Airflow In Buildings Research Articles

A calibration method for whole-building airflow simulation in high-rise residential buildings

The simulation results for airflow in high-rise buildings may not match actual behavior due to various airflow paths and impact factors, such as temperature, wind direction, wind velocity, and building characteristics (airtightness, layout, and others). When conducting whole-building airflow simulation for high-rise buildings, it is important to reasonably define uncertain input parameters in order to minimize the difference between measurement and simulation results. This study proposes a calibration method for airflow simulation modeling of high-rise buildings using the data-driven method and estimating uncertain input data through output data.The output data for comparing measured values with simulated values were focused on pressure distributions in buildings, because this value indicates the driving force of the airflows between building partitions and in the entire building. Based on the measured pressure distribution of the analyzed building, the unknown input parameters were deduced primarily using the Thermal Draft Coefficient (TDC). The uncertain input parameters (leakage area, flow coefficient, and exponent) were then optimized using Genetic Algorithm (GA). Through the processes suggested in this study, the uncertain input parameters for whole-building airflow simulation can be optimized, and the discrepancy between simulation results and measured values can be minimized. The advantage of this method is that the input parameters can be optimized for reasonable simulation modeling using limited measurement results in high-rise buildings.

Simulating buoyancy-driven airflow in buildings by coarse-grid fast fluid dynamics

Fast fluid dynamics (FFD) is an intermediate model between multi-zone models and computational fluid dynamics (CFD) models for indoor airflow simulations. The use of coarse grids is preferred with FFD in order to increase computing speed. However, by using a very large mesh cell to represent a heat source that could have a much smaller physical size than the cell, coarse-grid FFD would under-predict the thermal plume and thermal stratification. This investigation integrated a thermal plume model into coarse-grid FFD. The integration first used the plume model to calculate a source for the momentum equations and then corrected the temperature at the plume cell. The integration enabled coarse-grid FFD to correctly predict the plumes. When applied to displacement ventilation, coarse-grid FFD with the plume model can accurately predict the mean air temperature stratification in rooms as compared with experimental data from the literature. The improved model has also been used to calculate the ventilation rate for buoyancy-driven natural ventilation. The calculated ventilation rates agree well with the experimental data or predictions by CFD and analytical models. Coarse-grid FFD with the plume model used only a small fraction of the computing time required by fine-grid FFD, while the associated errors for the two grid sizes were comparable.

Accelerating fast fluid dynamics with a coarse-grid projection scheme

Fast fluid dynamics is an intermediate model that can provide fast and informative building airflow simulations. Although reasonably good simulation accuracy is important for fast fluid dynamics, computational efficiency is the primary concern, and it is necessary to further increase fast fluid dynamics speed. Because the most time-consuming part of fast fluid dynamics is solving the stiff pressure equation, this study proposed the application of a coarse-grid projection scheme, which solves the momentum equation on the fine grid level and the pressure equation on the coarse grid level. Therefore, appropriate approaches for mapping velocity and pressure information between different grid levels were investigated in this study. To evaluate the accuracy and computational efficiency of fast fluid dynamics with the coarse-grid projection scheme in simulating building airflows, this study tested it with building airflows of varying complexity. The results showed that the coarse-grid projection scheme would not have a negative impact on the accuracy of fast fluid dynamics in the simulation of building airflows, and it could significantly reduce the fluctuations that occur within the simulations. The coarse-grid projection scheme was able to accelerate fast fluid dynamics by approximately 1.5 times, and thus fast fluid dynamics with the coarse-grid projection scheme achieved a computing speed that was 30 to 50 times faster than computational fluid dynamics models.

Experimental investigation of the influence of the air jet trajectory on convective heat transfer in buildings equipped with air-based and radiant cooling systems

The complexity and diversity of airflow in buildings make the accurate definition of convective heat transfer coefficients (CHTCs) difficult. In a full-scale test facility, the convective heat transfer of two cooling systems (active chilled beam and radiant wall) has been investigated under steady-state and dynamic conditions. With the air-based cooling system, a dependency of the convective heat transfer on the air jet trajectory has been observed. New correlations have been developed, introducing a modified Archimedes number to account for the air flow pattern. The accuracy of the new correlations has been evaluated to±15%. Besides the study with an air-based cooling system, the convective heat transfer with a radiant cooling system has also been investigated. The convective flow at the activated surface is mainly driven by natural convection. For other surfaces, the complexity of the flow and the large uncertainty on the CHTCs make the validation of existing correlations difficult.

Numerical Analysis of Elevator Piston Effect on Building Airflow for an Air-Conditioned High-Rise Building in Winter

A model of a 24-storey building (94.5m high) with air-conditioning system was developed to analyze the elevator piston effect on building airflow by dynamic mesh technique of computational fluid dynamics (CFD). The results of the pressure distribution and airflow paths show that with the upward movement of elevator cabs, due to the elevator piston effect, changes in the pressure distribution and airflow paths occur in all the building; the pressure difference across the elevator door is enlarged, which is likely to cause some security issues; but the air exfiltration rate is hardly affected.

