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Testing Glazing in the Field: Performance Classes

Up until the 2008 edition of American Architectural Manufacturers Association/Window and Door Manufacturers Association/Canadian Standards Association (AAMA/WDMA/CSA) 101/I.S.2/A440, North American Fenestration Standard/Specification for Windows, Doors, and Skylights (NAFS), there were five performances classes of windows with differing requirements for test pressures, allowed leakage rates, and other variables. The current four types, and their minimum performance grades are:

  • R ([15 psf]);
  • LC ([25 psf]);
  • CW ([30 psf]); and
  • AW ([40 psf]).

Water

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penetration resistance test pressure (for laboratories) is 15 percent of the performance grade for R, LC, and CW classes; 20 percent for the AW Class.

To read the full article, click here.

Testing Glazing in the Field: Specifying procedures now avoids trouble later

Photo © Bruce Damonte. Photo courtesy Wausau

Photo © Bruce Damonte. Photo courtesy Wausau

by Dean Lewis

Water penetration through the building envelope is a serious concern, involving issues ranging from what constitutes reasonable performance during a hurricane to resolving liability for interior water damage and possible toxic reactions to moisture-induced mold. Fenestration is the prime candidate for being the weakest link in the weather-resistant barrier, and thus typically receives the greatest scrutiny.

However, faulty fenestration design is not likely to be the cause of leakage problems. Products that meet the appropriate Performance Class and Grade defined by the code-mandated American Architectural Manufacturers Association/Window and Door Manufacturers Association/Canadian Standards Association (AAMA/WDMA/CSA) 101/I.S.2/A440, North American Fenestration Standard/Specification for Windows, Doors, and Skylights (NAFS), must pass laboratory water leakage spray tests of increasing stringency, depending on the applicable onsite Design Pressure (DP) as based on the wind speed contour maps of American Society of Civil Engineers/Structural Engineering Institute (ASCE/SEI) 7-10, Minimum Design Loads for Buildings and Other Structures.

These laboratory tests simulate wind-driven rain according to ASTM E547, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Cyclic Static Air Pressure Difference, and ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference, by simultaneously applying air pressure at 15 percent of DP for all window classes, except the AW Class, for which it is 20 percent. (For more, see “Performance Classes.”)

Field testing of a storefront system to American Architectural Manufacturers Association (AAMA) 503, Voluntary Specification for Field Testing of Newly Installed Storefronts, Curtain Walls, and Sloped Glazing Systems. An exterior pressure chamber establishes the pressure differential, and a calibrated spray-rack is located inside the chamber. Photos courtesy AAMA

Field testing of a storefront system to American Architectural Manufacturers Association (AAMA) 503, Voluntary Specification for Field Testing of Newly Installed Storefronts, Curtain Walls, and Sloped Glazing Systems. An exterior pressure chamber establishes the pressure differential, and a calibrated spray-rack is located inside the chamber. Photos courtesy AAMA

These are not trivial conditions. For example, a 290-Pa (6.0-psf) water test pressure (WTP) is equal to that exerted by an 80-km/h (50-mph) wind. Such pressure develops an equivalent hydrostatic water head of 30 mm (1.2 in.), which may be enough to force water over a windowsill and into a building.

Yet, there are limitations on the extent to which even this rigorous testing can predict performance in the field. Water leakage may occur during a heavy rainstorm because the wind velocity pressure exceeds that for which the water penetration resistance of the window or door was designed and tested.

Additionally, laboratory tests cannot account for water penetration that actually may originate from the surrounding wall or roofing construction, causing water to run down the wall’s inside surface. Most importantly, lab tests do not account for window leakage due to improper installation, which—because building construction is rarely perfect—is the more likely culprit.

Product samples tested in the laboratory are positioned perfectly plumb, level, square, and true within a precision test fixture opening. In the field, although installed within acceptable industry tolerances, products are unlikely to find such exacting conditions. Shipping, handling, acts of subsequent trades, aging, and other environmental conditions all may have an adverse effect on product performance as installed when compared to the test results.

Specifiers are advised to require verification of the actual installed performance of fenestration products by insisting on field testing during or immediately after construction and before occupancy.

