Estimating the Energy, Economic, and Durability Benefits of Installing an Air Barrier System in Commercial Buildings Using a Web-Based Calculator

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Photo Credit: Pixabay image by Pexels.
ABSTRACT
Uncontrolled heat, air, and moisture
transfer through the building enclosure has
a significant impact on energy usage, comfort,
indoor air quality, and building enclosure
durability. Air leakage in commercial
buildings in the United States accounts
for about one quad (one quadrillion Btu)
of energy annually, costing approximately
$10 billion.[1] As the thermal resistance of
commercial building enclosures continues
to improve, the relative contribution of
air leakage to heating and cooling loads
is increasing. A wide variety of air barrier
technologies and construction practices to
reduce the air leakage in buildings are
available to the architect and designer. To
promote more energy-efficient and durable
building enclosure design, advances in
easy-to-use tools for determining the impact
of air leakage are needed.
Oak Ridge National Laboratory (ORNL),
the Air Barrier Association of America
(ABAA), and the National Institute of
Standards and Technology (NIST) partnered
to develop an online calculator
that estimates the potential energy,
cost savings (due to energy use
reduction), and moisture transport
due to improvements in airtightness.
The calculator estimates the
energy and cost savings potential
based on the pre- and postretrofit
air leakage rates for
prototype commercial buildings.
The tool does not include
the energy and hygrothermal
impacts of air intrusion
or air that flows into and
out of the building enclosure
from the same side.
This article reports on
the development of the
Energy Savings and
Moisture Transfer
Calculator. This
online tool aims
to fill this void,
is based on
the best science
available,
and
is easy to
use.
INTRODUCTION
Commercial buildings in the United
States consume about 19 quads of energy
per year,[1] which represents about 20
percent of all the energy used in the U.S.
annually. Air leakage through the enclosure
of these buildings is responsible for approximately
6 percent of their energy use.[1] The
air leakage in commercial buildings mainly
affects heating energy consumption. The
U.S. Energy Information Administration’s
(EIA’s) Commercial Building Energy
Consumption Survey (CBECS) indicates
U.S. commercial buildings consume 1740
TBtu for air leakage associated with
space heating.[2] Previous studiesshow that infiltration is responsible
for an average of 33 percent
of the heating load and 3.3
percent of the cooling load in
the U.S.[3] Air barrier systems are
combinations of materials
designed and constructed
to control airflow between
a conditioned space and an
unconditioned space. The
air barrier system is the primary
air enclosure boundary that separates
indoor (conditioned) air and outdoor
(unconditioned) air. There are numerous
test methods available for determining
the air leakage of an air barrier material
and system with ASTM E2178, Standard
Test Method for Air Permeance of Building
Materials[4] and ASTM E2357, Standard Test
Method for Determining Air Leakage Rate
of Air Barrier Assemblies[5] being the most
widely used methods in the U.S.
Although air leakage has long been recognized
as a key contributor to heating and
cooling loads and moisture flow, methods
that estimate its effects on energy consumption
and durability vary due to the complexity
of this task.[6-9] Comprehensive building
design and energy simulations should consider
the fact that air leakage rates vary
due to the operation of heating, ventilation,
and air-conditioning (HVAC) systems, occupancy,
the size of apertures in the
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Figure 1 – General procedure to estimate potential energy costs for different levels of
enclosure airtightness in DOE commercial prototype buildings.
3 8 • I I B E C I n t e r f a ce S e p t e m be r 2 0 1 9
enclosure, and weather (i.e., indoor-to-outdoor
temperature difference and wind). Due
to the complexity of the analyses and the
number of variables involved, typical energy
simulations tend to take shortcuts to
expedite the analysis, such as assuming
constant leakage rates and/or using simplified
algorithms, which can lead to under- or
over-estimated energy usage.
THE TOOL
The online energy savings and moisture
transfer calculator (henceforth referred to
as the calculator) for commercial buildings
(https://airleakage-calc.ornl.gov/#/) is
described in Figure 1.
The tool uses a database of EnergyPlus
pre-run simulation results for Department
of Energy (DOE) commercial prototype
buildings.[10] The main difference between
the online calculator and the procedure
followed in the DOE prototypes is that the
calculator utilizes CONTAM-calculated air
changes per hour (ACH) or air leakage rates
as inputs, whereas the prototypes make simplified
assumptions. CONTAM[11] is a multizone
airflow and contaminant transport
analysis software developed at NIST. This
software considers multiple variables, such
as weather conditions, enclosure airtightness,
and HVAC system operation, to calculate
air leakage rates through the building
enclosure. The CONTAM-calculated hourly
air leakage rates are imported into DOE’s
whole-building energy simulation software,
EnergyPlus,[12] with the CONTAM Results
Export Tool.[13] EnergyPlus is then used to
calculate the effect of air leakage on energy
consumption and moisture transport.
