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Real-time prediction of smoke layer temperature and height of tunnel fires are crucial in guiding emergency rescue. However, current fire simulation tools are often not able to provide reliable modeling results due to poorly known input parameters and model errors. Besides, fire modeling are subject to computer resources, for instance, fire modeling by computational fluid dynamics (CFD) tools is often time-consuming. Moreover, sensors located in tunnels can only detect certain physical quantities within a certain level of uncertainties. In order to gain more reliable predictions of temperature and smoke layer height of tunnel fires in real time, a proposed method, inverse modeling based on Ensemble Kalman Filter (EnKF), is presented in this study to improve the predictability and address problems of demanding computer resources of tunnel fire simulation by doing data assimilation. The basic formulas of EnKF method are introduced and the application of EnKF to tunnel fires is implemented by connecting the fire simulation tool, CFAST, with a data assimilation software, OpenDA. In current study, observation data are generated under the framework of Observation System Simulation Experiment (OSSE), i.e., synthetic observations are generated by CFAST simulation assuming true value of control parameters are known. Studies are conducted to show the feasibility of real-time predicting smoke movement during tunnel fires. Results show that prediction performance are improved after applying the EnKF method compared to the standalone tunnel fires modeling.

Thermal stratification in large warehouses is a common phenomenon in winter, especially for cold climates. Buoyancy-driven warm air tends to move upwards towards ceilings creating vertical temperature gradients with upper higher temperatures, and consequently leading to excessive heat losses through roofs. These warehouses therefore require thermal destratification through certain air mixing strategies, the selection of which often relies on engineering rules of thumb and experiences but can be better determined through combined experimental and numerical approaches. This paper investigated different thermal destratification methods in two industrial warehouses based on field measurements and CFD simulations with the focus on the quantification of thermal stratification, and the suitable methods modeling air mixing devices, e.g. ceiling rotating fans and bucket fans. The numerical models were first validated by field measurements and then used to simulate different destratification strategies and to compare associated energy impacts. The CFD methods for modeling air mixing devices and their performances can be applied to other similar cases.

There is concern about the hazard of acute residential CO exposures from portable gasoline-powered generators, which can result in death or serious adverse health effects in exposed individuals. To address this hazard, the U.S. Consumer Product Safety Commission has developed low CO emission prototype generators by adapting off-the-shelf emission control technologies onto commercially available generators. A series of tests was conducted to characterize the indoor CO concentrations resulting from portable generators operating in the attached garage of a research house under seven different test house/garage configurations. The tested generators include both unmodified and modified low CO emission prototypes. It was found that CO concentrations varied widely, with peak house CO concentrations ranging from under 10 ppm to over 10,000 ppm. The highest concentrations in the house resulted from operation of the unmodified generator in the garage with the garage bay door closed and the house access door open. The lowest concentrations resulted from operation of a modified low CO emission prototype in the garage with the garage bay door open and the house access door closed. These tests documented reductions of up to 98% in CO concentrations due to emissions from two low CO emission portable generators compared to a stock generator.Improper portable generator use has caused 800 U.S. deaths in the past 14 years. Generators operated in attached garages can cause CO to quickly reach deadly levels. Two low-emission prototypes generators were tested and had CO emissions reduced by up to 98%. Low-emission generators can reduce the risk of consumer poisonings and deaths.

Building entrance doors are a major source of air infiltration and energy loss in commercial buildings. Previous studies have calculated entrance doors air infiltration and energy saving potential of vestibules with the simplified method which is based on pressure factors. However, challenges are still faced in estimating the pressure difference and the resultant infiltration rates across doors as well as validating the used airflow coefficients under different flow conditions. In this paper, an experimental study is used to validate the airflow coefficient for a fully open single door under both infiltration and exfiltration conditions. The study presents four methods for modeling air infiltration across automatic single and vestibule doors for two reference building models: two methods use the pressure factors and the two others are based on airflow simulations. Energy simulations are then conducted using the air infiltration rates obtained from each method. The results revealed that the design methods overestimate the pressure difference across doors, the air infiltration rates as well as the vestibule savings potentials in comparison to the simulation methods. In conclusion, airflow simulations were found to provide more realistic estimates of pressure differences and infiltration rates across entrance doors when compared to the widely-used design methods.

