Improving IAQ Via Air Filtration
- By Brian Monk
- March 1st, 1999
The college market has experienced an increased awareness of Indoor Air Quality (IAQ) in the past several years. Many buildings have been diagnosed as having deficient air quality, and administrators are searching for ways to improve their environments while keeping the remedial action cost-effective. ,/p>
IAQ affects both the comfort and well-being of building occupants. The building industry relies on organizations like the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) to set the standards for the quality of air within buildings. ASHRAE has found that buildings with little or no ventilation are more susceptible to occupant complaints and health problems like sore eyes and respiratory illnesses. But ventilation alone is not the answer to better-quality air.
A sensible approach to acceptable IAQ is to use ventilation in conjunction with air filtration, which works in concert with the building’s HVAC system to improve air quality in several ways.
Particulate Contaminant Control
Particulate matter can be controlled through the use of filtering media installed in the building’s ductwork. Filters are available in a variety of densities to catch large contaminants like dust and dirt, and there are high-efficiency filters that remove micron-sized particles like mold spores.
Newer electronic filters are also available and can be more effective under certain conditions. Particulate filtration is the most common type of contaminant control, and it is incorporated into most HVAC systems. However, in high-pollution environments where there are occupant complaints, special filter systems with air-tight frames may need to be installed.
Gaseous Contaminant Control
Gasses are emitted by a building’s occupants, machinery and materials, as well as from outdoor sources like manufacturing plants. These gasses must be addressed because they affect the performance and productivity of the building’s occupants.
Chemical filtration systems are the preferred method of gaseous contaminant control because they remove rather than mask the offending problem. Chemical filtration systems have been in existence for many years in industrial applications and are just now becoming popular in commercial buildings. These systems operate by passing the building’s air supply through a chemical medium such as activated charcoal and potassium permanganate. The filtration medium is mixed precisely for the type of gas to be removed, and the condition of the filtration material is continuously monitored for its effectiveness.
In high-occupancy areas like classrooms, people produce bioeffluents, and the outdoor air entering the space may include sulfur and nitrogen compounds that produce odors. Harmful gasses, like those given off by furniture and carpeting, glues and manufactured wood products, break down in time and emit VOCs.
A chemical filtration system can be included as part of the building’s HVAC during new construction, or it can be retrofitted into existing systems when an air deficiency problem is detected. Stand-alone units can also be installed in individual areas if the problem is localized or if retrofitting the building’s entire HVAC system is economically unfeasible.
Besides the clear benefits of removing unwanted odors and dangerous gasses, a chemical filtration system can reduce operating costs for heating and cooling by lowering the ventilation requirements established by ASHRAE. The standards for air quality in colleges recommend at least 15 cubic feet per minute of outside air for each student in a classroom. The ASHRAE standard also allows the use of air cleaning techniques for energy conservation. A chemical filtration system can effectively lower the ventilation requirements by half, reducing heating and cooling expenses proportionately.
Chemical filtration can also be used to preclean outside air before it enters the building’s HVAC system. This technique is especially important in urban areas.
Colleges in warm, humid climates suffer from relative humidity greater than those in temperate and colder climates. For maximum efficiency in heating and cooling, outside air should be preconditioned before it enters the building’s air circulation system. Dehumidifi-cation systems are available to reduce excess moisture to a tolerable level, reducing the load on the air conditioning system.
There are a number of systems on the market to remove moisture, with one of the more efficient models using mechanical refrigeration technology. In this type of system, moist outside air passes over a coil cooled by refrigerant, where the moisture in the air condenses and is removed. The heat energy recovered during the dehumidification process can be placed back into the air stream when conditions call for heat or be removed to the outside as waste heat during cooling cycles. The dry, pretreated air then passes through the building’s standard heating/cooling system.
Ventilation in colder climates presents a unique problem with regard to IAQ and energy efficiency. Many building managers limit ventilation, especially in winter months, because of the high cost of energy needed to heat the considerably colder outside air. This results in a condition known as stale air that leaves the occupants with a stuffy feeling along with eye and skin irritation. Systems known as air-to-air recovery units are designed to capture heat energy from the already heated air being exhausted from the building and transfer it to the cold outside air being used for ventilation. In that way the outside air requires less heat energy in order to be brought back up to a comfortable indoor air temperature.
Brian P. Monk, P.E., is vice president of marketing at Circul-Aire, a Division of Dectron Internationale, Montreal, Canada, a North American leader in air purification and energy recovery equipment design and manufacturing.