“Structural Performance of Thermal Barrier Framing Systems” (AAMA TIR-A8-16) is the first update since 2008. Rich Rinka, the AAMA’s Technical Manager for Standards and Industry Affairs and one of the report authors, highlighted the importance of thermal barriers in an email to Energy Manager Today:
“The presence of a thermal barrier is very important for stopping energy flow, which has the benefit of reducing energy consumption of the building,” he wrote. “This document gives guidance to the designer of a framing system regarding the properties of the thermally separated composite extrusion. It gives tips and tricks for the end product being what you want it to be, and what you want it to be is energy efficient.”
The popularity of aluminum as a fenestration material puts thermal barrier design front and center. The foreword to the document points to the challenge: Aluminum has high thermal conductivity. Thus, steps must be taken to keep the conveyance of heat and cold under control. This is done by what in essence is a divide and conquers strategy:
With a properly designed thermal barrier product, the transfer of the thermal energy through an architectural framing system is reduced. This interruption of energy flow has obvious benefits in substantially reducing the total energy consumption of the building of which the end product is a part. The thermal barrier will also effectively improve the resistance of the framing members to condensation or frost formation. These thermal barrier systems allow aluminum to provide thermal performance comparable with other framing materials.
The document discusses the most common systems on the market.
Fenestration is a huge and very complex issue because so many interdependencies impact conditions. For instance, tightening a building’s envelop is a good thing. That can lead to an increase in condensation on windows, which is not.
Facility Executive says that tighter envelops or smaller fenestration envelops lead to reduced air infiltration, less air infiltration and “a subsequent increase in indoor relative humidity.” This can lead to greater condensation on windows. Controlling the condensation can be done by use of insulating glass, improving the thermal performance of the framing (essentially, what is suggested in the AAMA report) and warm edge technology.
A deeper dive on heat loss and gain is taken at Sourceable. One metric that is used is U value, which the feature – using the definition from wers.net – says is the “measure of the rate of non-solar heat loss or gain through a material or assembly.” It is the opposite of another key metric, R value, which measures the resistance to heat gain or loss.
The details are complex. The bottom line is that the important issues of air flow through a structure, envelop integrity and thermal barriers is an important topic for energy managers to track.