Air Infiltration Research Articles

Mesoscopic-scale study of convection-induced morphological evolution of solid-air dendrites in liquid hydrogen

The trace amount of air infiltration that may occur during the utilization of liquid hydrogen may be confronted with a severe security risk. Considering the effect of convection, a six-fold symmetric solid-air dendrite growth numerical model is established for the coupling of flow field, temperature field and solute field during solidification process. For regular Cartesian grids, a factor is introduced to reduce the anisotropy of grids, and its validity is verified. The reliability of the model is evaluated by comparing the numerical results of the growth of ice-dendrite with the same face-centered cubic structure with the experimental results, and the subsequent numerical results of solid-air dendrites growth rate match well with the results of analytical theory. On this basis, the growth characteristics of solid-air dendrites under diffusion condition and natural convection and forced convection conditions are studied. The results show that the tip of each dendrite arm has a consistent growth rate under diffusion condition, and the dendrites present a six-fold symmetric morphology. The dendrite growth is promoted in the upstream and inhibited in the downstream under both natural convection and forced convection conditions, and the morphology of the reshaped dendrites lose symmetry. Forced convection promotes upstream more than it inhibits downstream. The mechanism of the two conditions affecting the growth of solid-air dendrites and the differences between them are explained in detail.

Particle radioactivity from radon decay products and reduced pulmonary function among chronic obstructive pulmonary disease patients

BackgroundRadon (222Rn) decay products can attach to particles in the air, be inhaled, and potentially cause airway damage. Research questionIs short-term exposure to particle radioactivity (PR) attributable to radon decay products emitted from particulate matter ≤2.5 μm in diameter (PM2.5) associated with pulmonary function in chronic obstructive pulmonary disease (COPD) patients? Study design and methodsIn this cohort study, 142 elderly, predominantly male patients with COPD from Eastern Massachusetts each had up to 4 one-week long seasonal assessments of indoor (home) and ambient (central site) PR and PM2.5 over the course of a year (467 assessments). Ambient and indoor PR were measured as α-activity on archived PM2.5 filter samples. Ratios of indoor/ambient PR were calculated, with higher ratios representing PR from an indoor source of radon decay. We also considered a measure of outside air infiltration that could dilute the concentrations of indoor radon decay products, the indoor/ambient ratio of sulfur concentrations in PM2.5 filter samples. Spirometry pre- and post-bronchodilator (BD) forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were conducted following sampling. Generalized additive mixed models were adjusted for meteorologic variables, seasonality, and individual-level determinants of pulmonary function. We additionally adjusted for indoor PM2.5 and black carbon (BC). ResultsPR exposure metrics indicating radon decay product exposure from an indoor source were associated with a reduction in FEV1 and FVC. Patients in homes with high indoor PR (≥median) and low air infiltration (<median) compared to others had a −26.9 (95% CI: −61.4, 7.7) mL and −75.4 (95% CI: −128.6, −22.2) mL reduction in post-BD FEV1 and FVC, respectively. These associations remained similar after PM2.5 and BC adjustment. InterpretationOur findings raise concern about the harmful effects of PR exposures attributable to residential radon on pulmonary function in patients with COPD.

Modelling and real-data validation of a logistic centre using TRNSYS®: Influences of the envelope, infiltrations and stored goods

In this paper, the authors aim to support users when modelling scenarios with complex processes entailing thermal loads and infiltrations. The large building analysed is a logistics centre for the replenishment and distribution of perishable foodstuffs where cold chains must be maintained. The logistics centre, with 96 loading/unloading docks, handles large turnovers of different goods. This produces heat inside the facility. Due to continuous loading/unloading, the infiltrations in the building, and the fixed and variable thermal loads, this facility consumes a large amount of energy.Aiming to optimise the centre and contribute to sustainable development goal SDG7, this building has been modelled with a classical non-D envelope using TRNBuild® and also with the more sophisticated 3D software, SketchUp®, to compare and validate their results over a year with real consumption, as well as to assess the main sources of energy consumption. To obtain reliable results, the authors provide some methodology models to identify the sources of the building's thermal losses and quantify the different sources of consumption. These models are useful tools to support decision-makers (to improve insulation and arrange loads, among other things) when trying to reduce energy use in large buildings with intense operating processes.The results indicate that by modelling the entire facility with 3D software, the model estimation differs from real consumption by around 7.22%, while using a non-D model increases the difference to 26%. Additionally, the results show that around 47% of the energy consumption in the building is due to air infiltrations during loading/unloading, 18% is due to perishable products, and around 30% is due to building insulation. The methodology and models presented here, including the possibility of modifying the thermal load profiles, have demonstrated their capacity to reduce and optimise the load demand of refrigeration for warehouses if reliable data records are available.