AAMA provides four field testing methods:1

  • AAMA 501.2, Quality Assurance and Diagnostic Water Leakage Field Check of Installed Storefronts, Curtain Walls, and Sloped Glazing Systems, which should be used as a spot-check during construction of a curtain wall or storefront system;
  • AAMA 502, Voluntary Specification for Field Testing of Newly Installed Fenestration Products, which is the proper test method for verifying field air leakage and water penetration resistance of newly installed operable windows and doors;
  • AAMA 503, Voluntary Specification for Field Testing of Newly Installed Storefronts, Curtain Walls, and Sloped Glazing Systems, which is the proper test method for field testing of new storefronts, curtain walls and sloped glazing for air leakage resistance and water penetration resistance; and
  • AAMA 511, Voluntary Guideline for Forensic Water Penetration Testing of Fenestration Products, which is intended for performing a systematic forensic investigation of observed, known leaks.

AAMA 501.2
Intended to be used during the construction process, AAMA 501.2 is inappropriate for testing operable windows and doors. It neither simulates the effects of wind-driven rain nor provides quantitative performance information. Rather, it is a simple, economical water spray quality check to reveal leaks in non-operable glazing, including gaskets, sealant, perimeter caulking, splices, and frame intersections.

Architectural skylights can also be field tested using AAMA methods.

Architectural skylights can also be field tested using AAMA methods.

The designated test area is divided into 1.52-m (5-ft) sections of the framing and joint. The area selected must include typical, representative samples of each part of the construction—usually a minimum of 9.3 m2 (100 sf), with no outstanding punch list items or other visible defects.

The test is conducted using a hose (19-mm [¾-in.] diameter suggested) and a special nozzle as specified in the standard. The water pressure to the nozzle must be 205 to 240 kPa (30 to 35 psi), unless a lower pressure is unavoidable, such as at a multistory building, but not lower than 172 Pa (25 psi). The nozzle is held at a distance of 305 mm (12 in.) from the location under test. Each section is evaluated for five minutes by slowly moving the nozzle back and forth over the test section. If leakage occurs, modifications are made and the test is repeated.

AAMA 502
The correct field test for air leakage and water penetration of newly installed fenestration units is AAMA 502. Testing is to be conducted before issuance of the building occupancy permit, but in no case later than six months after installation. It is based on ASTM E783, Standard Test Method for Field Measurement of Air Leakage Through Installed Exterior Windows and Doors, and ASTM E1105, Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Curtain Walls, and Doors by Uniform or Cyclic Static Air Pressure Difference.

To implement AAMA 502, a temporary test chamber is sealed to the interior (or, optionally, the exterior) side of representative fenestration products at appropriate stages of the product installation, subject to a minimum of three units. The test chamber is to be in such a manner as to apply the pressure differential to all joinery conditions with the wall. The number of products tested, and the frequency of testing, should be clearly specified by contract. (On large projects, tighter construction monitoring may be performed by testing at approximate intervals of five, 50, and 90 percent completion of the installation.)

Depending on whether installed on the interior or exterior, air is supplied to, or evacuated from, the test chamber at the rate necessary to establish and maintain the desired air pressure difference across the specimen. The maximum pressure needed is equal to two-thirds of the lab-tested and rated water test pressure as prescribed for the applicable product performance grade designation in NAFS, but not less than 91 Pa (1.9 psf).

For example, a product tested or rated as H-CW50 is field tested for water penetration resistance at a pressure differential of two-thirds of 360 Pa (7.5 psf), which equals 240 Pa (5 psf). This one-third reduction of the test pressure for field testing is considered to be a reasonable adjustment to account for the variables inherent in a field test environment.

Wind-driven rain from storms can account for moisture leakage into office tower curtain walls and windows. Photo © BigStockPhoto/Aleksey Fursov

Wind-driven rain from storms can account for moisture leakage into office tower curtain walls and windows. Photo © BigStockPhoto/Aleksey Fursov

Once the test pressure is established, a calibrated spray-rack applies water against the outside surface—with all operable portions of the specimen closed and locked—while technicians observe for any water penetration at the interior. ASTM E1105 Procedure A (uniform static air pressure difference; used for AW performance class windows) requires a 15-minute test with continuous pressure and water application. Procedure B (cyclic static air pressure difference; for all but the AW class) applies four water spray cycles of five minutes each under pressure, interspersed by one minute with the pressure released. To pass the test, there can be no penetration of uncontrolled water beyond a plane parallel to the product’s innermost edges.

AAMA 502 also provides for an air leakage resistance test, conducted per ASTM E783 at a minimum uniform static test pressure of 75 Pa (1.6 psf) except 300 Pa (6.2 psf) for the AW class; or as specified for the project, but not to exceed 300 Pa (6.2 psf). The acceptable air infiltration rate is limited to 2.3 L/s•m2 (0.45 cfm/sf) or 0.8 L/s•m2 (0.15 cfm/sf) for AW Class products. It is important to remember that air leakage is to be tested before the wall is wetted for water leakage testing—otherwise, water trapped within the wall components will tend to reduce air leakage.

