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Simulation and Optimization of Efficient District Energy Systems

NREL researchers and collaborators develop advanced capabilities for district-scale simulation of cooling, heating, and waste heat recovery energy systems.

A city skyline view with blue skies.
NREL researchers and collaborators are developing advanced capabilities for district-scale simulation of heating and waste heat recovery energy systems in support of NREL's URBANopt tool and other modeling tools. Photo by Dennis Schroeder, NREL

These systems efficiently provide thermal energy to dozens—or hundreds—of buildings using a network of shared infrastructure. Effectively modeling these systems enables quantification of the value of a district energy system and its potential for waste heat recovery.

Benefits of Grid-Interactive Efficient District Energy Systems

NREL's open-source models enable the evaluation and optimization of district energy systems to better utilize low-temperature waste heat from nearby commercial and industrial buildings. This allows developers and engineers to easily quantify the potential value and cost savings of community energy systems for producers and consumers (also called prosumers) and prospective consumers of waste heat. Models include:

  • Commercial and residential buildings
  • Building HVAC systems
  • District central plant equipment, including boilers, chillers, and cooling towers
  • Network distribution equipment to connect buildings
  • Waste heat recovery devices to capture industrial waste heat and use it within the district.

Leveraging URBANopt for Detailed Analysis

To enable a detailed analysis of waste heat sources within a district of connected buildings, the Urban Renewable Building and Neighborhood Optimization (URBANopt) software development kit is integrated with the open-source Modelica programming language, TEASER (Tool for Energy Analysis and Simulation for Efficient Retrofit), and the next-generation Spawn of EnergyPlus™, a building energy simulation program supported by the U.S. Department of Energy.

This integration uses the GeoJSON to Modelica Translator to transform an URBANopt GeoJSON file into a fully articulated Modelica-based model. The GeoJSON to Modelica Translator leverages and extends models from the Modelica Buildings Library for district central plant equipment, energy transfer stations, and base classes for the building loads. Functionality has been added to the GeoJSON to Modelica Translator to support connecting the various types of building loads to the central plants, including the addition of a first-generation district heating system (steam-based) and fourth-generation district cooling system with scalable chillers and cooling towers.


Enabling Technology Transition

Connecting these open-source developments with the established base of EnergyPlus users will help increase awareness of efficient district energy systems, ultimately improving the business case for district cooling, district heating, and integration of waste systems. This can help facilitate the growth of high-performance district energy systems, resulting in cost savings, greater economic security, environmental and economic benefits, and more favorable grid profiles.

Demonstration Sites

The developed models will be validated using data collected from two community energy systems in Colorado and Ohio. These locations represent two distinct climates: ASHRAE climate zones 5B (cool and dry) and 4A (mixed-humid), respectively. Both sites have district energy systems with combined heat and power and microgrids, with owners interested in retrofitting or expanding the systems. Detailed design and retrofit of these two community energy systems will be conducted by using the Optimal Co-Design Platform.

These demonstration sites will enable detailed analysis to provide insights on how to improve the resilience and energy efficiency of current systems, and how to retrofit current systems to increase energy efficiency and reduce operating costs. This will allow for the development of recommendations on system optimization that will be proposed to the facility managers and can be applied to future sites.


NREL is partnering with the University of Colorado Boulder; Lawrence Berkeley National Laboratory; Rensselaer Polytechnic Institute; the University of Texas at Austin; Amzur Technologies Inc.; Utility and Energy Services; Shell, Engie, and Ohio State on this work.


Nicholas Long

Senior Engineer