January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
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.
Highlights
► Test chamber experiments have been conducted. ► Chilled ceiling and displacement ventilation is characterized. ► Ceiling convection and mixing are examined. ► Ceiling convection tends to be forced in nature. ► Plume momentum induces mixing at higher heat gains.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
Glare indices have yet to be extensively tested in daylit open plan offices, as such there is no effective method to predict discomfort glare within these spaces. This study into discomfort glare in open plan green buildings targeted full-time employees, working under their everyday lighting conditions. Three green buildings in Brisbane were used for data collection, two were Green Star accredited and the other contained innovative daylighting strategies. Data were collected on full-time employees, mostly aged between 30 and 50 years, who broadly reflect the demographics of the wider working population in Australia. It was discovered 36 of the 64 respondents experienced discomfort from both electric and daylight sources at their workspace.The study used a specially tailored post-occupancy evaluation (POE) survey to help assess discomfort glare. Luminance maps extracted from High Dynamic Range (HDR) images were used to capture the luminous environment of the occupants. These were analysed using participant data and the program Evalglare.The physical results indicated no correlation with other developed glare metrics for daylight within these open plan green buildings, including the recently developed Daylight Glare Probability (DGP) Index. The strong influence of vertical illuminance, Ev in the DGP precludes the mostly contrast-based glare from windows observed in this investigation from forming a significant part of this index. Furthermore, critical assessment of the survey techniques used are considered. These will provide insight for further research into discomfort glare in the endeavour to fully develop a suitable glare metric.
Highlights
► We investigate green buildings in Brisbane, all are open plan. ► We use a post occupancy evaluation to assess discomfort glare in these spaces. ► Physical luminance measurements are acquired using High Dynamic Range Images. ► The results are evaluated using Evalglare. ► The data does not strongly correlate with existing daylight glare indices, DGI or DGP.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
This study aims at studying by modeling and experimentation the performance enhancement of ceiling-mounted personalized ventilation (PV) nozzle when assisted by small desk-mounted fans to reduce the effect of thermal plume generated by the occupant. Detailed computational fluid dynamics CFD simulations were performed to study the flow, thermal, and CO2 concentration fields around an occupant using a single jet ceiling-mounted PV nozzle in the conditioned space while the fans are on. The CFD model was integrated with a bioheat model to determine the corresponding human body segmental heat fluxes and convective plumes for predicting the occupant segmental and overall comfort. The CFD model was validated with experiments using a cylindrical heat source and comparing measured velocity, temperature and CO2 concentrations in the vicinity of the nozzle and the cylinder. Good agreement is found between the measured and the numerically predicted values. The performance of the PV nozzle assisted with desk fans is assessed by evaluation of ventilation effectiveness in the occupant microclimate and comfort conditions and results are compared with single jet PV and co-axial jet PV, both without the use of desk fans. The desk-mounted fans were able to reduce the convection plumes around the occupant and improved the performance of the single jet PV nozzle by doubling the ventilation effectiveness and improving comfort. They permitted also to achieve a reduced energy saving by up to 13% when compared with conventional mixing ventilation systems.
Highlights
► A ceiling-mounted PV nozzle assisted by desk-mounted fans was modeled. ► The predicted flow characteristics were validated experimentally. ► The nozzle was able to deliver improved air quality to the occupants breathing zone. ► The fans permitted efficient delivery of fresh air by suppressing the rising plumes. ► The system provided considerable energy savings when compared to mixing systems.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
An air-to-water heat pump system for the heating of a one-family home is numerically analysed. The influence of the supply temperature on the seasonal performance factor of the heating system is examined by varying the heating curve. Furthermore, an adaptive control algorithm is studied which lowers the supply temperature according to the actual heating demand. The study includes a variation of control parameters. The different configurations are evaluated with respect to their efficiency (seasonal performance factor) and the comfort (room temperature).In systems with correctly parametrized heating curve controlling the room temperature is likely to be too high because of inner loads and solar gains. Instead of dealing with these gains by lowering the mass flow using thermostatic valves, the supply temperature can be dropped. This has a positive effect on heat pump efficiency because it decreases the total temperature lift. The control algorithm adapts the supply temperature in discrete time steps depending on the position of the thermostatic valve. Special attention has to be paid for the resulting room temperature and its deviation.With the control algorithm presented in this paper, the seasonal performance factor can be increased by up to 0.19, depending on the allowed variability of room temperature. Savings in annual primary energy demand compared to a standard controlling are up to 6.8%.
