The evolution of district energy – an introduction
Travel from 1895 to the new millennium to understand the basics of district energy
By 2050, the world’s population will have grown from 7 billion to 9 billion people. And 70% of these will live in cities. To meet the energy demands of tomorrow, we need sustainable solutions that are both energy-efficient, cost-effective and ready for large-scale implementation. Luckily, such a solution already exists: district energy. In this module, we’ll have a closer look at district energy and how the technology has evolved to become a viable answer to many of today’s energy challenges. But first a definition:
District Energy is a heating and cooling system in which heated or chilled water is transported from a central plant to a range of consumers through a closed network of pipes. The water is used to regulate indoor temperatures and, in terms of district heating, heat household water. The centralised production of heated and chilled water removes the need for individual solutions and offers a far more efficient utilisation of the fuel.
The fuel itself presents an opportunity to reduce both production costs and CO2 emissions, as many plants are able to run on renewable energy such as solar thermal, geothermal, municipal waste, or wind energy. In a District Energy system, you can also switch between energy sources, making it much easier to make radical changes than in other supply systems.
For the consumer, district energy means ready-to-use energy right at the doorstep. There’s no need for boilers or chiller units that take up space and demand expensive maintenance and there’s no capital investment.
District energy has been around for over a century. Today, it provides entire cities, colleges, large-scale businesses, and even the White House with energy. Roughly put, the evolution of district energy can be divided into four generations:
The 1st generation of district energy was mainly driven by oil-fired boilers that produced vast amounts of steam at 200°, while leading 2/3 of the energy out the smokestacks. The systems covered small areas, but suffered from extensive heat losses due to poorly insulated pipes and the extreme high temperature. Though hardly efficient compared to the standards of today, it was a true heating revolution at the time, and certainly lived up to its objective of reducing pollution in cities.
2nd generation district energy fixed some of these initial problems by switching from steam to pressurised water and increasing the quality of the pipes. This allowed for district energy to be implemented on a much larger scale. During this time, the use of combined heat and power plants grew increasingly popular. By using the surplus heat from the power production for heating purposes, these plants were able to reduce fuel costs radically.
The third generation, which covers most of today’s district energy systems’, consists in large part of combined heat and power plants. One of the biggest differences is that the temperature of the distribution water is now below 100°, which has made it possible to drive production with alternative sources of energy, like solar energy. Also, short-term storage of energy has enabled plant owners to reduce production costs by producing electricity when prices are high and storing the surplus heat for when prices are low.
However, the technology is still evolving and the first 4th generation systems have already seen the light of the day. The 4th generation district heating systems distribute water at a much lower temperature for heating – and a higher temperature for cooling. This means less energy used and less energy lost. It also provides an opportunity to use low-temperature sustainable energy sources such as geothermal energy, decreasing the environmental impact even further.
On top of this, new technology makes it possible to store energy for months. Moreover, plants can even out their daily energy usage, which allows them to use the necessary amount during peak periods while slowing down operation significantly during more quieter periods, thereby storing the energy for later.
Naturally, the initial investment that goes into constructing a district energy infrastructure is substantial. But all signs point toward the fact that in densely populated or industrialised areas district energy is the energy solution of the future. In conclusion, the benefits of district energy include:
- More reliable heating and cooling
- Low costs through economy of scale
- A significantly reduced environmental impact
- And convenience for consumers
- Avoid unforeseen costs
- No headache, no maintenance