Airflow Network Research Articles

Totally Enclosed Self-Circulation Axial Ventilation System Design and Thermal Analysis of a 1.65-MW Direct-Drive PMSM

This paper presents a totally enclosed self-circulation (TESC) axial ventilation system (AVS) for large direct-drive permanent magnet synchronous machines (PMSMs). The configuration and the cooling air circulation process of the cooling system are described in detail. Then, the lumped parameter (LP) based airflow analysis and thermal analysis applicable to large PMSMs with the presented TESC AVS are proposed. The airflow network model and thermal network model are set up, respectively, and both of them are programmed. In order to verify the feasibility of the ventilation system and the accuracy of the LP models, a 1.65-MW PMSM prototype with the proposed ventilation system is developed and manufactured, and the temperature rise of the prototype is tested under generator operation mode. The accuracies of the developed airflow network model and thermal network model are verified by comparing the calculation results of the temperature rise with the test results. The LP models can be used to investigate the effects of different geometrical and operational conditions on the distributions of the airflow rate and the temperature of PMSMs with the TESC AVS.

学校施設におけるナイトパージの手法に関する研究 熱・換気回路網プログラムを用いたシミュレーションによる技術資料の整備

学校施設におけるナイトパージの手法に関する研究 熱・換気回路網プログラムを用いたシミュレーションによる技術資料の整備

Design Method to Prevent Airborne Infection in an Emergency Department

This study investigated design recommendations to reduce airborne infection risk in an emergency department by using airflow network simulation. The main design concepts include isolating the source of the airborne pathogen and increasing the ventilation rate. A conventional emergency department is selected as a base model, and influenza is selected as the airborne pathogen examined in the study. The Wells—Riley equation is used to model airborne infection risk in a zone. The simulation results indicate that airborne infection risk exists when a patient releases an influenza pathogen in the emergency department with a ventilation rate of 3 ACH according to the Korean building code. The findings reveal that isolating the airborne pathogen source and increasing the ventilation rate are good methods to prevent airborne infection risk. However, the isolation method can increase the infection risk in a zone with an airborne pathogen source. Thus, it is necessary to simultaneously increase the ventilation in a zone with an airborne pathogen source. Additionally, airborne infection risk continuously increases the cumulative exposure time, and it is desirable to increase the ventilation rate required for a zone based on the residing time of a patient releasing airborne pathogens in a target zone.

Comparative investigation on building energy performance of double skin façade (DSF) with interior or exterior slat blinds

Advanced passive control technologies attract a great deal of attention by architects and engineers as a way of achieving both high indoor environmental quality and energy efficient buildings. This study investigates the thermal and daylighting effects of a double skin façade (DSF) system with interior and exterior blinds. A buffer type DSF and slat type blinds are used for this comparative study. To investigate thermal and daylighting effects of three passive control models, evaluation of annual heating, cooling, and lighting loads is conducted using a widely-accepted whole building energy modeling program, EnergyPlus. A simulated DSF model is developed using the air-flow network (AFN) model in EnergyPlus and calibrated against measured data from an experimental DSF facility installed to an office building in Daejeon, South Korea. After a proper calibration of the simulated DSF model, the impact of blinds in the cavity of the DSF is also evaluated by adopting a slat blind model in EnergyPlus. For exterior and interior blind models, the simulated DSF model is modified by removing a DSF box and adding slat blinds at inner and outer surfaces of the windows. A Radiance-based daylighting simulation program, Daysim, is used to evaluate daylighting aspects of blinds and lighting controls within an office building with simulated DSF, interior blind, and exterior blind models. Generated lighting and blind raise/lower control schedules from Daysim are used as input values in EnergyPlus for annual thermal and lighting load calculations. In addition, the impact of natural ventilation to reduce trapped hot air within the cavity of the DSF box is considered in this study during a cooling period only for the DSF model. Results indicate that the simulated DSF model can save up to 40%, 2%, and 5% for heating, cooling, and total loads, respectively, when compared to the baseline (i.e., no passive technologies) without any blinds or controls. With the combination of the daylight-based dimming control based on the indoor illuminance levels and the blind raise/lower control, the simulated DSF and the exterior blind models could potentially reduce the building thermal loads and lighting energy consumption by around 27–52%., respectively.