Highlights
► An air-to-water heat pump system for the heating of a one-family home is numerically analysed. ► An adaptive control lowers the supply temperature according to the heating demand. ► The control strategy leads to savings in annual primary energy demand for heating. ► Control parameters have an influence on primary energy demand and thermal comfort.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
At day-times building façades and ground surfaces are heated by solar radiation. Due to the increased surface temperatures, buoyancy is induced which changes the flow field around buildings significantly. Wind tunnel measurements were conducted to study the influence of buoyancy on the flow in a scaled urban street canyon with heated surfaces. Particle image velocimetry was used to measure the flow field in a section of the street canyon. The two wall and the bottom surfaces of the street canyon were heated either individually or all together. A wide range of Froude numbers between 0.65 and 17.3 was covered with surfaces temperatures raised up to 70 °C–130 °C and freestream velocities between 0.68 m/s and 2.32 m/s. The velocity and turbulent kinetic energy (TKE) fields were analysed, and for some cases also the air temperatures inside the street canyon were measured. For most cases one main vortex is formed in the centre of the street canyon. This main vortex is strengthened, and the TKE inside the street canyon increased by, heating of (in order of importance) the ground, the leeward wall, and all three surfaces for low freestream velocities. For windward wall heating a second counter-rotating vortex is formed due to buoyancy and the flow direction close to the windward wall changes from a downward to an upward motion. The centres of the main and secondary vortex change their position for different windward wall temperatures with increasing freestream velocities. For low Froude numbers the air exchange rate is increased due to buoyancy.
Highlights
► Solar radiation induced buoyancy plays an important role in urban street canyons. ► Wind tunnel measurements are conducted for a 1:1:9 cavity with heated surfaces. ► Time averaged turbulent kinetic energy and velocity fields are measured with PIV. ► For low freestream velocities the flow field significantly changes due to buoyancy. ► The flow field is influenced most if the windward façade is heated.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
This paper presents a comprehensive global uncertainty and sensitivity analysis of daylighting and energy performance for private offices with automated interior roller shades using an advanced integrated thermal and lighting simulation model. The purpose was to identify the more important factors with respect to building thermal and lighting energy performance so as to facilitate decision making in building design stage and simplify further investigation such as optimization analysis. Seven studied parameters were selected: window-to-floor ratio, shading transmittance, shading front and back reflectance, space aspect ratio, insulation thermal resistance and glazing type. The performance metrics include useful daylight illuminance (500–2000lux), annual lighting, heating and cooling demand per unit floor area and annual source energy consumption per unit floor area. The uncertainty analysis is based on the Monte Carlo method with Latin Hypercube Sampling, showing the possible ranges in these performance indices. The sensitivity analysis uses a variance-based method in the extended FAST implementation. Application of the analysis to perimeter private office spaces for the climate of Philadelphia showed the first order and total order effects of each studied parameter to determine the building parameters that have the most significant impact. Results are presented for different facade orientations.
