Performance Attributes of Secondary Window Systems

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Performance Attributes of
Secondary Window Systems
Therm-O-Lite Inc.
3502 W. Sample Street
South Bend, IN 46619
Tel: 574-234-4004
Fax: 574-234-4005
Email: info@thermolitewindows.com
Web: www.thermolitewindows.com
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Performance Attributes of
Therm-O-Lite Inc.
3502 W. Sample Street.
South Bend, IN 46619.
Provides an overview of the significant role that interior secondary window systems have
in energy savings, efficiency, security, and comfort for existing buildings where window
replacement is not desirable.
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Purpose and Learning Objectives
Purpose: Provides an overview of the significant role that interior secondary window
systems have in energy savings, efficiency, security, and comfort for existing buildings
where window replacement is not desirable.
Learning Objectives:
At the end of this program, participants will be able to:
• list the options available for reducing energy loss through windows and discuss their
pros and cons related to cost, efficiency, and installation.
• discuss the basics of interior secondary window applications and describe how and why
they increase thermal performance, and therefore, occupant comfort .
• explain how interior secondary window systems can be used to enhance the safety and
security of a building in terms of blast mitigation, hurricane protection, signal defense,
and sound control, and.
• identify the ways in which interior secondary window systems contribute to a variety of
energy savings strategies for commercial building applications.

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Table of Contents
Energy Use in Buildings 7
Secondary Window Systems 25
Security Options 40
Case Studies 51
Summary and Resources 66
Click on title to view

Energy Use in Buildings
United States Army/Army Corps of Engineers Project – Ft Sill, Oklahoma.

Energy Consumption
Of all the energy consumed in the United States, 19% is used in commercial buildings.
Source: Energy Information Administration (EIA). Annual Energy Review 2011. Washington, DC: U.S. Department of Energy (DOE), 2012.
http://www.eia.gov/totalenergy/data/annual/pdf/aer.pdf Accessed September 2014.

Commercial Building Insulation
As concerns over energy consumption and climate change grow, policy makers continue to
be called upon to make their buildings more green, such as through more environmentally
friendly energy technologies and measures to reduce greenhouse gas (GHG) emissions.
On the chart on the following slide, the below-the-line items on the left side are GHG-
reduction measures that save more money than they cost. Most of these are sheer
efficiency measures (e.g., insulating buildings, switching to more efficient lights). The
above-the-line escalating figures on the right are the rising costs of other abatement
measures. The most expensive of them are high-tech “carbon capture and sequestration”
systems.
The chart shows that “commercial retrofit energy waste reduction,” e.g., commercial
building insulation, has the best return lowering GHG compared to all technologies. This is
primarily due to reducing the demand for energy and the very long lifecycle of insulation. In
high-rise buildings with large glass facades, window retrofits are literally spelled out in this
report as the best macro strategy to reduce GHC.
Source: Enkvist, Per-Anders, Tomas Nauclér, and Jerker Rosander. “A Cost Curve for Greenhouse Gas Reduction.” McKinsey Quarterly. McKinsey & Company,
February 2007. http://www.mckinsey.com/insights/sustainability/a_cost_curve_for_greenhouse_gas_reduction Accessed September 2014.

Commercial Building Insulation
GHG-reduction
measures
Rising costs of
other abatement
measures.

Inefficient Windows
Inefficient, single pane windows are still in service today in 53% of commercial buildings.
Source: Energy Information Administration (EIA). Annual Energy Review 2011. Washington, DC: U.S. Department of Energy (DOE), 2012.
http://www.eia.gov/totalenergy/data/annual/pdf/aer.pdf Accessed September 2014.

Reducing Energy Loss Through Windows
The options include:
1. Window Films and Blinds – These only affect the solar heat gain/radiation portion of
the heat transfer into the building.
2. Replacement Windows – These are very expensive and disruptive to the tenants and
are not a good option for retrofits.
3. Doing Nothing – This is by far the most common choice, which is why 53% of all
commercial buildings still have single pane glass according to the DOE Annual Energy
Review.
4. Secondary Windows – They install on the interior of the building with minimal (if any)
disruption to the tenants, and may provide an immediate ROI when energy savings and
capital cost reduction is required.

Reducing Energy Loss Through Windows
Window enhancements could be the most under-utilized energy saving technology. The
EPA building pictured here is a prime example. This facility was built in 1934, so it is 80
years old and still has the original single glazing.
Why have these
windows not been
replaced?
Is it because:
• they want to maintain
the historic look of the
building.
• is it too expensive
• is it too cumbersome
for tenants, or.
• it has been
overlooked?

