February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
Control of airborne infectious agents in hospitals is critical both to effective healthcare and to the control of direct and indirect health care costs. Current hospital design guidelines focus on ventilation rates, room pressure control and air filtration to control the spread of airborne infectious agents. Studies indicate, however, that there is much variability in hospital design strategies used by engineers to control airborne pathogens. This study focuses on a number of questions concerning current hospital design practices and provides an overview of the tools and methods that can be used to answer some of these questions. Multizone airflow and contaminant transport simulations are used to examine different control strategies and some related issues of design and application. Design issues associated with room pressurization, filtration, and ultraviolet germicidal irradiation (UVGI) are also reviewed. The results provide some important insights into the following issues: 1) using a ventilation flow differential based on building leakage better captures the relevant airflow physics of space pressure control; 2) anterooms can be effective barriers for reducing contaminant transport due to pressure differential disruptions; and, 3) filtration can provide significant protection, with more effective protection provided by additional UVGI systems.
Highlights
► Current control strategies for airborne pathogens are reviewed. ► Multizone airflow simulations of airflow and contaminants are performed. ► Effects of building leakage, weather and HVAC system operation are highlighted. ► Insights into issues in design guidelines for hospitals are provided. ► Design issues associated with pressurization, filtration, and UVGI are reviewed.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
The microclimate model ENVI-met Version 4 was evaluated with field data in terms of the thermal behavior of different types of ground surface. A field experiment was conducted in a real construction project in Guangzhou, South China, from 29 August to 2 September in 2010. The surface types of concrete, tile, asphalt and grass were investigated. The comparison between observation and prediction was performed for both sub- and above-surface variables, including soil temperature at different depths, soil heat flux at the surface, surface temperature, and air temperature and humidity at different heights. The results show that the ENVI-met model is capable of reasonably modelling the diurnal thermal behavior of different ground surfaces and their effects on local air temperature and humidity. The comparison of spatial distributions of air temperature and humidity shows that the hotter/drier and cooler/wetter spots predicted by ENVI-met were generally consistent with the observations. The quantitative evaluation shows that the ENVI-met model is capable of predicting the microclimate in terms of different variables with good accuracy.
Highlights
► The latest version of the microclimate model ENVI-met was evaluated with field data for the first time. ► Both sub- and above ground variables were investigated. ► Both spatial and temporal distributions of outdoor thermal envrionment were investigated.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
Decisions made during a building's early design stages critically determine its environmental impact. However, designers are faced with many decisions during these stages and typically lack intuition on which decisions are most significant to a building's impact. As a result, designers often defer decisions to later stages of the design process. Life-cycle assessment (LCA) can be used to enable better early stage decision-making by providing feedback on the environmental impacts of building information modeling (BIM) design choices. This paper presents a method for applying LCA to early stage decision-making in order to inform designers of the relative environmental impact importance of building component material and dimensioning choices. Sensitivity analysis is used to generalize the method across a range of building shapes and design parameters. An impact allocation scheme is developed that shows the distribution of embodied impacts among building elements, and an impact reduction scheme shows which material and thickness decisions achieve the greatest embodied impact reductions. A multi-building residential development is used as a case study for introducing the proposed method to industry practice. Results show that the method can assist in the building design process by highlighting those early stage decisions that frequently achieve the most significant reductions in embodied carbon footprint.
Highlights
► A building is analyzed to see which design decisions determine embodied impact. ► Sensitivity analysis software is integrated with design and analysis software. ► Designers receive environmental impact feedback on design choices for many designs. ► Cladding decisions consistently contribute the most to the embodied impact. ► Services contribute less to the impact and can be deferred to later design stages.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
Space heating accounts for a large portion of the world's carbon dioxide emissions. Ground Source Heat Pumps (GSHPs) are a technology which can reduce carbon emissions from heating and cooling. GSHP system performance is however highly sensitive to deviation from design values of the actual annual energy extraction/rejection rates from/to the ground. In order to prevent failure and/or performance deterioration of GSHP systems it is possible to incorporate a safety factor in the design of the GSHP by over-sizing the ground heat exchanger (GHE). A methodology to evaluate the financial risk involved in over-sizing the GHE is proposed is this paper. A probability based approach is used to evaluate the economic feasibility of a hypothetical full-size GSHP system as compared to four alternative Heating Ventilation and Air Conditioning (HVAC) system configurations. The model of the GSHP system is developed in the TRNSYS energy simulation platform and calibrated with data from an actual hybrid GSHP system installed in the Department of Earth Science, University of Oxford, UK. Results of the analysis show that potential savings from a full-size GSHP system largely depend on projected HVAC system efficiencies and gas and electricity prices. Results of the risk analysis also suggest that a full-size GSHP with auxiliary back up is potentially the most economical system configuration.
