Ventilation Performance Of Buildings Research Articles

A modified decay method based on a proposed uniformity index for measuring air change rates in non-uniform air mixed spaces

Building ventilation is essential during COVID-19 to reduce airborne viral transmission risks, while accurately estimating air change rates remains quite challenging. Due to the tracer gas method's assumption of uniform air mixing in a space, which is often not the case. However, the existing mixing models such as mixing factor (K) and zone distribution effectiveness (Ez) are limited to decrease the uncertainty of this assumption since their reported data are subjective, rough estimates, and inconsistent across different standards (e.g., ASHRAE and AIHA). Therefore, in this study, a novel modified decay method (MDM) is developed, where a proposed uniformity index (Ui) is integrated into the original decay method (ODM) to quantify the non-uniform air mixing and thereby improve the estimation of air change rates. We validated the proposed method in a real classroom using CO2 as a tracer gas. Wherein, the spatial variations of CO2 concentrations were measured at various locations using an automated system of a mass spectrometer with a 16-position valve. Later, the estimated air change rates using both the ODM and MDM were compared with the measured ones. It was found that the proposed Ui significantly decreased the error caused by the uniform-mixing assumption of estimated air change rates using ODM from 25.6 % to 3.4 % estimated by MDM at the outlet location. Similarly, the average concentrations of 16 distributed sensors at the breathing level also showed a decrease in error from 25.0 % to 2.5 %. This study can be applied to improve ventilation performance in buildings.

The use of Taguchi, ANOVA, and GRA methods to optimize CFD analyses of ventilation performance in buildings

We present a method that can be used to optimize CFD analyses of ventilation performance in buildings; the method was successfully applied in other disciplines. In the method, three statistical methods are used - the Taguchi method, ANOVA, and Grey Relational Analysis (GRA) to achieve optimization. We then model the risk of draft and the mean age of air in a two-dimensional benchmark test case to exemplify the application of the method. We use five independent variables for modeling: temperature, air velocity, and three room dimensions, each with five levels. In short, the method is implemented as follows: At first, using an L25 orthogonal array in the Taguchi method, we decreased the total number of cases to be modeled from 3125 (55) to 25. Then, we modeled the 25 cases with CFD and used the Taguchi method and ANOVA analyses to find the best solutions for draught risk or the age of air, while with the GRA method we found the best solution for both of them considered jointly. Finally, new CFD models for the variables describing the best solutions were run to confirm their superiority within the 25 cases selected for modeling within the orthogonal L25 array. They were not compared against all possible 3125 cases because the computational time would have been prohibitive. Nevertheless, we believe, that the results are credible in identifying the best solutions. This is based on experience in other disciplines. We, therefore, propose that the presented method is considered when complex problems are analyzed related to ventilation performance requiring large computational power.

CFD modeling of natural ventilation in a void connected to the living units of multi-storey housing for thermal comfort

The void has been widely used in the multi-storey housing to induce natural ventilation in the living units for health and thermal comfort purposes. This research investigates the provision of the void to enhance natural ventilation performance in the living units of multi-storey housing. Malaysian affordable multi-storey housing (MAMSH), which is located in Malaysian suburban areas have been selected. The methods employed by the research are field measurement and computer simulation using CFD software. This study revealed that the indoor air velocity (m/s) in the living units of the studied building did not achieve the required rate for thermal comfort. However, by enlarging its size to 50% of the living units, natural ventilation performance in the living units is increased by up to 50.88%. The appropriate configuration of void been recommended based on the findings and venturi effect principle. This research contributes to the development of knowledge in enhancing natural ventilation performance in buildings. The suggestions might help the building industries to provide better designs option to enhance natural ventilation performance in the living units of multi-storey housing by providing an appropriate configuration of the void, and in turn, a sustainable living environment can be established.

Ventilation performance prediction for buildings: Model assessment

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.

Ventilation performance prediction for buildings: A method overview and recent applications

This paper presented an overview of the tools used to predict ventilation performance in buildings. The tools reviewed were analytical models, empirical models, small-scale experimental models, full-scale experimental models, multizone network models, zonal models, and Computational Fluid Dynamics (CFD) models. This review found that the analytical and empirical models had made minimal contributions to the research literature in the past year. The small- and full-scale experimental models were mainly used to generate data to validate numerical models. The multizone models were improving, and they were the main tool for predicting ventilation performance in an entire building. The zonal models had limited applications and could be replaced by the coarse-grid fluid dynamics models. The CFD models were most popular and contributed to 70 percent of the literature found in this review. Considerable efforts were still made to seek more reliable and accurate models. It has been a trend to improve their performance by coupling CFD with other building simulation models. The applications of CFD models were mainly for studying indoor air quality, natural ventilation, and stratified ventilation as they were difficult to be predicted by other models.

What we Think we Know about Ventilation

The amount of outdoor air ventilation in buildings is one of the most important determinants of indoor air quality, but many critical questions and misunderstandings exist. First, given the importance of ventilation, how well do we know how much outdoor air is even needed in buildings? While research has been done on ventilation and odour perception and on ventilation and symptom prevalence, is it adequate to support the ventilation requirements in our standards and regulations? While this research and many years of designing and operating buildings have been used to develop ventilation requirements in standards and regulations, these requirements treat all buildings the same. Can we provide understandable and practical ventilation requirements that address the tremendous variability in buildings and occupants? While much time and effort is spent developing and debating ventilation requirements, compliance with these requirements in design and ultimately operation is rarely given the attention that it deserves. Addressing actual ventilation performance in buildings requires measurement, which is more difficult to conduct in the field than often realized and is too often omitted from building management practice as well as indoor air quality research. When ventilation rates are measured, the results often reveal significant gaps between design intent and actual performance, which can have serious implications for both indoor air quality and energy. Given the importance of ventilation, the research that has been done and the many questions that remain, it is reasonable to ask how much we really know about ventilation.

Effect of Integrating Wind Catchers with Curved Roofs on Natural Ventilation Performance in Buildings

In an investigation into wind-induced natural ventilation performance in buildings, this study uses Computational Fluid Dynamics to examine the effect of integrating wind catchers with curved roofs, implementing three-dimensional modelling. It is intended to give more value to the symbolic role of the dome, vault and tower in architectural design. The early findings of this study revealed that curved roofs induce natural ventilation in buildings by suction. This is generally true for the central and upstream zones of deep-plan buildings, but not for the downstream zone. Thus, wind catchers can be used to overcome this problem. This has been investigated by considering different geometrical and climatic parameters. The results show that the proposed ventilation system increases airflow rates and improves internal airflow distribution.

Ventilation performance of large buildings: Prediction using pressurisation measurements

This paper provides a model which uses whole-building leakage measurements to predict the ventilation performance of buildings and illustrates its use by applying it to a large, industrial building. Air leakage measurements with the building 'as found' and then with its loading doors sealed showed a 14% reduction at an inside/outside pressure differential of 25 Pa. Using these leakage characteristics, the model predicted ventilation rates which corresponded well with measured values. Meteorological data at the site for the heating season were combined with the ventilation characteristics of the building (given by the model) to predict the ventilation performance of the building over that period. The results indicated that the building 'as-found' would have, on average, an air change rate of 0.5 h-1 which reduces by 24%, i.e. to 0.38 h-1, when the loading doors are made airtight. Calculations also indicate that such a retrofit measure would reduce by 14% the total energy required for space heating over that period.