 Hello and welcome to the seventh webinar of the engineering rising to the challenge initiative from Purdue engineering. My name is Arvind Raman. I'm the executive associate dean for faculty and staff here in the college. Now this initiative began in May 2020 in response to the National Academy of Engineering's call to action for engineers to tackle some of the challenges posed by the COVID-19 crisis. But our initiative also looks to the longer term future to rethink and re-engineer the very systems that our modern society has come to depend on so that they might be more resilient to such shots in the future while also serving society better. Now part of the initiative involves webinars where distinguished panelists come together and unpack some of these challenges for us, providing us a glimpse into what the future might look like. And today's panel is about various transmission and mitigation and buildings, a topic of very timely interest. And it is my honor to introduce the moderator for today today's discussion, Panagita Karava, the J&K Hakama Professor of Civil Engineering. Let me say a few words about Professor Karava. Dr. Karava is an expert in smart buildings technology, sustainable energy systems, human building interactions, systems identification and model predictive control of buildings. She's also interested in an expert in socio technological systems for smart and connected energy aware residential communities. She is a member of the Center for High Performance Buildings here at Purdue, member of the Ray W. Herrick Labs and the Bowen Labs at Purdue. She has served in many capacities, including in leadership. She was the associate dean of engineering for facilities. And she's been recognized in many ways, including the Roy E. and Myrna G. Wansek Research Excellence Award in the School of Civil Engineering. She was also awarded the new investigator award from the American Society of Eating Refrigeration and Air Conditioning Engineers. Over to you, Panagita. Thank you very much, Arvind, for the kind introduction. I would like to welcome our panelists, our distinguished panelists and also the participants of this webinar. I'm very excited to be part of this effort. This is a timely and significant topic here at Purdue. We have a center dedicated to buildings, the Center for High Performance Buildings where we conduct research related to energy efficiency, healthy environments and occupant well being. So this webinar has been organized in collaboration with the Center for High Performance Buildings and in particular the director, Professor Jim Brown, a professor in mechanical engineering. So we are very devoted to make impact in the way we design and operate buildings and we think that this webinar would be very enlightening on a topic that is particularly significant as it affects our health and life even and very timely as well. Without taking more time, I would like to proceed by introducing our panelists. Specifically, I will be introducing the panelists one by one as they speak. The first panelist is Professor Yan Chen, who is a professor of mechanical engineering, the James Joyer Professor in mechanical engineering at Purdue. He has a very distinguished career and currently serves as the editor-in-chief of the International Journal of Building an Environment. Professor Chen has received numerous awards from various associations. For example, the International Building Performance Simulation Association. He has received the gold, rainbow gold metal for outstanding contributions to the advancement of modeling and measurement of ventilation and air distribution in buildings from the Scandinavian for duration of hitting ventilating and sanitary engineering. Also, a word from the Institute of Environment Sciences and Technologies. Dr. Chen's research includes indoor environments, aircraft cabin environments, energy efficient, healthy and sustainable building design and analysis. Yan, please start with your presentation. Hi, and thank you very much. It's really very kind of you to give this introduction. Okay, where is my slides? Okay, I hope I could share. All right, I find that. Okay, so I hope you could read my slides here. First of all, I'd like to give a general overview how this COVID-19 is transmitted in buildings. So according to the US CDC, the transmission route actually is three different routes. The first one is really through the closer contact. For example, I covered directly very closer to your face and then loads of droplet that could be in your breathing area. You could inhale or could project it directly to your eye, nose area, so it could be absorbed by you through the membrane or skin. Then the second one, now CDC found that it's very important that this will be the airborne type because a lot of our human activities like coughing, talking, sneezing, etc. We produce a lot of small particles. So those particles are pretty small in size, could hang in the air for a long time. So this is really a major concern at this moment. Then the third one, it was a bigger concern. Now CDC actually tom down this a little bit is a format transmission, which means for example I am now touching my computer keyboard and I leave the computer here and then someone else is using my computer a few minutes later. And then, of course, I leave my virus on the keyboard and then that person could get infected. So I'm going to talk more on the most important one that's the airborne transmission. So now I just wanted to show you an animation show a typical coughing. So this is a typical coughing we covered with a droplet with the size of between 0.3 micron and up to like 100-200 micron in size. And then you can see large particles just drop down due to the gravity. And on the small particles or droplet, you see that with the size about 20 micron or smaller, so they can reach it to the other person. So this animation, let me play one more time. It really shows the distance between two people, right? This distance is about six feet or two meters. And then you can see this small droplet really can travel from one side to the other person. And that's how CDC recommended we should really keep the social distancing. And of course, this one is just a cough, you don't cover the mouth. However, if you look at our coughing activity, right, this is normally what we'll do. I mean, the one on the upper left, this is what you saw in animation. You hardly see this type of cough in reality. So in most cases, we really try to hide the mouth and nose in certain way. And this is animation by using smoke. You definitely can see with and without a covering can make a huge difference. So this type of study was done a long time ago before the COVID-19. But we find this could really play an important role inside our buildings. And here now I just want to show you the simulated result. Okay, so the one you saw before was by using smoke. Now, when we use a computer simulation, we can reproduce that type of transmission. So you can see this is one without covering. And even if you sit just face to face with another person, then of course, at least a large crowd of droplet could reach to the other person. But when you cover with your mouth and nose, then you see this different cover method, then this distance is much smaller. And that's I think it's very important. And of course, when you use a mask, nobody is just a closed mask, surgical mask, and the effect will be much better than those by hand or tissues you see in the slides. Now, of course, people will argue when we do the simulation, then could be garbage in garbage out because the computer model is on as good as your assumptions is good. And now I want to show you this is a typical indoor airflow distribution as a preference seating return near the floor. And what do we calculate using the so-called Lagrangian method, this is CFD model, and this is the particle concentration distribution in the room. And we compare our simulation without with the measured data. This was measured by a professor in Japan long time ago, and then you can see they are very close. And we also have another different type of method is so-called Lagrangian method, which means we release the particle just like the coughing and so on. And then you can trace easily each particle trajectory, then you know the history of what is particle coming from, etc. Then again, you can calculate the concentration and this right bottom corner slices shows the concentration. So you can see no matter which model we use, we get a very close result. So that's what I think this method is good. And now I want to show you because with this method, you know, as an HVAC engineer, we could really use it to develop a new type of ventilation system. You know, traditional one I showed you just in the last slide, you supply the air in the seating and return on the floor, return on the seating. Now, let's leave it on, you know, just like I show here, this is animation. And let's say three dimensional view you probably see somebody coughed there, the particle go everywhere, it's not very clear. So this is a two dimensional one, it's in a classroom. Okay, so you see the air supply on this two blue inlet and exhaust in the two green outlets. And of course you can see after a couple of minutes of the particle is everywhere. And that's the traditional design of HVAC systems. And now I think that we can do a little bit smarter. So we usually so-called dispersion induction system, you supply the air in the lower part, and then return in the upper part. And then you supply it with the temperature a little bit lower, so the cool air will stay in the floor level, and then your body is warm, so it will generate a thermal prune. Then you will see a little bit of different scenario here. Again, I released the same amount of particle from one of these students in the room. Now, because less 3D is not very clear. I like you to look at the least 2D animations here. So you see, most of the particles will just stay in the person who released this job, and then being exhaust on the ceiling level. The particles are unlikely mixing ventilation. It doesn't go to verify, but of course the floor is very flexible. They always have a diffusion, etc. A few could go a little bit further. But generally speaking, you can see the left figure is much cleaner on the right figure. So I think at least it's something we as a VAC engineer can do. So finally, I will also mention one more slide here. I don't have the time to do that, but I wanted to just say that when you use masks, like a surgical mask, our studies show that you can reduce the infection risk by an additional 50%. And now, of course, a lot of new technologies are available to disinfect and clean the air. So if I use this bipolar ionizer as an example in this classroom, and our study found that you can reduce the invasion risk by an additional 20 to 30%. So let's conclude my little bit of introduction here. Thank you. Thank you very much, Professor 10. And now we will proceed with our second panelist. I would like to inform the audience that we have to construct the webinar