Unraveling the Drivers Controlling the Transient and Seasonal CO2 Dynamic in a Shallow Temperate Cave

Understanding the dynamics and spatial distribution of gases in the subterranean atmospheres is essential to increase the reliability of carbon balances in karst ecosystems or the paleoclimate reconstructions based on cave deposits. This scientific information is also very valuable for cave managers to ensure the safety of visitors and the conservation of the subterranean heritage. Through a comprehensive monitoring of the main air parameters in a shallow temperate cave, we decipher the physical drivers and mechanisms involved in the CO2 and radon exchange between the cave and the outer atmosphere, and how this process is triggered by the changes of local weather. Our results reveal that the biphasic infiltration (water plus air) in the network of penetrative structures from the overlying soil and host rock exercise remarkable control over the cave environment, delaying the thermal response of the cave air to the outer climate-driven changes and also the gaseous transfer between the cave atmosphere and the exterior. The cave location concerning the karstified outcrop determines that this subterranean site acts as a gas emitter during summer, which is contrary to what happens in many other caves. Prominent gas entrapment at a micro-local level is also registered in some upper galleries.

INFILTRACIÓN EN UN EDIFICO COMPLEJO

The air infiltration through building envelope mainly depends on the doors and windows tightness considered by means of the corresponding effective leakage areas and the pressure difference between the building exterior and interior. Although the standards provide simple methods to estimate the parameters that control the air movement, significant differences in the volumetric flow of fresh air are observed between the standardized and the most accurate traditional methods. Our aim is to evaluate the infiltration in a two-storey building with a large central atrium during the typical day in January by considering all the relevant parameters. The analytical result is incorporated to the numerical simulation with EnergyPlus to determine the internal temperature evolution that is sensitive to the air intake. Simulation results are compared with in-situ measurements. It is found that the air infiltration rate calculated from the standardized procedure only enables the internal temperature evolution to be reproduced with a substantial adjustment of the design air infiltration rate. The methodology developed is useful to calculate the infiltration in buildings under actual use conditions and assess the air leakage when measurements are not available.

Experimental and numerical analysis of indoor air quality affected by outdoor air particulate levels (PM1.0, PM2.5 and PM10), room infiltration rate, and occupants' behaviour

This study conducted an experimental analysis of how indoor air quality (IAQ) is influenced by the outdoor air pollutants levels, infiltration rate, and occupants' behaviours. The impacts of these factors on IAQ were analyzed using on-site measurements and numerical simulations. The results contribute to a better understanding of how to control the Indoor Particulate Level (IPL) for the specific conditions of the studied building. Results showed that occupant behaviour was the primary factor in determining the IPL, significantly changing the number of outdoor particles introduced to the building. Moreover, it was found that the IPL was exponentially correlated to the Outdoor Particulate Level (OPL). Based on numerical simulations, this study concluded that smaller particles do not always have more chance than larger particles of accessing the indoor environment through the building envelope. Meanwhile, a steady-state indoor particle concentration numerical model was established and verified using the 4-fold cross-validation method. Finally, simulation results identified that the room infiltration rate had a positive linear impact on IAQ if the OPL was under 30 μg/m3. This is because the increased air exchange rate can help to dilute indoor air pollutants when the outdoor air is relatively clean.

