AHU Specification: The Case for Performance-Based Design

Writing specifications for high-performance air-handling units (AHUs) used to mean detailing cumbersome construction requirements, accompanied by long lead times and a high price. Today, it is possible to spec AHU performance—not construction—for custom units that are produced economically and quickly.

There have always been facilities that required high-performance AHUs, such as hospitals, cleanrooms, pharmaceutical manufacturers and performing-arts theaters. These facilities have unique needs regarding AHU capacity, acoustics, casing integrity and/or thermal capability. For consulting engineers, it is a large and important market.

However, the AHU market is changing. Organizations such as ASHRAE, U.S. Green Building Council, International Code Council and others are actively addressing indoor air quality, energy and acoustics by setting performance standards for air handling. Virtually all buildings today have stringent requirements for air-handling performance. These higher standards are creating challenges for designers by requiring custom AHUs, which historically are more time-consuming to specify, are more expensive and require longer lead times.

To address these challenges, some AHU manufacturers are now applying mass-customization techniques that have been successful in other industries such as personal computers. This approach allows the manufacturer to combine the economies of large-scale production with the ability to build custom-designed and manufactured products to meet the specific needs of each customer. It also allows unprecedented flexibility in AHU dimensions, materials and components. The result is a high degree of AHU customization, with individual units built cost-effectively and shipped quickly.

This new generation of AHUs no longer requires the consulting engineer to specify unit construction to ensure required performance. Specifying construction is usually proprietary and therefore limits competition. In fact, specifying construction places the liability for performance on the designer rather than the manufacturer.

The solution, however, is at hand: Consulting engineers should write performance-based AHU specifications that are tied to industry standards. Where standards don't exist, engineers should require testing and written guarantees. In other words, place the burden on manufacturers to ensure performance and deliver a cost-effective AHU within reasonable lead times.

In addition to saving design time and minimizing risk, the engineer can actually increase competition for a project bid. That's because specifying performance is not proprietary; it levels the playing field for competing manufacturers.

The design community continues to raise the AHU performance bar to improve the safety, health and welfare of the public. Consulting engineers can use performance-based specifications to deliver outstanding performance and flexibility to the exact requirements of the customer. Equipment manufacturers who wish to meet customers' expectations will continue to innovate, with practices like mass-customization of AHUs.