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Aybars Asci SOMElizabeth Boone SOM Gary Haney SOMChristopher Olsen SOMTeresa Rainey SOM

Bottom Left: Perception of a glass tube: reflec-tion, refraction, and transparency (Pottle 2012)

ABSTRACT This early research explores the potential of Vacuum Insulated Glass as a unitized building enclo-

sure system. With particular emphasis on thermal performance, the research pursues a modular,

evacuated, self-supporting, and solar collecting unit. This paper describes the visual, structural,

and environmental attributes of the prototype, manufacturing considerations, and the multi-disci-

plinary computational approach which was taken to arrive at a schematic level proof of concept.

2

Right: Modular interlocking building enclosure study model

3

Top Left: Vacuum insulated tube enclosure study model (Pottle 2012)

1

VACUUM INSULATED TUBES MODULAR, SELF-SUPPORTING EXTERIOR ENCLOSURE SYSTEM

638ACADIA 2014 DESIGN AGENCYDATA AGENCY

INTRODUCTION

Understanding the trajectory of local and international energy code

requirements towards net zero energy buildings, the efficiency of

the building envelope is becoming increasingly critical. The highest

energy transfer from building enclosures occurs on the glazed por-

tions of buildings, contributing to large heating and cooling loads

and high-energy consumption. The reduction of glazed areas along

with uses of high performance coatings and/or triple glazing are

strategies currently used to mitigate this problem, but can create

others. Minimizing glazed areas reduces the energy transfer, but it

has the adverse effect of limiting views to the outside and reduces

incoming daylight. This increases the need for energy consuming

artificial lighting, which diminishes the interior quality of light with

a poor color rendition index. Given the opportunity to design an

enclosure system for a tower in midtown Manhattan, the design

team sought out a singular system which would outperform a typi-

cal glazed system and provide a dynamic visual effect.

Visually, the perception of a glass tube creates a complex phenom-

enon through a play of reflection, refraction, and transparency. The

convex and concave surfaces of the glass tube create both con-

verging and diverging reflections. The arrangement of the tubes

into an array provides a multiplicity of these visual effects, which

are enhanced by movement of the viewer (Figures 2–4). Prior to hy-

pothesis-testing, a set of performance objectives was established

to be studied computationally. The design criteria consisted of:

1. Vacuum Insulated Glass unit formed by two uniform-radii-

curved pieces of laminated glass, which are joined to form

a vacuum chamber. The absence of air in the evacuated

chamber eliminates conductive and convective heat trans-

fer, creating a thermal buffer for both hot and cold climates.

2. The convex inner half glass-lite of the cylinder reflects the

incoming solar radiation to its center, concentrating the en-

ergy to a single focal point, enabling an efficient solar collec-

tor to generate power. Redirection of solar radiation limits

the amount which passes through the glass tubes and into

the conditioned space, thus minimizing solar heat loads.

3. Self-supporting due to the structural cross section, the

tube’s geometry allows for the negative pressures of the

vacuum chamber without any additional structural support.

Due to the complex nature of the claims, assumptions were

discussed with environmental, structural, and manufacturing

partners in order to run analyses confirming that the performance

objectives were achievable and assist in the design development

process. In forthcoming stages of the research these claims will

be further investigated.

THE UNIT

In the earliest engineering stages the modules are conceived to

arrive at the project site as thermally broken, evacuated, sealed

units, to be assembled in a grid (Figure 5). The units are to be

pre-fabricated in a controlled shop environment from a kit of

uniform, custom-fabricated components. The modular tube unit

is constructed of two uniform-radii-curved pieces of laminated

glass; thermally broken extruded vertical and horizontal end-cap

plate framing; gaskets; structural and weather seals; setting hard-

ware and metal trim (Figure 6–Figure 7). For solar-exposed orienta-

tions a PV rod is inserted at the center of the cylindrical tubes. A

sub-structural suspension system allows the units to be precisely

placed and secured in repeating rows and columns, and their pe-

rimeter detailing allows the units to seal against each other, thus

creating a building enclosure (Figure 8). The assembly can be prac-

tically used for the enclosure of any building type, and the ability

to alter the unit’s translucency or opacity allows for flexibility in

adapting to different programmatic demands.