Development and application of an updated whole-building coupled thermal, airflow and contaminant transport simulation program (TRNSYS/CONTAM)

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.

THE IMPROVEMENT OF THE COMPUTATIONAL PERFORMANCE OF THE ZONAL MODEL POMA USING PARALLEL TECHNIQUES

The zonal modeling approach is a new simplified computational method used to predict temperature distribution, energy in multi-zone building and indoor airflow thermal behaviors of building. Although this approach is known to use less computer resource than CFD models, the computational time is still an issue especially when buildings are characterized by complicated geometry and indoor layout of furnishings. Therefore, using a new computing technique to the current zonal models in order to reduce the computational time is a promising way to further improve the model performance and promote the wide application of zonal models. Parallel computing techniques provide a way to accomplish these purposes. Unlike the serial computations that are commonly used in the current zonal models, these parallel techniques decompose the serial program into several discrete instructions which can be executed simultaneously on different processors/threads. As a result, the computational time of the parallelized program can be significantly reduced, compared to that of the traditional serial program. In this article, a parallel computing technique, Open Multi-Processing (OpenMP), is used into the zonal model, Pressurized zOnal Model with the Air diffuser (POMA), in order to improve the model computational performance, including the reduction of computational time and the investigation of the model scalability.

Air filtration in buildings – a potential technique for protecting occupants against fine particles from outdoor sources

People spend almost 90% of their time indoors. Thus, the supply air filtration in buildings plays an important role in the occupant exposure to fine particles of outdoor origin. Besides supply air filtration, room air cleaner is a potential measure for reducing the health risks of urban air fine particles. The primary aim of the study was to investigate the role of air filtration when protecting occupants against fine particles from outdoor sources. Efforts were also put to improve the efficiency of supply air filtration, and to clarify the feasibility of room air cleaners. Long-term measurements were made in three locations in urban and suburban environments (school building, apartment in multistorey building, and single-family house). Sophisticated aerosol instruments together with an automatic sampling system were used to measure indoor and outdoor aerosol concentrations and size distributions (size range 0.01 – 10 mm). The results were used to determine the efficiency of air filters and indoor/outdoor (I/O) ratios for fine particles of outdoor origin. The efficiency of supply air filtration can be easily improved up to 90%, and the I/O ratio can be significantly reduced, when compared to existing practices. The uncontrolled leakage air flows in buildings, however, limit the feasibility of supply air filtration, i.e. the achieved I/O ratios (particle size 0.3 mm) were in the range of 0.2-0.3. By using room air cleaners in combination with effective supply air filtration, the I/O ratio could be further reduced, in favorable conditions even below 0.1. The concentration of indoor fine particles originating from outdoors can be effectively reduced by improving the level of supply air filtration. This requires, however, that the uncontrolled leakage air flows are negligible compared with the supply air flow. Room air cleaner, with adequate capacity and acceptable noise level, is another potential option for reducing the occupant exposure to fine particles.

Numerical investigation of wind-induced airflow and interunit dispersion characteristics in multistory residential buildings

Compared with the buoyancy-dominated upward spread, the interunit dispersion of pollutants in wind-dominated conditions is expected to be more complex and multiple. The aim of this study is to investigate the wind-induced airflow and interunit pollutant dispersion in typical multistory residential buildings using computational fluid dynamics. The mathematical model used is the nonstandard k-ε model incorporated with a two-layer near-wall modification, which is validated against experiments of previous investigators. Using tracer gas technique, the reentry of exhaust air from each distinct unit to other units on the same building, under different practical conditions, is quantified, and then, the possible dispersion routes are revealed. The units on the floor immediately below the source on the windward side, and vertically above it on the leeward side, where the reentry ratios are up to 4.8% and 14.9%, respectively, should be included on the high-infection list. It is also found that the presence of balconies results in a more turbulent near-wall flow field, which in turn significantly changes the reentry characteristics. Comparison of the dispersion characteristics of the slab-like building and the more complicated building in cross (#) floorplan concludes that distinctive infectious control measures should be implemented in these two types of buildings.

CHAMPS-Multizone—A combined heat, air, moisture and pollutant simulation environment for whole-building performance analysis

A computer simulation tool, named “CHAMPS-Multizone,” is introduced in this article for analyzing both energy and indoor air quality (IAQ) performance of buildings. The simulation model accounts for the dynamic effects of outdoor climate conditions (solar radiation, wind speed and direction, and contaminant concentrations), building materials and envelope system design, multi-zone air and contaminant flows in buildings, internal heat and pollutant sources, and operation of the building HVAC systems on the building performance. It enables combined analysis of building energy efficiency and indoor air quality. The model also has the ability to input building geometry data and HVAC system operation related information from software, such as SketchUp and DesignBuilder via IDF file format. A “bridge” to access static and dynamic building data stored in a “Virtual Building” database is also developed, allowing convenient input of initial and boundary conditions for the simulation and for comparisons between the predicted and measured results. This article summarizes the mathematical models, adopted assumptions, methods of implementation, and verification and validation results. The needs and challenges for further development are also discussed.

