Design efficient ventilation with simulation of air flow

As a preventive measure against COVID-19, ventilation is recommended at least two air changes per hour [ACH] to avoid closed spaces with poor ventilation. Ventilation two ACH means bringing twice as much outside air as room volume per hour.

The Japanese government recommends opening windows twice an hour as a way to do that.

However, it is difficult to assess if it is really effective in COVID-19 prevention. In order to secure two ACH for the ventilation in this way, there has to be a premise that rooms are thoroughly ventilated by opening windows. Although in reality, it is difficult to figure out if rooms are fully ventilated. Viruses and air are invisible.

For example, office buildings are usually ventilated by mechanical ventilation systems such as ventilation fans. In this case, the capacity of a room is determined in the design phase of the building, and it is designed to take fresh air inside by 30 m³ per hour per person.

However, in many cases, there is little consideration for whether fresh air circulates all over the room ventilating it efficiently. This is because the required ventilation capability is legally specified by the air flow rate and there is little consideration on air flow which determines its efficiency. In order to design a system, the air flow has to be calculated. In other words, visualization of the air flow is needed, and the time-consuming process prevents its popularization.

However, visualization of air flow doesn’t instantly solve the ventilation problem. Regarding existing buildings, there are few things that can be done in order to improve ventilation efficiency even though its routes are analyzed in detail through air flow visualization. For example, it is possible to place a circulator where air doesn’t flow, however, in reality, it is difficult to replace air vents or to put in new windows that are influential to ventilation efficiency.

In other words, if visualization of air flow is implemented in order to improve ventilation efficiency, it would be most effective to do it at the design phase of the building.

This means visualization of air flow in buildings which haven’t been built yet. However, it is possible using simulation technology, including computational fluid dynamics.

Recently, for example, you might have seen a video of the trajectories of droplets when coughing, which was made by the supercomputer Fugaku on TV. This is also a simulation result which visualized the behavior of invisible droplets by computational fluid dynamics. People might recognize the importance of face masks after watching the video.

In the same way, the simulation of invisible air flow and behavior of pollution generated indoors enables the design of efficient ventilation systems.

Important readjustment on a major event

Simulation of a building design is started by constructing a building under design in a virtual space. That is to say, a building to be constructed is constructed in advance in the virtual space.

And in the virtual building, air flow and the flow of heat and dust are simulated by computational fluid dynamics.

From the simulation, we obtain the information on ventilation efficiency, including the relation between placements of windows and mechanical ventilation systems and indoor air flow or whether rooms are ventilated efficiently. Then we work out where to place windows and supply and exhaust ducts of the ventilation systems effectively.

In the architecture, engineering & construction industry, this simulation technology was already being used in designs as a trial in the 2000s when I started my career as an engineer. The major reason why this technology is drawing so much attention in the construction industry is the fact that buildings are one-off products.

It is difficult for building design to make samples and repeat trial and error to introduce better products into the market like other industrial goods. Repeating trial and error in virtual buildings in the virtual space is expected to avoid unexpected results.

I feel these attempts have recently become more common through the remarkable development of computer resources.

Talking about ventilation, as I mentioned above, it is designed to take fresh air inside by 30 m³ per hour per person. However, it doesn’t immediately provide safe and secure environment. This is partly because of negligence in building design that hasn’t considered air flow by ventilation adequately. The fact that there has been little need for it in society has allowed the situation at large. To change people’s attitude, something has to happen.

For example, in building design, the way of thinking about emergency power generators was changed after the Great East Japan Earthquake in 2011. Until then, emergency power generators were installed in order to use for a certain period of time to fight a fire in case of emergency, and its fuel storage was only for that purpose. However, their design has been changing into larger capacity generators with larger fuel storage to maintain the function of a whole building for a few days when a natural disaster occurs.

It is an iconic example of a change by a major event, changing social consciousness, people’s needs and common practice of the whole industry. At the same time, this event spread the term BCP (Business Continuity Plan), and companies which have worked with BCP seem to have responded to the COVID-19 pandemic flexibly, including a rapid transition to remote working. Keeping problems raised by a past major disaster in mind and addressing them is good preparation for unexpected disasters.

In this COVID-19 pandemic, there is a movement to reconsider indoor ventilation and the working and living space. Simulation technology, which enables visualization of air flow and in the future, comfort, is expected to be a great help.

The idea of the society changing digital twin

For example, since a few years ago, advanced companies adopting Activity Based Working (ABW), which doesn’t fix working space in the office, have been attracting much attention.

If the introduction of ABW improves the ease of work and increases the motivation and contentment of employees working there, which strengthens intellectual productivity, it is beneficial for companies to pay the cost for its introduction. Remote working accelerates this trend as one of the ways to add options to workplaces.

Still, it was considered necessary only for advanced companies with so-called creative people. However, in this COVID-19 pandemic, remote working, which was considered far removed from the general work style, has rapidly become common practice.

On this trend, an increasing number of people have started thinking that offices as they were will not be needed or at least that a reduction in office space is possible. On the other hand, employees experiencing remote working rediscovered the importance of sharing the same space occasionally. Employees’ needs for office space are changing from a place for work as before to a place for communication.

Then, what form should this take? One attempt to seek an answer has started by evaluating various functions and capabilities of buildings, including offices, by points and labels the environmental performance of buildings by total points. For example, there are evaluation systems such as CASBEE in Japan, LEED and WELL on a global basis.

These lead to attempts to visualize invisible values, including functionality, comfort, sanitation, health, safety and security, when considering the office space.

On the other hand, simulation technology is moving toward advanced utilization with a digital twin. This is a way of thinking that utilizes virtual buildings in various ways.

For example, today, to construct a building, first of all, design drawings are made and shared by various parties concerned, and they do their own work.

However, considering the ongoing labor shortage, various work has to be replaced by robots in the future. On that occasion, people only have to manage the whole process if inputting data of virtual buildings to robots instead of directing robots using a drawing on paper.

Furthermore, checking real conditions of buildings through collaboration of virtual buildings and IoT and continuing simulation of the future, which visualize abnormal behavior and deterioration of systems over time, enable fault prediction and maintenance.

In other words, in a building operation, it may be possible to eliminate the labor involved in current periodic inspections and prevent accidents and problems.

The digital twin is realized by Building Information Modeling (BIM), which utilizes digital technology in each process from design and construction of a building to the operation and maintenance, and building simulation technology. The proof tests of a building operation with a digital twin have already started, and it is expected to become common in the near future.

I think the development of this technology will significantly change our way of working.

For example, you may check evaluation points of a provided office environment when choosing your job. Then companies will seek high-level building operations by a digital twin aiming to improve the office environment in order to secure talented employees. Such social needs will lead to the popularization of building design with Building Information Modeling, which realizes such needs, and then provide a comfortable workplace with visualized secure and comfort and create a virtuous circle.

Furthermore, this technology is expected to be applied to residential buildings. It means that we, the consumers, will also create our own house together with designers, visualizing a wealth of living space instead of choosing a house based on basic specifications such as layouts, earthquake resistance and thermal insulation alone.

In that sense, not only designers but also you as the client are required to have knowledge and literacy on this technology. In order to secure such a future, I think it is required to foster social awareness that a comfortable society is created by constantly acquiring information on new technology and utilizing it thoughtfully.

* The information contained herein is current as of March 2021.
* The contents of articles on are based on the personal ideas and opinions of the author and do not indicate the official opinion of Meiji University.
* I work to achieve SDGs related to the educational and research themes that I am currently engaged in.

Information noted in the articles and videos, such as positions and affiliations, are current at the time of production.