|26 Jul 2022|
|Advancing Architecture and Design|
As we learned more about how Covid-19 works by transmitting the virus through the air, from one person to another, we learned to wear face masks, avoid direct contact with potentially contaminated surfaces (although those concerns have abated as we follow the science), wash our hands frequently, and seek more fresh air movement in our spaces. That last one is the hardest, especially during winter months. In this article we will discuss these issues, methods that can be used to improve indoor air, and a look to the future as we help make life inside healthier by design and engineering.
Schoolrooms have been studied using computerized 3D analysis of air movement. Various techniques for opening windows and adding fans were evaluated. Worst case scenarios happen in which one student that is sick with the virus, sitting in the classroom, and spreading particles in the air as he/she breathes. Is it best to locate that student in the back, or the front? Is it best to place an exhaust fan in the window opening, or an intake fan? Should the fan be set high in the room or low? Should it run at high speed or low speed? These studies are explained and illustrated in an interactive New York Times article by JB&B Engineers. (See Figure 1 from www.nytimes.com/interactive/2021/02/26/science/reopen-schools-safety-ventilation.html)
Other modest approaches have been researched, proposed and used in classrooms and school rooms that may be applicable in other commercial areas. Using simple “box air filters” that utilize a box fan with added MERV 13 filters is shown to be somewhat effective for cleaning pathogens from the air. The fluid dynamics in this case study show the effectiveness of several locations for air filters with a single heating and cooling unit ventilator shown against the wall. Case A1 appears to be the most effective location for the filter but that only applies when the teacher/speaker may be broadcasting the virus. The authors suggest that Case 2, placing the air filter next to the unit ventilator is most likely to be effective when the broadcast can start from any place in the room. Providing additional box fan filters further help the process and add little cost. (See Figures 2 and 3 from [email protected] https://doi.org/10.1063/5.0050058 11 May 2021 and “Airborne transmission of COVID-19 and mitigation using box fan air cleaners… [email protected]; “Estimating COVID-19 exposure in a classroom setting…” [email protected])
In September 2021, ASHRAE issued its “Guidance for Re-opening Buildings” (See Figure 4 from ASHRAE) which includes new guidelines to:
• “deliver non-infectious air to the breathing zone as efficiently as possible
• and avoid systems that cause strong air currents…
• Evaluate outdoor air ventilation…
• combine the effects of outdoor air, filtration, and air cleaners…
• Focus on removing bio-burden pre- or post-occupancy.
• Flush space or building for a time to achieve three air changes of outdoor air…”
Office workplaces have been in a process of transformation over recent decades. As we may recall, in the past office floors were lined with private spaces along the window walls and open offices in the center, often wrapped about the central core of elevators, bathrooms and support spaces. The offices were usually for higher ranked employees and the interior open spaces for general staff. In theory the perimeter offices could have operable windows, allowing those occupants to choose to open and close windows for “fresh air” from the outside. That option became rarer as office buildings have fixed glazing, no actual “windows”. The interior work areas had no option. The recent Comcast headquarters building uses a different configuration with the circulation core to one side, a large work area with access to the window walls on three sides, and private offices on the interior. This arrangement should allow more universal access to view, daylight and potentially to outside fresh air. (See floor plan See Figure 5, from www.pinterest.com/norman-foster)
Generally, for new office buildings, outside or fresh air had to be supplied by mechanical systems providing ventilation throughout the interior space with air pulled in from above, usually on the roof. These systems run ductwork, usually above a suspended acoustic ceiling, or in exposed ductwork hung from a floor structure. The source of the outside air must be carefully planned to avoid being close to exhaust systems on the roof, otherwise the fresh air is not so fresh. The amount of air coming in usually balances with the amount of exhaust air that is ducted out of the space, otherwise there is uncomfortable air pressure in the rooms. Seems like a good solution, right?
Problems arise during very cold winter days and very hot and humid days when the ventilation system can be pulling in air that is uncomfortable to the occupants. The heating or cooling system needs to run at a higher rate and energy use increases, efficiency drops, and utility costs rise. So, building managers might close off some outside air intakes or drastically reduce the volume of air brought in. The result was very little fresh air for the people in the spaces. Not a good solution.
