Air Permeability Rate Research Articles

Study on the influence of the fully enclosed barrier on the vortex-induced vibration performance of a long-span highway–railway double-deck truss bridge

Long-span highway–railway double-deck truss bridges are mostly located in urban centers, where noise pollution and traffic safety issues have a great impact. The fully enclosed barrier has excellent sound insulation and windproof performance and has been widely used in double-deck truss bridges in recent years. However, the large volume and the low air permeability rate will affect the aerodynamic characteristics of the bridge, resulting in vortex-induced vibration (VIV). To analyze how the fully enclosed barrier influences the highway–railway bridge VIV performance, this study analyzes the Huangjuetuo Yangtze River Bridge, combined with the wind tunnel test and the numerical calculation method to study different variations of the static three-force coefficient, the change of VIV response, and its influence mechanism after setting the fully enclosed barrier. The results show that the static three-force coefficient of the double-deck truss bridge changes significantly, the drag coefficient increases, and the absolute values of the lift coefficient and the moment coefficient decrease after the fully enclosed barrier is set. The aerodynamic performance of the bridge is significantly reduced after the fully enclosed barrier is set, and the amplitude and range of the VIV response are increased. Vertical bending VIV increased by an average of 58.5%, and torsional VIV increased by an average of 21.9%. Considering driving comfort and safety, attention should be paid to the double-deck truss bridge with a fully enclosed barrier.

A Heat Loss Sensitivity Index to Inform Housing Retrofit Policy in the UK

A substantial number of dwellings in the UK have poor building fabric, leading to higher carbon emissions, fuel expenses, and the risk of cold homes. To tackle these challenges, domestic energy efficiency policies are being implemented. One effective approach is the use of energy models, which enable sensitivity analysis to provide valuable insights for policymakers. This study employed dynamic thermal simulation models for 32 housing archetypes representative of solid-walled homes in the UK to calculate the heat loss and the sensitivity coefficient per building fabric feature, after which a metric Heat Loss Sensitivity (HLS) index was established to guide the selection of retrofit features for each archetype. The building fabric features’ inputs were then adjusted to establish both lower and upper bounds, simulating low and high performance levels, to predict the how space heating energy demand varies. The analysis was extended by replicating the process with various scenarios considering climates, window-to-wall ratios, and overshadowing. The findings highlight the external wall as the primary consideration in retrofitting due to its high HLS index, even at high window-to-wall ratios. It was also established that dwelling type is important in retrofit decision-making, with floor and loft retrofits having a high HLS index in bungalows. Furthermore, the analysis underlines the necessity for Standard Assessment Procedure assessors to evaluate loft U-value and air permeability rates prior to implementing retrofit measures, given the significance of these factors in the lower and upper bounds analysis. Researchers globally can replicate the HLS index approach, facilitating the implementation of housing retrofit policies worldwide.

Experimental Study of Envelope Airtightness in New Egyptian Residential Dwellings

In residential buildings, air infiltration impacts energy, indoor air quality, and thermal comfort considerably. While air infiltration in residential buildings has been the focus of many studies, most published field-testing results pertain to developed countries, with little or no data on air infiltration in developing nations. This paper presents the results of one of the first field investigations into envelope infiltration in the residential buildings of the hot-arid climatic area of Egypt. To analyze the air permeability of the building envelope, the fan pressurization method, often known as the blower door test (BDT), is used, following ISO 9772. The study focuses on 20 residential dwellings built with heavy construction materials and subjects them to extensive characterization and testing. The average air leakage and the air permeability rate for the tested sample were 6.14 h−1 and 17.3 m3/(h∙m2), respectively. However, significant variations in airtightness were observed across the dwelling, leading the team to test several building-related parameters statistically to study their impact on airtightness. Fenestration quality appeared to be a critical factor in determining air infiltration, showing a strong correlation with the air change and leakage. A further investigation underscored that the specific aperture factor and the fenestration quality can predict the infiltration rates to a large degree. Thus, we recommend further investigation of these characteristics in heavy construction material building. Finally, we strongly recommend that building codes in developing countries such as Egypt include minimum performance requirements for fenestration.

