Home AEC This is Air.

This is Air.

VITAL, PAE, Digifabshop, Overhead VAV
Image courtesy of VITAL/PAE
Josh Emig, Digifabshop

By Nash Hurley, Josh Emig and Marco Alves

Last month, before our outside air was filled with smoke, we set out to write an article about the fresh air systems in our buildings. We wanted to unpack how these fresh air systems typically work in order to provide better context in the evaluation of the latest coronavirus guidance. In our professional discussion, we quickly lapsed into our personal decisions. How will we return to work? Where will we send our kids to school? Despite decades of designing offices and classrooms, we didn’t know. We weren’t asking the most basic questions about the fresh air systems in our own office spaces or our kids’ schools. Why?

Rationally, we understand the value of fresh air. Research, like the Cognitive Function studies from T.H. Chan Harvard School of Public Health, shows with little doubt that quality of fresh air improves cognitive functioning, amplifies learning and benefits long term health. Long before COVID-19 made indoor air quality and aerosols part of the common parlance, this knowledge empowered us to advocate for investment in improved air filtration and increased outside air. It was the right discussion for our clients, so why not for us? Did it show a lack of trust in our school administrators or office facility staff? Did it seem disrespectful to them? Was it that we simply took fresh air for granted?

It reminded us of a story told by David Foster Wallace: “There are these two young fish swimming along and they happen to meet an older fish swimming the other way, who nods at them and says ‘Morning, boys. How’s the water?’ And the two young fish swim on for a bit, and then eventually one of them looks over at the other and goes ‘What the hell is water?’” In this now-famous commencement speech, Wallace goes on: “The real value of a real education […] has almost nothing to do with knowledge, and everything to do with simple awareness; awareness of what is so real and essential, so hidden in plain sight all around us, all the time, that we have to keep reminding ourselves over and over: ‘This is water.’ ‘This is water.’”

Today, there is another medium that is in plain sight and all around us. It is influencing not only our actions and thoughts but also our health.

This is air.

It is no surprise that most people are largely unaware of the fresh air systems in our buildings. For generations, engineers have perfected their design to be neither seen nor heard. Instead, these systems have been evaluated by their ability to deliver the elusive concept of “comfort.” Comfort is complex, being both culturally-dependent and activity-based. To define it, the engineers created societies and international standards to codify what it means to be comfortable; culminating in extensive technical manuals, such as The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Standard 55 Thermal Environmental Conditions for Human Occupancy (ASHRAE 55). In practice, the most common and approachable definition of comfortable space is much simpler and falls between the two interrelated dimensions, temperature and relative humidity – more precisely: 72°F and 50% RH. If you deliver a space with those two key characteristics, you can expect the overwhelming majority of people in that space to declare themselves as comfortable. Or to use the more engineering-appropriate terminology, we can predict a low percentage of people dissatisfied.

Today, fresh air systems need to deliver more than comfort — they need to deliver health. So, what is the difference between a fresh air system designed for comfort and one designed for health? 

To keep it simple, we are going to focus on office buildings, but this logic also translates to schools. Across the many types of mechanical systems, there are essentially two broad categories to consider when it comes to fresh air delivery: mechanical systems that deliver fresh air that is integral to the heating and conditioning of the space; and mechanical systems that deliver fresh air that is independent of heating and conditioning of the space.

Marco Alves, PAE

Into the category of independent systems falls many currently fashionable technologies like radiant slabs, passive chilled beams and natural ventilation. This category also captures antiquated building systems like old-school operable windows and high-capacity radiators that you are likely to find in a historic office building or on an older college campus. These systems are fashionable for a reason: by decoupling the conditioning of air from the delivery of fresh air, fresh air requirements can be met without as much energy to heat, cool or dehumidify. By their very nature, independent systems give you the opportunity to think about fresh air independently of comfort.

The alternative to independent systems is integrated systems. Integrated systems provide heating and conditioning as part of a mixture of filtered air recirculated from inside the building and fresh air from outside the building. The most common form of integrated systems is the Overhead Variable-Air-Volume (VAV), which also happens to be the most ubiquitous mechanical system for office buildings in the United States overall. There is a long list of reasons for its ubiquity, including the low cost of energy in the United States, ease of coordination and a large number of suppliers. For our conversation here, we will highlight the Overhead VAV’s ability to cost effectively deliver those two key conditions: 72°F and 50% RH. Therefore, it is no surprise it is the system of choice for the speculative office developer. The rub of the Overhead VAV, or any integrated system, is that when you bring in higher volumes of outside air, you also use more energy to heat and condition that air. As concerns over energy efficiency have increased, engineers are incentivized to design code minimum outside air with an integrated system – delivering comfort and minimizing energy.