Coupled thermal-electrical-optical analysis of a photovoltaic-blind integrated glazing façade

PV-blind embedded double skin façade (PVB-DSF) is a promising façade system for building energy efficiency. This paper developed a coupled thermal-electrical-optical model for analyzing, evaluating and optimizing the system performance. The ray-tracing method, radiosity method and net radiation method are used for the optical model. The single diode RP-model and Lambert-W function are adopted in the electrical model. The airflow network and energy balance equations are coupled for system thermal model. A complex simulation algorithm is proposed for the thermal-electrical-optical model solution. A series of experiments were implemented for model verification. The comparisons between simulation and measurement data show a good agreement. Specifically, the relative mean square error (RMSE) for simulation result in optical model is 2.02 W/m2 in sunny day and 5.21 W/m2 in cloudy day; 2.24 V for output voltage and 1.47 W for output power; 0.67 °C, 0.41 °C and 2.17 °C for external, internal glass pane and PV-blind. On top of that, the model is used as a tool for understanding the system performance under different configurations and position of PV-blind, solar cell efficiency and airflow rate. PV-blind angle and width under different spacing settings are optimized for balancing system energy performance and indoor daylighting comfort level. This study offers a useful simulation tool and a deeper understanding of PVB-DSF, which is beneficial for the design, control, optimization and evaluation of this effective glazing façade and can contribute to building energy efficiency.

Parametric Analysis of the Factors Influencing Airborne Infection

This study investigated the influence of the various factors such as airborne pathogen type, space magnitude, ventilation rate and exposure time on the airborne infection risk. The parametric study is performed by airflow network simulation tool, CONTAMW 3.2. In addition, Wells-Riley equation is adopted to calculate airborne infection probability in a controlled volume. The results indicate occupancy time of infector significantly influence the airborne infection probability. In addition, smaller room size also affected to the increased infection risk. Especially, in the case of infector reside in a small room (30 m2) for 4 hours with 6 ACH of ventialtin rate, Tuberculosis infection risk of inpatient around infector increased to 21.0% (Influenza: 90.6%). Even though ventilation rate of 6 ACH looks appropriate in general condition to prevent airborne infection, increased ventilation over 6 ACH must be implemented to these critical environmental conditions involving smaller room size and long occupancy time.

Prediction of wind pressure coefficients on building surfaces using artificial neural networks

Knowing the pressure coefficient on building surfaces is important for the evaluation of wind loads and natural ventilation. The main objective of this paper is to present and to validate a computational modeling approach to accurately predict the mean wind pressure coefficient on the surfaces of flat-, gable- and hip-roofed rectangular buildings. This approach makes use of artificial neural network (ANN) to estimate the surface-average pressure coefficient for each wall and roof according to the building geometry and the wind angle. Three separate ANN models were developed, one for each roof type, and trained using an experimental database. Applied to a wide variety of buildings, the current ANN models were proved to be considerably more accurate than the commonly used parametric equations for the estimation of pressure coefficients. The proposed ANN-based methodology is as general and versatile as to be easily expanded to buildings with different shapes as well as to be coupled to building performance simulation and airflow network programs.

Development of an adaptive discharge coefficient to improve the accuracy of cross-ventilation airflow calculation in building energy simulation tools

Airflow network (AFN) model embedded in building energy simulation tools such as EnergyPlus is extensively used for prediction of cross-ventilation in buildings. The noticeable uncertainty in the measurement of the surface pressure, discharge coefficient, and simplifications applied to the orifice-based equation result in considerable discrepancies in the prediction of the cross-ventilation airflow rate. Computational Fluid Dynamics (CFD) provides more accurate results comparing to the orifice-based equations although with an excessive computational cost.The aim of this study is to improve the accuracy of the orifice-based model by development of an adaptive correlation for the discharge coefficient using CFD. Hence, a validated CFD model for the cross-ventilation of an unsheltered building is firstly developed using an experimental study. In the next step, by exploiting Latin hypercube sampling approaches, a large CFD dataset of 750 scenarios for different building geometries (i.e. square cube, cuboid and long corridor) is generated; the dataset is then coupled to the AFN cross-ventilation model to obtain an adaptive correlation for the discharge coefficient as a function of the openings' geometries and location using response surface and radial basis function models.Results show that the newly developed adaptive correlation successfully increases the accuracy of AFN model for the cross-ventilation modeling of unsheltered buildings as the relative errors for the airflow rate prediction of different building geometries are decreased up to 28% in comparison with the cases with constant discharge coefficient. Results also demonstrate the importance of considering the value of the local-surface wind pressure in the AFN model.