The arrangement of the tubes into an array provides a multiplicity of visual effects4

639 VACUUM INSULATED TUBESASCI, ET AL.

Thermally broken, evacuated, sealed unit5 Preliminary vertical perimeter detail6

Preliminary horizontal perimeter detail7 Propagation of unit stacked both horizontally and vertically8

640ACADIA 2014 DESIGN AGENCYDATA AGENCY

ENVIRONMENTAL

As the condition of the climate crisis escalates, it triggers more

stringent requirements addressing the energy consumptions of

the built environment, as buildings account for 47.6 per cent of

U.S. energy consumption.1 In North America, ASHRAE 90.1 has

been adopted as the basis for local energy code. The American

Society of Heating, Refrigerating and Air-Conditioning Engineers

(ASHRAE) has issued ASHRAE Vision 2020 which states that

“the building community will produce market-viable net zero

energy buildings by the year 2030” (ASHRAE 2008). Similarly the

American Institute of Architects is advocating for carbon neutral

buildings by the year of 2030 with the 2030 Challenge for new

buildings and major renovations.2 In Europe, regulations by The

European Directive for Energy Performance of Building have put in

place Directive 2010/31/EU to insure that by the year 2010 all new

buildings are “nearly zero-energy buildings” (EPBD 2010).

When isolating the most influential factors regarding energy effi-

ciency building operations alone are responsible for 41.7 per cent

of all energy consumed in the United States.3 In commercial sec-

tor buildings HVAC accounts for 26 per cent of energy use, while

lighting accounts for 22 per cent.4 It is then critical then that en-

closure design and engineering is approached as an opportunity

to contribute to net zero energy objectives. A successful solution

must address the criteria of embodied energy, thermal perfor-

mance, access to natural light, and energy harvesting in order to

meet these and future requirements.

In many cases, high performance envelopes are achieved

using triple glazing, or double facade systems. However the

amount of embodied energy required manufacturing the system

begins to negate the thermal benefits. It may take over ten years

before the building recovers this savings in thermal performance

benefits for years. When considering the embodied carbon, the

self-supporting unit eliminates the need for additional structural

framing materials.

Because the vacuum chamber eliminates conductive and convec-

tive heat transfer, it acts as a thermal buffer for both hot and cold

climates. The invention provides dramatic thermal performance

improvements over other glazed facades through the use of vacu-

um insulation, by limiting heat transfer through the unit to only ra-

diation over the glazed portion. A combination of two-dimensional

building heat-transfer modeling, day-lighting, and energy modeling

methods were established to test the unit against a benchmark of

a typical metal framed curtain wall or storefront (Figure 9–Figure 11).

Daylight visualizations (a) 9am September 21st, (b) 12pm September 21st, (c) 3pm September 21st, (d) 6pm September 21st

9

c

a b

d

Glare visualization10

Pont in time illuminance (a) 9am September 21st, (b) 12pm September 21st, (c) 3pm September 21st, (d) 6pm September 21st

11

a b

c d

641 VACUUM INSULATED TUBES

Preliminary simulations completed by SOM’s Performative

Design Group have returned results of .06 Btu/hr-ft2-f for a 100

per cent window wall ratio, outperforming a baseline envelope

of 40 per cent window wall ratio (.55 Btu/hr-ft2-f), and a standard

opaque envelope (.104 Btu/hr-ft2-f) in ASHRAE Climate Zone 4A.

Furthermore, heat transfer modeling using THERM, a state-of-the-

art software program developed by Lawrence Berkeley National

Laboratory (LBNL), illustrated that the surface temperature of the

unit’s inner lite as closer to room temperature, therefore creating a

higher level of thermal comfort for the occupants (Figure 12).