in a way that first we're going to introduce the mechanisms of transmission of COVID-19, then we'll talk about mitigation strategies and design guidelines. So in the first two presentations by Professor Chen and the next by Professor Bohr will cover the first topic in general, the way this webinar will work will have eight minutes presentations by each of the four panelists covering the topics that I mentioned and then we will have a Q&A session, so feel free to submit your questions and I will be presenting those to our panelists. So now we are ready to proceed with our second panelist, Professor Brandon Bohr, who is an assistant professor of civil engineering at Purdue. He also has a bi-courtesy appointment with the division of environmental and ecological engineering. He conducts research on the physics and chemistry of indoor air. His group applies state-of-the-art measurement techniques to explore the dynamics of indoor air pollutants in diverse indoor environments. He has many accomplishments, among which recently in 2019 he received the National Science Foundation Career Award. Brandon, we're pleased to have you here, so please start with your presentation. Thank you, Professor Carabaugh. So today I will be discussing the important and governing role of park of size as it pertains to the transmission and mitigation of COVID-19 in buildings. So the overall aim I would say moving forward with the future of buildings is to reduce the number of viral aerosols in indoor air. And to do so, we must consider how the size of these viral aerosols affects their physical transport. So below you can see an illustration of particle size. We can start with a single viron of the SARS-CoV-2 virus. That is about 125 nanometers in size or 0.125 microns. But while that is very small, we know that the virus is transported in indoor air on larger aerosols and droplets, and these can range from a fraction of a micrometer up to 10s of 100 plus microns, as you can see here. In the community, there's different distinctions, whether it's an aerosol or a droplet based on size. Moving forward, I will consider everything that is suspended in the air as a viral aerosol. So to frame mitigation strategies for buildings, we can apply a physics-based material balance model and do that to describe the size-resolved behavior of these viral aerosols. So we can consider their source and loss processes. So a material balance model is illustrated here. This is a simple model considering a single-zone reactor. And what we can do is we can evaluate the accumulation of viral aerosols in an indoor space by looking at the balance between source processes that act to increase the number of viral aerosols indoors and lost processes that act to remove the number of viral aerosols from the air. So this material balance model encapsulates the concentration of the viral aerosols within a well-mixed space that is related to source processes described mathematically through a source rate. So number of particles produced per unit time. And then we subtract off that lost processes. Part of this are lost rates, which are per unit time that govern the rate of removal of these particles from the air. So source processes, we can go through a few examples. These are processes that act to release viral aerosols into the air. So the first of which would be respiratory emissions. So this would of course include speaking, breathing, singing and coughing and sneezing without a mask. If we add on a face mask, that can act to reduce these emissions. So the face mask is not only to protect you, but to reduce the emissions that propagate from your mouth and your nose. Another source would be resuspension of dust. So these viral aerosols can settle onto the floor, onto other indoor surfaces, then they can be stirred up and released back into air due to resuspension. We can also have the flushing of toilets that can act to release viral aerosols into the air. So all these processes shown here, their emission rates are very much a function of size. So as an example, I can show what a curve would look like in an illustrative sense for coughing. So for coughing and other respiratory activities, these emission rates are very much size dependent. And there's a lot of emissions, although one micron in size. And these are the smaller particles that can stay in the air for longer periods of time. Some recent research has shown that singing produces lots of particles, more so than speaking, which is more so than or more than what you would have for just breathing, but all respiratory activities will release some amount of viral aerosols into the air. And looking at loss processes, we can consider where do these viral aerosols end up within a building. So the first process we had that's very important for these larger particles above a micron is deposition to indoor surfaces to flooring to furniture. And for larger particles, this is primarily governed by a gravitational settling, smaller particles diffusion is important. Then we have removal via filtration systems within HVAC systems. So we have various types of filter media that can be used to remove these articles from the air. We have removal via portable air cleaners that can use fiber based filter media. We have removal via the face mask on people that are exposed to the viral aerosols. And then we have removal via outdoor air ventilation. And this is something that is not size dependent but still incredibly important for buildings. And looking at the size dependency of some of these loss processes, looking at deposition to surfaces and the deposition rate. This is a very strong function of size is deposition rate tends to increase the particle size from about a micron to 10 microns. It's dependent on the surface type, it's orientation airflow conditions, and for particles above about three microns it can be a very important process governing the residence time of viral aerosols and buildings. Then we have filtration mechanisms this is pertinent to HVAC filter media filter media and portable air cleaners as well as face mask. And this is strongly size dependent. And we see that for particles above a micron efficiencies tends to increase, but there's generally a minimum between point one and one microns this filtration efficiency tends to have a U shaped curve. So these smaller particles below micron, which are respiratory activities produce an abundance of are the most challenging to remove with different types of filter media. Along with the source and loss processes and buildings particle size is very important in governing the fate of those particles once they're inhaled into our respiratory systems. So I'm looking at where viral aerosols end up in the long. When we breathe in air, first they will some of those particles of deposit in the head airways or nose and nasal cavity in our throat. Some will be transported to deeper regions of our lung including the tracheal bronchial region. And then finally to the pulmonary region and this is where gas exchange takes place. So this process of lung deposition is very much dependent on size. Here you can see example of a lung deposition fraction curve for each region to long plus the total. And a lot of particles are deposited very efficiently in all three regions of the long across the size range of relevance to viral aerosols. And I like you like you to note that we do see a lot of deposition for particles and tracheal bronchial and pulmonary regions between just one and 10 microns so these particles get the deepest regions of our lungs. So in summary, you know in terms of working towards buildings that protect us from virus exposure, we can use mathematical modeling and aerosol physics to describe the source and loss processes that these particles, as well as as well as exposure and lung deposition so So looking at this we want to minimize the source rates and we want to increase the loss rates we want to reduce emissions, number of people that are in a space producing these particles. We want people where face masks to capture some of these emissions, and then we want to use various types of filter media to remove these particles efficiently from the air, as well as increase outdoor air ventilation. So this framework is incredibly useful and should guide our medication practices in buildings moving forward. Thank you. Thank you very much Professor bore. And now we're moving on with our next speaker, and we're moving on on slightly different topic we covered the basics of virus transmission in buildings now we will start talking about short term communication strategies to address the COVID-19 pandemic and we have the best panelists we could hope for for this. This is Professor William Banffleth from architectural engineering at Penn State University I'm saying he's the best we could hope for for this topic because he actually served as the president of the American Society of hitting, representing and conditioning engineers in 2013 2014 so he has been heavily involved in the society and in standards development. He's been recognized for his work in us through numerous awards, including the Lewis and Billy holiday distinguished fellow award and the K come Bella world and the Paul Anderson award. Research interest cover a wide range of variety of indoor environment control topics, including protection of building occupants from indoor virus solar releases and ultra violent again inside the irradiation systems. Professor Banffleth, we look forward to your presentation. I've got to unmute myself very glad to be with you all and I was going to say that while I'm a researcher in various related areas in in professional life I've done a lot of work with ash right. And I'm here really to talk about what ash Ray has recommended as guidance for HVAC systems in buildings and I won't be able to cover all of that in the short time that we have here. I'll hit the high points and we can address other things in q amp a. So ash Ray, very briefly is the main technical society for the HVAC and our profession and in North America and also a worldwide organization so 55,000 members and 130 plus countries and it's an organization that writes the standards for indoor air quality in buildings and other things as well that are used, particularly throughout the US and in North America but also referenced in other places. And back in March I was asked to lead an ash right task force addressing cove at 19 we call it the epidemic task force because we're addressing the issues of infectious disease transmission in buildings more broadly, and I'll point here to the website ashway.org slash cove at 19 or you can find the guidance that's been posted so far and also a lot of other related resources that will expand on what I'm covering here. Professor Chen mentioned the modes of transmission and of course if you have follow this you know that there's been a great deal of controversy between public health organizations WHO CDC and other scientific and professional groups aerosol scientists and engineers about whether airborne transmission occurs at all, but ashway and other