Highlights
► Ground Source Heat Pumps (GSHPs) performance is highly sensitive to building loads. ► Case studies of GSHPs show that design loads often deviate from actual loads. ► As a result, currently many GSHPs in the UK do not perform as designed. ► It is important to incorporate the uncertainty in loads in the design of GSHPs. ► Reduction in installation costs will make GSHPs more financially competitive.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
The Urban Heat Island (UHI) effect is defined as the increase of the urban air temperature compared to surrounding rural areas. The phenomenon is experienced at all latitudes and, combined with the global warming, has a severe impact at environment, energy and health level. The increasing of solar reflectance of urban materials is a strategy aimed at reducing surface and air temperatures and at mitigating the UHI. Cool materials applied to conventional asphalts are a viable technology for such purposes. The optical and thermal characterisation was carried out in laboratory and outdoor, and showed the enhanced properties and performances of several cool asphalt samples compared to conventional materials. The experimental data were used as input to simulate the thermal environment of a densely populated neighbourhood in Rome, estimating the effect of the roads albedo on the temperature air profile. Simulations performed with the software ENVI-met showed a significant reduction of air temperature closely correlated with the road solar reflectance. The air temperature profiles were used as input to calculate the impact of the albedo change at the building level. Simulations on the peak cooling demand of typical Italian dwellings were carried out by means of the TRNSYS dynamic simulation tool. Peak reductions of almost 19% were calculated for the highest solar reflectance configuration.
Highlights
► Spectral reflectance and emissivity of cool asphalts were measured. Integrated values were calculated. ► Outdoor thermal monitoring of cool asphalts was carried out. ► The impact of cool asphalts on the mitigation of urban air temperatures was calculated. ► The impact of cool asphalts on the residential buildings' cooling peak demand was calculated.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
A water-flow window was constructed at the front wall of an environmentally controlled test cell to monitor its performance under full-scale real-building-like condition. The window was consisted of three layers, including one layer of clear glazing at the outside, one layer of insulated glazing unit at the inside, and one layer of water flowing in between. A heat exchanger was provided at the top of the window, and connected to the glazing cavity through connecting pipes and distribution headers. Through this, a cold feed water circuit removed the absorbed heat away from the buoyant water circulation in the window circuit. The heat removal allowed a reduction of energy consumption in air-conditioning and services hot water systems. Year round energy performance was then predicted by numerical models, which were successfully validated by the experimental data. A comparative study was also carried out with the use of different glazing types. The economical payback periods of the different glazing combinations are found less than 5 years under the Hong Kong subtropical climate. Amongst these, the energy performance of water-flow window with double absorptive glazing appears to be most promising.
Highlights
► A water-flow window was constructed and its performance tested experimentally. ► Buoyant flow is able to reduce air-conditioning and services water heating loads. ► Year round energy performance was predicted by validated numerical models. ► Comparative study was carried out with different glazing types. ► Their economical payback periods are found generally less than 5 years.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
Under natural conditions, air change rates are very sensitive to specific building elements and to climate conditions, even more so in the case of airtight buildings. Consequently, applying general correlations to such cases may lead to inaccurate predicted air change rates. Still, this approach remains valuable because of its simplicity compared to other methods such as wind tunnelling and CFD simulations. In this paper, the tracer gas concentration decay technique was selected to contribute additional information to classical air-tightness measurements. The measurements were used to fit the coefficients of a general single-node pressure model. Simulation results were found to be consistent with tracer gas measurements most of the time. However, the closeness of the fit is strongly related to the average pressure coefficients from the literature, which were estimated more precisely using the other techniques mentioned above. From a general point of view however, it would seem promising to extend this method to other buildings.