Why Secondary Windows Are an Option
Secondary windows: offer cost savings; they preserve the aesthetic of the original
windows; they are quickly and easily installed; and they offer a variety of other benefits
beyond energy savings.
They are available in a range of laminated, suspended film, insulated, and low-emissivity
coatings. Between-glass blinds are an option that helps lower solar heat gain in the
summer and raise it in the winter. Systems easily attach to fixed, storefront, and curtain
wall framework. Sound control window systems are available, as well as hurricane and
blast protection options that don’t affect sight lines.
Secondary window systems are the optimum choice when building envelope issues in the
glass facades need to be addressed in terms of energy conservation and comfort. They
are used when energy engineers want a certain R-value for the building envelope―
windows increase insulation value. They are an ideal solution when the building is occupied
and tenant disruption is not an option. They are a serious window upgrade without actually
replacing the existing windows and outperform film, as film does nothing to improve
insulation.

Energy Savings
Secondary window systems are designed to multiply the performance of existing windows;
they reduce heating and cooling use as well as demand.
+ =
Reduces thermal energy
loss by adding air gap
and low-e coating.
Adding blinds controls
solar heat gain up to 90%.
Solar film reduces 99% of
UV light rays.
Reduces overall energy demand
for the building which allows a
“downsize” of HVAC systems in
modernization projects.
Reduces building energy
consumption by at least 20%.

Zeroth Law of Thermodynamics
This is the most fundamental law of thermodynamics that was actually developed and
articulated after the other three laws―hence the name.
If system A is in thermal equilibrium with system C, and system B is in thermal
equilibrium with system C, then system A is in thermal equilibrium with system B.
Thermodynamics is the study of the movement of heat over time within a system. A system
is a group of entities. For our discussion, we are talking about a building in an environment
and how the temperature flows in and out of this building system. This means that systems
always work towards an equilibrium state with each other when allowed to interact.
A building interior at room temperature will always seek equilibrium with the exterior
through interaction through the perimeter. This will always happen fastest at places with the
largest temperature difference.
Poor insulation means high heat transfer.
Windows are the weakest link in this system, and all heat eventually flows here as it is the
last to achieve equilibrium.

U-Value – Conduction
Heat flow from the warmer side to the colder side of a window and window frame is an
interaction of three basic heat transfer mechanisms―conduction, convection, and
radiation. The ability of the window assembly to resist the heat transfer is referred to as the
insulating value. Heat will flow from warmer to cooler bodies, therefore, from inside to
outside. The direction of the heat transfer reverses in summer during periods when the
outside temperature is greater than indoors. Conduction occurs directly through the glazing
material itself as well as through the solid parts of the window frame.
The U-factor or U-value, as sometimes described, is the standard method used to quantify
insulating values. It indicates the rate of heat flow through the window. The U-factor is the
total heat transfer coefficient of the window system (in Btu/hr-ft2-°F), which includes
conductive, convective, and radiation heat transfer. It represents the heat flow per hour (in
Btus/hr) through each square foot of window for a 1°F temperature difference between the
indoor and outdoor air temperature. The R-value is the reciprocal of the total U-factor
(R=1/U). As opposed to an R-value, the smaller the U-factor of a material, the lower the
rate of heat transfer.

Air Infiltration – Convection
Air infiltration is the rate of air movement around a window, door, or skylight in the
presence of a specific pressure difference across it. It is expressed in units of cubic feet
per minute per square foot of frame area (cfm/ft2). A product with a low air leakage rating is
tighter than one with a high air leakage rating.
Air infiltration is difficult to simulate and is typically tested in the laboratory or in situ. Whole
building simulations show that when secondary glazing systems are used, over 30% of the
building’s energy loss through the window openings is caused by air infiltration and
exfiltration. 55% of the loss is due to thermal properties, and 15% is a result of solar heat
gain.
In general, total building energy efficiencies can improve by 15% to 25% in cold weather
climates when secondary glazing is used.

