by Katie Daniel | April 1, 2016 1:42 pm
by Andre Desjarlais, Amy Wylie, and Mugdha Mokashi
Sixty percent of U.S. commercial buildings were constructed before 1980. (This comes from Energy Information Administration’s (EIA’s) “2012 Commercial Buildings Energy Consumption Survey,” which can be accessed at www.eia.gov/consumption/commercial/reports/2012/buildstock). Retrofitting them for energy efficiency is essential to achieve the Department of Energy (DOE) Building Technologies Office’s (BTO) goal of halving building energy use by 2030. (For more, see DOE’s Office of Energy Efficiency and Renewable Energy (EERE) 2014 paper, “Windows and Building Envelope Research and Development: Roadmap for Emerging Technologies”). Most existing buildings have masonry construction with uninsulated wall assemblies, which offer good potential for wall improvement strategies. Effective analysis of these retrofits is essential to ensure improved durability when insulating masonry walls on the interior. Now, best practice retrofit recommendations have been evaluated based on the results of hygrothermal analysis, laboratory tests, and field performance evaluations.
Standard component retrofits, such as HVAC or lighting upgrades, present a limited scope for retrofit. They prevent the building from realizing greater energy savings that can be achievable when considering an envelope retrofit along with a standard component retrofit. (See the American Institute of Architects (AIA) and Rocky Mountain Institute’s 2013 publication, “Deep Energy Retrofits: An Emerging Opportunity.” Visit www.aia.org/practicing/AIAB09924).This integrated retrofit approach is essential in order to achieve more than 50 percent reduction in energy consumption.
Older masonry buildings often require a retrofit on the interior due to factors such as historic preservation, zoning issues, space restrictions, or aesthetics. However, without effective analysis, adding insulation to the interior of a masonry wall can result in potential performance and durability issues such as condensation, particularly in cold climates. (See John Straube et al’s 2012 paper for Building Science Corporation, “Measure Guideline: Internal Insulation of Masonry Walls”). This is a concern because most of the pre-1980s buildings with masonry construction are located in the Northeast. (For more informaton, see K. Otto’s “CoStar Statistics on GPIC Mid-sized Class A Office Buildings” [Robust Systems and Strategy LLC, 2011] and E. Fratto’s “Identification of Unreinforced Masonry Buildings (URMs) in the United States” [Northeast States Emergency Consortium, 2012]).
The objective of this project was to identify best practices for energy-efficient and cost-effective retrofits for commercial buildings with masonry construction. The metrics used to evaluate the best practice recommendations were intended to exceed performance of American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) 90.1-2010, Energy Standard for Buildings Except Low-rise Residential Buildings, and achieve a payback in less than 15 years. The target market for the project was ASHRAE Climate Zones 4 and 5, representing a majority of the northeastern United States. While the field data collection for the project is currently ongoing, this article explains the process of evaluation for the recommended retrofit scenarios.
Market engagement for the project
The Consortium for Building Energy Innovation (CBEI), headquartered in Philadelphia’s Navy Yard, is a group of 14 member organizations funded through the DOE and led by Pennsylvania State University. It works to develop and deploy market-tested pathways to achieve 50 percent reduction in overall building energy use by 2030 for existing small and medium-sized commercial buildings (SMSCB). The research project profiled in this article supports the CBEI goal by providing envelope solutions for an integrated retrofit strategy.
The project team included collaborators representing diverse areas of the retrofit value chain. A manufacturer of raw materials for building insulation led the project, while Oak Ridge National Laboratory (ORNL) provided third-party verification for simulation and laboratory test evaluations. The Air Barrier Association of America (ABAA) and another manufacturer served as market partners, offering industry expertise for the project and guiding the commercialization of the project results.
A Technical Advisory Group (TAG) of industry experts in the area of building envelope was also engaged for this project. Their role was to provide technical advice, ensure the project outcomes were relevant to the market, and confirm set deliverables were met. The TAG members for this project were Fiona Aldous from Wiss, Janney, and Elstner (WJE) Associates, Brian Stroik from a sealant/waterproofing company, and Pat Conway from the International Masonry Institute (IMI).
In 2012, CBEI identified a potential demonstration project in the Navy Yard to show energy savings using integrated retrofit strategies. The identified building was a two-story masonry building built in the early 1940s, which required a retrofit on the interior of the masonry wall. Numerous integrated retrofit solutions were analyzed to identify an optimal solution providing energy and cost benefits. This analysis of an integrated retrofit required a longer time than a conventional retrofit analysis, which typically considers only the most cost-effective single-component retrofit. Although the building owner appreciated this analysis, a change in the business strategy resulted in the owner not pursuing the proposed retrofit.
Nevertheless, the analysis and interactions with the building owner were instrumental in identifying market barriers for envelope retrofits such as initial upfront costs and lack of information regarding options and benefits. This not only requires extensive evaluation at the initial stage to identify solutions and ascertain potential savings, but also indicates a need for making more information available on interior insulated masonry buildings through validated case studies. Those case studies could then reduce the need for extensive evaluations and help accelerate adoption of wall retrofits in the market.
