Buildings account for 41 % of the primary energy consumption and 74 % of the electricity consumption in the United States, while accounting for 39 % of the CO2 emissions. To minimize the costs associated with building energy consumption, NIST will develop and deploy the measurement science to move the nation towards net-zero energy, high-performance buildings in a cost-effective manner while maintaining a healthy indoor environment. The research program will target the objective of net-zero operation by 1) reducing heating and cooling loads within the building, 2) developing measurement science for efficient heating and cooling equipment, 3) advancing the measurements of onsite energy generation technologies such as photovoltaics, 4) evaluating the energy consumption, greenhouse gas emissions, economics, and sustainability from a whole-building perspective, and 5) aggressively promoting implementation of program results in building energy codes, standards, and practices.
What is the problem?
Buildings consume 41 % of the primary energy and 74 % of the electricity in the United States, while accounting for 39 % of the CO2 emissions. (i) Such energy consumption and emissions from the building sector pose a national challenge, and the Office of Management and Budget has thus stated as two of its multi-agency science and technology priorities for the 2016 budget to be research that addresses "Clean energy" and "Global climate change." (ii) To reduce dependence on energy imports while curbing greenhouse gas emissions, the building community has embraced the idea of net-zero energy buildings, which are buildings that generate as much energy through renewable means as is consumed by the building. This vision has been documented in a Federal R&D agenda produced by the National Science and Technology Council (iii) (NSTC) as well as by leading industry organizations such as the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) (iv). Furthermore, the United Nations Intergovernmental Panel on Climate Change (v) reports that "buildings offer the largest share of cost-effective opportunities for greenhouse gas mitigation among sectors examined," a charge taken up by the American Institute of Architects in its 2030 Challenge that calls for new buildings to be carbon neutral by 2030 (vi).
To achieve net-zero energy buildings, an approach is needed that implements the use of existing energy-efficient building technologies, develops new equipment and approaches to increase efficiency, and increases on-site generation of energy. NSTC reports that improved implementation of existing building technologies can reduce energy consumption by 30-50 %. The remaining 50-70 % of energy savings will result from advanced technologies and on-site energy production. Measurement science is lacking, however, in a number of areas for both improving the implementation of existing technologies and advancing new technologies, as documented in the "Measurement Science Roadmap for Net-Zero Energy Buildings." (vii)
While moving towards net-zero energy buildings, it is paramount to keep in mind key constraints. In particular, the indoor air quality (IAQ) should be maintained or improved, the new technologies should be cost-effective, and new approaches should be sustainable in reference to other environmental criteria.
What is the new technical idea?
To help the U.S. building industry achieve net-zero energy, high-performance buildings, NIST will focus on four thrust areas. The first thrust examines whole building metrics, while the final three thrusts view the building from a component perspective.
Thrust 1: Whole Building Metrics. The first thrust will view the building as a complete system, evaluating the energy consumption, cost-effectiveness, greenhouse gas emissions, and overall sustainability of the whole building. Work in this area will build on that from the other thrust areas and will ensure that the goals of achieving energy savings while meeting the constraints of sustainability, economics, and indoor environmental quality are met.
Thrust 2: Building Envelope Load Reduction. Space conditioning, consisting of heating, cooling, and introduction of outdoor air, is the largest energy consumer in buildings. In the U.S., it accounts for 40 % of primary energy consumption in commercial buildings and 43 % in residential buildings. (viii) Space conditioning is required because of heat loss or gain through the building envelope, unwanted infiltration of outside air, or buildup of contaminants within the building. The first step in reducing energy intensive space conditioning is by reducing the need for it, and NIST will work to minimize this need by evaluating the insulating capabilities of the envelope and assessing unwanted infiltration as well as controlled flows of fresh air across the envelope.