Flat vacuum insulated glass is commercially available and pro-

duced by manufactures such as Guardian Industries Corp, and

Nippon Sheet Glass. While more efficient than a typical insulated

glass unit with R values of 10+ the product also has disadvan-

tages; flat glass of a traditional vacuum insulated glass unit is

susceptible to bowing under the pressure of the 10-4 torr vacuum.

In order to overcome this pressure, spacers are required between

the two pieces of glass. These spacers act as thermal bridges that

create inefficiencies. Additionally, traditional vacuum insulated

glass units are not self-supporting and require additional structural

support. The structural cross section of the tube allows for the

implementation of vacuum insulated glazing without intra-cavity

supports, which would act as performance-degrading thermal

bridges and visual distractions.

SOLAR COLLECTION

The tubular geometry’s properties as a light reflector and refractor

provide the opportunity for energy collection. The convex inner

half glass-lite of the cylinder reflects the incoming solar radiation

to its center, concentrating the energy to a single focal point, en-

abling an efficient solar collector to generate power. This energy

collection redirects the solar radiation, which would have other-

wise traveled through the glass tubes and into the conditioned

space, resulting in a greater reduction of solar heat loads. In order

to validate the refraction through the thickness of the glass and

reflections of the glass surfaces, computational solar simulations

were run. The laws of refraction and reflection were translated

from Radiance, a ray-tracing software tool developed by Lawrence

Berkeley National Laboratory, into a definition which calculated

time-based solar path data to three-dimensionally analyze the

tubular geometry (Figures 13–Figure 14). The results allowed for an

optimization of the relationship between the tubular form and the

location of the solar collector within. A variety of glass configu-

rations were explored. Digital models included variations on the

tubular cross sectional shape, the introduction of optical lenses

within the unit, and a reflective coating applied to the inner half

cylinder (Figure 15).

The vacuum chamber eliminates conductive and convective heat transfer12

Law of Refraction13

Law of Refraction14

ASCI, ET AL.

642ACADIA 2014 DESIGN AGENCYDATA AGENCY

Variations on the tubular cross sectional shape for redirection of solar radiation. Solar collector ray analysis – Baseline

15e

15a Variations on the tubular cross sectional shape for redirection of solar radiation. Solar collector ray analysis – Reflective backing

Variations on the tubular cross sectional shape for redirection of solar radiation. Solar collector ray analysis – Frontal lens

Variations on the tubular cross sectional shape for redirection of solar radiation. Solar collector ray analysis – Center lens

Variations on the tubular cross sectional shape for redirection of solar radiation. Solar collector ray analysis – Parabolic reflective backing

Variations on the tubular cross sectional shape for redirection of solar radiation. Solar collector ray analysis – Elliptical alternate

15b

15c 15d

15f

643 VACUUM INSULATED TUBES

STRUCTURAL

Designed to be a modular interlocking building enclosure, the

system can be stacked both horizontally and vertically. Due to the

structural depth of the tubes, the individual unit is self-supporting.

The curvature of the tube provides a cross section which is able

to resist lateral loads, eliminating the need for additional framing

or support. The geometrical properties of the glass tube also

allow for the negative pressures of the vacuum chamber without

any additional structural support (Figure 16).

To solve for the longest possible span of the unit, a specific script

was developed. Calculations completed by SOM Structure’s engi-

neers parameterize three different criteria: strength, serviceability,

and buckling. Strength considerations include the tube’s pressure

stresses, which account for the difference in interior and exterior

pressure caused by the vacuum, the dead load of the unit’s own

weight, and lateral forces such as wind pressures. These loads

are governed by limitations of the maximum allowable glass

surface stress. Appendix X6 of ASTM E1300–12a describes allow-

able glass surface stress for glass lites continuously supported

along all edges of the lite as a relationship between fracture me-

chanics and surface imperfections factors (ASTM 2012). When ver-

ifying serviceability against maximum deflection limits the glass

tube, it is calculated as a simple beam under lateral load in either

a pin-pin or fix-fix condition (Figure 17). Mid span deflection is then

checked against global buckling limit values (Catinaccio 2009). Local

bucking can then be calculated per AISC 2005 which defines the

critical buckling load for tubes (AISC 2005).

