimetry was used to characterize and visualize the interaction between the cough-generated multiphase flow and PV-induced flow in the inhalation zone of the thermal breathing manikin. A dose-response model for unsteady imperfectly mixed environment was used to estimate the reduction in infection risk of two common diseases that can be transmitted by airborne mode. PV was able to both reduce the peak aerosol concentration levels and shorten the exposure time at all the examined injection distances. PV could reduce the infection risks of two diseases, influenza A and tuberculosis, by between 27 and 65 per cent. The protection offered by PV is less effective at a distance of 1.75 m than the other distances, as shown in the risk assessment results, as the PV-generated flow was blown off by the cough-generated flow for the longest time. Results of this study demonstrate the ability of desktop PV to mitigate the infection risk of airborne transmissible disease.

On the Control of Environmental Conditions Using Personal Ventilation Systems

The concept of personal control is examined as this relates to the conceptual design of personal ventilation systems based upon the body's physiological and psychological homeostatic requirements. Literature on the effects of personal control of environmental conditions is reviewed. The concept of a “just noticeable difference in discomfort” that underpins the desire to initiate some personal control action is discussed. The concept of personal control is symmetrical for thermal conditions (hot or cold) but, apart from some pleasant fragrances, is asymmetric for indoor air quality (where less pollution is better). Factors that may influence the exercise of personal control will be summarized. Finally, important information for the design of PVS systems that are both energy efficient and effective in optimizing the micro-environmental conditions for workplace employees will be presented.

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.

Design of an individually controlled system for an optimal thermal microenvironment

Individually controlled microenvironment has potential to satisfy more occupants in a space compared to a total volume uniform environment typically used at present. The performance of an individually controlled system comprising a convection-heated chair, an under-desk radiant heating panel, a floor radiant heating panel, an under-desk air terminal device supplying cool air, and a desk-mounted personalized ventilation as used and identified by 48 human subjects was studied using a thermal manikin at room temperatures of 20 °C, 22 °C and 26 °C. At a room air temperature of 20 °C, the maximum whole-body heating effect of the heating chair, the under-desk heating panel, and the floor heating panel corresponded to the effect of a room temperature increase of 5.2 °C, 2.8 °C, and 2.1 °C, respectively. The effect was 5.9 °C for the combination of the three heating options. The higher the room air temperature, the lower the heating effect of each heating option or heating combination. The maximum whole-body cooling effect of the tested system was only −0.8 °C at a room air temperature of 26 °C. The heating and cooling capacity of the individually controlled system were identified. These results, analyzed together with results obtained from human subject experiments, reveal that both the heating and the cooling capacity of the individually controlled system need to be increased in order to satisfy most occupants in practice.

Energy-saving strategies with personalized ventilation in cold climates

In this study the influence of the personalized supply air temperature control strategy on energy consumption and the energy-saving potentials of a personalized ventilation system have been investigated by means of simulations with IDA-ICE software. GenOpt software was used to determine the optimal supply air temperature. The simulated office room was located in a cold climate. The results reveal that the supply air temperature control strategy has a marked influence on energy consumption. The energy consumption with personalized ventilation may increase substantially (in the range: 61–268%) compared to mixing ventilation alone if energy-saving strategies are not applied. The results show that the best supply air temperature control strategy is to provide air constantly at 20 °C. The most effective way of saving energy with personalized ventilation is to extend the upper room operative temperature limit (saving up to 60% compared to the reference case). However, this energy-saving strategy can be recommended only in a working environment where the occupants spend most of their time at their workstation. Reducing the airflow rate does not always imply a reduction of energy consumption. Supplying the personalized air only when the occupant is at the desk is not an effective energy-saving strategy.

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.

Experimental investigation of reduced-mixing personal ventilation jets

This paper presents an investigation of the design and performance characteristics of personalized ventilation (PV) systems that, in combination with general ventilation, deliver high quality air to the breathing zone (BZ) with no more clean air supply than indicated by ANSI/ASHRAE 62.1-2004, while satisfying acceptable ergonomic and aesthetic considerations. Under these conditions, the energy used for conditioning the clean air will not exceed that of a conventional ventilation system. We introduce a novel PV nozzle that achieves high BZ air quality with a small fraction of the clean air indicated by the ANSI/ASHRAE Standard. Tracer gas experimental results presented in this paper demonstrate the advantages of the novel nozzle relative to conventional PV nozzles. The results show that, at a PV clean air supply of only 2.4 l/s, the new nozzle achieves a BZ ventilation effectiveness close to 7 versus less than 2 for a conventional nozzle delivering the same amount of clean air. A companion paper presents a computational analysis of the same concept, validated against the experimental results of the present paper.