Highlights
► The air change rate of a single-room test house exposed to natural conditions were assessed. ► Measurements were achieved using the tracer gas concentration decay technique. ► Measurements were then used to fit the coefficients of a general single-node pressure model. ► Air change rate was 23% accurately assessed for various outdoor conditions. ► Wind incidence was shown by the mean of two sets of Cp values issued from literature.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
Three mesoporous silica materials were selected as coatings to provide humidity buffering in retrofitted ‘closed’ environments. The aim was to investigate the resultant indoor climate conditions and energy usage achieved in a representative indoor environment when compared against the traditional building materials spruce and gypsum. Simulation was carried out using the hygrothermal numerical model WUFI Plus v2.1.1.73, and validated against experimental results emerging from a series of physical models that were conducted inside a climatic chamber. Parametric analysis of key variables including ventilation rates, moisture loads and coating surface area using numerical simulation was then undertaken. The MS materials show consistent reduction in fluctuating relative humidity amplitudes for both occupied and unoccupied spaces in daily and annual cycles, providing humidity buffering within ASHRAE comfort limits and a potential reduction in humidification/dehumidification energy demand of up to 100% when compared against a conventional gypsum-lined indoor environment.
Highlights
► Validation of WUFI Plus was achieved with the statistical variance between the physical and numerical models presented. ► Sensitivity analysis of the numerical model was performed in terms of relative humidity and material surface area. ► The MS materials displayed outstanding humidity buffering performance under moisture and ventilation overloading scenarios. ► Occupant comfort was maintained within ASHRAE limits when using the MS materials. ► The MS materials can provide up to 100% savings on operational HCHD energy compared to a standard material.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
This study presents a method for predicting wind-induced cross ventilation using wind tunnel testing coupled with Computational Fluid Dynamics (CFD). First, in a boundary layer wind tunnel, facade pressures near openings of a test house were recorded for multiple incident wind angles using a 1:25 scale building model. The wind tunnel pressure data was then converted into appropriate boundary conditions for an indoor CFD airflow model of the test house. Both steady state and transient CFD simulations were conducted to capture averaged flow and instantaneous flow rates of the cross ventilation flow. The CFD simulation result was compared to the full scale experimental data from a previous study. The steady state result shows that it is possible for this combined wind tunnel-CFD method to predict the averaged cross ventilation through small openings adequately. Similarly, the transient result shows the fluctuation of the flow at the openings could be predicted at a frequency as high as 0.1 Hz. As many buildings design processes now include wind tunnel testing as a part of structural analysis, this proposed method could utilize the wind tunnel pressure data for assessments of a building's cross ventilation potential.
Highlights
► Weather data and wind tunnel measurements were used to produce CFD boundary conditions. ► Both steady state and transient indoor CFD simulations were conducted. ► The steady state method predicted similar average flow rate compared to full scale values. ► This transient method predicted the unsteady flow fluctuation at frequency as high as 0.1 Hz. ► This combined method predicted the indoor flow distribution when no flow reversal is present.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
Installing roofs with high solar reflectance and high thermal emittance, known as “Cool roofs,” are becoming increasingly popular because of their cooling energy saving potentials, cost effectiveness and sustainability. Lower surface temperature of cool roofs may affect the hygrothermal performance of roofing systems and hence their performance should be characterized in different climates.We simulated the performance of several roofing systems including: typical, smart, and self-drying roofs for residential and commercial buildings. In addition, we proposed vented roofs with smart vapor retarders in very cold climate regions across North America. We also developed an algorithm to investigate the effect of snow on hygrothermal behaviour of dark and white roofs.Results showed that office buildings never experience moisture accumulation problems during the simulation period (5 years). In residential buildings, white typical roofing compositions with conventional vapor retarders experienced moisture accumulation problems in very cold cities such as Anchorage, Edmonton and St. John's. Using smart vapor retarder (smart roofs) or self-drying roofs helped to decrease risk of moisture accumulation. In these climates, adding a ventilated air space along with using smart vapor retarder eliminated the risk of moisture accumulation and prevented excessive OSB (oriented strand board) moisture content. The risk of mold growth was significantly lowered in vented smart roofs. Simulating the effect of snow on the roofs for Anchorage, Montreal and Chicago showed that the hygrothermal performances of white roofs improved with snow accumulation on the roof.
Highlights
► The hygrothermal performance of cool and dark roofs is almost the same in hot and moderate climates. ► Proper design of roofs in cold climates is essential to avoid moisture problems in both cool and dark roofs. ► In cold climates, snow accumulation of the roof slightly improves the moisture behaviour of roofing assembly.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
In recent decades many studies have focused on the thermal performance of massive and lightweight constructions of energy-efficient houses. Surprisingly, temperature and humidity profiles have been addressed relatively rarely, despite the fact that they can influence the living conditions, the lifetime of the construction materials, as well as the energy efficiency of the house and consequently the environment as well. In the present study we compare different lightweight building blocks and the associated temperature and relative-humidity profiles. The studies were performed on residential as well as test passive houses. Small differences in the building blocks were identified as having a large influence on the performance of the building. The structural elements should be placed in such a way as to prevent shear forces due to humidity differences. It has been proven that ventilated wooden facades, in comparison with classical façade plaster, protect the building blocks from high thermal loads. Last but not least, the use of vapor barriers instead of vapor retarders and a lack of moisture-buffering materials led to a higher indoor relative humidity, as well as higher moisture loads on construction that could have an impact on the durability of a building and also on the energy performance of the house.
