Analysis of modeling effort and impact of different levels of detail in building information models

The main objectives of this paper are to evaluate the modeling effort associated with generating building information modeling (BIM) at different levels of detail (LoD) and the impact of LoD in a project in supporting mechanical, electrical and plumbing (MEP) design coordination. Results show an increase in total modeling time ranging from doubling the modeling effort to eleven folding it, when going from one LoD to another. When comparing modeling time per object, rates ranged from 0.2 (decreased modeling time) to 1.56 (increased modeling time). Based on the experiments done in MEP design coordination, it was observed that the automatic clash detection process using BIMs, with its consistently higher recall rate, provides a more complete identification of clashes, with the cost of false positives (low precision). This study showed that additional modeling effort can lead to more comprehensive analyses and better decision support during design and construction.     

Analysis of building maintenance requests using a text mining approach: building services evaluation

ABSTRACT

End users’ maintenance requests gathered from computerized maintenance management systems (CMMS) configure a rich source of information to evaluate the occupants’ satisfaction and the building systems. Nevertheless, the non-standardized data gathered from CMMS makes it difficult to carry out analytics. This paper presents a text mining approach to extract information from end users’ maintenance requests and an analysis of 6,830 maintenance requests derived from 46 buildings including offices, academic buildings and laboratories over two and a half years. The research results reveal that the most common maintenance requests during building operation and maintenance are related to problems in electrical and HVAC fixtures. Although the year of construction is not related to the occupants’ maintenance requests, the type of building use and building property do influence them. The implementation of control and preventive strategies based on these results may increase facility managers’ productivity and building systems’ performance.     

Validation of CFD simulations of wind-driven rain on a low-rise building facade

For decades, the assessment of the amount and intensity of wind-driven rain (WDR) falling onto building facades has been performed either by measurements or by semi-empirical methods such as the WDR index and the WDR relationship. In the past 15 years, numerical assessment methods based on Computational Fluid Dynamics (CFD) have secured their place in WDR research. Despite the widespread use of these methods at present, very few efforts have been made towards validation of CFD simulations of WDR on buildings. This paper presents a detailed validation study for a low-rise building of complex geometry, supported by a recently published, high-resolution full-scale wind, rain and WDR measurement dataset. It is shown that the CFD simulations can provide quite accurate predictions of the amount of WDR impinging on the building facade, for a number of very different rain events, and that the main discrepancies, in this study, are due to a simplification of the upstream wind conditions.     

An evaluation of the embedment of a Radio Frequency Integrated Circuit with a temperature detector in building envelopes for energy conservation

Concrete is the primary material for building envelopes in some parts of the world, and its ability to store heat as well as its dynamic temperature changes will not only affect the deterioration rate of the exterior wall but will also greatly influence the energy efficiency of interior air conditioning. There are many methods for measuring the inner temperature of concrete, but they often have limitations, such as indirect estimation, cable installation requirements, high cost, or heterogeneity of the sample structure. In order to measure the internal temperature of concrete, this study integrated a Radio Frequency Integrated Circuit (RFIC) with a temperature sensor chip and embedded the device in concrete structures. A Smart Temperature Information Material (STIM) was thus developed. This device overcomes the aforementioned constraints, allows direct measurement and wireless transmission, and is able to constantly monitor temperature changes from a distance. The experiment embedded STIM into 5 concrete specimens that simulated rooftop insulation (50 cm × 50 cm × 15 cm) to measure the thermal performance of each insulation material, and the effect of weather conditions and the heat release/absorption rates on the thermal performance. The results of the study can be used as a reference for selecting materials for building design or maintenance and analysis of the energy efficiency of building envelopes.     

