Air Infiltration In Buildings Research Articles

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.

Determining building-specific wind pressure coefficients to account for the microclimate in the calculation of air infiltration in buildings

ABSTRACT Wind pressure coefficients (Cp ) are important for the correct calculation of the air infiltration of a building. Cp depends on wind direction, position on the building façade and site exposure, and is therefore influenced by the microclimate. The external coupling between building energy simulation (BES) software and computational fluid dynamics (CFD) pre-processing allows calculating building-specific wind pressure coefficients that can account for the microclimate. BESs have been performed in order to calculate the infiltration rate of a reference building using surface-averaged Cp values from two different sources; a standard database and CFD simulations from OpenFOAM. Tracer gas measurements were performed in the reference building in order to validate the simulation results. The results show the coupled CFD/BES method gives building-specific Cp values that represent adequately the microclimatic conditions, leading up to 45% more accurate air infiltration rates compared to conventional methods.

A novel method for measuring air infiltration rate in buildings

Measuring the air infiltration rate in buildings is essential for reducing energy use and improving indoor air quality. This rate has traditionally been determined by means of the blower door method, which is disruptive to building occupants, cannot identify the location of infiltration, cannot provide the infiltration rate for a section of the envelope, and requires considerable effort for setup and tear-down. Therefore, this study has developed a novel technique to measure air infiltration in buildings using an infrared camera. A thermographic image of a building envelope produced by an infrared camera and the measured indoor/outdoor air parameters (velocity, temperature, and pressure) were used to identify the effective crack size and air infiltration rate by means of theoretical heat transfer and fluid mechanics analyses. The proposed method was validated by experimental measurements in an environmental chamber and an office. The experiment in the environmental chamber constructed a small-scale room with known crack size. The experimental setup was comparable to actual conditions. The proposed method was able to predict the crack size within a relative error of 20%. For the experiment in the office, this study used the tracer-gas decay method to measure the air infiltration rate, and the relative error of the calculated air infiltration rate was only 3%.

Investigation of the pressure coefficient impact on the air infiltration in buildings with respect to microclimate

Wind pressure coefficients (Cp) are important for calculating the air infiltration rate of a building. Cp depend on a wide range of parameters, such as wind direction and speed, position on the building surface and façade exposure. Most Building Energy Simulation (BES) programs generally calculate air infiltration using simplified pressure coefficients. The Norwegian technical software (SIMIEN) do not consider them. The effect of the pressure coefficients on the air infiltration of the building, taking into consideration the microclimate of the building area, is studied. The wind pressure coefficients are defined through computational fluid dynamics (CFD) simulations. The air infiltration in the building is determined based on the calculated pressure coefficients. Tracer gas measurements were used for validation of the results. Two cases of fully exposed and partially sheltered building were examined. The results indicate that wind pressure coefficients derived from CFD simulations calculate more realistic values for the air infiltration of the building.

Consideration of a new extended power law of air infiltration through the building’s envelope providing estimations of the leakage area

This paper proposes a new extended power law (EPL) of air infiltration in buildings as an alternative in certain cases to the widely used power law (PL) and quadratic law (QL). Specifics: it separates the airflow rates in laminar and turbulent components; improves the estimation of the leakage area; new evaluation of the airflow rate at low pressure differences. In various numerical comparisons several advantages of EPL are revealed and we appreciate that will raise interest and adoption by the software platforms that evaluate the airflow in buildings.Based on the measurement data (MD) of the Passive House Politehnica from Bucharest (Romania), EPL is validated and compared with other laws of infiltration. Four statistical indicators (PCC, RMSE, MBE and MAE) show that EPL has the best fit to MD. A generalized function of air leakage is developed and may serve in certain cases for a higher level of processing the MD for improved evaluations.An inverse problem approach finds the leakage area of the cracks in linear-perimetral and in circular-compact distributions respectively. They are alternative to the consecrated notions ELA and EqLA. The leakage areas are estimated to be from 5cm2 (the case of LFCorrLA11The symbol "*" is used for the circular-compact formulation of the crack’s area.* at pressurization in circular-compact formulation) up to 2085.7cm2 (the case of LFCorrLA at depressurization in linear-perimetral formulation). Among the surveyed leakage areas we appreciate that CorrLA offered the most realistic result.Through linear extrapolation of the laws of infiltration at low pressure difference EPL is compared with PL and QL and the differences are discussed.