Passive Night Cooling Potential in Office Buildings in Continental and Mediterranean Climate Zone in Croatia

The envelope is one of the most important driving factors in the energy efficiency of buildings. Typical for office and commercial buildings, curtain wall facades allow solar heat gains to be used during the winter but can lead to difficulties in reducing the cooling load during summer. The cooling load is dominant in most building types in the temperate maritime climate, while in the temperate continental climate, it is dominant mainly in office and commercial buildings. The goal of this research was to determine the potential of night passive cooling in an office building model in the most populated urban areas in Croatia-Zagreb and Split, which are located in two different climate zones. Suitable to the climate on-site, an appropriate building envelope and various types of passive and mechanical ventilation systems were selected for each location and case. Additional factors included and analysed were climate conditions, heat gains, the heat accumulation of the building, night ventilation through openings, unwanted air infiltration, and cooling loads. Through a detailed description of the model, passive cooling potential calculations, and Computer Fluid Dynamics (CFD) simulations, the results showed a potential of up to 43.5% savings in the cooling energy need for the temperate continental climate and 32.2% in the temperate marine climate. It was found from the analysis that night ventilation is expected to cool down the building enough to delay a need for cooling by several hours and improve fresh air requirements, thus saving power for cooling, and effectively reducing the need for air conditioning.

Evaluating Indoor Carbon Dioxide Concentration and Ventilation Rate of Research Student Offices in Chinese Universities: A Case Study

This work provides a case study on the indoor environment and ventilation rate of naturally ventilated research student rooms in Chinese universities. In the measured room, air temperature, relative humidity and carbon dioxide (CO2) concentration were monitored during the heating period for 4 weeks. The number of indoor occupants, occupied time of the room and window/door-opening cases were simultaneously recorded. Results showed the research student room was occupied for an average of 12.0 h each day. Due to a large indoor and outdoor temperature difference during the heating season, and occupants’ adaption to indoor environment, indoor occupants seldom open windows/doors for ventilation. Air exchange of the room only by air infiltration cannot meet the ventilation requirement. As a result, an average of 77.6% of measured CO2 data each day exceeded 1000 ppm during occupied time. In fact, according to CO2 data, it was observed that window/door opening could effectively decrease indoor CO2 concentration. Therefore, intermittent window/door opening or CO2-based demand-controlled ventilation facilities were suggested for improving indoor air quality of such rooms. Additionally, special attention should be paid to other possible outdoor pollution.

RH simulation model for canvas paintings protected by an aluminium backplate and an additional hygroscopic layer

To protect a canvas easel painting, a common conservation strategy is to add a back plate at the stretcher, creating a closed air void. This plate protects not only from dust but mainly from temperature and relative humidity (RH) variations in the room and moisture changes in the wall on which it is hanging. The addition of hygroscopic layers can reduce the amplitude and change phase of humidity oscillations. This paper proposes a new mathematical model that can be used to predict moisture levels within the canvas when this conservation strategy is applied. The model is compared against the temperature and RH detailed experimental data, captured and shown in the latest paper by Padfield et al. Back protection of canvas painting. Our paper presents values of T, RH and mixing ratio (MR) obtained at the different layers of an easel painting, protected and unprotected, with cotton and without it, submitted to different room and wall temperature and RH cycles. The experimental results show a phase displacement between the canvas temperatures and the corresponding RH values in the canvas air boundary layer. In some cases this phase shift, which is an unexpected behaviour, allows RH and temperatures to achieve their maximum value at the same time. The purpose of the model is to simulate the RH response at the different air boundary layers inside the air void, such as the canvas, the aluminium back plate, and the hygroscopic cotton protection, produced by cyclic variations of temperature in the room or the wall. The model is built simulating four interrelated processes: the canvas permeation flow, the air infiltration rate between room and void, the equilibrium moisture content (EMC) and the vapour sorption rate for the canvas and the cotton. A key innovation of the model is the dependence between EMC, sorption rate, and RH condition, which captures the counter-intuitive behaviours observed in the data. The model results agree with the experimental results. The developed tool allows the interpretation of the processes involved and to extend the simulations to other cases, materials, and conditions.

Moisture control design has to respond to all relevant hygrothermal loads.

Moisture-related damage is still a formidable cost factor in the building sector. Besides installation deficiencies, moisture control design failures are the most frequent reasons for moisture problems. Therefore, adequate moisture control analysis has become the key for sustainable buildings. However, by only focusing on vapour diffusion other important moisture loads such as driving rain, construction moisture or air infiltration are mostly neglected. Therefore, international moisture control standards often refer to simulation models for more realistic analysis, leaving many practitioners wondering how to handle these tools. To overcome this dilemma, the updated German moisture control standard has introduced a three-pathway approach for design evaluation: first, deemed to satisfy list, second, restricted Glaser calculation and third, fully fledged hygrothermal simulation. The third pathway includes the option to account for small leaks or imperfections in building envelope components. Guidelines in other countries are also embracing similar moisture control approaches which gives hope for more durable and sustainable building design. To reach this aim, moisture control should also become an integral part of the design process instead of a secondary chore.