Highlights
► We performed a comprehensive global uncertainty and sensitivity analysis. ► Factors related to daylighting and energy performance were examined. ► The Monte Carlo LHS and the extended FAST method were used. ► Application to perimeter offices showed the first order and total order effects.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
Well planned natural ventilation strategies and systems in the built environments may provide healthy and comfortable indoor conditions, while contributing to a significant reduction in the energy consumed by buildings. Computational Fluid Dynamics (CFD) is particularly suited for modelling indoor conditions in naturally ventilated spaces, which are difficult to predict using other types of building simulation tools. Hence, accurate and reliable CFD models of naturally ventilated indoor spaces are necessary to support the effective design and operation of indoor environments in buildings.This paper presents a formal calibration methodology for the development of CFD models of naturally ventilated indoor environments. The methodology explains how to qualitatively and quantitatively verify and validate CFD models, including parametric analysis utilising the response surface technique to support a robust calibration process. The proposed methodology is demonstrated on a naturally ventilated study zone in the library building at the National University of Ireland in Galway. The calibration process is supported by the on-site measurements performed in a normally operating building. The measurement of outdoor weather data provided boundary conditions for the CFD model, while a network of wireless sensors supplied air speeds and air temperatures inside the room for the model calibration.The concepts and techniques developed here will enhance the process of achieving reliable CFD models that represent indoor spaces and provide new and valuable information for estimating the effect of the boundary conditions on the CFD model results in indoor environments.
Highlights
► The reliability of the results of the CFD simulations is a big concern. ► Systematic methodology for calibrating CFD models of indoor spaces is proposed. ► CFD models should be validated with trusted experimental data. ► The most important input boundary conditions on the model results are estimated. ► The parametric analysis supports the CFD model calibration process.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
Indoor Air Quality (IAQ), energy efficiency through passive building design strategies and sustainable construction practices have been highly prioritized in recent years. This paper presents a Boundary Layer Wind Tunnel study on wind-driven natural ventilation for a low-rise building at a model-testing scale of 1:20. The experiment consists of testing various size openings in a single wall, opposite side walls and adjacent side walls with and without portioning walls, with and without opening cover screens, with and without internal volume correction for 36 different wind angles of attacks (unless symmetrical). For the size of the building and openings considered, the experimental analyses indicated that internal volume correction using velocity scaling was important, although this criterion could be relaxed for cross-ventilation with openings in opposite walls. The internal pressure due to cross-ventilation was 1.5–2.5 times higher for Ainlet/Aoutlet > 1 compared with ratios Ainlet/Aoutlet < 1. In general, the lower the opening ratio (or inlet to outlet ratio), the higher the pressure drop inside the building. For an equivalent opening ratio, openings on opposite-walls generated a higher pressure drop compared to openings on adjacent-walls. Room-partitioning significantly affected the distribution of internal pressures, and hence the pressure drop that favored the ventilation in each room for the considered partitioning case. In addition, the total discharge coefficient Cd_total and the ventilation rate Q/(VrA) increased with an increase of the opening ratio. The inlet discharge coefficients obtained in this experiment ranged from 0.65 to 1.08, similar to the results of various early studies.
Highlights
► The paper presented evaluations of wind-driven natural ventilation in a low-rise building. ► Effects of size and location of openings, room partitioning, inlet-outlet ratio, screens were investigated. ► Necessity of volume correction during wind tunnel studies for cross-ventilation were investigated. ► Pressure drops and inlet and total discharge coefficient were evaluated.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
Capturing daylight into an unevenly lit lecture room with north-facing windows has been analyzed with the help of Photopia and Radiance. Two different daylighting systems, a light tube and a fiber-optic solar dish concentrator, are considered as means to lead light rays into an interior space with insufficient illumination from daylight. Photopia is used to photometrically model the daylighting systems as light travels through highly reflective light guiding elements of these systems. The candela power distribution curves (CDCs) generated by Photopia are imported by Radiance to produce photometric data and images of different locations in the lecture room. These results clearly reveal the functional benefits of each system when harvesting daylight for indoor illumination. For solar altitudes of less than 50°, more daylight can be harvested by the solar tracking dish concentrator system. Also, its minimum-to-average (illuminance) uniformity ratio on the work plane remains between 0.55 and 0.72, varying quite less than that of the light tube, ranging from 0.46 to 0.88.
