The history of Danish district heating is more than 100 years old and still very much a part of modern society and the future. What started as a way of getting rid of waste in an efficient way is today a billion dollar business and a cornerstone in the Danish energy system. In this section we will focus on the different important periods in the history of Danish district heating and look into the most important tipping points and technological developments.
Early development 1898-1972
Once upon a time – more than 100 years ago, both the environment and a future-orientated heat supply were put on the agenda of the city council of Frederiksberg which is an independent municipality situated in the western part of Copenhagen City. Combined heat and power production based on household waste incineration then became the starting signal for the development of district heating in the municipality.
In the 19th century, Frederiksberg develops from being a village to being a town with the nature of a big city. In the middle of the century – in 1857 – Frederiksberg becomes an independent municipality ranking as market town, and during the 19th century, the city develops rapidly. Industrial enterprises are being built and the factories attract manpower. The city grows bigger and bigger – the industry grows and the population increases. A railway station is built, a fire service is established, schools and a library are built, and the city is provided with gas, running water, sewers and electricity.
100 years ago, daily waste was collected and transported by horse carriages to the city dump”
However, the busy activity has a natural – though difficult – “by-product”: waste. Concurrently with the increase in population and the building of the outer area of Frederiksberg, the price of land increases, and it becomes even more expensive for the municipality to buy land for dumping grounds. At the same time, people are fully aware of the risk of e.g. cholera by having dumping grounds that are placed too centrally.
By the end of the 19th century, it was therefore a dubious affair to walk around in the streets of Frederiksberg. Many of the free space areas were bursting with piled up garbage with consequent odour problems. The municipality struggled with mountains of waste from the rapidly growing population. The lack of dumping grounds meant that the waste from the 75,000 inhabitants accumulated and the fear arose that epidemics would break out. The municipality therefore had to come up with new thoughts.
In 1898 therefore, a few railway carriages were loaded with typical Frederiksberg waste and driven to Germany in order to investigate the possibility of following the example of Hamburg. Here, in 1896, a plant had been developed to burn waste with the facility to utilise the generated heat. The test result came out positive and in the spring of 1902 Frederiksberg Municipality decided to build Denmark´s first waste incineration plant, which not only produced heat but also electricity.
“Open burning of garbage in a city dump was the only solution to get rid of the garbage and prevent diseases to spread “
In September 1903, the first waste collection was received at the new waste incineration plant and the plant was inaugurated. From December 1 that same year, the district heating production was put into regular operation. On horse-drawn carriages the waste was loaded into silos and from there, in portions, loaded further into the ovens. In the shape of steam, the heat was led through tunnels to the newly built hospital, a children´s home and a poorhouse.
“The first waste incineration and CHP plant in Denmark was inaugurated in 1903. Today, the buildings serve as a cultural centre”
In this way, Frederiksberg municipality killed two birds with one stone: the problems of disposing of household refuse in an environmentally sound way were solved by establishing a waste incineration plant and at the same time, the waste heat from the combustion process could be utilised for heating municipal institutions. By doing so, Frederiksberg Municipality gave birth to the first district heating system in Denmark.
This district heating initiative inspired many communities in Denmark and already in the beginning of the 1920's, a number of small and medium-sized diesel-powered electricity generating plants had been established in many small towns. Also here, the surplus heat in the cooling water was utilised for the customers closest by – mainly substations for public offices and houses.
“In some waste incineration plants, horse carriages were lifted by elevators to dump the waste into the plant “
The centralized form of heat supply grew steadily in the 20's and 30's, and gradually regular district heating substations appeared in connection with the development of large adjoining housing areas. When the power stations in the large cities changed from diesel to steam heating in the 30's, many of them were carried out as combined heat and power plants, since the earlier development had obliged the stations to deliver heat as well.
During the Second World War the lack of diesel oil made it difficult to maintain the heat supply from the combined heat and power plants, and some plant owners were therefore forced to establish back-up heating, using solid fuel heat-only boilers. After the normalisation of the oil deliverances, these plants represented excess capacity and therefore created a basis for expanding the heating supply networks.
After the war, the structure in the electricity supply in Denmark changed towards large central power plants, and consequently many of the local plants were closed down. This made it necessary to build heating stations, in order to supply the already established district heating systems.
Already in the beginning of the 1960'es, Denmark had more than 50 years of experience in using district heating and the development was now strengthened by the fact that some Danish suppliers launched the idea of town development with district heating based on a low supply temperature (up to some 90°C). Hereby the district heating stations and the distribution network would become cheaper. Also on the operational side this led to savings since the demands on personnel etc. did not have to live up to the regulations for hot-water plants or power stations.
