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Measuring Performance of Net-Zero Energy Homes Project

Summary:

Uncertainty in the realized performance of green buildings is a barrier to increased adoption and investment in energy efficient and environmentally friendly technologies. NIST’s new Net-Zero Energy Residential Test Facility will provide a platform for comprehensive, accurate measurements that will be used to assess the in-situ performance of a net-zero energy home. By its completion, this project will outfit the test facility with a full suite of high-quality monitoring equipment, measure its energy use over the course of a year, compare actual performance to that predicted from computer models, evaluate integrated performance metrics for net-zero energy homes, and publish guidelines for designing, operating, and monitoring net-zero energy homes.

Description:

Objective: Develop the measurement science necessary to assess the performance of net-zero energy homes through the evaluation of performance monitoring techniques, assessment of integrated performance metrics, validation of building energy and ventilation models, and development of design, operation, and monitoring guidance by 2015.

What is the new technical idea? NIST’s “Measurement Science Roadmap for Net-Zero Energy Buildings”1 and the National Science and Technology Council2 have emphasized the need for improved monitoring techniques, metrics, and models that would assess the energy performance of net-zero energy buildings (NZEB). Understanding how to measure the performance of NZEB will enable stakeholders to resolve differences between design intent and actual performance, enable comparisons of NZEB with conventional buildings, and allow governing bodies to enact measurable high-performance goals.

NIST’s newly-constructed Net-Zero Energy Residential Test Facility (NZERTF) will contribute to this understanding through the collection of comprehensive, highly accurate performance measurements of the energy flows within the house. The facility will be operated for one full year to obtain data and the results will be published to help the building community better understand the approaches to achieve net-zero energy operation. Computer modeling tools will be utilized to determine how well predictions match actual data, to determine how slight changes in operating conditions would affect performance, and to better comprehend interactions between energy use and indoor air quality. Guidelines will be written that document the design, construction, measurement, and operation of net-zero energy residences. Following this initial phase, the test facility will be prepared to test a range of technologies to compare alternative means of achieving a net-zero energy residence.

What is the research plan? The NZERTF includes over 200 sensors to monitor energy use, water use, indoor conditions, and photovoltaic energy generation on a continuous basis. To mimic occupant behavior in a controlled manner, the facility includes devices to simulate occupant heat and moisture generation, water usage, lighting activation, and appliance and electronics usage. This vast array of sensors will enable researchers to examine different ways to measure the performance of subsystems within the house and the house as a complete system.

In FY14, the focus will be on analyzing and interpreting data continuously during the one-year test period. This analysis will ensure that the monitoring systems are operating as expected and will help researchers understand the key differences in performance between systems installed in a net-zero house compared to those in conventional houses. Concurrently, simulation models using EnergyPlus will be run with actual weather data to determine the accuracy of model predictions to actual data and, if those predictions differ from measured data, why those discrepancies arise. This process may involve adjustment of the computer models, and newly proposed procedures for doing so will be evaluated in this effort. The use of multizone air flow simulations and in-depth equipment simulations will help explain any such discrepancies. These models will then be utilized to document how changes in operational parameters such as occupant behavior or weather data could affect the goal of achieving net-zero operation.

The major outcome in FY14 will be a series of seven manuscripts describing in detail the performance of the house and its subsystems. Ultimately, the project will result in a set of guidelines for designing, constructing, monitoring, and operating a net-zero energy house. In FY14, the guideline on design and construction will be written. The guideline on monitoring and operating will be written in FY15 after the lessons learned from the one year monitoring period are collected. In addition to discussing the key types of measurements that are needed when monitoring a net-zero energy house, the guideline on monitoring will also include metrics that will be important in rating energy efficient homes and in developing standards for their construction. By the end of the project, the facility will be ready to begin investigating alternative technologies and operational strategies for achieving net-zero energy operation.

 


[1] National Institute of Standards and Technology, “Measurement Science Roadmap for Net-Zero Energy Buildings: Workshop Summary Report”, March 2010.

[2] National Science and Technology Council, “Net-Zero Energy, High Performance Green Buildings” October 2008.

 

Major Accomplishments:

Impact of Standards and Tools:

  • Net-Zero Energy Residential Test Facility completed for use by industry in assessing technologies for achieving net-zero energy status.