The described procedure is comparable to
what was followed by Emmerich et al.[3] and
Emmerich and Persily,[14] but the calculator
makes this complex procedure available to
those who don’t have the expertise to calculate
hourly air leakage rates. In contrast,
typical energy simulations tend to expedite
their analyses by assuming constant air leakage
rates and/or using simplified algorithms
that can lead to less-accurate energy usage
estimates. Ng et al.[15] estimate that simplifications
in the EnergyPlus models for the prototype
commercial buildings lead to underestimations
of average electrical and gas use by
HVAC systems. Shrestha et al.[16] show that
the discrepancy in the predicted cost savings
between the simplified tools and the proposed
methodology could be as high as 40 percent.
The moisture transport calculation is
simplified. The tool is only computing the
total amount of water that is transported
through the building enclosure component
into the interior building space due to
air leakage. It is a measure of the potential
moisture source but does not look at
whether the moisture is accumulating in
the building enclosure. Both moisture due
to infiltration and exfiltration is calculated
and then summed. The thesis is that the
greater the amount of moisture transported
through the building enclosure, the greater
the likelihood of having a durability issue.
As stated earlier, the calculator uses the
DOE prototype building models, given that
these represent 80 percent of U.S. commercial
building floor area.[17] The current suite
of commercial prototype building models
covers 16 common building types. Figure 2
shows the prototype buildings as a percentage
of total U.S. commercial building floorspace.
The calculator includes simulations
in its database to cover seven of the building
types. These are depicted in Figure 2 by a
solid green-colored bar and represent over
55 percent of U.S. commercial floorspace
and represent building types that would
typically be temperature conditioned and
benefit from an air barrier system.
Figure 2 – Prototype buildings as a percentage of total U.S. commercial building floorspace.
Green-shaded bars are those for which the calculator includes simulations.
Table 1 – Modeling specifications of standalone retail building prototype.
These prototypes were developed by
DOE as a standardized baseline for energy
savings calculations. The enclosure assembly
and HVAC unit for each of the prototypes
vary based on geographical location
and the building code that the building
complies with. The features of the building
models and a detailed description of their
development are provided by Goel et al.[7] and the Building Energy Codes Program
website.[18] In particular, the calculator uses
the prototype buildings that comply with
ASHRAE Standard 90.1-2013.[19] For example,
building characteristics of a standalone
retail building as defined by the prototypical
models are shown in Table 1. Similar
characteristics of other prototype buildings
are described in Goel et al.[7] Models that
represent typical commercial buildings in
Canada are not available in the public
domain; therefore, the DOE prototypes were
also used there.
The calculator’s current database
includes 52 U.S. cities and five Canadian
cities. The selection of cities was based on a
reasonable distribution of major metropolitan
areas throughout the U.S.; therefore,
not every state or province is represented.
If the specific city for which you are interested
in obtaining results does not appear
on the list, the selection of a city that
has similar meteorological conditions (wind,
temperature, solar radiation, and rain) is
recommended. This is not always the city
geographically closest to your target city.
Cities in Canada were recommended by our
Canadian partners.
Table 2 lists the four levels of airtightness
that were assumed to build the simulation
database. These include the slab and belowgrade
enclosure area in the normalization
of the air leakage rate, which is why they
are referred to as “six-sided enclosures,” as
well as the assumption that the air leakage
is equally distributed over all exterior surfaces.
The six-sided value is used in many
building codes and standards; however, the
CONTAM and EnergyPlus models assume
no air leakage through the exterior enclosure
that is not exposed to ambient air. The
baseline value in Table 2 was calculated
using the average leakage rate for commercial
buildings reported by Emmerich
et al.[3] of 9 L/s·m2 (1.77 CFM/ft2) at 75
Pa for a five-sided enclosure. The baseline
of 5.4 L/s·m2 (1.06 CFM/ft2) at 75 Pa was
obtained by multiplying the average leakage
rate by the five-sided to six-sided enclosure
area ratio of the standalone retail building
prototype. Similar ratios were applied to
the other prototypical building types. Table
2 also lists three target levels for improved
airtightness at 75 Pa: 2 L/s·m2 (0.39 CFM/
ft2) is the whole building option in the 2015
International Energy Conservation Code;[20] 1.25 L/s·m2 (0.25 CFM/ft2) is the airtightness
required by the U.S. Army Corps of
Smarter Testing. Faster Response.™
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Table 2 – Assumed building enclosure airtightness levels for a six-sided enclosure (standalone
retail building).