HVAC organizations really adopted what we call a precautionary principle at the outset and have been assuming that controlling airborne exposure is important so all the things I'm talking about here. Relate to controlling airborne transmission because that's really all we can do with HVAC systems. But so now recently, since beginning of October we at least have from CDC and WHO, some recognition that under some circumstances airborne transmission can occur in closed spaces prolonged exposure to respiratory particles, and also an adequate ventilation system so there's there is a recognition that HVAC systems have a role to play, both transmitting and controlling COVID-19 and other infectious diseases. So, let's talk about the main elements of guidance that are being applied by ashway we have over 400 pages of guidance documents now but really you can put the essentials of it on one or two slides. The first one is follow public health guidance, meaning wear masks and practice distancing and use hygiene and in no way does protecting yourself from airborne transmission by making modifications to your HVAC systems. I would give you a justification to not practice these other controls for different modes of transmission and in particular, close range. Many may have seen this image on the left from Lydia Brueva at MIT that shows an uncontrolled sneeze moving almost eight meters away from person and another image on the right shows how effective a cloth mask can be at stopping that respiratory jet and also probably removing as much as 50% of the infectious material. So we want to do that now what we do with HVAC systems. We should probably provide at least the amount of outdoor air that's required by minimum standards this is essential for controlling all sorts of indoor air contaminants. It's also a good baseline, although not sufficient for controlling infection risk, as far as air distribution is concerned avoiding strong currents that are going to extend close contact. So to ventilation we need to add filters that actually work on those small particles that Dr. Bohr was talking about. So we upgrade from low MIRV ratings, the ASHRAE standard 52.2 system, MIRV 6 or 8, to MIRV 13 or equivalently ISO EPM 1 which will control the micron and sub micron particles. And we can enhance that further with air disinfection technologies, ultraviolet and others that are available. But this slide shows why it's important to use different filters. I'm showing here one of the most widely distributed images of respiratory droplet size spectrum. And most of them, as we noted, that are of concern are smaller than 10 microns and actually a lot of them are smaller than that. And I've overlaid on it the three ranges within which the ASHRAE standard 52.2 rates a filter. So let's just look at MIRV 8, which has no requirement at all to remove particles that are smaller than one micron, 20% for one to three microns and 70% for three to 10. So it's really not going to help us very much if we're trying to reduce infection risk. But if we go to the level of MIRV 13, it's recommended. We now have a filter that will move 50% at least from 0.3 to 1, 85% from one to three and 90 from three to 10. It's important as we think about strategies for risk management to think about how to put together different controls. We can have more outdoor air. We can put in very high efficiency filters. There's probably a balance between them. Combining them in the most effective way is important. Ventilations, expensive and affects operations. And as some work by Brett Stevens and his student Izimi at Illinois Institute of Technology showed, at least for looking at influenza, improving filter efficiency can get us to the same level of relative risk as ventilation at a much lower cost. So that tends to be preferred as the first thing you do to enhance beyond what minimum standards would have you do. For HVAC operations, we can talk a lot about humidity in the discussion, but there is some reason to believe that controlling humidity, particularly at the low end of the scale to 30 or 40% has some protective value. Systems should always be operated when people are present. Don't shut them off just because it's the end of the business day. And don't use things like demand control ventilation to save energy when that's going to reduce the amount of ventilation. And also importantly, do things that will reduce the amount of recirculation and this is an important point because initially we were saying or some were saying shut off energy recovery wheel so you can't operate them safely but they have to be evaluated. And then a final point here, commissioning of systems is really important that we could have a whole webinar just on on how badly most HVAC systems work, but schools are a big point of discussion right now and not that long ago the GAO published a report on K-12 schools that found that over 40% of school districts had 50% or more of their HVAC systems that either needed to be replaced or repaired. And they also had significant problems with windows and with monitoring of indoor air quality so there's an important need to evaluate systems here. So that is in a nutshell the main points of this guidance and other things we can pick up in the question and answer. Thank you very much. Thank you very much, Professor Banflith, a very enlightening talk and it's scary to see how badly building operates. I hope we can take them more seriously in the future. We will move on with our, towards our next topic that includes mitigation strategies but also their impact on energy use, operation of buildings and in general virus proof designs and strategies for buildings. Our next distinguished speaker is John Douglas. He's the director of advanced development for the Global Control Groups, Global Controls Group at Johnson Controls. He currently leads Johnson Controls Building Infection Control WG technical team tasked with developing solutions to mitigate COVID infection risk in buildings. So he's very qualified to be on this panel and we're very excited to have him. We should proudly say that he's a Purdue alumni. He graduated with his bachelor's and master's degree at Purdue. And he has 25 years of experience in HVAC and our industry, 34 patents issued and he's well known. He has a very good reputation as an innovator. Start with experience, the ranging from small technology startups to large Fortune 500 companies. So, without further ado, I would like to warmly welcome John Douglas on this panel and I look forward to his presentation. Thank you. Thank you for the opportunity to present here. I'm looking for learned already quite from the previous presenters and I'm on my talk here today what I'm going to do is take a lot of the science that's been presented earlier and share with you a method that we've used to put that science together and help our customers quantify the benefits associated with infection control measures as they're applied to buildings. This first slide I think we've covered this quite a bit there's three modes of infection. HVAC solutions tend to affect primarily the aerosol mode of infection. And I just like this picture because I think when we think about aerosol infection we need to think about a smoke filled room. And so think of everyone as a potential smoker and we're all generating smoke. And as if you don't do anything that smoke slowly builds up in the room, and eventually you're going to breathe some smoke in. So, so just kind of think about when you think of aerosol infection think about that smoke filled room analogy. So first thing I want to talk about are the different air cleaning methods. And so if you think about air cleaning we can break them down into three basic methods. The first one is ventilation where you basically dilute the pollutants in the air with fresh clean air from outside. Filtration where we mechanically remove the particles in the air and take them out or disinfection where we actually deactivate the bacteria and viruses in the air. And if you look at these, they each have a different effect on the different pollutants in the air. Ventilation tends to be preferred in a lot of the ASHRAE standards because by the nature of it diluting it actually addresses all the pollutants in the air. It takes care of dust, chemicals in the air, the biological gases in the bathroom, and the viruses and bacteria. The good thing is when the context of COVID and particles that contain COVID viruses, all three of these air cleaning technologies can be useful tools in our toolbox to address it. So we can use all three to address COVID. So this next slide, what I want to do is talk about the concept of clean air delivery rate. So clean air delivery rate is a measure of the amount of removal of virus containing particles you can do in the air. So the way we calculate clean air delivery rate, it's you take the air flow through the device, times the removal efficiency. And, and let me give you a couple examples. On the on the upper left hand side over here we have a portable room air cleaner. It is, it moves about three, this one moves 324 CFM air flow, it has a HEPA filter in it so it's 99.9% efficient at COVID sized particles. When you multiply the two together you get about 324 CFM of clean air delivered to the space. You can kind of compare that to ventilation, this is a rooftop unit. This one set up we've got 30% outside air. In the context of COVID and COVID late late in particles we're going to assume that the outside air is 100% COVID free so 100% clean air. When you take that 30% outside air times the 1200 CFM of a three ton rooftop unit, you get about 400 CFM of clean air coming from that ventilation system. And then there's just another example where you can take a Merv seven filter, roughly 42% efficient not super efficient but because it's moving a ton of air it still actually does some air clean so you get some air flow rate and cleaning from that that unit you get 504 CFM of clean air. So the good thing about this, the good thing about this is this is a means of quantifying the air cleaning rate of different types of IQ mitigation measures so we have one common measure to put them all together. So the next slide, I'm going to introduce the Wells Riley model so this is a model that's been used by scientists to quantify the risk of infection. And it's been used actually the first paper was published in 1978, and it's been used to quantify the risk of infection of influenza, TB measles, etc. The equation assumes that the air in the room is perfectly mixed so it's a little bit different than what Dr. Chen is doing where you're actually modeling the specific details of the particles flowing through the room we're actually assuming that the particles that you breathe out are all perfectly mixed up, and we're calculating the concentration. And so when you take this equation, there's a lot of parameters here but when you plot it in the most basic form you get a risk curve that looks like the plot we have here. So the vertical axis is a measure of the risk of infection, and, and then the horizontal axis what