Green building practices and sustainable development have emerged as important strategies to mitigate the negative impacts that the construction industry can have on society, the environment and even the economy. Yet, with the immense benefits that the same industry brings to our lives and its continued growth over the years, it has become even more important to tackle issues that can arise such as noise and air pollution, waste and energy consumption during the initial construction stages and throughout a building’s life cycle. In fact, according to the International Energy Agency, “the buildings and buildings construction sectors combined are responsible for 36% of global final energy consumption and nearly 40% of total direct and indirect CO2 emissions.” For green buildings, the processes used are environmentally responsible and resource efficient in all stages: design, construction, operation, maintenance and renovation. There are several factors that determine if a building is green, including but not limited to:
In designing a building, energy efficiency is one of the most important aspects to consider. Major factors that influence this are a building’s insulation (considering factors like thickness and materials used), the overall building design (windows, positioning) and the HVAC system.
Green building is a highly-regulated field, with 31 green building certification programs used in different countries around the world, with the most prominent being LEED and BREEAM. Natural ventilation, energy recovery ventilation, whole-house fans or energy-saving exhaust fans are the main solutions used by HVAC design engineers, architects and—of course—building and sustainability engineers involved in designing green buildings to ensure efficient ventilation. To be certified by LEED and the Living Building Challenge (LBC), natural ventilation is a key component of green building today. According to LEED, the purpose of natural ventilation is to “provide mechanical or natural ventilation systems that result in improved occupant comfort over conventional designs, increasing occupants’ well-being and productivity while reducing energy consumption of ventilation systems.” As for further requirements, buildings using natural ventilation need to comply with the ASHRAE 62.1 standard on Ventilation for Acceptable Indoor Air Quality (paragraph 5.1). When it comes to LBC and its seven performance areas (site, water, energy, health and happiness, materials, equity and beauty), natural ventilation falls under the equity and health petals. To be in sync with the equity petal, an urban project must not “block access to, nor diminish the quality of fresh air, sunlight and natural waterways.” For the health petal of LBC, the usage of natural ventilation must ensure indoor air quality and thermal comfort. When the climate and location allow, natural ventilation might be used as a technique for ensuring indoor air circulation, renewal of fresh air, and cooling in a building as a replacement for mechanical ventilation. This is one of the main methods for limiting the energy consumption while ensuring quality of life for occupants. Natural ventilation allows for air exchange inside of a building by taking advantage of physical properties of air. As natural ventilation is not suitable for all regions and weather conditions, a comprehensive testing process needs to be undertaken. The main technique for accurately testing natural ventilation in a building’s design is numerical simulation with computational fluid dynamics (CFD). This method allows engineers and architects to not only test airflow inside the building and wind outside, but also easily take into account additional relevant factors such as topography and surrounding buildings. With CFD simulation, multiple elements can be investigated, including the pressure field around buildings, wind speed and air exchange rate.
Screenshot of a CFD simulation of natural ventilation in a shopping mall (Source: SimScale) In the case study presented below, CFD simulation was used to investigate the design of a three-story shopping mall with a natural ventilation system. The configuration of its windows was evaluated to determine if acceptable thermal comfort could be achieved. This public simulation project was used for the analysis. For commercial buildings, the performance of a passive ventilation system is based on two critical factors, each needing to meet an official standard. These are:
To predict the effectiveness of natural ventilation in this commercial building, the engineers from SimScale, involved in developing this project, considered five scenarios with different window configurations, as below:
CAD model of the three-story shopping mall used in this simulation project It was assumed that a 5 m/s breeze was blowing directly at the entrance of the shopping mall. A steady-state, laminar flow simulation type was chosen, with air as the selected fluid. The following boundary conditions were applied.
This CFD simulation took five hours of computing time to run in the cloud. The results for all cases can be seen in the 3D visualizations pictured below. Scenario 1: All Windows Open (Source: SimScale) Scenario 2: All Windows Open on the Ground Floor (Source: SimScale) Scenario 3: All Windows Closed (Source: SimScale) The simulation results prove that for this building design and particular conditions, the amount of air provided will not be sufficient in ventilating the entire shopping mall. This conclusion makes passive ventilation an unsuitable design choice for this case. Further conclusions from the simulation results were as follows.
The insights above revealed by the CFD simulation results are important in determining further changes that could be made to the building’s design. Changes include the placement of windows, which would not only maximize the efficiency of natural ventilation while ensuring indoor air quality and thermal comfort for the visitors and employees of the shopping mall, but also help meet regulations.
Until recent years, engineering simulation required a high investment in hardware, expensive licenses, expert professionals for onboarding and support for widespread use. With the emergence of online simulation tools, however, this technology has become much more affordable through yearly subscription pricing models, easy-to-use interfaces, and learning resources created by their providers.
Simulation, and especially CFD, enables engineers working in the green building field to virtually test and improve their designs, ensuring an optimized ventilation system (mechanical or natural), energy efficiency, thermal comfort, and proper indoor air quality—all crucial factors in obtaining LEED or similar certification.
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