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Mission: HVAC 2016 – Challenge Three: Improve Indoor Air Quality

by | Jun 28, 2016 | Mission HVAC

They say we spend 90 percent of our day indoors – whether in our homes, at school, at work…

So, it’s critical we work to control the amount of indoor pollution we come into contact with. Things like pollen, dust and dander, dirt, bacteria, viruses, mold and more can negatively impact the indoor air quality (IAQ) of the spaces we frequent.

Given its job to bring air in and either heat it or cool it, our HVAC system is not immune to contaminants. So, for this Mission, we challenged the students to freshen up on IAQ.

Derick: Indoor Air Quality is Important

90 percent of Americans spend most of their time inside their homes.

Why does that matter?

Because The U.S. Environmental Protection Agency (EPA) studied human exposure to air pollutants and indicated that indoor levels of pollutants may be two to five times — and occasionally more than 100 times — higher than outdoor levels.

Those are some big numbers and important due to the fact that we breathe that in on a daily basis. So, what can improve overall IAQ?

A couple of important systems can help. One being an ultra violet light that attaches above or to the air conditioning coil. This UV light helps by deactivating airborne and surface contaminants like mold, bacteria and viruses. It also neutralizes household odor.

Another key system to improve IAQ is an electronic air cleaner. This device is attached to the return portion of the duct system in place of where the filter would go. It captures up to 99 percent of airborne particles passing through the system. Though there are many variations of electronic air cleaners, they all have the same purpose – and that’s to greatly improve IAQ.

These helpful IAQ devices are just a few compared to the wide variety of systems that can improve the air you breathe.

Jacob: Ridding Common Pollutants

Recent studies have shown that indoor air is becoming more polluted instead of less.  This situation is generally attributed to two issues:  chemical products used in building materials and the increased quality, or “tightness,” of the modern building envelope, which traps these chemicals and organic compounds in the building. Additionally, it is estimated that most people spend up to 90% of their time inside, with individuals most susceptible to pollutants (the very young, elderly and chronically ill) spending even more.

The most common pollutants are radon, biological contaminants, mold and pollutants from the combustion of oil, gas and wood fired appliances.

  • Radon is a colorless, odorless and radioactive gas and has been found to cause lung cancer. New construction is required to have a vent stack specifically for radon installed from beneath the slab or crawlspace up through the roof.  This results in existing homes built before the current code requirements being the most likely to have problems with radon.  Fortunately, home sampling kits are available where a sample is taken and mailed to a lab for results or certified radon technicians can check a home and make recommendations.
  • Biological contaminants consist of dust mites, mold, mildew, bacteria and viruses.  Dust mites are too small to see, but are commonly found in bedding, carpets and other fabrics.  The main issue with dust mites is that they contribute to a constant source of dust as they decompose, which can be countered with a better filtration system and/or more frequent changes of the air filters.  Mold and mildew can be countered with a dehumidifier.  We recently installed a whole house dehumidifier in the basement of a customers’ vacation home.  “Whole home” is a bit of a misnomer as it was only hooked into the basement system (they had a main level system and a basement system).  I mentioned this to a coworker and he explained that in our humid climate in western North Carolina, a basement generally has more moisture, and therefore mold, problems.  The main level system could keep up with removing condensation through a correctly sized heat pump.  Correct sizing of the unit is extremely important as an oversized unit can cool the space quickly without sufficient run time to condense and remove indoor moisture.
  • The other biological contaminants of bacteria and viruses can be eliminated with a UV light mounted in the duct work.  On a recent maintenance visit, I saw one that had burned out and needed to be replaced.  Fortunately the date the light was installed was written on the outside of the duct work and was covered under warranty.  The person training me explained that the bulb was probably touched with a bare hand causing it to burn out prematurely, similar to a halogen bulb.  He also showed me how to open the packaging in order to preserve the materials with the explanation being that the bulb itself contains chemicals.  The bulb we replaced was located in the supply side of the duct work close to the indoor coil as the moist environment is most likely to support the growth of biological contaminants.
  • Mold prevention from the beginning is by far the best way to go in spite of the higher initial cost.  Once mold is established, it is not as simple as cleaning off what is visible.  Depending on the number of square feet affected, someone capable of removing the contaminated materials will need to have a minimum of OSHA certified training all the way up to hazardous materials training and high quality personal protective equipment.  When we have had service calls or equipment change out jobs at homes with crawl spaces, I always mention to the homeowner if there is excessive moisture present.  While I don’t pass myself off as some sort of expert, I may suggest that they may want to have someone else take a look at their situation.  It may be as simple as knowing when to open and close foundation vents or as expensive as grading a slope away from the structure.  Again, I don’t make these suggestions, just let the customer know that they may have a bigger issue than I am capable of determining.
  • Pollutants from combustion are the last source of contaminants I would like to mention, with carbon monoxide being the most dangerous.  Carbon monoxide is a poisonous, odorless, lighter-than-air gas produced by incomplete combustion in an oil or gas fired appliance and can only be detected by a specific test device.  Carbon monoxide levels are measured in parts per million (ppm) and can be fatal with levels as low as 400 ppm.  On a better note, reasonably priced detectors similar to a smoke detector can be purchased at hardware and home improvement stores.  Another detrimental effect of the tightness of modern construction is a higher possibility of carbon monoxide in a house.  For example, if the negative pressure produced by a large stove hood is too great, it can actually pull a backdraft from a chimney or the exhaust stack of a gas furnace.  Basically it is creating a vacuum that is filled by exhaust air.

A solution to just about all of these problems can be found in an energy recovery ventilator.  These have been common in Canada for quite a long time, but have only recently become known in our area.  A friend from Alberta, Canada, told me that exterior walls there have been required to be built with a minimum of 2×6 lumber on the exterior walls since the late 1970’s to take advantage of the greater R-value.  Similarly, other aspects of their building codes have been adjusted to create much tighter construction and they have had to find ways to maintain ventilation.  In such extreme climates, the heat recovery ventilator was the first heat exchanger on the market.  This machine would use a desiccant-coated heat transfer disc to remove heat from the inside air as it is expelled to the outside, and then that heat would be exchanged back to the outside air as it is drawn in.  This air exchange is set on a timer to occur a specified amount of times in a 24-hour period.  The newer generation of energy recovery ventilators works both ways.  In winter, the disc operates as described above.  However, there is another set of inlets and outlets for summer operation – these remove heat and moisture from outside air and transfer it to the exhausting indoor air.  I believe that this device is the best option for moisture control and the introduction of fresh air into the building and will only become more popular as the benefits are realized by the public.



“Why Indoor Air Quality Is Important.” EPA. Environmental Protection Agency. Web. 02 June 2016. https://www.epa.gov/iaq-schools/why-indoor-air-quality-important-schools

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