I plotted is the clean air delivered to the space so what you can see from this curve is that as you increase the amount of clean air delivered to the space, your risk of infection goes down pretty quickly. And then as you get further out to clean air delivered the risk. The risk goes out. So, so, and I forgot to mention this bottom axis the clean air axis here is air changes per hour so we're talking about four air changes per hour or 10 air changes per hour. When you look at this equation, the parameters that are in this equation can can be divided up into three logical groups, I kind of call them the coven science, building operation and clean air delivered. The coven science, there's a term here q, which is is the quanta infection rate and quanta generation rate and that's really a measure of the degree of effectiveness, the virus is. And, and the way that numbers calculated is actually back calculated out by looking at actual case studies of infections and then back it out, because coven so new we're still learning, and so there's a lot of variation this q value. So I put these air bars on to kind of show that we're still really learning that the how to build the relationship between the risk. And the air delivered so that there's kind of a pretty significant air bar, but the good thing is is that there's still a consistent trend which is as you increase the clean air delivered, you reduce the risk of infection. So the next group of parameters are building operation I'm going to go to the next slide to talk about that. So key parameters and building operation are how many people in your building are infected. What is the activity level, how much time is in the space right, and then mask usage. And so so I built this plot over here to kind of illustrate that. And this is this is modeled based on a classroom, and I modeled typical measures that classrooms would do to mitigate the risk of infection. So this orange line is the baseline case. Nothing done, kids are going to school normal occupancy normal behavior. And then if we modeled mask we've talked about mass as being that basically reduce the amount of virus particles generated by about 50% we put that in the model and you can see that the, the risk of infection drops quite a bit actually the risk drops by more than a factor of two. I mean you see it goes from 1.1 down to to less than a half at four clean air changes per day. So the mass are really really important. The next thing I said is some schools have gone to a case where they have some students in school and some students at home. So they're running at a 50% occupancy. So by reducing the occupant density you can see we further reduce the risk curve and so we're going down to a lower curve here. And then the other thing that schools have done is they've gone to a half days they reduced exposure time from the normal seven hours to three and a half hours and you can see that would further reduce the risk curve. So a way to think about this is how you run your building determines which of these curves you're on, and then how you run your HVAC determines where you are along the curve. So, so for the rest of slides I'm going to assume that best practices is at least wearing masks or uses blue curve for the rest of slides. The next slide goes into showing how the typical HVAC measures influence the risk of infection. So what I did was I took the first thing you always want to do is do your ASHRAE 62.1 required ventilation. So in this space, the ASHRAE ventilation gives you about two and a half clean air changes per hour. So I added that in, and you can see it's we took our risk from one, all the way down to about 0.45. And then the other other recommendations, as Bill mentioned, is a MERV 13 filter. So we added in the clean air delivered for the MERV 13 filter and you can see that that takes a risk down from about 0.45 to like 0.28. And so you can see there's quite a bit of risk reduction associated with just applying the standard 62.1 ventilation and MERV 13. So you can see that the curve stops at six. And the reason I did that is that this system only delivers six air changes per hour. So the best we can actually do with a centralized HVAC system would be 100% clean air, which would be six air changes per hour. If we want to reduce the risk further by going down this line, we need to add a source of clean air. The reason an important thing to get here is that the amount of risk reduction delivered by the HVAC system is a function of the airflow delivered by the HVAC system. So in this next slide, I want to illustrate what happens when you have a variable air volume system, and it runs at this lowest airflow. So variable air volume systems vary the airflow rate based on the load. It's designed to save energy. And so in this case, the VAD system is at a low load and it's reduced its airflow rate. We can still get the benefit of the ASHRAE ventilation because the outdoor air dampers are going to adjust to maintain a constant ventilation rate because the occupancy is constant. But because the airflow rate is lower, we don't get that much benefit from the MERV 13 filter. So again, the benefit is a function of load. So what can we do about it? What we can do is add another source of clean air. And so what we do is in-zone filtration. This box shows the benefit of a 600 CFM. It gives you about two and a half air changes per hour fan filter unit. And so this in-zone filter makes up for the difference of the reduced air flow rate from the centralized HVAC system and gets our clean air to your infection risk back down to the same levels we had with the full airflow or the full design HVAC system. So once you've got all this in place, it's important to think about what you do after you saw your equipment. So it's important to really think about monitoring. And the reason I say that is, is that when you think about building operations and HVAC systems are primarily designed for comfort, we actually have natural fault detection for buildings. If your HVAC stops working, people get hot or cold and they start complaining, the maintenance is notified and somebody goes and fixes it. Also, we've got a lot of focus on energy efficiency. So most large building automation systems, even most medium-sized building automation systems have energy monitoring. So there are alarms out there that tell you you're consuming too much energy. There's not really any way that people can tell that they're getting poor IQ or that the building automation systems really know that you're getting poor IQ. So there's a need as we move forward to provide monitoring systems in which we're actually monitoring the clean air delivered by these systems. So this is just an example of a chart that we have. We're actually measuring the amount of clean air delivered to the space and comparing it to the alarm level. And this plot is showing that we're actually delivering at least the minimum amount of clean air for this space. And in the last slide, we wanted to talk about the future of buildings. How does this outbreak affect the future of buildings? So the way I'd like to frame it is to think about it from a timescale. So if you look at natural disasters, I've got a picture of the COVID virus. We've had talks of wildfires in California and Canada, hurricanes, right? They generally happen on a short timescale, really fast. Then over here, you have the timescale buildings, right? It takes a while to design and build a building. You've got to go through the design cycle, the construction cycle is pretty long. And the other thing to think about is I've got a picture of a new building here compared to an old building. Buildings tend to last a long time, right? So the building life cycle is pretty much a long timescale. So how do we put these two together? And my feeling is the keyword is flexibility. So as we think about designing and operating buildings, we need to design flexibility and such that we can adapt to these natural disasters. So it will be here. It'll be gone hopefully soon. But we need to design our buildings to be prepared for the next disaster so that we can quickly adapt. I think that's the last slide. Yeah. Thanks. Thank you very much, John. Very inspiring talk and very interesting ending slide. So we have a lot of questions from our audience. It's very exciting. I have been monitoring and it's a very, very dynamic audience. So I will start asking in somewhat random order. The question that relates to the latest discussion about future design of buildings is related to kind of we change the architectural design of buildings to make them more resilient to the exposure to COVID-19. So architecturally, what can we do to make the buildings more strong? Maybe John or Bill can take this question. Well, sure. I'll take a shot at it. I'm a mechanical engineer at an architectural engineering department. I want to make that clear. But I think architecturally things that can be done would help to make it possible to keep people separated during normal activities. So I think a lot of buildings we discover that they actually have pinch points in it that make distancing hard to practice. And there's certainly work being done on low transfer surfaces. So if there's concern about phone might transfer, we can can have surfaces are going to be less likely to transfer. And another very important thing is no touch technology. So you use your phone to call the elevator. You don't have to touch a door to go into the restroom. So those are a few things that come to mind that are on the architectural side. Great. Thank you, Bill. I'll continue with another question. I think John, the practical side of things. I think John can take these. There was a question about your talk, John. How about the combined effect if you wear a mask and 50% occupancy and half day operation. Have you looked at those combinations? Oh, just to be clear, that was the combined I was adding them on. Okay, this is what I thought but I wanted to double check and clarify. Excellent. There are a lot of questions for all the panellists. So there is a question about Professor Chen how feasible would be to run safety model for the major classrooms on campus and have room specific information on ventilation geometry and settings in these rooms. I think there's a very interesting question. I think typically if you look at some auditorians, we might house like 200 or 300 C's. Right. So, to simulate this type of a classroom say it's not very easy because you probably need about 20 30 million grades. In reality, you need a reasonable size of computer in order to do the job. But in addition to that, because for classrooms, we have very complex air diffusers. And that normally when we run the CFD, we just assume there's a whole there, but in fact, it's not a whole. So there's already some technologies available there. And I think at least really is a very challenging aspect of CFD simulation. But with the development in the past 20 years, I think that there are a number of things already available. So if you have a computer cluster, then you can just run a note and