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Ventilation, Filtration, and Humidity Control: The Holy Trinity of IAQ
At the time of the publication of this article, COVID-19 (coronavirus) is spreading across the world at an alarming rate, and many people have self-quarantined to help slow or stop the spread of the virus. These precautionary measures are prudent and responsible. However, with the increased amount of time people spend inside their homes, there is a hidden factor to be aware of, which many people won’t think about. The prolonged occupancy of homes with increased cooking, bathing, and cleaning will significantly impact these homes' indoor air/environmental quality. An issue like this may not be measurable, but it is inevitable. In a time when many technicians, companies, and manufacturers will use this health crisis as a way to promote the sale of IAQ products in ways that can only be judged as unethical, it is imperative for the honest and curious technician to understand how to do their part in educating customers and keeping everyone healthy.
This article will avoid talking about specific types of boxed devices out there that “purify” the air because that’s a topic for another day. The focus here is on the three main processes available to technicians and homeowners to improve indoor environmental conditions: ventilation, filtration, and humidity control. Taking these one-by-one, technicians should have a thorough crash-course understanding of each and its importance to indoor air quality (IAQ).
The first step in understanding a healthy indoor environment is to recognize the villains one must fight against in order to keep an environment healthy. Particulate matter (PM), volatile organic compounds (VOCs), humidity (high or low), carbon monoxide (CO), carbon dioxide (CO2), ozone (O3), etc., are just a few. These are the elements that tend to concentrate in tight indoor environments. Each of the “Holy Trinity of IAQ” is designed to deal with these undesirables in their own dedicated way.
Everyone should know what a bath fan is. If you don’t have a bath fan, you probably live in a house that hasn't been updated since the 1970s, and you likely have other decor issues to deal with as well. Bath fans are the most common mechanical ventilation in homes today. They are a form of negative pressure ventilation. As the fan pulls air from the room and expels it (hopefully not in your attic), this creates negative pressure on the building envelope. Air from outside is pulled in through the cracks and crevices around your windows, door frames, attics, and through Jerry’s mouse hole (which everyone has… right?). This type of ventilation is by far one of the least desirable because you have zero control over the quality of the air you are bringing into the home. The air could be high in humidity and temperature, or it could be passing through layers of blown-in insulation inside your attic, neither of which is ideal. Air from these places isn't really fresh.
The general consensus is that positive or balanced pressure ventilation is best. Examples of positive pressure ventilation include make-up air (MUA), dedicated outdoor air systems (DOAS), and the use of a scuttle (a small duct run from outdoor air into the return ductwork for HVAC systems). Balanced pressure ventilation is accomplished through mechanical equipment like energy recovery ventilators (ERV), heat recovery ventilators (HRV), and conditioning energy recovery ventilators (CERV). Each of these technologies has its advantages and ideal applications. The reason positive/balanced ventilation is desirable is for its ability to control the fresh air. If you can control the air you breathe, you can keep it “fresh.” For all of these options, there are applications for which they can be used that actually improve upon the quality of the air entering the space. But why do we care about ventilation? What’s so important about it?
Houses used to be built loosely. This isn’t to say they were built poorly, but houses used to be loose enough to allow for tons of natural ventilation. The codes and standards have evolved, and we now construct assemblies more airtight than in the past. This is why the EPA has published that indoor environments are often 2-5 times higher concentrations of air pollutants than outdoor levels—they can reach upwards of 100 times worse! This is because as people bathe, clean, and cook, VOC concentrations, particulate matter, and humidity levels increase dramatically. People thought bath fans were for bathroom odors, but really that’s just a nice side effect. They are for removing water vapor during and after showers/baths. Ventilation is utilized to dilute VOCs, CO, CO2, and other chemicals in order to maintain a comfortable indoor environment. I know of people who grew up watching their mother open all the windows for a couple of hours a week to “flush” the house. Mechanical ventilation is just like that except more controllable and technologically advanced.
Particulate matter is another indoor environment characteristic that can cause a variety of health concerns. Particulate matter is categorized by its size in diameter, which is measured in micrometers (or microns). There's a lot of buzz around PM 2.5, which is particulate matter with a diameter of 2.5 microns; that is due to PM 2.5’s ability to do major damage to the human respiratory system. To give you an idea of the size of PM 2.5, the EPA has published that PM 10 is considered inhalable. PM 2.5 is 75% smaller than that! This means PM 2.5 tends to stay in the air stream longer than larger, denser particles. However, PM 2.5 is not the smallest particulate matter that can potentially do harm. PMs 1 and 0.5 are also in the air, and they can easily make their way to our lungs and bloodstream. In order to combat these airborne particles, it is important to filter the air with a high-quality air filter. There are filters designed to trap PM 2.5 and smaller (MERV 11 up to HEPA), and they are a critical component of any air distribution system. The third edition (2018) of the EPA Technical Summary of Residential Air Cleaners states that a MERV 13 is recommended for every HVAC system or as high a MERV rating as the system will allow.
