Fan Energy – The Often Overlooked Energy Hog

Posted on November 20th, 2012 by
   


HVAC accounts for about 40 percent of the energy used in U.S. commercial and residential buildings, making HVAC systems a logical focus for potential cost savings. According to the U.S. Department of Energy, adopting energy-efficient design and technologies – in HVAC and other areas – within new buildings can cut energy costs by as much as 50 percent. Options such as MacroAir ceiling fans can significantly cut energy cost. And in existing buildings, renovations that replace older systems with more efficient technologies can yield savings of up to 30 percent. Compressor and fan motor efficiency have a major impact on HVAC energy, but there is another often overlooked energy hog, fan energy used as a result of filtration.

Filtration and the subsequent indoor air quality found in the vast majority of commercial buildings is still primarily driven by economics and front end cost. The majority of filters manufactured and installed today are disposable filters that do little to remove fine particles, its primary purpose being to protect the mechanical systems from dust and debris. But an obvious yet commonly ignored struggle in building efficiency is the energy impact from client expectations for a higher grade of indoor air quality. The more that is observed about people and process efficiency losses from poor indoor air quality, the greater the desire for higher quality filtration.

Historically, as efficiency increases in disposable filters, so does static pressure resistance.  A decision to upgrade indoor air quality with approximately 80-85 percent passive filters will consume a great deal more energy – specifically fan energy – as the HVAC system works harder to push air through tightly woven filter fibers.

But there is a solution. Today’s newer air cleaners – such as polarized-media electronic air cleaners – operate with a much lower static pressure than conventional high efficiency filters. Lower static pressure means less fan energy (horsepower) required to push air through the HVAC system.

Standards & Codes

The American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE), has recently set allowances for brake horse power based upon system type and application in Section 6.5.3 of ASHRAE Standard 90.1-2010. In many reviewed cases, traditional filtration systems exceed the allowance. Newer systems, however, help to lower fan energy and may be the only method for compliance with the ASHRAE standard.

For many years, polarized-media air cleaners have contributed to fan energy reduction programs all over the world. In any building using pre and post filtration of MERV 8 and 13 or even higher, this technology can reduce mid-life static pressure by more than 1 inch and design static by more than 1.75 inches. This has the ability to make these systems an easy and effective tool for compliance to the new standard. Like other aspects of ASHRAE 90.1, the more the standard is exceeded, the higher the perceived building value and acceptance of performance. Ultimately, systems like these not only comply with the allowable adjustments for filtration, they can make the capital investment a no brainer.

Case in Point

In a 2010 energy audit of an office building in Boston with traditional filtration, 23 percent of the total annual electric consumed was HVAC fan energy. This compared to 20 percent for HVAC heating and cooling. As you can see in the following example using a 34,000 cfm air handler and a $.16 blended utility rate, using polarized-media air cleaners instead of 85 percent cartridge filters saves over $8,000 per year in fan energy costs. Just from the reduction in static pressure in this model, design brake horsepower is reduced 14.3 bhp.

 With polarized-media air cleaners, and using the prescriptive option under section 6.5.3 of ASHRAE 90.1, engineers are able to reduce energy and provide clients with a payback worth investing in.

Other Savings

In addition to fan energy savings, some air cleaners can reduce outside ventilation air requirements.  Ventilation standards specify a certain number of cfm per person for various types of buildings.  For example, in office spaces and schools the HVAC system must bring in 13 to 16 cfm/person of outdoor air, depending on occupant density. Reducing outside ventilation air can mean significant additional savings in the energy required to condition incoming outdoor air.

MERV13-15+ Dynamic V8 Air Cleaning System

Lastly, filtration systems like polarized-media air cleaning systems can extend routine service and replacement intervals from once every several months to once every several years. There’s a good deal of work that goes into filter service, and with a reduced need for monthly maintenance, costs are greatly reduced.

 Today’s green standards, such as the U.S. Green Building Council’s LEED® program, encourages above average (MERV 13 minimum) filtration in addition to other energy efficient and sustainable practices. According to the USGBC, over 12,000 commercial projects have earned LEED certification. For facilities with MERV 13 or better filtration, the savings can be dramatic.

Robert F. Goodfellow is Vice President of Marketing with Dynamic Air Quality Solutions and a certified indoor air quality professional with over twenty years experience in the heating, ventilation, air conditioning and refrigeration industry. Contact him at rgoodfellow@DynamicAQS.com.

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