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Air Filter Series: A Lesson From The Home

May 16, 2013

Air Filter Series:

A Lesson from the Home

by Dave Ruede, Product Evangelist at Temperature@lert

What air filters do in your house, and what they mean for the IT space

We can learn many valuable lessons from owning a home, but the learning curve is (at times) steep for home improvements and renovations. It was only a year ago that my wife and I bought a house, and one of these valuable lessons surfaced almost instantaneously. I realized afterwards that this lesson is applicable to any space where filter quality can affect HVAC efficiency (and energy costs!).

Soon after the purchase, our gas-fired forced air furnace needed replacement due to a crack in the heat exchanger.  The unit came with a standard 1” (25 mm) air filter; you know the kind, the ones in your air conditioner ducts. These filters remove dust. Air passes through the pleated non-woven fabric and extracts larger dust particles and bugs from the air.  The filter plenum was able to accept a deeper filter, up to 4” (100 mm) deep. The filter was scheduled to be changed quarterly, but since summer was upon us I waited until the heating season began in the fall.

To frame this issue, keep in mind that filters do their job by trapping dust particles that are too big to pass through the holes in the fabric. Smaller particles and air molecules pass through easily, or at least easily enough to let the air circulate as designed. Filters are made with specifications that balance the removal properties (efficiency in removing particles) with the resistance to airflow compared to no filter being present (pressure drop).

The surface area of the pleated filter media has a direct affect on the pressure drop. If everything else is constant, the pleated media’s surface area is inversely correlated with the low pressure drop. Put more simply: the higher the surface area, the lower the drop. The same low pressure drop can be achieved by making the non-woven more porous, thereby having a negative effect on removing particles since larger spaces would let more dust through. Low pressure drop is beneficial because the fan motor will require less energy to move the amount of air required to heat the house, and helps to lower energy costs.

A  Portable Air Conditioner

To address this very issue, I removed the 1” filter in the fall and saw that it had changed from black to brownish-gray.  Immediately afterwards, a 4” filter was installed that was also rated to reduce pollen and other allergens. The deeper pleats and advanced non-woven design balanced the increased pressure drop, due to the smaller openings needed to remove pollen and such. Six months later when I took it out, the outlet side was still white. Even though we believed that we had kept a clean house, the inlet side was covered with a thick layer of dust and lint. The filter performed significantly better in removing dust and the like (versus the 1’’ filter), and did so without compromising the performance of the heating system.

To connect this issue to IT and server rooms, keep in mind that an office air conditioner (that feeds the server closet or the HVAC and CRAC units in data centers) contains a filter like the one in my home. A server room’s HVAC system can be similarly affected by the surface area of an air filter. A poor or makeshift filter can diminish the efficiency of these units, and the energy costs will remain the same regardless. The combination of high power usage and low efficiency is hardly ideal.

Regardless of size (closet, room, warehouse), these seemingly “insignificant” filters are important for assuring HVAC effectiveness and efficient energy usage in the IT space. The next piece in this series will cover the performance of air filters in server rooms (both positive and negative), and will also outline other key environmental issues in the IT space. Stay tuned, and stay cool! 

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