Aerogel Insulated Double-Glazed Windows
Double-pane Window Glazing: Translucent Aerogel Insulation vs. Conventional Double-Glazed Vinyl Frame Window
A transluscent or opaque material with an insulating value up to R-20 per inch that can be used in windows, skylights, and walls (Aerogel, Kalwall).
Item ID: 290
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 variants in the market with different properties. Important to sort out the particular application and its needs. Cost is an issue. Need to predict performance for the specific cases of interest
- Excellent technology for non-view fenestration. Beautiful distribution of high quality sunlight with high thermal resistance. Best for top daylighting through skylights, clerestories and atria. Can also work with vertical windows at levels above and sometimes below view apertures.
- These technologies do not provide the quality of daylighting that you would want to support, given the glare that results from a bright translucent or opaque surface. If people want a translucent glass, these kinds of panels provide improved insulation, but in the grand scheme of things, this is not a significant gain in EE.
Silica-based aerogels have low thermal conductivity (high R values), are light weight, and can be sandwiched between sheets of glass or plastic to provide "superinsulating" glazing. This glazing can be used in existing and new residential and commercial buildings. Aerogel glazing is now becoming available in the insulation market.
Aerogels thermal properties can offer R-values of 14 to 105 for 3.5 inch thick bat depending on the structure. By comparison, typical fiberglass or cellulose wall insulation has an R-Value of 3 for a 3.5 inch thickness. A half-inch of aerogel has about the same insulating properties of three inches of fiberglass insulation.
Aerogels are now available in skylights, double glazed windows and translucent wall and roofing materials. Translucent wall and roofing material achieves an R-value of 20---equivalent to a solid wall and four times greater than insulated glass units. R-10 per inch aerogel insulated double glazed windows have no inert gases to leak out, are lighter than triple glazed window units, and provide better light transmittance without requiring low-e coatings. Aerogel filled skylights feature polycarbonate layers with an aerogel fill and provide an R-value of 4.6, making them up to six times more energy efficient than comparable products.
Aerogels offer superior thermal performance, transmit glare free, full-spectrum light; are moisture resistant, do not support the growth of mold or mildew, are UV stable, reduce sound transmission, and do not degrade in performance over time. Cost is the barrier to widespread market utilization. Aerogel production capacity is small scale at present.
Baseline Description: Residential single-glazed window
Baseline Energy Use: 42 kWh per year per square foot of glazing
To estimate the electrical energy use of a square foot of single-pane glass in a window in a building in the Northwest, we use the traditional heat-loss equation of
H = UAxHDDx24. In this case:
- U = A = 1
- Typical HDD (heating degree days) in the Northwest is 6000
So heat loss (H) = 144 kBtu/sf/yr = 42 kWh/sf/yr
There will be gains because of solar heat gain and supplemental heat (wood, etc.), and additional losses due to infiltration, and losses through the window, in the case of a forced air furnace, will be supplied by a furnace with some losses to the outside at the furnace and through the ducts. In an attempt to account for those differences, we make the simplifying assumption that these factors essentially cancel each other out, so we use the calculated value of 42 kWh/sf/yr. (Note: this is per square foot of single-glazed window area).
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 83%
Energy Savings Reliability: 3 - Limited Assessment
Use of R10 per inch aerogel in windows results in an overall R-value of R6. This provides an 83% savings relative to an R1 single-pane window.
Energy Use of Emerging Technology:
7.1 kWh per square foot of glazing 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.))
