As the 2013 Title 24 Standards Part 6, The Energy Code, took effect many new requirements rolled out, one of the most challenging being the prescriptive requirements for metal framed windows. It became apparent that many windows previously considered “high performing” with their dual pane, low-E glass and thermally broken frames could no longer meet the requirements.
Title 24 requires that windows obtain an NFRC label to certify that they meet the necessary U-factor, Solar Heat Gain Coefficient (SHGC) and visual transmittance (VT) required. Otherwise the energy modeler must assume a center of glass performance which most certainly does not meet the prescriptive requirements.
So what are options to architects who need to comply? Should we put vinyl windows on storefronts, airplane hangars, and classrooms? Yeah, we didn’t think so. There are really two options.
NFRC Compliant Windows
The first can be hard to achieve, but the architect can search the NFRC database. Simply enter in the window type you want, select a manufacturer you think can provide the performance you need and then you have the option of adding the performance criteria the energy modeler indicates is necessary to comply prescriptively. Get in touch and we will send that data to you. Here are a few that come close to complying:
You will notice that they are triple pane and would require some level of shading to meet the SHGC value. You also need to be careful that they meet the minimum visual transmittance criteria, which many of these don’t. If you look more, you can find a handful of double pane windows that meet the requirements as well.
The problem with this solution is even when you find a window that complies these windows are, as we’ve been told, extremely expensive.
Performance Compliance Path
So what else might the project do? Well, the project could be modeled using the performance compliance path. While this does cost more in terms of energy modeling, often a project using LED lights can use the energy credit from the lighting to pay for lower performing windows (read that as cheaper, but still relatively high performance windows). The LED’s are going in anyway so why not pay a little more to build a better energy model in order to pay a lot less for the cost (and possible hassle sourcing) of the windows.
Utilizing the performance energy model approach to arrive at a lower overall project cost has other benefits. Metal framed walls, prescriptive window requirements, economizers and numerous other items can often be “modeled out” of the project.
If you want to explore these potential benefits, get in touch and let us know how we can help you bring your clients lower overall project costs through effective performance modeling.