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Adding Glass While Saving Energy

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Adding Glass While Saving Energy

The key to a bright, healthy interior includes high-performance windows and a good software model.

March 3, 2021

One of modern architecture's hallmarks is glass. Homes that incorporate glass features have lots of windows and doors that bring in ample amounts of natural light, which is why they are so pleasant to live in. But glass can bring performance challenges. Energy modeling can address those challenges while offering additional benefits. To understand why, you need to understand the challenging role of glass in today's homes.

Take the example of the 2021 New American Remodel in Orlando, which was sponsored by Professional Remodeler magazine and the National Association of Homebuilders. Design/build remodeler E2 Homes created a light-filled modern interior with 5400 square feet of air-conditioned space and exterior walls that are more than one-third glass— mostly high-performance JELD-WEN windows and doors alongside LaCantina door systems. 

Jeld Wen

As with any new construction and home renovation, glass performance is crucial here. Highly insulated walls and roofs have reduced heating and cooling loads so much that energy transfer through glass has become a higher percentage of the remaining load. 

As a result, designers are paying more attention to the Solar Heat Gain Coefficient (SHGC), which measures how much solar radiation the glass lets through. Lower numbers denote less solar gain, and the windows and doors in the New American Remodel have SHGC's as low as 0.20, which is very good.

Jason Kantola, JELD-WEN's coordinating certification manager, says a Zero Energy home will need at a minimum Energy Star rated windows and glass configuration will depend on the climate. Those installed in Northern climates either need an argon gas fill for a lower U-value, while those used in the South need a darker low-e coating for lower SHGC numbers.

Even in Florida, however, you may not want the lowest possible number for every window or door. You may want more solar gain through a shaded north-facing window and might opt for an SHGC of 0.30 there. But those choices are best made in the context of whole-house performance.

Kantola says that JELD-WEN's architectural consultants (ACs) work with architects, remodelers, and energy consultants to choose the right windows and doors for the home, climate, orientation, and budget. This is one place an energy model really earns its keep: the specific windows and doors suggested by the AC will depend on the performance needs specified by the model.

That was the case on this project. Sustainability consultant Drew Smith of Two Trails Inc. entered the home's details into a program called Energy Gauge. The software let him do what-ifs, like calculations of how bottom-line energy use would be affected by different insulation levels, glazing values, roof overhangs, and mechanical system efficiencies.

Although modeling isn't standard practice among remodelers yet, it can be a real differentiator. For instance, Smith modeled this home before work began, calculating a HERS score of 147; then he modeled the finished project and got a final score of -11. "That helped us quantify the performance improvements we were making for the homeowners," he says.

Another reason for doing this on a remodel is because making a home more efficient can lower cooling loads so much that the heat pump ends up oversized. It can then short cycle, which means it will cool the air but won't remove enough humidity. "I see big jobs where the old equipment doesn't get replaced," says Smith. "Mold starts growing and you end up with a sick building and sick homeowners." In fact, he says that just replacing old windows with high-efficiency units can reduce cooling loads enough to leave the current heat pump oversized.

In other words, remodelers can use modeling technology to show how they ensure healthy buildings and healthy air while using highly efficient glass to make a home bright and pleasant. That's a win for everyone. 


LaCantina Doors

The key to a bright, healthy interior includes high-performance windows and a good software model.

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