For the research project highlighted in this article, the team used ORNL’s two-story Flexible Research Platform to test wall assemblies and generate a validated case study. Energy-efficient and cost-effective solutions, identified through extensive evaluations conducted for the building at the Navy Yard, formed the basis of evaluation for this particular project.
Several wall retrofit scenarios were evaluated through multiple stages to identify the best recommendation. An industry expert review vetted a list of wall retrofit scenarios, and evaluated them against pre-determined critical parameters using hygrothermal modeling and industry data.
Three top-performing scenarios identified through this evaluation were constructed as mockup walls and tested in the ORNL laboratory for thermal performance and air leakage. The laboratory test evaluations were then used to identify two top-performing scenarios, which were installed on the two-story Flexible Research Platform at ORNL.
Field data collection for the two retrofit scenarios is ongoing, continuing to span over three seasons. The field performance evaluation will help identify the best-practice retrofit recommendation.
Industry expert review
In August 2014, a team of building science experts, contractors, and envelope consultants conducted an expert review. They vetted a list of seven retrofit scenarios designed for the baseline wall assembly of ORNL’s two-story research platform (Figure 1). The objectives of the expert review were to:
The experts recommended adding two additional scenarios, resulting in a final list of nine retrofit possibilities (Figure 2).
Another recommendation was to categorize the nine retrofit scenarios into three major groups:
1. Retain the existing insulation and drywall within the assembly; install retrofit over existing assembly.
2. Retain the existing studs, remove existing insulation and drywall; install retrofit within existing studs.
3. Remove existing insulation, studs, and drywall; install retrofit over concrete masonry unit (CMU) wall.
Six critical evaluation parameters were identified, along with the weighted percent for each parameter:
Evaluating scenarios against
The nine retrofit scenarios were evaluated against the six pre-determined parameters identified at the expert review. Data for the scenarios came from multiple sources:
The data collected for each parameter had different units, all of which were normalized to a range from ‘0’ to ‘1’ to facilitate objective evaluation. The normalized data values were then applied with the respective weighted percentages for each parameter, which were then added and compiled in a final performance evaluation matrix to provide overall performance for each scenario.
As shown in Figure 3, three top-performing scenarios were identified through the performance evaluation matrix, to be evaluated through the next stage.
The first scenario involved retaining the existing insulation and gypsum wallboard, and installing 50 mm (2 in.) of polyisocyanurate (polyiso) foam board insulation with taped seams on the existing wall.
In the scenario that ranked second, the existing insulation, steel studs, and drywall would be removed. Then, 63.5 mm (2 ½ in.) of polyiso foam board insulation would be installed, with a separate air barrier layer applied on the inner face of the concrete block.
For the third scenario, the existing insulation, steel studs, and drywall would again be removed. This time, 90 mm (3 ½ in.) of closed-cell sprayed polyur-ethane foam (SPF) would be used, of which 38 mm (1 ½ in.) is installed as a continuous insulation (ci) layer on the inner face of the concrete block.
Laboratory test evaluations
The three top-performing scenarios were then constructed as mockup walls and tested at ORNL for thermal performance (in accordance with ASTM C1363, Standard Test Method for the Thermal Performance of Building Assemblies by Means of a Hot Box Apparatus) and air leakage (per ASTM E283, Standard Test Method for Determining the Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen).
The results obtained for the two tests were used as inputs for an existing energy model created by ORNL for the two-story research platform. This energy model provided potential energy savings and payback period for the three scenarios, and their performance was evaluated against two baselines (Figure 4):
1. Baseline with no existing insulation on the interior of the masonry wall. (R-value for baseline assembly was R-0.88 K·m2/W [R-5 h-sf-F/Btu]; air leakage was 8 L/s-m2 [1.6 cfm/sf].)
2. Baseline with existing fiberglass batt insulation on the interior of the masonry wall. (R-value for baseline was R-1.85 K·m2/W [R-10.5 h-sf-F/Btu]; air leakage was 8 L/s-m2 [1.6 cfm/sf].)
The results for the two laboratory tests and the estimated payback periods for the three scenarios were evaluated for compliance against the previously defined metrics for the project. Two top-performing scenarios chosen based on this evaluation are shown in Figure 5.
The closed-cell sprayfoam scenario provided a high payback against a baseline with existing insulation—however, the payback against a baseline without existing insulation bordered on the range of 10 to 15 years. Along with the fact sprayfoam provided the highest energy savings, this resulted in selecting this scenario for the next stage of the project.
Field test evaluations
The two top-performing scenarios were installed on ORNL’s two-story Flexible Research Platform to collect field data. The baseline wall assembly was created to represent the typical wall for a majority of the existing commercial buildings built before 1980. The two-story platform is divided into eight zones, with four on each floor. Each zone has the capability to be monitored separately. The two top-performing scenarios were installed in two of these eight zones, having similar orientation.
The intent of field analysis was to analyze the performance and constructability for the two retrofit scenarios.