Highlights
► Choice of building materials and building blocks influences living conditions. ► Vapor retarders and moisture-buffering materials maintain indoor comfort. ► Building blocks can be designed in a way to prevent large humidity differences. ► Ventilated wooden facades protect building blocks from high thermal loads.
March 2013 Publication year: 2013 Source:Building and Environment, Volume 61
The investigation of moisture transfer in building materials is of great importance for the characterization of performance-related durability, water resistance and thermal performance. The aim of this study is to develop a numerical model using finite elements to simulate the behavior of a masonry wall and compare the results with those of the water penetration and leakage test. It was considered in this model that moisture movement is governed by capillary absorption. A large-scale wall was built with a frontal surface of rendering mortar. The prototype consisted of a large-wall specimen of a 1.20 m wide and 1.20 m tall masonry wall with a 0.02 m thick lining, comprised of a total of 25 concrete blocks. In total, three walls were produced with three types of mortar, varying the degree of replacement of natural sand (0%, 50 and 100%) in the composition of the bedding and rendering mortars. The tests were conducted for a period of 7 h, according to the experimental water penetration and leakage test, described in ASTM E514-90. The formation of appearance of dampness (percentage area of dampness) and the sorptivity characteristics of the blocks and bedding mortar were also evaluated at the end of the test. The moisture values predicted by the model were compared to the experimental data through a measurement error. The results indicated good agreement with the actual moisture measurements and experimental results obtained in an experimental large-scale wall (prototype test).
Highlights
► We model the water penetration and leakage test. ► We tested the leakage in masonry wall with a frontal surface of rendering mortar. ► The 100% of bottom in rendering mortar can reduced the area of dampness. ► The moisture movement is governed by capillary absorption.
March 2013 Publication year: 2013 Source:Building and Environment, Volume 61
Computational Fluid Dynamics (CFD) simulations can be used to assess indoor natural ventilation by solving the interaction between the urban wind flow and the indoor airflow. The air exchange rate (ACH) can be obtained from the simulated volume flow rates through the ventilation openings or by the concentration decay method that is often used in experimental studies. This paper presents 3D unsteady Reynolds-averaged Navier–Stokes (RANS) CFD simulations to reproduce the decay of CO2 concentration in a large semi-enclosed stadium. The study focuses on the hours after a concert, when the indoor CO2 concentration generated by the attendants has reached a maximum. The wind flow, indoor airflow and dispersion of heat, water vapour and CO2 are modelled on a high-resolution grid based on a grid-sensitivity analysis. The simulations are validated with on-site measurements of wind velocity and CO2 concentration decay. The validated CFD model is used to analyse the significant horizontal and vertical CO2 concentration gradients in the stadium, showing local differences at t=300s up to 700ppm (i.e. 37% of the maximum of 1900ppm). A specific piecewise-linear technique is applied for the concentration decay method to determine the ACH values for smaller time-intervals. This is needed because the plotted semi-logarithmic decay curve itself is not linear because the ventilation rate changes over time, due to the changing buoyancy forces. It shows that the ACH values decrease from about 2h−1 at the beginning of the concentration decay simulations to about 0.3h−1 at the end.
Graphical abstract
Highlights
► CFD simulations have been performed to model CO2 concentration decay from a large stadium. ► Effects of air temperature and water vapour concentration on flow field are included. ► Coupled modelling approach to model indoor and outdoor airflow simultaneously in one domain. ► CFD model is validated using full-scale measurements of wind velocity and CO2 concentration. ► A piecewise-linear method is applied to obtain ACH values for small time-intervals.