Thrust 3: Equipment Efficiency. Once building loads are reduced, the next step towards net-zero energy buildings is through the use of efficient equipment. In this program, NIST will focus on space heating and space cooling, as these end uses are the largest consumers of primary energy in buildings. NIST will improve the design and installation of vapor compression heat pump systems for energy efficient buildings and will evaluate the effectiveness of low global-warming potential alternatives to hydrofluorocarbon refrigerants. An affiliated project in NIST's Physical Measurement Laboratory will assess the quality of solid-state lighting, a technology that DOE projects can reduce lighting electricity consumption by one-fourth (ix). NIST addresses other equipment through partnerships with other agencies, specifically through DOE-sponsored work on appliances.
Thrust 4: On-Site Energy Generation. After loads are reduced and efficient equipment is installed, the remaining energy must be supplied by on-site generation to meet the goal of net-zero operation. NIST will address measurement science issues associated with photovoltaics, which are currently the predominant means of harnessing renewable energy for building use.
What is the research plan?
The research plan will follow the four thrusts described previously.
Thrust 1: Whole Building Metrics. Knowledge of the overall sustainability of buildings and the economics of high-performance buildings will be advanced through the evaluation of the cost-effectiveness of energy code compliance, by developing databases of the environmental performance of building technologies, and through the development of online tools for evaluating sustainability. Novel methods to measure energy consumption in residences will be explored to provide feedback to occupants, identify retrofit opportunities, and create guidelines for measurement of net-zero energy home performance. Greenhouse gas (GHG) emissions will be addressed through the development of a testbed with a well-characterized source of GHG for use in calibrating instrumentation and through computer modeling to predict the source strength of distributed sources of emissions.
Thrust 2: Building Envelope Load Reduction. NIST will aim to minimize the unwanted heat losses and gains through the building envelope by developing reference materials that allow precise evaluation of thermal insulation and by investigating the missing measurement science that impedes the use of advanced insulation. Work will also address another key energy flow across the building envelope, that being air infiltration and the introduction of ventilation air. NIST will develop the measurement science necessary to determine required ventilation rates by developing reference materials that can be used to assess emissions from building products and measurement methods to characterize the most important contributors to adverse indoor air quality. NIST will build upon previous work at integrating the EnergyPlus building energy simulation software with the CONTAM airflow and contaminant transport software by improving the user interface to enable more widespread use of the tool. Additionally, work will be conducted to define approches to measure and document indoor air quality in high-performance buildings.
Thrust 3: Equipment Efficiency. NIST will focus specifically on vapor compression (used for heating and cooling) equipment. In particular, research will be conducted to provide industry greater understanding of system performance as buildings become more efficient and will address industry challenges in modifying equipment in light of looming regulations on refrigerants. As building envelopes become more efficient, heating and cooling systems must manage smaller thermal loads, but moisture buildup and the need to mechanically ventilate buildings impose alternative demands on the systems. NIST will work with an International Energy Agency annex to develop guidelines for heat pumps and air conditioners in energy-efficient buildings. Potential regulations that limit refrigerants due to their global warming potential will force manufacturers to adopt alternative refrigerants for use in heat pumps. To optimize those systems, designers need to understand the heat transfer performance of the refrigerants in heat exchangers and the thermodynamic performance as they move through the refrigeration process. NIST will capture these key data for use by manufacturers in developing equipment meeting the environmental regulations.
Thrust 4: On-Site Generation. NIST will promote the use of photovoltaics (PV) through experiments aimed at improving predictive models of their performance, development of techniques to better rate PV performance, and generation of the measurement science to assess the service life of polymers used in the construction of PV modules. The first effort will involve the detailed monitoring of four PV systems on the NIST campus, with the data being fed to a national database that will be used to assess model performance. The second effort will focus on decreasing the uncertainty in PV ratings by improving the critical measurement of PV spectral response, a measurement that currently leads to uncertainties of 10-30 % in the rating of new PV technologies. The third effort will provide information and standards on the lifetime of polymers in PV systems through accelerated aging tools and model development that will help assess long-term performance.