Uncertainties in Non-Domestic Energy Performance Certificate Generating in the UK

In light of the recent launch of the Minimum Energy Efficiency Standard targeting the energy performance of commercial buildings, this study compares the energy performance certificates of three UK hotels generated by two different software, EDSL TAS and SBEM, both accredited by the UK government for the purpose. Upon finding the results discrepant, the study finds that the two software’s different assumptions for the air permeability rate contribute to the discrepancy. While modifying this value makes the results from the two software more aligned, further issues regarding the validation process arise. The study continues to find that the underlying issue can be found within the National Calculation Methodology’s assumption about domestic hot water consumption in hotels. These assumptions are compulsory to follow when generating a non-domestic energy performance certificate in the UK, therefore, any uncertainties within them can affect all the buildings seeking an energy performance certificate within that sector. Finally, the study discusses that, for meeting the carbon dioxide mitigation goals, it is necessary to make changes to the current procedure of energy performance certificate generating in the UK to increase its reliability.

Parametric Study of Air Infiltration in Residential Buildings—The Effect of Local Conditions on Energy Demand

Airtightness is nowadays one of the physical parameters which determine overall building energy performance. In a wide range of states, the upper limit for air change rate at a Pa (na), air permeability rate at a Pa (qa), or specific leakage rate at a Pa (wa) is determined by the formal regulations. It should be highlighted that airtightness requirements are mainly the same around the world, disregarding any site and climatic conditions. The main goal of the presented work was to reveal the effect of individual location and surrounding infiltration rate and heat demand. The analyses were done using numerical techniques and computational models of the three buildings developed and calibrated based on the blower door test results. The compared buildings characterize by a similar geometry but differ in the air change rate at 50 Pa (n50). Analyses done for different locations and levels of sheltering by surrounding elements allow the determination of the real effect of local conditions. The obtained differences in energy demand between two locations from the same climatic zone were from 70% to 90%, depending on the airtightness of the buildings. Considering different sheltered conditions, the differences for the same location can be even 200%. The obtained results allowed for the formulation of the general conclusion that building location and level of exposure could be considered in future airtightness regulations.

Electrospun cellulose acetate and poly(vinyl chloride) nanofiber mats containing silver nanoparticles for antifungi packaging

Nanofiber mats of poly(vinyl chloride) (PVC) and cellulose acetate (CA) encapsulated with silver (Ag) nanoparticles were fabricated via electrospinning for potential use as antimicrobial food packaging materials. 16 wt% PVC was prepared in 1:1 w/w tetrahydrofuran—N,N-dimethylformamide while 16 wt% CA was prepared in 3:2 (w/w) Acetone—N,N-dimethylformamide. Scanning electron microscopy analysis showed that thinner fibers could be electrospun from cellulose acetate as compared to poly(vinyl chloride) at the same solution concentrations with fiber diameters ranging from 70 to 130 nm for cellulose acetate and 180–340 nm for poly(vinyl chloride). Nanofiber diameter reduced with addition and increase of silver nanoparticles from 0 to 1 wt%. Due to the smaller cellulose acetate nanofiber diameter, its mats had lower air permeability rates. Tensile strength tests indicated that the nanofiber mats had marginal to good tensile strength values relative to film based packaging materials. Antimicrobial examination of the nanofiber mats against yeast and mould indicated that there was inhibited growth of the microorganisms on mats containing silver nanoparticles.

Energy impact of the air infiltration in residential buildings in the Mediterranean area of Spain and the Canary islands

Air infiltration through the building envelope has already been proven to have a significant energy impact in dwellings. Different studies have been carried out in Europe, but there is still a lack of knowledge in this field regarding mild climates. An experimental field study has been carried out in the Mediterranean climate area of Spain and the Canary Islands in order to assess the air permeability of the building envelope and its energy impact. A wide characterization and Blower Door tests have been performed in 225 cases in Alicante, Barcelona, Málaga, Sevilla and Las Palmas de Gran Canaria for this purpose. The obtained mean air permeability rate for the 225 studied cases was 6.56 m3/(h·m2). The influence of several variables on airtightness was statistically analysed, although only location, climate zone and window material were found to be significant. Air infiltration has an energy impact between 2.43 and 16.44 kWh/m2·year on the heating demand and between 0.54 and 3.06 kWh/m2·year on the cooling demand.

Airtightness of residential buildings in the Continental area of Spain

Infiltration plays a relevant role regarding the energy performance of buildings. Many European countries have already established standards which aim to limit the energy waste through the envelope following the European Energy Performance of Buildings Directive guidelines. However, in Mediterranean countries there is still a lack of knowledge in this field. An extensive study has been carried out in order to characterize the air leakage through the envelope of the existing housing stock in the Continental climate area of Spain. Results of 129 dwellings tested, including different typologies and periods of construction, are shown. Blower door tests were performed, and thermal imaging was used to locate leakage paths. Single-family dwellings were found to be more airtight than apartments, given that the mean air permeability rate at 50 Pa (q50) was 5.4 m3/h·m2 and 6.8 m3/h·m2 respectively. The mean air change rate at 50 Pa (n50) was 6.1 h−1 for single-family dwellings and 7.1 h−1 for multi-family housing. Nevertheless, great dispersion of results and extreme values were found. In addition, the influence of several construction characteristics on permeability results was assessed.