The pipes of the first piping networks were made of iron and insulated with cellular concrete, but this turned out to cause corrosion of the distribution pipes, especially in cases of the nets being placed in poorly drained soil. In order to fight this problem, the pipes were insulated with mineral wool and hung up in concrete ducts, so that they were secured against humidity. However, this solution was expensive, which made it suitable only for heat supply to major heat customers such as hospitals and industries with considerable heat consumption. Therefore the development of new district heating systems in housing areas partially came to a halt for a period.
The breakthrough for the heat supply of the housing areas came when a number of Danish companies developed the pre-insulated district heating pipes. Here the iron pipes from the factory were covered with a heat insulating layer of polyurethane finished by a dense non-corrodible plastic jacket. The problem with this solution was how to obtain a completely tight assembling of the pipes; but with a special technique where the joints were assembled with muffs that had been welded or screwed on, it proved a success as well. In addition, electrodes were built into the insulation layer of the pipes, which made it possible to discover any intrusion of water and identify a leak so that it could be repaired relatively easy.
Initially the plastic jacket allowed only low temperature, with flow temperatures preferably not exceeding about 90°C. Soon the material was improved and the allowed temperature was raised to 120°C. The low operation temperature made it possible to utilise the surplus heat from industrial enterprises, and not least from waste incineration plants for solid waste, which in Denmark at that time was most often based on heat disposal by means of hot-water boilers. The combination of these two facts caused a boom in the establishment of district heating networks and waste incineration plants. Thus the first post-war waste incineration plants were built at the beginning of the 1960's.
It is important to note that district heating in Denmark developed in the same manner as in other countries before the energy crisis hit the western countries in 1973/74. At that time, energy consumption per inhabitant was extremely high. The energy crisis created an urgent need for crucial change in the Danish energy system. As a country the whole economy was threatened because Denmark at the time imported almost 100% of all the fossil fuels required to generate heat. For the single costumer the heating budgets were all of a sudden multiplied. The Danish government was forced to devise methods for saving fuels in order to safeguard the interests of society and to reduce the consumers costs. A number of initiatives were launched, including:
• Systematic planning of the heat supply in all areas
• Greatest possible CHP generation on the basis of such planning
• Insulation of buildings
• Development of highly effective district heating pipe systems, pre-insulated pipes with high insulation properties and low installation costs
• Reduction of operating temperatures in district heating systems and a variable flow in the pipelines to secure the most economical operation in the overall production and distribution system, while at the same time allowing the possibility to apply pre-insulated pipes
For the next 40 years and still today, district heating first became and later prooved itself to be a reliable, cost efficient and green source of energy to the benefit of Denmark. Due to a firm energy policy and cooperation between central and local authorities, heat supplying companies and private companies, considerable results were achieved in Denmark during the period since the energy crisis. This has, among other things, meant that here at the beginning of the 21st century, the energy requirements per inhabitant for space heating have dropped a little more than 50% of the requirement in 1973. The success story was created by several technical and political initiatives, the following describes some of the most important.
In the fuel area, a number of initiatives have been launched. In the large cities, former small areas with their own heat supply have been consolidated into major overall areas, in which heat can be distributed everywhere through integrated networks from CHP units, waste-to-energy systems, industrial enterprises, etc. The existing heat plants are mostly maintained as peak and reserve load units which will start to operate in critical supply situations.
“Vestforbrænding, the largest waste-to-energy plant in Denmark handling more than 700,000 tons of waste anually”
In rural areas with as little as 250-500 inhabitants, so-called decentralised CHP plants have been established. They are designed on the basis of the heat demand and connected to the overall power supply network. This means that in principle, these systems are only in operation when heat demand makes it necessary, and since almost all of them are equipped with heat accumulators, the overall power and heat generation can be controlled and optimised. The plants are fired by means of natural gas, straw, wood waste, biogas and other indigenous fuels, which only affect CO2 emission to a limited extent.
“The wood-fired CHP-plant in Assens supplies approximately 5,400 inhabitants of the community”
In 1979, a new heat supply act was implemented which started a heat planning process in the municipalities with the aim of introducing a complete new infrastructure for domestic natural gas to cover 15% of the heat marked (by direct supply) and with the aim of raising the district heating market share up to around 60% in year 2000. The central authorities issued guidelines, supervised the planning and approved the plans, and the municipalities did the planning in collaboration with energy utilities and consultants.
The main result of the heat planning was a least cost zoning of natural gas networks and district heating networks to substitute individual oil boilers. Another result was the zoning of new integrated district heating transmission systems to supply local systems from large CHP plants and waste incinerators.