Air-Infiltration Measurements in Buildings Using Sound Transmission Loss Through Small Apertures

The objective of this investigation is to determine air infiltration in buildings using sound transmission loss (STL) through various types of holes and cracks. The method is based on the use of a sound source that radiates sound waves at a known frequency inside the building and two sound level meters, which measure sound pressure level inside and outside the building. To develop a correlation between STL and air infiltration, experiments have been performed using various types of materials. A test chamber was divided in two sub-chambers to simulate interior and exterior air conditions. Various materials, each with a small hole of varying shapes and sizes, were positioned between the two sub-chambers. A pressure difference has been generated between the sub-chambers and air infiltration in each experiment was measured through each hole. Filed testing in several buildings has been performed to determine air infiltration. The results of field measurements compared with the blower door readings show that the proposed method has promise to be used to measure air infiltration in buildings.

Effectiveness of urban shelter-in-place. III: Commercial districts

In the event of a toxic chemical release to the atmosphere, shelter-in-place (SIP) is an emergency response option available to protect public health. This paper is the last in a three-part series that examines the effectiveness of SIP at reducing adverse health effects in communities. We model a hypothetical chemical release in an urban area, and consider SIP effectiveness in protecting occupants of commercial buildings. Building air infiltration rates are predicted from empirical data using an existing model. We consider the distribution of building air infiltration rates both with mechanical ventilation systems turned off and with the systems operating. We also consider the effects of chemical sorption to indoor surfaces and nonlinear chemical dose-response relationships. We find that commercial buildings provide effective shelter when ventilation systems are off, but that any delay in turning off ventilation systems can greatly reduce SIP effectiveness. Using a two-zone model, we find that there can be substantial benefit by taking shelter in the inner parts of a building that do not experience direct air exchange with the outdoors. Air infiltration rates vary substantially among buildings and this variation is important in quantifying effectiveness for emergency response. Community-wide health metrics, introduced in the previous papers in this series, can be applied in pre-event planning and to guide real-time emergency response.

Evaluation of the Alberta air infiltration model using measurements and inter-model comparisons

The Alberta air infiltration model (AIM-2) is a simplified single-zone model for predicting building air infiltration rates with a number of salient features. This paper presents an empirical study of this model using measured data from 16 detached houses in Ottawa, Canada. A single-fan depressurization test was first conducted for each house to determine its leakage characteristics. Then, the tracer gas concentration decay technique was employed to measure air infiltration rates under a wide range of weather conditions. The AIM-2 model was used to predict air infiltration rates for each of the 16 houses for the measured weather conditions. These model predictions were then compared with the air infiltration rates determined with the tracer gas tests. Additionally, the predictions of the AIM-2 model were compared with those of another model, the Lawrence Berkeley Laboratory (LBL) model. The AIM-2 model tended to underestimate air infiltration rates but performed better than the LBL model. On average, the AIM-2 model has an error of 19% while the LBL model has an error of 25%. The AIM-2 model requires an estimation of the house's leakage distribution, which may have contributed to some of this disagreement. An attempt was made to use genetic algorithms to reduce the uncertainty caused by estimating these model inputs.

Basic air infiltration

Some fundamental properties of building air infiltration are derived starting from propositions stressing the underlying assumptions. Possible structures of air infiltration models relating the flow to a leakage area are considered. Approximate expressions are derived for the value of the reference pressure necessary for mass conservation to hold. These results are applied to the case of enforced building pressurization. It is demonstrated that some currently used models of air infiltration violate mass conservation. Other models are shown to lead to unnecessarily large errors when applied to pressurization.

Wind shielding effects of trees on low buildings

Tree windbreaks form an important mechanism for reducing wind-induced air infiltration in buildings. However, they also affect wind loading determined mainly by wind standards and building codes of practice for a homogeneous terrain environment. A wind tunnel study was carried out to examine the effects of various tree configurations on wind-induced air infiltration and structural loading of low-rise buildings. The results showed that a single row, high density windbreak reduced air infiltration by about 60% when planted approximately four tree heights away from the building. Thiscorresponded to a 15% reduction in energy costs. The efficiency of windbreaks depends on the direction of dominant winds. Results have also shown that pressure coefficients are generally lower than those specified by wind standards and codes of practice with the exception of side wall regions and certain roof areas.

