Remember the days of waiting for an oil change in a cramped room, accompanied by lingering smells of burnt popcorn and stale coffee? Those times may seem distant today, but concerns over indoor air quality (IAQ) have increased drastically in the wake of the COVID-19 pandemic. Free popcorn no longer guarantees repeat business. Customers want to feel safe from potential pathogens. More building owners draw inspiration from environments where cleanliness and occupant comfort are the highest priority.

There’s more to IAQ than limiting the spread of pathogens. Unpleasant odors, humidity imbalance, stale air and pressurization all indicate poor indoor air quality, affecting every building type and occupant. The good news is these items can be rectified by partnering with a qualified engineer and architectural team who can provide proper systems planning and coordinated design.

So, what can be done to ensure quality indoor air? In a perfect world, every space — even that auto shop’s showroom — would be designed beyond the same standards as a hospital’s operating suite, which, for the sake of this article, is the pinnacle of IAQ. However, we know that’s not practical or cost-effective. 

There are no one-size-fits-all solutions to IAQ. Instead, we must select and right-size the heating, ventilation and air-conditioning (HVAC) systems to match each project’s specific needs and goals. We must take an integrated approach to evaluating potential contaminants, considering not only the building’s indoor environment but also the building’s neighborhood and region.

IAQ is important

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines IAQ as “attributes of the respirable air inside a building (indoor climate), including gaseous composition, humidity, temperature and contaminants.” When mechanical engineers discuss IAQ, we think about the air quality within buildings and structures, particularly as it relates to the health and comfort of building occupants. 

Poor IAQ markers may not be as apparent as the scent of overcooked popcorn. When IAQ is not at the front and center of planning, design and operation, it may lead to occupant discomfort, lightheadedness and even respiratory infections. 

Just as important as air quality within buildings is air quality around buildings. Outdoor air quality can quickly diminish indoor air quality. Think about an idling delivery truck at a loading dock. An unexpected change in wind performance or a building renovation could reintroduce diesel fumes into the building. 

On a much larger scale, wildfires have the potential to send ash-laden smoke hundreds, if not thousands, of miles away for an unknown amount of time. These culprits challenge even the best building HVAC systems.

Code minimum (anybody can meet code)

I was fortunate to gain a valuable lesson learned early in my career: code is dirt. The plant operations lead on the renovation project I was working on expressed that to me and quickly followed it with their preference for solutions beyond the baseline. 

For healthcare applications, ASHRAE Standard 170 (2013) is commonly used as a starting point for different spaces. Many healthcare clients have added standards and best-practice methods to future-proof their buildings. Space use in healthcare applications changes due to many factors. What may have been an exam room during initial construction could have accommodations to become a procedure room down the road.

Outside of healthcare, ASHRAE Standard 62.1 provides minimum ventilation rates on a wider range of room types. 

Not all jurisdictions recognize these standards or have adopted the latest and greatest. For example, Wisconsin has not adopted the most current codes and standards. International Mechanical Code 2015 (IMC) is the baseline for the state with amendments. The challenge, as you may see, is understanding how much better than dirt the project budget will allow. How do we go beyond code and limit the spread of contaminants?

The common IAQ factors 

Let’s look at some best practices to optimize IAQ. I’ll explain what mechanical engineers think about when they begin a project. Though not exhaustive, these considerations provide a good foundation for healthier buildings of all kinds. 

1. Bringing in fresh outdoor air

Somebody who has been in our industry for a while has probably heard the catchy phrase: “The solution to pollution is dilution.” It sticks because it’s true: poor IAQ is somewhat synonymous with pollution.

One way to increase IAQ is to provide more filtered outdoor air. Continuing with our car dealership example, the design is based upon a defined people load in spaces for outdoor air. The IMC requires each person in a space to have a minimum of 5 cubic feet/minute (cfm) of outdoor air. 

A 100-square-foot finance office with a 10-foot ceiling may be designed for three people or 15 cfm of outdoor air. On the healthcare side, if this same volume of space were an operating room, the minimum required would be 66 cfm. Most healthcare spaces following ASHRAE 170 include outdoor air requirements in air changes per hour (ACHR). This value is how often the air in a room will be completely removed and replaced with fresh air every hour. An operating room has four ACHRs of fresh outdoor air.

If we zoom further out system-wide, it is not uncommon to see healthcare facilities approach 100% outdoor air handling units due to high outdoor air rates. Typical commercial spaces like our car dealership see 15% to 20% outdoor air.

