The Art of the Filter Change (Part 2)

In Part 1 of The Art of the Filter Change in the July issue of College Planning & Management, we began our look at filter changes by covering the critical points of this process. We looked at why we need to replace filters, knowing where and what our air handling assets are, and information about filter efficiency as well as how to dispose of them. (Please follow this link to view "The Art of the Filter Change Part 1.") Replacing our filters on a regular interval provides a healthy learning, living, and working environment for our students, faculty, and staff. Additionally, it is important to the operational longevity of our air conditioning equipment.

When to Make the Change, and Who Makes It
Once we have identified the size, type, and quantity of filter, we must decide who will be performing the filter changes and how often they will be done. Up to a point, filters become more efficient as they load with dust, so changing out filters before they have reached their useful life will cost your facility money in the long run, both in terms of material as well as labor costs. Outside units, units that draw a lot of outside air, and units near busy roads or open land will all require filter replacement sooner than a filter in a more pristine environment. The timing of each change can be determined in a number of ways. I imagine that a large majority of our facilities send a technician out on periodic PM visits to visually inspect the filters and change them out as appropriate. Those that perform the PM on a rotating basis generally know how long their filters last and, through institutional knowledge, have the appropriate filter changes set on a fixed time schedule.

We schedule this work out in a couple different ways. Our primary HVAC technician typically performs all the routine service and majority of the PMs on our large (25 ton and larger) equipment. We also have HVAC assistants; one whose only function is to vacuum, clean coils, and replace filters on all of our FCUs on campus. This is a number in the hundreds of units and keeps this one person busy on a constant cycle. Another HVAC assistant receives duties split between major PMs and routine service calls and filter changes as needed.

A number of institutions have differential pressure gauges on their large air-handling units. These show the difference in pressure on either side of the filter, and the filter requires changing at a certain percentage of airflow resistance. This figure varies either by filter manufacturer specification, equipment specification, design specification, or good old-fashioned trial and error, which while it may not be all that scientific, is often the best as the technicians in the field begin to know their equipment well. A generally accepted practice is to replace the filter when the pressure reaches between one and three times the initial pressure drop, as measured when a new filter is installed. Many building automation systems contain points for monitoring this automatically and to automatically report or send an alarm when the pre-set flow resistance has been met.

Outside Assistance
Additionally, there are a number of contract firms that will perform coil cleaning and filter changes as a service contract. These companies oftentimes will assure or guarantee energy savings as part of their service contract, making it a win-win for the institution and the company. Actually, in some instances the school wins twice, in that they can redirect the labor that once spent time changing filters into performing other customer-oriented maintenance and repairs and they can enjoy the energy savings that come with a routine program. Of course, these same energy savings can be had by simply managing a similar program in-house… but remember, the plan must be fully adhered to in order to reap the estimated savings.

No matter how your institution’s filters are changed, the important thing is that they are changed! So much of our customers’ time is spent indoors, and we must do our part to provide a healthy and clean environment in which to live and learn. Set and maintain the filter change program, and your facility will reap the rewards of long equipment life cycles, reduced energy costs, and buildings that your customers will be happy to inhabit.

Finally, I would like to thank Nalco Company for their assistance in providing some basic supporting information for this article.

About the Author

Michael G. Steger is director, Physical Plant, for Berkeley Preparatory School in Tampa, FL. He can be reached at

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