Simulation of mean flow and turbulence over a 2D building array using high-resolution CFD and a distributed drag force approach

A numerical simulation has been performed of the disturbed flow through and over a two-dimensional array of rectangular buildings immersed in a neutrally stratified deep rough-walled turbulent boundary-layer flow. The model used for the simulation was the steady-state Reynolds-averaged Navier-Stokes equations with linear and non-linear eddy viscosity formulations for the Reynolds stresses. The eddy viscosity was determined using a high-Reynolds number form of the k-ε turbulence-closure model with the boundary conditions at the wall obtained with a standard wall-function approach. The resulting system of partial differential equations was solved using the SIMPLE algorithm in conjunction with a non-orthogonal, colocated, cell-centered, finite volume procedure. The predictive capabilities of the high-resolution computational fluid dynamics (CFD) simulations of urban flow are validated against a very detailed and comprehensive wind tunnel data set. Vertical profiles of the mean streamwise velocity and the turbulence kinetic energy are presented and compared to those measured in the wind tunnel simulation.It is found that the performance of all the turbulence models investigated is generally good—most of the qualitative features in the disturbed turbulent flow field through and over the building array are correctly reproduced. The quantitative agreement is also fairly good (especially for the mean velocity field). Overall, the non-linear k-ε model gave the best performance among four different turbulence closure models examined. The turbulence energy levels within the street canyons and in the exit region downstream of the last building were underestimated by all four turbulence closure models. This appears to contradict the ‘stagnation point anomaly’ associated with the standard k-ε model which is a result of the excessive turbulence energy production due to normal straining. A possible explanation for this is the inability of the present models to account properly for the effects of secondary strains on the turbulence and/or for the effects of large-scale flapping of the strong shear layer at the canopy top.The results of the high-resolution CFD simulations have been used to diagnose values of the drag coefficient to be used in a distributed drag force representation of the obstacles in the array. Comparisons of the measured spatially-averaged time-mean mean velocity and turbulence kinetic energy in the array with predictions of the disturbed flow using the distributed drag force approach have been made.     

CFD simulation of VOCs concentrations in a resident building with new carpet under different ventilation strategies

This paper investigates the effect of ventilation strategies on the concentrations of volatile organic compounds (VOCs) emitted from a new carpet in an apartment with the VOCs emission characteristics taken from chamber test data. The commercial software FLUENT 6 has been employed to solve the continuity, momentum, turbulence and concentration equations under five different ventilation strategies. Numerical results show that ventilation strategies have a small effect on VOCs emission from carpet. Continuous ventilation keeps a low level of VOCs concentration in the air. Flushing ventilation has a significant effect on the VOCs concentration in the air. During a period without ventilation, VOCs concentration in the air usually increases to a high level. Thus, the ventilation should be carried out before the arrival of residents to ensure a low level of VOCs concentration. At the startup of ventilation run, the sudden flow strongly promotes the mixing of VOCs, which may lead to local high concentration.     

Application of CFD plug-ins integrated into urban and building design platforms for performance simulations: A literature review

The transformation of urban and building design into green development is conducive to alleviating resource and environmental problems. Building design largely determines pollutant emissions and energy consumption throughout the building life cycle. Full consideration of the impact of urban geometries on the microclimate will help construct livable and healthy cities. Computational fluid dynamics (CFD) simulations significantly improve the efficiency of assessing the microclimate and the performance of design schemes. The integration of CFD into design platforms by plug-ins marks a landmark development for the interaction of computer-aided design (CAD) and CFD, allowing architects to perform CFD simulations in their familiar design environments. This review provides a systematic overview of the classification and comprehensive comparison of CFD plug-ins in Autodesk Revit, Rhinoceros/Grasshopper, and SketchUp. The applications of CFD plug-ins in urban and building design are reviewed according to three types: single-objective, multi-objective, and coupling simulations. Two primary roles of CFD plug-ins integrated into the design process, including providing various micro-scale numerical simulations and optimizing the original design via feedback results, are analyzed. The issues of mesh generation, boundary conditions, turbulence models, and simulation accuracy during CFD plug-in applications are discussed. Finally, the limitations and future possibilities of CFD plug-ins are proposed.     

