10/07/2019 | Robert F. Goodfellow, CAFS
Today, some high efficiency air cleaners, such as polarized-media electronic air cleaners, have low static pressures and high dust-holding capacities that are capable of cleaning air without increasing costs.
A 2006 national report, Greening America’s Schools, concluded that environmentally-friendly school buildings lead to lower operating costs, improved test scores and enhanced student health. The report, produced by Capital E and co-sponsored by The American Institute of Architects (AIA), concluded that environmentally-friendly schools save an average of $100,000 each year. The benchmark study examined 30 green schools built between 2001 and 2006 and determined that the total financial benefits of green schools are 20 times greater than their initial cost difference. Measurable benefits include energy and water savings, improved student health and higher test scores.
The findings also indicate that there are tremendous benefits from energy efficient school design, not only from an economic standpoint, but also from far healthier environments through enhancements such as improved air quality. Among the study’s conclusions:
- On average, green schools use 33 percent less energy.
- A study of Chicago and Washington D.C. schools concluded that better facilities could add three to four percentage points to a school’s standardized test scores.
- Green schools typically have better indoor air quality (IAQ), which contribute to fewer sick days.
Where could it possibly be more important to have cleaner air than in our schools? But the key to cleaner, healthier air may not be as simple as A-B-C.
The Key to Cleaner, Healthier Air
The conventional approach to air quality in schools is to introduce fresh, outside air to dilute contaminants. The amount of outside air introduced to the indoor environment depends on the number of building occupants. Most schools’ HVAC systems are designed for 15 CFM per person. This can be costly, in terms of conditioning outside air, and sometimes ineffective, when the outside air is polluted. Cleaning the air, rather than diluting it, can save energy and money and improve IAQ.
Although the air outside is usually cleaner than indoor air, it can also contain unwanted particles and odors. “Air intake vents can pull a lot of air into a school,” says Jeff Watcke, Southeast Regional Manager with Dynamic Air Quality Solutions. “Because of the nature of our business, we often get involved when there’s a problem. We’ve seen a number of instances where school buses get close to school buildings to load or unload and the engine exhaust from the idling school buses gets sucked into the building’s HVAC system. In worst cases, the ultrafine particles in smoke or vehicle exhaust can trigger asthma attacks.”
Such was the case during the past few winters in Fairbanks, Alaska. At least six students at Woodriver Elementary School suffered asthma attacks caused by smoke from nearby residential wood-burning boilers. One of the downsides of these asthma attacks is that the children are typically sent home from school. This could be prevented if the culprit _ in this case, ventilation air — was improved.
Filtration and Ventilation
Historically, increasing filter efficiency meant increasing energy and operating costs. It takes more fan horsepower to push air through denser, more efficient filters. These filters can load quickly and require replacement often. And diluting indoor air with more outdoor air means heating cold, unconditioned outdoor air in the winter and cooling hot, humid air in the summer.
Today, some high efficiency air cleaners, such as polarized-media electronic air cleaners, have low static pressures and high dust-holding capacities that are capable of cleaning air without increasing costs. These air cleaners can be used for cleaning indoor, re-circulated air, and also for eliminating odors and ultrafine particles from incoming outdoor air, such as vehicle exhaust emissions.
ANSI/ASHRAE Standard 62.1-2016, 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.
Impacting the Bottom Line
So, we can see that reduced outside air can save money and pay for the cost of the air cleaning equipment. Here’s the breakdown:
Energy Consumption. In a typical building with no smoking and no unusual contaminant sources, outdoor air levels can often be reduced to between 7.5 and 10 CFM per person. For example, a school with a 60-ton rooftop unit can expect annual savings on utility costs in the range of $3,000 to $12,000 depending on the geographic location of the building, the utility rates and the hours of operation.
Capital Investment. Reduced outside air can favorably impact equipment selection. Lower fan horsepower requirements can translate into smaller tonnage equipment.
Maintenance. Polarized-media electronic air cleaner media pads last longer than conventional passive filtration, extending change-out intervals and saving labor costs. Maintenance personnel like the light-weight pads that are lighter, less bulky than equivalent efficiency bag or cartridge filters, and easier to store and handle.
But Wait, There’s More!
High efficiency air cleaning systems offer other benefits for schools, as well:
Improved IAQ. High efficiency air cleaners remove dangerous airborne particles that other air cleaning systems miss — including odors, VOCs, smoke, bacteria, allergens, fine dust, molds and pollen — without producing any harmful ozone.
Mold Prevention. Air cleaners that collect mold spores reduce the risk of potential mold problems by removing mold spores from the air stream, as well as sub-micron particles, which can provide a food source for mold growth.
Versatility. Few air cleaners offer the same versatility when it comes to application in the types of HVAC equipment used most frequently in schools. Versatile air cleaners can be applied to packaged terminal units, unit ventilators, rooftop units, water-source heat pumps, as well as large custom air handling units.
Increased Attendance. Studies document the correlation in the reduction of student and staff absenteeism to cleaner air in schools. Poorly controlled asthma can more than double healthcare costs and threaten educational achievement.
Cleaner Air Means Happier, Healthier Students
Dynamic’s Watcke sums it up this way: “It’s important to remove barriers to learning in our schools and to offer a safe and healthy environment for our children. It’s good to know that you can do so, and that it can be done at zero net cost.”