Air Inlet Filter Screens – A bio-medical facilities main air handling units had been experiencing on-going problems during the winter; 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; thus exposing the expensive MERV 15 bag filters which they relied upon to provide fine filtration to help in delivering optimal indoor air quality.

Snow Damaged Pre-Filters In Air Chamber

Snow Damaged Pre-Filters In Air Chamber

Because of this on-going winter problem, the maintenance team had  to change 30 pre-filters every two weeks during the winter season (8 times) per winter and another four (4) times during the spring, summer and fall for a total of 12 times per year.  Every time pre-filters were changed it would take 2.5 man hours and cost approximately $215 in filter & labor cost.  Bag filters were changed two times per year and it would take 4 man hours for per change, costing $1,095 in filter & labor cost.  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.  When changing the pre-filters it took two round trips up and down the stairs (24 filters per box) and when changing the bag filters it required 15 round trips up and down the stairs (3 large filters per box).  During the winter, they had to constantly check on the filters because if the pre-filters got blinded-off with snow it would impact air flow – and if they collapsed between inspections the bag filters would become damaged and compromise indoor air quality.  Because this air handling unit services critical laboratories, they simply could not allow the filtration system to be compromised – They needed a solution.

Approximate annual cost for managing this problem = $4,770 (excludes constant inspection time)


In 2006, the maintenance team became aware of Air Intake Filter Screen Technology – The filter screens are specifically engineered to have little impact on air flow and static pressure and stops 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 to mount them to the outside of the intake louvers which would limit accessibility as the outside of the louvers were located several stories up in the air and not accessible.    The idea was to use the air intake filters to significantly reduce the amount of snow reaching the pre-filters and bag filters.

Since putting the filters in, they not only eliminated snow related damage, but they realized another benefit – The Air Intake Filters stopped cottonwood seed and other matter from pre-maturely fouling out our 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.

Filter Screen Shown With Cottonseed

Filter Screen Shown With Cottonseed

Since installing the Air Intake Filter Screens on their air handling unit, pre-filter changes have been reduced from twelve times per year to only three; and instead of changing bag filters twice annually, they now change them one time per year and anticipate that when nearby construction is completed that they will be able to reduce bag filter changes to one time every other year.   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 – less waste goes to land-fill.  As a result of these impressive results, the university maintenance team is working with their filter screen representative 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.

Cost Justification.

Because of the durable nature of the Air Intake Filter Screens, they will provide 15+ years of service.  Therefore, when weighing the cost of annual maintenance on the air handling unit without the Air Intake Filters vs. with them, the annualized cost of managing the system with the Air Intake Filter Screens yields a significant annual savings and a 2.9 year investment payback.

Old Method Cost (without Air Intake Filter Screens)

1. Annual Maintenance including pre-filters, bag filters & labor = $4,770

New Method Cost (with Air Intake Filter Screens)

1.  Total Cost for Air Intake Filter Screens, Frames and Installation = $7,885

2. Annualized Cost of Using Filter Screens ($7,885 / 15 year service life) = $525

3. Total Annual Cost for pre-filters & labor (3 changes per year) = $645

4. Total Annual Cost for bag filters & labor (1 change per year) = $1,095

TOTAL New Method    $2,265

TOTAL SAVINGS $4,770 – $2,265 = $2,505

By Randy Simmons