The Filter Factor: LEED and ASHRAE 52.1 and 52.2


Building owners or developers pursuing LEED (Leadership in Energy and Environmental Design) certification must evaluate several things relating to energy efficiency, water efficiency, indoor environmental quality, related materials and resource selection. But the question the consulting engineer must ask is: Are you focusing on all the right things in seeking LEED-oriented benefits of cost efficiencies, productivity, occupant well-being and property values?

In addition to the obvious strategies, such as upgrading to Energy Star-qualified appliances and low-flow toilets, there may be some not-so-obvious ways to achieve LEED prerequisites and credits. One option is to take a closer look at ASHRAE 52.1 and 52.2, which characterize air filtration efficiency. Filter systems are often overlooked in many HVAC designs, yet they're a tangible way to improve temperature control, indoor air quality (IAQ) and energy efficiency.

Careful selection of the right HVAC filter and filter media can actually save money in the long run, helping LEED proponents answer critics' charges that green buildings always have to cost more.

Filter selection basics

To understand how the right filter can help to achieve green building standards, it's important to understand how filters should be selected to meet IAQ and energy efficiency requirements.

One of the biggest determining factors is filtration efficiency, which defines how well the filter will remove contaminants from air passing through the HVAC system. Initial and sustained efficiency are the primary performance indicators for HVAC filters. Initial efficiency refers to the filter's efficiency out of the box or immediately after installation. Sustained efficiency refers to efficiency levels maintained throughout the service life of the filter. Some filters have lower initial efficiency and do not achieve high efficiency until a "dirt cake" builds up on the filter. Other filters offer both high initial, as well as sustained, efficiency, meaning they achieve an ideal performance level early and maintain that level.

An understanding of ASHRAE 52.1 and 52.2 goes a long way in identifying what to look for. The first standard, ASHRAE 52.1, measures the following:

  • Dust spot efficiency. A measure of the ability of the filter to remove atmospheric dust from the test air.

  • Pressure drop. How the filter affects airflow and energy costs. A low pressure drop typically translates into higher energy efficiency. A high pressure drop means reduced airflow to the HVAC unit, requiring more energy to operate the unit.

  • Arrestance. The amount of synthetic dust a filter is able to capture.

  • Dust holding capacity. The amount of dust a filter can hold until a specified pressure drop is reached. Higher capacity means a longer filter life.

ASHRAE 52.2 measures the fractional particle size efficiency (PSE) of an HVAC filter. This indicates the filter's ability to remove airborne particles of differing sizes between 0.3 and 10 microns in diameter. A MERV, or minimum efficiency reporting value, is assigned to filters based on their minimum filtration efficiency at various particle sizes. A rating of "1" is least efficient, while a rating of "16" is most efficient. Lower ratings typically reflect a more cost-conscious choice as well.

In addition to the performance factors measured under the ASHRAE 52.1 and 52.2 standards, consider these additional variables when selecting a filter:

  • Moisture resistance. How high humidity and moisture affect the filter.

  • Temperature limitations. How the filter performs at application temperature.

  • Flammability. How the filter performs in flammability tests. Check to see if UL Class I- or Class II-rated filters are needed to conform to local building codes.

An efficient life cycle

HVAC systems typically account for about 40% of a commercial building's electricity expenses. HVAC filters play a significant role in the energy used to operate an HVAC system; the lower the filter's resistance to air passing through it, the lower the energy consumption will be.

Unfortunately, many filter manufacturers look at the media used in their filters as a commodity, and initial purchase price tends to drive the selection process. It's important to understand, though, that the cost of energy used by filters far outweighs the initial cost of the filter itself. In fact, energy costs can be 10 times the initial filter cost for a standard pleated filter and four to five times the initial filter cost for higher-efficiency final filters.

Fortunately, there is a way to use filters as an energy conservation tool: Consider the total life-cycle cost of the filter and the long-term impact on energy costs it will have. The three major components of filter life-cycle costs are initial investment/maintenance, energy consumption and disposal. On average, energy cost accounts for 81% of the total life-cycle cost of a filter system. The initial investment and maintenance accounts for 18%, and disposal is only 1%.

How can life-cycle costs of filters be applied to energy efficiency? While the cost of a filter decreases with time, the pressure drop of the filter increases with time, resulting in increased energy consumption. 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 simultaneously improve IAQ and reduce electricity costs. Electric technology and electrostatic filter media have been the key technologies enabling this seemingly contradictory concept to become a reality. Switching to a lower pressure-drop filter is one of the easiest changes a building owner can make to save energy.