Evaluating the influence of building fabric, services and occupant related factors on the actual performance of low energy social housing dwellings in UK

This paper empirically investigates the influence of building fabric, services and occupant related factors on actual energy use of six case study dwellings, located in three new low energy social housing developments in UK, covering a variety of built forms and construction systems (timber frame, hempcrete, steel-frame). Physical monitoring of indoor environment and window-opening is cross-related with building fabric and systems’ performance, and qualitative data gathered through occupant surveys, review of control interfaces and handover guidance, to understand the causes of the gap between modelled and measured energy use. Actual energy use is found to exceed design expectations by a factor of three, questioning the need for whole-house mechanical ventilation heat recovery (MVHR) systems at measured air permeability rates of 6 m³/(h.m²) against the design target of 3 m³/(h.m²). Lack of proper commissioning of MVHR and heating systems, combined with inadequate user comprehension about their operation and control leads to occupant ‘misuse’ wherein systems are de-activated, thereby negatively affecting indoor air quality. This is confounded by occupant factors related to higher demand temperatures, unexpected opening of windows during winters due to under-performance of MVHR combined with habitual behaviours, and over-use of heating systems to compensate for higher than expected air permeability.

Polydimethylsiloxane‐modified polyurethane–poly(ɛ‐caprolactone) nanofibrous membranes for waterproof, breathable applications

ABSTRACTIn this study, we prepared polydimethylsiloxane (PDMS)‐modified polyurethane–poly(ɛ‐caprolactone) nanofibrous membranes with excellent waterproof, breathable performances via an electrospinning technique. Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and mechanical testing were used to characterize the morphologies and properties of the composite nanofibers. The fiber diameter and porous structure of the membranes were regulated by the adjustment of the temperatures of thermal treatment and the PDMS concentrations. The fibrous membranes obtained at a typical temperature of 70 °C possessed an optimized fibrous structure with a diameter of 514 ± 2 nm, a pore size of 0.55–0.65 µm, and a porosity of 77.7%. The resulting nanofibrous membranes modified with 5 wt % PDMS were endowed with good waterproof properties (water contact angle = 141 ± 1°, hydrostatic pressure = 73.6 kPa) and a high breathability (air permeability rate = 6.57 L m−2 s−1, water vapor transmission rate = 9.03 kg m−2 day−1). Meanwhile, the membranes exhibited robust mechanical properties with a high strength (breakage stress = 11.7 MPa) and excellent thermal stability. This suggests that they would be promising candidates for waterproof, breathable applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46360.

Cost-effective envelope optimisation for social housing in Brazil's moderate climates zones

Brazil faces a housing deficit of more than 5.5 million units and nearly 11 million existing homes present inadequate living conditions. In response, the Brazilian government launched in 2009 a mass social housing programme with a target of delivering 24 million new units for low-income households by 2022. Their standardised design is relatively cheap to build but does not take into account climatic conditions, thermal comfort and energy efficiency. This could result in poor performance and uncomfortable indoor environments that could impact of the occupier's health and lead to the unnecessary use of energy-hungry space conditioning systems. Given the scale of this programme, the potential impact on Brazil's already debilitated socio-economic and environmental balance is very substantial. In this work, the authors have deployed sensitivity analysis to explore a variety of envelope combinations through dynamic building simulation for three southern Brazilian cities, Curitiba, Sao Paulo and Porto Alegre, aiming to achieve better than the typical performance. Thermal transmittance properties and air permeability rates were tested from the most common construction characteristics in Brazil to some of the highest levels of fabric energy efficiency. These combinations were also analysed in terms of their cost-effectiveness. The results suggested that optimised envelopes could improve thermal comfort by up to 97% in comparison to a typical envelope, but also cost nearly 50% more. Other envelope combinations investigated were shown to be more cost-effective with a significant increase of thermal comfort levels and were therefore considered to be a more adequate solution for the context.

Do deep low carbon domestic retrofits actually work?