住宅用全熱交換換気ユニットの有効換気量率測定法に関する研究 : 第2報-各種ユニットへの測定法の適用と換気回路網モデル

住宅用全熱交換換気ユニットの有効換気量率測定法に関する研究 : 第2報-各種ユニットへの測定法の適用と換気回路網モデル

Field study of infiltration rate and its influence on indoor air quality in an apartment

In recent years, especially in winter, the concentration of outdoor PM2.5 in large areas of China remains at a high level. The research shows that there is a strong positive correlation between indoor and outdoor air quality. The premise of effective prediction of indoor air quality is to ensure accurate infiltration simulation model. In this study, the long-term indoor and outdoor PM2.5 concentration of an apartment and the outdoor meteorological condition have been monitored. Combined with the Airflow Network module in EnergyPlus, the infiltration and the indoor air quality caused by the infiltration are studied. The results show that for different rooms in the apartment, the infiltration rates are different because of the characteristics of envelope and the meteorological parameters. The infiltration rate of the Second lie ranges from 0.05 to 0.3h-1, while that of the master bedroom ranges from 0.2 to 0.6h-1. The change of infiltration rate caused by different wind directions is not so obvious, while that caused by different wind speed is quite different.

Intelligently controlled naturally ventilated mosque – a case study of applying design tools throughout the design process

ABSTRACTWhile numerous models to aid the design of naturally ventilated buildings have been developed and validated, few studies have demonstrated how a variety of tools have been applied to an actual project. This paper presents a case study of the design of a naturally ventilated mosque to document the application of rules of thumb, airflow network models, computational fluid dynamics (CFD) models, and other design tools to inform the design of an actual project throughout the design process. Both airflow network and CFD models are validated against full-scale experiments. The airflow network model predicts experimental flow rates and temperatures with an RSME of 0.23 m3/s and 1.26 °C respectively, while the CFD model qualitatively predicts the correct velocity vectors measured with particle image velocimetry and simulates indoor air temperatures with an RSME of 1.2 °C. These and other tools are used to assess a night purge system for the thermally massive mosque that helps to reduce indoor temperatures above 32 °C by 74% and indoor temperatures between 29 and 32 °C by 53%. Low-energy exhaust fans help further reduce the hottest temperatures in the mosque by 59% by facilitating the cooling of the thermal mass when needed.

Influence of input data on airflow network accuracy in residential buildings with natural wind- and stack-driven ventilation

The airflow network (AFN) modeling approach provides an attractive balance between the accuracy and computational demand for naturally ventilated buildings. Its accuracy depends on input parameters such as wind pressure and opening discharge coefficients. In most cases, these parameters are obtained from secondary sources which are solely representative for very simplified buildings, i.e. for buildings without facade details. Although studies comparing wind pressure coefficients or discharge coefficients from different sources exist, the knowledge regarding the effect of input data on AFN is still poor. In this paper, the influence of wind pressure data on the accuracy of a coupled AFN-BES model for a real building with natural wind- and stack-driven ventilation was analyzed. The results of 8 computation cases with different wind pressure data from secondary sources were compared with the measured data. Both the indoor temperatures and the airflow were taken into account. The outcomes indicated that the source of wind pressure data had a significant influence on the model performance.

