Note: See the updated information about DOE’s Triple Pane program: 12/9/2011
I bet you just got used to hearing about double pane, Low-E glass, Argon filled windows. You know the ones. The ones labeled as ENERGY STAR? Now, there is a new babe in town getting a lot of attention from the Department of Energy. The R-5 window has all the right curves and significant energy savings compared to its distant cousin, the ENERGY STAR window. Yep, this R-5 is energy efficient beauty with triple panes of either high solar-gain, Low-E Glass, Argon/Krpton Gas or high solar-gain, Low-E Glass, Argon/Krpton Gas, depending on your area of the country. According to the DOE,
“Common ENERGY STAR windows only have an R-value of 3. Increasing the R-value from 3 to 5 reduces average heat loss through the windows by 40% and saves consumer money on energy bills.”
But why are the R-5 windows the darlings of the DOE?
“Windows in the U.S. account for 30% loss of building heating and cooling energy, representing an annual impact of 4.1 quadrillion Btu (quads) of primary energy. Windows have an even larger impact on peak energy demand and on occupant comfort.”
So are these babes for everyone? They are best suited for cold and mixed climate areas. So, why isn’t everyone jumping on the R-5 bandwagon? Cost versus energy efficiency. That energy type rope. (Isn’t that always the problem?)
Well, never fear; the DOE developed an affordable volume purchase program. How affordable? Prior to the development of the program, the DOE estimated a price premium of $4/ft² compared to today’s typical ENERGY STAR windows. To find out the volume pricing for specific types of windows in various climates, see here. To compare costs versus savings for highly insulated windows in different climates, see here.
What make the R-5 windows so special?
According to the Efficient Window Collaborative,
“Triple-Glazed** with High-Solar-Gain Low-E Glass, Argon/Krypton Gas
This figure illustrates the performance of a window with a very low heat loss rate (low U-factor). In this case there are three glazing layers and two Low-E coatings, 1/2″ argon gas or 1/4″ krypton gas fill between glazings, and low-conductance edge spacers. The middle glazing layer can be glass or plastic film. Some windows use four glazing layers (two glass layers and two suspended plastic films). With this window, both Low-E coatings are spectrally selective in order to minimize solar heat gain. This window is best suited for climates with both significant heating and cooling loads.
Triple-Glazed** with Low-Solar-Gain Low-E* Glass, Argon/Krypton Gas
This figure illustrates the performance of a window with a very low heat loss rate (low U-factor). In this case there are three glazing layers and two Low-E coatings, 1/2″ argon gas or 1/4″ krypton gas fill between glazings, and low-conductance edge spacers. The middle glazing layer can be glass or plastic film. Some windows use four glazing layers (two glass layers and two suspended plastic films). Both Low-E coatings in this product have high visible light transmittance. The use of three layers, however, reduces the beneficial solar heat gain. This product is suited for buildings located in very cold climates, although Double-Glazed with High Solar Gain Low-E should be considered if passive solar heat gain is desired.”
For more detailed information about different glazing area of windows, see here.
If you are like me, you probably still have questions. The DOE created an informational presentation about the program.
Residential Case Study
Sometimes it is hard to understand the cost savings without seeing an actual cost case study. The DOE cites various studies ranging from residential to commercial applications. The agency used the Wisdom Way Solar Village retrofit job as an example of residential cost savings associated with the installation of triple pane windows.
“One successful example is Wisdom Way Solar Village, a small residential development comprised of 10 duplexes in western Massachusetts. These homes were designed and built to showcase energy-efficient building performance at affordable price points. Duplexes of this project range in size from 2-bedroom units at 1,137ft² to 4-bedroom units totaling 1,773ft². Successful use of triple-pane high performance windows in concert with an improved overall building envelope allowed for the scale-down from a conventionally sized heating system to a 12,000 Btu natural gas unit. This heating unit reduction represented a $4,500 savings in the total cost of the system. Additionally, due to the superior insulating properties of the windows and overall envelope, occupants can expect to save over $1,000 annually on energy. Despite a $7,000 incremental cost for an enhanced building envelope—$3,500 of which was spent on window upgrades—achieving building performance that allows for a more compact heating system can offset much of this incremental cost and significantly reduce the payback period.”
Light Commercial Case Study
In addition, to the above case study, the DOE cites the 34,500 square foot Cambria Office Facility retrofit in Ebensburg, PA, as an example of energy cost savings to support the installation of R-5 windows:
“This facility incorporates highly insulating, triple glazed windows at an incremental cost of $15,000 compared to traditional double glazed windows. These windows permitted the complete elimination of the perimeter heating system priced at $25,000.The air conditioning system was also downsized from 120 to 60 tons, saving $40,000 of which 15 tons or $10,000 was directly attributable to the triple glazed windows. Operating energy costs for this facility are less than a similar-sized office building in PA with traditional double-glazed windows.”
So, readers, what are your thought about the new IT kid on the block, the R-5 window? Is its premium cost worth the energy savings? Let me know your thoughts.
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