AAMA 503
Similar to AAMA 502 but applicable to storefronts, curtain walls, and sloped glazing systems, AAMA 503 is also applied soon after the specimen is installed and sealants are cured, but before installation of gypsum wall board, insulation, or other finish materials, and no later than six months after issuance of the occupancy permit. Like AAMA 502, AAMA 503 bases its testing protocols on ASTM E1105 and E783.

AAMA 503 calls for testing to be conducted on at least a single 9.3-m2 (100-sf) area of installed product that is representative of the project.

Under AAMA 503, as with 502, the water penetration resistance test is performed per ASTM E1105’s Procedure A (uniform static air pressure difference), with the test pressure set at two-thirds of the specified project water penetration test pressure, but not less than 200 Pa (4.18 psf). In the event the project does not have a specified water penetration test pressure, the default value is 20 percent of the positive design wind load times 0.667. Water leakage is defined as any water not contained in an area with provisions to drain it to the exterior or the collection on an interior horizontal framing member surface of more than 14 g (0.5 oz) of water in the 15-minute test.

While ASTM E783 is referenced by AAMA 503 for field air infiltration testing, and may be used to evaluate the installed air leakage of ‘punched opening’ curtain walls, storefronts, and sloped glazing, it is not recommended for a portion of continuous systems due to the complexity of compartmentalizing air chambers and cavities. It is impractical to install a chamber on a segment of a continuous horizontal or vertical member.

If conducted, the air infiltration test proceeds at the same pressures called for in AAMA 502. However, the maximum allowable rates of measured air leakage must not exceed 1.5 times the project specification rate, or 0.45 L/s•m2 (0.09 cfm/sf)—whichever is greater. Or, the specifier may require project-specific air leakage.

This photo shows AAMA 503 field testing of an upper floor with the spray-rack supported by a telescoping boom. The air chamber under negative pressure is interior to the building. Photos courtesy AAMA

This photo shows AAMA 503 field testing of an upper floor with the spray-rack supported by a telescoping boom. The air chamber under negative pressure is interior to the building. Photos courtesy AAMA

Importance of early testing
Once it is installed, changes needed to repair a wall can be difficult and expensive. Thus, defining the acceptance criteria and field testing requirements in the project specification and performing the tests as soon as practical before a substantial portion of the project is completed (but no later than six months after installation) can help determine whether problems are present.

The advantage of testing prior to closing up interior walls and before building occupancy is design, fabrication, and installation problems can be revealed early enough that remedial work will be easier and less expensive.

Short-form specifications
AAMA 502 and 503 each provides a recommended short-form model specification that allows the specifier to prescribe the test pressures for both air infiltration and water resistance, depending on the location and wind exposure of the specific project as determined using the principles of ASCE/SEI 7. These are used by merely inserting the following paragraph(s), completed with the indicated information, into the project specifications.

AAMA 502 Short Form Field Testing Specification

  1. Newly installed fenestration product(s) shall be field tested in accordance with AAMA 502, Voluntary Specification for Field Testing of Newly Installed Fenestration Products.
  2. Test three (unless otherwise specified) of the fenestration product specimens after the products have been completely installed for air leakage resistance and water penetration resistance as specified.
  3. Air leakage resistance tests shall be conducted at a uniform static test pressure of ___ Pa (___ psf). The maximum allowable rate of air leakage shall not exceed ___ L/s•m2 (___ cfm/sf).
  4. Water penetration resistance tests shall be conducted at a static test pressure of ___Pa (____ psf). No water penetration shall occur as defined in AAMA 502.

AAMA 503 Short Form Field Testing Specification
The newly installed (storefront, curtain wall, and/or sloped glazing system) shall be field tested by an AAMA accredited independent laboratory, in accordance with AAMA 503, Voluntary Specification for Field Testing of Newly Installed Storefronts, Curtain Walls and Sloped Glazing Systems. The area(s) to be tested is (are) as follows: [(exact description of the area(s) to be tested by referencing an architectural drawing that clearly shows the intent of the area to be field tested.)]