Polyiso foam board retrofit
The polyiso foam board retrofit scenario was designed as an integrated solution addressing improved thermal performance, reduced air infiltration, and improved durability for the wall assembly.
The high R-value per inch for the polyiso foam provided better energy performance at minimized thickness. The low air permeance of the board, along with taped seams and sealed junctions, qualified the material as an air barrier according to ASTM E2178, Standard Test Method for Air Permeance of Building Materials. The foam board, with coated-glass facers, provided a vapor permeance of less than 1 perm, minimizing the risk of interior moisture reaching the cold surface of the masonry block wall. This reduced the potential for moisture accumulation and mold probability.
Installation of this scenario over the existing assembly eliminated the cost of demolishing existing insulation within the assembly. However, installing a retrofit over the existing assembly requires investigation of the insulation to ensure effective performance. As a result, the applicability of this scenario depends on the condition of the existing insulation. For this project, investigation of existing insulation was not required as the insulation installed for the two-story research platform baseline was relatively new. As a result, the cost estimates used to predict payback for this scenario did not take into account the cost needed to investigate the existing insulation.
The energy modeling conducted for this scenario estimated a payback of 14 years against a baseline with existing insulation (Figure 6). However, the field data being collected will be employed to calculate a refined estimate of the payback period.
Closed-cell spray foam retrofit performance
The closed-cell sprayfoam served as an air and moisture barrier, along with providing thermal insulation. This scenario required teardown of existing insulation within the assembly. The steel studs were offset from the wall by 38 mm (1 ½ in.) to provide for continuous insulation.
Closed-cell SPF is considered ‘air-impermeable’ at a minimum thickness of 19 mm (¾ in.), providing the air barrier within the assembly. With a perm rating of less than 1 perm at 38 mm, the insulation serves as a Class II vapor retarder. This helped minimize the risk of interior moisture being transported to the cold surface of the masonry block wall and reduced the potential for moisture accumulation and related mold probability.
For this scenario, the installation of closed-cell sprayfoam eliminated the need for additional materials to address air and moisture infiltration, resulting in lower labor and material costs. The energy modeling conducted for this scenario estimated a payback of 16 years against a baseline assembly with no existing insulation, and 25 years against a baseline with existing insulation (Figure 7, page 41). However, the field data being collected will be utilized to calculate a refined estimate of the payback period.
Constructability for the installed retrofit scenarios
The constructability for the two scenarios was evaluated based on the interior floor space consumed by the retrofit scenarios, ease of construction, ability to address critical details, and the disruption to building occupants. The findings are shown in Figure 8.
The next stage of the project is to finish collecting field data for the two retrofit scenarios demonstrated with ORNL’s two-story Flexible Research Platform. The field data will be evaluated to identify the best practice retrofit recommendation.
This project identified two top-performing wall retrofit recommendations for commercial buildings with masonry construction based on a multi-stage evaluation process. While the project is still ongoing, the selection of the two scenarios is based on the performance results achieved up to the current stage of the project.
The polyiso foam board scenario evaluated as a retrofit installed over existing assembly was identified as the most cost-effective retrofit scenario, as it provided HVAC energy savings of 30 percent at a payback of 14 years. However, this scenario depends on the condition of the existing insulation and is applicable only when the insulation is in effective condition to be retained. Increased steps in the installation (e.g. taping of board seams, and sealing junctions or sealing boards to wall surface) require vigilant inspection onsite to ensure quality installation.
The closed-cell SPF scenario was identified as the most energy-efficient retrofit, providing HVAC energy savings of 41 percent. However, this strategy requires the teardown of existing insulation within the assembly, which can be an added cost in terms of time and labor, resulting in a payback of 16 years. The spray application method by a single trade (i.e. certified sprayfoam contractor) can help ensure installation quality onsite.
The evaluation conducted through the project compared the two integrated retrofit solutions based on cost, energy performance, and constructability. This information will provide the industry with guidelines for best practice retrofit recommendations and help building owners and design professionals make informed decisions regarding the most suitable option for their buildings.
André Desjarlais is the program manager for the Building Envelope Research Program at the Oak Ridge National Laboratory (ORNL). He has been involved in building envelope and materials research for more than 40 years, specializing in building envelope and material energy efficiency, moisture control, and durability. Desjarlais is the past chair of ASTM Committee C16 and was awarded Fellowship in the association. He chairs ASTM’s committee on Technical Committee Operations (COTCO), and has also been a member of American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) since 1991. Desjarlais can be reached at firstname.lastname@example.org.
Amy Wylie is the buildings and transportation platform leader for Covestro LLC’s public sector and business growth services division. She has vast experience in various material science disciplines and functions including coatings, plastics, and polyurethane materials. Wylie is a principal investigator dedicated to the Consortium for Building Energy Innovation (CBEI). She can be reached at email@example.com.
Mugdha Mokashi was a building science specialist with Covestro at the time of this article, analyzing value-added propositions for integrated envelope retrofits for commercial buildings. Her primary responsibilities included performing energy modeling and providing retrofit recommendations specific to the Northeast United States.
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