HOT|COOL NO.4/16 - "From one generation..."

I hope this issue of Hot Cool can create inspiration for the further development of district heating everywhere - whether the district heating systems are developed from 1st G DH systems to 3rd G DH systems or from 3rd G DH systems to 4th G DH systems. The important thing is that we always make sure to communicate to politicians and the public that well-run district heating systems allow the utilization of vast energy resources, which without a district heating systemwould be lost to our society. Furthermore, district heating systems facilitate renewable energy to be utilized on a large scale for the economic benefit of citizens and society.

N0. 4 / 2016



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By Lars Gullev, Managing Director VEKS and Chairman of DBDH THE COLUMN


This issue of Hot Cool highlights • how US and Canadian universities are converting district heating systems from steam (1st G DH systems) to hot water (3rd G DH systems), thus reducing the heat loss, for example to between 33% and 50% of the current loss. • how in Copenhagen, Denmark, the last of the original steam system, established from 1906, is converted to hot water, so that the total district heating system in Copenhagen in 2021 will be a 3rd G DH system. • how in Albertslund, Denmark, the first projects to convert the current 3rd G DH system have now been launched so that the entire municipal district heating system in 2026 will be a 4th G DH system. • how existing district heating systems in older buildings can be converted from 3rd G DH systems to 4th G DH systems. I hope this issue of Hot Cool can create inspiration for the further development of district heating everywhere - whether the district heating systems are developed from 1st G DH systems to 3rd G DH systems or from 3rd G DH systems to 4th G DH systems. The important thing is that we always make sure to communicate to politicians and the public that well-run district heating systems allow the utilization of vast energy resources, which without a district heating systemwould be lost to our society. Furthermore, district heating systems facilitate renewable energy to be utilized on a large scale for the economic benefit of citizens and society. That is the Christmas present that we in the district heating sector can give to everyone. Thank you for a pleasant 2016 and welcome back to an even more exciting 2017 – happy new year!

The first steam-based district heating systems were put in commission in the 1880s in the United States. The systems are today known as 1st G (generation) DH systems, and it was steam that was the energy transferring medium in the district heating systems until around 1930. At that time, water took over, and the flow temperature was reduced from the present more than 200 degrees C to about 120 degrees C - we had now started the 2nd G DH systems. In Denmark, we began to see the first heat accumulators as part of the district heating systems - primarily in order to provide greater flexibility in the operation of the CHP plants that produced district heating for the transmission network. The next major development leap within district heating technology occurred in about 1980, when pre-insulated district heating pipes replaced steel in concrete channels. The 3rd G DH systems were born. The flow temperature of the district heating network was lowered, which meant that the heat loss was also reduced. Renewable energy began to contribute to the production of district heating - partly in the form of biomass replacing fossil fuels, but also the construction of large solar plants, which began supplying heat into the district heating network, took place in more and more countries. The flow temperature had now been lowered to 70 -90 degrees C. We have now addressed the 4th G DH systems where the flow temperatures are as low as 50-60 degrees C. This low temperature level means that the heat loss from the pipes is further reduced, but what is most important is probably the fact that low temperatures enable a use of energy resources in the community that was previously lost – most prominently the utilization of waste heat from the industry. Furthermore, the potential is increased for utilization of renewable energy on a large scale - for example by utilising solar heat which can be seasonally stored in large heat storages for use in the winter. A flow temperature of 50-60 degrees C is low, but test district heating systems are already conducted where the water temperature is as low as 35-50 degrees C, so the development certainly has not come to a hold yet.