Any of the following optional paragraphs may be added to modify the standard AAMA 503 specification:

  1. Optional air leakage resistance tests shall be conducted at a uniform static test pressure of ___ Pa (___ psf). The maximum allowable rate of air leakage shall not exceed ___ L/s•m2 (___ cfm/sf).
  2. Water penetration tests shall be conducted at a static test pressure of Pa (psf).

The specifier may increase the field water test pressure to the value specified for the project. In the event the project does not have a specified water penetration test pressure, the value would be equal to 20 percent of the positive design wind load times 0.667.

AAMA 503 includes field testing for storefronts. Here, the interior air chamber is sealed to a representative section including at least one of each profile, intersection, and joint. The exterior calibrated spray rack is visible through the glass.

AAMA 503 includes field testing for storefronts. Here, the interior air chamber is sealed to a representative section including at least one of each profile, intersection, and joint. The exterior calibrated spray rack is visible through the glass.

Forensic investigation of existing fenestration
In addition to field testing before occupancy, situations may arise where a forensic investigation of an actual problem in an occupied building can pinpoint the leakage path by recreating the known water leaks. This is done by researching the actual weather events that produced the reported water penetration, using the procedures of AAMA 511. Unlike quality assurance (QA) field testing during or shortly after installation, forensic investigators are required to provide more information than pass/fail criteria.

AAMA 511 expands on the investigative process set forth in ASTM E2128, Standard Guide for Evaluating Water Leakage of Building Walls, which recommends a total of seven investigative, review, and preparatory steps prior to actual testing, as well as post-testing steps. Pretest inspection and data gathering include a review of project documents, design concept evaluation, and a review of service history and inspections—all aimed at developing a hypothesis for the water intrusion’s source.

The process begins by calculating the differential air pressures the suspect specimens experienced during the actual wind-driven rain conditions coinciding with the original leak. This calculated pressure defines the test pressure to which the fenestration product is subjected during the actual field testing. If this calculated wind pressure is greater than two-thirds of the rated WTP for the product, it may be the product was not the most appropriate selection for the project.

The investigative process then moves to actual testing—the protocol for which is similar to that of AAMA 502 or 503. An optional sill dam test, also described in AAMA 511, can be used as necessary to further investigate the leak path.

Some caveats
Generally, field testing accounts for the unavoidable fact that performance of installed exterior wall systems likely will be somewhat less than laboratory performance, due to accumulated manufacturing and installation tolerances. Built-in allowances accommodate this, as well as the difficulty that may be encountered in conducting field tests with the same precision as laboratory tests.

In many cases, investigators have used inappropriate field testing adaptations to AAMA 502 and AAMA 503 to investigate the reported water penetration. A common, incorrect adaptation involves performing water testing at a differential pressure higher than the pressure the fenestration product experienced during the wind-driven rain events that produced the water penetration. Field testing at these high pressures may result in new leaks and the false conclusion the fenestration product is the cause of all the reported water penetration. Field testing at elevated pressures also may conceal defects that would have produced leakage at lower pressures.

Determining which units to test is an important step when planning field testing. It is important the units chosen as the test specimens include typical perimeter and joint conditions that occur throughout the wall system between fixed glass, fixed panels, and the framing members.

The University of California at Berkeley’s (UC Berkeley’s) newly opened Energy Biosciences Building is the most energy-effi cient facility on campus, thanks in part to its windows. According to lead architect Johnny Wong of San Francisco-based SmithGroup JJR, the building was designed and constructed to meet Silver under the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) program. Photo © Bruce Damonte. Photo courtesy Wausau

The University of California at Berkeley’s (UC Berkeley’s) newly opened Energy Biosciences Building is the most energy-efficient facility on campus, thanks in part to its windows. According to lead architect Johnny Wong of San Francisco-based SmithGroup JJR, the building was designed and constructed to meet Silver under the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) program. Photo © Bruce Damonte. Photo courtesy Wausau

However, the quantity and location of the specimen(s) selected for AAMA 503 testing can markedly affect the cost of testing. ASTM E122-09e1, Standard Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process, provides guidance on how to establish the number of test specimens required to measure the quality of a production lot with prescribed precision. Obviously, a situation where the cost of testing and building remediation approaches the cost of the glazing system should be avoided. Selecting as few as one specimen (or surface area as small as 9.3 m2 [100 sf] of glazing) may be sufficient to provide the information needed. On larger projects, a formal cost-benefit analysis is appropriate.