will be sufficient to simulate a classroom. Thank you. Thank you again. I'm sure you can do it all with the experience that you have in time in record time. The other question is related to filtration, maybe I'll have Brandon answer this question. Some people claim that many building owners due to fun capacity, they cannot use high filter efficiencies. So what do you think? Do you think that higher filtration is not worth the reduced air flow? Thank you for that question. So I think John touched on this nicely. It's a balance between both the efficiency of the filter, the size is all the efficiency, and the flow rate of air moving through that filter. So I think that if you are constrained by the blower that you have and just can't handle the pressure drop of a really high efficient, high efficient Merve 16 filter, you know, then you will have some issues there because if the blower is struggling, the flow rate will be decreased depending on a particular blower design. Others can adjust the flow rate based on the pressure drop. But I think that's a balance that we need to think about, you know, the blower capacity and also the energy consumption of that blower, especially if something like a VFD blower, if it's working harder to provide more air for a given pressure drop, you know, you're going to assume more energy. But that being said, you know, I think that we have other factors to consider now beyond just energy consumption of the blower. I think another thing that could be done, especially in residential environments and maybe dormitories and other shared spaces is using portable air cleaners, which John touched on, you know, that have high cleaner delivery rates. I think those are quite effective because they can be placed in the occupied space. So if the blower is not able to handle something like a HEPA filter, but you can purchase a portable air cleaner from Home Depot or Walmart that does have a HEPA filter, put it in the occupied space, I think that can be a nice addition and something that should be considered. Yes, please. So I think that a lot of people have the perception that MERV 13 filters have a high pressure drop. And in the data that I've seen it's not as high as you think. We have a filter division I've looked at our filtration data. And for the same filter, it was, I think it was a two inch filter, a MERV 8 filter was 0.12 inches of static pressure drop. The size filter at the same airflow rate, it was 0.19 for MERV 13. So, so in the context of system that probably has a total of a one inch static pressure drop, it's really not that much of an increase in pressure drop. So take a look at the filters you're looking at. A lot of times the added pressure drop isn't as much as you think. We've got a couple of add-ons there as well. Going backwards here with filters, it's true there's probably more variability across a particular MERV rating than there is between one of the next but those two inch filters get to MERV 13 because they're electrostatically charged and the charge can wear off very quickly there's another rating called MERV A that conditions the filter to take away the electrostatic effect. And that filter is going to hold its performance, but you probably need a four inch filter or a bag filter to do it. The issue or the concept of supplementing central filtration with portables was covered. I want to mention one other thing though. If you have a dedicated outdoor air system, and let's say you have radiant panels as the conditioning equipment in the space, you have no filtration for particles in that space. You get whatever you get from the ventilation because the filter in your DOAS air handling unit only filters the outside air. So you have to in those cases rely on something in the space, whether it's a portable you add or if you've got fan coils or VRF cassettes or something of that sort, that's going to be your source of particular removal in the space to get beyond whatever your air changes of ventilation are. Thank you all very much. A related question, since it's a mitigation strategy, I will have a question about how do you see the role of upper room air UVG as a part of a permanent strategy. Associated with some of others, for example, protective equipment, surface disinfection, ventilation and remote work. I think Bill, you may have some experience with this technology. Sure. Well, you know, upper room UV was first tested in the 1930s against measles, outbreaks in schools in Philadelphia worked very well. It's a fairly expensive technology. The equipment might cost three to $5 a square foot and then you've got to install it. So I think once you put it in, you're going to use it. And it's tremendously effective systems that are properly installed have been measured to have equivalent air change rates of 10 air changes and up even to close to 100. So it's very effective. The question is, is it right for every space note is very expensive. There are a hundred and places where it would likely be having a beneficial effect all the time. There are other less expensive ways to use UV like putting it in your air handling unit, which is less than $1 a square foot installed, but but less less air change effectiveness. Hey, thank you very much. Very insightful answer. And I will move on, change the topic a little bit. What does the research show for the existence of the virus in an enclosed environment once a known infection has been present to have any data or any information related to this any of the panelists can can take this question. So how long does it stay. Yes. Of course, please. I did a lot of research in the airplanes, right? The airplanes is an enclosed environment just like a building and the airplanes use a hyperfilters. And recently DoD also conducted a really good study together with the United Air. And they found that, yes, definitely hyperfilters work where they find and they even somebody with coffee and talking and sneezing will have some impact in the same role because the airflow pattern in the airplane is really going like that. So in the same cross-section where they have a high invasion rate. And there's a number of flights already demonstrated the risk is there. For example, on March the 2nd, Benang Air from London to Hanoi, one person infected 12. And recently also in March it was another flight from Boston to Hong Kong. To COVID-19, two flight attendants. So those are just a few cases that demonstrated this infection risk is there because they use the INA technology so they can identify the same string of providers. But on the other hand, a number of other flights show no infection at all. And we did a little bit of analysis, we found that every person wearing masks then the risk becomes very, very low. We found that it's a flight from Singapore to Hanzo in February. And that's an air bus of flight with more than 300 people and one getting infected and let a person get infected because that person lowered the mask for one hour during this three and a half hours of flight. And although in a plane there was more than 15 confirmed COVID-19 patients. So wearing masks is a huge difference in this enclosed space. Thank you. Thank you very much, Professor Chen. I think one distinct difference between planes and buildings is that buildings are uniquely designed and here is a nice question related to building design. So how do spaces like cubicle cubicles compared to new open plan office areas for their resistance to spread of aerosols. So how we were talking earlier about how we configure buildings, for example, if we have really small cubicles compared to open areas, how would that affect the spread of the virus. I think, Jan, you might be able to take this question as well. I mean, cubicles and depends on what type of ventilation systems you have, right. If you design like a modern buildings with the underflow air distribution so then the cubicles are very good because you supply the air on the floor, and then go one dimension up to the ceiling level is very good. But when you look at the traditional mixing ventilation, then the air flow doesn't go to very deep in the cubicles, especially when you have at least cubicles with a little bit higher partition walls. And according to our past study, we find that the air is more or less under stagnation. And which means that the particle will not be easy to move it out. That's a good thing or better thing, good thing. Even you stay in the neighborhood in cubicles probably you don't get a lot of particles right away. But on the other hand, you accumulate this in such a way, and then eventually particle will go out so you will be subject to the infection. An example to think about is our school district when they first opened schools was talking about putting plastic walls around the kids desks, right. And if you think about it, imagine, it's kind of weird to think about a kid smoking but imagine somebody sitting behind a desk behind an acrylic divider smoking a cigarette right that first puff. The acrylic does a decent job of keeping that from blowing in your face but over time that smoke builds up in the room. And, and, and you start smelling smoke. So I think that that kind of work is a way to think about it in terms of the layout of building cubicles and things like that. Having a cubicle wall short term right probably blocks the immediate discharge and the larger particles but over time the smaller aerosol particles fill up the room if you don't have other mitigation measures. Thank you very much. Both of you. There are several questions in the chat about the bipolar ionization as a measure to reduce virus transmission and any thoughts from any of the panelists, perhaps bill or anybody. Sure, well, we've seen the claims about how effective bipolar ionization is and you can get research reports from some of the manufacturers and certainly it seems that ions have an effect on on removing viruses and other pathogens from the air and from surfaces the question is how effectively do they do it, compared to to other things that you might do like filtration and, and UV and more ventilation and sometimes you know that there are all sorts of manufacturers. So in the studies carefully, the application conditions are pretty different than than the conditions and the tests and the literature on what happens when you put anything reactive into the air is not as conclusive as as we wish it would. It would be so I think that some are using it and they're they're finding that it's effective but there are many who have questions they'd like to have answered before we put lots of ions or hydrogen peroxide gas or hydroxyl radicals or other things into the air that that are already there. Thank you, Bill. A question. Interesting. It makes me think, can we use a CO2 sensor as a proxy of the infection in the room. I'll take that one. Brand or oh yeah, John or Brandon. Yeah, I think CO2 is a good measure of the number of people in a space relative to the ventilation rate. That's, that's really what it's good for. And so if you assume everybody's sick right then it is a good measure of, you know, the