March 2013 Publication year: 2013 Source:Building and Environment, Volume 61
As the main regulation tool of indoor thermal environment in warm seasons, air-conditioners are used to keep a cool environment. However, this causes problems of huge energy consumption and poor indoor air quality. In contrast, electric fans promise an indoor cooling effect with lower energy consumption. This makes the exploration of air flow utilization significative. This paper discusses the results of a research with both an online survey and a series of climate chamber experiment to study user requirements for air movement in their daily life. The online survey results showed that electric fans were widely accepted in both homes and offices because they were environmental friendly, low-cost and could provide a fresh feeling. The results of climate chamber experiment identified suitable range of indoor temperature to use electric fans and their corresponding range of air speeds. The air flow generated by electric fans could be used as an effective cooling method to maintain a comfortable environment at 28 °C–32 °C. Compared with the acceptable range of temperature and air speeds for the comfort zone recommended by the ASHRAE Standard 55-2010, this study showed that air speeds over 0.8 m/s were acceptable and they could offset a higher temperature. With reasonable utilization, electric fans could provide a healthy and energy-efficient way to control indoor environment.
Highlights
► An online survey showed large demand for fan use in both homes and offices. ► Appropriate air flows can help to maintain thermal comfort between 28 °C and 32 °C. ► The capacity to control could improve the subject's thermal comfort level. ► Temperatures over 32 °C would require the combination of fans and air-conditioners.
Available online 2 January 2013 Publication year: 2013 Source:Building and Environment
Indoor air humidity is an important factor influencing air quality, human comfort, energy consumption of buildings and the durability of building materials. As a result, the aim of this study is to put forward a numerical approach for conjugate thermo-solutal-convection and condensation of humid air phenomena in rooms. The numerical model pertinence is thoroughly analyzed using experimental data for ventilated enclosures (isothermal conditions, cold air supply, hot air supply and specific study of water vapour condensation on a cold glazed wall). Consequently, we first describe the experimental set-up (the test cell), focusing particularly on the elements concerning the humidification system and condensation qualification system, especially added for this study. This is followed by the numerical model description. The approach is essentially based on the computational fluid dynamics technique, adding a convection-diffusion conservation equation of water vapour to the basic equations for a turbulent non-isothermal air flow. In addition, detailed presentation of water vapour surface and volume condensation modelling is given. The results from our work can find a direct applicability in several fields: residential and commercial buildings (thermal comfort and energy consumption), museums and industry (microclimate control and technological conditions), vehicles (freezing prediction on the windshield).
Highlights
► comprehensive thermo-solutal-convection CFD model for humid air in rooms. ► in addition: water vapour surface and volume condensation modelling. ► experimental validation based on full scale test cell (ventilated enclosure). ► focus on the experimental humidification and condensation qualification systems. ► analysed cases: isothermal/cold/hot air supply; condensation on glazed walls.
February 2013 Publication year: 2013 Source:Building and Environment, Volume 60
Limited data suggest that whole-house ventilation systems in California don't always perform as code and forecasts predict. Deficiencies occur because systems are usually field assembled without design specifications, and there is no consistent process to identify and correct problems. The value of such activities in terms of reducing energy use and improving indoor air quality (IAQ) is poorly understood. Commissioning such systems, either when they are installed or during subsequent building retrofits, is a step towards eliminating deficiencies and optimizing the trade-off between energy use and IAQ.The goal of this study was to determine the potential value of commissioning residential whole-house ventilation systems that are intended to comply with California's Title 24 residential ventilation requirements. A computer modeling approach was used to assess the impact on occupant health and building energy use of malfunctioning whole-house ventilation systems. Energy and IAQ impacts were quantified and then compared by using the Time Dependent Valuation (TDV) approach for energy and a Disability Adjusted Life Year (DALY) approach for IAQ. Results showed that health benefits dominated energy benefits independently of house size and climate. The metric for commissioning whole-house ventilation systems should be net present value of the combined energy and IAQ benefits to the consumer. Commissioning cost decisions should be made relative to that value even if that means ventilating to exceed the ASHRAE 62.2 minimum.As a consequence of combining IAQ and energy costs, the beginning of an approach to optimize the ventilation rates of homes was established.
Highlights
► Ventilation health costs dominate energy costs when using DALY and TDV approaches. ► This is independent of house size and climate. ► Potential health impacts are large when ventilation airflows are low. ► Decisions about tuning whole-house ventilation rates should be made with knowledge on indoor pollutant emission rates. ► Combining health and energy costs via their monetization leads to an approach to find the optimal ventilation rate for homes.