Tracer gas mixing with air

The tracer gas method is one of the most widely used methods for measuring flow rates for building air infiltration and ventilation. The accuracy of this method depends vitally on the spatial uniformity of the tracer/air mixing. However, information on this critical problem has been scarce, largely due to the practical difficulty in experimentally obtaining data. In the last decade a new tool for building research has emerged, namely computational fluid dynamics or CFD. A study of tracer/air mixing has been carried out using a time dependent CFD method, supported by conceptual/dimensional analysis. In this study, 12 cases of tracer/air mixing in simulated tracer decay tests were computed. Each case had a different zonal volume or other boundary or initial conditions. By comparing these results, it was found that there were many factors affecting tracer/air mixing and, contrary to a previous report, there does not exist a universal critical value of air change rate below which satisfactory mixing is guaranteed, although lower air change rates are generally beneficial to mixing. In addition, it has been demonstrated that smaller building zones and higher inlet air flow velocities have positive effects on tracer/air mixing while the initial tracer concentration level has no effect. Finally a statistical parameter of concentration spread coefficient for assessing tracer mixing has been introduced.

Simulation of the effects of duct leakage and heat transfer on residential space-cooling energy use

A detailed building energy simulation, FSEC 2.1, has been used to determine the relative significance of duct leakage and heat transfer on space-cooling energy use in Florida houses. A comprehensive calculation procedure has been developed to predict duct air leakage based on duct leakage areas and associated operating pressures. The effect of the leakage on building air infiltration and air-conditioning electrical demand is estimated based on the mass transport and the sources of the various airflows. Heat transfer to the duct system is estimated using calculations based on previous experimental research on duct conductances. Results show that the impacts of duct systems on air-conditioning loads are strongly time-dependent, exacerbating electrical demand during utility summer peak periods and increasing air-conditioner run-time. The impact of duct leakage was found to be of the largest magnitude followed by heat transfer to the duct system itself. Air handler return-side air leak source temperature and enthalphy were also found to be significant in terms of air-conditioner loads. Detailed measurements of air-conditioner electrical demand taken in a house before and after duct leak repair is provided for comparison with simulation results.

Characterizing the Occurrence, Sources, and Variability of Radon in Pacific Northwest Homes

A compilation of data from earlier studies of 172 homes in the Pacific Northwest indicated that approximately 65 percent of the 46 homes tested in the Spokane River Valley/Rathdrum Prairie region of eastern Washington/northern Idaho had heating season indoor radon (222Rn) concentrations above the U. S. EPA guideline of 148 Bq m-3 (4 pCi L-1). A subset of 35 homes was selected for additional study. The primary source of indoor radon in the Spokane River Valley/Rathdrum Prairie was pressure-driven flow of soil gas containing moderate radon concentrations (geometric mean concentration of 16,000 Bq m-3) from the highly permeable soils (geometric mean permeability of 5 x 10(-11) m2) surrounding the house substructures. Estimated soil gas entry rates ranged from 0.4 to 39 m3h-1 and 1 percent to 21 percent of total building air infiltration. Radon from other sources, including domestic water supplies and building materials was negligible. In high radon homes, winter indoor levels averaged 13 times higher than summer concentrations, while in low radon homes winter levels averaged only 2.5 times higher. Short-term variations in indoor radon were observed to be dependent upon indoor-outdoor temperature differences, wind speed, and operation of forced-air furnace fans. Forced-air furnace operation, along with leaky return ducts and plenums, and openings between the substructure and upper floors enhanced mixing of radon-laden substructure air throughout the rest of the building.

A stochastic model of user behaviour regarding ventilation

Airflow rates are directly affected by the amount of open area connecting rooms to the outside and consequently by the inhabitant behaviour with respect to window opening. In this paper, a stochastic model using Markov chains is proposed to generate time series of window angle. It is based on data from four office rooms and a whole heating season (from October to May). The model is then validated by a comparison of the real and generated data. The use of this model within building air infiltration design programmers should significantly improve their realism.