The Influence of Evenly Distributed Ceiling Mounted Personalized Ventilation Devices on the Indoor Environment

The advantage of conventional personalized ventilation (PV) is to considerably improve the fresh air percentage near PV air terminal devices (ATDs). However, the distribution of the fresh air percentage is very uneven in the field. Occupants are confined to their working zones in order to obtain good inhaled air quality. Ceiling mounted PV can overcome the disadvantages of conventional PV, although the fresh air percentage is lower than that of conventional PV near working zones. A typical office workplace consisting of either ceiling mounted PV ATDs or conventional PV ATDs and ambient air supply diffusers is simulated, based on an indoor air quality chamber at the National University of Singapore. Based on the numerical results, it is concluded that ceiling mounted PV can improve inhaled air quality for both seated occupants and moving occupants over a longer occupied area although conventional PV can improve inhaled air quality much better in the immediate breathing zones at the work stations.

Verification of dC(1) Parameter for Measuring the Effectiveness of a Personalized Ventilation System

An analysis of the ventilation effectiveness of a prototype personalized ventilation system of working places named PERMICS-LOS1 (Personal Microclimate System) was made, based on measurements of the air velocity field and of tracer gas concentrations using the decay method. The emphasis of the analysis was mainly on an experimental verification of a parameter based on the relative decrease of tracer gas concentration in the first minute of system operation dC(1) and on local ventilation efficiency using the local air-change index ∊L.. A system analysis was made for several different operating regimes of personalized ventilation, where changes in air quantity and the direction of supplied air in the breathing zone were applied. The results of the experimental analysis were statistically evaluated, compared, and included in the existing database of previous research for use as supplementary values. The performed analysis has confirmed previous findings as well as the connection between the dC(1) parameter and ventilation effectiveness parameters, especially with the local air-change index.

Editorial

Between the March issue of 1999 and the December issue of 2007, the Indoor Air has published more than 437 articles, among which the word ‘ventilation’ has appeared in the ‘title’ of 30 of them, and in ‘abstract’ of 140. There are 39 articles where the word of ‘ventilation’ is present in both the ‘title’ and ‘abstract’. The articles published have covered, in fact, as wide a spectrum of topics as most can possibly study for the role of ventilation in relation to the quality of indoor air and effect on human health. Categorized based on the direct reading of listed title and the overall objectives delivered, themes of these publications have included the review (7)** Number of articles in the category. , ventilation and pollutant removal (12), ventilation and indoor chemistry (1), maintenance of ventilation systems (1), ventilation and health (5), ventilation vs. human response (5), ventilation and indoor environmental quality (7), and others (2). The review articles published have discussed issues both as focused as ‘PERSONALIZED VENTILATION’ and as general as ‘HUMAN RESPONSE TO VENTILATION’. In the topic of ‘ventilation and pollutant removal’, the Journal has published investigations conducted in a great diversity of indoor environments as well as information generated through either computational and theoretical modeling or direct measurements. As human welfare has been historically the origin of public concerns for indoor air quality, a higher percentage of studies have reported how ventilation, either in terms of efficiency or maintenance, may affect human health and how the human response to changing indoor air quality can be more sensitively detected. An obvious phenomenon is also observed in most recent years as studies present the rising attention on researching how ventilation system may better perform, and therefore improve the overall quality of indoor environment. Limited research has successfully demonstrated how ventilation influences the reactions of indoor air pollutants, and the thirst for gaining a more in-depth understanding cannot be more apparent as the global climate change has challenged an ever-changing profile of outdoor air, the direct parent source of indoor air in most circumstances. As needed and sought-after as the previously mentioned topic is probably the theme on ‘effective maintenance and control strategy for operating ventilation system’ wherever there is one, a topic not adequately addressed before in the Journal, but likely to be of great desire in the time to come. The aforementioned statistics is merely a conveniently available, yet much-too superficial way of highlighting how the notion of ‘ventilation’ by itself has dominated a significant percentage of the discussion for the research of ‘indoor air quality’ over the past decade. In this issue, articles are, again, assembled from either theoretical or field study, from system evaluation or human response when the role of ventilation is discussed in the aspiration of good indoor air. Previously available mechanism and apparatus is also being examined in a new setting. Judging from the recent publications, the research activities orientated toward studying the fundamentals and implication of ventilation to achieve or sustain good indoor air quality are likely to remain as the focal interest in the foreseeable future.

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).

Human Response to an Individually Controlled Microenvironment

The response of 48 subjects to an individually controlled microenvironment was studied at room air temperatures of 20°C, 22°C, and 26°C. An individually controlled system (ICS) comprising personalized ventilation, an under-desk air terminal device supplying cool air, a chair with convectively heated backrest, an under-desk radiant heating panel, and a floor-heating panel were used. The temperature of the air supplied from the personalized ventilation and the under-desk device was 20°C. The subjects were provided with control of the flow rate and direction of the personalized air, the under-desk airflow rate, the temperature of the convection flow from the chair, and the surface temperature of the heating panels. The results reveal that the thermal and air quality acceptability was significantly higher with the ICS at all room temperatures compared to the reference condition at a room temperature of 22°C without ICS. Thus, ICS will increase the number of satisfied occupants when applied in practice. The design and control of the ICS, as well as the background air distribution in a room, should be carefully considered in order to obtain the maximum number of occupants who are comfortable with their microenvironment.