Solar Heat Gain Coefficient – Radiation
Solar heat gain coefficient (SHGC) is the fraction of solar radiation admitted through a
window―either transmitted directly and/or absorbed, and subsequently released as heat
inside a home. SHGC is expressed as a number between 0 and 1. The lower the SHGC,
the less solar heat it transmits and the greater its shading ability. A product with a high
SHGC rating is more effective at collecting solar heat during the winter. A product with a
low SHGC rating is more effective at reducing cooling loads during the summer by blocking
heat gain from the sun. The building’s climate, orientation, and external shading will
determine the optimal SHGC for a particular window, door, or skylight.
The nationally recognized rating method by the National Fenestration Rating Council
(NFRC) is for the whole window, including the effects of the frame. Alternately, the center-
of-glass SHGC is sometimes referenced, which describes the effect of the glazing alone.
Whole window SHGC is lower than glass-only SHGC, and is generally below 0.8.

Energy Transfer Through Fenestration

Single / Double / Triple Pane Windows
q = R * A * ∆T
q = heat transferred Btu/hr
R = heat transfer coefficient
A = area (30 ft2)
∆T 40 = 70 inside and 30 outside
As the R-value goes up, the heat flow
reduces, indicating the savings (heat flow
reduction) diminishes as R-value increases.
For windows: single pane = R-1; double
pane = R-3; and triple pane = R-5. It makes
economic sense to go from single to double
pane, but not to go to performance glazing
of R-5 or greater.
0
200
400
600
800
1000
1200
1400
1 2 3 4 5 6 7 8 9 10 11
HeatTransferRateBtu/hr
R-value
Diminishing Returns of q with R-value
Improvement
For example, why choose an R-10 window with a 120 Btu/hr flowrate when an R-3 is at
400 Btu/hr, when the existing window is 1200 Btu/hr. The savings is greater, but it might
cost ten times more to achieve this.

Window-to-Wall Ratio
This case study considered the effect of a different percentage of window-to-wall ratios with
different glass types to see if there were situations for diminishing returns. A very slight
flattening of the curve indicates that there is some of this, but the relationship is basically
linear. As the percentage of window increases, the total building percentage of savings will
increase almost proportionally.
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
30.0%
35.0%
30% 40% 50% 60% 70%
CostSavings
Percent Glass
New York Cost Savings.
Double To Triple
Single to Double
Single to Triple

Where Do the Savings Come From?
NYC Building Model – This compares different methods of
heat transfer (convection, conduction, and radiation) in a
building with a secondary window system.
The U-value (conduction/insulating value) represents
almost rds of the savings. Air infiltration (convection) is
approximately rd. Solar heat gain (radiation) reduction is
the smallest amount of savings.
Radiation plays a small factor because: this building is in a
cold weather climate; is shaded by surrounding buildings
for some of the day; has high wind speeds resulting in
higher than usual air infiltration and exfiltration; and
secondary windows reduce the solar heat gain by a small
amount.
Window film does nothing for air infiltration, little or nothing
for insulation, but does reduce some of the solar heat gain.
It is not dynamic like blinds. Some solar heat gain is
desirable in the winter to warm up the room. Between-
glass blinds would be recommended over solar film.
62%
33%
5%
Electric Heat.
U-value
Infiltration
Shading
Coefficient
61%
31%
8%
Steam Heat.
U-value
Infiltration
Shading
Coefficient

National Defense University – Washington, DC.

Features and Benefits
Low installation cost compared to other window options:
These systems are placed on the inside of the existing glass in a new frame which seals
the glass from the inside of the building. They use a simple frame system to recycle the
existing glass and incorporate it into a new window system. Typical installations are 50%
less expensive than new glazing and are more energy efficient.
Reduces or eliminates air infiltration through older window openings:
Undesired air coming into the building through leaky windows has a profound effect on the
energy used to maintain temperature. It is similar to a bucket full of small holes leaking
water. Rather than spending resources on new and efficient ways of putting water back into
the bucket, it is reasonable to first start with plugging the holes in the most cost-effective
way before you start looking into better ways of filling the bucket when it runs low.
Are made from sustainable aluminum and glass materials:
Aluminum is the most abundant and recyclable metal in the Earth’s crust. Glass is made
from silicon, and low emissivity glass coatings use a thin layer of silver.