Using CONTAM to design ventilation strategy of negative pressure isolation ward considering different height of door gaps

Infectious disease departments in hospitals require pressure gradient to create unidirectional airflow to prevent the spread of contaminants, typically by creating active air infiltration through the difference between supply and exhaust air volumes. The door gap is the channel of air flow between rooms, so its height has an important influence on the pressure difference and infiltration air volume of the room. There is still a lack of research on setting reasonable ventilation strategies according to the different heights of door gaps at different positions in the building. In this study, model of a set of isolation wards was established and analyzed using the multi-zone simulation software CONTAM, and the ventilation strategies with different heights of door gaps were applied to the actual infection diseases department. The results show that in a building with ventilation system divided by functional area, the difference in the height of the door gaps requires different active infiltration air volumes. Pressure fluctuations in the medical and patient corridors are greater than in other rooms. The significance of this study is to understand the active infiltration of air to guide the design and operation of ventilation systems in infectious disease hospitals or building remodeled to isolate close contacts of COVID-19 patients. It is also instructive for the design of pressure gradients in clean workshops, biological laboratories, and other similar buildings.

Residential Building Envelope Energy Retrofit Methods, Simulation Tools, and Example Projects: A Review of the Literature

As one of the biggest energy consumers, buildings are the focus of the energy conservation market, and the building envelope, which has the highest impact on heating and cooling loads, is one of the main targets in retrofit projects. Several materials, systems, methods, and simulation tools are used in these projects, and it is critical to understand the impact of these methods in different locations, their frequency of use, and the effectiveness of market-ready new solutions. In that context, it is necessary to review the energy conservation measures (ECMs) that are suitable for residential building envelope retrofitting, and that are commercially available or under research and development. This paper provides an overview of these ECMs. A literature review was conducted on different building envelope ECMs, including traditional and innovative energy retrofit methods, such as aerogel and phase change materials on opaque and transparent components of existing buildings. Results show that the most effective retrofit projects include bundles of ECMs, and the traditional ECMs can be as effective as more innovative solutions in terms of energy saving. Moreover, computer energy models were created for a typical residential building in the US for cold and warm climate zones to determine the impact of different retrofit approaches based on a sensitivity analysis. Results show that envelope ECMs have higher energy saving potentials in cold climate zones, of up to around 30%, and reducing the air infiltration has the highest impact in both cold and warm climate zones in a typical small residential building.

A Potential Solution for Solid Particulate Matter Reduction in Large Indoor Spaces

Air filtration is an essential process in indoor air conditioning and its physical removal of particulate matter is critical for enhancing indoor air quality, especially in arid regions including United Arab Emirates. In such regions, meeting indoor air quality standard is challenging during sporadic sandstorms when common air conditioning systems are unable to maintain indoor air quality properly. Such inability occurs either due to air infiltration through building’s fenestrations exposing indoor air to excessive particulate matter or the failure of inlet air filters after rapid clogging and high pressure drops. Such failure may be observed frequently in buildings with frequent openings such as public buildings and warehouses. Aerosolized pathogenic microorganisms, e.g., SARS-CoV-2 virus, can be modelled through air particle matter and be removed to a certain degree. In addition, the recent global pandemic raised more awareness towards the necessity of particulate matter filtration in indoor environment. Employing independent air filtration units might be a great solution for intermittent or emergency situations, when primary or additional air filtration process is required to attain proper indoor air quality. The main objective of this paper is to attempt designing, manufacturing, and utilizing an easy to set portable filtration unit and to assist buildings’ existing air conditioning systems in airborne dust particle elimination. The unit is designed and manufactured with additional feature accommodating easy installation of commercially available filters for further performance studies. The unit was equipped with all necessary performance monitoring sensors to detect key parameters such as air velocity, pressure differential, temperature, humidity, and particulate matter before and after filtration. The results revealed interesting information associated with the performance of commercially available filters and the feasibility of such independent filtration units.

