Jiwu Rao

The influence of turbulent wind on air change rates—a modelling approach

Abstract Turbulence in wind-induced pressures on a building envelope causes fluctuating air infiltration. The resultant airflows are influenced both by building characteristics, the resistance of the openings to flow, the inertia of the air mass in the openings and the compressibility of room air, and by frequency characteristics of wind pressures, their power spectra and the correlation among them. A new approach using the spectrum analysis technique is proposed to model the pulsating flows through openings of a building. The governing equations for fluctuating airflow behaviour are obtained from the pressure/force balance between the turbulence pressure differences across openings and the forces required to overcome the flow resistance and inertia of air. The proposed approach is applied to a single-zone enclosure with a single opening and with two openings, and can be easily extended to multi-zone buildings.

Modelling air infiltration due to wind fluctuations—a review

Abstract Wind-induced air infiltration is caused not only by the average wind velocity but also by the turbulent wind fluctuations. This paper discusses the importance of considering the fluctuations when the air flow rate is predicted. The features of turbulence are outlined and a review of existing fluctuating infiltration models is performed. Finally, important areas of future research are identified.

Evaluation of radiance's genBSDF capability to assess solar bidirectional properties of complex fenestration systems

Complex fenestration systems (CFS) need to be evaluated to quantify how well they contribute to avoid glare and manage the solar heat gains through building façades. It is possible to use solar bidirectional properties of CFS in some building energy simulations tools in order to evaluate more accurately their impact on lighting, cooling and heating energy consumption. genBSDF is a Radiances program whose capabilities of assessing the bidirectional solar properties of CFS are evaluated in this paper. This evaluation was carried out for 16 cases of a venetian blind varying the solar properties and slope angle of the slats. Results of directional and bidirectional solar properties obtained by genBSDF with radiosity assumptions were compared with the results of the radiosity-based WINDOW algorithm. Results show an excellent agreement between the two approaches which demonstrates that genBSDF is a very precise and robust tool for assessing the solar bidirectional properties of CFS.

Computer-aided building ventilation system design — a system-theoretic approach

Abstract An understanding of the pattern of airflow is an important element in the design of ventilation systems. The airflows are caused by wind effect, stack effect and mechanical ventilation systems. Several models have been developed to analyse the airflow in buildings. So far, the focus has been on the modelling process. In this paper, the modelling and analysis of building ventilation systems using a system-theoretic procedure are presented. The emphasis is on presenting a theoretic derivation of nodal-governing equations for building airflow systems and obtaining efficient procedures for automatic formulation of the system equations. This approach is based on matrix algebra, therefore is easy to implement on a computer.

A procedure for measurement of ventilation effectiveness in residential buildings

Abstract Ventilation effectiveness is expressed by two newly defined terms: relative contaminant removal effectiveness and removal efficiency. The relative removal effectiveness is defined as the relative ratio between the rate of contaminant removal and rate of room air replacement. The removal efficiency is the percentage of the total generated contaminant removed by purpose-provided openings. A series of tracer gas tests was performed to simulate the contaminant migration and the removal of the contaminant generated by a point source in a residential building. The values of relative removal effectiveness are calculated from test results. The removal efficiency is then obtained from the values of relative removal effectiveness for two concerned tests. The new terms can be used to assess the air quality related building problems and help in the design stage in decisions among alternative schemes.

A procedure for sensitivity analysis of airflow in multi-zone buildings

Abstract This paper describes a general procedure for analyzing airflow sensitivities with respect to input parameter variations. The derivation is based on a matrix representation form using the system theoretic approach. The sensitivity analysis provides both valuable insights about the effects of input parameter variations on the accuracy of multi-zone airflow models and necessary information for additional analyses. A case study is used to show the procedure for the airflow sensitivity calculation, and to demonstrate how to use sensitivity information in the error analysis and design assistance.