Highlights
► Two different daylighting systems were analyzed to compare their performances. ► Light distribution curve of the daylight guidance system was generated by Photopia. ► Photometric data and images were generated by Radiance for comparative analysis. ► Dish concentrator daylighting systems were more effective at lower solar altitudes. ► Dish concentrator daylighting system showed smaller variations in uniformity ratio.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
Clothing affects people's perception of the thermal environment. Two dynamic predictive models of clothing insulation were developed based on 6333 selected observations of the 23,475 available in ASHRAE RP-884 and RP-921 databases. The observations were used to statistically analyze the influence of 20 variables on clothing insulation.The results show that the median clothing insulation is 0.59 clo (0.50 clo (n = 3384) in summer and 0.69 clo (n = 2949) in winter). The median winter clothing insulation value is significantly smaller than the value suggested in the international standards (1.0 clo). The California data (n = 2950) shows that occupants dress equally in naturally and mechanically conditioned buildings and all the data has female and male dressing with quite similar clothing insulation levels. Clothing insulation is correlated with outdoor air (r = 0.45) and indoor operative (r = 0.3) temperatures, and relative humidity (r = 0.26). An index to predict the presence of a dress code is developed.Two multivariable linear mixed models were developed. In the first one clothing is a function of outdoor air temperature measured at 6 o'clock, and the second one adds the influence of indoor operative temperature. The models were able to predict 19 and 22% of the total variance, respectively. Climate variables explain only a small part of human clothing behavior; nonetheless, the predictive models allow more precise thermal comfort calculation, energy simulation, HVAC sizing and building operation than previous practice of keeping the clothing insulation values equal to 0.5 in the cooling season and 1 in the heating season.
Graphical abstract
Highlights
► We developed two models to dynamically predict clothing insulation levels, Radj2 = 0.19–0.22. ► Winter clothing insulation values are significantly lower than 1.0 clo. ► In California occupants dress equally in naturally and mechanically conditioned buildings. ► Clothing values are correlated with outdoor air and indoor operative temperatures. ► Climate variables explain only a small part of human clothing behavior.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
An essential part of a performance-based service life design format for wood exposed in outdoor applications is the effect of proper detailing in terms of avoiding moisture traps. Models for predicting degradation and non-performance caused by decay are functions of arbitrary climate history of combined moisture content and temperature. Therefore it is crucial to be able to predict the behaviour of different detailing in terms of moisture content exposed to outdoor climate. An experimental study was made with continuous moisture content measurements of different details. The different detail set-ups are selected to represent a wide range of sawn timber dimension details of non-treated Norway spruce. Hourly moisture content values are recorded by a wireless monitoring system and the climate is monitored using a weather station. A simple horizontal board with no detailing is chosen as reference detail. This is, apart from a vertical board and sheltered details, what can be expected to be a good detail in terms of not trapping water. The remaining details show higher moisture content levels. It was found that the ratio between moisture content in a detail and in the reference detail showed a reasonably constant value over time. Consequently the behaviour of an arbitrary detail can be estimated by scaling the behaviour of the reference detail up or down using a constant value. Depending on the design the constant will be higher for more water trapping details and vice versa. This is important information and input for evaluating and developing details with acceptable performance.
Highlights
► Method to continuously monitor moisture content in different wood detail designs. ► Number of days during a year with moisture content >25% ranged between 0 and 130. ► Ratio between arbitrary detail and reference detail could be modelled as constant. ► Results can be implemented in a performance-based model for service life design.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
This study suggests a new control algorithm which applies the concept of a personal air-conditioner and a local cooling method to a floor-standing room air-conditioner (FSAC). The control algorithm can be divided into three wind patterns: strong cooling using direct wind, normal cooling using direct wind, and indirect wind. Strong cooling is to make an occupant who is exposed to a hot environment thermally neutral rapidly, while normal cooling is used to maintain a thermal-neutral state continuously. A suitable control method for each cooling mode was determined through subject experiments. The indoor thermal environment was evaluated using the temperature, PMV (predicted mean vote), and TSV (thermal sensation vote).The occupants exposed to the hot environment reached their thermal-neutral state in approximately five minutes due to the strong cooling (16.4 CMM) by the direct wind of the FSAC. When the FSAC changed its control mode to normal cooling (13.9 CMM), it was easier to maintain the thermal-neutral state by swinging direct cool air directionally controlled by vertical vanes. When indirect wind was used, an upwards direction at an angle of 15° was effective in spreading the cooled air and preventing cold drafts.
