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.
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