You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Energy management for user’s thermal and power needs: A survey 
Chapter Title:  A.4. Energy hubs 
1. Abstract of Cited Paper (BIB001):  MES (multi-energy systems) whereby electricity, heat, cooling, fuels, transport, and so on optimally interact with each other at various levels (for instance, within a district, city or region) represent an important opportunity to increase technical, economic and environmental performance relative to “classical” energy systems whose sectors are treated “separately” or “independently”. This performance improvement can take place at both the operational and the planning stage. While such systems and in particular systems with distributed generation of multiple energy vectors (DMG (distributed multi-generation)) can be a key option to decarbonize the energy sector, the approaches needed to model and relevant tools to analyze them are often of great complexity. Likewise, it is not straightforward to identify performance metrics that are capable to properly capture costs and benefits that are relating to various types of MES according to different criteria. The aim of this invited paper is thus to provide the reader with a comprehensive and critical overview of the latest models and assessment techniques that are currently available to analyze MES and in particular DMG systems, including for instance concepts such as energy hubs, microgrids, and VPPs (virtual power plants), as well as various approaches and criteria for energy, environmental, and techno-economic assessment.

Literature Review:
An energy hub can be described as a ''block'' that exchanges energy with the neighboring systems via input and output ports. Inputs can be in the form of both primary energy, e.g., natural gas, and secondary energy coming from external grids, such as electricity or district heat. Outputs are usually electricity and heat, locally produced and converted by means of generation and transformation units, such as transformers, CCHP systems, and boilers BIB001 BIB002 . Both thermal and electric storage are often included in the energy hub model as well, which is traditionally described by a coupling matrix that determines the outputs given the inputs and generation/conversion/storage units. Several real systems can be modeled as an energy hub, from power plants to buildings and districts BIB001 .