The type of windows and other fenestration products specified in the building envelope significantly impact energy use. Today’s high-performance windows and curtain walls often incorporate double or triple panes, exotic gas-filled insulating glass units and high-performance coatings. Incorporating high-performance fenestration products reduces HVAC loads by limiting heating or cooling loss through windows, and may even increase a project’s Leadership in Energy and Environmental Design (LEED) score by improving the entire building’s energy performance. The use of high-performance windows also allows more daylight to enter a building, which reduces energy loads from artificial lighting and has been linked to increased productivity and health benefits.
Choosing the proper high-performance fenestration can be challenging. Unlike residential windows, commercial fenestration often is assembled on the project site, so rating and labeling the energy performance of each product is not practical. Last year, the National Fenestration Rating Council (NFRC) introduced an easy-to-use program, called the Component Modeling Approach (CMA), to address this issue.
CMA generates third-party energy performance ratings for fenestration products, which simplifies code compliance. Using this approach can help designers and contractors choose the right windows for their nonresidential projects. The party responsible for building energy codes on a commercial project—whether an architect, general contractor or specialty contractor—can rely on the CMA program to provide the most accurate ratings for fenestration energy code compliance documentation. Under the CMA program, the responsible party or the “specifying authority” enters into a CMA license agreement with the NFRC.
Building Codes Require NFRC Ratings
CMA provides U-factor, solar heat gain coefficient (SHGC), and visible transmittance (VT) ratings according to NFRC 100 (Procedure for Determining Fenestration Product U-Factors) and NFRC 200 (Procedure for Determining Fenestration Product Solar Heat Gain Coefficient and Visible Transmittance at Normal Incidence). ASHRAE 90.1-1999 and later versions (Energy Standard for Buildings Except Low-rise Residential Buildings) and the International Energy Conservation Code (IECC) both require NFRC 100 and 200. Many states use ASHRAE 90.1 or IECC as the basis for local building energy codes.
California specifically lists CMA in its Title 24 energy codes as one of three options for demonstrating compliance with fenestration energy codes for commercial buildings. The other options involve using default values or simple equations. A study conducted by the Heschong Mahone Group, comparing CMA to default fenestration rating values in California buildings, found the use of CMA provided an increase of 11.7 percent in energy compliance margins.
How CMA Works
CMA combines existing NFRC ratings for pre-approved window components (i.e., glazing, frames and spacers) to generate a whole product rating. The CMA Software Tool (
CMAST) allows the specifying authority to input design criteria and obtain preliminary ratings for various configurations. The user can see how changing one component affects the energy performance of the entire product, all in a virtual environment.
Once satisfied with the product, the specifying authority contacts an NFRC-approved calculation entity to obtain a CMA Label Certificate. This document lists the performance ratings for NFRC-rated fenestration systems in the entire building project for code compliance purposes. The Label Certificate clearly indicates U-factor, SHGC and VT values for each product, making it easy to assess code compliance. After a product is certified, the same product design can be used in successive projects without requiring recertification.
Added Benefits
In addition to identifying the most appropriate fenestration for a project and simplifying the certification process, CMA offers building professionals several other benefits.
- CMA can demonstrate fenestration products specified in bids will meet energy codes. CMA provides the most accurate fenestration rating values so design and construction professionals can be confident they selected the right windows for their project.
- CMA may increase LEED scores by facilitating the selection of windows with higher energy efficiency ratings. The LEED program calls for the use of ASHRAE 90.1-04, which requires NFRC 100 and 200. CMA uses NFRC 100 and 200 to provide the most accurate fenestration energy performance values.
- CMA makes it easier to conduct a total building energy analysis. CMA’s software, CMAST, makes it easy to transfer detailed values for angular-dependent SHGC and VT to software programs such as EnergyPlus and DOE-2.
- CMA may lead to more benefits from above-code incentive programs. More accurately rated fenestration and more precise whole building energy calculations could help building owners qualify for programs that provide financial incentives for building above code.
- CMA may reduce a building owner’s or tenant’s operating costs. CMA users can calculate more accurate thermal load estimates and install right-sized HVAC systems, which may lead to decreased utility bills.
Just as the NFRC’s residential label program transformed the selection of home windows, CMA is changing how the building industry selects, rates and certifies nonresidential fenestration systems. CMA not only streamlines the selection, certification and code compliance processes for fenestration, but it also helps building professionals select the most appropriate windows for every project.