It is important to note AAMA 502, AAMA 503, and AAMA 511 all require the indicated testing to be performed by an AAMA-accredited testing laboratory—that is, one recognized as meeting the current requirements of AAMA 204, Guidelines for AAMA Accreditation of Independent Laboratories Performing On-site Testing of Fenestration Products. This ensures the laboratory has the qualified staff and calibrated equipment to properly perform field testing. One should be wary of any self-proclaimed window-tester, and ask to see the AAMA certificate of accreditation.

Finally, AAMA 501, Methods of Tests for Exterior Walls, is a good general reference that provides an overview of field testing. It places the individual protocols in context with one another, and also provides a comprehensive guide specification to cover all field testing protocols and options.

Notes
1 These and other AAMA documents may be obtained online from www.aamanet.org. (back to top)

Dean Lewis is the educational and technical information manager for the American Architectural Manufacturers Association (AAMA). He began his career in the fenestration industry at PPG Industries with positions in project engineering, product design, and sales and customer technical support, and has served on committees of American National Standards Institute (ANSI), ASTM, and the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE). Further experience includes teaching in the industrial and military sectors, and 35 years of managing technical training, publishing, and certification. Lewis has served on standards and certification committees of a dozen national and international organizations. He can be reached at dlewis@aamanet.org.

Meeting Efficiency Codes without Compromising Design: Technology that Meets Specifications

A full-scale mockup incorporating architectural insulation modules.  [CREDIT] Photo courtesy Dow Corning Corporation

A full-scale mockup incorporating architectural insulation modules. Photo courtesy Dow Corning Corporation

by Stanley Yee, LEED AP

To help overcome concerns about adoption of new technology, a full-scale mockup of a high thermally performing curtain wall incorporating architectural insulation modules was recently successfully tested by an independent third-party. Testing was conducted in accordance with American Architectural Manufacturers Association (AAMA) 501, Methods of Test for Exterior Walls, ensuring acceptable performance for air and water penetration resistance, structural capacity, and vertical and seismic movement requirements.

To read the full article, click here.

Meeting Efficiency Codes without Compromising Design

Photo courtesy of University of Birmingham

Photo courtesy of University of Birmingham

by Stanley Yee, LEED AP

Creating an effectively insulated envelope is necessary for buildings to meet the latest demands of ever-tightening energy codes. Innovative use of high-performance insulation technologies enables architects to achieve improved insulation performance using common building techniques without sacrificing aesthetics.

Thin-profile, high-performance insulation materials that seamlessly integrate into conventional glazing systems now give designers flexibility to better manage and balance thermal performance and façade aesthetics. Materials such as vacuum insulation panels (VIPs), architectural insulation modules (AIMs), and aerogel building insulation blanket materials are becoming more prevalent.

For many years, inexpensive energy made it possible to design buildings without regard for energy performance. The global movement toward sustainability has led to tightening regulations often restricting design freedom.

Local, national, and global organizations continue to develop codes that mandate increased thermal performance in insulation and, in turn, reductions in energy consumption. Construction in the United States can be subject not only to prevailing building codes, but also standards such as American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, with increasing pressure to comply with voluntary standards and certifications such as the United States Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) v4. Other drivers include:

  • 2012 International Energy Conservation Code (IECC);
  • Living Building Challenge;
  • growing demand for net-zero buildings; and
  • American Institute of Architects’ (AIA’s) 2030 Challenge.

From a design standpoint, simply increasing the amount of conventional insulation used in a building is neither practical nor aesthetically pleasing. New insulation technologies provide the performance advantages necessary to achieve effective building envelope insulation without sacrificing design aesthetics.

Integrated use of high-performance insulation in the curtain wall spandrel, in Calgary, Alberta, enables high window-to-wall-ratio designs that meet energy codes. [CREDIT] Photo courtesy BIG

Integrated use of high-performance insulation in the curtain wall spandrel, in Calgary, Alberta, enables high window-to-wall-ratio designs that meet energy codes. Photo courtesy BIG

Thermal performance of commercial insulation materials. [CREDIT] Images courtesy Dow Corning Corporation

Thermal performance of commercial insulation materials. Images courtesy Dow Corning Corporation

 

 

Balancing design trends with energy performance
Cognizant of the need for energy performance, architects are put in a challenging position. Designers are pressured by current building trends to include as much glazing and vision area as possible for optimal aesthetic value, striving to create iconic buildings of aluminum and steel with floor-to-ceiling glass. However, this rise in the use of glass means increasing energy performance can be challenging.

Unfortunately, extensive use of vision glazing is generally lower in thermal performance. To achieve an overall desired level of exterior wall performance, architects and designers must depend on the non-vision spandrel sections.