The efficiency of air curtain in reducing infiltration and associated energy usage is currently evaluated statically by using an efficiency factor, η air, based on single steady/static condition, which is often not the case for actual buildings under variable weather conditions and door usages. Based on a new method to consider these dynamic effects on air curtains, this study uses a dynamic efficiency factor η B in terms of whole building site end-use energy to assess the efficiency of air curtains when compared to single doors (i.e. without air curtains) and vestibule doors. Annual energy simulations were conducted for two reference building models considering their specific door usage schedules in 16 climate zone locations in the North America. The variations of the proposed efficiency factor for different climate zones illustrated the dynamic impacts of weather, building, unit fan energy and door usage frequency on air curtain efficiency. A sensitivity study was also conducted for the operation temperature conditions of air curtain and showed that η B also considers these operational conditions. It was thus concluded that using whole building site end-use energy to calculate the efficiency factor, ηB, can provide more realistic estimates of the performance of air curtains operations in buildings than the existing static efficiency factor.

The ability to predict the concentration of hydrogen in a partially confined space is significant to the safe use of hydrogen-related products such as fuel cell vehicles. Hydrogen release and subsequent dispersion are frequently investigated using commercially-available computational fluid dynamic (CFD) models once those are calibrated with available experimental data. Due to the explosion safety concerns of using hydrogen, accidental scenarios are often replicated with helium as a hydrogen simulant in experiments. Currently, there is no validated, theoretical analogy to correlate the helium data in order to predict the spatial and temporal distribution of hydrogen in the enclosure. The aim of this paper is to assess different theoretical relationships for the similarity between hydrogen and helium leakage in an enclosure. Experiments were first carried out to obtain measured data with helium leakage in a set of scenarios and to validate the present CFD model. Three methods, namely equal volumetric flow rate, equal buoyancy and a newly proposed correlation derived from equal concentration, were employed to determine the equivalent hydrogen release rate, using which the validated CFD model was then used, with the physical property values for hydrogen, to stimulate hydrogen dispersion as compared to that of helium. The accuracy of these different methods at different stage of release and location is discussed. The present result thus provides a guide when using helium experiment to validate hydrogen simulation in different scenarios, which is of importance to the investigation of hydrogen safety.

Forecasting building fire growth and smoke dispersion is a challenging task but can provide early warnings to first responders and building occupants and thus significantly benefit active building fire protection. Although existent computer simulation models may provide acceptable estimations of smoke temperature and quantity, most simulations are still not able to achieve real-time forecast of building fire due to high computational requirements, and/or simulation accuracy subject to users’ inputs. This paper investigates one of the possibilities of using ensemble Kalman filter (EnKF), a statistical method utilizing the real-time sensor data from thermocouple trees in each room, to estimate the spread of an accidental building fire and further forecast smoke dispersion in real time. A general approach to forecasting building fire and smoke is outlined and demonstrated by a 1:5 scaled compartment fire experiment using a 1.0 kW to 2.8 kW propane burner as fire source. The results indicate that the EnKF method is able to forecast smoke transport in a multi-room building fire using 40 ensemble members and provide noticeable accuracy and lead time. Unlike other methods that directly use measurement data as model inputs, the developed model is able to statistically update model parameters to maintain the forecasting accuracy in real time. The results obtained from the model can be potentially applied to assist mechanical smoke removal, emergency evacuation and firefighting.

Air infiltration through building entrances is one of the main sources of energy loss in modern buildings. Previous studies have shown that air curtains, when used at building entrances, can reduce infiltration-related energy loss significantly. A recent computational fluid dynamics (CFD) study proposed a new empirical model to capture air curtain door infiltration/exfiltration characteristics under varying operation conditions and pressure differences. Extending the recent CFD study, this paper presents an experimental study to verify and further investigate the flow characteristics of building entrances equipped with air curtains. A small scale chamber of 2.44 m × 2.44 m × 1.3 m (L × W × H) was constructed and used for the measurements of infiltration/exfiltration and pressure differentials, which were then used for developing the empirical model across the operating air curtain. A 2-D particle image velocimetry (PIV) system with helium filled soap bubbles as seeds was used to visualize the airflow fields captured at the doorway. Both the PIV and the measurement-based correlations were also compared to CFD simulations. The flow/pressure measurements confirmed that, for the tested pressure difference range, air curtains can significantly reduce infiltration. The PIV results confirmed the existence of multiple flow characteristics subject to pressure differences across the air curtain. The experimental results also validated the CFD modeling methods for air curtain, and verified that the empirical model of air curtain from the literature is valid in estimating infiltration through building entrances equipped with air curtains.

