Abstract

District heating and cooling systems have been undergoing continuous development and have now reached the fifth-generation. In this innovative technology, connected buildings share local excess energy that otherwise would be wasted, which consequently reduces primary energy demands and carbon emissions. To date, the issue of implementing fifth-generation district systems on existing buildings has received scant attention, and our research addresses this challenging gap by proposing a novel method for designing these systems. We first explain the possible thermal interactions between connected buildings, and then present an analytical solution for the network energy balance, pipe design, and the prediction of fluid temperature under a fixed temperature difference control strategy. The analytical solution was validated against numerical simulations performed on 11 existing buildings located in Lund, Sweden using Modelica models. A diversity index metric between heating and cooling demands was also included in these models to assess the efficiency of the district system in the building cluster. The results from the analytical and numerical solutions were in complete agreement since Modelica is an equation-based modelling language. The developed models pave the way towards future investigations of different temperature control strategies and new business models that arise from the shift to the fifth-generation.

Highlights

  • The global population is expected to reach 9.7 billion by 2050 where up to 68% will reside in urban areas [1]

  • The validation of the analytical solution and the results of the Modelica simulations performed on the case study are presented

  • Because the behaviour of physical models developed in Modelica is described by differential algebraic equations, the results from the Modelica simulations were in complete agreement with the analytical solution

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Summary

Introduction

The global population is expected to reach 9.7 billion by 2050 where up to 68% will reside in urban areas [1]. District Heating and Cooling (DHC) systems are an effective technology and considered most feasible in urban areas with high heat density [3]. Compared to their counterparts, DHC systems have high resilience to integrating renewable energy sources that would increase energy efficiency and reduce carbon emissions. The first district cooling network was realized in Hartford, USA in 1962 and in Hamburg, Germany in 1967. Due to their higher security of supply and low carbon emissions, the implementation rate of DHC networks exceeds 50% in some countries like in Denmark and Sweden

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