March 2013 Publication year: 2013 Source:Building and Environment, Volume 61
The concentration of contaminant in a room is not always uniformly distributed and hence it is important to evaluate the ventilation efficiency at various points or domains in the room to optimize and reduce the ventilation rate and the air-conditioning load of the room. Various ventilation indices have been developed to evaluate the ventilation efficiency of a point or a domain based on the contaminant concentration, for example, the age of air, the Scale for Ventilation Efficiency series, Visitation Frequency and Purging Flow Rate.This paper presents a new concept of ventilation index, Net Escape Velocity (hereafter NEV), as an index for ventilation efficiency in an indoor environment. NEV represents the effective velocity at which the contaminant is transported/diluted from a target point. The objectives of the present work are to clarify the definition and concept of NEV on the basis of CFD simulation and to investigate the calculation methods of NEV. NEV is defined by contaminant concentration, convective flux and diffusion flux at a point. Using NEV normalized by the convection velocity at a target point, we can obtain information of the turbulent diffusion effect for removal/dilution contaminant and of the direction of diffusion flux which is the same or not with convective flux. It can be said that NEV is an index of ventilation efficiency that can evaluate the ventilation performance at a point and enable understanding of the forming structure of a contaminant concentration at a point.
Highlights
► We provided a new concept of ventilation efficiency for an indoor environment. ► Net Escape Velocity presents the efficiency of contaminant transport at a point. ► Purging Flow Rate and NEV are fundamental ventilation concepts. ► The relationships between NEV and existing indices were clarified. ► NEV is predicted by RANS model in CFD analysis.
March 2013 Publication year: 2013 Source:Building and Environment, Volume 61
Reduction of noise is one of the multiple benefits of building envelope greening measures. The potential of wall vegetation systems, green roofs, vegetated low screens at roof edges, and also combinations of such treatments, have been studied by means of combining 2D and 3D full-wave numerical methodologies. This study is concerned with road traffic noise propagation towards the traffic-free sides of inner-city buildings (courtyards). Preserving quietness at such locations has been shown before to be beneficial for the health and well-being of citizens. The results in this study show that green roofs have the highest potential to enhance quietness in courtyards. Favourable combinations of roof shape and green roofs have been identified. Vegetated façades are most efficient when applied to narrow city canyons with otherwise acoustically hard façade materials. Greening of the upper storey’s in the street and (full) façades in the courtyard itself is most efficient to achieve noise reduction. Low-height roof screens were shown to be effective when multiple screens are placed, but only on conditions that their faces are absorbing. The combination of different greening measures results in a lower combined effect than when the separate effects would have been linearly added. The combination of green roofs or wall vegetation with roof screens seems most interesting.
Highlights
► Full-wave numerical models were used to study many building envelope greening measures. ► Green roofs are most interesting to achieve noise reduction at quiet sides. ► Roof edge screens and façade vegetation can lead to significant noise reductions too. ► Combinations of green walls or green roofs with roof edge screens are efficient.
Available online 4 January 2013 Publication year: 2013 Source:Building and Environment
Graphical abstract
Highlights
► Outdoor air quality is one of the major environmental problems today. ► Micro-scale pollutant dispersion covers the building scale and the meteorological micro-scale. ► Computational Fluid Dynamics (CFD) is increasingly used for micro-scale dispersion studies. ► Virtual Special Issue groups papers published previously on this topic in Building & Environment. ► Some trends and directions for future research are outlined
Available online 5 January 2013 Publication year: 2013 Source:Building and Environment
Air tightness is an important parameter for both smoke suppression in a fire and for the energy efficiency of buildings. A transient method using a sudden expansion of compressed air (SECA) was recently introduced to measure the air tightness, or effective leakage area, with the least amount of labor or preparation. Although the feasibility of SECA has been reported, relevant experimental data has been limited to small leakage areas of up to 20 cm2, which has not been sufficient to cover the leakage of rooms in buildings. In this study, a test room and the test module for SECA were modified and the basic equation of the transient method was improved. As a result, the application limit of the leakage area can be extended up to 700 cm2, and further extension would be possible simply by increasing the chamber volume or its initial pressure. The experimental results of SECA can be related theoretically to the results of a steady method, and they were not affected by the volume of the room. The results of this study will help prove the most convenient measurements for air tightness and for the effective leakage areas in rooms and ventilation systems.
Highlights
► The air tightness was measured with an improved method using a sudden expansion of compressed air (SECA). ► SECA showed very good linearity in the relationship with the actual open area and the measurable range can be easily extended. ► The relationship between the SECA and the blower method can be explained theoretically. ► SECA is the most convenient method for the practical inspection of air tightness in buildings.