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By Roman Geyer, Research Engineer, AIT Austrian Institute of Technology GmbH, and Ralf-Roman Schmidt, Research Engineer, AIT Austrian Institute of Technology GmbH

Making the current district heating (DH) systems future proof required substantial changes. The existing district heating networks in Austria already have to struggle with unstable market situations and new requirements. In order to increase the economic and energetic efficiency as well as the share of renewable energies, DH operators have to adapt their business models and also have to consider completely new aspects. Background to the Austrian DH situation Currently, more than 2,400 district heating (DH) networks are operating in Austria, besides some larger networks in urban areas the majority are small biomass bases rural DH networks. About half of the total supply is based on fossil fuels, the remaining share is distributed between waste incineration, biofuels and others – the total share of CHP is about 2/3. Due to unstable fuel and electricity prices, the long-term perspective of these systems is becoming increasingly insecure. The integration of alternative heat sources (such as solar- and geothermal energy as well as residual or ambient heat via heat pumps) can minimize investment risks, maximize the security of supply and reduce the CO2 emissions. However, many existing systems in Austria are not designed for a significant share of alternative heat sources which are fluctuating and/or decentral and/or have a low temperature level. Weaknesses of current business models Typical business models for urban and rural DH-operators in Austria are shown in Figure 1 and Figure 2 (black print). They are based on “classical” heat distribution to the customer: heat is produced and delivered to the customers without a deep customer relationship. Moreover, the contracts are usually rigid and don’t have many degrees of freedom for the customers. Having fixed and variable prices (consumed energy) is the most used tariff system of DH operators in Austria. Due to (mostly) high fixed prices, customers do not see too much financial incentives for energy savings or optimization of their heating system. Although DH operators see their customers as key partners, they actually do not play a big (active) role in existing business models. Further on, DH network operators rely mainly on high temperature supply units. This is a barrier for lower system temperature and in turn prevents the transition towards the 4th generation. As a consequence, far-reaching changes (technical-ecological structural transformations) are necessary for suitable future business models in order to make greater efforts to meet customers' needs and increase the system efficiency.

Figure 1: Typical business model for an urban DH-network in Austria (presentation form: Business Model Canvas; picture source: Stratego), the new elements of the business models are red underlined

Introducing innovative elements Within the STRATEGO project a coaching scheme was implemented for the two largest cities in Austria (Vienna and Graz) and two small biomass-based rural DH networks being representative for many others. In multiple coaching sessions together with Swedish partners, side visits and national workshops with local stakeholders as well as meetings with national authorities, different solution options for tackling selected key challenges in Austrian DH networks have been developed. In this framework, following innovative elements for business models in a) urban and b) rural networks have been discussed (new elements are printed in red colour and are underlined in Figure 1 and Figure 2): a) Urban district heating networks: Although many urban district heating operators have their focus already on providing their customers different services and packages, the existing business models lack of financial benefits and incentives for reducing the network temperatures, integrating alternative heat sources and increasing the flexibility. Possible new elements include: Figure 2: Typical business model for a rural DH-network in Austria (presentation form: Business Model Canvas; picture source: Stratego), the new elements of the business models are red underlined



b) Rural district heating networks: Many small DH networks struggle with profitability, especially during summer when the operation is inefficient due to high heat losses due to high network temperatures. Possible new elements include: • Network optimisation (Figure 2: Value Proposition 4 ): Onemain reason for high return temperatures are faults at the substations on the customer side due to inappropriate installations and operation. Very often, planners and installers (Figure 2: Key Partnerships 1 ) of district heating networks in rural areas are not aware of the requirements of DH networks in connection with the installation of the secondary side respectively the consequences if they are not fulfilled. Therefore, workshops (Figure 2: Value Proposition 4 ) are planned to integrate the relevant stakeholders at an early stage to show them the importance of the customer side . In addition, the cooperation between different DH networks should be strengthened for knowledge transfer (Figure 2: Key Activities 2 ). Final remarks For the implementation of innovative elements in the current business models, additional efforts are required. This is including an integrated cost-benefit analysis in order to evaluate the feasibility of the new elements and strategies for the transformation of the current business model. Here, major barriers are the organizational structures and philosophies of many companies as well as regulatory conditions and the market design in which the business model is implemented. However, following approach for developing innovative elements of business models supporting future proof district heating networks can be described: • Motivate the stakeholder to think “out of the box” and allow also new and creative ideas (e.g. show international best practice examples) • Involve key partners, local stakeholders and possible new actors (such as energy contractors) to develop new business models for creating a win-win situation • Identify the needs of the customers and allow them to take part in the development process • Deliver a sound concept featuring economic and ecologic advantages and at the same time addressing technical and non-technical barriers Acknowledgement This work is a result of the STRATEGO project, supported by the Intelligent Energy – Europe (IEE) programm (Contract N°: IEE/13/650/SI2.675851).