The location of neutral plane level (NPL) of a high-rise shaft is an important factor for the evaluation of risks of smoke spreads in high-rise buildings, where the shaft internal pressure is equal to that of the building floor at the same height. The current method to determine the location of NPL assumes uniform temperature distribution inside a shaft, which causes concerns over accuracy of the predicted NPL for high-rise shafts with non-uniformly distributed temperatures during fires. To address the effect of temperature distribution on NPL location, this paper introduces a method to calculate temperature distribution and its associated NPL location based on a coupled model of smoke temperature profile, flow rate and pressure distribution inside a shaft. The measured data from a 1/3 scale experiment is used to validate the method and used to develop two empirical equations for NPL locations in terms of dimensionless numbers: one empirical equation based on shaft top temperature and the second based on shaft bottom temperature. A sensitivity study of the empirical equations is then conducted to evaluate the applicability of the developed equations when compared to the existing NPL method. It was found that for the existing NPL equation based on uniform temperature assumption may under-/overestimate the NPL locations, and the NRMSE would be over 50%, while the NRMSE of the empirical equation is only around 6% based on the results of coupled equations. For non-adiabatic shafts, the effects of non-uniform temperature distribution on NPL should be considered and the suggested empirical equations can predict NPL locations with a reasonable accuracy.

Forecasting simulation of an unknown compartment fire is challenging and usually accompanied with a large number of uncertainties. As the simulation progresses in time, the forecasted physical conditions such as fire heat release rate, room temperature, and vent airflow rate may sway from reality in a highly dynamic environment. Conventional deterministic fire simulation tools using one set of initial inputs to predict fire smoke transport may not easily generate satisfactory results. In this article, a new application of Ensemble Kalman Filter to forecast smoke dispersion during compartment fires is presented. The model utilizes measurement data from multiple sensors in multi-room compartments and is able to predict the fire heat release rate and smoke dispersions within several minutes. In addition, detailed formulation of the Ensemble Kalman Filter model and three case studies are also discussed in this article. The resulting model can be considered as a prototype forecast simulation system to assist occupant evacuation, firefighting, and smoke extraction in a building fire accident.

The TRNSYS energy analysis tool has been capable of simulating whole-building coupled heat transfer and building airflow for about 10 years. The most recent implementation was based on two TRNSYS modules, Type 56 and Type 97. Type 97 is based on a subset of the airflow calculation capabilities of the CONTAM multizone airflow and contaminant transport program developed by the National Institute of Standards and Technology. This paper describes the development of new CONTAM capabilities in support of an updated combined, multizone building heat transfer, airflow and contaminant transport simulation approach using TRNSYS. It presents an illustrative case that highlights the new coupling capability and also presents the application of this coupled simulation approach to a practical design problem of the energy use related to airflow through entry doors in non-residential buildings.

Air curtains have been widely used as a barrier against infiltrations and associated energy losses through building entrances while still permitting an unobstructed pedestrian entryway. However, the evaluation of the energy performance of an air curtain often needs to quantify the infiltration rates under variable ambient conditions and door usage patterns. This study develops an approach to determine the infiltration and the exfiltration characteristics of building entrance equipped with an air curtain. A detailed parametric study for different ambient temperatures, pressure differences across the air curtain and different door usage frequencies was conducted by using computational fluid dynamics simulations. The calculated air infiltration rates were then correlated to the pressure differences across the air curtain. The numerical approach was first verified by comparing the obtained correlations for the building entrance without the air curtain to the published data in the literature. New infiltration/exfiltration correlations of the modeled air curtain were then developed as the functions of pressure difference, flow coefficient, and flow modifier. Compared to the single door without air curtain and the door with vestibule, the air curtain was found to reduce the infiltration significantly, especially for the mild ranges of pressure differences.

The hot smoke test is often used for commissioning fire smoke management system in atrium buildings, in which liquid fuel is burnt to generate a buoyant plume mixed with artificial tracer smoke to model a fire smoke. The method is usually costly and often causes safety concerns. This paper studied an alternative method of using a cold smoke test, in which pure helium is used to create the buoyant plume. A method was developed to determine the supply rate of pure helium necessary to achieve the same buoyancy effect as that of the corresponding hot smoke test. Computational fluid dynamics (CFD) simulations of the helium smoke tests were conducted and compared to the measured hot smoke tests in a full-scale naturally ventilated atrium and a sub-scale atrium with mechanical ventilation. A new method was added in the CFD model to track the smoke layer height for the simulations of helium smoke based on the concentrations of smoke and helium. It is found that the predicted smoke layer heights based on the mass fractions of the tracer smoke are generally close to the measured ones in the hot smoke tests of different heat release rates. A non-dimensional temperature in the hot smoke test is also found closely related to the dimensionless helium concentrations in the helium smoke test for the atria modeled. Although the consumption of pure helium for a full-scale helium smoke test can be very high, it is promising to use the pure helium smoke test in the lab-scale experiments as the preliminary tests of full-scale and/or lab-scale testing of real fires.