amount of code in the air but but again, all of us breathe out CO2. It's diluted by ventilation air and so you do if you do all the math it sort of ends up that CO2 levels are sort of a good measure of number of people in the space divided by the ventilation rate. Maybe it's getting a little academic but there's a really interesting paper by Rudnick and Milton, Don Milton now at Maryland, where they they actually use the CO2 concentration in the air as a surrogate for how much infected air someone was breathing from an infected person they embedded that in the Wells Riley equation that you were talking about and show that there was was maybe some usefulness for that. Okay, good to know very interesting. Another question, a little timely since we enter winter. I think I'll have Brandon take a first pass on this. What would the mask effect be if it's winter and people are coming back from outside with running nose and since large droplets fall on the floor, how is the reentraintment model so maybe the second part is related to Jan's model but here. Model could also be some of the things that Brandon has talked about Brandon would you like to comment on please. I'm not so sure about the impact of the season, per se on the effectiveness on the face mask. The running nose, so it may have a running yeah. That I'm not quite sure about one day I would like to point out with face mask and also HVAC filtration which we were discussing earlier, the efficacy of either mitigation technique will be dependent on bypass. The face mask, whether it's winter or summer, especially surgical mask and other improperly fitted, you know, fabric based mass that people are wearing nowadays, there could be rather significant bypass. And you know sometimes you can see that if you feel kind of air passing up across your eyes, the same thing with a filter and a HVAC system if it's not properly installed there can be a lot bypass. That bypass is a significant issue because there's no filtration occurring, either on the exhalation with the face mask or the inhalation. So I think making sure that the face max is properly fitted to the face is something that we need to factor in. I think it can play a role in filtration efficiency and the pressure drop of the filter. So that's something that can vary seasonally. But I think the bypass is something that needs to be seriously thought of just on your face and there's a lot of bypass. It's not going to be so effective. Thank you very much. So there is a question for Dr. Chen, is there a good way to correlate the virus concentration distribution from the safety results to COVID-19 infection risk? Yeah, that's a very good question. I think John just showed that if you want to do the correlation, you can use a well rated equation. But on the other hand, they are not exactly the same because CFD you really calculate the local concentration and well rated equation just based on well mixing condition. So you needed to do a little bit of collaborations there. And even you look at the quantum number released by a patient, well rated equation also give you a very wide range of the quantum number. So that's why I think it's very difficult to give you a quantitative answer on this one. But definitely there's a correlation there. So we definitely in the academic field, we use a well rated equation under this non-uniform concentration and we still can give you a risk estimate. For example, 10, 15%. But how good is the model, as I mentioned, the assumptions we have used. I think one place you can look for guidance on air change rates is health care standards. You know, independent of the disease and our ability to do risk calculations for COVID-19, you can look at the air change rates and the filter efficiencies that are used in, I say ash by standard 170 that's used for your health care and actually it puts in about the same place. It looks like about six total air changes up to maybe as many as 12 or 20 depending on whether it's a really critical space. And they're using filters that are typically more 14 for the ones that aren't really critical and have a filters in operating rooms and protective environments and isolation rooms. So six air changes with 14 filters, not a bad place to start because that's what they're already doing. And the only kind of facility we have it's designed to prevent infections. Great. Thank you very much. I think there is a whole discussion here about models and how we can trust them. I know Brandon is there are many questions in the chat and in the Q&A I'm going to lump them together and maybe ask Brandon to take a first pass with an experimentalist primarily Brandon I know you're doing really high quality state of the art measurements. How far do you think are we from really having trustful models in the case of COVID-19 transmission in buildings in indoor environments. I'm not exactly sure I think Professor Chen maybe a better person to answer that I think the model I showed kind of the simplified material balance modeling I think is rather straightforward but it does work on the assumption that air is well mixed so I think that's something that's you know as we can see is not true and I think Professor Chen is the expert on looking at the spatial dispersion of these viral aerosols. And you know I think based on his work some of the models are quite reliable and can really inform building design. I'm asking you as an experimentalist to criticize the models to create a little bit of to generate some heat in the panel. Of course I know Professor Chen's work and I truly respect it. I would say that this is a great question you know now people do use advanced models like a CFD to do a lot of simulations and the results so beautiful right we often call this a color through mechanics so it's so appearing and then the computer giving you a accuracy like a seven or eight digit behind the decimal point. Now I've been doing CFD for more or less my entire career but to be honest I don't really trust the CFD result unless I can validate that. So in actually handbook that's indoor environment modeling that's a very good guideline tell you how you could really develop and how could really use the CFD or other type of models to predict a good result and then you validate yourself because often I also heard that oh I use a very good commercial software they using everywhere and therefore my results are good. No, just like you buy a car right you can just turn this knob on that knob off you can have a very different air conditioning systems in your car because it is saying you know when you use CFD you can just change a lot of different parameters you get a different result. And therefore I like you know like a brand's approach you do a number of the experimental measurement to validate your CFD and then you continue to use the CFD to do the prediction that will give you a reasonably good result. Thank you. I think this is really challenging us as an engineers because in a normal world what we do is we we put 10 people in a room, know where the sick person is and see you get sick, right. That's the way engineers would work, can't exactly do that with with viruses right so so I mean we can't run experiments where we infect people right that that's that's why I asked. You know, so so we have to rely on kind of stitching together smaller scale experiments to kind of create what we think is the best knowledge right so we work with the well as Riley analysis you work backwards with field examples of where people have gone sick, right, then there's the laboratory studies where we're measuring particle sizes. And then, you know, even questions about are the virus particles evenly distributed in those different particle sizes, do you have our, is there more virus in the bigger particles versus the smaller particles right, and then questions about how much does it take to get sick. Is it just one virus or does it take a certain critical mass. Those are all questions that individuals are working on and we're trying our best to stitch it together because we can't just experiment on people. Let's correct. I mean John make a very good argument on the how experiment should be conduct, and I believe there's a lot of rooms for us and public health scientists to work together. Because for engineers, we can calculate the virus concentration, then you look at the exposure time, and then you're in health rate so you can get the number of the say, salivar with the virus there, but the public health scientists, they really did a very detailed study. And of course for them they consider a little bit different. They also have to consider the uncertainties how good your immune system, etc. So they will give you a range of how many virus you inhale them probably will get sick. So by working with them, I think we can get a pretty good result without really use using the actual human being to do the any measurement. I think at least a type of measurement is almost impossible to get the IRB approval. Yes, that's true, which is difficult anyway and reminds me what my professor used to say that the people who do research in buildings have the tough job they do the real things right we're doing full scale real people real environments it's not in a lab something tiny like this that we're going to mimic. Anyway, there are numerous questions regarding to the safety models and boundary conditions that I'm going to skip for now will come back to them if time allows because I want to talk about the future. There are many questions also related to that. What do we expect in general do we think that the future design of buildings would include, for example, virus transmission as a parameter as it does for a fire or earthquake. How do you see john for example first the industry moving forward. Yeah, that's a tough one. You know definitely have the idea of infection control and the design of the buildings. The challenge is we've been thinking about it is is just talking about Dr. Chin's work on airflow modeling and just signing how you design your ductwork. You really need to know where the people are. And because the people are essentially the sources of the contaminants and unfortunately people move around on you, which makes designing a building kind of tough. So that's something that you've got to think about is is can we maybe the better answers can we design buildings in a way that they're robust, and that they're, you know, can do the best they can given people can be anywhere in that building and you know, you know furniture moves around to right so you can design it for a certain furniture arrangement and then and then somebody else comes in and rearranges the furniture so it's a real challenge. Yes, it is even more challenging, more heterogeneity and variation and there is a question. I would like Professor Banff left to try to answer. Do you expect a new standard to come that would be focused on on virus mitigation of buildings. Since you are heavily involved in these activities. Certainly we expect standards to change I don't know if creating a new infection control standard would be