Waste heat from data centres and industrial processes (Figure 1: Key Partnerships 1 ): For the integration of alternative heat sources into district heating networks, data centres offer a high potential especially in larger cities. In Vienna, about 1 – 2 new data centres per year were built in the last ten years and the waste heat could be used to feed into the DH network or supply to new development areas . Reducing system temperatures (Figure 1: Value Proposition 4 ): The long term structure of the current heat delivery contracts is a main barrier for modifications on the building side. As a consequence, customer contracts should be continuously adapted to lower temperatures if possible e.g. in new or renovated buildings. Also the compliance of the customers to the prescribed return temperatures will be more strictly pursued. Special services (Figure 1: Key Activities 2 ): The largest customer should get a service which includes analysing heat consumption (load profile), energy savings, measures for reducing the return temperature, shaping / flattening peak loads to harmonize the profile, etc. New tariff models (Figure 1: Revenue Streams 9 ) • Flexible tariff: Flexible tariffs could be offered for better addressing the customer needs and to give them possibilities to influence their heating costs. New tariff models could be time dependent (e.g. daily and seasonal variations) or include a bonus/malus systems, i.e. customers could get a financial bonus for lower return temperatures. However, flexible tariff are at the current status not so easy to implement because of the Austrian weights and measures act and very often, high quality heat measurement systems with remote access are not yet extensively implemented. • Alternative energy tariffs: New tariffs for alternative heat supply (e.g. solar thermal, heat pump, etc.) should be offered to the customers. The customers have the chance to select their own “green” heat supply through deciding between different energy sources with different prices. Similar models already exist for several years for electricity tariffs, e.g. “Ökostrom”. Experience shows that some customers are willing to pay higher energy bills for a more sustainable supply. • Experience from Sweden in implementing new tariff models shows: The level of acceptance depends upon 1) the precision of the communication and 2) the outcome for the specific customer. Here, following customer requirements need to be considered:

• pay for what they consumed (variable costs) • transparency and easily understandable pricing • feel monetary effects from energy efficiency and energy saving

For further information please contact:

AIT Austrian Institute of Technology GmbH Giefinggasse 2 1210 Vienna, Austria Att.: Roman Geyer Phone: +43 50550-6350

New financing and contracting solutions (Figure 1: Key Resources 3 ): For developing and implementing new business models, specialists from law, financing, contracting and other frameworks are needed.

Att.: Ralf-Roman Schmidt Phone: +43 50550-6390

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thermal storage in individual houses. The rationale for heat and electricity sector integration in a district heating system therefore is remaining but should change in character in a transition from a fossil- to a renewable energy based energy supply system. (Lund, Mathiesen, et al. 2014). However, if these technical and economic potentials should be realized across the European continent, it would require changes in politics and regulation. It is of especial importance, as fluctuating renewable energy sources are continuously expanding, to look at the balance between investment in international interconnectors between neighboring electricity sectors and the investment in local/regional/national integration of the fluctuating renewable energy based electricity into its neighboring heat (and cooling) sector. The European Union already has policies and institutions that financially support investments in international interconnectors between neighboring electricity sectors. What is still lacking is a materialization of the newly developed political awareness of heating and cooling into changes in policies that sustain the development of the heating and cooling sectors as an integrated part of the European energy policy. In this article, we will point out some concrete policy structures that do not support an efficient allocation of investments. These structures have in common that they disfavours electricity-to-heat integration in district heating systems and subsidizes electricity-to-electricity integration. If these issues are not addressed politically, they may severely weaken the prospects of a cost efficient European energy system based upon increasing amounts of fluctuating renewable energy sources. Four instances of distortive regulation Change and adjustment of policies are probably necessary at many levels and further research should be conducted on this issue. In the following, we highlight four identified regulative focus points which are important for a cost-efficient development of the European electricity and heat supply.