Features and Benefits
Reduces the heating and cooling demand load in the facility:
Once the building envelope is sealed, only then will the demand capacity selection of the
heating and cooling system be optimized. Significant savings will be realized at the
beginning of the modernization project by reducing the size of the heating/cooling systems.
Allows control of solar energy into the building in winter months:
Between-glass blinds can be opened and closed, which will allow visible light into the
building and create heat gain. This is desirable in winter months in colder climates.
Increases comfort of the occupants/reduces sound transmission:
Commercial buildings with older windows can create cold and hot spots in work areas.
Secondary window systems will reduce this and limit the amount of street noise by 50 to
90%, depending on the existing glass.
Will last the lifetime of the building:
Unlike all other equipment modernization options, secondary window systems will last
hundreds of years if properly maintained. They will not rust, fade, or fail in any way.

Increase Thermal Performance
The basic premise of a secondary window
system is to reuse the existing glass and
window frame and mount a new frame and
glass lite behind them. Installation and material
cost is greatly reduced, and the basic thermal
performance of the original window is not only
maintained, but amplified. By placing a window
behind the existing glass, an air gap is created
and works in a similar fashion as insulated
glass units. The secondary frame is oftentimes
mounted on an area which is inside the existing
frame. Not only will the air infiltration be
prevented from leaking into the building, but a
thermal break is created between the original
frame and the secondary window frame.

The next most important factor of a secondary window system is the selection of glass
coating. Low emissivity (low-e) hard coats can be placed on either side of the glass, which
will reduce the flow of infrared energy through the glass. In warm months, this energy is
bounced out of the building, and in cooler months, near infrared radiant energy from the
building’s heating system is directed inwards. Low-e coatings are proven to increase the
insulating attributes of the glass and should always be considered.

Solar heat gain films are another excellent option to
place on the glass surface either as stand-alone or used
in tandem with low-e coatings. These films will reduce
the intensity of light coming into the building and serve as
a shade with minimal effect to the visible light spectrum.
Between-glass blinds have further effect on the
performance of the system. Not only do they keep
radiant light energy from flowing through the window if
the blinds are drawn, they also serve as a buffer which
breaks up the air gap between the glass into two, further
improving the thermal performance.

Thermal Benefits
These thermal imaging examples show the thermal benefits of a secondary window system
compared to an untreated window it is installed beside. The examples are of three different
buildings taken in December and in April on fairly cold days. The temperature on the upper
left was the temperature taken at the crosshairs. The blue surfaces are cooler, and the red
surfaces are warmer. These images show heat flowing from the inside to the outside in
winter months, and a ∆T of 10 degrees in two of the photos. The cooler window in each
image is upgraded with a secondary window system.

Additional Benefits
The use of secondary window systems can realize historic building tax credits while
preserving the building’s historic appearance.
Maintain the
architectural character
of the building.
Preserve the existing
windows.
There is no change to
sight lines and can be
framed to match
interior décor.
Achieve historic tax
credits.

Installation of Secondary Windows
Systems come with the frame either preframed or in knockdown form. Preframes are for
historical applications (usually) and knockdown is for modern aluminum curtain wall
storefront or window wall.
A typical basic system consists of five total pieces:
1 - a piece of glass with an aluminum sash with magnetic
extrusion: 2&3 - jambs consisting of powder coated steel
which creates a seal with the magnetic jamb; 4&5 - head
and sill consist of aluminum extrusions.
If the system is framed, then the extrusions and jambs are
built in. The installation consists of placing the frame into
the opening and securing it with fasteners. The glazing
can be done in seconds by using a glass cup to pocket
the window into the channels.
For curtain wall: the head and sill channels are installed
first; steel angles at the jambs, second; and the glass,
third. Fastening the components to the inside of the frame
is done by using tape and adhesive so no noise is
experienced or fasteners required.

Curtain Wall Retrofit Secondary Window System.

The installation of a secondary window system is a non-interruptive process.
There is minimal interference with office staff
and no exterior indication of construction.
There is minimal mess and noise,
no disruption in productivity, and
installation is low cost or DIY.

Security Options
The Federal Reserve Bank System Annex – Washington, DC.

Types of Security Window System Options
Bomb blast window frames and laminated or filmed glass are an excellent choice for
historic buildings which may be located by a state or federal building. These systems can
be quickly installed on the interior, which will not alert either tenants or terrorists that the
building is being “hardened” for blast mitigation.
Hurricane window systems can be installed in the exact same fashion. These systems will
prevent windows from breaking out completely and creating a positive air pressure inside
the structure that places the building roof at risk.
Signal defense film can be placed in the laminate material which will eliminate the amount
of radio frequency leakage and guard against data theft from internal routers. Electrofied
film is also specified by Homeland Security to guard against laser enabled eavesdropping.
Sound control can be achieved with interior glazing. STC ratings can be improved to
above 40, and OITC ratings can be improved to at least 35 in single pane exterior systems.
All of these security options will produce similar, if not enhanced, energy performance of
the secondary window system.

