Objective - To enable energy savings in buildings through advanced sensing technologies and approaches by developing testbeds to evaluate energy monitoring systems and sensor networks for determining the thermal transmissions through envelopes.
What is the new technical idea? Advances in sensing technologies through miniaturization of sensors, wireless communications, and the integration of sensors with microprocessing capabilities enable emerging applications to better understand the performance of buildings in hopes of improving the indoor environment while reducing energy consumption. Two areas where such sensing technologies promise to reduce energy consumption in buildings is through better monitoring of the heat flows through the building enclosure and better monitoring of energy consuming devices within the building.
In residential buildings in the United States, 53 % of site energy consumption in 2015 is projected to be attributed to space heating and cooling. Improving the thermal envelope is key to reducing this energy consumption, but, as stated in a recent DOE roadmap on Building Envelope Technologies, a lack of awareness of energy saving opportunities associated with improved envelope approaches often leads to inaction, and improved building diagnostics and measurement technologies would help to inform building owners about the benefits of envelope upgrades. This project aims to explore such technologies to utilize new sensing approaches to better evaluate the efficiency of the walls, roofs, and foundations. This topic was also identified in NIST's roadmap for measurement science for net-zero energy buildings.
A second area of energy consumption in buildings that could be reduced through the use of advanced sensing technologies is miscellaneous electrical loads, which are an increasing concern in buildings with the proliferation of devices that plug into electrical sockets. A number of systems have emerged on the market to sense the energy consumption of these devices, but it is not clear how effective they are under real load profiles. NIST will develop test approaches and metrics that will determine how well these systems measure energy consumption by electrical devices in buildings, with an initial focus on residential energy usage.
What is the research plan? To enable improved sensing of building envelope performance, NIST will research the ways that different sensors can be combined as part of a sensor network that is placed in a building for a short period of time (on the order of 1 week) to capture the heat loss coefficient of the building envelope assembly. NIST will examine the use of small temperature and relative humidity sensors, heat flow transducers, infrared sensors, and air speed sensors to determine the key measurements needed for an accurate determination of the heat loss through a wall assembly. The advantage of using emerging sensor network technology is that the sensors can be left in place to capture performance under a range of weather conditions. Fluctuating weather conditions often complicate the determination of these factors. Additionally, sensor networks enable a larger density of sensors so that uncertainty in key quantities can be reduced. In FY16, NIST will complete a literature review that describes techniques used to assess building envelope thermal performance in an in-situ manner, and will compare predictions of heat loss in buildings to actual measured values as documented in the literature. This study will help identify key characteristics of a sensing system that will accurately determine the thermal performance of the buildng enclosure. NIST will then identify the specific sensors needed to most accurately monitor building envelope thermal performance, will develop approaches to fuse the data from the multiple sensors, and will build a prototype of a sensor network that could be used to evaluate building envelope thermal integrity.
To assist in development of sensing systems to monitor the flows of electricity in buildings, NIST is building an emulator that will allow for all loads within a residence to be simulated in any pattern desired. This emulator will enable evaluation of the performance of sensing systems, but its primary purpose will be to aid in development of test methods for evaluating the performance of such systems. This emulator will also include the ability to supply energy such as through on-site renewable generation systems for evaluation of sensing systems that may be part of a residential energy management system. In previous years, NIST developed the testbed at a reduced power rate to serve as a proof-of-concept. In FY16, newly installed electrical service that will deliver the same amount of current as seen in typical American homes will be integrated with the testbed to evaluate sensing systems designed for whole-house applications in addition to those previously examined that were specifically designed to sense end-uses. A full profile of usage patterns will be developed for emulation, and test methods to evaluate sensing systems will be checked on this expanded testbed. Furthermore, the testbed will be expanded to simulate on-site energy generation sources such as photovoltaics and energy storage capabilities such as batteries. These latter steps will be valuable in evaluating sensing systems appropriate for net-zero energy homes that will involve consumption, generation, and storage of electricity.
1) U.S. Department of Energy, Buildings Energy Databook. Available at: http://buildingsdatabook.eren.doe.gov
2) U.S. Department of Energy. Windows and Building Envelope Research and Development: Roadmap for Emerging Technologies. February 2014. http://energy.gov/sites/prod/files/2014/02/f8/BTO_windows_and_envelope_report_3.pdf
3) National Institute of Standards and Technology. NIST Technical Note 1660. Measurement Science Roadmap for Net-Zero Energy Buildings: Workshop Summary Report. March 2010. http://www.nist.gov/customcf/get_pdf.cfm?pub_id=905024