The real-time control of indoor thermal conditions needs dynamic models of air temperature and humidity in rooms. The single-zone dynamic model may be inappropriate to depict the spatial variations of the air parameters, and the computational fluid dynamics model (CFD) is too computationally costly for real-time applications. In comparison, the multi-zone model, which models a space by several zones, may be a better choice. This paper presents a three-zone dynamic model to investigate the dynamic behaviors of indoor air temperature and humidity. By the means of linear approximation, the ordinary differential equations describing the dynamic thermal behaviors of indoor air are transformed into a state space form. The state equation is solved analytically, and the calculated results are then compared to a series of dynamic response experiments. It shows that the dynamic model developed in this paper predicts well the dynamic thermal responses of air in different indoor zones. The average errors of the calculated results compared with the experimental data are all less than 12% for the transient response with a time period of 2400 s. This paper also demonstrated the developed room model to simulate the transient responses of the indoor air temperatures and humidity ratios under different perturbations including a step change of supply air temperature, supply air flow rate, indoor occupant number and ambient temperature. The proposed modeling procedure may be especially useful for the development of the dynamic toolbox for the control design of HVAC components.

The US Centres for Disease Control and Prevention has reported that up to half of non-fatal carbon monoxide (CO) poisoning incidents during the hurricane seasons in 2004 and 2005 involved generators operated outdoors but within 7 ft of the home. Current guidance for safe operating distances of generators is often neither specific nor consistent. A study was conducted to examine the impact of generator distance on indoor CO exposure. The study was based on computer simulations of CO transport outdoors and subsequently into a generic two-storey house. This paper presents the simulation results when using an indoor air quality model coupled with a computational fluid dynamics model to predict CO concentrations near and within the home. Fire Dynamics Simulator was validated against the measured contaminant dispersion data in a wind tunnel. A parametric study was then conducted for the two-storey house to consider the effects on indoor CO levels of generator location, distance, exhaust temperature and speed and weather conditions. It was found that in most cases, to reduce CO levels for the conditions modelled, it was more effective to point the generator exhaust away from the house and position the generator at a distance of >4.6 m.

Gasoline-powered electric generators are widely used during power outages such as those caused by hurricanes and winter storms. Based on currently available data, about 95% of generator-related carbon monoxide (CO) fatalities were associated with operating carbureted, spark-ignited and gasoline-powered generators in enclosed spaces. To investigate the indoor CO exposure associated with running a generator indoors, the generation of CO was measured from a generator in an enclosed shed. Correlations of CO generation and O 2 consumption rates were developed as functions of O 2 level and actual generator load output. An indoor air quality and ventilation model was then used to predict the air change rates and CO levels in the shed, which were then compared with measured values. This study also used the simulation model to calculate CO generation and dispersion, and occupant exposures to CO, with a generator running in the garage of a house during weather conditions consistent with the days after Hurricane Katrina in the summer of 2005. For the simulation conditions, it was found that the resultant CO could reach dangerous levels in most rooms of the house about 2 h after the generator started.

Many contaminants in the living space of a house, such as carbon monoxide, benzene, toluene, and ethylbenzene, originate from attached garage. As more airtight and energy-efficient houses are designed and constructed, these contaminants may be retained in indoor air for a longer period of time, jeopardizing the occupants' health. In this study, CONTAM, a multi-zone model, is employed to analyze the effect of garage-house interface on the contaminant transport from an attached garage to the living space. Parametric studies of two buildings are carried out to investigate the effect of ventilation on the transport of contaminant from the garage to living space, based on experimental data of five Effective Leakage Area (ELA) of a typical garage-house interface. The results show high concentration of indoor pollutants for typical leaky garage-house interface. Parametric simulations also indicate that the improper design of mechanical exhaust systems can cause higher infiltration of contaminants from the garage to the house, resulting in higher indoor air pollution concentration.