Blast Mitigation
When protecting the most valuable part of your building, the people inside, blast mitigation
is an important consideration. These are examples of testing conducted at Energetic
Materials Research and Testing Center (EMRTC).

Blast Physics
An understanding of blast physics
helps explain the types of property
and human health damage that can
occur during these events. Explosive
detonations create a blast wave,
characterized by an almost
instantaneous increase in
atmospheric pressure to a peak
overpressure.
As the shock front expands, pressure
decays back to ambient pressure,
and a negative pressure phase
occurs that is usually longer in
duration than the positive phase as
shown, but not as powerful.
Pressures are shown on the y-axis
and impulse (time) is on the x-axis.
+ Pressure
Atmospheric
Pressure
- Pressure
Positive Pressure
Phase
Peak Incident
Pressure
Time of
Arrival
Negative Pressure Phase
Impulse Waveform
Pressure Waveform

Blast Window Importance
Damage from blasts to both people and buildings
stems from the both positive and negative blast waves
generated. High explosive blasts typically have a
positive pressure wave lasting 20 ms before the less
powerful but longer lasting negative phase occurs.
This air-blast may break windows and damage
buildings structurally. It could cause eardrum damage
as well as lung collapse. Broken building parts turn
into missiles which may cause impact injuries. Finally,
the air-blast pressure can cause occupants to be
thrown against objects or to fall.
In the Oklahoma explosion, a significant portion of the
injuries received were as a result of flying glass. 40
percent of the survivors from the building cited glass
as contributing to their injuries, compared to 25 to 30
percent for nearby buildings.
Undamaged
structures are not
show on map.

Blast Window Strategies
The goal of blast mitigation glazing strategies is to prevent physical harm to occupants
from flying broken glass fragments or entire windows forced from their frames. Typical
strategies consist of: removal of windows and replacement with new blast windows;
installation of blast film; or installation of interior blast windows.
New blast windows can be single or double pane and consist of laminated or composite
glass. Replacement blast windows are anchored into structural steel around the window
opening that is tied into the building structure. If no structural steel is present, it must be
installed, which drastically increases the price and installation time. Typically, structural
steel is used in all levels of protection of blast windows with a rigid (static) system. Of all
the strategies, replacing windows results in the highest level of occupant disturbance and is
the most expensive option.
Blast film can go onto the interior surface of any window and holds all of the pieces of
broken glass together in the event of an explosion. Most film is not anchored and is simply
placed onto the glass only. Other film is either sealed with structural silicone or
mechanically fastened into the frame. Blast film typically offers a low level of protection and
is only guaranteed to work for 10–15 years and then has to be replaced. This strategy
offers the lowest level of occupant disturbance. This option has the lowest initial cost.

Types of Interior Blast Windows
Interior blast windows are placed on the inside of the building and anchored into the
building with structural steel or masonry anchors. There are two types of interior blast
windows—rigid and dynamic.
Rigid secondary glazing blast systems require structural steel reinforcement. They are
anchored with structural steel reinforcement (or masonry anchors) of the window opening.
They provide a medium level of protection, and installation results in less occupant
disturbance than window replacement. It is also a less expensive option than window
replacement.
Dynamic secondary glazing blast systems do not require structural steel reinforcement—
only masonry anchors (tapcons or epoxy concrete anchors) are required, drastically
reducing cost and installation time. The systems can be double pane, single pane, and
laminated. As with rigid systems, they provide a medium level of protection; however,
installation is less expensive and results in less occupant disturbance than either window
replacement or rigid secondary glazing.

Types of Interior Blast Windows
Rigid blast windows are most common, absorb the entire force of the blast pressure, and
as mentioned, require structural steel reinforcement of the window opening.
Dynamic blast windows allow the glass or sub-frame to move during the positive phase (15
to 20 ms, typically) and do not fully engage the window frame until after the positive phase
has passed. Therefore, minimal load is transferred into the frame and from the frame to the
building.
“A balanced design” is one where: the glass will withstand the pressure; the glass will stay
attached to the window frame; and the frame will stay within the structure of the building.
One cannot put blast glass into the frame of a regular window and have a balanced design.
Nor can a building have a blast window installed without proper steel reinforcement unless
it is a dynamic window.