Used on the façades of commercial buildings, these opaque spandrel sections—typically composed of metal, stone, or glass panels—are used to conceal the floor lines. The spandrels are often designed to visually blend so closely with the vision glass they are not even perceptible, creating the effect of a uniform, all-glass building (Figure 1). They also are manufactured in various colors and designs, adding additional visual interest to the curtain wall’s appearance.

More importantly, the spandrels can be highly insulated to contribute to the façade’s overall thermal performance. Leveraging technical design opportunities in the spandrel sections allows designers to maximize the vision area and still meet prescribed thermal performance requirements of energy conservation codes, such as ASHRAE 90.1 and IECC.

Mineral wool requires eight to 10 times the thickness to provide the equivalent insulation value of a vacuum insulation panel (VIP).

Mineral wool requires eight to 10 times the thickness to provide the equivalent insulation value of a vacuum insulation panel (VIP).

Traditionally, spandrel areas need to be supplemented with an additional layer of thick mineral wool or similar conventional insulation to achieve the necessary thermal value. However, in higher climate zones, such as Climate Zones 4 and 5, this approach may require additional space within the curtain wall to accommodate the required thickness to achieve thermal performance targets. Thin-profile high-performance insulation technologies can solve these challenges.

Beyond the building’s outward aesthetics, architects are also facing the challenge of mitigating uncontrolled thermal losses due to thermal bridging across the building envelope. These heat losses typically occur at transitional conditions in building envelopes, such as:

  • exposed slab edges;
  • where glazing systems meet cavity wall components;
  • where below-grade and above-grade systems meet; and
  • where parapets meet roofs.

Building codes and regulations now require mitigation of thermal bridging conditions. They can make it especially challenging for architects to retrofit existing designs with insulation solutions meeting both performance requirements and available space limitations.

New applications for high-performance insulation technologies
Architects and designers have additional flexibility to respond to insulation performance challenges with high-performance insulation technologies, such as vacuum insulation panels. VIPs can be integrated into architectural insulation modules to enable whole-wall envelope thermal performance improvements; aerogel building insulation blankets can also be included to help address detail-specific thermal bridging issues. These materials not only demonstrate a step-change in thermal performance compared to traditional insulation materials, but also enable designs using current construction techniques to meet demands of the next generation of thermal requirements.

Figure 2 shows the thermal resistance (i.e. RSI, R-value) which is typically expressed as R-value per inch, of various insulation products, including materials typically found on a job site such as expanded polystyrene (EPS), mineral wool, and polyisocyanurate (polyiso). As demonstrated by Figure 2, the change to higher-performing materials is significant, with silica-fume-based vacuum insulation panels as high as RSI 5.63 to RSI 6.16 per 25 mm (R-32 to R-35 per inch) and the aerogel building insulation blanket at RSI 1.73 per 25 mm (R-9.8 per inch).

Composition of vacuum insulation panel.

Composition of vacuum insulation panel.

Thin-profile vacuum insulation panels
Vacuum insulation panel technology provides designers with new options. Offering insulation in a slender profile, a VIP’s thermal performance gives it the equivalency of eight to 10 times the thickness of mineral wool insulation typically used on a construction site (Figure 3).1

Forms of vacuum insulation were invented more than a century ago, and interest has grown over the past several decades in applications where constrained space and weight benefits justify the higher cost, such as commercial applications, as well as in ‘cold-chain’ applications, such as insulated shipping and transport containers. Now, the technology is finding its place in commercial façade insulation applications.

VIP construction (Figure 4) is based on a pressed fumed silica core, which is formed and heated to drive out the moisture. It is then inserted into a handling bag (i.e. core bag) and then into a multilayer, aluminized bag. As that bag is put under full vacuum, its edges are heat-sealed. When the vacuum is released, a full vacuum is contained within the bag. With the vacuum, all the atmospheric gases around the fumed silica are removed, therefore eliminating convective heat transfer from the gases within. With the full vacuum, the unit achieves the initial RSI 5.6 to RSI 6.2 per 25 mm (R-32 to R-35 per inch) center-of-panel (COP) performance. Without the vacuum, the material provides about RSI 1.4 per 25 mm (R-8 per inch), which is approximately twice as good as typical foam insulation—so even if the material loses its vacuum, it continues to provide good insulation performance.2

VIP offers many advantages. It has low nominal thermal conductivity—approximately 4 mW/mK at COP. The metalized bag around the panel is inherently moisture-resistant. The fumed silica core is an ash created by burning a silane. Essentially, the material has already been burned, providing a high degree of fire resistance. The VIP’s thin profile can also allow it to solve various problems; for example, increasing thermal performance requirements not being met by conventional means, or maintaining thermal performance requirements while allowing for increased vision area.

