Article Date: 08/08/2014

Researcher Explains How the Hybrid Modeling Method Will Work and How It Could Help Make Buildings More Energy Efficient

By Steve Rizer


One the 14 research projects recently receiving funding support from the U.S. Department of Energy (DOE) to improve the energy efficiency of America’s buildings involves a “hybrid energy modeling method” that Lawrence Berkeley National Laboratory (LBNL) and California Energy Commission (CEC) are developing (ConstructionPro Week/CPW, Aug. 1, 2014, “Several New Technologies Expected to Save Significant Amounts of Energy in Buildings”). But, how will this method work, and in what unique way will it benefit the buildings community? During a recent interview with CPW, Tianzhen Hong, computational research scientist within the Simulation Research Group of LBNL’s Building Technology and Urban Systems Department, provided an in-depth response to this inquiry.


Hong explained that traditional physics-based energy modeling for existing buildings relies on user inputs, some of which are unknown or difficult to measure, such as air infiltration rate and interior thermal mass, and can vary significantly by time and buildings; however, these parameters are key drivers of uncertainty in simulated energy performance. LBNL and CEC are striving to develop a new hybrid approach to energy modeling that will do the following: avoid the use of parameters that are difficult to measure as traditional inputs; use the measured data of space temperature as new inputs; and improve the accuracy of simulation results, he reported.


“The hybrid modeling approach reformulates the space heat balance equations, based on the new set of inputs, to derive a more accurate estimate of the building energy performance by solving the partially inverse problem,” Hong said. The approach will be implemented in EnergyPlus, DOE’s flagship whole-building energy simulation engine, and its results “will be verified in two ways by comparing to results from the current EnergyPlus simulations and to the measured results from LBNL’s FLEXLab.”


The hybrid modeling approach is expected to be “innovative and scientific,” Hong said. “It combines the physics-based modeling in EnergyPlus with nowadays easy-to-obtain measured space air temperature data to significantly ease the use of EnergyPlus simulations in retrofit analysis and improve the reliability of simulated results…. The hybrid modeling in EnergyPlus enables more accurate energy performance assessment of existing buildings, which supports better decision making on energy retrofit of buildings by owners, managers, and stakeholders.”


The ConstructionPro Network member version of this article includes a complete transcript of CPW's interview with Hong.



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