Ai Flow Dynamics and Fresh Air
Air-flow Dynamics
Air Flow _ Dynamics? We breathe in, and we breathe out. But we can only do so comfortably when the air pressure is about one atmosphere, or more technically about 14.7 pounds per square inch (PSI), and composed of about 21% Oxygen, 78% Nitrogen, and various trace gases. Additional necessary factors that play in the picture are the temperature of that air, what else it may contain in the form of those trace gases, particulates, and velocity. Velocity, you ask? Well, I\\'m glad you asked, because you\\'d have a very tough time breathing properly if you were downwind of a jet engine exhaust, the heat notwithstanding. Granted, not likely to happen. How about downwind of a leaf blower? Not as likely? Maybe. I visited a client who, among other things, was perceiving airway distress when her air conditioning system was on. Her home was older, and the air conditioning system was retrofit into the structure. However, to make the install least invasive they installed a high velocity system with narrow pipes in place of common air ducts. The system was off on my arrival. To "share" her experience, she turned it on during my visit, and I lasted about three minutes before I asked her to turn it off. You see, the narrow pipes caused high velocity and turbulence on the air\\'s exit. This was the equivalent of having several leaf blowers in use simultaneously. Recall those dust tumbleweeds referred elsewhere on this site? Well, when the AC was on, they instantly became fragmented and airborne. Ideally suited for inhalation. I wonder what village idiot dreamt up that system. With such a system, there is no way you can let your guard down and let any dust accumulate. How many residences do you know where vacuuming is done daily? Yours? Really?
If the space we are in is confined or sealed, then eventually the Oxygen supply will run out. 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 higher concentration of CO2 into a much larger air space, and simultaneously change 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. That is, if you have a good quality filter in place.
But I have an air purifier, you say, with a good quality filter, you add. That simply traps airborne particulates in the air, and maybe reduce VOCs if equipped with activated charcoal media, but 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. I have seen many instances where the HVAC systems are located in the basement, with large supply and return air ducts in that basement, but not a single opening in either, in that basement. This forced the use of additional dehumidification. I\\'ve walked into some of these, and witnessed mold growing on ceiling lumber, not longer that three months out of the builder\\\'s hands.
VOCs (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 "green and scent-free" 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 / HRVs (Energy Recovery Ventilators / Heat Recovery Ventilators), or other reliable means of air exchange. I\\'ve walked into some basements, smelled paint, and was advised paint was applied several years prior.
On a similar note, the placement of air supply registers is crucial. Not cool to have a forced air system blow cold (or hot) air at your legs, or your face, especially in your sleep area.
Fresh Air
Whether for aromatics from domestic structures of whatever kind, or even from our own breathing, we need regular and ongoing fresh air. In Parts Per Million (ppm) the typical environmental presence of CO2 is about 400. In percent that would be 0.04%. We breathe out about 4% CO2, or 40,000 ppm. What we breathe out will make us unconscious, unless the CO2 is immediately and regularly replaced with a similar amount of Oxygen. When people gather indoors, the effect is more pronounced, as when sitting in an automobile with the ventilation off - it soon gets stuffy . . .
When we are indoors, this typically does not include (intentional or controlled) air exchange with the outdoor environment, except when doors are used to exit or enter the structure. One alternative is an HRV / ERV. 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, while some units will also control the humidity and VOC levels. Some advanced units such as the PuriFresh ERV (www.purifresh.com) are easily installed in a window or other wall opening, and can retain the internal moisture concentration, regardless of that outdoor. Amazingly, the Purifresh units were even available for rental when checked some time ago, as in temporary forced fresh air to vent out aromatics due to painting or other operations.
Caveat #1: ERVs or HRVs have a heat exchanger core that transfers heat from one air stream to the other. As long as the volumetric air flow in both airstreams is the same, these are wonderful machines. But cause the airstreams to have different volumes, and now the heat exchanger core does not work as intended, and the air coming in may be too cold or too hot. This difference is volume can be caused by an exhaust fan operating somewhere else in the controlled space. In a small space in a metropolitan area with few openings this may not be an issue, while in a residential setting with several exhaust fans of one type or another, the space may no longer be "controlled."
Caveat # 2: "Fresh air," is defined by the percentages of expected gases, and the lack of relevant particulate or aromatic contributions. The concept may be wonderful, but if you live near a neighborhood laundromat, a hog farm, or if a skunk walks by, all bets are off, because now you have to treat the aromatics in addition to the controlled inbound volume, before it\\'s brought indoors. This may mean relocating the intake opening, or having aromatic filtration in the inbound air stream. The latter will provide some resistance to flow, rquiring the addition of another air mover to overcome the resistance, so that the two airstreams pass the same air flow volume.
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.
The supply of fresh air, whether accidental or intentional, also serves to reduce the indoor concentration of mold and their emissions. When that air supply is complemented by a central HVAC set up to maintain a minimum of airflow regularly, the fresh air comfort is available in all occupied spaces. This has the added benefit that any dust generated by normal activities (as well as airborne mold spores) will be routed to filtration and captured, providing for cleaner air to breathe, given the air filter is of good quality.
NOTE: mention of any device on this site does not constitute endorsement.