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Engineers;[21] and 0.25 L/s·m2 (0.05 CFM/
ft2) is the leakage rate targeted by the DOE
buildings enclosure roadmap.[1] Emmerich and Persily[14] analyzed the
NIST U.S. commercial building air leakage
database and found that the 79 buildings
categorized as having an air barrier had an
average six-sided leakage of 1.39 L/s·m2
(0.27 CFM/ft2) at 75 Pa, which was 70 percent
below the average leakage of the 290
buildings without an air barrier (i.e., 4.33
L/s·m2 or 0.85 CFM/ft2 at 75 Pa) and is similar
to the second target level above. Zhivov
et al.[22] reported the average six-sided leakage
for a set of 285 new and retrofitted military
buildings constructed to the U.S. Army
Corps of Engineers (USACE) specifications
to be 0.9 L/s·m2(0.18 CFM/ft2).
Air leakage data for the four different
airtightness levels were curve fitted for each
building type and geographical location.
The calculator will interpolate between the
baseline six-sided air leakage and the tightest
level of 0.25 L/s·m2 (0.05 CFM/ft2) at 75
Pa to any intermediate air leakage value.
Extrapolation should not be used because
the curve fits are non-linear and not validated
beyond the cited endpoints.
To convert energy savings into an economic
benefit, the user has the option to
either select the default value for energy
prices from the following sources or to
input their own electricity and natural gas
prices. Electricity and natural gas prices
were collected from numerous sources.
Prices for electricity for U.S. cities are
maintained by the U.S. Energy Information
Administration, and 2016 year-to-date average
prices for commercial customers were
used in the calculations.[23] For natural gas,
average 2015 prices for commercial customers
were obtained.[24] Energy prices for
Canada were taken from the rates used to
develop the National Energy Code of Canada
for Buildings 2011.[25] The calculator does
not account for demand charge savings.
Updates in the default energy prices are
planned for the next update cycle.
THE WEBSITE
Figure 3 depicts the input page of the
Energy Savings and Moisture Transfer
Calculator. The user decides whether to
input data and see results in the metric
system or in traditional imperial units. One
is then prompted to select a geographical
location. This selection can be made either
by using drop-down menus or by manipulating
the map screen. Cities included
in the database are highlighted with red
flags on the map. The user then selects
the commercial building type from the
drop-down menu. He/she selects from the
following list of building types: standalone
retail, mid-rise apartment, medium office,
high-rise apartment, hospital, large hotel,
or secondary school. Once selected, the
default footprint of the building is displayed.
This footprint can be changed to any other
size. The calculator determines the annual
energy savings and moisture transport per
square foot of wall area and will adjust the
results based on different footprints. The
user is then prompted to input two levels
of airtightness: the baseline and the target
air leakage after completing the air barrier
retrofit. The calculator will assess the
energy savings, economic, and moisture
transport differences between these two set
levels. Recommendations can be obtained
by pressing the “Help” button. Energy costs
are input when the user selects the city for
evaluation. State or provincial energy costs
for electricity and natural gas are input
from the database. However, if the user has
better energy costs, one can input them in
lieu of the default state and provincial values.
Then you can press “Calculate” and…
The output screen is shown in Figure 4.
A summary of the user selections is posted
at the top of the page. The calculator determines
the equivalent leakage area (ELA) for
the baseline case and the improved airtight
construction, along with the amount of
energy saved and the total savings in the
appropriate currency. The ELA is defined as
the area of a sharp-edged orifice that would
leak the same amount of air as the building
does at a pressure of 10 Pa. Finally, the calculator
computes the total amount of moisture
that would be transported through the
enclosure into the building interior space
for both the baseline and retrofit cases.
SUMMATION
An online airtightness calculator has
been developed to estimate the energy and
Figure 3 – Input page for the Energy Savings and Moisture Transfer Calculator. economic benefits of an air barrier system
along with its contribution to reducing the
potential moisture load that a building
enclosure must endure. The tool uses a
database of EnergyPlus pre-run simulation
results for DOE commercial prototype
buildings and is simply computing the total
amount of water that is transported through
the building enclosure component due to
air leakage. This calculator is different from
other common methods used in enclosure
analysis in that it uses hourly air leakage
rates that are estimated by considering key
variables such as building leakage rate,
weather conditions, and HVAC operation.