In order to analyze various design scenarios engineers from SOM

Structures produced a macro script in Microsoft Excel. Given the

design parameters of a 14 inches diameter tube composed of

one fourth inches thick heat strengthened laminated glass under

wind pressures of 50psf initial simulations returned an achievable

span of 44 feet in a fixed-fixed condition, with normal stress as the

governing limit state.

FABRICATION

Until recently, the maximum size of curved glass lites were limited

by factors of fabrication, primarily, the length of the autoclave and

the length of a sheet of interlayer. With the increasing demand for

larger pieces of glass, fabricators are acquiring autoclaves over 15

feet in length. Reacting to this advancement, manufactures of ion-

oplast interlayers such as Dupont SG’s SentutryGlas have begun

production of a .035 inches product which is available in rolls rath-

er than sheets. Several fabricators were approached to produce

15 feet tall samples at a 7 inches radius. Successful specimens

were created by Cristacurva of Mexico, Cricursa of Spain, and SFL

Technologies of Austria (Figure 18). Simultaneously, a visual mock-

up of a reduced height was produced in order to test the behavior

of light through an array of tube assemblies (Figure 19).

CONTINUED DEVELOPMENT

As part of the ongoing research, a patent was applied for in order

to protect the invention in the next phases of development (Figure

20). Research was completed to determine existing art, which

would preclude a patent of the invention. Related patents include

flat evacuated glass units, and United States Patent Number

4,038,787 which is composed of non-thermally broken extruded

glass tubes. While functionally as an exterior enclosure, existing

patents were different with regard to the configuration of the

glass and resultant thermal bridging.

The structural cross section of the tube allows for the implementation of vacuum insulated glazing without intra-cavity supports

16 The glass tube as a simple beam under lateral load in either a pin-pin or fix-fix condition

17

ASCI, ET AL.

644ACADIA 2014 DESIGN AGENCYDATA AGENCY

15 feet tall, 7 inches radius glass specimens created by Cristacurva (Cristacurva 2012)18

Visual mockup of a reduced height assembly19

645

The next steps of the research include a higher level of computa-

tional performance analysis, and prototype fabrication for National

Fenestration Rating Council testing. Prior to prototype production,

engineering will be performed to determine the articulation of

the metal frame system, the length of adhesive bond required,

the nature of the evacuation port, etc. Six evacuated modules

of equal size will be completed to create an assembly capable

of rearrangement on different configurations for performance

testing. The prototype will be evaluated in an accredited facility to

determine actual performance under National Fenestration Rating

Council (NFRC) standards. The following tests will be performed:

U-factors, thermal transmittance, solar heat gain coefficient and

visible light transmittance at normal incidence, optical properties,

air leakage, condensation resistance values and daylight levels to

determine glare discomfort, and thermal comfort testing.

These results will be compared against the computation analysis

and to a benchmark of an ASHRAE 90.1 compliant envelope to as-

sess the improved performance of the evacuated tube envelope.

As the design is in its earliest stages, there is further study to be

completed to resolve the complex technical aspects which are

involved in the realization of an architectural element suited for

mass production. The possibility of thermally-broken vacuum-insu-

lated tubes is the subject on ongoing multi-disciplinary research,

which has the potential for the application of a high performance

building enclosure.

Patent Figures - Patent Pending20

VACUUM INSULATED TUBESASCI, ET AL.

646ACADIA 2014 DESIGN AGENCYDATA AGENCY

ACKNOWLEDGEMENTSThis body of work was conducted as an initiative of SOM. The authors wish to acknowledge Mark Sarkisian structural and seismic engi-neering partner in SOM’s San Francisco office and his team for their contributions throughout the research, and thank the other consulting members of SOM’s New York, and Francisco office.

