Custom air handling units take the definition of the system—a box that includes a fan, filter, and at least a coil—and turns it completely on its head. When debating whether off-the-shelf or semi-custom units make sense rather than floor-up solutions, mechanical engineers should consider not just budget, but building envelope, installation concerns, equipment life expectancy, maintainability, and other specific needs when deciding on custom air handling units and manufacturers.

Baseline Expectations of Construction and Reliability

Since there are far fewer issues regarding cost-cutting with custom air handling units, specifying engineers should be able to expect several things when they work with a manufacturer on a design to implement their specific requirements. These include:

1. Much longer lifetimes: 50 years, or roughly 2 to 2.5 times the average expectation for an off-the-shelf AHU, is a reasonable expectation for a custom-built unit.
2. Improved maintainability and acoustic performance: Both can be considered part of the “usability” factors, where engineers who understand their facility maintenance team's needs and organizational acoustical mitigation requirements can provide for easier access and noise attenuation.
3. Meeting specific energy consumption and recovery goals: By being able to source specific components, like variable-frequency drives, fan arrays, coils, and more, a specifying engineer working with a manufacturer to design a custom AHU can meet very stringent requirements for energy costs.

Understanding How Design Criteria Works with Custom Manufacturers

In an ideal world, an air handler for every building and every need would be mass-manufactured and easily available, but that’s simply not feasible. However, the idea of modular and semi-custom air handling units has created a conundrum for specifying engineers: just how much customization does the project require? Below are some key considerations for engineers:

1. Unit sizing: In many cases, the overall shape of the air handling unit is a key reason to look for custom options. Truly custom manufacturers will offer a variety of material thickness, variable aspect ratios, and types in terms of the outer envelope, along with thermal breaks and other efficiency/equipment protection features.
2. Component needs: Custom air handling units come with custom-formed coils and the ability to source a variety of compressors, motors, filtration strategies, and drives. If these need to reach certain specifications, it’s crucial to consider a custom manufacturer rather than one that will try to use off-the-rack coils and a small number of “known components” for use.
3. Expectations during runtime: Operational expectations are crucial for custom units. This can include noise requirements, bearing lifetime, resistance to corrosive elements, non-standard temperature and moisture conditions, different climates, etc.

An anecdote from one manufacturer might illustrate the last point more fully. Well into the fabrication stage of a custom air handling unit, a company found out that the unit would have to operate in conditions that could include Category 5 hurricane winds of well over 170 miles per hour. The ability to change cross members to ones that had nine times the surface area of the original design simply would not have been feasible in modular construction.

Custom AHUs, Delivery and Commissioning

Many air handling units occupy space on either the grounds outside a building or on its rooftop. Access to some spaces can be a major difficulty, and often why using off-the-shelf options wasn’t possible in the first place. It remains crucial to keep the actual installation process in mind at the very beginning of the design process.

While many contractors use cranes to bring larger components up to rooftops, some factors—for example, doorway openings in historical structures—may limit the ingress of other parts, especially interior AHUs. Finding a combination of properly sized components for requirements and ones that will also fit into the spaces needed for them to end up in the eventual shell can be two separate calculations.

The final issue comes with building and shipping the product. As with any custom-built equipment, custom AHUs need extra time. A reasonable expectation for lead time could be 12‒24 weeks, but it all depends on the components ordered.

Find the Right Custom Air Handling Units for Your HVAC Project

Windy City Representatives represents leading manufacturers of custom air handling units, and we understand how important it is to take multiple considerations like budget and existing systems into account when specifying these units. Call us today at 630-590-6933 for a quote or bid.