The calculator provides energy cost estimates
as a function of building enclosure
airtightness for DOE commercial prototype
buildings in cities in the U.S. and Canada.
The calculator is a powerful, credible, and
easy-to-use tool that designers and contractors
can utilize to estimate the energy
and financial savings that building owners
could achieve by reducing air leakage and
the improved durability they could attain by
reducing the potential moisture load.
ACKNOWLEDGEMENTS
The authors would like to thank the
U.S. Department of Energy and the Air
Barrier Association of America for funding
this research. This manuscript has
been authored by UT-Battelle, LLC, under
Contract No. DE-AC05-00OR22725 with the
U.S. Department of Energy.
REFERENCES
1. U.S. Department of Energy. Windows
and Building Envelope Research
and Development: Roadmap for
Emerging Technologies. 2014.
https://www.energy.gov/sites/
prod/files/2014/02/f8/BTO_windows_
and_envelope_report_3.pdf.
2. U.S. Energy Information Administration.
Commercial Buildings
Energy Consumption Survey
(CBECS). 2012. https://www.eia.
gov/consumption/commercial/.
3. S. Emmerich, A. Persily, and T.P.
McDowell. “Impact of Commercial
Building Infiltration on Heating
and Cooling Loads in U.S. Office
Buildings.” Presented at 26th AIVC
Conference, Brussels. September
21–23, 2005.
4. ASTM. ASTM E2178-13, Standard
Test Method for Air Permeance
of Building Materials.
West Conshohocken, PA: ASTM
International. 2013.
5. ASTM. ASTM E2357-11, Standard
Test Method for Determining Air
Leakage of Air Barrier Assemblies.
West Conshohocken, PA: ASTM
International. 2011.
6. D.B. Crawley, J.W. Hand, M.
Kummert, and B.T. Griffith.
“Contrasting the Capabilities of
Building Energy Performance
Simulation Programs.” Building and
Environment 43(4):661–73. 2008.
7. S. Goel, R. Athalye, W. Wang, J.
Zhang, M. Rosenberg, Y. Xie, R. Hart,
and V. Mendon. Enhancements to
ASHRAE Standard 90.1, Prototype
Building Models. PNNL-23269.
Richland, WA: Pacific Northwest
National Laboratory. 2014.
8. K. Gowri, D. Winiarski, and R.
Jarnagin. “Infiltration Modeling
Guidelines for Commercial Building
Energy Analysis.” PNNL-18898.
Richland, WA: Pacific Northwest
National Laboratory. 2009.
9. M. Deru, K. Field, D. Studer, K.
Benne, B. Griffith, P. Torcellini, M.
Halverson, D. Winiarski, B. Liu, M.
Rosenberg, et al. DOE Commercial
Reference Building Models for
Energy Simulation–Technical
Report. National Renewable Energy
Laboratory: Golden, CO, USA, 2010.
10. https://www.energycodes.gov/
development/commercial/prototype_
models.
11. W.S. Dols and B. Polidoro.
“CONTAM User Guide and Program
Documentation.” Technical Note
1887. National Institute of Standards
and Technology: Gaithersburg, MD,
USA, 2015.
12. Department of Energy (DOE).
Auxiliary EnergyPlus Programs—
Extra Programs for EnergyPlus;
DOE: Washington, DC, USA, 2016.
13. B. Polidoro, L.C. Ng, and W.S. Dols.
“CONTAM Results Export Tool.”
Technical Note 1912. Gaithersburg,
MD: National Institute of Standards
and Technology. 2016.
14. S. Emmerich and A. Persily. “Analysis
of U.S. Commercial Building
Envelope Air Leakage Database
to Support Sustainable Building
Design.” International Journal of
Ventilation. 12, 331–344. 2014.
15. L.C. Ng, N. Ojeda Quiles, W.S.
Dols, and S.J. Emmerich. “Weather
Correlations to Calculate Infiltration
Rates for U.S. Commercial Building
Energy Models.” Building and
Environment. 127, 47–57. 2018.
16. S. Shrestha, D. Hun, L. Ng, A.
Desjarlais, S. Emmerich, and L.
Dalgleish. Online Airtightness
Savings Calculator for Commercial
Buildings in the United States,
Canada, and China. In Proceedings
of the Thermal Performance of the
Exterior Envelopes of Whole Buildings
– 13th International Conference,
S e p t e m be r 2 0 1 9 I I B E C I n t e r f a ce • 4 1
Figure 4 – Output page for the Energy Savings and Moisture Transfer Calculator.