It is important to note that particulate matter does not refer to just dust. Particulate matter can be made up of pollen, viruses, bacteria, fibers, fungal spores, vehicle exhaust, etc. This fact clarifies that filtration is important for the HVAC system and the incoming air to any mechanical ventilation system. Humans are constantly submerged in this fluid called air. We must give more thought to the quality of the air we breathe.
The final head of our three-headed IAQ dragon is humidity control. This can refer to either high or low humidity levels. Either extreme is unhealthy and can create an environment prime for health risks. On the one hand, high humidity can cause respiratory issues, encourage dust mite life, allow viruses and bacteria to increase, allow VOCs to become airborne, allow increased chemical reactions, and allow microbiological growth to take place. On the other hand, low humidity levels can also cause respiratory issues, irritate mucous membranes, allow viruses and bacteria to increase, and allow for ozone production. The happy medium is the generally accepted ideal humidity index, which falls between 35%-60% relative humidity.
To control humidity indoors, a technician must be aware of their climate zone and whether they must work to increase or decrease humidity levels indoors in relation to outside levels. For arid climates, humidification is necessary, and options such as higher airflows and in-duct steam humidifiers are great solutions. For humid climates, running lower airflows and adding mechanical supplemental dehumidification is ideal. Some dehumidification systems allow for ventilation as an option, and they include a high MERV filter to cover all the bases. This option is an ideal solution for certain applications. Humidity must be controlled in an occupied space for that space to be comfortable. People are much more sensitive to humidity than temperature.
As we look at these three paths to creating and maintaining healthy air inside a home, it is important to realize these are Indoor Air Quality (IAQ) solutions. To create and maintain a fully comfortable indoor environment, we would need to address other issues, such as air leaks, insulation, and load matching. However, in addressing the current issues with air quality in homes, this “Holy Trinity” is all any technician needs to exert energy into to help keep occupant air clean. There is a mindset that humans are never more intimate with their surroundings than when they inhale the air into their bodies. Technicians must take action to educate consumers and recommend the most effective solutions for IAQ improvement.
Many companies and manufacturers have also been using this health crisis to promote the sales of popular air “purifiers” that use chemistry to “clean” the air in lieu of ventilation, humidity control, and filtration. We will discuss those technologies in a later article, but the most important takeaway at this juncture is how important it is to maintain control over the humidity, the outdoor air coming into the space, and the concentration of particulate matter in the air stream. The methods of dealing with the issues mentioned in this article are the only methods that have been time and volume tested over decades, and they have standards in place to help ensure their effectiveness on IAQ.
So, what do technicians do right now? Many homeowners may not want to spend the money on advanced in-duct filtration, mechanical ventilation, and humidity control during this time of uncertainty. Joe Medosch from HaywardScore.com has shared a very ingenious and affordable solution for many people to filter indoor air effectively.
This DIY method is a great way to help encourage homeowners to remain healthy as they spend more time inside their homes. This “box fan filter” may also make it more viable for sensitive people to open their windows and doors for longer periods of time during pollen season; this enhances air circulation inside and adds filtration throughout the home. Another recommendation for homeowners is to utilize the bath fans and kitchen exhaust as a way of ventilation. ALWAYS run a bath fan during bathing activity, and continue to run it 10-15 minutes afterward to prevent as much water vapor as possible from remaining inside the home. Portable dehumidifiers and humidifiers are also available.
Another recommendation for every technician, business, and homeowner is the use of IAQ monitors throughout the home. Real-time monitoring/translation of data over time allows people to see the effects of their activities on IAQ. It is a great way for technicians and businesses to track the effectiveness of their work over time. Without measurements and testing, you can only guess!
As we work together to combat the spread of viruses in our communities and worldwide, the HVAC/R industry has a large opportunity to help educate customers on creating and maintaining a healthy indoor environment. We must take care to avoid fear-mongering and sales tactics geared toward the exploitation of people’s vulnerability and miseducation. Practice integrity, do your research, and always implement industry best practices.
P.S. – Neil Comparetto wrote a great little article of four considerations for IAQ, and you can read it HERE.