Residential Building Research at NREL

January 04, 2011
January/February 2011
A version of this article appears in the January/February 2011 issue of Home Energy Magazine.
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The Residential Building Research Team at the National Renewable Energy Laboratory (NREL) focuses on improving the energy efficiency of, and reducing carbon emissions from, approximately 130 million U.S. homes. Cost-effective improvements in the energy efficiency of U.S. homes would save energy, lower homeowners’ utility bills, and create jobs.

Many homeowners do not invest in energy conservation measures because they lack the necessary information. The Vice President’s Middle Class Task Force, Council of Environmental Quality, recently recognized this as one of three main barriers to a self-sustaining retrofit market:

Consumers do not have access to straightforward and reliable information on home energy retrofits that they need to make informed decisions. (Excerpted from the White House “Recovery Through Retrofit” report, October 2009.)

NREL research addresses this need to support large-scale energy efficiency improvements in new and existing homes. This article summarizes some of NREL’s current activities.

Collaborative Research Program

NREL is the national technical leader for DOE’s Building America program, including collaborative projects with industry teams and other national laboratories. In July 2010, NREL selected 15 multidisciplinary research teams to support the development of cost-effective, risk-free strategies to reduce home energy use by 30–40%. NREL, the teams, and other DOE laboratories will conduct research to accelerate the development of reliable and effective whole-house packages of energy efficiency measures. These can be broadly implemented to reduce risks, increase durability, and provide a reasonable return on investment. These improvements require a multiscale approach that includes systems development, systems integration, large-scale field implementation and evaluation, and effective communication of key research results and systems-based strategies. The near- and long-term performance targets for Building America reflect current economic, grid integration, energy, and carbon reduction performance targets. The program also provides technical support for new residential initiatives such as BetterBuildings, which awards grants to communities around the country to experiment with a variety of marketing, outreach, audit, and financing strategies to significantly accelerate communitywide building energy retrofits.

National Residential Efficiency Measures


Figure 1. Schematic overview of the National Residential Efficiency Measures database.

DOE Community-Scale Initiatives

DOE is interested in expanding the scope of residential energy retrofits from individual homes to entire communities. In support of BetterBuildings, NREL’s Residential Building Research Team is helping to design a database to capture project information. We anticipate analyzing parts of this database to improve our knowledge of successful approaches to residential retrofits and the associated energy savings. NREL is working to establish a Going Deep working group among the program participants to explore deep energy retrofit strategies.

NREL is also working with the Sacramento Municipal Utility District (SMUD) on deep energy retrofits of foreclosed homes. Four homes were remodeled and then instrumented to measure whole-house and system energy performance. These homes provide feedback to hone a set of retrofit measures aimed at 50% postretrofit versus preretrofit source energy savings for this type of home in Sacramento.

National Residential Efficiency Measures Database

Our focus is to develop and maintain an integrated database of regularly updated information about the performance characteristics and costs of retrofit technologies that improve the energy efficiency of residential buildings. NREL hosts this publicly available database and coordinates the update process. The data can be viewed via the Web interface or downloaded in an XML format. The overall project concept is shown in Figure 1.

The data are currently utilized in the Home Energy Saver software developed by Lawrence Berkeley National Laboratory. Plans are under way to link NREL’s BEopt software, a building energy optimization software tool, to the database.

Planned enhancements include expanded performance characteristics (for example, complete performance maps for air conditioners); links to measure guideline documents; standardized operational assumptions; and more detailed cost data.

Residential Energy Use Characteristics & Energy Use Database


Figure 2. Schema of the Residential Building Characteristics & Energy Use database.

Residential Energy Simulation Accuracy and Software Test Suites

NREL is investigating the ability of software tools to predict energy savings from efficiency measures, such as insulation and air sealing, and how uncertainties in building descriptions are propagated through simulations to affect energy use predictions.

In August 2010, NREL published a building energy simulation test for existing homes. Software developers, program managers, and other institutions can use it to assess the accuracy of audit software tools and their utility bill calibration methods. Results from tested audit tools are compared to reference results. NREL designs software test cases based on empirical data and conducts focused research to address specific software accuracy issues identified by a working group of experts. This work will lead to improvements in the accuracy of industry audit software tools and research tools developed by the national laboratories.

Public Energy Perfomance Database

NREL is compiling and organizing a public repository of residential building characteristics and energy use data (see Figure 2). The goal is to develop a robust database that comprises building characteristics data (sufficient to generate energy models) coupled with energy use data. This will provide researchers with the information they need to answer residential retrofit research questions such as these:

  • How accurately do software tools predict energy use and savings in residential buildings? How can they be improved?
  • How many audit data are needed to accurately estimate energy savings from retrofit measures?
  • Can we successfully identify retrofit-candidate homes from bulk utility billing data?

NREL will work with industry partners and the Building America teams to leverage past and current retrofit programs to obtain the needed data. Program managers wishing to contribute to the project can upload data to the project Web site (see “For more information”).

Plot of High-Efficiency Dehumidifier


Figure 3. Efficiency plot of a lab-tested, high-efficiency dehumidifier.

Whole-House, System, and Measure Performance Maps

Energy performance of any residential efficiency measure will vary as its operating environment—temperature, humidity, and so on—changes. For example, some 16 SEER air conditioners operate more efficiently in a hot-humid environment; others operate more efficiently in a warm environment. To understand how system performance changes across the installed operating conditions, NREL is actively testing mechanical equipment (heat pumps, water heaters, air conditioners, ventilation systems, dehumidifiers, furnaces) in its Advanced Thermal Conversion Laboratory. The mathematical representation of these data is called a performance map. NREL is also engaging outside test laboratories, manufacturers, and field test contractors to gather the necessary data to accurately simulate legacy and new systems. Performance maps make it possible to compare energy performance of similar—or even drastically different—systems; for example, between different air conditioners or among an air conditioner, an evaporative cooler, and a geothermal heat pump. Figure 3 is an example of a performance map on a stand-alone dehumidifier derived from various lab-controlled test conditions. It shows the dehumidifier latent load removal and efficiency as a function of inlet air dry-bulb and dew point temperatures. The full technical report on which this performance map is based is available from the NREL web site.

Least-Cost Curve


Figure 4. A least-cost curve allows users to determine minimum-cost building designs at various levels of energy savings and under various sets of economic assumptions.

Optimization and Least-Cost Curves

Since 2003, DOE has used BEopt to determine cost-effective, energy-efficient building designs for new construction. BEopt evaluates the incremental energy and cost impacts of various building designs relative to a reference building (a building that complies with the International Energy Conservation Code) and provides a least-cost curve that allows users to determine minimum-cost building designs at various levels of energy savings and under various sets of economic assumptions. (See Figure 4.)

Recently NREL began to extend BEopt analysis capabilities to existing homes, addressing fundamental changes required to perform simulations and optimizations in the context of home energy retrofits. The method uses an optimization scheme that considers average energy use (determined from energy simulations) and equivalent annual costs. It recommends optimal retrofit packages specific to the building, occupant, and location that simultaneously reduce overall costs and produce energy savings.
 

Marcus Bianchi is a senior research engineer at the National Renewable Energy Laboratory, where he performs research on deep energy retrofits of existing houses.

For more information:

For information about all the residential Building research taking place at the National Renewable Energy Laboratory, go to www.nrel.gov/buildings/residential.html.

For the complete text of the Recovery Through Retrofit report, go to www.whitehouse.gov/administration/eop/ceq/initiatives/retrofit.

To access NREL’s National Residential Efficiency Measures database, go to www.nrel.gov/ap/retrofits.

To upload data to the Public Energy Performance database, go to www.nrel.gov/ap/retrofits/upload/index.cfm.

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