Clearwater, FL, USA, December 4–8,
2016.
17. Department of Energy (DOE).
Commercial Prototype Building
Models. 2016. Available online:
https://www.energycodes.gov/commercial-
prototype-building-models.
18. Department of Energy (DOE).
Auxiliary EnergyPlus Programs—
Extra Programs for EnergyPlus;
DOE: Washington, DC, USA, 2016.
19. American Society of Heating,
Refrigerating and Air-Conditioning
Engineers. ANSI/ASHRAE/IES
Standard 90.1-2013, Energy
Standard for Buildings Except Low-
Rise Residential Buildings. ASHRAE:
Atlanta, GA, USA. 2013.
20. IECC. International Energy
Conservation Code. Illinois:
International Code Council. 2015.
21. USACE. Air Leakage Test Protocol
for Building Envelopes. U.S. Army
Corps of Engineers. 2012.
22. A. Zhivov, D. Herron, J.L. Durston,
M. Heron, M., and G. Lea. “Air
Tightness in New and Retrofitted
U.S. Army Buildings.” 2013. AIVC
Workshop.
23. U.S. Energy Information Administration.
“Electricity Sales, Revenue
and Average Price.” Available online:
https://www.eia.gov/electricity/
sales_revenue_price/.
24. U.S. Energy Information Administration.
Natural Gas. Available
online: https://www.eia.gov/dnav/
ng/ng_sum_lsum_a_EPG0_PCS_
DMcf_a.htm.
25. National Energy Code of Canada
for Buildings 2011. Available
online: https://nrc.canada.ca/en/
node/1236/.
4 2 • I I B E C I n t e r f a ce S e p t e m be r 2 0 1 9
André Desjarlais
is the program
manager for the
Building Envelope
and Urban
Systems Research
Program at the Oak
Ridge National
Laboratory in Oak
Ridge, TN. Areas of
expertise include
building enclosure
and material energy
efficiency, moisture control, and durability.
Desjarlais is a founding director of the
RCI Foundation. He has been a member of
ASTM since 1987 and was awarded the title
of Fellow in 2011. He has also been active
in ASHRAE since 1991.
André Desjarlais
Mahabir Bhandari
is a scientist in
Oak Ridge National
Laboratory’s Building
Envelope & Urban
Systems Research
Group.
His research area
includes fenestration
product development
and analysis,
whole-building
energy modeling,
and the evaluation and integration of energy-
efficient technologies in buildings. He
is an ASHRAE-certified Building Energy
Modeling Professional, LEED™ Accredited
Professional BD+C, and Certified Energy
Manager. Bhandari currently serves on the
board of directors of the Attachment Energy
Rating Council (AERC).
Mahabir Bhandari
Som Shrestha is
a building scientist
at ORNL. His
research is focused
on experimental
and analytical
studies to improve
the energy performance
of building
envelope components,
equipment,
and systems.
In the last three
years, he has been developing the Energy
Savings and Moisture Transfer Calculator
that estimates potential energy and cost
savings, and reduction in moisture transport
from improvements in airtightness in commercial
buildings. He is an ASHRAE-certified
Building Energy Modeling Professional.
Som Shrestha
Laverne Dalgleish
has been involved
in the construction
industry for
over 30 years and
has specialized in
energy efficiency
of building enclosures.
He has
been involved with
the International
Organization for
Standardization
(ISO) and has participated in building
research projects with ORNL, Syracuse
University, University of Waterloo, and NRC
of Canada. He has worked on a number of
utility demand-side management programs
with various government departments, such
as the U.S. DOE, Natural Resources Canada,
the EPA, Environment Canada, and Canada
Mortgage and Housing Corporation.
Laverne Dalgleish
The memberships of the American Architectural Manufacturers Association (AAMA) and the Insulating Glass
Manufacturers Alliance (IGMA) have voted to proceed with combining into one organization with a new name:
Fenestration and Glazing Industry Alliance (FIGA). They will retain separate brand equity in certain services
such as technical standards and certification programs. IGMA was created in 2000 as a result of the merger
between the Insulating Glass Manufacturers Association of Canada (IGMAC) and the Sealed Insulating Glass
Manufacturers Association (SIGMA). Today, IGMA represents 140 members across North America. AAMA was
founded in 1936 and represents over 300 members producing window, door, skylight, glazing, curtainwall, and
storefront products and components.
AAMA and IGMA to Merge as FIGA