the right way to do that you know after 911 and the anthrax mailings we created a guideline on protecting building occupants from from bio terrorist incidents and they probably are still on the original printing of that standard I think we need to put those sorts of requirements into minimum standards like 62.1 and 62.2 in an appropriate way. And I don't know exactly how that will happen but I think there's pressure already to raise minimum standards from the point of view of wellness, healthy building ideas, and now we have what's essentially an aspect of resilience being put into the next phase. So, I expect significant changes over a period of time that may involve higher filtration requirements the ability to adapt to emergencies that isn't currently in the minimum standards, and perhaps encouragement of other uses of technology. It's going to take a while for that to happen because of the consensus process and because these things wind up being laws. Thank you and more specific question related to future design of buildings I like it as an example for example how do we select their handlers. So we design select them to full full performance requirements using 100% outside air for pandemic usage. So can that same handler be designed to be easily converted or adjusted to perform for non pandemic use. Do you see these questions john in the industry popping up already. You're in there I mean it all depends on, you know, your tolerance for risk I mean as you invest more in your air handler for for kind of a potential outcome in the future right it costs more upfront in your building so that it's really a customer question, but things that I think are low standards are making sure that you design your handler to have the space for a deeper filter on that's relatively inexpensive to add you don't have to put the filter in, but at least you have the space. So making sure that you have increased your duck sizing and enables you to have more airflow, which gets you more out of the space so there's some things that are lower cost things that they're relatively inexpensive to put in when you're building the building that that are easy hitters. I think that the filter issues easy one that that's the low hanging fruit and I think everyone who's building a new building should be putting a more 13 filter better in any way more 13 is now the standard in California title. 24, I put in four inch wraps you can get real more 13th. The original question though is should I design the system for 100% outside air. And that really means those systems will handle 100% outside air now if they have have economizer mode. What you're really asking is should I size my heating and cooling coils for five times the outside air on the design day. And I say, no, I bet that's why we should be looking at air cleaners and filtration as a way of getting to these targets using the equivalent air exchange approach that you were talking about john. Thank you bill for again a lot of debate here in the Q&A and talk about filters. Many people clay, like one person is claiming that the, a lot of the exhaust really gets into the ducts rather than the filter. So, the, there is debate how effective the filter will be if if the virus actually will be getting to the ducts of the equipment rather than the filter, what your thoughts are on these. Brandon, I know you have done very significant filtration projects for us today. Yeah, well I just like to add on to the previous question regarding filtration and I think the future of buildings and so forth so I think there's a lot of added benefits to using higher efficiency filters. You know, wildfires were noted wildfire smoke, and of course just fine and ultra fine particles that are generated indoors from cooking indoor combustion sources and so forth so I think that, you know, working towards better filters and buildings makes a lot of sense for other reasons and on just control of virus transmission so in regard to both the particles reach the filter well I think there we have to look at the deposition mechanism so once the particles are released from these respiratory activities and there's a number of fates that they'll ultimately have. And we could model that you know some particles are larger will settle out the air faster others will remain in the air for longer periods of time they may. You know, deposit on to vertical surfaces and so forth and then once they get into the age back system yes they can deposit onto the duck work. And if you ever, you know look into the ducks in your house. They can be quite dusty because particles deposit and accumulate over time that's why we have things like duck cleaning so yes there could be deposition of particles that contain the virus in the duck work. And if that's upstream of the filter, you know that stuff's not being filtered out at all and could be something that needs to be looked into that can all be modeled and and accounted for. Thank you very much Brandon, there is another question related to future design of buildings or not exactly design but future thinking. For example, for general public familiar with her quality index there is 0 to 500 less than 100 is safe. How close are we to a similar metric for COVID related I a q. Well, ash rate hasn't what's called an indoor air quality procedure and in standard 62.1. And it, you know, doesn't include microbials at all. It's, it's organic chemicals and oxidants like like ozone and PM. So nobody's come up with a metric yet that really addresses microorganisms because you got the ambient ones that are there and maybe allergens, but then you got these pathogens that come along now and then and we have no idea how much of it we can be exposed to without risking a serious infection. So I think we're pretty far from a universal IQ metric myself. Thank you bill. There are many detailed questions related to modeling and assumptions. If I don't get a chance to ask all the questions posted in the chat and q amp a I would encourage our participants to email Professor Chen or Dr. Nicholas John and Brandon, we will have this recording publicly available and you can watch it and you can also email our participants their emails are public anyway, mostly, john I'm not sure about yours and ask, but another question here that people ask it's not very technical I want to make it a bit lighter is it Hi, I know Professor Chen traveled recently so maybe I like to jump into this equation, you know, in a past few months, a lot of media interviewed me, and always asking me let's save to fry. And it really depends on how you protect yourself, you know, the fry is not only in the cabin, you have a ground transportation, you will spend time in the terminal then of course in the cabin, etc. So I think in general, you know, so far there's a very few passengers there. I don't think it's a problem. The airline is definitely the measures and, for example, like a body in the plane procedure, then the seat arrangement, etc. And they also do the disinfection recently well. So if I wanted to fly, I will take the first flight in the morning because overnight they will clean it very well. But in the afternoon or overnight in the last flight, the property they don't clean that very well so you have to do a little bit of disinfection yourself by using why percent to especially why for those many people will touch like an unrested tray tables, etc. So, according to the International Association of a transport. International aviation transport association. They have a trace about 150,000 passengers and they are defined to case of transmission. So the risk is pretty low and the DOD study also somehow confirm that the chance of getting information is like a 99. No, they are 0.03%. So let's let risk it now. Thank you. Another question that is a good for a sort of summarizing. Epidemiologists make predictions there all over the media these days. The people think on this webinar that us engineers should work more closely with epidemiologists. What do you think how far or how close are we in doing this. Bill, maybe you'll take a first pass. Well, you know, I think we should work more closely. We've mostly been, you know, arguing with each other about airborne transmission because the engineers don't understand an infection mechanisms and the epidemiologists understand aerosol science. You know, I think there's a need to have communication that bridges the gap there and I'd like to see more of that in the future. That's certainly something we're trying to do within ASHRAE is to bring in people. Awesome. Yeah, we're not going to get a great solution if we don't do that. I think so, John, do you have an epidemiologist in your task force group? No, we don't. We should. I mean, so I mean, I think for at least for us at our company right it's a new thing right so for the most of us in the HVAC industry, thinking about, we're used to thinking about what we can do in general indoor air quality but specifically mitigating the risk of a specific virus is new and all learning and we're trying to grab as much data as we can and put it together and help our customers make decisions based. I mean, it's a learning process and, you know, just keep learning as we go. Great and Professor Chen, I'm curious, have you, a lot of models we see on the TV every day, I've seen a lot of your work in New York Times and other journals, etc. I think it's been approached by this system of system modelers, epidemiologists to include some of your work in their models, because I do think that these models would be wrong inside buildings, right, and we do need to include our expertise there in something more sophisticated and integrated. What do you think? I think it's very important. In the past, we did a worker with the epidemiologist on the SARS transmission, H1N1 influenza and we find this very beneficial. And although it's a little bit difficult to work in the beginning because we use a very different terminologies, you know, just to learn those terminologies that consume us a lot of time. But especially like in an airplane type of study, you can see airliners really, you know, get to the different type of people working together also medical doctors and epidemiologists, engineers, and also the policy makers. So let's say I think to solve this COVID-19 crisis, we need really to have a multi and interdisciplinary team to work together. I agree. I think it's a really complex problem and it would require some different way of thinking. We, there are a lot of good ideas that have been already discussed in this webinar. And I really hope that we can somehow engage practically in the design of resilient buildings in collaboration with doctors and epidemiologists and other disciplines because it hasn't happened so far. In the past, the way we design buildings, we have of course our own standards and codes, but we do take some inputs from other disciplines as inputs. There's not really a lot of back and forth and iteration and integration. So let's hope that this will happen this time to make buildings more safe and efficient as well as we move into the