What if the air outside is not clean? 

The human nose is sensitive, especially to diesel fumes. That’s hazardous because diesel exhaust contains particles and gases that can irritate the respiratory system and worsen existing health conditions, notes ScienceDaily (https://bit.ly/3VNF16p). One study in Allergy, Asthma & Clinical Immunology found that diesel emissions may mimic allergic asthma and rhinitis, causing symptoms such as coughing, wheezing and nasal blockage (https://bit.ly/3DkHG0N).

Let’s return to the example of the idling vehicle at a loading dock. Picture and compare a parts delivery truck at the auto shop and an ambulance at a clinic. It should come as no surprise that the auto shop has less stringent exhaust requirements for outdoor intake distances. The IMC requires a minimum of 10 feet to 0 inches of separation. An ambulance garage at a clinic, following ASHRAE 170, requires 25 feet to 0 inches between the exhaust and outdoor air intake. 

The outdoor air intake should be as far from the exhaust-producing source as possible to reduce the risk of reintroducing diesel fumes into the supply airstream. Understandably, at any distance, there is potential for fumes to be reintroduced further into the building due to an interior pressure imbalance or exterior environmental challenges.

2. Filtering outdoor air

With the cleanliness of outdoor air in flux, filtration is necessary. MERV 8 filters are what is typically seen on baseline commercial applications. ASHRAE defines MERV as the minimum efficiency reporting value; how effectively the filter captures airborne particles of a particular size.

MERV 8, for our purposes, is the lowest acceptable for commercial applications. A surgery suite may require MERV 14 or higher filtration. The higher the number, the more densely packed the filter media is to capture contaminants. 

It may not be as simple as replacing a MERV 8 filter for a MERV 14 from a baseline commercial air handling unit for a few reasons. Prior to upgrading, it is of the utmost importance to confirm the air-handling unit can handle the additional static of the improved filter density. Failure to do so could cause the unit fans to fail prematurely. Furthermore, MERV 14 filters cost more and must be replaced more often than MERV 8 due to their ability to capture finer particles. 

All hope is not lost if the air-handling equipment cannot accept a MERV 14 filter. A proven technology for higher air cleanliness is the introduction of UV lights into the air-handling unit. Again, this should be discussed with the mechanical engineer as some economy-grade units may not include UV-safe parts inside.

UV lights, or ultraviolet lights, attack and break down the cellular structure of organic compounds, including odor-causing compounds, bacteria and mold. After ensuring the internals of the air-handling equipment are UV-resistant, an added feature of UV lights is that they improve the lifespan of the air-handling equipment by keeping the internal components clean of organic matter.

3. Stale, dirty air 

Let’s say a building reeks of that obnoxious burnt popcorn smell I mentioned earlier. We’re smelling the popcorn because, typically, the air gets returned to the air distribution device and blown back throughout the entire building, not only the room with the popcorn machine. 

We can eliminate the offending odor via the building’s general exhaust. For nonlife-threatening contaminants such as microwaved popcorn smell, we can tie into the building’s general exhaust system and discharge it outside. A standard exhaust grille in the ceiling near the microwave will pull the odorous air away from the main return system and exceed the code minimum. 

In extreme cases, such as a hospital isolation room with highly infectious airborne pathogens, we need more than tying into a general exhaust system. Per ASHRAE 170, these spaces require a dedicated exhaust system with a special exhaust fan capable of discharging contaminated air high into the atmosphere. These exhaust fans have a high stack with a nozzle and want to be a minimum of 10 feet above the highest roofline. 

Under no circumstances would we want to do the bare minimum and put an outdoor intake 25 feet away. This space also has pressure requirements for adjacent spaces to ensure the room truly isolates contaminants from the rest of the facility and the outdoor environment. 

Isolation rooms have a large impact on energy use. We need to provide tempered, clean, filtered supply air to make up the exhaust. An isolation room requires 12 ACHR of exhaust, equating to 200 cfm in our earlier 10-foot by 10-foot by 10-foot space. These spaces have pressure monitors at the entry door with visual and audible alarms to protect staff from exposure. These spaces must be coordinated with the architect to ensure tight construction without leaks. Additional air may be needed for pressurization.

4. Pressurization (clean to dirty spaces)

Depending on the contents of a space, mechanical engineers will design for positive or negative pressure. Spaces are positively pressurized to keep contaminants out. Reversely, where contaminants are present, the space will be negatively pressurized to contain the hazard.