square foot of glazing
Potential number of units replaced by this technology:
We can only count in the technical potential of those homes currently heated by electrical appliances. We assume that aerogel-filled windows will get minimal penetration in the multifamily market in the foreseeable future. According to estimates in the Northwest Energy Efficiency Alliance's (NEEA's) 2011 Residential Building Stock Assessment (RBSA), 34.2% of single-family homes and 70.1% of manufactured homes in the Northwest are heated with electricity (Baylon, 2012 Pg 53, Table 51). We make the simplifying assumption that electrically-heated homes are the same average size as each category of home with all heating sources, so to get an estimate of square footage, we multiply the total square footage of each type of home times the percentage of homes that are electrically heated in that category. According to the RBSA, the square footage of glazing is approximately 12% of the floor area. Also according to the RBSA, about 12% of glazing is single-pane, but 10.8% of homes have storm windows. Assuming that most of the storm windows are on homes with single-pane glazing, that leaves only 1.2% of single-family homes with single pane and no storm windows. The corresponding numbers for manufactured homes are not available, so we estimated the given numbers (20% single-pane and 8% with storm windows). Note: Aerogel-filled windows can also be used in the commercial sector (particularly the small businesses). Note that aerogel-filled windows will also provide a substantial savings over double pane windows in either residential or commercial applications. Large commercial buildings tend to be cooling-dominated and utilize a 1/2-inch thick single layer of glazing that is often tinted for limiting solar heat gain.
Square Footage of Single-Pane Glazing in Electrically-Heated Homes
| Type Home || Homes || % Electric Heat || Electrically-Heated Homes || Avg. sf per Home || Total sf || % Glazing || sf Glazing || % Single-pane || % Storm Windows || sf Potential |
| SF || 4,023,937 || 34.2% || 1,376,186 || 2,006 || 2,760,630,027 || 12% || 331,275,603 ||12% || 10.8% || 4,000,000 |
| MH || 543,730 || 70.1% || 381,155 || 1,280 || 487,878,054 || 12% || 58,545,367 ||20% || 8% || 7,000,000 |
| Total || 4,567,667 || || 1,757,341 || || 3,248,508,081 || || 389,820,970 || || || 11,000,000 |
Source: (Baylon, 2012)
Regional Technical Potential:
0.77 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: square foot of glazing
Emerging Technology Unit Cost (Equipment Only): $134.16
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.01
Baseline Technology Unit Cost (Equipment Only): $22.36
Riffat and Qui, in "A Review of State-of-the-Art Aerogel Applications in Buildings" (Int'l Journal of Low-Carbon Technologies, April 20, 2012) state that aerogels are still relatively expensive, with the cost of an aerogel window six times that of a conventional double-glazed window. The reference that they extracted this information from, however, is somewhat dated. Aerogel is a technology that is still hoping for a reduction in unit costs given large-scale manufacturing. That is unlikely to occur, however, until aerogel products achieve cost competitiveness with conventional products. The material cost of a conventional insulation material is about 10 times lower for the same thermal resistance. In a niche application, Thermoblok offers 1-1/2″ wide strips, which are used to cover framing studs and help prevent thermal bridging. The cost is about $1.99/ft.
For lack of better information, we will assume six times the cost of a conventional double-pane window. HomeWyse indicates that the cost of a 42 in x 48 in window is $261 to $365 (equipment only) with a midpoint of $22.36/sf. Six times this value is $134.16/sf.
Simple payback, new construction (years): 35.6
Simple payback, retrofit (years): 42.8
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:
Total Pacific Northwest Building Stock Based on Preliminary Numbers from the 2013 Update to the CBSA
Northwest Energy Efficiency Alliance
Northwest Commercial Building Stock Assessment (CBSA): Final Report
Prepared by the CADMUS Group for the Northwest Energy Efficiency Alliance
University of Minnesota ,
Windows for high-performance commercial buildings
University of Minnesota
Aerogels: Much Ado About 'Nothing'
High Technology Careers Magazine
Aerogel Research at LBL: From the Lab to the Marketplace
Lawrence Berkeley National Laboratory
Aspen Aerogels ,
Highly Insulating Windows With a U-Value Less than 0.6 W/m2K
Development of windows based on highly insulating aerogel glazings
Technical University of Denmark
Aerogel: Energy-Efficient Material for Buildings
Center for Building Sciences Newsletter
NASA Research in Space May Redesign Household Windows
A review of state-of-the-art aerogel applications in buildings
International Journal of Low-Carbon Technologies
Breakthrough Aerogel 37x Better than Fiberglass
Aerogel Insulation for Building Applications: A State-of-the Art Review
Energy and Buildings