Personal Exposure Between People in a Room Ventilated by Textile Terminals—with and without Personalized Ventilation

This paper describes an investigation made in a room ventilated by an air distribution system based on a textile terminal. The air distribution in the room is mainly controlled by buoyancy forces from the heat sources, although the flow from the textile terminal can be characterized as a displacement flow with a downward direction in areas of the room where no thermal load is present. The system was extended by a personalized ventilation system to study the improved protection of people in a room. The investigation involved full-scale experiments with two breathing thermal manikins. One manikin is the source and the other the target. In general it was found that when the air is supplied from the textile terminal alone, the flow in the room is fully mixed with limited protection of the occupants. Selected locations of supply, return, and heat sources can produce a displacement flow in the room with increased protection of the occupants. It is shown that personalized ventilation improves the protection of occupants by increasing the personal exposure index.

Investigating Indoor Air Quality and Thermal Comfort Using a Numerical Thermal Manikin

In this paper, we investigated the pollutant exposure reduction and thermal comfort that can be achieved with personalised ventilation (PV) design when a PV system is combined with two types of background air conditioning systems. For the investigation of inhaled air quality, pollutants emitted from building materials are the targeted pollutants; and for the investigation of thermal comfort, local discomfort associated with nonuniform thermal environment is focused upon. These investigations were performed by combining CFD simulation of the 3D air flow and a multi-nodal humanbody thermo-regulation model. The results reveal some new characteristics of the three typical air distribution designs, i.e. mixed ventilation, displacement ventilation and PV, and provide insight into the possible optimisation of system combinations.

Protection of Occupants from Exhaled Infectious Agents and Floor Material Emissions in Rooms with Personalized and Underfloor Ventilation

The performance of two personalized ventilation systems supplying air at the breathing zone was tested in conjunction with underfloor ventilation generating two different airflow patterns in a full-scale test room. Two breathing thermal manikins were used to simulate occupants. The distribution of pollutants associated with exhaled air and floor material emissions was evaluated at various combinations of personalized and underfloor airflow rates. Compared to underfloor ventilation alone, personalized and underfloor ventilation provided excellent protection of seated occupants from any pollution, while the concentration of exhaled air pollution increased in the room. The two types of personalized ventilation performed differently. Subsequent analyses of airborne infection transmission risk indicated that personalized ventilation could become a supplement to traditional methods of infection control.

Performance of Personalized Ventilation in Conjunction with Mixing and Displacement Ventilation

Two types of air terminal devices for a personalized ventilation system in conjunction with either a mixing or a displacement total-volume ventilation system were installed in a mock-up of an office. Two occupants were simulated by means of breathing thermal manikins. A constant amount of clean air was distributed between the systems at different combinations of airflow rates. The performance of the systems was evaluated based on the contaminant concentration in and temperature of the inhaled air, as well as temperature, velocity, and contaminant distribution in the occupied zone. The results showed that personalized ventilation will always be able to improve the inhaled air quality in rooms with mixing ventilation. In rooms with displacement ventilation, personalized ventilation will improve the inhaled air quality with regard to pollution emitted from the floor covering. The inhaled air quality with regard to human-produced contaminants, such as virulent agents associated with exhaled air or bioeffluents, may be improved as well. The improvement will depend on the efficiency of the personalized ventilation system and its ability to promote mixing. The experimental data document that the design of air terminal devices for personal ventilation and their use have a large impact on the inhaled air quality and thermal comfort of occupants.

Human Response to Five Designs of Personalized Ventilation

Human response to five different air terminal devices (ATDs) for a personalized ventilation system (PVS) was studied in an experimental office under well-defined conditions. A group of 30 human subjects assessed air quality and rated their thermal comfort and perception of draft. Two temperature levels, 23°C and 26°C, and two background levels of air quality in the office, high and low, were studied during the experiments. Under all conditions the personalized ventilation system provided outdoor air at a temperature of 20°C. All PVSs allowed for individual control of the airflow rate as well as for adjustments of the supply air direction. Results showed that all ATDs studied significantly improved perceived air quality at the workstation. The greatest improvement was obtained when the pollution level and the temperature in the office were high. The thermal environment created with all systems was assessed as acceptable. Subjects were able to improve thermal comfort with all ATDs studied. The subjects identified which of the tested ATDs they preferred.