Special report: Fan efficiency guidelines
Despite the fact that fans in commercial HVAC systems consume more than 1 Quad of energy (1015 Btus) annually in the U.S., they have not had explicit efficiency requirements in federal regulations or model codes and standards for energy efficiency and high-performance/green construction.
Those days are over.
The 2012 International Green Construction Code (IgCC) and ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings (2013 Edition) have requirements for minimum fan efficiency. These requirements are based on a standard published by the Air Movement and Control Association International (AMCA International), AMCA 205: Energy Efficiency Classification for Fans. AMCA 205 was first published in 2010, and its 2012 revision is ANSI accredited. The 2012 IgCC’s fan efficiency provisions are based on AMCA 205-10; ASHRAE 90.1-2013’s provisions are based on ANSI/AMCA 205-2012.
Additionally, AMCA and ASHRAE collaborated on fan-efficiency proposals for the 2015 International Energy Conservation Code (IECC), which were based on the ASHRAE 90.1-2013 language. The proposals cleared the first level of hearings in April 2013 and will undergo public review later in the year leading up to final-action hearings in October. AMCA International also is developing a proposal for ASHRAE 189.1: Standard for Construction of High-Performance, Green Buildings Except Low-Rise Residential Buildings.
Meanwhile, the U.S. Dept. of Energy recently initiated the development of a federal efficiency regulation for commercial and industrial fans, with completion of the regulation expected in 2015/2016 and enforcement beginning as early as 2019/2020.
This article describes the fan efficiency provisions that are in place in IgCC-2012 and ASHRAE 90.1-2013, and briefly discusses what could lie ahead in future codes, standards, and regulations.
Rating fan efficiency
AMCA 205 defines a metric, called a fan efficiency grade (FEG), that rates a fan’s ability to convert shaft power to air power, independent of motors and drives. FEGs are indices calculated from data taken at the peak total efficiency point on a fan curve developed during ratings certification tests.
AMCA developed FEGs as a dimensionless index to characterize the aerodynamic quality of a fan. The metric accounts for the reduced peak total efficiency that occurs for smaller fans compared to that of larger fans of the same type. This characteristic is due to nongeometric manufacturing tolerances, disproportionate bearing losses, and other aerodynamic factors that have a greater impact on smaller fans than on larger fans. When plotted as a graph, the differences in efficiency across fan sizes define a banana-shaped curve. The nature of this curve prohibits setting a straight-line efficiency requirement (e.g., all fans must have a minimum efficiency of 65%) because doing so would eliminate many smaller fan sizes of even the most efficient types of fans (see Figure 1). Smaller fans inherently have smaller efficiencies because bearing losses, manufacturing tolerances, and the fan structure all have a larger impact than they do for larger fans of the same design. The smaller fans, however, are designed for specific applications and duty points (airflow and pressure). Eliminating them wholesale via an efficiency standard would not serve the industry well.
Figure 1 also superimposes FEG curves defined by AMCA 205 on the straight-line efficiency of 65%. Setting a fan efficiency requirement based on FEGs is as simple as a straight-line efficiency requirement (e.g., all fans must have a minimum efficiency of FEG 67). Note in Figure 1 how the FEG curves penetrate the box that defines the smaller sizes that would have been prohibited by a straight-line efficiency requirement.
The FEG curves are defined in such a way that all fans of a particular design, having geometric proportionality, should have the same FEG, although there are sometimes exceptions to this rule.
If an energy code has a minimum fan efficiency requirement of FEG 67, any fan model with that rating or higher will comply. The FEG is a simple metric to segregate fans that do or do not meet a specific code requirement or regulation. Readers can learn more about AMCA 205 and FEGs at www.amca.org/feg/best-practices.aspx, and download a free copy of the standard at www.amca.org/feg/codes-and-standards.aspx.
Limiting sizing/selection practice
Commercial HVAC fans are usually sized and selected using software that yields a range of fan sizes for a specific fan model for given airflow (cfm) and pressure conditions. Construction budgets generally favor lowest-first-cost approaches, so the smallest fan size is generally selected. Although they may have the same FEG rating (as described earlier), the difference in actual efficiency and energy performance between the smallest and largest fan sizes is considerable.
