High Performance Windows
Highly insulated (R-5 or higher) windows, also known as super windows.
Item ID: 540
Building Envelope--Windows & Skylights
Technical Advisory Group: 2014 Commercial Building TAG (#9)
Average TAG Rating: 3.26 out of 5
TAG Ranking Date: 03/17/2014
TAG Rating Commentary:
- Several technology pathways; need to optimize overall properties as well as high. Multiple suppliers
- The extra value from today's standard double pane windows is for very cold climates.
- This technology has enormous potential and if products were more readily available here in the NW, as well as incentivized, market penetration would be strong.
- Part of an integrated strategy for net zero buildings
High performance windows are those with a U-Factor of 0.22 or lower (roughly an R-5 window). In contrast, a common double pane, clear glass window with an aluminum frame has a U-Factor of about 0.67. A "typical" highly insulating window might be a triple-pane vinyl-frame slider or patio slider window with a Low-E coating. For this design, the U-Factor is about 0.2 while the solar heat gain coefficient is about 0.19.
While these advanced high performance window designs do save energy, reduce peak loads, provide additional occupant comfort (through more uniform temperature distributions), and reduce condensation, they are expensive. The U.S. Department of Energy Volume Windows Purchase Program indicates a cost of $25/sf to $46/sf with an average cost of $34/sf. A 1500 sf 3-bedroom/2-bath home might have 196/sf of window area, leading to window upgrading or retrofit costs of $4,900 to $13,600. Incremental costs for new construction are lower but energy savings are also reduced when the high performance window is compared to code-required windows.
The Pacific Northwest National Laboratory (PNNL) conducted side-by-side tests of standard double pane windows versus advanced windows. While the energy savings were substantial, resulting in heating and cooling system energy savings of about 1,784 kWh/year in Eastern WA, the simple paybacks on investment in a retrofit project are on the order of 23 to 42 years. The test homes were equipped with a heat pump (SW Widder, PNNL, "Side-by-Side Field Evaluation of Highly Insulating Windows in the PNNL Lab Homes", PNNL-21678, August, 2012).
Baseline Description: House Equipped with Old Double-Pane Metal-Framed Windows
Baseline Energy Use: 7796 kWh per year per household
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 12%
Energy Savings Reliability: 6 - Approved Measure
PNNL side-by-side studies of two houses equipped with heat pumps indicated a savings over the heating season of 11.6% with a savings during the cooling season of 18.4%. For a 1,500 sf house located in the Tri-Cities area, annual energy savings due to the provision of advanced, versus common double-pane/metal frame windows are on the order of 1,784 kWh/year. This savings may be generous if applied to all homes within the region, as EUI's for homes with electric baseboard systems are on the order of 17.74 kBtu/sf-yr while forced-air furnace EUI's require about 23.37 kBty/sf-year (from Ecotope, "Residential Building Stock Assessment: Metering Study", prepared for the Northwest Energy Efficiency Alliance, April 28, 2014). A 1,500 sf home with baseboard heating (and no cooling) would require on the order of 7,796 kWh/year for heating and 11.6% of that amount is only 904 kWh/year.
A comparison of advanced high performance windows against code minimum windows indicates a potential savings of only 363 kWh/year with an incremental cost of about $3.87/sf. Simple payback is about 32 years.
This is a deemed measure under the October 1, 2014 BPA "Energy Efficiency Implementation Manual". The deemed amount is $6.00 to $8.00 per square foot of glazing area when it is replacing a single pane window of any frame type or a double pane patio door or windows with a metal frame type.
Energy Use of Emerging Technology:
6,860.5 kWh per household per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
The 2011 "Residential Building Stock Assessment: Single-Family Characteristics and Energy Use" indicates that 13.2% of the households within the region are equipped with double-glazed metal frame windows. An additional 12% have single glazing with metal, wood, vinyl, or fiberglass frames (See Table 40 on Page 43, 'Distribution of Window Types by State'). It is evident that 25.2% of the households in the region would greatly benefit from the installation of advanced high-performance windows. The study also shows a total of 4,023,937 single family utility customers (Page 10) indicating that about 1,014,932 households within the region should be considered for energy savings window upgrades.
Regional Technical Potential:
0.95 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: household
Emerging Technology Unit Cost (Equipment Only): $6664.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.01
Baseline Technology Unit Cost (Equipment Only): $1.00
The U.S. Department of Energy Volume Windows Purchase Program indicates a cost of $25/sf to $46/sf with an average cost of $34/sf. A 1500 sf 3-bedroom/2-bath home might have 196/sf of window area, leading to window upgrading or retrofit costs of $4,900 to $13,600. Incremental costs for new construction are lower but energy savings are also reduced when compared with code-required windows. At a cost of $34/sf, the total costs of a high performance window upgrade are about $6,664 per household.
Simple payback, new construction (years): 79.1
Simple payback, retrofit (years): 79.1
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
Reference and Citations:
Side-by-Side Field Evaluation of Highly Insulating Windows in the PNNL Lab Homes
Pacific Northwest National Laboratory