Highlights
► An air-conditioner with a sensor for detecting an occupant was introduced. ► Control algorithms to provide proper air supply patterns were examined. ► The strong cooling method with direct wind can cool an occupant in five minutes. ► Normal cooling with a 15° position can mostly maintain the thermal comfort.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
This paper presents the results of a field monitoring study of three medical wards at Padua General Hospital (Orthopaedics, Internal Medicine and Paediatrics), based on measurements of indoor conditions and on a survey of patient and medical staff perceptions. Microclimatic conditions were measured over an extended period using data loggers with a time step of 5 min. Maximum in-patient room temperatures exceeded 29 °C while mean values were around 26–27 °C. Generally, microclimatic conditions differed between in-patient and staff rooms. Spot and long-term monitoring was used to calculate PMV profiles which were compared to thermal comfort showing non uniform correspondence among wards and their occupants. Innovative statistical nonparametric methods were applied to analyse the survey, comparing the wards from both patient and staff points of view. Staff complained mostly about lack of privacy, room size, amount of common areas, poor air quality and acoustic discomfort, with significant differences between wards in relation to levels of satisfaction with building-related aspects. Patients, on the other hand, were more satisfied with both building-related aspects and indoor conditions than medical staff. Such a global assessment could easily be used, for example, to rank the necessity or the priority of changes or improvements to buildings as well as determine the most important features, both individually and globally, to be taken into consideration.
Highlights
► Objective and subjective analysis of 3 Italian medical wards. ► Long-term and spot measurements of indoor conditions and survey. ► Comparison between PMV profiles, measurements and thermal comfort. ► Innovative statistical methods to compare patients, staff and wards. ► Complaint of lack of privacy, room size, poor air quality and acoustic discomfort.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
There is very little information about human exposure to gaseous indoor air pollutants in the sleeping environment, even though the conditions in this environment are at least worrisome. The exposure during sleep is characterized by long exposure time, both absolute and relative, prevalence of specific pollutants and uncustomary proximity of sources to the breathing zone. This paper reports experimental results that show the impact of the proximity of possible emission sources such as a mattress, pillow and toy, on exposure of the sleeping subjects to these emissions. Based on full scale experiments in an environmental chamber using a breathing thermal manikin the intake fraction for gaseous pollutants are measured as well as the occurrence of rebreathing. Intake fractions for several sleep positions as well as different bedding arrangements are reported. The results show that human metabolism and corresponding heat release by the human body are dominant factors in the dilution of pollutants emitted in close proximity of the nose, reducing exposure by 40% compared to a case without metabolic heat output. This effect is more important than the sleep position. An important finding is that sleeping with the head under the covers increases intake by a factor 24 and results in a rebreathing rate of over 60%.
Highlights
► Intake fraction in prone position 70% higher for mattress emissions. ► 60% rebreathing with head under the covers. ► High spatial sensitivity of exposure to emissions from small sources. ► Thermal plume dominant flow mechanism in breathing zone while sleeping.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
This study examines a scenario for realizing large-scale reductions of operational carbon dioxide (CO2) emission in commercial districts in temperate and tropical zones. In warm climates, energy usage for heating is not dominant in a building's energy usage, and hence, every available emission reduction technology must be fully utilized to achieve a large overall reduction in emissions, as in the scenario examined in this study. The focus is on commercial buildings in Nakanoshima area, a sandbank 3 km long and 50 ha wide, a central business and cultural area in the city of Osaka, Japan. The commercial buildings in Nakanoshima with approximately 1.2 million square meters of total floor area emitted 88 thousand tons of CO2 in 2008. The method used in this paper combines: 1) energy flow analysis, 2) community-scale building performance simulation validated with actual energy consumption and supported by detailed field survey and reference survey, and 3) what-if analysis assuming technological deployment and social change based on a long-term perspective. It enables a comprehensive understanding of how much energy is consumed for what purpose as well as how much energy can be reduced by implementing which technologies and measures. The result showed that approximately 65% emissions of the present operational CO2 emission could be reduced in the coming decades.
