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IAQ (Indoor Air Quality) Irritants

Air-flow Dynamics, - the key to pollution is dilution


We are Oxygen consumers. While air normally contains about 21% O2, we only use about 4% of that amount, although we need the 21% in order for our lungs to extract the necessary amount. As we consume Oxygen, we replace it with CO2 (Carbon Dioxide). If the space we are in is confined or sealed, then eventually the Oxygen supply will run out. The amount of Oxygen we exhale (about 17%) is insufficient to remain conscious, so whether we like it or not, we need an ongoing source of air that comes far from where we are. If we are in a motor vehicle with the windows closed, and the ventilation turned off, we will quickly note the amount of water vapor we also exhale begin to fog the windows, and gradually feel discomfort due to the reduction of Oxygen. While a home is a much bigger air space, the same thing can happen therein. If we are sitting reading a book, and there is no ventilation, we will easily begin to feel stuffy. A gentle breeze from a fan will dilute the locally high concentration of CO2 into a much larger air space, and simultaneously increase the local depletion of Oxygen with that from the same larger air space. More noticeable is the discomfort when a group of people are sitting at a table, in a room for more than a few minutes. It will quickly get "stuffy," as we inhale each other's exhausts, unless there is some ventilation, albeit intermittent.

It is not uncommon to find an expensive mansion with lots of gadgetry and controls, and during times when the heating or cooling system is not required, there is a minimum of air motion. Comfort then is only possible with a local fan to maintain some air motion. Any central air circulation system can be set up to maintain a minimum of airflow at all times, or to more frequently ventilate than the temperature controls demand. This has the added benefit that any dust generated by normal activities will be routed to filtration and captured, providing for cleaner air to breathe.

During inclement weather, whether hot or cold, we spend much of our time indoor. Typically this does not include air exchange with the outdoor environment, except when doors are used to exit or enter the structure. One alternative is a Heat Recovery Ventilator or Heat Recovery Air Exchanger. This device exchanges air with the outdoor environment, causing the two separate air paths to flow through a heat exchanger, allowing for reduction of heat loss or gain. Basic ones (http://purifresh.com/erv.html) will simply exchange the air through good quality filtration, while some will also filter the air for particulates, and more complex ones will also control the humidity and VOC levels.

A novel application is an APD, or Air Purifying Dehumidifier. Thermastor makes several models based on volumetric capacity, that filter the incoming air stream, and dehumidify it (if necessary). The novelty of this unit is that it can be used to produce a slightly Positive Pressure indoors, relative to outdoors, so that any possible air leaks are directed outwards. Without any intentional pressure controls, a residential environment will usually exhibit a slighly negative air pressure. If it happens to be raining, then that negative air pressure will also draw water in, through whatever path(s) it may take. This is certain to gradually destroy the structure, and the health of the occupants, due to mold growth. Unfortunately, the majority of homes in North America use an Open Combustion process for heating with fossil fuel, causing that negative air pressure. Doing water intrusion repairs in such homes, will only be a stop-gap measure, as the problem will reoccur.

But I have an air purifier, you say, with a good quality filter, you add. That simply purifies the air, and does not produce additional Oxygen. Whether in a space station or a submarine, there are systems needed to regenerate Oxygen. No home I have ever been in had those systems in place. So it's not been uncommon, to find a mansion where the basement smells like a dump, because there was no intentional provisions for fresh air, nor climate conditioning provisions, as if the basement was a space for punishment of undesirables. VOC (Volatile Organic Compounds) are forever. Despite the precautions employed by sensitives to lay new equipment outdoors for outgassing, the process will continue until that equipment is discarded or destroyed. Leave your home for a week, and upon return you will detect a peculiar smell, that of accumulated VOCs from everything indoors. While you occupy your space, you intermittently open the window(s), or the door(s), and there is some exchange of air with fresh from outdoors. Stop that for as little as a week and the place will smell. So it's imperative for those with extreme chemical sensitivities to employ ERVs as described above.

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