Consequently, setting a minimum fan efficiency grade will not guarantee reduced fan-energy consumption unless care is taken to properly design the air distribution system and an appropriate fan selection is made. For this reason, AMCA 205 also prescribes that fans should be sized and selected to operate within 15 percentage points of the fan’s peak total efficiency. The sizing/selection window helps practitioners to right-size fans so they operate in their most efficient ranges of speed and pressure. The result is a higher first cost, but energy savings quickly recoup the higher cost. Table 1 shows the output of a manufacturer’s sizing/selection program for a double-width, double-inlet fan sized/selected for 80,000 cfm at 3-in. static pressure. The operating costs are based on a run time of 16 hr per day, 250 days per year, and electricity cost of $0.10 per kWh.
Structuring a fan efficiency requirement
Fan-efficiency codes and standards written around AMCA 205 define a minimum FEG and a sizing/selection window. Fan efficiency provisions can be further refined by specifying applicable sizes, types, and exemptions, as well as requirements for third-party certified FEGs and energy labels. The following are examples of where fan-efficiency requirements based on AMCA 205 have been adopted or proposed for model codes and standards for energy efficiency and green/high-performance construction.
IgCC-2012: The 2012 IgCC’s fan-efficiency provision includes a minimum FEG rating of 71 and sizing/selection window of 10 percentage points from peak static or total efficiency. It applies to stand-alone supply, return, and exhaust fans in buildings less than 25,000 sq ft.
This provision was based on AMCA 205-2010, which had a sizing/selection window of 10%, not 15%. AMCA 205-2010 also listed fan types that it does not cover, including air curtains and jet fans, because these types do not conform to the conditions supporting FEG calculations. AMCA will be proposing significant changes to this language for the 2016 version of this model code.
ASHRAE 90.1-2013: The significance of having a new fan efficiency requirement in ASHRAE 90.1 cannot be overstated. ASHRAE 90.1 is the benchmark state energy code for federal efficiency programs, many utility rebate programs, and state energy codes. It also is a compliance path for the model energy code, International Energy Conservation Code. ASHRAE 90.1 also forms the basis for the ASHRAE standard for high-performance (green) construction (Standard 189.1), and the International Association of Plumbing and Mechanical Officials (IAPMO) Green Supplement to the Uniform Mechanical Code and Uniform Plumbing Code.
Fan efficiency provisions in ASHRAE 90.1-2013 are written into the section that includes fan power limits. The fan power limits section encourages low-static-pressure air distribution systems, which save energy; however, it does not place appreciable constraints on efficient fan efficiency or right-sizing of fans.
ASHRAE 90.1-2013 specifies a minimum FEG rating of 67 and a sizing/selection window of 15 percentage points of the fan’s peak-total-efficiency rating (Figure 2).
The Standard 90.1 provision applies to fans with a nameplate hp rating > 5 hp and fan arrays that have an aggregate motor nameplate rating > 5 hp. The provision has a number of exemptions, including powered roof/wall ventilators, fans intended to operate only during emergencies, and fans in packaged equipment that has a third-party certification for air or energy performance. These exemptions will help engineers, contractors, building owners/operators, commissioning providers, and code officials learn how to implement fan efficiency requirements for the first time.
To learn more about the ASHRAE 90.1 fan efficiency requirement, read the article by John Cermak, PhD, and Michael Ivanovich in the April 2013 issue of ASHRAE Journal, which is available at www.amca.org/feg. To learn how fan power limits and fan efficiency grades interact during a fan selection, read the article by Michael Brendel, PhD, in the May 2013 issue of HPAC Engineering.
IECC-2015: The fan efficiency provisions in ASHRAE 90.1-2013 were proposed for IECC-2015, with a few refinements: FEG ratings would have to be “approved” and “labeled,” measures that are defined within the IECC, and were included to support compliance checking and enforcement:
APPROVED. Approval by the code official as a result of investigation and tests conducted by him or her, or by reason of accepted principles or tests by nationally recognized organizations.
