A flow rate dependent 1d model for thermally stratified hot-water energy storage

Joseph Rendall; Fernando Karg Bulnes; Kyle Gluesenkamp; Ahmad Abu-Heiba; William Worek; Kashif Nawaz

doi:10.3390/en14092611

A flow rate dependent 1d model for thermally stratified hot-water energy storage

Joseph Rendall, Fernando Karg Bulnes, Kyle Gluesenkamp, Ahmad Abu-Heiba, William Worek, Kashif Nawaz

Multifunctional Equipment Integration

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9 Scopus citations

Abstract

Stratified tank models are used to simulate thermal storage in applications such as residential or commercial hot-water storage tanks, chilled-water storage tanks, and solar thermal systems. The energy efficiency of these applications relates to the system components and the level of stratification maintained during various flow events in the tank. One-dimensional (1D) models are used in building energy simulations because of the short computation time but often do not include flow-rate dependent mixing. The accuracy of 1D models for plug flow, plug flow with axial conduction, and two convection eddy-diffusivity models were compared with experimental data sets for discharging a 50-gal residential tank and recharging the tank with hot water from an external hot-water source. A minimum and maximum relationship for the eddy diffusivity factor were found at Re <2100 and >10,000 for recirculation of hot water to the top of the tank and vertical tubes inletting cold water at the bottom. The root mean square error decreased from >4^◦C to near 2^◦C when considering flow-based mixing models during heating, while the exponential decay of the eddy diffusion results in a root mean square error reduction of 1^◦C for cone-shaped diffusers that begin to relaminarize flow at the inlet.

Original language	English
Article number	2611
Journal	Energies
Volume	14
Issue number	9
DOIs	https://doi.org/10.3390/en14092611
State	Published - May 1 2021

Funding

Funding: This project was supported in part by an appointment to the Oak Ridge National Laboratory Higher Education Research Experiences (HERE) program, administered by Oak Ridge Associated Universities (ORAU) through the US Department of Energy Oak Ridge Institute for Science and Education (ORISE). This work was sponsored by the US Department of Energy’s Building Technologies Office under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. The authors would like to acknowledge Mr. Antonio Bouza, technology manager of HVAC&R, Water Heating, and Appliance, US Department of Energy Building Technologies Office. This project was supported in part by an appointment to the Oak Ridge National Laboratory Higher Education Research Experiences (HERE) program, administered by Oak Ridge Associated Universities (ORAU) through the US Department of Energy Oak Ridge Institute for Science and Education (ORISE). This work was sponsored by the US Department of Energy?s Building Technologies Office under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. The authors would like to acknowledge Mr. Antonio Bouza, technology manager of HVAC&R, Water Heating, and Appliance, US Department of Energy Building Technologies Office.

Funders	Funder number
HERE
Oak Ridge National Laboratory Higher Education Research Experiences
US Department of Energy Building Technologies Office
US Department of Energy Oak Ridge Institute for Science and Education
Oak Ridge Associated Universities
Oak Ridge Institute for Science and Education
Bioenergy Technologies Office	DE-AC05-00OR22725

Keywords

1D flow model
Hot-water tanks
Stratification
Thermal-energy storage

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.3390/en14092611

Cite this

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abstract = "Stratified tank models are used to simulate thermal storage in applications such as residential or commercial hot-water storage tanks, chilled-water storage tanks, and solar thermal systems. The energy efficiency of these applications relates to the system components and the level of stratification maintained during various flow events in the tank. One-dimensional (1D) models are used in building energy simulations because of the short computation time but often do not include flow-rate dependent mixing. The accuracy of 1D models for plug flow, plug flow with axial conduction, and two convection eddy-diffusivity models were compared with experimental data sets for discharging a 50-gal residential tank and recharging the tank with hot water from an external hot-water source. A minimum and maximum relationship for the eddy diffusivity factor were found at Re <2100 and >10,000 for recirculation of hot water to the top of the tank and vertical tubes inletting cold water at the bottom. The root mean square error decreased from >4◦C to near 2◦C when considering flow-based mixing models during heating, while the exponential decay of the eddy diffusion results in a root mean square error reduction of 1◦C for cone-shaped diffusers that begin to relaminarize flow at the inlet.",

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AB - Stratified tank models are used to simulate thermal storage in applications such as residential or commercial hot-water storage tanks, chilled-water storage tanks, and solar thermal systems. The energy efficiency of these applications relates to the system components and the level of stratification maintained during various flow events in the tank. One-dimensional (1D) models are used in building energy simulations because of the short computation time but often do not include flow-rate dependent mixing. The accuracy of 1D models for plug flow, plug flow with axial conduction, and two convection eddy-diffusivity models were compared with experimental data sets for discharging a 50-gal residential tank and recharging the tank with hot water from an external hot-water source. A minimum and maximum relationship for the eddy diffusivity factor were found at Re <2100 and >10,000 for recirculation of hot water to the top of the tank and vertical tubes inletting cold water at the bottom. The root mean square error decreased from >4◦C to near 2◦C when considering flow-based mixing models during heating, while the exponential decay of the eddy diffusion results in a root mean square error reduction of 1◦C for cone-shaped diffusers that begin to relaminarize flow at the inlet.

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A flow rate dependent 1d model for thermally stratified hot-water energy storage

Abstract

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Keywords

UN SDGs

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