Enter the concept of Heat Recovery or Energy Recovery Ventilation (ERV). Think of this as a heat exchange wheel or chamber where the interior air that is being exhausted from the space passed next to the outside air that is being pulled in. As they pass through the chamber with a separating filter system, the outside (cold) air picks up a bit of the warmth of the interior exhaust air as it leaves the chamber. This is a surprisingly effective way to capture waste heat (or coolness in the summer) and pre-treat the fresh air coming into the people places. It also significantly reduces the amount of energy needed to heat (or cool) the fresh air, improves efficiency and reduces utility costs. And using more outside air with a good number of air changes per hour inside the workspace may reduce the effect of contagious virus transmission, although not eliminate it completely. The Building Sciences Corporation published a key research document in 2013 showing various ways to improve ventilation within a whole-house context, recommending the HRV. (See Figure 6 from FanTech.com and Figure 7, from Info-611: Balanced Ventilation Systems (HRVs and ERVs) Building Science Corp, September 2013)
This type of system is not used in all office buildings. It is not required by all building codes although it is becoming more common in newer structures. These systems do “add cost” to the mechanical work when first installed but the savings in energy occur indefinitely, compared to using only direct outside air without an ERV. With these systems in operation the spaces are generally healthier for the tenants.
Similar ERV type systems are being employed in residential construction. These were first demonstrated with Passive House Institute single-family houses in which a small ERV is running continuously to provide fresh air year-round inside the house. They are now being used in other types of housing at all scales. Generally, we think of having the option to open windows for fresh air in any house, apartment, or bedroom, but is that really the case? We rarely open a window in February, or in July, and if we do it is only briefly.
In 2020, MaGrann Associates issued a “Position Paper on Whole House Ventilation” with insights into how to achieve improved outdoor air ventilation, maintain good energy efficiency, and provide a healthier indoor environment. They note a “good” method is using exhaust-only ventilation with a bathroom fan that runs continuously, and a passive make-up air path, perhaps with a small duct from the outside wall, or using a “trickle vent” at the window. In Europe the “trickle vents” are more common as part of a window assembly and are required in some jurisdictions. These vents can be installed in the top or bottom of windows to allow very small amounts of outside air into the room. Coupled with a good exhaust fan, actual fresh air can be moved through the space without a major hit on the heating system. (See Figure 8, from Reynaers Ventalis)
Their “better” approach is to use supply-only ventilation with a dedicated in-line fan, or balanced ventilation where the intake and exhaust both run at the same air volume. Their “best” method is using an ERV for the balanced ventilation by bringing in pre-conditioned outside air year-round, improving energy savings and preventing condensation in the exterior wall assembly.
There are options for using smaller ERV units placed in each apartment, or for a small group of apartments, or even for portions of an office space. These units can have a direct, ducted connection to the outside wall with small louvers, to bring in outside air and treat it with exhaust air, at modest initial cost. If properly sized and running 24/7, they can provide a modest amount of air movement with fresh air, to reduce the contamination from the virus and provide comfort. It is also possible that running these systems would reduce the need to turn on the larger heating and cooling systems, if people feel comfortable enough and want to save operating costs. Running a small ERV for moving air within a space is much more efficient than running a large air handling unit or even a through wall air conditioner when cooling is not actually required for human comfort.
Perhaps as we plan our lives around the idea of possible pandemics in the future, or just plan for improved interior space comfort, the use of energy recovery systems, better outside air ventilation, and coordinated efforts at efficiency will become more commonplace in our planning, design and construction, making our places better for our people. As we continue to learn from science and from our recent experiences with indoor and outdoor spaces, we can apply these lessons to our architecture.
Sherman Aronson AIA LEED BD+C is a Senior Associate at BLT Architects - A Perkins Eastman Studio, Co-Chair of BLTa Green Design Committee, Chair of BLTa Quality Assurance Team, amd member of AIA Philadelphia COTE.
Note: The writer is an Architect, not an Engineer or Scientist. The article is intended as a general review for other Architects to inspire concern for our interior human environments.
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