Residential Building Design and Performance
NREL building researchers were among the first in the nation to document a whole-building design approach. A whole-building design approach focuses on whole-building integrated design. Integrated building design is a collaborative, integrated planning and design process that uses an integrated project team in all stages of a project's planning and delivery, starting with design.
NREL's residential building researchers conduct performance evaluations of builder home designs and make recommendations for improvement. We also conduct research on advanced residential building systems to improve performance. In addition to developing energy analysis tools for improving building design, we work with ASHRAE on performance metrics or standards of measurement for energy performance in buildings.
Performance Metrics Research
For more than a decade, NREL has worked with DOE's Building America Program evaluating both old and new homes as well as novel building energy systems. During this time, NREL has established a set of common metrics for analysis so comparisons can be made between typical homes and new model homes. NREL uses these metrics to establish benchmarks for design and construction of its prototype homes.
- Evaporative Cooling Systems
- Ventilation Systems
- Novel High COP AC Systems
- Prototype House Evaluations
- Misc. Electric Loads
Metrics for advanced evaporative cooling systems
Evaporative coolers use as much as 75% less electricity than air conditioning. In addition, unlike traditional air conditioners, evaporative coolers are also less expensive, they don't need special high-amperage circuits, they add moisture to and help clean the air, and they provide better ventilation. However, barriers to market acceptance of these systems include the need for a hot, dry climate for optimal system efficiency and larger air ducts currently required by these systems to cool a larger home. More advanced systems have been developed that pre-cool the air before it goes through the moistened pad, but these systems are still quite expensive. Some newer systems also use solar power (a perfect match in desert areas) to run the blower and water pump. NREL's research in advanced evaporative cooling systems focuses on developing accurate hot climate "building installed" performance evaluations for several new evaporative cooling systems including indirect/direct evaporative cooling systems, and evaporatively cooled condensers used with conventional air-conditioning systems. It is important to establish metrics to measure energy performance for these advanced systems. NREL has established metrics for capacity, energy efficiency ratio, coefficient of performance or COP, and wet-bulb effectiveness.
Metrics for ventilation systems
In striving for increasing levels of overall energy efficiency in homes, well-controlled ventilation is needed for proper indoor air quality without wasting energy through excess ventilation. In addition to the amount of outside air provided, the distribution of the air within the home is also important. Non-uniform outside air distribution can lead to over-ventilation in one part of a home and under-ventilation in another part at the same time. More sophisticated ventilation systems, such as ducted ventilation or forced-air-integrated ventilation, may provide significantly improved uniformity of ventilation throughout the home. However, testing is needed to verify the performance improvements of these advanced systems. The results from this task are required to reliably design homes at the 40% or high efficiency performance levels. We are establishing performance metric protocols for the design of whole-house ventilation systems.
In addition, metrics also need to be established for hardware and installation procedures for ventilation systems. Previous field studies by NREL and others have demonstrated that flex duct is not a reliable component for use in residential ventilation systems. Other components, including control systems and dampers, are often installed improperly. Advanced "plug and play" residential ventilation system components, including snap together rigid ducts with smooth transitions that minimize pressure drops and "fail safe" dampers and controllers, are required to improve ventilation system reliability. Testing is also needed to identify and evaluate metrics for issues such as these.
Metrics for Novel high COP AC systems
Air conditioners move energy in the form of heat from your house to the outside. These systems generally move 2 to 3 times more heat than the energy required to run them. This ratio is called the Energy Efficiency Ratio or Coefficient of Performance (COP) and is used as the basis for determining the system's rating for energy efficiency. The efficiency of the system depends on the components used (their design and how well these are matched) and the temperature difference between inside and outside (as the temperature difference increases, the system becomes less efficient).
NREL is evaluating high COP air conditioning systems to provide detailed performance evaluations of new or advanced cooling technologies that are in a pre-production phase or in early full-scale production that have not had significant market penetration but show potential to save energy and contribute to NREL's net zero energy buildings goal. We have established metrics for energy efficiency ratio, COP, and capacity.
Metrics for prototype house evaluations
NREL conducts research on new homes in different climate zones throughout the United States for the Building America Program. To measure the program's progress, annual research milestones have been established for five major climate regions in the United States. The system research activities required to reach each milestone take from 3 to 5 years to complete and include research in individual test houses, studies in pre-production prototypes, and research studies with lead builders that provide early examples that the specified energy savings level can be successfully achieved on a production basis. The performance metric we use is whole-house source energy savings.
In addition, because there are more than 101 million residential households in the United States today, existing residential buildings represent an extremely large source of potential energy savings. Because thousands of these homes are renovated each year, NREL investigated for the Building America Program the best ways to make existing homes more energy-efficient, based on lessons learned from research in new homes. The existing buildings project focuses on the establishment of metrics for adapting the results from the new homes research to retrofit applications in existing homes. Research activities include a combination of computer modeling, field demonstrations, and long-term monitoring to support the development of integrated approaches to reduce energy use in existing residential buildings. Analytical tools are being developed to guide designers and builders in selecting the best approaches for each application. In addition, NREL works with DOE and the U.S. Environmental Protection Agency (EPA) to increase energy efficiency in existing homes through the Home Performance with ENERGY STAR program. More (PDF 1.1 MB). Download Adobe Reader.
Metrics for Miscellaneous Electric Loads
Miscellaneous electric loads comprise the small and diverse collection of energy-consuming devices found in homes such as televisions, stereos, microwaves, and blenders as well as security and sprinkler systems. Currently, these small devices use about 30% of the total energy consumed in homes and this number is expected to increase in the future as more and more small electronic devices are being developed everyday. We are working with DOE's Building America Program and other organization and groups on the development of a comprehensive plan to find cost-effective solutions for reducing miscellaneous electric loads. A major challenge that needs to be overcome is building occupants usually control small electronic devices. Establishing metrics and specifications for the advanced components needed to meet future energy performance goals will be an important research activity for this project area over the next several years.
Benchmarks
A benchmark is a standard of measurement for comparison purposes, usually considered the "standard of excellence" for a particular industry. Benchmarks can be difficult to create due to differences in opinion among industry professionals. To help the residential research program track progress toward aggressive multi-year whole-house energy savings goals of 40%-70% and onsite power production of up to 30% on a community scale, NREL has developed a Research Benchmark in consultation with home developers and builders within the Building America Program. The research benchmark includes series of user profiles, intended to represent the behavior of a "standard" set of occupants, was also created for use in conjunction with the Benchmark. NREL continues to update the Benchmark and to create performance analysis procedures to meet current system research needs. The creation of this Benchmark will provide the basis for sound evaluations of communities leading to widespread confidence in and adoption by production builders of Building America design packages for specific savings levels in given climates.
Community Scale Evaluation
NREL is using our research benchmark to assist production builders in the adoption of Building America design packages for specific savings levels in various climate zones. The design packages will for on energy savings, but also emphasis non-energy issues important to builders, such as cost, code issues, occupant comfort, and marketability of energy features.
Tools
Researchers at NREL are developing energy simulation software tools for evaluation of energy efficiency, renewable energy technologies, and sustainability in buildings. For more information, see Energy Analysis and Tools.
Case studies
Researchers at NREL have worked with the Building America Program on numerous case study prototype homes. For more information, see Building America Projects
