THE GENERATION BATTLE 4 th
GENERATION OF DISTRICT HEATING
By Oddgeir Gudmundsson and Jan Eric Thorsen, Danfoss Climate Solution, Denmark.
In recent years, the 5 th generation of DH has been emerging. But what are the drivers behind the development, and how is it positioned compared to the prior generations? Before a meaningful answer, one needs to know how the 5 th generation's definition deviates from the definition of the 4 th generation and what impact the difference has on the supply system.
“The fifth generation” In recent years, the fifth generation of DH has been emerg- ing. But what are the drivers behind the development, and how is it positioned compared to the prior generations? Be- fore a meaningful answer, one needs to know how the fifth generation's definition deviates from the definition of the 4 th generation and what impact the difference has on the supply system. To answer this, one needs to know what the original idea was behind the definition of the 4 th generation. This can be read out of the generation figure, Figure 1, which shows the transi- tion from fossil fuels to a renewable energy source; it further shows an intelligent integrated energy system where the heating sector is coupled with the power, industry, and cool- ing sectors. It is about energy efficiency, it is about sustainabil- ity, and it is about demand-driven energy systems. When looking into the main ideas behind the 5 th generation, one quickly finds that it is identical to the 4 th generation. It is about energy efficiency, sustainability, and demand-driven thermal supply. The difference between the generations does not lie in the purpose of the system but in how the systems are designed to fulfill their purpose.
District heating (DH) is here to stay. Looking back on the history of DH, it goes quite some years back. During the years, it has developed to fulfill the demands as they came up, typically driven by the need for reduced investment and heat costs, low- er equipment space demands, concerns of energy efficiency, environment, longer lifetime, and lower fire risks. In 2014 an article  was published that categorized the historical devel- opment into four generations. Each generation was defined by significant changes in the technology or purpose compared to the prior generation. Currently, most DH schemes being operated are categorized as being at the 3 rd generation DH technology stage and starting its transition to the 4 th genera- tion. The transition is driven by the challenge of the future non-fossil and renewable-based energy system. At the same time, there is active work being performed in the research community to see how this great technology can be innovated even further. This has led to the concept of an ambient temperature distri- bution grid, commonly called the 5 th generation DH. Each end- user operates his heat pump to adapt the supply temperature to his own needs. The research has mainly been focused on case studies and few small-scale concept validation projects. What has generally been missing is a direct comparison of the 5th generation to the 4 th generation. What are the differences between the generations that impact the integration potential of the energy supply system? This article tries to address that.
Before digging into the differences, we need to define what energy sources and heat plants mean:
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