A further reflection on ventilation.

After high school, I started my university studies at the Royal Institute of Technology (KTH) in Stockholm, Sweden. I really had no reason to choose it, but my grades made it possible… with better grades, I might have gone to Karolinska Institutet for medical studies. At that time, it was, however, a great achievement to go to such a good university. It all was because the Social Democratic Party in Sweden had made it possible, also for kids from low‐income families to study in universities. There was a good loan for housing and studying and a good system for those with children. I soon had two children when studying for my master's degree.

My study was first on energy engineering, and then, I chose heating, ventilation, and air conditioning (HVAC) engineering as my special focus topic. For my master's degree work, I decided to study ventilation in homes together with one of my high school mates, Bengt Carlsson. Possibly the greatest mistake in my life.

At that time in Sweden, the Professors arranged for your future work. I could choose between the newly set up Environmental Protection Agency (EPA) and then the new Board of Urban Planning and Building (Statens Planverk in Swedish). I chose the latter and became responsible for developing building codes on installations, including ventilation. In retrospect, I can imagine my life at EPA, with much greater resources…perhaps, I, in that case, would have seen PM2.5 as an important topic today?

Anyway, in 1969, I and Bengt Carlsson wrote our master thesis on “Bostadsventilation—en orienterende undersokning” (Home ventilation—an orientating study). It was actually a good study and historically very important. We measured airflows in supply and exhaust terminals, and we measured the pressure difference between rooms and between indoors and outdoors. So, we knew the main airflow direction. We found a mean air change per hour (ach) of 0.8 with much lower values for naturally ventilated homes at 0.27 ach. These values are certainly lower than actual values as we did not measure with a tracer gas method. It was commented in the report that sometimes you did not need measuring instruments to indicate the airflow direction. It was enough to use odors (the same as at offices in Tsinghua University and Tianjin University today), and the smell of feces odor from restrooms is all you need.

I started my work at Statens Planverk, being responsible for installations in buildings, including heating, ventilation, and water. After the oil embargo in the Middle East in 1973, the focus was on energy and ventilation. With good insulation in buildings, ventilation was very important for the total energy need in buildings.

The first idea was to use maximum allowable concentration (MAC) values for workplaces for indoor air pollutants. I soon realized that it did not work, as people in homes, schools, etc., are not working adults, they are young, old, and not always healthy. So MAC values could not be used. I could use C.P. Yaglou's study on human odor from 1936, but is odor health? Happily, we had a new study from The Radiation Protection Agency and the Building Research Institute in Sweden, a study on radon in homes. In Sweden, radon is coming from the ground but also from building materials like "blue concrete." The latter is a rest product from uranium mining. With the building as the main source, ventilation is important. The data showed that if the ventilation rate is less than 0.5 ach, the radon concentration will increase. This is the main reason for 0.5 ach in building codes or standards. Soon after, an infestation of house dust mites (HDM) was shown to be closely associated with ventilation rate in homes. The HDM data (as affected by outdoor–indoor relative humidity (RH) continuum) showed that while 0.5 ach was ok in Stockholm, we might need 0.7 in Copenhagen.

Anyway, 0.5 ach (I would call it the "Sundell number") is widely used today in many national regulations and standards, but very few know its origin.

From that time, I understood that my interest in ventilation was just mine. Who else cared about ventilation? I soon learned that the big companies in this field did not have good ventilation in their offices, and the big professors did not have it in their offices at all. And today, the ventilation in new offices is still poor, and many have no ventilation. In China, we have some 200‐300 universities lecturing about HVAC, but no one lecturer has a well‐ventilated office.

The main thinking must be that ventilation may be needed in some industries or hospital settings. And even when it is needed, ventilation can be easily managed by opening windows.

I personally think that ventilation always meant industrial ventilation in China with the knowledge coming from Russia (e.g., V.V. Baturin, who wrote a textbook on Fundamentals of Industrial Ventilation) and that the focus in China has been on air conditioning with the knowledge from the United States (e.g., ASHRAE Fundamentals). To me, air conditioning is simple, like heating. You know exactly what to design for, that is, thermal comfort and thermal loads. Is ventilation being taught adequately? We know that ventilation is much harder to design for than is heating and air conditioning. For example, how much outdoor air is needed? Should we use ach or L/s per person? And finally, what about energy?

So far, in China and most of the world, energy has been the top priority. And ventilation has always been seen as having a negative impact (as it means more energy being consumed).

The main problem is that ventilation has been mainly seen as an engineering problem, but in reality, it is a public health topic.

What was discussed in Sweden in 1974? We had to reduce energy use in buildings, and the easiest way is to reduce ventilation. How to do it?

Natural ventilation needs no energy for fans, so perhaps that is the best solution? Sadly, natural ventilation has difficulties for controlling building tightness, with openings for inlet and outlet, controlled by wind speed and direction, and the temperature difference between indoor and outdoor. In reality, this means that the natural ventilation rate may be too high in a cold climate. A special problem with tight buildings is that you can get back draught in either kitchen or bathroom, meaning that the air was coming in either of these rooms and going out in the other. When this happens, it is very hard to change the flow direction until the climate gets warmer. This led Sweden to set the mandatory ventilation to stop the back draught in natural ventilation systems.