Review of natural ventilation models

ABSTRACTNatural ventilation (NV) is an important and efficient passive technique to reduce building cooling energy need and improve indoor air quality. NV design requires profound knowledge and accurate prediction of air flow and heat transfer in and around buildings that are highly dependent on varying external and internal conditions, as well as the building geometry and local site conditions. This paper reviews the important NV models and simulation tools and the comparisons of their prediction capabilities. A review of the analytical models reveals that these models are generally only applicable to specific geometries and driving forces. The complex interactions between combined driving forces and complex geometries results in sets of non-linear equations which must be solved numerically. Prevalent network airflow models are identified and compared, which generally use the same theory, and yield similar, often nearly identical results in inter-model comparison studies. Airflow network models incorporated into whole building energy simulation tools are also assessed. Results have shown that the current airflow model can be used to model most NV mechanisms, with an exception of wind-driven single-sided ventilation. For the predictable cases, the most accuracy is achieved for cases with small and simple openings. For larger openings and especially complicated openings, the model's predictions are less accurate. Furthermore, the model is heavily dependent on several somewhat ambiguous coefficients including: wind profile exponent, pressure coefficient, and discharge coefficient.

Taming the killer in the kitchen: mitigating household air pollution from solid-fuel cookstoves through building design

In this study, we attempt to mitigate household air pollution (HAP) through improved kitchen design. Field surveys were conducted in ten kitchens of rural western India, which were then modelled and simulated for dynamic indoor airflow network analysis. The simulated results were statistically clustered using principal component analysis and hierarchical agglomerative clustering, to construct a cumulative built environment parameter called ‘Built Factor’ for each kitchen, and subsequently a derivative matrix was developed. Categorization of better performing kitchens from this derivative matrix enabled in deriving the built parameter thresholds for a ‘better’ kitchen design. This derived kitchen showed 60 % reduction in PM2.5 peak concentration during cooking hours. The evaluation described here is essentially a “proof of concept”, that effective building design can be an alternative way to reduce HAP without the introduction of chimneys, improved cookstoves or shifting to cleaner fuel.

Dynamic modeling of the ventilated double skin façade in hot summer and cold winter zone in China

An improved zonal approach with a dynamic optical model of the venetian blind and airflow network model is proposed to model the mechanical ventilated double skin façade (DSF) in hot summer and cold winter zone in China. It is validated by the experiment in both cooling and heating season cases. The comparison results show that the simulated results fit well with the measured results. The effects of the ventilation rate and slat angle on the inner glass temperature and heat gains through the DSF are discussed. Both increase ventilation rate and slat angle can decrease the inner glass temperature and heat gains through the DSF, but the decrease range is greater by increasing the slat angle. Compared to the slat angle at 0°, heat gains can be reduced by 63% when the slat angle at 60°. The proposed method can not only meet the requirements of engineering application, but also spend less computational time in modeling DSF dynamically in hot summer and cold winter zone in China. It can be used to evaluate the thermal performance and simulate the annual energy consumption of DSF.

Development of concepts for cost-optimal nearly zero-energy buildings for the industrial steel building sector

After 2020, all new buildings in Europe must be built as “nearly zero-energy buildings” (NZEB). For residential and certain commercial building types, significant experience in both research and practice is already available for such ambitious building standards. However, for industrial buildings, such as warehouses and production buildings, NZEB is still a new field. To date findings for residential and office buildings are often used to define standards for the entire building sector. However, industrial buildings have completely different thermal behavior due to their different building shapes, materials, interior temperatures, usage times and internal gains from processes and machines. Therefore, new concepts are required for nearly zero-energy industrial buildings.In this research, such concepts were developed based on large parametric studies simulating more than 1800 different variations in a building simulation model coupled with a 3D transient finite difference ground model and an air-flow network simulation. To gain the required input data for the air infiltration simulation, extensive leakage measurements in a therefore built air-tightness test stand were conducted.According to the EU directive stipulating the NZEB standard, NZEBs have to be cost-optimal. Thus, the focus of this work was on developing cost-optimal solutions to meet the NZEB standard. The results are building concepts for warehouses and production buildings that have 50–75% lower heat energy demand than current (2015) building standards in Germany. These heat energy savings are primarily achieved by increased air tightness, decreased thermal bridges, optimized floor slab insulation and solar optimization. Significantly increased insulation thicknesses are only cost-effective for industrial buildings with low internal gains but relatively high interior temperatures. Previous standards almost exclusively concentrated on increasing the thermal insulation, while the other parameters were often neglected.