Example of a least-cost zoned area between gas network to one-family houses (green) and district heating supply to large buildings (red)
As district heating networks are much more capital intensive than gas networks, districts with sufficient heat density could have a district heating monopoly network for heating and a gas network for cooking.
A typical objection to zoning is that it eliminates market forces. However, this need not be true. On the contrary zoning of the modern district heating system, which is regulated by a flexible national least cost planning, will make even better use of the market forces. About zoning in general it can be concluded:
1. A natural gas network in a city district will link the district to one strong monopolist, namely one supplier of gas, which delivers gas in accordance with the heat load curve. Even when the gas market opens, one may question the real competition as there will be only few dominating suppliers, often integrated by cross ownership and other measures. This will, in fact, reduce competition.
2. A district heating network in a city district will open for real competition among all suppliers of all kinds of fuels and surplus heat sources, summer, winter, day and night. As a special case the district heating network with heat accumulators will form an efficient link between the power and the gas market, but only if there is a stable and fair competition in both networks.
In the municipal heat planning, the zoning can be regarded as a result of a co-ordinated competition between the district heating company and the gas company. The company, able to offer the alternative that best meets the objectives of the national energy strategy, such as lowest long term costs, high security of supply, low environmental impact, use of local resources etc., will win the competition. That will give the basis for monopoly of heat supply in the district in question in at least a period equal to the economic lifetime of the investment. That could, e.g., be 25 years for district heating and 10 years for natural gas. The alternative would be wild competition, duplication of investments, bankruptcy and loss of assets.
Today, the objectives of the planning are fulfilled. Denmark is a net exporter of oil and gas, and the consumers can easily afford to pay the real costs of heat.
Copenhagen, the capital of Denmark, had to enter entirely new ways of thinking when the planning started back in the beginning of the 1980s. This meant that five municipalities, which differ widely in sizes as well as in political views, agreed to join forces in order to comply with the requests of the government. This was achieved even though their experiences with district heating were also very heterogeneous; thus two of the participating municipalities did not have any consumer networks established at all beforehand.
From the outset, some district heating systems were already established in the central part of the Greater Copenhagen area, which were supplied by a variety of small and medium sized plants each connected to its own pipeline network. At the same time three large power blocks were located on the island of Amager, but due to the specific geographical conditions it was not possible to utilise the full capacity on the heat side, i.e. to extend the field of activity beyond the borders of the island. A link was thus missing which could connect the different district heating networks and which could also utilise the full capacity of the large power blocks. The link that was found, and which has afterwards been established, was a so-called inter-municipal or regional transmission network.
Installation of transmission pipelines in Central Copenhagen
Fundamentally, a transmission network is a connecting link between the local district heating networks and the production plants. The design concept of a transmission system thus implies that production, transmission and distribution are separated into three different areas of operation. This means that the transmission company buys heat from the production units, transports it through the network and sells it to the partner municipalities, which on their side take care of the further transportation to the individual consumers.
One of the major advantages of this design concept is that the transmission company can choose freely among the various production plants due to the integrated structure of the system. The choice is among others based on which production plant is the cheapest to take into operation at the moment, which one is the most suitable to cope with the environmental directives prescribed by the government and which one should merely be operated occasionally and be given status as peak load and reserve unit.
What has been experienced in the Copenhagen area is that district heating is an incredibly flexible system both with regard to choice of production plant and with regard to the fuels used at the production plants.
In this connection, it has also been possible to kill two birds with one stone. As in most metropolitan areas all over the world we are faced with the problems of the increasing amounts of waste despite the best intentions of reversing this development. Recently, the capacities at the two large waste incineration plants in the area have therefore been extended. The heat produced during this process is sent into the transmission network. An increasing part of the waste incineration is producing combined heat and power. Looking at the figures for year 2003, waste incineration was thus able to cover more than 25 per cent of the total heat demand in the Copenhagen area.
Today, the Copenhagen district heating system is one of the world´s largest, supplying heat for a floor area of around 50 million square metres. The transmission system connects four CHP plants, four waste incinerators and more than 50 peak load boiler plants to more than 20 distribution companies in a one pool-operated system with a total heat production of around 30,000 TJ.
The transmission network in Greater Copenhagen
Concurrently with the development and expansion of the district heating systems in Denmark, the industry supplying components and systems to the sector also carried out intense research and development of their individual products. The objective was that each component in the systems should provide more efficient operation and contribute to the overall energy saving targets. In fact, very early the industry became aware that if their products did not meet these objectives in a cost efficient way, they would not be able to compete as suppliers to the sector because the district heating companies would evaluate operational cost and efficiency equally with the price of the components.
During the past 25 years, the industry has provided results that have made it possible for the Danish district heating sector to achieve results appreciated world-wide.