A further problem with natural ventilation is that it needs more ducts and hence building construction costs, as you need exhaust ducts (shafts) going through the roof.

In total, the discussion in Sweden found that natural ventilation does not work well, using more energy and being more expensive than mechanical systems.

The solution was mechanical ventilation with heat recovery—a simple solution to get reasonable ventilation and save energy. This has been the standard in Sweden since 1975.

Mechanical ventilation is a very simple system with ducts, fans, and perhaps filters (in homes).

The main problem with such systems is that they need good design and maintenance.

When I started at the Swedish Occupational Safety and Health Agency (OSHA), I was responsible for ventilation. I soon started a study with the best person in industrial ventilation in Sweden, Göran Allhammar, to see whether mechanical ventilation works. We studied some 30 buildings, measuring ventilation, and comparing it with design values and values from commissioning.

The result was shocking to us as what we measured was far away from what was designed for or commissioned. To have an outdoor airflow in a room was like winning on a lottery. A total catastrophe! (I have the results in Swedish—reports, and articles).

So mechanical ventilation did not work, as no one cared about it. Just installing ducts and fans, …… and filters, that are not properly checked.

I thought we needed a mandatory control of ventilation installation, which we eventually got ten years later. But obviously, the control did not work well. Can you trust an HVAC engineer?

In summary, ventilation is something that some companies make money on (by selling ducts, filters, fans…), but no one seems to realize, as I have, that it is important to make it work.

So, I am sorry I have ever got into this business… NO ONE CARES.

And of course, today in the United States or China students are not taught properly about ventilation. They are taught to design air conditioning!!!

A serious discussion about ventilation, that is, the need, how, how much, has not started yet.

And then, we have the "new" ideas about intelligent ventilation…. "MY GOD, THEY KNOW NOTHING!!"

In China today with new campuses in Tianjin for Tianjin University, a top university in HVAC, and Nankai…. and 14 other universities…. and in Tsinghua and all universities with HVAC education…. NO functioning VENTILATION…like in the United States. The same…

And the negative energy consequences are huge! Natural ventilation is NOT saving energy. Heat recovery in a well‐functioning mechanical system does.

I am sorry I ever got into "ventilation"… no one takes it seriously!

I received this editorial contribution by email from our former Editor‐in‐Chief, Jan Sundell, on February 17, 2019. Jan probably wrote it from his hospital bed. To my regret, I did not submit his editorial on his behalf earlier. Indoor Air published an editorial "In Memory of Professor Jan Sundell (July 10, 1943‐May 27, 2019)" (Indoor Air. 2019; 29:701‐703). What would he do if he were with us in the ongoing COVID‐19 pandemic? He warned us of the risk of poor ventilation in his life, in his publications, in his presentations, and during his many conversations with many of us. Why weren't we ready? While the world is combating the pandemic, I sincerely recommend this editorial to our readers for us to remember Jan’s life, work, and friendship on his second death anniversary.

Jan’s words ring so true in our Time of COVID‐19. Over the summer of 2020, we assisted local school districts struggling to reopen. We found building management systems were dysfunctional, unit ventilators in a classroom being used as an extra shelf space with vents covered, and a basic lack of understanding about the importance of ventilation. Sadly, the only reliable way to provide a safe environment was to install supplemental air cleaners to provide higher clean air delivery.

In our current Aviation Public Health Initiative with airlines, airports, and aircraft manufacturers, we again had to demonstrate the importance of ventilation as a critical mitigation strategy, particular when mask wearing, and physical distancing were not enough. It took the evidence from measurements we made on airplanes and terminal buses to convince the air carriers and airport operators of the importance of ventilation. We made the case that high ventilation rates needed to be maintained throughout the gate‐to‐gate time on a plane.

Jan had a huge influence on our field on Indoor Science. He always seemed to be ahead of many of us. His influence is still present. My doctoral student Jose Cedeno demonstrated higher use of University Health Services for respiratory illnesses was associated with high occupancy of dorms. The earlier work of Jan and his colleagues at Tianjin University inspired us.

Jan’s living legacy and testimony to his vision and persistence are the China Children Health and Housing studies conducted in numerous Chinese cities. He has inspired a generation of students and young investigators to appreciate the health implications of indoor environments.

Jan was an extraordinary person. It is seen in the above text, probably one of his very last. He was a philosopher, yet a very pragmatic one. He did not follow the mainstream and had his opinions; they made you think. This is how I remember him when we first met in 1996, and he talked about the lost TVOC. Jan was passionate about public health. His passion was ventilation and big data, besides good jazz and few other things. He taught me (us) how to read and use scientific literature. His series of multidisciplinary reviews, unique at that time, laid the ground for new scientific developments. Jan wanted to collect big data. He believed that by monitoring in many places we would learn more. He launched studies in Europe, America, and Asia. Today, big data is a buzzword; back then, it was much more difficult to implement when he started. But he tried and made it happen. Jan had a special contact with students and young scientists; he promoted and introduced them to the big scientific world. I am privileged to be one of them. Jan believed that multidisciplinary research and especially focus on health were a way forward for indoor air field. We see today he was absolutely right. If only we had followed his advice on ventilation back then, we would be much better off today. We miss him….