Towards net energy-producing buildings
by M M Jenior, US Department of Energy, retired

Based on research in the USA, the building industry (comprising professions and trades with different perspectives and experience) is proving the validity of the climate-responsive, whole-building approach to low-energy buildings, both for renovations and new construction.

The Solar Energy Research Facility in Golden, Colorado  Photograph: Warren Gretz, NREL

A new approach

Builders have already shown that high-quality, low-energy buildings can cost little more than traditional buildings to construct or renovate. The owners pay much less to operate these buildings compared to traditional ones, and the occupants are usually more comfortable. Today, practical means exist for constructing low-energy buildings and the associated costs are well understood. Unfortunately, simple procedures are often overlooked, considered insignificant, or ignored because of a misunderstanding of the physics of interactive building systems. Under the climate-responsive, whole-building approach, designers consider carefully how systems will interact. Low-energy goals and local climatic conditions are important in the selection of materials and components.

The long-term objective is to reduce building energy loads in a cost-effective manner such that renewable sources of energy can meet and exceed energy demands in the building. The first step is the reduction of loads through passive solar, climate-sensitive strategies. Remaining loads may then be met by other renewable resources. A key step along this path is to increase the capability of, and confidence in, computer design tools, such as SUNREL for residential buildings and ENERGY 10 for small commercial buildings. The US Department of Energy’s (DOE) Office of Building Technology, and State and Community Programmes are spearheading the enhancement and verification of these tools.

The process

Working with researchers at DOE’s National Renewable Energy Laboratory (NREL) in Golden, Colorado, industry partners have recently constructed a number of high-performance buildings that are providing important data for designing the efficient, net-energy-producing buildings of the future. The aim is to reduce energy consumption in these buildings by 70% compared to those conforming to current US energy standards (ASHRAE’s standard 90.1 for commercial buildings). This means the buildings meet almost three-quarters of their energy needs for heating, cooling and daylighting from passive solar design. These buildings are built at little or no additional cost compared to similar ones constructed using traditional designs – one even cost less to build.

The buildings are constructed in collaboration with the owner, developer, architects, engineers, contractors, building management team and researchers, using a whole-building approach.

A commitment from each of these partners is required for the process to work. The owner is responsible for all construction costs. The researchers work with the owner to develop the appropriate design concepts and check the construction specifications. The research team also places the sensors needed for monitoring. Performance data are crucial to determine that the building works as designed and, if not, what changes are required to achieve the desired results. The data are also used to verify the computer modelling tools used during design.

Based on these performance data, researchers identify R&D issues that need to be addressed and produce better designs for future buildings. Multiple means are employed to address the R&D issues, including opportunities provided by collaboration under the International Energy Agency’s Solar Heating and Cooling Programme and with small businesses as well as universities. The performance data and design revisions provide the basis for case studies published by the industry.

Performance and lessons learned

To date, 11 commercial or institutional buildings and six residential buildings have been built and monitored as part of the NREL programme.

One commercial building, the Zion National Park Visitors Center, Utah, cost less to build than a conventional visitors centre. The building design employs daylighting, a cost-effective thermal package, natural ventilation and downdraught evaporative cooling (ie air that is cooled by contact with water), direct solar gain, and a Trombe wall design. The downdraught evaporative cooling will keep the visitors centre and surrounding outdoor patio area comfortable in the hot, dry summer months. By creating a cooler outdoor micro-climate, this space can be used for exhibits. The smaller building saves an estimated $1.5 million (where $ is the US dollar) in construction costs. In the future, there is an option to use photovoltaics to meet the building’s energy needs and, at times, become a net producer of electricity.

The Zion National Park Visitors Centre in Utah  Drawing: Warren Gretz, NREL

Another building, the Solar Energy Research Facility at NREL, employs renewable energy and energy efficiency options throughout. These include daylighting in the office area, direct/indirect evaporative cooling, a Trombe wall, heat recovery, and variable frequency motors. The daylighting design creates the building’s architectural character and results in a substantial reduction in the electrical load from lighting. The actual load reduction, performance, and occupant satisfaction with the daylighting system are currently being analysed. The results will be used to improve daylighting systems and the design of spaces using daylighting, and will provide a better understanding of how the controls and sensors perform.

The process has also been used for residential buildings. For example, the Tierra Concrete Homes of Pueblo, Colorado, use tilt-up walls of concrete exposed with exterior insulation. The inside surfaces can be finished smooth to resemble drywall or stone and the exterior can be finished to the owner’s preference. These buildings operate at about half of the energy consumption of typical buildings in the Pueblo area.

Researchers are using performance data to verify the computer design tools and improve the design of future low-energy buildings. First, they focused on the glazing algorithms used in building energy simulations. The initial design was expected to perform over 70% better than one built to existing standards, but it actually performed only 45% better. Analysis of the data revealed that solar gains were 33% lower than predicted for the selected glazing, and that ground losses can be significant in very low-energy building designs. In subsequent designs, wall and slab insulation have been increased and sensors were placed in the slab to better understand and quantify ground losses. Results of the research are available on the World Wide Web at: www.nrel.gov/buildings/highperformance/projects.

For more information contact the CADDET US National Team at Golden, Colorado.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

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