CONTAM is a multizone building airflow and contaminant transport computer program often used for ventilation and indoor air quality analysis. The program was recently enhanced to incorporate CFD capabilities for both outdoor and indoor environmental analysis. This paper introduces the CFD features implemented within the most recent version, CONTAM 3.0. The outdoor or external CFD link predicts wind pressure coefficients and contaminant concentrations for airflow paths at the building surface. A converter computer program translates the wind pressure coefficients to the CONTAM data format. This external CFD link is useful for parametric studies of the impact of outdoor air quality on indoor environment when considering different wind directions or contaminant locations, especially simulations under transient conditions. The ability to embed a single CFD zone in a CONTAM network model has also been implemented. This enables the detailed modeling of a zone when the well-mixed multizone assumption is not appr...

The U.S. Centers for Disease Control and Prevention (CDC) has reported that up to half of non-fatal CO poisoning incidents during the hurricane seasons in 2004 and 2005 involved generators operated outdoors but within seven feet of the home. The guidance provided on the safe operating distance of a generator is often neither specific nor consistent. Furthermore, some generator manufacturers recommend the use of extension cords to be “as short as possible to prevent voltage drop and possible overheating of wires”. This study modeled multiple scenarios of a portable generator operated outdoors using the CONTAM indoor air quality model coupled with a computational fluid dynamics (CFD) model to predict CO concentrations near and within a home. The simulation cases included both human-controllable factors (e.g., generator location and exhaust direction and window opening size) and non-controllable factors (e.g., wind, temperature, and house dimensions). For the house modeled in this study, a generator positioned 4.6 m (15 feet) away from open windows may not be far enough to limit CO entry into the house. It was also found that winds perpendicular to the open window resulted in more CO infiltration than winds at an angle, and lower wind speed generally led to more CO entry. To reduce CO entry, the generator should ideally be positioned outside of airflow recirculation region near the open windows.

Designing ventilation systems for buildings requires a suitable tool to assess the system performance. This investigation assessed seven types of models (analytical, empirical, small-scale experimental, full-scale experimental, multizone network, zonal, and CFD) for predicting ventilation performance in buildings, which can be different in details according to the model type. The analytical model can give an overall assessment of a ventilation system if the flow could be approximated to obtain an analytical solution. The empirical model is similar to the analytical model in terms of its capacities but is developed with a database. The small-scale model can be useful to examine complex ventilation problems if flow similarity can be maintained between the scaled model and reality. The full-scale model is the most reliable in predicting ventilation performance, but is expensive and time consuming. The multizone model is a useful tool for ventilation design in a whole building, but cannot provide detailed flow information in a room. The zonal model can be useful when a user has prior knowledge of the flow in a room. The CFD model provides the most detailed information about ventilation performance and is the most sophisticated. However, the model needs to be validated by corresponding experimental data and the user should have solid knowledge of fluid mechanics and numerical technique. Thus, the choice for an appropriate model is problem-dependent.

Current simulation tools for airflow and contaminant dispersion in built environments cannot provide detailed information with little computing effort, which is critical for emergency management. Multizone airflow network models are fast but cannot provide detailed flow and contaminant transport information in an indoor space. Computational fluid dynamics (CFD), on the other hand, gives very detailed information but requires hours or days of computing time on a PC. A coupled multizone-CFD model can offer detailed information on contaminant dispersion while reducing computing time. The study presented in this paper applied the coupled model to calculate airflow and contaminant dispersion in a three-story, naturally ventilated building with a large atrium, assuming that a contaminant was released in the atrium. This investigation studied the effectiveness using emergency ventilation to protect the building occupants. It was demonstrated that the coupled model can provide important information of contaminant...

Multizone airflow network models assume that in a zone air temperature and contaminant concentrations are uniform, and air momentum effects are neglected. These assumptions could cause errors for airflow with strong buoyancy, large contaminant concentration gradient, or strong momentum. This study has found the correlations of the errors and some dimensionless air parameters. The assumption of uniform air temperature is acceptable when the dimensionless temperature gradient is smaller than 0.03. The assumption of uniform contaminant concentration is valid if the corresponding Archimedes number for the source zone is greater than 400. The assumption of neglecting air momentum effect is reasonable when the jet momentum effect is dissipated before reaching an opening in downstream.