NOTES1. http://www.eia.gov/totalenergy/data/annual/#consumption

2. http://architecture2030.org/2030_challenge/the_2030_challenge

3. http://www.eia.gov/totalenergy/data/annual/#consumption

4. http://buildingsdatabook.eren.doe.gov/ChapterIntro3.aspx

REFERENCESAmerican Institute of Steel Construction, Inc. 2005. Code of Standard Practice for Steel Buildings and Bridges.

American Society of Heating, Refrigerating and Air-Conditioning Engineers. 2008. ASHRAE Vision 2020.

ASTM International. 2012. “Appendix X6.” In ASTM Standard E1300-12a Standard Practice for Determining Load Resistance of Glass in Buildings.

Catinaccio, Andrea. 2009. Pipes Under Internal Pressure and Bending. CERN Tech Note-2009-004.

The European Parliament and of the Council. 2010. “Directive 2010/31/EU.” Official Journal of the European Union. 19 May 2010.

IMAGE CREDITSAll figures Copyright SOM unless noted

Figure 1. Pottle, Jock (2012).

Figure 3. Pottle, Jock (2012).

Figure 18. Cristacurva (2012).

AYBARS ASCI leads an award winning design group at SOM’s New York office, embodying a design philosophy that combines conceptual clarity with analytical processes. Mr. Asci has worked in designing complex institutional and commercial projects, including the United States Census Bureau Headquarters in Suitland, Maryland, Al Rajhi Bank Headquarters in Riyadh, Qatar Petroleum Headquarters in Doha, Baccarat Hotel & Residences in New York and etc. Mr. Asci has given lectures in academic institutions, including Architectural Association, Tsinghua University and MIT. He is teaching a graduate studio at Northeastern University as a part-time faculty member. He holds a Master’s Degree from Columbia University.

ELISABETH BOONE is a senior architect engaged in ad-vanced computation, working for SOM as a contributor to the Digital Design Group. She received her Master of Architecture from the College of Architecture and Planning at Ball State University, focusing on advanced fabrication and interactive installations. Currently she is developing the design of a 1025’ tall mixed use tower at Hudson Yards on Manhattan’s west side. Ms. Boone is the winner of the ACADIA 2011 Design+Fabrication Competition, and recipient of a 2010 Architect Magazine R+D Award.

GARY HANEY has over 29 years of experience at SOM. He has served as Design Partner on a broad range of international projects including office and residential buildings, hotels, and educational facilities. Recent work includes the redesign of the Smithsonian’s National Museum of American History in Washington, D.C.; and BBVA Bancomer Operations Center in Mexico City. Mr. Haney has served on the advisory council to Northeastern University’s School of Architecture and the advisory boards at Pratt Institute and Miami University Department of Architecture and Interior Design. In addition to these academic contributions, he has led design studios at MIT, Miami University, and Ball State University.

CHRISTOPHER OLSEN is an Associate Director at SOM NY, with a specialty focus on Building Enclosure. After an early career at I.M. Pei & Partners/Pei Cobb Freed & Partners, he joined SOM in 1999 and has worked on a wide variety of significant domestic and international projects. Christopher has acquired and continues to seek additional state-of-the-art expertise in curtain wall, architectural metals, and specialty glazing systems.

TERESA RAINEY is the Director of High Performance Design at SOM. Her studio integrates technical tools with sustainable strate-gies to inform building designs such that high performance goals are achieved. A LEED® Accredited Professional, Ms. Rainey is commit-ted to remaining on the cutting-edge of environmentally responsible technology through research, continuing training, and a willingness to consider innovative design solutions. Ms. Rainey’s active involvement with ASHRAE/USGBC/IESNA SSPC 189.1, Standard for the Design of High-Performance, Green Buildings Except Low-Rise Residential Buildings; GSA Design Excellence National Peer Review Program; and the Building Security Council Certification Program Development Committee, establish her as an industry leader in the design of high performance buildings.