VIP is a pre-engineered product and must be customized by the manufacturer or packaged as part of a system; it cannot be cut to size onsite, as cutting or puncturing the material would cause a vacuum loss and resulting loss of thermal performance.

Cutaway view of architectural insulation modules incorporating VIP technology.

Cutaway view of architectural insulation modules incorporating VIP technology.

Architectural insulation modules are available in various finishes to meet aesthetic requirements.

Architectural insulation modules are available in various finishes to meet aesthetic requirements.

 

AIMs–integrated curtain wall application of VIP
The façades of modern glass curtain walls typify an ideal application for vacuum insulation panel technology. Curtain walls create the iconic artwork and unique character of a building. The ability to maintain a slim façade with a high thermal performance gives the architect the design freedom to maximize the wall’s vision area and/or thermal performance while still meeting local building codes.

For curtain wall applications, VIP technology is provided in an integrated façade module known as an architectural insulation module, which combines a VIP with a protective architectural finish (Figure 5). The module has a back pane of a rigid structural panel material, joined with a warm edge spacer (as used in the insulating glass industry) around the perimeter. VIP is inserted into the space—which typically is the air space in an insulating glass unit—and covered with a finished panel on the front. Modules are available in various architectural options, including opaque, metal, and glass with ceramic frit or ceramic frit patterns (Figure 6).

Performance of architectural insulation modules of various thicknesses.

Performance of architectural insulation modules of various thicknesses.

Modeling and guarded hot-box testing demonstrates the performance characteristics of architectural insulation modules technology (Figure 7). A 25-mm (1-in.) thick unit modeled with a two-dimensional finite element thermal analysis software package, resulting in an effective RSI 1.90 (R-10.84) and a COP value of RSI 3.84 (R-21.8).

A 50-mm (2-in.) thick unit is tested with ASTM C1363, Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus. Figure 7 shows actual test results of a 50-mm thick structural panel, which includes a 6-mm (1/4-in.) piece of glass on each side and a 38-mm (1.5 in.) VIP in the interspace, sized at 1.5 x 1.5 m (5 x 5 ft), indicating an effective RSI of 3.4 (R-19.05). The effective R-value is lower due to factors including heat losses around the insulating glass spacer assembly.

In addition to demonstrating superior thermal performance, the AIM is designed to meet the physical demands of commercial façade applications, withstanding typical windloads and meeting structural requirements. Constructed to standard or custom spandrel size specifications, the modules require no special installation techniques, eliminating need for specialized installer training.

Effect of VIP on U-value and window-to-wall ratio performance.

Effect of VIP on U-value and window-to-wall ratio performance.

Whole-wall insulation performance
Designing a slim façade with a higher percentage of vision requires the lowest possible U-values for spandrel areas to augment thermal performance characteristics. VIP-integrated façade modules enable additional vision area while still complying with thermal performance requirements, improving the curtain wall’s overall whole-wall performance.

When this technology is applied to a building design, it increases thermal performance by maintaining the same window-to-wall ratio, but its replacing of traditional insulation with architectural insulation modules, increases overall curtain wall thermal performance (Figure 8, Arrow 1).

Further, it increases design freedom as architects gain ability to potentially increase window-to-wall target ratios substantially, without compromising on the insulation value of the curtain wall configuration (Figure 8, Arrow 2X).

Blanket insulation
Like the vacuum insulation technology, aerogel is not a new concept, but it has been optimized for the next generation of building challenges. Invented in the 1930s, the material is composed of 95 to 99 percent air, making it one of the lightest materials. Its nanoporous structure minimizes thermal transport, giving it low thermal conductivity. It has been used in various applications, especially aerospace, but with tightening environmental requirements and increasingly complex building designs, aerogel insulation has now found a new niche providing thermal protection in space-restricted areas.

An aerogel building insulation blanket is made from synthetically produced amorphous silica gel. It features a small particle size, with the diameter of the spaces between aerogel particles similar to the fumed silica in the vacuum insulation panels. Manufacturing this material in a blanket form (Figure 9) creates a usable, flexible, construction-friendly material that can be cut-to-size onsite and applied to reduce the thermal bridging at specific locations in a building envelope assembly. Aerogel building insulation blankets are highly resistant to flame, with an ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, Class A fire rating (flame spread index 5, smoke developed index 10).

Flexible, highly insulating aerogel building insulation blanket.

Flexible, highly insulating aerogel building insulation blanket.

Linear transmittance reductions with aerogel building insulation blankets.

Linear transmittance reductions with aerogel building insulation blankets.

 

Minimizing thermal bridging
Updating architectural details to address thermal bridging concerns has become more common due to increasingly explicit and stringent building codes. The availability of a thin, flexible insulation material reduces the need to make trade-offs in design to meet codes and regulations, and it eliminates bulky or messy insulation from those tight areas of building designs.

Based on ASHRAE Research Project (RP) 1365, Thermal Performance of Building Envelope Details for Mid- and High-rise Buildings, three common construction details were modeled to demonstrate the effect of using aerogel building insulation blankets to minimize thermal bridging. These models are:

  • curtain wall-at-grade detail with the aerogel building insulation blanket applied from the neck of the curtain wall to the below-grade rigid insulation, resulting in a reduction in linear thermal transmittance approaching 25 percent;
  • curtain wall jamb at the exterior and interior insulated steel stud assembly with the aerogel building insulation blanket applied around the adjacent steel stud and at the wall-to-curtain wall transition, resulting in a reduction in linear thermal transmittance approaching 70 percent; and
  • rehabilitated window-wall system with the aerogel building insulation blanket at the slab edge and around vertical and horizontal glazing mullions, resulting in a reduction in linear thermal transmittance approaching 53 percent.

Lineal transmittance values can readily be incorporated into thermal models. This eliminates the guesswork and improves the predictability of the heat loss due to thermal bridging at those locations. (See Figure 10.)

Additionally, two whole-building energy models were created to demonstrate the effect of using aerogel building insulation blanket with conventional and higher-performance assemblies to minimize thermal bridging:

  • for a building with the glazing system covering 100 percent of the façade area, addition of the an aerogel blanket, with conventional assemblies resulted in a 3.56 percent energy savings;3 and
  • for a façade with curtain wall glazing and a steel stud wall assembly, addition of the aerogel blanket and higher-performing assemblies resulted in a 6.78 percent energy savings.4 (See Figure 11)
Annual heating energy savings for Chicago climate.

Annual heating energy savings for Chicago climate.

Conclusion
Vacuum insulation panels, architectural insulation modules, and aerogel building insulation blankets have been introduced in a range of construction projects in the United States and Europe, with positive response.

In an age of increasingly dramatic building design, architects can take comfort in knowing design does not have to take a backseat to performance and energy efficiency issues in current designs can often be addressed with innovative application of high-performance insulation materials.

Notes
1 For more information, see ASHRAE Fundamentals Handbook 2009. (back to top)
2 Visit Vacuum Insulation: Panel Properties and Building Applications at www.ecbcs.org/docs/Annex_39_Report_Summary_Subtask-A-B.pdf. (back to top)

Stanley Yee, LEED AP, is a façade design and construction specialist for Dow Corning High Performance Building Solutions. He joined the company in 2012 with nearly 20 years of experience in the building enclosure industry, working with curtain wall contracting, façade consulting, and enclosure detailing specialists both nationally and internationally. Yee earned a bachelor of engineering degree from Concordia University (Montréal, Québec). An active member of several industry organizations, he is an elected officer of the Board of Directors for the Glass Association of North America (GANA), representing the Energy Division. He can be contacted via e-mail at stanley.yee@dowcorning.com.

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An Advanced Frame of Mind: The Window-to-wall Ratio Dilemma

Reducing the window-to-wall ratio (WWR) could compromise human views and comfort.

Reducing the window-to-wall ratio (WWR) could compromise human views and comfort.

by Chuck Knickerbocker

In 2013, the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) proposed an addendum to ASHRAE 189.1, Standard for the Design of High-performance Green Buildings. The proposal seeks to reduce the window-to-wall ratio (WWR) area from 40 to 30 percent in small and medium-sized prescriptive-path buildings (buildings fewer than 23,226 m2 [250,000 sf]). ASHRAE 189.1 would allow building and design professionals using the performance-based approach to increase the glazed area.

While the purpose of the

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proposed reduction in glazing is to improve the building envelope’s energy-efficiency, numerous building and design professionals oppose the proposed change. Reducing the glazed area could compromise occupant views, human comfort, and the benefits of natural sunlight. Today, the WWR debate continues, bringing with it a renewed focus on specifying high-performance glazing systems in the building envelope.

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