future. Sustainability is also another big target and occupant well being that we need to consider. I think we have passed the time. We do have plenty of questions that we weren't able to answer. We can keep going. I'm not sure if we're supposed to do that. Stephanie and Arvin, what do you think? Yeah, I would say, you know, this is what we might do is also an opportunity to have the Q&A's can also be answered post and be posted actually on the website as well. So if you're out of time, but it's your discretion if you want to take a few minutes to wrap this up. Okay, thank you very much. So maybe we'll take a few more questions. Dr. Tseng, there was a question about your plume, it's going up from the head. The plume, I apologize. The particles travel over the head, is there a thermal plume there? Yes, it is. Because the latest animation was done on a steel air with 24 degrees C environment and then the body's temperature I believe was 30 or 31 degrees C. So you do get the thermal plume induced by your body and therefore when you cough and then the warm air will go up and therefore go a little bit to the head level. Okay, and people are asking if you have a particle tracking in your models? Yes, we do have a particle tracking in the model. You can really just track every particle if you use Lagrangian model, but of course the computing cost is a little bit higher. And some other design related questions, if you could comment, I think for Professor Banflith on a proposal to operate a laboratory building with fume hoods, with hood susses open to increase ventilation, what are your thoughts there? Well, if it's a hood dominated laboratory, it could be troublesome for air balance if you open up the sashes, not to mention it's going to burn a huge amount of energy. And some of the lab people I've talked to have been concerned that if the hoods are dictating the flow patterns in the space, then you could get horizontal air currents that could actually increase risk for some and you'd have the highest concentrations of contaminants near the hoods themselves. So I think the lab people that we've talked with have been a little bit skeptical of that approach. They don't really want to mess around with their air balance very much and air cleaners might actually be a better strategy that maybe John has dealt with owners and has other things to add to that. I think, I mean, the hoods are there for very specific purpose, which is to maintain a face lost in the hood to keep the chemicals in the hood. And it's actually a pretty expensive thing to operate. I mean, there's a quite a bit of airflow in those hoods. So leaving them open all the time, really, really expensive from an energy perspective. I mean, they're designed to do it right systems are designed to have the makeup air, but it's a lot of makeup air and it's really expensive. So, so what we're finding and it kind of gets back to the original idea is that, you know, filtration right have a filter that's recirculated within the room does a pretty good job of removing particles from the air. And that is a much more cost effective than diluting the particles with fresh air from outside. So if you're going to do something, you know, an in room filtration unit is more cost effective way to go. Okay, thank you. And another question. That is interesting. Yeah, and so I will ask how accurately you think you can model that coughing and what velocities do you assume so since we talked about models and how we can trust them to make decisions. Actually, the coughing model we use is not a numerical model. We really have a good number of students, and we asked them to do coughing, real coughing. And we have a very good equipment to measure that. But of course, I mean the model, the flow rate, the velocity varies a great deal. So we usually average value for the model in the simulation. All right, great. And who and with regards to how we move forward, I would like to to make maybe some comments from our panelists. I think the world has responded to this pandemic really fast and I'm surprised to see all these solutions that we have for building design, installation, filters and etc. So and we have, it looks like we have already thought about some quick fixes and things to do, but I would like us to think a little bit more deep into the future. So what do you think we should change in the way we design or operate buildings to really make them more resilient and also sustainable and promote well being any thoughts that you would like to share as a closing remark for this webinar. Well, I see you smiling. You must have some good solutions. Sure, I think that's the important thing and I just touched on it earlier was that we're really trying to bring together resilience and sustainability and healthy buildings, all at the same time and so some of the things that we might need to do are going to And energy cost if we do them in the same way that we design buildings now so one of the things I see being important in the future is sensor development and demand control being applied much more granularly than it is now so not just on the scale of the whole building but really where the person is and trying to really deliver high quality indoor environment when there's somebody there to benefit from it and not conditioning huge amounts of space and buildings that we're all of that cost is wasted so you know the other thing is I think not huge increases in ventilation to generate but trying to really crack the problem of how do we use air cleaners for all the different types of contaminants to limit our outdoor air to something that's not going to have a really negative energy impact. Thank you, Brandon. I know you have been working on, in addition to your chemistry and physics of droplet size also on some low cost sensors for massive integration in environments indoor and outdoor. I think that some of these ideas that you have explored could be also beneficial in future buildings to be more resilient with regards to virus transmission. I believe so. So I think we now have a lot of low cost sensor technology available and integrating them into building on an operation makes a lot of sense. I think that, as Bill pointed to, you know, these sensors can be used for improved occupancy detection. I mean carbon dioxide is one thing, but we could be measuring other things as well. Of course and find particles of people. I think an obvious thing to add on to kind of a, you know, an air handler and building, you know, management system. And I think a lot of these low cost sensors are quite promising, but they need to be carefully evaluated. Some of them are not very accurate. We talked a lot about these submicron particles, especially they're producing respiratory activities. A lot of these lower cost optical particle sensors that people are starting to use on kind of a larger scale are not so sensitive to these smaller particles. So I think that, you know, using sensors that are carefully calibrated and and very strategies to improve their robustness would be important. But I think that just kind of general monitoring a variety of your pollutants would be better than just CO2 tracking, which has been the most conventional thing that we've been doing. So particles involved organic compounds ozone and a number of other species would be, I think, could just in general. Thank you very much and I think you could be a key person since you have this high quality equipment and also low cost sensor passion to sort of calibrate the sensors and develop this new technology. I think I would suggest the future also be more CFD modeling into the integration of virus transmission and also integration of, you know, how we respond to the pandemic, Professor Chen, how far do you think are we from this or how do you see this happening. Yeah, well, thank you very much. I think it's CFD just a tool, but I think the future buildings need to be designing in such a way we don't have to really find these quicker figures like what do we do now. Exactly. This disease will come and go every a few years. You know, it's just looking in the past 20 years, we have a SARS in 2003 and it's a one and one influenza in 2009. And now the 2020 right. I don't know what happens in the next next next decade. And to solve this type of problems we really needed to work together with the architects, the health scientists that just take a national ventilation is an example. We found that it's a very cost effective way to ventilate the building and lower the virus concentration inside the buildings. You look at the Purdue which building you could open the window. Well, at least the building that being there's no possibilities to open the window. So this type of thinking you know we needed to change. Let's also have a huge impact on the energy right on our mentality because the human behavior also will change a lot if you could operate the window occupant will be happier. So let the type of thing I think we needed to work together as a team. So no matter which area you are from so then we can make it a future building more resilient. Thank you. Thank you, Jan. I know john you already touched upon this in your talk if there is anything that you would like to add please go for it. I think the idea to think about is, in light of COVID we're asking more of our buildings right prior to COVID we standard indoor air quality metrics 62.1 is a good example of that. And most of our customers in order to mitigate the risk of COVID they're doing things above and beyond 62.1. And so that's probably going to consume more energy. But at the same time those customers also are coming to us and saying, we've made carbon reduction commitments to our investors and to our to our customers. And how do we do this additional work of mitigating infection risk in our buildings while still maintaining our commitments to reduce our carbon footprint. There's going to be a lot of work, not necessarily, there's going to be some work directly related to buildings right and infection risk reduction but also additional work and making buildings generally more efficient to make up for the additional energy associated with this new task that we've asked the building to do right which is was protect us from getting sick. So I think there's going to be work in in making the buildings efficient. Great. Thank you. In summary we have even more work to do. So I would like to close this panel we are already over time but there were a lot of interesting questions and many that we didn't have time to answer today so I would like to take this opportunity to warmly thank once again our excellent panelists. I appreciate you for your time I know you're all very busy doing many things this semester, I would like to thank our participants and of course, Arvin for the opportunity to organize this seminar and showcase the importance of buildings in the case of virus transmission and also demonstrate our passion about buildings and providing solutions. So with that, I would like to close this session and thank again everybody. Thank you. Enjoy the rest of your day. Bye.