District energy (district heating and cooling) is here to stay – with the green transition, it is more relevant than ever before. District energy has been around for some time and its development makes it a key solution to decarbonize heating and cooling.
During the years it has developed to fulfill the demands as they came up, typically driven by the demand for reduced investment and heat costs. It also adapted to lower equipment space demands, concerns of energy efficiency, and reaching sustainable goals. The development is categorized into 4 generations that indicate major changes in technology.
How did the systems change and develop, what sources and technologies have been and are in use today? What are the new upcoming technologies? Find all the answers below.
From steam to sector integration
The main characteristic of the first generation DH system was the transportation of heat with steam at temperatures reaching up to 200°C. The consumer groups were to some extent small urban industries that used steam in their processes and large heat consumers such as hospitals and big residential building complexes. The high heat content resulting in low mass flows was one of the main drivers for maintaining/applying this technology that was a normal way to design new DH systems until 1930.
The main characteristic of the 2nd generation DH system is that the heat is transported by pressurized superheated water at temperatures above 100°C. This is a significant difference compared to the 1st generation DH systems, where steam is used to transport the heat.
This generation enabled energy-efficient waste heat utilization from power plants, transitioning them into combined heat and power (CHP) plants. By using the waste heat from power plants, fossil fuel consumption was reduced by 50% compared to separate production of heat and power, as was done in the first generation.
The main driver for the development of the 2nd generation DH system was increased operational safety, increased efficiency of both the heat distribution and operation of heat plants and the possibility of using a wider variety of heat sources than the 1st generation.
The 3rd generation DH system brought about the material and labor lean components applied combined with generally lower temperatures (below 100°C).
The main benefit of the third generation DH system compared to the 2nd generation DH system is the increased energy efficiency due to lower operating temperatures and the reduced investment and operation costs due to more prefabrication, pre-assembly, and pre-insulation at the factory. Also, the fuel mix has been altered by feeding in greener and renewable sources, resulting in lower emissions.
Following the 3rd generation, a new development path is characterized by transforming the energy system towards a sustainable and interconnected energy system. This system is based on a high share of fluctuating renewable sources for heating and cooling, smart integration of the energy sectors and at the same time reduced specific building energy consumption as well as supply and return temperatures.
Future developments: what is coming next?
Currently, most district heating (DH) schemes being operated are categorized as being at the stage of 3rd generation DH technology starting its transition to the 4th generation to address the challenge of the future non-fossil and renewable-based energy system. To meet the demands of the future energy system, existing DH schemes will transition into the next generation, the 4th, and the most advanced generation.
There is a lot of talk around district energy generations in the industry about new upcoming generations. At the same time, it is becoming clear that the proposed development from the 4th to the 5th generation is not at all sequential, but rather parallel.
Low temperature or ambient temperature district heating?
Our experts from the Danfoss' Application Center, Oddgeir Gudmundsson and Jan Eric Thorsen, have recently published a study where they compare the 4th and 5th generations. They base the comparison on key parameters, such as cost-effectiveness and flexibility, while the study is applied to Denmark and United Kingdom.
For locations investigated, the study reveals that the 4th generation remains the most attractive solution in light of the costs of establishing and operating the system. The study concludes that 4th generation district heating is not only more cost-effective compared to the 5th generation, it also performs better when it comes to security, reliability, flexibility, and resilience.
You can access the complete study on ScienceDirect or explore the resources below: