Roofs Are Cool..Why Not Walls?

By Scott Kriner, Green Metal Consulting

A new three-year Research and Development project on Cool Walls has begun in California. The purpose of the project is to evaluate the energy-saving and environmental benefits of solar reflective walls, and to assess and advance available and emerging cool wall technologies. This will include cool paints, cool claddings, self-cleaning surfaces, fluorescent cool pigments and other novel solar reflecting technologies. Another important purpose of the project will be to develop an infrastructure to eventually promote cool walls and certify their performance. The work supports the efforts of California to reduce CO2 emissions by saving energy and improving efficiencies in buildings. The research also supports the California energy code as it increases wall insulation levels.

The project team includes scientists and researchers from Department of Energy's Lawrence Berkeley National Laboratory, University of California – San Diego, and the University of Southern California. Support is coming from the California Energy Commission, the California Air Resources Board, Pacific Gas and Electric, the Environmental Protection Agency (EPA) and the Department of Energy (DOE).

Like cool roofs, cool walls can be designed to reflect more solar energy which reduces unwanted heat gain into buildings. That can help the building to save cooling electricity and lower peak demand for cooling energy. Cool walls can also help to lower ambient temperatures in large cities, which helps to mitigate the urban heat island effect. One aspect of the R&D project is to analyze the interaction between cool walls and cool pavements – which is another topic of research in California as a method to reduce urban heat island effects. The cool wall project will look at how new technology could possibly help to reflect more solar energy away from a wall surface and even control the direction of any reflected light.

In addition to characterizing the wall systems currently in the marketplace, the project will also be developing metrics to rate self-cleaning wall materials. An ongoing DOE effort to develop fluorescent cool pigments for metal coatings will be supported by this project as well. And another über reflective technique, with the use of retroreflectors that strongly reflect sunlight, will be integrated into wall systems and analyzed.

The development of new pigment types and novel techniques to boost wall reflectance are included in the tasks of this project, for those partners who wish to work with LBNL through a special product development arrangement.

To-date, several metal wall system manufacturers have become partners in the project and are providing a variety of metal wall samples for the project. Other types of wall products in the evaluation include stucco, plaster, cement, fiber cement, wood, vinyl siding and architectural fabrics. One of the first tasks of the project is to evaluate the aging properties of wall materials using controlled outdoor exposure in three different climates in California. Samples will be exposed for two years and evaluated quarterly.

Modeling of the wall systems on 10 prototype buildings will be done to determine impacts on the energy usage in these types of buildings with the various wall materials and systems. The project has brought to light yet another acronym for our industry : “TUF-IOBES” which is Temperature of Urban Facets Indoor Outdoor Building Energy Simulator. In laymen’s terms, this is a model that takes into account the outside face temperatures, inside face temperatures and thermal load and air temperatures to predict the heat balance in a building.

After the analysis and modeling have been completed, the project has a task of developing some sort of infrastructure that can independently evaluate and certify cool walls. This is being compared to the Cool Roof Rating Council’s program or the Energy Star Roof Products Program.

As California gets closer to their Net Zero Energy mandates, all efforts to improve building energy efficiencies are ramping up. Walls may not have the same level of impact on a building as a roof when it comes to heat gain, but a slight improvement in wall performance can add to the reduction in cooling and heating energy. The cumulative reductions in cooling energy can bring that building ever closer to the point where the building could be off the grid for significant periods of time. The coatings that are currently used on metal roofing and walls should perform well in this project, given that the formulations are designed to be durable, self-cleaning and cool due to the unique pigments used in the formulations. Use of those coatings on metal wall products such as Metal Composite Materials and Insulated Metal Panel systems have high promise in the project.

Scott Kriner is the president and founder of Green Metal Consulting Inc. He is a LEED Accredited Professional who began his career in the metal construction industry in 1981. His company is a member of the U.S. Green Building Council, the California Association of Building Energy Consultants and the Residential Energy Services Network (RESNET).

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