ENERGY STAR® 7.0 Making Intelligent Design Decisions

Maximize operations’ bottom-line profitability and increase products’ market share by making intelligent fenestration design decisions.

Since the 7th version of the ENERGY STAR® eligibility criteria draft was released, the industry expressed concerns about the aggressiveness of the proposed requirements, how they may impact current product designs, and the depth of the associated productivity and financial implications these changes will have on window and door manufacturing operations.

Now that ENERGY STAR® 7.0 eligibility requirements have been finalized, it is important that we fully understand their impact. I will address this by publishing this article, among others that will follow in the future. I will use comparative data analysis of existing window systems that were modeled and simulated to validate compliance with ENERGY STAR® 7.0 requirements after specific design changes have been made. My intent is to publish multiple articles accompanied by simulation and modeling results.

Using simulation and modeling, we debunk speculations and present a factual view of the possibilities to meet ENERGY STAR® 7.0 requirements cost-effectively, without hindering operations’ productivity.

Can we meet ENERGY STAR® 7.0 requirement using Double Pane IGUs?

A lot of the industry focus recently revolved around this question, “Is the only way to meet the requirement to use Triple pane IGUs in our window products?”

Many have attempted to answer that question. Some may have inferred that triple-pane IGUs are the only way to meet the criteria. Data adds more depth to the story.

It makes common sense that triple pane IGUs should not be the first “go to” option if a double pane IGU can provide adequate performance to meet the new requirements. Triple pane IGUs can be designed to provide exceptional thermal performance due to the presence of two IG cavities and three panes of glass. They can be the preferred choice when the products’ targeted performance cannot be met with double pane IGUs or if the cost of making the fenestration product with double pane IGUs exceeds that of triple pane IGUs due to the use of special product treatments or components. One of the trade-offs when using triples is the production time. This issue has been addressed by GED with The Automated Tri-Lite Assembly System (ATLAS). ATLAS produces more triple-pane IGUs in a shift today than most other systems can produce double-pane IGUs. Additional trade-offs when trying to use triples as a direct replacement for an existing window include their weight and size. They are heavier and may require upgrades to the sash, the frame and the sash lifting components in the case of Double Hung and Single Hung windows. Sash and frame upgrades typically require retooling, making changes time-consuming and even more costly to manufacturers.

Our data shows that some dual pane IGU configurations can be used to meet ENERGY STAR® 7.0 requirements.

Focus on Equal Performance Method:

The ENERGY STAR® 7.0 eligibility criteria for Northern climate has a prescriptive method and an equal performance method. Unlike the prescriptive method, which calls for the lowest U-Value of 0.22 Btu | h-ft²-F, the equal performance method uses both U-value and Solar Heat Gain Coefficient (SHGC) criteria to meet requirements. This distinction is especially beneficial in the case of Dual pane IGU design considerations.

The equal performance method contains the following matrix:

Although all window components play a role in dictating a window system U-value, not all components contribute to the overall system U-Value equally. Glass plays the dominant role in the performance of fenestration products. After all these systems are built with more surface area of glass than anything else. Thanks to glass manufacturing technology advancements, we can meet the U-value and SHGC requirement of ENERGY STAR® 7.0 with double pane IGUs. Other consideration factors are the type and concentration of noble insulating gas, spacer type, overall windows and door extrusion designs, reinforcement type(s), and whether framing members use spray foam or foam inserts selectively.

Effective product design efforts should be focused on meeting today’s challenges and energy requirements considering true and tested available technologies at the most cost-effective rational, not the challenges of a decade from now at the expense of today’s cost premiums.

This means manufacturers’ products that meet the 0.26 U-value and ≥ 0.40 SHGC are technically the same as the ones hitting the 0.22 U-value. The obvious difference lies in the cost and the amount of product and process changes required.

Summary of data from a simulation case study:

The case study used a dated double-hung window system that existed for more than 15 years. This window system was precisely selected because it represents a wide base of average-performance vinyl double-hung windows in the market.

The window system used a Double Pane IGU with an Intercept Ultra spacer. It used a passive solar control glass on surface 2 and a 4th surface low-E on surface 4. The IGU had a 5/8” cavity and an overall under 7/8” with a 95% Argon fill.

The IGU center of glass U-Value came at 0.212 Btu | h-ft²-F and an SHGC of 0.636.

The overall product U-Value came at 0.24 Btu | h-ft²-F, and 0.49 SHGC, making it eligible for ENERGY STAR® 7.0.

Takeaways:

• Utilize glass technology advancements to your advantage and make sure the most recent LBNL Insulating glass database is used to obtain the most recent glass types.
• Using a passive solar control glass on surface 2 and a 4th surface Low-E on surface 4 will yield a low U-value and a high SHGC combination that has a high probability of meeting the Northern ENERGY STAR® equivalent performance eligibility requirements.
• Choose design elements carefully to achieve ENERGY STAR® 7.0 eligibility without sacrificing manufacturing capacity or pushing the limits of production costs.

In upcoming articles, I will address other fenestration product design considerations and reveal their advantages, disadvantages and expand on improving production efficiency for volume-centric IG production operations. This article, and the upcoming ones, are intended to serve the interest of the industry and its customers by providing manufacturers with facts that allow them to make the best products, cost-effectively.