Basics of Indoor Air Quality
We all hear about mold,sick buildings, contaminated schools, and global warming. What I'd like to do is introduce you to some buzzwords and some definitions concerning this complex subject.
What is Sick Building Syndrome?
• It's a condition where 20% or more of the structure's occupants suffer similar symptoms for 2 weeks or more.
• Relief is almost immediate upon leaving the structure.
•Symptoms are vague and may include nausea, eye-, nasal-, or throat-irritations, general malaise; medical tests are negative or inconclusive.
What is Building-Related Illness?
•This is far more serious. Patients manifest clinical signs; specific pollutants can be identified, usually after chronic exposure.
• Examples would be heavy-metal poisoning, mesothelioma, lung cancer.
What are the things that can form the basis for an IAQ problem?
• Gases: Some heavier than air, some lighter than air. Examples would be CO2, CO, radon, methane, hydrogen sulfide.
• Vapors: Evaporating liquids form vapors. Examples would be mercury, solvents like toluene & xylene, gasoline.
• Fumes: Chemical or metal droplets, produced by chemical reactions or high temperatures. Welding fumes are an example.
•Particulate: Any dust- or smoke-type contaminant. Examples would belead dust, pollen, silica dust, asbestos fibers, tobacco and cooking smoke, soot, mold spores.
Other factors such as a lack of ventilation, too much or too little moisture, and temperature extremes can combine with these substances and magnify their effects on health.Some individuals may be very sensitive to certain pollutants that have little or no effect on others within the same space. Only a medical professional can determine who is allergic to, or otherwise affected by, these substances.
We heating-and-cooling professionals can offer a lot of solutions to problems that pop up, and it's our job to design systems in such a way as to avoid the pitfalls that can cause common IAQ problems. An ounce of prevention is better than a ton of cure when it comes to IAQ. For example, a bad mold infestation can often be traced to a minor water leak from any source. Give a mold spore water, and paper, cloth or wood to eat, and it will grow, spewing spores and mycotoxins into the air. A poorly vented combustion device can allow CO to escape, with potentially fatal results. The kitchen,laundry, baths and hobby spaces all can add to the pollutant load within the structure. Sealing the home to save energy can concentrate potentially harmful contaminants, and also can starve the combustion appliances of the air needed for proper burning. This may lead to soot formation and excessive CO2 and CO emissions, which can contribute to global warming. And inefficient combustion also wastes expensive fuel.Providing adequate ventilation air and combustion air is vital.
Moisture can be controlled by adding or removing it as needed. Humidifiers and de-humidifiers of all sizes and types are widely available in both portable and permanently installed models. A range of 40-60% is optimal. Below that, static electricity can be an annoyance, and hardwood floors and decorative woodwork can crack, shrink or cup. Dry eyes, irritated nasal passages, or upper respiratory problems can result. Above that level, condensation on windows or the inside of walls can lead to damage to windowsills, insulation failure or possible mold.
Particles can be removed with filters or electronic air cleaners. Filter efficiency is measured by MERV value, the higher the number, the more efficient a filter is. Retail and trade models are available, and these range from totally ineffective to 99.8% effective.The one-inch retail throwaway filters have no air quality function;they just keep "dust bunnies" out of the equipment. Media types range upward from there, with better retail models, or basic trade models,starting at about MERV 8, on up to MERV 12. Electronic air cleaners work best on smoke and smaller particles of 10 microns or less. In general, media filters and electronic air cleaners have no effect on gases, vapors or odors; although CPZ-loaded filters (Charcoal,Permanganate and Zeolite) can remove some gases or vapors.
Gases and vapors are best handled by eliminating the source, or by diluting and exhausting them with an energy- or heat-recovery ventilator. These units feature heat exchangers that pre-warm or pre-cool incoming air in a heat exchanger with outgoing air on the other side. ER/HRVs bring in and exhaust equal amounts of air, so they neither pressurize nor depressurize the structure. They run at about 80% efficiency, and work well to provide fresh air to tightly sealed homes.
Bioaerosols(air-borne germs) and slimes that grow on condensate pans can be controlled with UV lights that are placed either over the AC coil or in the return duct. The intense UV kills mold, slime and algae that grow in poorly drained condensate pans or AC coils. In the return, they can minimize the number of viable germs and viruses that circulate in the air.
To summarize, IAQ problems are best prevented rathe rthan cured. Good design, attention to detail, and common sense should be used liberally. The house is a system, and failure of any one subsystem affects everything else. No IAQ accessory will make up for a poor initial design.
Some final thoughts.Heating-and-cooling professional are not medical professionals, so be very careful about what you promise when it comes to IAQ products. No IAQ accessory can "cure" anything! Also, we are not industrial hygienists or biologists, so don't try to identify what type of contamination you may find.