Air-system awareness blowing in the wind
Educate yourself on energy-saving approaches to improve air movement.
By Michael Ivanovich, The Ivanovich Group LLC, Oak Park, Ill.
Air systems for commercial buildings and some specialty facilities, such as data centers and labs, are getting a getting a sharp look these days from energy savers. This is happening in the field with existing buildings, in the design community, and in the regulatory arena where codes and standards are promulgated.
So, here are some insights on where things are going.
Retro-commissioning providers are finding a big bang for the buck around air handlers and rooftop units replacing fossilized filters and cleaning clogged cooling coils; controlling 24-7 exhaust fans serving 9-to-5 spaces; unloading one-speed fans that serve variable-sized loads; sealing leaky ducts and straightening torturous turns; fixing economizers that are anything but; and re-enabling dampers defeated open with 2x4s, shut with plywood, or just plain broken.
And that’s for existing buildings with in-your-face issues. Fix those, air-balance, and let the measuring and monitoring begin to find the subtler problems to fix.
In the design community, engineers are learning to right-size fans so they operate closer to their peak efficiency, which quickly pays back the first cost increment of a slightly larger fan. Typical practice is to go with a smaller fan that operators have to run harder and less efficiently to get the proper airflow. Or, designers pile on too many safety factors and get a fan that runs too fast, using much more energy (power varies with the cube of fan speed). Engineers also are learning how to avoid system effect losses, which occur when there is insufficient distance at the inlet and discharge for the fan to operate efficiently.
System leaks in ducts and dampers are also being dealt with by specifying leakage tolerances and dampers certified for low leakage rates. Fewer and smaller leaks also make systems easier to balance.
There also is a movement for control-system designers to develop sequences of operation first, then specify the controls before they design the HVAC systems. This inside-out approach can reduce first costs by eliminating some equipment and reducing the size of others. Most importantly, the documentation of what the system needs to do, when, and how are developed and documented early in the design process, not toward the end.
Energy codes and standards have been tightening up prescriptive requirements for air systems for some time by requiring economizers, variable speed drives, and smart control strategies. Lately, their focus has included fans. The Air Movement and Control Association International published Standard 205 Energy Efficiency Classification for Fans that defines how fan efficiency grades are determined for many types of fans. ASHRAE Standard 90.1 and the International Code Council (ICC) International Green Construction Code have undertaken change proposals to adopt AMCA 205. Similar (harmonizing) proposals are envisioned for the ICC International Energy Conservation Code and ASHRAE 189.1 (Standard for High-Performance Green Buildings Except Low-Rise Residential Buildings).
Additionally, the U.S. Dept. of Energy recently initiated a rulemaking process that will eventually establish energy efficiency standards for commercial and industrial fans, similar to federal standards for lighting and other HVAC equipment. It will take several years for the rulemaking to play out, but it’s certainly a sign of the times for air systems.
Ivanovich is the president of The Ivanovich Group LLC, which provides research, analysis, and consulting services to the buildings industry. For more information, visit www.theivanovichgroup.com.
Word on the Street
Whether you are a consulting engineer, commissioning provider, contractor, or owner, there are resources available for improving air system performance.
AMCA International: www.amca.org/feg. Includes technical articles about AMCA 205 and news about air system energy codes and standards.
Functional Testing and Design Guides: www.peci.org/ftguide. Online resource that provides detailed design and commissioning guidance for HVAC systems.
ASHRAE Advanced Energy Design Guides: www.ashrae.org/technology/page/938. Collaboratively developed guidelines meant to help save 30% energy consumption (relative to ASHRAE 90.1-1999) for many building types.
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