Numerical simulation of dispersion around an isolated cubic building: Model evaluation of RANS and LES

Several studies have been carried out on CFD prediction based on a RANS (Reynolds Averaged Navier–Stokes equations) model for dispersion around buildings, but it was reported that a RANS computation often provides extremely high concentration, which are not observed in usual measurements. These results suggest that transient simulations such as the large-eddy simulation (LES) might be required to achieve more accurate results. Nevertheless, very few studies have evaluated the basic performance of LES in modeling the dispersion field for a simple configuration in comparison with the RANS model. Therefore, relative performance of these simulation methods for dispersion problem around buildings should be clarified in order to make it possible to choose a suitable numerical method for its purpose. The purpose of this study is to confirm the accuracy of LES in modeling plume dispersion near and around a simple building model and to clarify the mechanism for the discrepancy in relation to the RANS computation. Simple LES modeling gives better results than RNG modeling of the distribution of concentration, although the difference for mean velocity is not so large. The horizontal diffusion of concentration is well reproduced by LES. This tendency is closely related to the reproduction of unsteady periodic fluctuation around cubical forms in LES.     

Pedestrian wind comfort around a large football stadium in an urban environment: CFD simulation, validation and application of the new Dutch wind nuisance standard

Three-dimensional steady Reynolds-averaged Navier–Stokes (RANS) Computational Fluid Dynamics (CFD) simulations are used in combination with the new Dutch wind nuisance standard to assess pedestrian wind comfort around a large football stadium in Amsterdam, before and after the addition of new high-rise buildings. The focus of the study is on the elevated circulation deck and the surrounding streets and squares. CFD validation is performed by comparison of the simulated mean wind speed at the deck with full-scale measurements. The important effect of local ground roughness specification on the simulated wind speed values is indicated. Application of the Dutch wind nuisance standard shows that wind comfort at the elevated circulation deck is only slightly influenced by the new buildings. Wind comfort at the surrounding streets and squares however significantly deteriorates. Finally, the results obtained by the Dutch wind nuisance standard are compared to those obtained by a more simplified procedure for the transformation of wind statistics to the building site, as used in earlier studies. The more sophisticated transformation procedure in the Dutch standard was successfully validated based on full-scale measurements in earlier research. Comparison of the Dutch standard results in this study with those of the simplified procedure shows that the latter provides overestimations by up to 25% for the highest discomfort probabilities. This type of large discrepancies can significantly change the outcome of wind comfort studies.     

High-resolution CFD simulations for forced convective heat transfer coefficients at the facade of a low-rise building

High-resolution 3D steady RANS CFD simulations of forced convective heat transfer at the facades of a low-rise cubic (10 × 10 × 10 m³) building are performed to determine convective heat transfer coefficients (CHTC). The focus is on the windward facade. CFD validation is performed based on wind tunnel measurements of velocity and heat transfer for reduced-scale cubic models. The CFD simulations employ a high-resolution grid with, for the 10 m cubic building, cell centres at a minimum distance of 160 μm from the building surface to resolve the entire boundary layer, including the viscous sublayer and the buffer layer, which dominate the convective surface resistance. The results show that: (1) the wind flow around the building results in highly varying CHTC values across the windward facade; (2) standard and non-equilibrium wall functions are not suitable for CHTC calculation, necessitating either low-Reynolds number modelling or specially-adapted wall functions; (3) at every facade position, the CHTC is a power-law function of the mean wind speed; (4) the CHTC distribution at the windward facade is relatively insensitive to wind direction variations in the 0–67.5° angle range; (5) the CHTC shows a stronger spatial correlation with the turbulent kinetic energy than with the mean wind speed across the facade; and (6) the CHTC distribution across the windward facade is quite similar to the distribution of wind-driven rain (WDR), with both parameters reaching high levels near the top edge of the facade. This suggests that also the convective moisture transfer coefficient will be higher at this location and that the facade parts that receive most WDR might also experience a higher drying rate.