Improvements of Fast Fluid Dynamics for Simulating Air Flow in Buildings

Fast fluid dynamics (FFD) can potentially be used for real-time indoor air-flow simulations. This study developed two-dimensional fast fluid dynamics (2-D FFD) into three-dimensional fast fluid dynamics (3-D FFD). The implementation of boundary conditions at the outlet was improved with a local mass conservation method. A near-wall treatment for the semi-Lagrangian scheme was also proposed. This study validated the 3-D FFD with five flows that have features of indoor air flow. The results show that the 3-D FFD can successfully capture the three dimensionality of air-flow and provide reliable and reasonably accurate simulations for indoor air flows with a speed of about 15 times faster than current computational fluid dynamics (CFD) tools.

Evaluation of Sub-Zonal Airflow Models for the Prediction of Local Interior Boundary Conditions – Natural and Forced Convection Cases

Currently, researchers are striving to advance the possibilities to calculate the integrated phenomena of heat, air and moisture flows in buildings, with specific focus on the interactions between the building zones and building components. This paper presents an investigation of the capability and applicability of the sub-zonal airflow model to predict the local indoor environmental conditions, as well as the local surface transfer coefficients near building components. Two test cases were analyzed for, respectively, natural and forced convection in a room. The simulation results predicted from the sub-zonal airflow models are compared to experimental data and numerical computational fluid dynamics (CFD) results. The study shows that sub-zonal models combined with an appropriate surface transfer coefficient model are able to give reliable predictions of the local indoor environmental conditions and surface transfer coefficients near the building component for the analyzed cases. The relatively short computation time and flexibility of the sub-zonal model makes the application attractive for transient simulation of heat, air and moisture transport in buildings. However, the availability of appropriate reference conditions, for example experimental or numerical results, is a prerequisite for the development of a reliable sub-zonal model.

Estimating building airflow using CO2 measurements from a distributed sensor network

An accurate estimate of airflow rates within a building, namely the infiltration and interzonal airflow, is needed when determining energy use and indoor air quality and for detecting contaminants. The objective of this article is to demonstrate the feasibility of estimating airflow in a commercial building using carbon dioxide (CO2) as a tracer. In this article, development of the proposed building airflow network inverse models (both deterministic and stochastic) is presented along with the methods used to test their performance. It is shown that the proposed inverse models would be able to determine the airflow for a one-story building of any size, as long as the rank of the known-information matrix is greater than or equal to the number of unknown airflow rates. Synthetic perfect and imperfect steady-state and transient CO2 measurements are used to test the performance of the proposed building airflow network inverse models.

Air Flow in Large Space Building with CFD Model and Local Test

Simulation with CFD and local test are two main methods in study on air flow in large space building. This paper tests and simulates thermal comfort and air distribution of existing air- conditioning mode of some exhibition center. Through comparison and analysis on existing and simulated air-conditioning pattern, draw a conclusion that it’s feasible to simulate thermal comfort and air distribution of air-conditioning. And the research is important to guide energy efficiency and design optimization of air-conditioning system in large space building.

Using CFD Capabilities of CONTAM 3.0 for Simulating Airflow and Contaminant Transport in and around Buildings

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 appropriate and then uses the multizone approach for the rest of a building, thus capturing the local distribution of air and contaminant properties in a zone and their impacts on other zones of a building. CFD capabilities are demonstrated using a generic residential house model to show how these two new CFD features enhance the existing CONTAM capabilities for both indoor and outdoor air quality analysis.

A Simplified Building Airflow Model for Agent Concentration Prediction

A simplified building airflow model is presented that can be used to predict the spread of a contaminant agent from a chemical or biological attack. If the dominant means of agent transport throughout the building is an air-handling system operating at steady-state, a linear time-invariant (LTI) model can be constructed to predict the concentration in any room of the building as a result of either an internal or external release. While the model does not capture weather-driven and other temperature-driven effects, it is suitable for concentration predictions under average daily conditions. The model is easily constructed using information that should be accessible to a building manager, supplemented with assumptions based on building codes and standard air-handling system design practices. The results of the model are compared with a popular multi-zone model for a simple building and are demonstrated for building examples containing one or more air-handling systems. The model can be used for rapid concentration prediction to support low-cost placement strategies for chemical and biological detection sensors.

Brominated flame retardants in offices in Michigan, U.S.A.

