DESCity: district energy simulation using CityGML models

Malhotra, Avichal; van Treeck, Christoph Alban (Thesis advisor); O' Donnell, James (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023


With a global upsurge in energy demands, the challenge to improve the energetic performance of existing buildings calls out for district and building level interventions through precise energy demand estimations, retrofitting measures and the recognition of energy efficient solutions within the built environment. Often the amount and type of data required for district-level energy calculations are unclear, and it leaves decision-makers in a dilemma within the development of low to high quality data sources based on its value as perceived by stakeholders. There exists a lack of robust indicators that could guide urban planners and policy makers to channelise their resources in reducing energy consumption based on the input data for district level energy simulation. Keeping in mind the inadequacy of coherent computational models and informing the users about the implications of acquiring different input data, it is vital to develop methodologies to optimally model, store and exchange city-wide physical, operational, environmental, geometrical and contextual data. Urban Building Energy Modelling (UBEM), a technique to model urban areas quantitatively helps define georeferenced building-related data and energy-specific attributes to compute and identify a building’s energy performance characteristics. UBEM assists the quantification of a building’s energy demand, consumption, and the effects it possesses onto its surrounding buildings’ energy requirements. The technique enables virtual modelling of the built environment and allows representing individual buildings in the form of data models. These models provide a standardised structure for storage and exchange of building-specific data and allow its extension with energy-specific attributes for energy simulations. One such model, the City Geographical Markup Language (CityGML) is prevalent within the UBEM community and is employed for applications related to energy. Although the model has an extensive usage, its limited availability, inconsistency, complexity, and reproducibility are always questioned upon. Therefore, this thesis highlights the strengths and shortcomings of CityGML and proposes novel solutions to overcome the identified limitations in using the format for UBEM. This thesis utilises a UBEM-based implementation methodology and introduces methods to assist stakeholders in individual stages of an urban-scale energy simulation process. The proposed methods facilitate the generation and deployment of CityGML building models using raw input data, and provide techniques to enrich the models with energy-specific attributes that are required for heating energy demand simulation. The developed methods, consolidated as DESCity, envision to increase CityGML’s usage in UBEM by allowing users of varying experience levels to use the methods semi-automatically. The incorporated mathematical computations and the developed process algorithms allow users to model, validate, transform, enrich, and simulate CityGML building models without the need of explicit modelling and in an uncomplicated manner. The proposed methodology for DESCity provides functionalities to analyse, search and validate existing CityGML building models incorporated within the CityGML Analysis Toolbox (CityATB). The methodology further includes CityGML Building Interpolation Tool (CityBIT) that helps generate new building models by using user-defined inputs and interpolation techniques. The functions incorporated within the DESCity’s CityGML LoD Transformation Tool (CityLDT) enable the trans formation of a CityGML model’s granularity as the implementation methodology enables users to upscale or downscale the CityGML Levels of Detail (LoD). The developed workflow of CityGTV facilitates geometric transformation and validation of building models as required by its users. For enhancing the geometric data models with energy-specific attributes, the methodology of DESCity includes CityGML Enrichment Tool (CityEnrich) and TEASER+ that enable manual and archetype-based enrichment, respectively. Apart from enriching the building models with energy-related data, both the implemented workflows enable the export of an enriched CityGML model in the form of Energy Application Domain Extension (Energy ADE). Each workflow within DESCity has its own user interface and the functionalities of the platform are available as open source. This thesis highlights the adapted methodology and implementation of the aforementioned functions and demonstrates the applicability of DESCity’s modules in urban-scale heating energy demand simulations. It further reflects upon the current limitations of the development and conclusively discusses the potential future research direction within the field. Urban planners, policy makers and engineers could use the developed methodology to model, enrich and simulate building models for determining and identifying the heating energy demands and energy-efficiency potential, particularly, at an urban scale. The devised approach reduces the necessity of explicit modelling of the city-wide buildings, and enables stakeholders to generate, validate, analyse and simulate 3D building models in CityGML. The work at hand could be used to develop digital representations of the urban buildings with limited data and resources, and the developed methodology could be integrated in existing workflows and software for supporting data exchange and reproducibility.


  • Institute of Energy Efficiency and Sustainable Building [312410]