Foam-Core Air Handler Panels: A Coming Standard

If you've been specifying or installing commercial modular or semi-custom air handlers recently, you've probably noticed that quite a few manufacturers have switched away from the traditional single (or double) wall fiberglass batt insulation design, to a newer double-wall injected foam core panel. What is driving this change in the industry?

In a word: Performance.

To examine this further let's look at a typical design:



What you have is a sandwich construction with thin gage sheet metal enclosing the rigid foam core. The foam actually acts as a structural component, adhering to the exterior sheet metal and causing the entire composite assembly to function as a single structural unit. This means that you can achieve much greater rigidity with 20 or 22 gage steel than can be attained in a traditional batt insulation design with 16 gage steel or thicker! In fact, panel deflections for this type of panel are generally around L/240 or less (1/240th of the longest panel dimension) when subjected to an 8" static pressure load. That's actually better than the deflection spec for most custom equipment.

So why do we care about deflection? Well, a minor advantage is that this type of construction resists dings and dents much better. A slightly more important criteria is that the panels, especially floor panels, are much less likely to 'oil-can' when under pressure or under the weight of foot traffic. Even more important is that these panels make the unit itself more rigid and less susceptible to deflection or deformation in shipping or rigging. But the real advantage of this construction comes in the realm of energy savings.

These panels in general just blow away the thermal performance of batt-type panels. The following table compares the R-value improvement of rigid foam insulation over that of batt insulation:

(click on image for larger view)

Generally speaking, you get twice the insulation from foam in the same depth. Note that this only takes into account the performance of the insulation itself--further advantage is gained by the thermal break that prevents heat conduction from occurring at the panel seams--which is almost impossible to prevent in a traditional batt-insulation panel.

What does this amount to? Well, for a rooftop unit operating in a heating climate, this difference in R-value could amount to as much as 2% of the total unit energy over the course of a year.

But let's talk about panel rigidity again--it is in thermal performance where this really becomes important. Because the overall thermal performance of an air handler casing is really a function of two things--Overall U-value (defined by the insulation and thermal break) and the leakage rate.

Think about it: Every cubic foot of air leaked out of a cabinet is a cubic foot that had system energy applied to it to condition it, but now will not reach the occupied space. Conversely, every cubic foot of unconditioned air that leaks into a cabinet is a cubic foot that needs to be compensated for by more work by the air conditioning system. And this is a criteria that is critically affected by better panel design.

Traditional batt-type commercial air handlers catalog leakage rates of about 3-5% at 4" of static pressure. But because foam-core panels flex much less, and therefore don't open up leaks at panel seams as much, they typically exhibit much smaller leakage rates. Aaon catalogs leakages of less than 1% of the design airflow at 8" of static pressure. (To make a true comparison with the batt panels described above, you have to remember that static pressure increases with the square of leakage).

If you assume that 4" is a typical pressure rating for a commercial air handler, you can see that you would typically waste about 3-5% more energy in leakage with a traditional design than you would with a newer foam-core panel design. And this is additive to the direct thermal losses due to conduction through the cabinet. (Check the cataloged leakage rating even of foam-core designs, details matter and the seal and fastening design can also affect these leakage numbers. Not all manufacturers meet the standards described here).

But what about custom equipment? While generally the design details of that class of equipment can reduce the conduction, deflections and leakages even with standard batt insulation, there are still some advantages to foam core design. Energy Labs has introduced a foam-core panel for jobs that demand this premium construction, if needed. The traditional batt panel design still affords more flexibility in layout and does not come at the premium price necessary for a fully custom foam core unit.