Hurricane Protection
A hurricane rated window system provides all the energy savings of a standard secondary
window system while protecting against excessive water and wind.
A hurricane window system is
designed, test completed, and
certified for up to 139 mph
force winds.
Systems are tested for large
and small impacts to meet and
exceed the strictest building
codes in the country.
Hotel Indigo, above, survived
Hurricane Isaac in 2012 with
0% window damage. The sister
building adjacent to Hotel
Indigo suffered a 15% window
loss due to pressure variances,
not impact of ¼" glass.

Signal Defense
A signal defense window system provides all the energy savings of a standard secondary
window system while utilizing laminated glass technology to block audio transmissions.
Organizations that need to properly secure locations handling sensitive and/or classified
information should consider this option.
ASTIC film, which was
classified until 2007, is now
available as option on interior
glass.
Provides protection against
infrared, radio frequency, and
audio espionage, and can be
combined in a window system
with energy, hurricane, and
blast attributes.
The technology is
compliant with U.S.
DoD TEMPEST
standards.

Sound Mitigation
Again, while maintaining all the energy savings of a standard secondary window system,
sound transmission and street noise can be significantly reduced, from 50 to 90%
depending on existing glass. Window sound control measures typically reduce sound
pressure by way of dampening. One way to dampen sound vibrations is by increasing
mass. The additional weight of the glass in a secondary window dampens sound vibrations.
If laminated glass is used in the secondary window, the dissimilar materials (glass and
A sound mitigation window will
significantly reduce street noise.
Loud speech is not
audible, and very loud
sounds are heard faintly.
plastic) further dampen
vibrations. Finally, installing
a secondary window
produces an air gap
between the primary and
secondary window. The air
gap promotes destructive
interference of the sound
waves, reducing the
harmonic oscillation of
outdoor noise, which
eliminates the passage of
many frequencies of sound.

Case Studies
Federal Trade Commission Building – Washington, DC.

Study 1: Energy Reduction / Historical Integrity
The Sidney R. Yates Federal Building is a
five-story historic complex located in
Washington, DC. The building consists of
152,329 ft2 of office and support spaces and
was given a Category III Landmark
designation by the National Register of
Historic Places. It was constructed from
1878–1880 in the Classical Revival style to
serve as home to the Bureau of Engraving
and Printing. The building now serves as the
USDA Forest Service headquarters, and also
contains a Visitors Center with museum and
the National Fire Center.
Please remember the exam password ENERGY. You
will be required to enter it in order to proceed with the
online examination.

Study 1: Energy Reduction / Historical Integrity
The facilities staff at the Yates Building was looking for ways to improve the energy
efficiency of the building, particularly due to the Visitors Center and National Fire Center
(NFC) being open outside of the normal office hours of the rest of the building’s occupants.
Maintaining temperature control for these two areas required the entire building’s heating,
ventilating, and air conditioning (HVAC) system. Since the Yates Building is a Category III
Landmark, exterior renovation options to improve energy efficiency are limited by the DC
Commission of Fine Arts (CFA).
The installation of an interior secondary
window system allowed for all historic
exteriors to remain untouched, while still
making the building more energy efficient.
With no other changes made to the building,
the results showed a:
• 33% reduction in heating steam.
• 7% reduction in electricity, and.
• 23% reduction in total utility cost.

Study 2: Capital Reduction
The Patrick M. McNamara Federal Building,
located in downtown Detroit, Michigan, is a class
A skyscraper. It features approximately
1,000,000 ft2 (93,000 m2) on 27 floors and is
designed in the brutalist architectural style. The
corners are recessed, providing additional
strength to the structure and eliminating the
battle for corner offices.
The building was named after former U.S.
Senator Patrick Vincent McNamara, who served
Michigan from 1955 to 1966, and houses a
variety of government agencies, including the
Consumer Product Safety Commission, Army
Corps of Engineers, Defense Contract
Management Agency, Federal Bureau of
Investigation, Internal Revenue Service, Peace
Corps, Railroad Retirement Board, and Social
Security Administration.

Study 2: Capital Reduction
As part of the GSA’s initiative to reduce the environmental footprint of federal buildings and
make them as green and energy efficient as possible, a series of projects to modernize
and improve the performance of the McNamara Building’s HVAC system was put into
place.
To accomplish the task of improving the building envelope, an interior secondary window
system was installed.
The results showed a:
• 50% reduction in heating loads.
• 21% reduction in cooling loads.
• $1.5 million decrease in HVAC upgrade costs.
• $400,000 annual energy savings, and.
• immediate ROI (window cost was 100% offset by savings in HVAC equipment).

