Net-Zero Energy, High-Performance Buildings Program

Credit: Building Science Corporation

Objective:
To develop and deploy advances in measurement science to move the nation toward net-zero energy, high-performance buildings while maintaining healthy indoor environments.

What is the problem?
Buildings account for 40 % of the primary energy consumption, 74 % of the electricity consumption, and 39 % of the CO2 emissions in the United States. (i)  Reducing the energy consumption from the building sector poses a national challenge and opportunity, as it will lead to significant financial and job growth of the HVAC&R industries and reduced costs for building and home owners.  To reduce dependence on energy imports and decrease building operating costs, the building industry has embraced the concept of net-zero energy buildings, which are buildings that generate as much energy through renewable means as is consumed by the building.  The goal of reduced building energy use has been documented by leading industry organizations such as the American Institute of Architects (AIA) (ii), the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) (iii), and the National Association of Home Builders (NAHB) (iv).  The movement towards green buildings is a key part of the building industry’s response to this goal, with the global green building market estimated at $260 billion in 2013.  It is also estimated that 20 % of all new U.S. commercial real estate construction is pursuing green building design, and that commercial building owners and managers will invest $960 billion globally between 2015 and 2023 on greening existing built infrastructure. (v)  

To achieve net-zero and low energy buildings, the building industry will use existing energy-efficient building technologies, develop new equipment and approaches to increase efficiency, and increase on-site generation of energy.  Industry groups including ASHRAE, HVAC&R equipment manufacturers through the Air-Conditioning, Heating, and Refrigeration Institute (AHRI), the American Home Appliance Manufacturers (AHAM), NAHB, and others are all heavily engaged in these efforts.  However, measurement science is lacking 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” (vi), an effort led by NIST to gather research needs from a range of industry stakeholders.  That roadmap reports that improved implementation of existing building technologies can reduce energy consumption by 30-50 %, with an additional 50-70 % of energy savings from advanced technologies and on-site energy production.  

While energy expenditures are a key operating cost that will be addressed in this program, it is vital to also ensure comfortable and healthy indoor environments for occupants.  This research program will also investigate ways to maintain healthy and productive indoor environments while decreasing energy consumption so that buildings continue to meet their intended objectives: to provide shelter for living, learning, healing, and working.  


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 covers whole building metrics, while the final three view the building from a component perspective.  

Thrust 1:  Whole Building Metrics.  The first thrust will address the building as a complete system, evaluating energy consumption, cost-effectiveness, and overall sustainability of whole buildings.  Work in this area will build on that from the other thrust areas and ensure the goal of achieving energy savings while meeting the constraints of sustainability, economics, and indoor environmental quality. 

Thrust 2:  Building Envelope Load Reduction.  Space conditioning, consisting of heating, cooling, and outdoor air ventilation, 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. (vii)  Space conditioning is required to manage heat loss or gain through the building envelope, unwanted leakage of outside air, or buildup of airborne contaminants within the building.  The first step in reducing energy intensive space conditioning is by reducing the need for it, and NIST is working to minimize this need by evaluating the insulating capabilities of the envelope, assessing unwanted air leakage and better controlling outdoor airflows into buildings. 

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 research will help industry to improve the design and installation of vapor compression heat pump systems for energy efficient buildings and evaluate the effectiveness of the low global-warming potential alternatives to hydrofluorocarbon refrigerants that industry is committed to using.  NIST addresses these equipment issues through partnerships with industry groups including AHAM, AHRI, and ASHRAE as well as other agencies, specifically DOE.  

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 on-site building use.  The solar industry has experienced tremendous growth in the United States in recent years, with an average annual growth rate of 16 % since 2012 and over 250,000 solar workers employed in 2017 (viii).  This growth heightens the need for measurement science to ensure systems operate as promised and are durable over their expected lives.  

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 local 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 create guidelines for measurement of net-zero energy home performance and to provide data on operations of various systems under field conditions.  Improved measurements of greenhouse gas (GHG) emissions will be addressed through the development of a testbed with a well-characterized source of GHG for use in supporting the stack-testing industry and through computer modeling to predict the source strength of distributed sources of emissions.  A relatively new research area related to water use and quality in buildings will continue, with the goal of developing data, models, and guidelines for designing effective plumbing systems given the current need to decrease building water usage.  

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 measurement science that is needed to support the use of advanced insulation systems.  Other work will address another key energy flow across the building envelope, i.e., air leakage and the introduction of outdoor 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 to integrate 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 approaches to measure and document indoor air quality in high-performance buildings. 

Thrust 3: Equipment Efficiency.  NIST will focus specifically on vapor compression equipment used for heating and cooling.  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 response to its transition to a new generation of refrigerants.  In addition, as building envelopes become more efficient, heating and cooling systems must manage smaller thermal loads, but moisture management and the need to mechanically ventilate buildings impose new demands on the systems.  NIST will develop software tools and data sets to support stakeholders in the optimal selection and installation of heat pumps and air conditioners in energy-efficient buildings.  The industry has committed to adopt a new generation of refrigerants for use in heat pumps and air conditioners.  To optimize those systems, designers need to understand the heat transfer performance of the refrigerants and the thermodynamic performance as they move through the refrigeration process.  The safety of these refrigerants is also of concern to industry as many are mildly flammable.  Therefore, NIST will develop rigorous test methods and data to assess the flammability of these compounds and their mixtures for use by manufacturers in developing efficient and safe equipment. 

Thrust 4:  On-Site Generation.  NIST will support the increasing 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 PV modules.  The first effort will involve transitioning data from the detailed monitoring of four PV systems on the NIST campus to a publicly-available database that will be used to assess model performance and to understand how the systems operate with regards to the utility grid.  The second effort will focus on decreasing the uncertainty in PV ratings by developing a measurement service for calibrating PV cells for use in test equipment.  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.