Modelling temperature and humidity in storage spaces used for cultural property in Japan

From rainy season to summer in Japan, the climate is humid. Especially in these seasons, it is difficult to maintain suitable conditions of temperature and relative humidity in exhibition and storage rooms in museums. Such climate conditions and problems are common to many countries in East Asia. Analysis using computer simulation can be a powerful tool because it is cheap and allows the simulation of a range of conditions without having to make changes to buildings and environments surrounding cultural objects. In this study, a storage building in which there is no air-conditioning unit was chosen as a target. The modelling of temperature and relative humidity in storage spaces was conducted using the Thermal and Airflow Network Model Simulation Program for buildings (NETS). The effect of seismic retro-fitting on the variation of temperature was predicted using NETS and the results were evaluated by comparing with the measured values. As a result, the heat transfer was successfully calculated and the modelled temperature represents the measured values reasonably well. Computing relative humidity by taking into account the effect of porous hygroscopic materials is challenging. In order to overcome this problem, the κ-ν model was adopted. We have some improvements but the study is still ongoing.

Experimental validation of a EnergyPlus model: Application of a multi-storey naturally ventilated double skin façade

Nowadays, energy simulation in many respects assists researchers and engineers in the design phase, as well as in the buildings operational phase. Reliability of the integrated simulation model and the knowledge and experience of the user are the cornerstones of good quality simulation prediction result. This study was preceded by a detailed and long-term experimental analysis of the building with a double-skin ventilated façade [10]. The paper presents results of the measurement, fine-tuning process and validation of the numerical simulation model. The simulation software tool, EnergyPlus in combination with Airflow Network Algorithm algorithm was used for the cavity air temperature and velocity prediction. When the model was verified, the criterion of eligibility were defined with the recommended statistical indicators. In order to achieve the better assessment, the validation process was done trifold: for winter, transitional and summer season. Overall, the research results highlight a very good agreement and a high level of matching between measured values and simulated results, which is a confirmation of the applied energy simulation tool.

Characterization of an airflow network model by sensitivity analysis: parameter screening, fixing, prioritizing and mapping

Due to the over-parameterized models in detailed thermal simulation programs, modellers undertaking validation or calibration studies, where the model output is compared against field measurements, face difficulties in determining those parameters which are primarily responsible for observed differences. Where sensitivity studies are undertaken, the Morris method is commonly applied to identify the most influential parameters. They are often accompanied by uncertainty analysis using Monte Carlo simulations to generate confidence bounds around the predictions. This paper sets out a more rigorous approach to sensitivity analysis (SA) based on a global SA method with three stages: factor screening, factor prioritizing and fixing, and factor mapping. The method is applied to a detailed empirical validation data set obtained within IEA ECB Annex 58, with the focus of the study on the airflow network, a simulation program sub-model which is subject to large uncertainties in its inputs.

Developing a method and simulation model for evaluating the overall energy performance of a ventilated semi‐transparent photovoltaic double‐skin facade

AbstractA comprehensive simulation model has been developed in this paper to simulate the overall energy performance of an amorphous silicon (a‐Si) based photovoltaic double‐skin facade (PV‐DSF). The methodology and the model simulation procedure are presented in detail. To simulate the overall energy performance, the airflow network model, daylighting model, and the Sandia Array Performance Model in the EnergyPlus software were adopted to simultaneously simulate the thermal, daylighting, and dynamic power output performances of the PV‐DSF. The interaction effects between thermal, daylighting, and the power output performances of the PV‐DSF were reasonably well modeled by coupling the energy generation, heat‐transfer, and optical models. Simulation results were compared with measured data from an outdoor test facility in Hong Kong in which the PV‐DSF performance was measured. The model validation work showed that most of the simulated results agreed very well with the measured data except for a modest overestimation of heat gains in the afternoons. In particular, the root‐mean‐square error between the simulated monthly AC energy output and the measured quantity was only 2.47%. The validation results indicate that the simulation model developed in this study can accurately simulate the overall energy performance of the semi‐transparent PV‐DSF. This model can, therefore, be an effective tool for carrying out optimum design and sensitivity analyses for PV‐DSFs in different climate zones. The methodology developed in this paper also provides a useful reference and starting point for the modeling of other kinds of semi‐transparent thin‐film PV windows or facades. Copyright © 2015 John Wiley & Sons, Ltd.