Statistical Analysis of Microbial Volatile Organic Compounds in an Experimental Project: Identification and Transport Analysis

This paper is based on an experimental project that investigated the capacity of wood frame stud walls to restrain the movement of mould products from the stud cavity into an investigative chamber, representing the indoor environment. While the programme of the research includes the investigation of spores and microbial volatile organic compounds (MVOCs), this paper reports only the analysis of MVOCs. Twenty full-scale wall specimens were constructed, incorporating six experimental factors (air leakage path patterns, mould presence, insulation, vapour barrier, sheathing material, and ambient humidity conditions). For each specimen, four VOC samples were taken simultaneously from the sampling chamber and from the stud cavity through the external sheathing, and one sample was taken from the background laboratory air for comparison. Multiple regression analysis was applied to identify the MVOCs, and subsequently to evaluate the effect of construction factors on the movement of these MVOCs through the envelope. Box—Cox transformation was applied prior to the regression analysis to normalise the data. Five VOCs were identified as related to the presence of mould in the stud cavity, at 5% level of significance. The transport of these MVOCs from the sampling chamber to the cavity was confirmed. However, no significant effect of the parameters related to wall configurations was detected.

Modelación CFD de casos básicos de convección en ambientes cerrados: necesidades de principiantes en CFD para adquirir habilidades y confianza en la modelación CFD

Prediction of airflow pattern and velocities, temperature, moisture and pollutants concentration is required to design healthy and comfortable indoor environments. Computational Fluid Dynamics (CFD) is the most advanced technique to model and predict the airflow in enclosed environments. However, the main errors in CFD models and their results are linked to the human factor. Beginners on CFD modeling do not account with skills, experience and engineering judgment to generate robust and reliable CFD models. This process is not intuitive and new CFD users need guidance. This paper aims to provide more complete information on CFD modeling of basic natural, forced and mixed convection cases that would allow CFD beginners to acquire skills and confidence. CFD modeling includes mesh generation, setting convergence criteria and under-relaxation factors, and evaluating different turbulence models for each convection case. Results show that users´ expertise is needed in each step of CFD modeling, even for these basic convection cases. Rev. ing. constr. [online]. 2014, vol.29, n.1, pp. 22-45. ISSN 0718-5073 http://dx.doi.org/10.4067/S0718-50732014000100002

Investigation of Thermal Performance of Structural Insulated Panels for Northern Canada

AbstractThe thermal performance of structural insulated panels (SIP) and connections, developed and used to build 142 homes in Nunavut, Canada, was studied by subjecting the panels to steady-state cold climate conditions in a laboratory test setup. Testing was carried out using an inverted test hut, in which the panels were installed such that the interior of the hut was cooled down to outdoor conditions, and the ambient lab conditions served as the indoor climate. This inverted setup provides an alternative to using a large-scale environmental chamber when this is not available. Results showed the methodology used in this test is adequate to characterize the thermal performance at both the center of the panel and the connections. In carrying out steady-state thermal simulations on both the panel and connection cross sections using both one-dimensional (1D) and two-dimensional (2D) programs, it was found that while the 1D simulation could adequately predict the performance at the center of the panel, a 2D...

To Apply Numerical Simulation to Assist Drying Capacity Experiment of Light-frame Wall Systems

HAM models represent and solve the underline physical heat-air-moisture transfer processing within the building envelope by governing equations and simulation programs. Using the weather data as the boundary conditions, these models have been used to study and predict the moisture performance of the building envelope systems. In this paper, an integrated experimental approach is present to apply a HAM model to the setup and conditions of lab tests and to provide further insight to the experiment setup and interpretation. The testing program investigates the drying capability of wood frame wall assemblies with variations in sheathing, cladding, and vapor barrier. The numerical simulation model handles moisture flow of vapor and liquid phases in 2D using material properties from ASHREA publication; and the lab condition and weather data works as the boundary conditions. From the comparison between simulation and preliminary experimental result, the factors could influence the accuracy of the experiment are detected and analyzed. The improvements are summarized and applied in the following full-size experiment. In addition, simulations based on parameters slightly different from the test setting are carried out to evaluate the influences of aspect ratio of stud cavity, boundary settings and initial moisture content to the evaporation rate of the water tray.