4 FM quick reads on indoor air quality
1. Common Sources of Indoor Air Contaminants
Indoor air quality can be negatively affected by airborne contaminants and excess moisture. There are some usual suspects when it comes time to investigate a potential source of harm to indoor air quality. These include:
Air-supply intakes. These can receive an inadequate air volume, are favorite roosting places for birds, and have the potential to introduce contaminated outdoor air.
Sub-roof or below-grade areas. These areas are subject to moist still air, which promotes mold growth. Crawl spaces where water can puddle unnoticed are a breeding ground for mold, pests and allergens that can cause respiratory illness.
Chemical storage areas. Cleaning chemicals, paints and other materials can evaporate and release toxic vapors and volatile organic compounds.
HVAC ducts. Water in ductwork from humidifiers in the winter and condensate in the summer can grow mold. Any time there is high temperature with no air circulation, mold can grow rapidly. Plus, mold can stick on substances that adhere to duct walls, loosen, then enter the air supply.
Another common culprit that's less in your face than mold growth is poor airflow. Diagnosing this problem will require using an air-balance multimeter, which measures individual air velocity, temperature, and pressure. A flow-hood kit saves time by taking multiple air-velocity readings simultaneously and converting them into average airflow rates.
Other tools can be used to provide a more refined analysis of the air to indentify specific particulates or gasses. These include:
- thermal imagers, which detect moisture from roof leaks or piping leaks inside walls, often hidden from view. Wet surfaces are colder than dry areas. The imager detects this temperature differential through building materials
- a hot wire detector, which uses thermal conductivity to measure concentrations of inorganic gases
- a flame ionization detector, which measures concentrations of aliphatic and aromatic hydrocarbons
- an electron capture detector, which detects chlorinated hydrocarbons
- a flame photometric detector, which measures concentrations of sulfur and phosphorus compounds
- a mass selective detector, which measures the volume of IAQ pollutants and can identify unknown chemicals.
Keep Humidity Just Right For Good Indoor Air
Today's tip focuses on how relative humidity, both too high and too low, can have a negative effect on indoor air quality. In general, the sweet spot for humidity is somewhere between 30 and 60 percent relative humidity.
Don't operate your building at low relative humidity. One of the most irksome contributors to poor IAQ, especially in wintertime, is low relative humidity. Lowering the temperature in the occupied spaces is one practical way to improve this situation.
When the relative humidity in commercial and institutional buildings is low, occupant's mucous membranes in the nose, mouth and throat dry out. The result is they become much more sensitive to the ubiquitous pollutants found in an indoor environment. More cases of colds, allergies, and even nosebleeds are not uncommon.
The solution to this problem is difficult. Installing a central humidification system into the building's air handling system is often impractical and cost prohibitive. Individual space humidifiers can help, but they have stringent maintenance requirements which, if not adhered to, can present IAQ problems of their own.
But don't go overboard and make the mistake of operating your building at high relative humidity either. High humidity provides conditions for microbial growth. If high relative humidity conditions are a problem at your facility, consider using dehumidification equipment. You can also consider the use of high limit humidifier controls to prevent condensation on the inside surfaces of the downstream duct. Lastly, consider using unlined ductwork with external insulation directly downstream of the humidifiers or cooling coils to help prevent microbial contamination.
You can refer to ASHRAE Standard 55, "Thermal Environmental Conditions for Human Occupancy" for more detail on acceptable ranges for humidity.
Manage Indoor Pollutants to Preserve Indoor Air Quality
Today's tip from Building Operating Management is to control sources of indoor pollutants to safeguard indoor air quality. Rather than making the HVAC system the first line of defense, try to control pollutant sources locally. Localizing large pollutant contributors in separate rooms is an effective method of controlling contamination. These rooms should be maintained under negative pressure in relation to surrounding rooms and exhausted directly to the outdoors. Large contributors include photocopier rooms or special process print rooms.
Contaminant sensing can be used as a means to ensure there is adequate ventilation. In areas of a building where occupancy or contaminant levels are variable, consider the use of carbon dioxide, volatile organic compound, carbon monoxide or other contaminant-sensing inputs. HVAC systems can use the information from the contaminant-sensing inputs to control the amount of outdoor air introduced into an area within a building. When contaminant level thresholds are exceeded and the system calls for increased ventilation, precautions should be made that the outdoor air being brought in isn't itself contaminated.
You might also consider a night purge cycle. HVAC systems can often be programmed to operate on a night "flush" cycle on 100 percent outside air to clear out any unwanted indoor pollutants on a daily basis. However, this strategy is not advisable when the outside air is especially warm, humid or contaminated.
A good filtration system will also play a key role in preserving indoor air quality, even with these other measures in place. When possible, design or retrofit HVAC systems to incorporate high-efficiency filters. Some filtrations strategies to consider include:
- Consider upgrading filtration with a 30 percent ASHRAE prefilter and a 90 percent ASHRAE final filter, but first make sure the system can handle the additional pressure drop.
- Consider using antimicrobial filters.
- Make sure the filter system is properly sealed to eliminate filter bypass.
- Inspect the air filter system regularly.
- Change filters at the proper intervals. To help with this, use reliable filter gauges.
Good HVAC Maintenance Practices Mean Good Indoor Air Quality
Even the most sophisticated HVAC system will fail to provide good indoor air quality if not properly maintained, which makes developing an HVAC maintenance plan crucial to assuring the proper operation of the building's HVAC system so it can provide an acceptable indoor environment. Facility managers interested in fostering good indoor air quality should make certain to have an HVAC preventive maintenance program that includes:
&mdash: Scheduled inspection, cleaning and service.
&mdash: Calibration of control system components.
&mdash: Replacement parts that at least meet design specifications.
&mdash: Proper procedure documentation.
To facilitate inspection and maintenance of the duct system, facility managers should consider installing access doors in the HVAC ducts. The access doors should be gasketed and provide a tight seal. In addition, facility managers may also want to install access doors in the HVAC equipment if access is insufficient for inspection or maintenance.
Another component of good maintenance practices to protect indoor air quality is to make sure you're using proper levels of biocide in water treatment systems. Cooling towers are prime sources of microorganism growth. They require continuous attention. Periodic testing is also advisable.