Brominated flame retardants (BFRs) are now ubiquitous contaminants with large reservoirs and high concentrations in buildings. Most of the information documenting BFR levels has been obtained in residences, and other environments that can lead to exposure have received relatively little attention, including offices that contain numerous BFR sources and where individuals spend considerable time. The aim of this study is to characterize BFR concentrations, potential emission sources, and migration pathways in office environments. We measure BFR levels in floor dust, indoor air, ventilation filter dust, and carpets in ten commercial and institutional buildings in Michigan, U.S.A. The median concentration of total BDEs in settled dust was 8754 ng g − 1 , at the upper range of levels previously reported. Especially elevated levels were found in offices in buildings that contained known or likely BFR sources, e.g., computer servers. A trends analysis in a newly constructed building showed remarkable increases in concentrations of BFRs in settled dust and indoor air, and apparent steady-state levels were reached 5 to 8 months after building completion, a particularly striking finding given that the building was constructed and furnished several years after the voluntary phase-out of the penta- and octa-mixtures. Airborne particulate matter collected in a building's HVAC system filters contained PBDEs, including BDE-209, at levels exceeding the concentration of floor dust. In conjunction with estimates of building air flow rates, filter efficiency and other parameters, mass balance calculations for this building were used to estimate the emission rates and reservoirs of PBDEs. The widespread distribution of BFRs found in offices in both new and old buildings suggests the significance of workplace exposures, the need for controls to minimize human exposure, intra-building migration, and environmental releases of these chemicals, and the need for monitoring in new buildings to confirm the effectiveness of the PBDE phase-out.

Overview of natural cross-ventilation studies and the latest simulation design tools used in building ventilation-related research

High-performance insulation, draught stripping and double glazing have effectively sealed off the fresh air routes and have made adequate natural ventilation impossible inside the modern energy-efficient home nowadays. Cross ventilation, a passive cooling method for buildings, is a major type of natural ventilation. Various study approaches have been reported; however, there is still no appropriate simulation tool that can predict the indoor thermal environment of natural ventilation. The typical building energy simulation for investigating a naturally ventilated building adopts thermal simulation and an airflow network. However, the airflow network approach for airflow estimation in building energy simulation cannot accurately predict indoor airflow by solving the pressure-flow algebraic equation, the mass balance equation and hydrostatic pressure variations. Recent advances in computer performance and computational fluid dynamics (CFD) software integrated with building energy simulation have made it possible to improve the accuracy to assess the performance of natural ventilation and also to give more realistic predictions of airflow in buildings. This chapter overviews and discusses various network airflow models integrated with CFD in the natural ventilation of buildings. Examples of results obtained with this approach are given to demonstrate the significant effects of such a coupling programme on natural ventilation prediction accuracy.

Real-Time Airflow Rate Measurements from Mechanically Ventilated Animal Buildings

This paper describes techniques used to determine airflow rate in multiple emission point applications typical of animal housing. An accurate measurement of building airflow rate is critical to accurate emission rate estimates. Animal housing facilities rely almost exclusively on ventilation to control inside climate at desired conditions. This strategy results in building airflow rates that range from about three fresh-air changes per hour in cold weather to more than 100 fresh-air changes per hour in hot weather. Airflow rate measurement techniques used in a comprehensive six-state study could be classified in three general categories: fan indication methods, fan rotational methods, and airspeed measurement methods. Each technique is discussed and implementation plans are noted. A detailed error analysis is included that estimated the uncertainty in airflow rate between ±5 and ±6.1% of reading at a building operating static pressure, air temperature, relative humidity, and barometric pressure of 20 Pa, 25 °C, 50%, and 97,700 Pa, respectively.

Comparison of airflow and particulate matter transport in multi-room buildings for different natural ventilation patterns

This study numerically investigates airflow characteristics and particulate matter (PM) transport in multi-room buildings for different natural ventilation patterns with the same air change rate. Four typical natural ventilation patterns (full-open, pass-through, right short-circuit and left short-circuit), representing the ratios of the outlet-to-inlet opening size ranging from 1.67 to 0.17, are considered to study multi-room airflow characteristics. A measured indoor PM 10 profile in Taipei Metropolis is input into the above four ventilation patterns as the initial condition of the PM size distribution. The time variation of indoor PM 10/PM 2.5/PM 1 concentrations in each room for various ventilation patterns is next investigated. The effect of ventilation pattern on particle removal mechanism is emphasized. The results show that although the air change rate of the building is the same, airflow characteristics and PM transport behaviors are quite different for various ventilation patterns. The removal efficiencies of PM 10 for the four ventilation patterns are all found to be much better than those of PM 2.5 and PM 1. Particle escape is the major mechanism to remove PM for rooms with double-sided ventilation, whereas particle deposition is important for single-sided ventilation rooms.