Highlights
► In warm climates, energy usage for heating is not dominant in commercial buildings. ► Thus available technologies must be fully utilized to achieve a large CO2 reduction. ► A potential reduction was estimated for Nakanoshima commercial Area, Japan. ► A community-scale simulation revealed that 65% of the emission can be reduced.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
Sizing rules in residential ventilation standards lack uniformity in both methodology and resulting design flow rates. Additionally, mere comparison of design flow rates is case sensitive and, due to effects of infiltration, adventitious ventilation and occupancy, ill-suited to assess performance of an exhaust ventilation system with regard to the achieved indoor air quality and energy cost in terms of heat loss. This paper presents a multi-zone simulation based performance assessment of residential mechanical exhaust ventilation systems, using five common dwelling typologies and the sizing rules put forward in the Belgian, British, Dutch, French and ASHRAE residential ventilation standards. The performance of the different cases proved to be substantially different, with an occurrence of poor perceived air quality in 5% or less of the occupation time for the Belgian, Dutch and French standard, and about 15% for the British and ASHRAE standard. When the trade-off between indoor air quality and heat loss is considered, the cases with the Dutch and ASHRAE standard did not achieve pareto optimal performance in comparison to the performances achieved by the other standards.
Highlights
► Performance with different standards is substantially different. ► Building geometry has large impact. ► French and British standard provide pareto optimal sizing.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
To analyse the moisture performance of wall systems with a ventilated rainscreen cladding, the air change rate per hour (ACH) is required. However, the average ACH and its variation depend on many factors. This study focuses on performing field measurements of air velocities and temperatures in south oriented wall cavities characterised by either vertical wooden battens or horizontal vented metal battens. A physical cavity airflow model together with laboratory test of loss factors were used to analyse the data and interpret the results.With vertical battens, findings estimated the average ACH during a measurement period to be 230–310 ACH. In the cavities with horizontal battens, the ACH was 60–70% lower. The daily variations were considerable and hours with solar radiation and clear skies resulted in ACH that exceeded the average values 2–3 times. In contrast to airflow induced by thermal buoyancy, wind-induced airflow was irregular with frequent changes in both velocity and direction. This pattern was observed independent of the angle between the wind and the cladding. The frequent changes in flow direction significantly reduced the efficiency of wind-driven airflow to create air exchange. The wind-induced airflow in wall cavities with a pronounced non-linear relationship between the driving force and the air velocity is suppressed in the presence of buoyancy. For rainscreen claddings exposed to many hours of solar radiation, this effect increases the possibility of accurate estimations of ACH.
Highlights
► Air velocities and temperatures were measured in three different wall cavities. ► Air change rates and driving forces were evaluated with a physical cavity airflow model. ► Average air change rates were high but the daily variations were considerable. ► The driving forces was less than 0.2–0.3 Pa during 50% of the time. ► Wind-induced airflow in the cavities was suppressed in the presence of buoyancy.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
Airborne Molecular Contamination (AMC) has become one of the major problems in nano-technology development and manufacturing facilities. To deal with this problem, a prototype Ultra-Pure Air (UPA) system with a targeted air quality level of 10 ppt impurity was experimentally developed.The prototype UPA system presently composes two process modules; pre-treatment and post-treatment. In order to deal with the hard-to-remove airborne organic molecular substances, UV185+254nm is first used in the pre-treatment module to provide the energy needed for breaking the molecules into smaller transitional compounds. Meanwhile aerosol water droplets are introduced; these combine with the transitional compounds to form hydrophilic substances. After the “Immersing Photochemical Oxidation” reaction, the hydrophilic contaminants go through compression and condensation processes, which comprise the post-treatment module. During the air compression and condensation processes, the collision probability of the contaminants and aerosol water droplets is highly increased. Later, a dehumidification process removes the water droplets within the condensed air; this removes both the water and the dissolved contaminants. These pre and post-treatment processes yield air quality levels of less than 1 ppb of volatile organic compound (VOC); the minimum detection limit for a measuring analyzer.The purpose of this paper is to introduce the developed UPA system and to present its experimental results.