Influence of building envelope characteristics on the effectiveness of PMV-based controls for schools located in Saudi Arabia

This paper summarizes the results of a comprehensive analysis to investigate the performance of both thermal comfort-based and temperature-based controls for schools in harsh hot climates of Saudi Arabia. The analysis considers the impact of building envelope characteristics including thermal insulation level of exterior walls and air leakage rate on the ability of both control options to maintain indoor thermal comfort while minimizing cooling energy consumption. The analysis utilizes a calibrated energy model for an existing Saudi school with monitored energy consumption data. The analysis results indicated that the thermal comfort-based control is able to maintain the predicted percentage of dissatisfied (PPD) value at 5% throughout the year for any combination of the exterior wall’s R-value and air infiltration rate unlike the case of the temperature-based controls that do not maintain acceptable indoor thermal comfort conditions. However, the thermal comfort-based controls consume more cooling energy than the temperature-based controls. The analysis also revealed that the difference between the annual cooling energy of the PMV-based control and the temperature-based controls increases almost linearly with the cooling degree days of the site where the school is located. The analysis results indicate that acceptable indoor thermal comfort levels can be achieved using temperature-based controls when optimal temperature set points are used.

Prediction model of air infiltration in single-zone buildings with high airtightness

Air infiltration through building envelopes has a considerable impact on the comprehensive performance of buildings, especially in terms of their energy demand and indoor air quality. Therefore, it is important to accurately predict building air infiltration rates under various scenarios. High airtightness is one of the typical characteristics of passive ultra-low energy buildings. With the rapid application of passive technology in building energy efficiency, the airtightness of new urban buildings has been significantly improved. The centralized air leakage path distribution assumption of current prediction model for building air infiltration rate is inconsistent with the actual situation of high airtightness buildings, which reduces its prediction accuracy and application range. Therefore, it is of great practical significance and academic value to carry out the research on the prediction model of air infiltration rate of buildings with high airtightness.This paper presents an air infiltration prediction model for single-zone buildings with adventitious openings. The building envelope was broken down into permeable parts and impermeable parts, and the air leakage pathways were assumed to be uniformly and continuously distributed in the permeable envelope. A linear pressure distribution over the building facade was assumed, and the airflow rate was integrated in the vertical and horizontal planes to theoretically predict the air infiltration rate. The feasibility of the proposed model was tested by comparing the air infiltration rates simulated by this model with those determined using the tracer gas attenuation method of an airtight building. The initial test results suggest that this model is mathematically robust and is capable of modeling the air infiltration of a building in a wide variety of scenarios. Reasonable agreement was found between the tested and simulated results. This study can provide basic theoretical support for the coupling performance analysis of high airtightness buildings.

Study on Thermal Performance Measurement and Construction of Passive Exterior Wall with Low Energy: Teaching and Laboratory Building of Shandong Jianzhu University

It can provide theoretical support for the optimal design of low-energy walls by measuring the actual thermal conditions inside the walls of passive low-energy buildings and studying the rationality of the wall structure design. Taking the teaching and laboratory building of Shandong Jianzhu University as an example, this paper explores the method of using temperature and humidity sensor to measure the air temperature and humidity inside the wall to represent the solid temperature and humidity of the wall. Based on the measured data and calculation results, the rationality of the structure of the test external wall is analyzed from four aspects: the performance of insulation, the moisture drain performance of wall, the ability of preventing the penetration of the hot and humid air of the inner wall, and the waterproof performance of the outer wall. Results show that the external wall structure of polystyrene board (200 mm thick) for external insulation and thin plastering has good practical operation effect in three aspects of thermal insulation, internal moisture discharge, and external wall waterproof, which basically meets the design requirements of external wall of passive house in Germany. In terms of moisture protection of the inner wall, the inner wall of cement mortar (15 mm thick) may not be able to effectively prevent the infiltration of indoor hot and humid air. Thus, the insulation layer should be added into the external wall. In addition, the moisture inside the wall is obviously affected by the season. The drain performance of moisture inside the wall mainly occurs in the sweltering heat, and the drain direction is from the indoor side to the outdoor side. In the external insulation structure, there are two layers of graphite polystyrene plate (100 mm thick), and the insulation effect of polystyrene plate near the outdoor side is better than that near the indoor side. The combination of anticrack mortar (5 mm thick) and paint cannot completely prevent the infiltration of rainwater, but the infiltration of rainwater in the wall will be quickly discharged in a short time.