LEED checklist

Armed with an understanding of how selection of the right HVAC filter media can influence IAQ and energy efficiency, it's time to review the role that filters play in helping to achieve LEED certification. No individual product or system itself can be LEED-certified; it can only contribute to the completion of a particular credit point. But as you consider your systems, you may find some surprising credits "hiding" in your HVAC filter strategy.

  • LEED-EB Energy and Atmosphere/Prerequisite 2: Minimum Energy Performance and LEED-NC Energy & Atmosphere/Prerequisite 2: Minimum Energy Performance . These prerequisites require a minimum level of energy efficiency for the base building. Upgrading to a more energy-efficient HVAC filter—i.e., one with a lower pressure drop—for reduced energy loads on the HVAC system motor is an example of an "energy-efficient retrofit and energy-saving technique to reduce energy use," as suggested under the potential technologies and strategies in the LEED Green Building Rating System for Existing Buildings.

  • LEED-EB Energy and Atmosphere/Credit 1: Optimize Energy Performance and LEED-NC Energy & Atmosphere/Credit 1: Optimize Energy Performance . The intent of these credits is to achieve increasing levels of energy performance above the prerequisite standard to reduce the environmental impacts of excessive energy use. Upgrading to a more energy-efficient HVAC filter—again, one with a lower pressure drop—for reduced energy loads on the HVAC system motor is described the same as the above credits under the LEED-EB potential technologies and strategies.

  • LEED-EB Energy and Atmosphere/Credit 5: Performance Measurement . The intent of this credit is to "demonstrate ongoing accountability and optimization of building energy and water consumption performance over time and add incentives for additional energy reduction." Continuous metering—one of the recommended strategies—can be applied to the HVAC system. Rather than change out HVAC filters according to a rigid, time-based schedule—e.g., every three months—try installing a pressure gauge on the filter bank to monitor pressure drop as an indication for when to change out filters. Changing out filters based on the appropriate pressure drop can potentially extend the useful life of the filter.

  • LEED-EB Materials and Resources/Prerequisite 1.1: Source Reduction and Waste Management: Waste Stream Audit . The intent of this prerequisite is to "establish minimum source reduction and recycling program elements and quantify current waste stream production volume." As a disposable product, HVAC filters are considered part of the waste stream. The right filter can help reduce generated filter waste. Final filters can also be upgraded so that changeouts are reduced from approximately once every 12 months—e.g., with conventional bag filters—to once every 18%%MDASSML%%24 months—e.g., with mini-pleat, v-bank style filters—thus reducing the amount of filter media and housing materials discarded on an annual basis.

  • LEED-EB Indoor Environmental Quality/Credit 3: Construction IAQ Management Plan and LEED-NC Indoor Environmental Quality/Credit 3.1: Construction IAQ Management Plan During Construction . The intent of these credits are to "prevent indoor air quality problems resulting from the construction/renovation process." They require a filtration media with a MERV of 8 at each return air grill if air handlers must be used during construction.

  • LEED-EB Indoor Environmental Quality/Credit 4.1: Documenting Productivity Impacts: Absenteeism and Health Care Costs Impacts . While use of a specific air filter will not help you with the documentation and reporting requirements of this credit, it is important to understand the role that a high-efficiency air filter can have on tenant health and wellness. Studies have reported that as many as one fifth of U.S. office workers experience decreased productivity levels based on discomfort or adverse health effects due to IAQ problems.

  • LEED-EB Indoor Environmental Quality/Credit 5.1: Indoor Chemical & Pollutant Source Control . The intent of this credit is to "reduce exposure of building occupants to potentially hazardous particle contaminants, which adversely impact air quality." It requires filters with particle removal effectiveness of MERV 13 or greater to be in place over the performance period for all outside air intakes and for the returns for the recirculation of inside air. A regular schedule for maintenance and replacement of these filters must be established and followed to keep unfiltered bypass air from entering the duct-work and breathing air.

Star power?

With a few notable exceptions, HVAC filters don't play a starring role in the LEED rating system. But perhaps they should. Facility managers and engineers working toward LEED credits should be encouraged to look at the significant role HVAC filters can play in reducing energy costs, reducing waste, eliminating sources of indoor pollution and improving a building's IAQ. While these achievements can be considered reasonable goals in and of themselves, they can also be counted toward credits in both the LEED-EB and LEED-NC rating systems.

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