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According to the U.S. Department of Energy, our nation’s K-12 schools spend $6 billion on energy, while colleges and universities spend close to $2 billion each year. Healthcare facilities also spend a staggering amount on energy—$5.3 billion annually.

In many cases, older buildings, with their aging mechanical systems, are to blame for energy inefficiencies. In fact, a significant portion of energy costs for educational and healthcare facilities can be tied to space heating and cooling, thanks in part to HVAC systems that are not optimized for energy conservation.

Improving an HVAC system’s energy efficiency does not have to be daunting or costly, however. For example, simply upgrading the HVAC air filtration system can help to reduce energy costs while also improving indoor air quality (IAQ)–an issue of increasing importance in terms of its effect on academic performance and patient comfort.

Using Filters to Conserve Energy
HVAC filters play a key role in the HVAC system: they remove contaminants from the air that passes through the system, and they protect HVAC equipment from dust that can increase operating costs. Filters also play a role in the energy consumed to operate  the system. The energy used is based on the resistance of the air passing through the filter: the lower the filter’s resistance, the lower the energy consumption will be. However, even though one speaks of filters, it is really the filter media that has the biggest effect on minimizing energy consumption, protecting HVAC equipment and providing clean air.

Unfortunately, many filter suppliers consider the media used in the filters as a commodity, resulting in the filter’s price being the determining selection factor. It is important to understand though that the cost of energy used by filters far outweighs the initial price of the filter itself. In fact, energy costs can be 10 times the initial filter price for a standard pleated filter and 4-5 times the initial filter cost for higher efficiency final filters. The good news is that more energy-efficient filters do not necessarily need to cost more, so energy savings can often be achieved without any investment, thanks to recent advances in filtration media technology.

Lifecycle Costs
The best way to use filters as an energy conservation tool is to consider the total life-cycle cost of the filter and the filter’s long-term effect on energy costs. The three major components of life-cycle cost for HVAC filters are: initial price and maintenance, energy consumption and disposal. On average, energy cost accounts for an astounding 81 percent of the total life-cycle cost of a filter system. The initial price and maintenance accounts for 18 percent and disposal accounts for 1 percent.

How can life-cycle costs of filters be applied to energy efficiency? The key issue is the filter’s pressure drop, as measured by two filter test standards from the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE): ASHRAE 52.1-1992 and ASHRAE 52.2-1999. Development of new materials has given the filter industry a chance to produce lower pressure-drop media while maintaining high particle capture efficiencies, thereby providing the ability to reduce electricity costs and improve IAQ simultaneously. Electret technology and electrostatic filter media have been the key technologies enabling this seemingly contradictory concept to become a reality. In fact, today, there are 95 percent efficiency synthetic media filters that have the same pressure drop as 65 percent efficiency glass media filters, providing the ability to increase filtration efficiency in commercial/institutional HVAC systems by 30 percent without increasing energy costs at all.

Switching to a lower pressure drop filter is one of the easiest changes for facility managers to make in an effort to reduce energy costs. That is because, with a lower pressure drop filter, the HVAC system motor needs to overcome less resistance to deliver the required air flow, thus reducing the motor’s energy consumption.

The following figures illustrate the impact of a filter’s pressure drop on annual energy costs. Note that the two commercially available filters are identical except for the initial pressure drop. In a typical scenario, one might use initial price as the primary criteria in choosing one of these filters over the other. However, as the example shows, this might not result in the correct filter choice for maximizing long-term cost savings. In this example, initial price is the same to illustrate the effect of pressure drop on operating costs.

Filter A provides a lower initial and average pressure drop and therefore saves approximately $29 in energy costs annually. While an energy

savings of $29 per year may not sound like a lot, keep in mind that those cost savings are per filter, not for an entire HVAC system. Another way to look at the information is to consider that $29 saved with Filter A offsets 41 percent of the initial filter price. That is equivalent to nearly getting half of your filters free each year.

Installation and Maintenance Issues
Once you have decided to upgrade your HVAC filter media to a lower pressure drop filter in an effort to reduce energy costs, it is time to swap out the old filters for new ones. The goal of proper filter installation is to avoid bypass air, which causes contamination in housings, coils, fans and ducts, and thus increases HVAC system operating costs. Do this by making sure all the air in the system goes through the filter. To avoid problems later on, consider these installation recommendations:
• Make sure the replacement filters are of the correct size and compatible with your housing.
• Check for filter media damage such as rips or holes, and discard damaged filters.
• Make sure media is sealed in the frame to avoid bypass air.
• Install the filter according to the air flow direction indicated on the frame. (Some filter manufacturers use a two-color filter media construction to help see which side faces upstream and which faces downstream.)
• Ensure that the filter fasteners are in place and correctly installed, especially if filters are serviced from the down-stream
side.
• Check to ensure that the bank of filter frames is rigid and well reinforced to avoid collapse.
• Caulk any cracks between filter frames or between the bank of frames and the duct wall to prevent leaking of unfiltered air.
• Pay special attention to filter holding frame seals, gaskets and filters that do not match the filter holding frame size–all of which can cause bypass air.
• Install a differential pressure measurement device across the filter bank to identify the appropriate change-out times.
• Place labels on the housing units with information such as the number and type of filters, date installed and pressure drop to make changing filters easier.

When inspecting filters, do not rely on a visual inspection for determining when to change filters. A dirty filter does not necessarily signify the end of a filter’s useful life. In addition, normal eyesight can only see particles of about 40 microns in size. Therefore, a filter rated at 10 microns can look dirty, yet still have an extensive useful service life. To extend the life-cycle of the filter, and reduce life-cycle costs, rely on the manufacturer’s suggested change-out frequency, or monitor the pressure drop of the filter and change the filter when it achieves its recommended final pressure drop.

It is important to remember that better filtration does not always result in higher total costs. That is why facility managers considering the energy cost implications of a filter upgrade should ask their filter suppliers the following questions:
• What pressure drop reduction offsets the difference in filter price?
• At what pressure drop would a filter upgrade pay for itself?
• At a given performance level, how much money could be saved by using a lower pressure drop filter?
• How much of my filter costs does that cost savings offset?

For an energy cost calculator to help determine the economic impact of various equally performing filters, visit www.kcfiltration.com.
Dave Matela, CAFS
Kimberly-Clark Filtration Products

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