Highlights
► Ultra-Pure Air System (UPA) was experimentally established for solving AMC problems. ► The UPA used UV185+254nm to pre-treat insoluble AMCs into hydrophilic substances. ► The hydrophilic substances were post-treated by dehumidification processes. ► Xylene was used to exemplify the UPA with a removal rate of 99.99%. ► The UPA process obtained air quality less than 1 ppb within 10 s.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
An improved air distribution system for aircraft cabin was proposed in this paper. Personalized outlets were introduced and placed at the bottom of the baggage hold. Its ratio of fresh air to recirculation air and the conditioned temperature of different types of inlets were also designed carefully to meet the goals of high air quality, thermal comfort and energy saving. Some experiments were conducted to evaluate and compare its performances with two other systems. First the Flow Visualization with Green Laser (FVGL) technology was used to analyze the air flow. The top-in-side bottom-out pattern may have the disadvantages of an indirect path to deliver fresh air to passengers, a low fresh air utilization ratio and the potential to widely spreading airborne infectious diseases. The bottom-in-top-out pattern can overcome these disadvantages very well, but it also faces the stratification of contaminated air above the head of the passengers. The improved pattern may overcome the above challenges quite well while also delivering good ventilation performance. The modified Personal Exposure Effectiveness (PEE) was measured to compare their performances with regard to inhaled air quality. The measured results suggest that personalized inlet should be designed to adjust its supply air angle according to the height of the passenger's face to provide a higher fresh air utilization effectiveness and better air quality for passengers in the improved pattern. Some simulations revealed that the improved pattern had the potential to save energy by decreasing the amount of fresh air without significantly affecting air quality and thermal comfort.
Highlights
► An air distribution system with personalized outlet for aircraft cabin was proposed. ► Flow visualization with green laser method was used to analyze airflow performance. ► Modified personal exposure effectiveness was measured to compare inhaled air quality. ► Simulations revealed that the improved pattern had the potential to save energy.
January 2013 Publication year: 2013 Source:Building and Environment, Volume 59
This paper presents the flow and temperature field within an office using impinging jet ventilation (IJV) under different heat loads ranging from 17 to 65 W per square meter floor area. The measurement was carried out in a full-scale test room to verify the reliability of three turbulence models, i.e., the RNG k–ɛ, SST k–ω and models. It is found that all the tested models show good agreements with measurements, while the model shows the best performance, especially on the overall temperature prediction.The model is used further to investigate a number of important factors influencing the performance of the IJV. The considered parameters are: cooling effect of chilled ceiling, external heat load as well as its position, number of occupants and supplied air conditions. The interaction effect of chilled ceiling and heat sources results in a complex flow phenomenon but with a notable feature of air circulation. The appearance and strength of the air circulation mainly depends on the external heat load on window and number of occupants. It is found that with higher external heat load on window (384 W and 526 W), the air circulation has a strong tendency towards the side wall in the opposite direction to occupant, while with lower power on window (200 W) the air circulation has a strong tendency in the center of the room and extends to a larger area. When two occupants are present, two swirling zones are formed in the upper region. The effects of air circulation consequently alter the temperature field and the level of local thermal comfort.
Highlights
► model shows better performance than RNG and SST k–ω for the type of impinging jet flow. ► The interaction effect of chilled ceiling and heat sources results in air circulation(s) in a room. ► The appearance and strength of the air circulation mainly depends on the external heat load on window and number of occupants. ► The effects of air circulation consequently alter the temperature field and the level of local thermal comfort.
