Experiment: Highly Insulating Windows
As wall insulating techniques and products have dramatically improved, windows have been the weak spot in the thermal envelope. Improving the insulation and solar heat gain characteristics of a home’s windows have the potential to significantly improve the home’s overall thermal performance by reducing heat loss (in the winter), and heat gain (in the summer) through the windows. A high-quality installation will also minimize or reduce air leakage through the building envelope, decreasing infiltration and thus contributing to reduced heat loss in the winter and heat gain in the summer. These improvements all contribute to decreasing overall annual home energy use.
In addition to improvements in energy efficiency, highly insulating windows can have important impacts on occupant comfort by minimizing the cold draft occupants often experience near window surfaces that are noticeably colder than the room air temperature.
To examine the energy, air leakage, and thermal comfort performance of highly insulating windows, a field evaluation was undertaken in the Lab Homes during the winter heating and summer cooling seasons in 2012. The heating season data were taken from February 3, 2012, to April 13, 2012, and the cooling season data were taken from July 6, 2012, to August 18, 2012. In this field test, the energy savings from highly insulating windows in the experimental home were compared to those of the standard double-pane clear glass windows in the baseline home.
In addition to the improved energy and thermal comfort performance, highly insulating windows must prove to be cost-effective compared to baseline, clear-glass windows to enable significant market penetration. Based on measured and modeled energy savings, as well as installed cost data from window manufacturers, PNNL’s work also examined the cost-effectiveness of windows in new construction and retrofit scenarios, with the results documented in the final report listed below.
Although PNNL found that the highly insulating windows were not cost effective in today’s market, additional improvements in manufacturing and/or market penetration that continue to drive down costs will make highly insulating windows much more viable as a cost-effective energy-efficiency measure. In addition, more consistent and uniform interior temperature distributions suggest that highly insulated windows, as part of a high-performance building envelope, may enable more centralized duct design and downsized HVAC systems. Shorter, more centralized duct systems and smaller HVAC systems could yield additional cost savings, making highly insulating windows more cost effective as part of a package of new construction or retrofit measures to achieve significant reductions in home energy use.
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Title
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Publication Date
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Citation
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| Field Evaluation of Highly Insulating Windows in the Lab Homes: Winter Experiment
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June 2012
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Parker GB, SH Widder, and NN Bauman. 2012. Field Evaluation of Highly Insulating Windows in the Lab Homes: Winter Experiment . PNNL-21524, Pacific Northwest National Laboratory, Richland, WA.
Abstract | Full Publication
Formal Report
"Lab Homes" located on the Pacific Northwest National Laboratory (PNNL) campus during the 2012 winter heating season. Improving the insulation and solar heat gain characteristics of a home's windows has the potential to significantly improve the home's building envelope and overall thermal performance by reducing heat loss (in the winter), and cooling loss and solar heat gain (in the summer) through the windows. A high quality installation and/or window retrofit will also minimize or reduce air leakage through the window cavity and thus also contribute to reduced heat loss in the winter and cooling loss in the summer. These improvements all contribute to decreasing overall annual home energy use. Occupant comfort (non-quantifiable) can also be increased by minimizing or eliminating the cold 'draft' (temperature) many residents experience at or near window surfaces that are at a noticeably lower temperature than the room air temperature. Lastly, although not measured in this experiment, highly insulating windows (triple-pane in this experiment) also have the potential to significantly reduce the noise transmittance through windows compared to standard double-pane windows. The metered data taken in the Lab Homes and data analysis presented here represent 70 days of data taken during the 2012 heating season. As such, the savings from highly insulating windows in the experimental home (Lab Home B) compared to the standard double-pane clear glass windows in the baseline home (Lab Home A) are only a portion of the energy savings expected from a year-long experiment that would include a cooling season. The cooling season experiment will take place in the homes in the summer of 2012, and results of that experiment will be reported in a subsequent report available to all stakeholders.
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| Side-by-Side Field Evaluation of Highly Insulating Windows in the PNNL Lab Homes: Final Report
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August 2012
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Widder SH, GB Parker, MC Baechler, and NN Bauman. 2012. Side-by-Side Field Evaluation of Highly Insulating Windows in the PNNL Lab Homes . PNNL-21678, Pacific Northwest National Laboratory, Richland, WA.
Abstract | Full Publication
Formal Report
To examine the energy, air leakage, and thermal performance of highly insulating windows, a field evaluation was undertaken in a matched pair of all-electric, factory-built “Lab Homes” located on the Pacific Northwest National Laboratory (PNNL) campus in Richland, Washington. The "baseline" Lab Home B was retrofitted with “standard” double-pane clear aluminum-frame slider windows and patio doors, while the "experimental" Lab Home A was retrofitted with Jeld-Wen® triple-pane vinyl-frame slider windows and patio doors with a U-factor of 0.2 and solar heat gain coefficient of 0.19. To assess the window, the building shell air leakage, energy use, and interior temperatures of each home were compared during the 2012 winter heating and summer cooling seasons. The measured energy savings in Lab Home B averaged 5,821 watt-hours per day (Wh/day) during the heating season and 6,518 Wh/day during the cooling season. The overall whole-house energy savings of Lab Home B compared to Lab Home A are 11.6% ± 1.53% for the heating season and 18.4 ± 2.06% for the cooling season for identical occupancy conditions with no window coverings deployed. Extrapolating these energy savings numbers based on typical average heating degree days and cooling degree days per year yields an estimated annual energy savings of 12.2%, or 1,784 kWh/yr. The data suggest that highly insulating windows are an effective energy-saving measure that should be considered for high-performance new homes and in existing retrofits. However, the cost effectiveness of the measure, as determined by the simple payback period, suggests that highly insulating window costs continue to make windows difficult to justify on a cost basis alone. Additional reductions in costs via improvements in manufacturing and/or market penetration that continue to drive down costs will make highly insulating windows much more viable as a cost-effective energy efficiency measure. This study also illustrates that highly insulating windows have important impacts on peak load, occupant comfort, and condensation potential, which are not captured in the energy savings calculation. More consistent and uniform interior temperature distributions suggest that highly insulated windows, as part of a high performance building envelope, may enable more centralized duct design and downsized HVAC systems. Shorter, more centralized duct systems and smaller HVAC systems to yield additional cost savings, making highly insulating windows more cost effective as part of a package of new construction or retrofit measures which achieve significant reductions in home energy use.
Report Appendices
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