Study 3: Physical Security / Energy Efficiency
Federal banking buildings have a unique set of needs
and challenges for their windows: government
mandates require them to follow both safety and
energy performance protocols, while historical
preservation guidelines prohibit work that changes the
appearance of the windows.
Washington DC’s 12-story Lafayette Building (top
right), the five-story Marriner S. Eccles Federal
Reserve Board Building in DC (bottom right), the
Federal Reserve Bank of Philadelphia, and the eight-
story Federal Reserve Banking Annex Building in NYC
(center right), remained in compliance of security,
energy efficiency, and historical integrity guidelines
through the installation of interior curtain wall retrofit
secondary window systems.

Study 3: Physical Security / Energy Efficiency
The use of secondary window systems provided the above-mentioned federal banking
buildings the unique opportunity to improve not only the security of their windows, but also
the energy performance―without any disruption of building operations or altering of the
exterior windows that would be against historical preservation guidelines.
An interior curtain wall retrofit secondary window system is an ideal solution for these
buildings with renovation limitations because the system installs on the interior of the
existing window. This type of installation is quicker and more cost-effective than traditional
window replacement. The bank building tenants reported very favorable results in terms of
the lack of disruption to their workdays during the installation, as well as observed daily
comfort and reduced need for temperature control afterwards.

Study 4: Energy Improvements
625 North Michigan Avenue is a 25-story tower
located in downtown Chicago. It was constructed
in 1970 and has approximately 350,000 ft2 of
conditioned space, mainly in the form of retail
space and open-plan offices. The tower structure
consists of exterior concrete frame, interior
columns, interior structural core, and concrete
slab floors. The exterior fenestration formed by
2,300 windows with the total area of 58,650 ft2
occupies 41% of the total facade surface area.
The building had previously been retro-
commissioned to perform to higher energy
efficiency standards.

To determine the benefits of
interior window retrofit systems in
increasing the thermal
performance of a building that
already had an above average
energy efficiency system in
comparison to similar buildings,
three window retrofit options were
installed:
• Window 1: ¼" laminated glass
with low-e hard coating
(interior side).
• Window 2: 1" insulated glazing
unit with low-e soft coating.
• Window 3: ¼" laminated glass
with low-e hard coating
(interior side) and 1" blinds in
the air cavity.
Thermal Imaging Examples of Three Retrofit Options.

After the installation of the three interior window retrofit systems, the windows were
monitored for three weeks to measure their energy and sound reduction performance.
The results showed a:
• 13–16% decrease in peak
energy usage.
• 33–37% decrease in annual
gas consumption.
• 5 dB reduction in sound level
intensity, and.
• 16% total energy savings
(average of all three windows).

Study 5: Sound Reduction / Improved Comfort
Travelers may welcome the
convenience of staying in a hotel
near an airport, but the noise from
the airplanes is not only a nuisance,
but repeated exposure to such high
decibels can be potentially
dangerous. Modern buildings often
deal with sound problems because
of inefficient windows with air
leakage that contributes to loud
outdoor noise entering the building.
A major hotel in close proximity to
the San Francisco International
Airport installed an interior curtain
wall retrofit secondary window
system and was able to reduce the
sound levels by approximately 50%.

Study 5: Sound Reduction / Improved Comfort
A sound control interior curtain wall retrofit system is very effective because it increases the
existing window’s insulating properties with a double pane and low-e glazing. This creates
an air gap between the panes of glass, which traps excess sound and prevents it from
reaching the interior of the room. Since it installs on the interior of existing windows, it also
seals up any air leakage which may contribute to noise entering the premises from the
outdoors.
Additionally, the system is not only affordable, but it saves money by improving the
building’s energy performance. Unlike using replacement windows for sound control, a
sound control interior curtain wall retrofit system has a quick and non-disruptive installation
that does not require hotels to inconvenience guests or close temporarily and lose
business.
Product. Glazing (Nominal Dimensions). STC. OITC.
Existing Curtain Wall.
1" IG (¼" heat-strengthened, ½" air space,
¼" heat-strengthened).
31. 26.
Curtain Wall Retrofit
Window System.
Primary 1" IG (¼" heat-strengthened, ½" air space,
¼" heat-strengthened) sound control glass.
47. 40.