Current multizone airflow network models assume air momentum effects, contaminant concentrations, and air temperatures are uniformly and homogeneously distributed in a zone of a building. These assumptions can cause errors for zones where air and/or contaminant are not well mixed. A coupled multizone-CFD program has been developed to improve the multizone model by applying a CFD model to those poorly mixed zones and the multizone model to the remaining zones. This paper validates the coupled multizone-CFD program by using experimental data obtained in a four-zone facility with nonuniform distributions of air momentum effects, contaminant concentrations, and air temperatures. The calculated results by the coupled program generally agreed with the experimental data although discrepancies exist in some cases. The coupled multizone-CFD simulations used less computing time than the CFD simulations for the whole flow domain.

The development of sensor technologies in recent years makes it possible to acquire real-time states of building environment and its systems with a major trend towards big data and wireless data transmission. How to use these vast real-time data sets to achieve a safer, more comfortable and energy efficient building becomes a major challenge for building engineering. This paper investigates one of the possibilities of using the real-time data for the prediction of future fire development states. Beyond simply reflecting the real-time states of a system, the sensing data will be able to forecast a highly dynamic problem of building fire growth and smoke dispersion inside building environment. This paper presents the forecasting method based an ensemble Kalman filter (EnKF) to predict building fire smoke temperature and smoke layer height at the real time. Detailed formulations of the zonal fire smoke models and the EnKF model are presented. The proposed real-time forecasting method is demonstrated and validated by a 1:5 scaled compartment fire experiment. The results indicate that real-time forecasting of building fires is achievable while the accuracy is noticeable which can be applied to assist emergency evacuation and firefighting.

A CMOS analog and audio front-end circuit includes an enhanced analog-to-digital converter (ADC) that achieves a desired signal-to-noise-and-distortion (SNDR) and an analog-front-end transmit (TX) digital-to-analog converter (DAC). The enhanced ADC includes an improved single Op-Amp resonator coupled to a feed-forward loop and can substantially reduce signal transfer function (STF) peaking of the enhanced ADC. The CMOS analog and audio front-end circuit is integrated with a baseband processor.

On the basis of currently available data, approximately 97% of generator-related carbon monoxide (CO) fatalities are caused by operating currently marketed, carbureted spark-ignited gasoline-powered generators (not equipped with emission controls) in enclosed spaces. To better understand and to reduce the occurrence of these fatalities, research is needed to quantify CO generation rates, develop and test CO emission control devices, and evaluate CO transport and exposure when operating a generator in an enclosed space. As a first step in these efforts, this paper presents measured CO generation rates from a generator without any emission control devices operating in an enclosed space under real weather conditions. This study expands on previously published information from the U.S. Consumer Product Safety Commission. Thirteen separate tests were conducted under different weather conditions at half and full generator load settings. It was found that the CO level in the shed reached a maximum value of 29,300 +/- 580 mg/m3, whereas the oxygen (O2) was depleted to a minimum level of 16.2 +/- 0.02% by volume. For the test conditions of real weather and generator operation, the CO generation and the O2 consumption could be expressed as time-averaged generation/consumption rates. It was also found that the CO generation and O2 consumption rates can be correlated to the O2 levels in the space and the actual load output from the generator. These correlations are shown to agree well with the measurements.

A monolithically integrated differential class E power amplifier capable of dynamically switching between 3.4 GHz and 4.3 GHz operation has been designed and fabricated in a 0.35 µm BiCMOS process; this power amplifier also includes an integrated CMOS-MEMS variable capacitor enabled LC balun for differential to single-ended conversion. The power amplifier achieves a maximum output power of 19.1 dBm and a maximum power added efficiency of 15.1% with a supply voltage of 3.3 V.

Multizone network models employ several assumptions, such as uniform temperature and pressure and quiescent air inside a zone, which may lead to inaccurate results in flow calculations. These assumptions can be eliminated in the zones, where the assumptions are inappropriate, by coupling a multizone network program with a Computational Fluid Dynamics (CFD) program. Through theoretical analysis, this paper proves that the solution of air distribution by using the coupled program exists and is unique. Three possible coupling methods are then discussed in the paper. The best method is pressure-pressure coupling that exchanges pressure between the multizone and CFD since it is most stable and can always lead to a converged solution. Numerical tests were further performed to verify the theory and it demonstrated that the coupled program is able to effectively improve the accuracy of the results. The results of this paper provides theoretical basis for improving the accuracy for modeling airflow and contaminant distributions in buildings. The coupled multizone and computational fluid dynamics can give high fidelity results so field measurements may not needed in the future. Designers of indoor environment in the future can use such a tool to evaluate different alternatives in design and identify the best solution for a building that can provide a healthy indoor environment. Nomenclature