LABELED. Equipment, materials or products to which have been affixed a label, seal, symbol or other identifying mark of a nationally recognized testing laboratory, inspection agency or other organization concerned with product evaluation that maintains periodic inspection of the production of the above-labeled items and whose labeling indicates either that the equipment, material or product meets identified standards or has been tested and found suitable for a specified purpose.
ASHRAE 189.1: AMCA has recently developed a “continuous maintenance proposal” that would insert a fan efficiency provision into ASHRAE 189.1. The provision is identical to the ASHRAE 90.1-2013 language, with the one exception being that the peak-total-fan-efficiency sizing/selection window is 10 percentage points instead of 15 percentage points. If the proposal passes committee votes, it could come out as an addendum for public peer review later in 2013.
U.S. Dept. of Energy: Development of the U.S. Dept. of Energy’s fan efficiency standard achieved a significant milestone with the publication of the Framework Document in the Federal Register on Feb. 1, 2013. The Framework Document presents DOE’s perspective of the fan market and the options it is considering for regulating commercial and industrial fans. AMCA International is collaborating with a number of industry stakeholders, including the American Council for an Energy Efficient Economy (ACEEE), the Appliance Standards Awareness Project, and the California public to jointly develop a proposal to DOE for the efficiency requirement.
Among the most significant differences a DOE standard will introduce is that a variety of fan types (DOE calls them classes) will be defined, and fan efficiency metrics and minimum energy efficiency performance requirements will be set for each class. Based on best-available information, a DOE requirement could be in place with enforcement between 2019 and 2020.
Future fan efficiency requirements
DOE’s approach to defining fan classes and assigning a potentially unique efficiency requirement for each of them is one that AMCA is looking to apply to future proposals for model energy codes and standards.
Additionally, because some types of fans are structurally integrated with motors and drives, a metric that incorporates the drive, motor, and control, is being developed. AMCA is working with European and Asian standards bodies and manufacturers to develop an internationally harmonized metric for “wire-to-gas” efficiency ratings, which could be applied to fan-motor and fan-motor-drive combinations. Also, some fan products, such as powered roof/wall ventilators, are assembled and sold with motors and drives, making a wire-to-gas metric more consistent with them, as well.
An example of a wire-to-gas metric is cfm-per-Watt, or W/cfm, which would provide a convenient way to establish fan efficiency requirements for fan-motor assemblies while FEGs are retained fans less motor and drive.
Beginning with the publication of AMCA 205 in 2010, the development of fan-efficiency provisions in model codes and standards for energy efficiency and green/high-performance construction began in 2012, and is picking up pace. A federal efficiency standard is under development by the DOE and might be active as early as 2019. Energy savings will come from requirements for minimum fan efficiency grades; however, greater energy savings is expected from provisions that have sizing/selection windows that encourage larger-diameter fans running at slower speeds and closer to peak-efficiency ratings.
First-generation fan efficiency provisions in U.S. model codes and standards are written around AMCA 205 and contain a minimum FEG rating, a sizing/selection window, and exemptions that limit applicability to specified sizes, types, and applications. Future, or second-generation fan efficiency requirements may include additional metrics, such as a wire-to-gas rating.
Michael Ivanovich is director of strategic energy initiatives with AMCA International. Ivanovich develops and advocates consensus positions among AMCA member companies worldwide on codes, standards, and government regulations for energy efficiency and green construction.
- International Code Council, International Green Construction Code (IgCC), 2012.
- ASHRAE, ANSI/ASHRAE/IESNA 90.1-2013, Energy Standard for Buildings Except Low-Rise Residential Buildings. In press.
- ANSI/AMCA 205-12 Energy Efficiency Classification for Fans, Air Movement and Control Association International, 2012.
- Cermak, J. and Ivanovich, M., April 2013. “New Fan Efficiency Requirements for ASHRAE Standard 90.1-2013,” ASHRAE Journal, ASHRAE.
- Brendel, M. May 2013. “The Role of Fan Efficiency in Achieving Energy Reduction Goals,” HPAC Engineering Magazine, Penton Media. (in press)
- Federal Register, Feb. 1, 2013, “Energy Efficiency Program for Commercial and Industrial Equipment: Public Meeting and Availability of the Framework Document for Commercial and Industrial Fans and Blowers.” Available at http://1.usa.gov/VLkOMx.