This paper uses a socio-technical building performance evaluation (BPE) approach to assess the pre- and post- actual performance of two discrete deep low energy retrofits in the UK – a Victorian solid-wall house and modern 1990s cavity-wall house. A ‘low-energy first, then low-carbon’ approach was adopted in both cases, to achieve an 80% reduction in annual CO2 emissions. Pre-retrofit, both houses had lower measured annual gas consumption as compared to predictions made by energy models, although the electricity consumption in the modern house was higher than modelled, due to occupancy pattern and occupant behaviour. Post-retrofit, it was found that the Victorian house achieved nearly 75% CO2 reduction, while the modern house achieved only 57% CO2 reduction over the baseline emissions. Key reasons were higher than expected air permeability rates, installation issues with micro-renewable systems, lack of proper commissioning, usability of controls, occupant preferences and behaviour. Despite the gap between expected and actual carbon emissions, occupant comfort and satisfaction was significantly improved across both retrofits. This evidence-based understanding of the process and outcomes of deep low carbon retrofits is vital not only for learning and innovation, but also for scaling-up deep retrofit programmes for meeting national and international carbon targets.

Preparation and characterization of ternary composite films of polyvinyl alcohol/sodium alginate/TiO2

Nano-TiO2 with anionic surface active agent sodium dodecylsulfate (SDS) modified, the poly(vinyl alcohol)/sodium alginate/TiO2 composite films were prepared by method of solution blending representing. The structure of the films was analyzed by XRD and SEM. In addition, air permeability rate, swelling ratio, light transmittance, mechanical properties, and antibacterial properties were tested. The results showed that in compound membrane there was a strong force between poly(vinyl alcohol)/sodium alginate and TiO2 particles, indicating that there was good compatibility between the sodium alginate and the poly(vinyl alcohol). The mixed membranes were of good water resistance, tensile strength, and closure. When the titanium dioxide content increased appropriately, they had very good mechanical properties. In addition, the antibacterial properties of composite membrane gradually increased with the increase in the TiO2content.

Influence of the Yarn Formation Process on the Characteristics of Viscose Fabric Made of Vortex Coloured Spun Yarns

In this study, based on the Box-Behnken design, regression statistical analysis is introduced to evaluate the influence of yarn formation process variables (nozzle pressure, yarn delivery speed and yarn count) on the properties (breaking strength, air permeability rate, dynamic drape coefficient and mass loss rate) of viscose fabric fabricated from vortex colored spun yarns. Quadratic regression models for response variables affected by different combinations of model items are given. Research results show that the air permeability rate and dynamic drape coefficient for viscose fabric decreases with an increase in the yarn delivery speed from 320 to 380 m/min, while the fabric mass loss rate and fabric breaking strength are less affected by the yarn delivery speed. The mass loss rate of viscose fabric increases, reaches a peak, and then decreases with increasing nozzle pressure, while its dynamic drape coefficient, affected by the nozzle pressure, takes on the opposite trend. However, nozzle pressure has less significant effects on fabric breaking strength and fabric air perme ability. The air permeability rate and mass loss rate of viscose fabric increases firstly and then decreases with a decreasing yarn count, while the effect of yarn count on the fabric breaking strength and dynamic drape coefficient exhibits an opposite trend. Decreasing the yarn count makes the fabric dynamic drape coefficient drop firstly and then augment.

The Effects of Air Permeability, Background Ventilation and Lifestyle on Energy Performance, Indoor Air Quality and Risk of Condensation in Domestic Buildings

Effective and efficient ventilation is essential when improving energy performance and Indoor Air Quality (IAQ) of buildings. Reducing air permeability can considerably improve the energy performance of buildings; however, making the buildings more airtight may result in lower rates of natural ventilation which may in turn increase the risks of condensation and unacceptable IAQ. This study evaluates the effects of different air permeability rates, background ventilation and occupants’ lifestyles on the energy performance as well as the risk of condensation and CO2 concentration in domestic buildings. Dynamic computer simulations were conducted in EnergyPlus. Results indicated direct relations between the ventilation rates, energy performance and IAQ. Higher air permeability along with background ventilation resulted in considerably better IAQ while energy consumption increased by up to four times. Occupants’ lifestyles were identified as a major contributor to the risk of condensation.

Air Permeability Tests of Masonry Structures

To date, the assurance of sufficient building‘s air tightness remains a problematic issue, because it is linked not only to the right technology solution selection and quality work, but also to the building envelope air permeability properties. Typically, when modelling building energy demand, it is considered that the building envelope is impermeable to air. Nevertheless, this claim is unjustified. Studies have shown that building materials are porous. However, there is no evidence how air permeability changes through the masonry construction, when it is heterogeneous. Therefore, this work is to determine the air permeability of the various types of masonry construction, also assessing the technological masonry aspects, determine the air permeability rate and evaluate the results obtained in the analysis by providing recommendations. DOI: http://dx.doi.org/10.5755/j01.sace.9.4.7913