Building management officials at a 65,737-sq-ft bio-medical building located on the campus of a major university in southeastern Michigan had reached a point where they had to do something about ongoing problems with the facility’s main AHUs: Snow would be drawn through the intake louver on one side of the building, where it would accumulate on the MERV 8 pre-filters until the weight and moisture from the snow caused them to collapse. That, in turn, exposed the expensive MERV 15 bag filters which they relied upon to provide fine filtration to help in delivering optimal IAQ.

The building, which houses biomolecular research labs, instructional labs, classrooms, student project space, and faculty offices, and the university’s Facilities Maintenance Group, had been forced to change 30 pre-filters every two weeks during the winter season (eight times) per winter and another four times during the spring, summer, and fall for a total of 12 times per year.

Unwanted Flights

Every time pre-filters were changed, it would take 2.5 man-hours and cost approximately $215 in filter and labor costs. Bag filters were changed two times per year and it would take four man-hours per change, costing $1,095 in filter and labor costs.  In the section of the building where this unit is located, there are no elevators, hence the overall cost includes the time needed to move the new filters up several flights of stairs from the dock, removing the old ones, installation of new ones and taking the old filters down to the dumpster.

Also, during the winter, they had to constantly monitor the filters because if the pre-filters got blinded-off with snow it would affect airflow - and if they collapsed between inspections, the bag filters would become damaged and compromise IAQ. Because this AHU services critical laboratories, the filtration system simply could not be compromised. In total, the approximate annual cost for managing this problem amounted to $4,770 (not including constant inspection time).

In 2006, the maintenance team became aware of air intake filter screen technology (commonly called cottonwood filters, and designed and engineered by Air Solution Company for use on high volume/high velocity HVAC and cooling tower systems). The filter screens are specifically engineered to have little impact on airflow and static pressure and to stop airborne debris at its point of entry.

Though this appeared to be the right solution, the filters needed to be mounted inside the air chamber behind the louver, where it was accessible from inside the building, rather than placement on the outside of the intake louvers, which would limit accessibility. The idea was to use the air intake filters to significantly reduce the amount of snow reaching the pre-filters and bag filters. 

Installing the filters not only eliminated snow related damage, but it also provided another benefit. The air intake filters stopped cottonwood seed and other matter from pre-maturely fouling out the pre-filters during the spring, summer, and fall.

“It wasn’t until we saw the cottonwood seed building up on the air intake filter screens that we realized just how serious our cottonwood seed problem was. The cottonwood seed and other fibrous matter in the air was increasing our maintenance cost and significantly reducing the efficiency and service life of our filters,” said the facility maintenance engineer.

Green Benefits

Using the air intake filter screens dramatically reduced filter changes and reduced maintenance to about 10 minutes per cleaning using a broom, as opposed to up to four hours to change and dispose of the filters. Pre-filter changes have been reduced from 12 times per year to only three. And instead of changing bag filters twice annually, they now change them one time per year; the staff anticipates that when nearby construction is completed, they will be able to reduce bag filter changes to once bi-annually. Presently, their annual savings on just this one AHU is $1,935 a year on pre-filter changes and $1,095 on bag filters, for a combined annual filter savings of $3,030.

Furthermore, reducing filter changes is consistent with the university’s campus-wide green building initiative - reducing the number of filter changes reduces filter waste and contributes to their aggregate waste reduction (i.e., less waste goes to a landfill). As a result of these results, the university maintenance team is working to integrate the technology on other equipment across campus. “The cost savings opportunity is simply too great not to pursue this on a campus-wide basis,” said the facilities maintenance engineer. ES