05/11/2020 | By Robert F. Goodfellow, CAFS
The IAQ problems that generally get the most attention are those that involve lots of complaints. Issues can be exacerbated by allergic reactions and health issues.
The Most Common IAQ Problems
Air contaminants indoors can either originate within the building or be drawn in from the outdoors. If pollutant sources are not controlled, indoor air problems can develop, even if the HVAC system is properly designed, operated and maintained. Sources of indoor air contamination include polluted outdoor air, underground sources (e.g., radon, pesticides, and leakage from underground storage tanks), and a variety of indoor sources (e.g., equipment, furnishings and cleaning supplies). Concentration levels of air pollutants can vary greatly by time and location within a building, or possibly a single room. Pollutants can be emitted from point sources, such as science storerooms, or from area sources, such as newly painted surfaces. And pollutants can vary with time, such as only when floor stripping is done. Indoor air often contains a variety of contaminants at concentrations that are well below any standards or guidelines for occupational exposure, so it can be difficult to relate specific health effects to exposures to specific pollutant concentrations, especially since the exposures may be to low levels of pollutant mixtures.
The IAQ problems that generally get the most attention are those that involve lots of complaints. Issues can be exacerbated by allergic reactions and health issues. These often involve outdoor contaminants that are being entrained into the building with outdoor ventilation air, such as wood smoke. One of the most common issues involves vehicle emissions. Vehicle exhaust can be problematic when the building is located in an urban setting or near heavily traveled roads, or when school buses drop off and pick up students near HVAC air intakes.
More outside ventilation air is commonly used to dilute airborne contaminants but outdoor air can be more problematic than indoor air, especially in urban areas. With today’s low-VOC emitting building materials, furniture and cleaning chemicals, and with the absence of indoor smoking, airborne particle and odor contaminants are much more apt to enter a building through the fresh air intakes. To cope with these issues, designers and facility managers have found that air cleaning systems can be incorporated into the HVAC systems to not only clean the incoming fresh air, but also to keep indoor air at contaminant levels below outdoor levels.
Even though good IAQ has real, tangible benefits, applications for better IAQ are still largely cost driven. So where are potential savings for designers and facility managers who implement these applications?
Energy costs present the largest opportunity. HVAC accounts for about 40 percent of the energy used in U.S. commercial buildings, making HVAC systems a good target for cost reductions and savings on a facility’s annual operating budget. In new buildings, according to the U.S. Department of Energy, adopting energy-efficient design and technologies – in HVAC and other areas – can cut energy costs by as much as 50 percent. And in existing buildings, renovations that replace older systems with more efficient technology can yield savings of up to 30 percent. With respect to only IAQ and the filtration component of an HVAC system, significant operational savings can be found through:
- Reduced fan horsepower from lower static pressure
- Reduced ventilation air requirements
- Reduced maintenance and disposal costs from longer service intervals
Addressing air filtration alone can reduce a buildings total energy footprint by five to ten percent. Historically, increasing filter efficiency has meant increasing energy and operating costs because it takes more fan horsepower to push air through denser, more efficient filter media. The denser the filter media, the higher the static pressure resistance. With a lower static pressure, less fan energy is required to move air through the HVAC system. Lower static pressure corresponds directly to energy savings.
Polarized-media air cleaners offer relatively low resistance. In some cases, there can be mid-life pressure drop savings of up to one and one-half inches versus passive, mechanical filters. This allows fans to be designed and selected with lower horsepower requirements and potentially less operational energy consumption.
Fine-tuning ventilation air requirements can have a big impact on energy consumption, particularly in situations where ventilation rates were based on a constant high average occupancy. A reduction in ventilation air can eliminate the need to heat or cool incoming fresh air. ANSI/ASHRAE Standard 62, which is the basis for many local mechanical codes, provides three alternative procedures for determining minimum outdoor airflow rates: the ventilation rate procedure, the natural ventilation procedure and IAQ procedure. The first two are prescriptive methods that are easy to calculate. The IAQ procedure is more complex and based on performance criteria. It allows HVAC system designers and operators to reduce outdoor air when it has been determined that the air inside the space is clean enough.
In a typical building with no smoking and no unusual contaminant sources, outdoor air levels can often be reduced from 13 to 16 cfm/person to between 7.5 and 10 cfm/person. Such a reduction can yield significant operational savings. For example, in a building with 60 tons of cooling, annual savings on utility costs alone can be expected in the range of $3,000 to $12,000 depending on the geographic location of the building — hot humid climates have the greatest costs/savings — the utility rates, and the hours of operation.
Maintenance costs present yet another area for savings and include labor, ordering, handling, storage and filter disposal costs in addition to materials. High efficiency air cleaning systems such as the Dynamic V8 Air Cleaning System, offer very high dust-holding capacities and can extend change-out intervals from every several months to every several years.
As a case in point, polarized-media electronic air cleaners were installed throughout the ASHRAE headquarters in Atlanta, Georgia. The building serves as a “living lab” where system performance and air quality are carefully monitored and tracked. The media in the air cleaners were not replaced in over five years during which static pressures never exceeded clean recommended levels — clean static pressure x 2. Measurements showed that indoor VOC and particulate levels were consistently better than outdoor levels.
Although cost controls may typically steer facility managers toward the low-cost options, particularly as it relates to filtration, sustainability initiatives are highlighting a broader goal. Increasingly, sustainability initiatives have been trumping cost initiatives. In some cases, a high efficiency filtration system can pay for itself in less than two years. As mentioned previously, fan horsepower and system static pressure greatly impact energy consumption. Filter replacement costs and length of maintenance intervals influence ongoing operational costs. These costs can be evaluated to determine the life cycle costs.
Whether today’s goals involve healthier learning environments, reducing absenteeism, or reducing operating costs, improving indoor air quality is a good idea. Studies show that better IAQ improves health, well-being and performance. Today, it’s possible to improve IAQ while reducing energy consumption and lowering operating costs at the same time.