Study 6: Hurricane Protection
In 2012, Hotel Indigo New Orleans completed the installation of a secondary window
system two days before Hurricane Isaac hit. The property had ¼" annealed glass, and a
Category 3 hurricane system was placed behind it. The property next to the subject
property of identical construction had 15% window loss, extensive damage, and many
upset guests. Not only does the secondary system help protect the building from natural
disaster, it also reduces energy consumption and the need for a larger HVAC system, while
preserving the historic integrity and granting the owners a 20% tax credit.
Tower without hurricane window
system after storm―15% window loss.
Tower with hurricane window system
after storm―no window loss.

Study 7: Blast Mitigation
The Department of the Interior, Washington, DC .
• Largest blast window installation since the Pentagon.
• Operable, historic blast/energy window—unique.
• Most elaborate blast window test known to date.
• Requires no structural steel reinforcing in existing buildings, reducing total cost by over
50%.

Study 7: Blast Mitigation
Secondary blast window systems are usually specified when the windows are historic. In
this particular case, a thermal/blast interior window system was designed to:
• install on the inside of the building.
• sustain a customer specified pressure-impulse.
• achieve a specific overall U-value.
• be operable, and.
• require no structural steel reinforcement.
Over 4,500 windows were installed which preserved the existing windows while
maintaining the new buildings’ specified blast pressures and U-values.

Summary and Resources
Hotel Allegro – Chicago, IL (photo credit: Igougo.com).

Summary
Interior secondary window systems are
designed to provide superior protection against
bomb blast, audio espionage, and hurricanes
while reducing noise, sealing the building
envelope, and preserving historic architectural
integrity.
• They increase energy efficiency and reduce
overall building energy consumption. They
can help earn LEED® energy credits, and are
ideal for modernization projects.
• In terms of security, they meet the needs for
blast and hurricane protection, signal
defense, and sound control.
• They can help achieve historic tax credits
while maintaining lines of sight, and keeping
the building tenant-occupied.
Energy
HistorySecurity

Summary
These systems save energy in buildings for three reasons:
• Air Infiltration Reduction: Small cracks in the window frame and glass areas act like
holes in a barrel of water, allowing water to leak out. An interior window system prevents
this from happening in the openings.
• Insulation Improvement: By placing a window pane behind an existing one, a dual pane
insulated glass unit is created which triples the insulating properties. This takes a
window with an R-1 rating to an R-3 rating.
• Solar Heat Gain Control: The sun’s light energy travels through the window and is
absorbed in the building, creating heat energy. This is sometimes desired in the winter
months but is not usually wanted during the summer.
In addition, secondary window systems lead to deferred capital costs in buildings where
older equipment can be used longer and maintenance costs cut by over 50%. When there
are smaller peak loads, smaller equipment (chillers, HVAC, boilers, fans) is needed to
deliver heating and cooling. Buildings with existing windows that have single pane glass
are the best opportunity to see immediate ROI―generally within a 5–8-year time frame in
energy applications.

Resources
ClimateWorks Foundation. http://www.climateworks.org/ Accessed September 2014.
Energy Information Administration (EIA). Annual Energy Review 2011. Washington, DC: U.S.
Department of Energy (DOE), 2012. http://www.eia.gov/totalenergy/data/annual/pdf/aer.pdf Accessed
September 2014.
Enkvist, Per-Anders, Tomas Nauclér, and Jerker Rosander. “A Cost Curve for Greenhouse Gas
Reduction.” McKinsey Quarterly. McKinsey & Company, February 2007.
http://www.mckinsey.com/insights/sustainability/a_cost_curve_for_greenhouse_gas_reduction Accessed
September 2014.
McKinsey & Company. http://www.mckinsey.com/ Accessed September 2014.
Therm-O-Lite Inc. http://thermolitewindows.com/ Accessed September 2014.
U.S. Department of Defense. “Unified Facilities Criteria (UFC): DoD Minimum Antiterrorism Standards
For Buildings.” 9 February 2012. http://www.wbdg.org/ccb/DOD/UFC/ufc_4_010_01.pdf Accessed
September 2014.

Conclusion
©2015 Therm-O-Lite Inc. The material contained in this course was
researched, assembled, and produced by Therm-O-Lite Inc. and remains its
property. Questions or concerns about the content of this course should be
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