In healthcare facilities, the goal is to keep the clean spaces clean by introducing pressure relationships. The cleanest space, an operating room, will be positively pressured to adjacent spaces. The operating room will have pressure monitors at the doors to alert if the space loses positive pressure. The entire operating suite is positively pressured to adjacent suites, and so on, until we reach a soiled room that is negatively pressured and exhausted from the building.

These pressure relationships are found beyond healthcare applications. For example, restrooms are exhausted; in other words, air flows in from adjacent spaces as they are negatively pressured. We do not want to put pressure monitors at the doors of restrooms, but a test and balance contractor will adjust the airflow to and from the space to ensure more air is exhausted than supplied or transferred.

Pressurization is vital because, when done correctly, it helps control the infiltration of outdoor air, which can carry pollutants and moisture. It also ensures consistent temperature and humidity levels, contributing to occupant comfort. Maintaining the correct pressure differential is crucial for infection control in critical environments, such as hospitals.

5. Humidification

Controlling humidity in buildings is about more than occupant comfort. It concerns public health and the life span of the building components. High humidity can promote mold growth and cause ducts to sweat, ruining ceilings from water damage or creating slipping hazards if the water drips to the floor. 

Low humidity can cause damage to the building’s amenities, such as sensitive artwork. Extreme cases of low humidity can cause sparks in operating rooms or static electricity in sensitive environments such as clean rooms in laboratories and manufacturing facilities.

In Wisconsin, it is common to see added humidification systems for operating suites. During winter months, the outside air is frigid and dry. An operating room will include a humidistat to monitor relative humidity to maintain AHRAE 170-recommended values.

For non-healthcare spaces, having additional humidification systems in the air-handling equipment is less common. To exceed baseline, planning for an added humidification system for an office space will increase occupant comfort during the dry winter months.

IAQ and a project’s timeline

As with any project, the best time to start discussing IAQ is at the beginning. Early discussions will give the design team enough time to investigate and present options, balancing cost and effectiveness.

While each project budgets for IAQ differently, we know it becomes increasingly difficult to implement IAQ solutions later in the project phases. 

For example, after the rooftop unit has been ordered, it may be impossible to increase filtration because of static pressure increases on filter loading. However, if the decision to increase filtration was made during design, the rooftop unit could be selected with a high static fan option to overcome the more efficient filter.

Everybody is responsible

I was inspired by a poem taped above the sinks in my middle school art class, “Who’s Job is it Anyway?” accredited to Charles R. Swindoll:

“This is a story about four people named Everybody, Somebody, Anybody and Nobody. There was an important job to do, and Everybody was asked to do it. Everybody was sure Somebody would do it. Anybody could have done it, but Nobody did it. Somebody got angry because it was Everybody’s job. Everybody thought Anybody would do it, but Nobody realized that Everybody wouldn’t do it. It ended up that Everybody blamed Somebody when Nobody did what Anybody could have done.”

The main Somebody leading the way on IAQ is the mechanical engineer. Architects also play a large and direct role in successful IAQ. They control how tight the building envelope will be, the shape and orientation of the building, the plenum space for ductwork, and the number and type of windows. 

Plumbing engineers join the IAQ discussion with waterborne infections such as Legionella. While it grows in stagnant water, Legionella is transmitted through the air. Electrical engineers must coordinate the backup generator type and location. While primarily used in emergencies, backup generators burning natural gas or diesel must be tested regularly. This dirty exhaust parallels an idling truck at a loading dock.

Everybody shares the responsibility for creating healthier buildings, and Anybody can ask questions about IAQ. It’s important to recognize that while the design team may not be the same individuals occupying the building after construction, engaging in the IAQ conversation is crucial. Nobody is excluded from the impact of IAQ. 

Everyone can breathe easier by working together

Achieving good IAQ requires more than meeting basic standards; it involves striving for excellence in every type of building. Whether it’s a car dealership or an operating suite, the key principles of IAQ remain the same: provide clean, filtered air, maintain appropriate humidity levels and ensure effective pressurization. 

By adopting an integrated approach considering both indoor and outdoor environments, we can create comfortable spaces that are also safe and healthy for occupants.

Throughout the project, it is important to remember that Somebody will be working or living in the buildings we have designed systems. Would you want your workplace or home to be uncomfortable? 

Mike P. Krueger, PE, is a senior HVAC engineer at Eppstein Uhen Architects (EUA). He has been designing HVAC systems for more than 16 years in various commercial building types, primarily specializing in the healthcare industry.