So how much fresh air does an Overhead VAV typically deliver for comfort and what’s the right amount for health? For that answer, we could dive into another technical publication (ASHRAE 62) or we could just state a rough estimate based on our past project experience. Broadly speaking, 20% of the air supplied through an Overhead VAV system is likely to be outside air. The rest of the air is recirculated, filtered air from other parts of the building. This recirculated, filtered air is not necessarily worse than outside air, and in many urban areas or areas prone to wildfires, may actually be healthier. General rule of thumb is to expect an 80/20 split between recirculated air and outside air.

But when the health concern is internal, like with COVID 19, as opposed to external like wildfires, that 20% may no longer be enough. To give you a sense of how not enough, below is a truncated list of the Center for Disease Control recommendations to prevent the spread of COVID-19 in office buildings:

  • Increase circulation of outdoor air as much as possible by opening windows
  • Increase the percentage of outdoor air potentially as high as 100%
  • Increase air filtration to as high as possible 

In most modern office buildings, opening a window is not an option. Outdoor is invisible to us but our awareness of it has a role to play. As our offices and classrooms move from a world where we are supplying 20% outside air to a world with 100% outside air, we may need to adjust our expectations around comfort, system performance and perhaps even environmental impact. 

Fortunately, we have options. Exercising those options may require an informed discussion with you and your place of work or school. One of your biggest hurdles may be how to begin that discussion. It was for us. To that end, here are five conversation starters to get you off on the right foot:

  1. Fresh air systems understanding – does the building have an integrated mechanical system (Overhead VAV) or an independent heating/cooling system with separate ventilation (Radiator and Operable Windows)?
  2. Human expectations – is there a broader temperature and humidity range that our staff or other parents can accept in the office space or classroom? Are we ok with additional noise from mechanical systems – whistling ducts or fan noise as we push in more fresh air than the system was originally designed for?
  3. Status Quo – what is the current level of outside air supplied to our office building (20%-100%)?
  4. Ability to make improvements – for additional filtration do you have the option of taking on a small project of going from MERV 7 to MERV 13 or MERV 15 (better for COVID-19) or a more complex project like carbon filters or  UV filters)? If your system was designed for MERV 7 are you ok to depreciate your mechanical equipment more quickly as it works harder to push air through the tighter MERV 13 or MERV 15 filtration?
  5. Environmental Impact – Are you ok to use additional energy for increased outside air or additional filtration of recirculated air? Does this exceed any of our corporate or school district’s sustainability goals? Should your sustainability goals be amended to distinguish between energy used to deliver health and energy used to deliver comfort?

If 100% is not possible with the fresh air systems in our work space or schools, going up to 50% may actually be a better target since there is evidence that 50% provides most of the benefits of additional outside air. This will be more practical and achievable in humid climates and when the outdoor air is at hot cold extremes. In order to avoid an undesirable use of energy we may need to accept warmer, more humid conditions in the summer and colder, dryer workplace conditions in the winter. Or because dryer conditions may actually increase the likelihood of flu transmission we may be forced to use much more energy than the building was originally designed for in order to both deliver high quality air and the healthiest overall environment. In short, we may need to be much more flexible in our old expectations of comfort and energy in order to get healthier air.

Like all things in nature when you optimize around narrow criteria, you get lopsided results. To deliver comfort, we focused on control and we limited variables like wind through windows, noise from the mechanical system and the amount of outside air. As we shift from an office space that is defined by comfort to one that is defined by health, we need to open up the possibility of letting in more of these variables into our thinking, into our awareness. In particular, we need to thoughtfully consider the amount of fresh air that we are letting in and the amount of filtration that is occurring for the air that will be recirculated. The perfect should not be the enemy of the good here, as the good and slightly improved fresh air systems will get many more people most of the benefits. But before all that we need to increase our awareness of what is so real and essential. This is air.

Nash Hurley, VITAL

About the Authors

Nash and Josh each have 20 years of experience in user-centered design, product development and architecture. Nash is currently a Principal with VITAL and Josh is Director of Projects at Digifabshop. Marco is an Associate Principal with PAE and has 20 years experience in sustainable mechanical systems design; delivering a wide range of project types including commercial office, laboratories, schools and government facilities. Nash, Josh and Marco share an interest in low-energy, high performance buildings and have worked on a range of office projects together.