Impact of meteorology on indoor air quality, energy use, and health in a typical mid-rise multi-family home in the eastern United States.

Heating and cooling requirement differences across climates not only have carbon emissions and energy efficiency implications but also impact indoor air quality (IAQ) and health. Energy and IAQ building simulation models help understand tradeoffs or co-benefits, but these have not been applied to evaluate climate zone or multi-family home differences. We modeled a four-story multi-family home in six U.S. climate zones and quantified energy, IAQ, and health outcomes with EnergyPlus, CONTAM, and a pediatric asthma systems science model. Pollutant sources included cooking and ambient. Outputs were daily PM2.5 and NO2 indoor concentrations, infiltration, energy for heating and cooling, and asthma exacerbations, which were compared across climate zones, apartment units, and resident behaviors. Daily ambient-sourced PM2.5 decreased and cooking-sourced PM2.5 increased with higher ambient temperatures. Infiltration air changes per hour were higher on the first versus the fourth floor and in colder climates. Window opening during cooking led to decreases in total pollutant concentrations (11%-18% for PM2.5 and 9%-15% for NO2 ), 3%-4% decreases in asthma exacerbations within climate zones, and minimal impacts on cooling, but led to increased heating demand (4%-8%). Our results demonstrate the influence of meteorology, multi-family building characteristics, and resident behavior on IAQ, energy, and health, focused on multi-zone methodology.

CFD simulation of heat transfer and airflows in an open refrigerated display cabinet

This paper uses CFD (Computational Fluid Dynamics) method to study the efficiency of the airflow curtain in an empty and full open refrigerated display cabinet. Numerical simulation results show that changing of the angle of the honeycomb can reduce the infiltration of warm ambient air into the refrigerator. It was established that the average intake air temperature in modified design decreased by 0.6 °C compared to the original design. The CFD model presented in the paper can be used to study airflows inside and to design and develop open-type refrigerated cabinets.

Potential Health Benefit of NO2 Abatement in China's Urban Areas: Inspirations for Source-specific Pollution Control Strategy

Potential Health Benefit of NO2 Abatement in China's Urban Areas: Inspirations for Source-specific Pollution Control Strategy

Study of Honeycomb Air Curtain for a Freezer Room to Enhance Protection against Warm Air Infiltration

The objective of this research is to present the energy-saving effect of applying an air curtain to prevent the penetration of warm air through a freezer door. Retail business is highly competitive in many aspects, including the factors affecting the cost of the store. The most important cost for many businesses is the cost of supplying energy to refrigeration systems. Therefore, the operator must try to reduce the energy consumption of the freezer room. Normally, a freezer room consumes cooling energy when its door is opened for the loading and unloading of goods, leading to the infiltration of warm air from outside. For this reason, we conducted experiments in which air curtains were used. We compared two types of air curtain grille: Common and honeycomb. The experiment was designed to assess whether the honeycomb grille could provide a stronger air curtain and more effectively prevent the penetration of warm air. For the experiment, we used a freezer with a temperature of −25 ๐C. The freezer room door measured 200 × 100 m2 and an air curtain was installed 5 cm above the outer freezer door. The velocity of the air curtain was 6.5 m/s. Simulations were carried out using solid workflow simulation software. The changes in temperature and air velocity were simulated in the room, considering three scenarios: Type 1: Leaving the freezer door open for 1 hour without the air curtain operating. This resulted in warm air inflow at the top of the door and cold air outflow at the bottom of the door. When a steady-state was reached, the room temperature was 6.05 ๐C. Type 2: Leaving the freezer door open for 1 hour, using an air curtain with a common grille to prevent the infiltration of warm air. The results showed that an air curtain could prevent the infiltration of warm air. The outside air tries to push through the air curtain, which can be seen from the curvature of the air curtain line in the model. When a steady-state was reached, the room temperature was −2.41 ๐C. Type 3: Leaving the freezer door open for 1 hour, using an air curtain with a honeycomb grille to prevent the infiltration of warm air. The honeycomb grille air curtain was slightly better at preventing the infiltration of warm air than the common grille. There was less curvature in the air curtain line, which means that the strength of the air curtain is greater. When a steady-state was reached, the room temperature was −2.64 ๐C. In conclusion, the results demonstrated that the honeycomb grille air curtain can prevent the infiltration of warm air 9.54% better than the common grille air curtain.