District heating is not only here to stay but should expand and change in a European energy future. But it requires changes in policies and regulation to realise the huge potentials of district heating infrastructure across the continent. A failure to meet the required changes would imply a less green and a less cost efficient common European energy system. European potentials of district heating In these years, a lot of interesting research and development is happening around the district heating sector. At the same time, international political awareness of the importance of the heat and cooling sector is on the rise. In February 2016, the EU commission released its first heating and cooling strategy. Meanwhile, the Heat Roadmap Europe studies conducted by Danish and Swedish researchers have demonstrated large potentials for district heating infrastructure across Europe. In the perspective of a European Energy Union, it therefore has important economic and environmental perspectives to integrate district heating infrastructure in the policy goals as well as in the regulation. Traditionally, the competitive edge of district heating has been the high fossil fuel efficiencies associated with combined heat and power production, as well as utilization of waste heat from industries. The amount of heat wasted from these sources across Europe are currently larger than the total heat demand in buildings (Connolly 2016). In the transition to a renewable energy supply, district heating infrastructure will continue to play a vital role for the efficiency of the total energy system. Questions about how district heating should change to create most value for a renewable energy system has been addressed in the 4DH research project (Lund, Werner, et al. 2014). A district heating system adjusted to the demands of a renewable energy supply has been termed 4th generation district heating (4DH). This concept entails, among others, lower distribution temperatures that would further enhance the supply of climate friendly heat sources. Likewise, a close integration with fluctuating electricity supply has shown to be of high environmental and economic value. Combined heat and power generation will in the long run be downsized as all thermal electric capacity based on fossil fuels are phased out. Meanwhile, district heating can (and should) retain its competitive edge by absorbing excess electricity from the steeply increasing share of fluctuating renewable energy sources. This can be accomplished in district heating systems with high efficiencies through a combination of large scale heat pumps and large thermal energy storage units. These storage units are 20-80 times cheaper per MWh storage than

National taxation schemes. Do national tax policies support an economic and fuel efficient development?

There are large synergies to be achieved through cross- sectoral integration in a situation where primary energy supply is dominated by increasing shares of fluctuating resources. However, it is determining for the energy systems' overall efficiency that tax structures support this cross sectoral integration. In aEuropeanperspective, it is important tobe aware



international integration, these distortions may be further enhanced through the European subsidy programmes. For example, at the same time as the Danish state prevents electricity-to-heat integration through high taxes, the European Union subsidises electricity-to-electricity integration. This results in a double process of distortion between local and national integration of heat and electricity and investments in international electricity interconnectors. An efficient European energy system would need both integration measures but the ability to strike the right balance requires changes in the overall pattern of subsidy and taxation programmes across Europe. arconsunmark. com

that national distortions may result in international spill-overs as energy is traded through international interconnectors in the electricity system. Studies into individual countries thus always entail an international perspective. For example, a country study into the Danish energy taxation structure has shown significant barriers to electricity-to-heat integration (Hvelplund & Djørup 2016). In the long term, this distorting taxation policy will necessitate larger investments in international interconnectors. The investments in international interconnectors and volume of international electricity exchange thus result in a non-optimal balance between investments in local heat and electricity integration and international interconnectors. The tax barriers for heat-to-electricity integration also prevent the district heating sector from innovating itself into a new competitive position. This position should be based on development of new technologies such as, in the Danish case, fluctuating renewable energy sources, heat pumps and thermal storage units: A combination of technologies which over a period of time should replace the hitherto fossil fuel and CHP based district heating system that is constantly losing markets shares in the electricity exchange due to the competition from wind and solar power. European subsidy schemes. At present, the European infrastructural subsidy schemes are directed towards electricity- to-electricity integration only.

Electricity grid tariff schemes. Do the applied grid tariffs provide the right price signals for the long-term development?

The financing of electricity grid expansions through the tariff structure may entail dynamics that cannot sustain a long term efficient development of the energy system. The problem with the electricity tariff structures is precisely that they historically have been designed for the development of the electricity system and not the development of the energy system. For example, current expansion in the capacity to trade electricity between Scandinavia and central Europe is financed by electricity consumers through a general rise in grid tariff so all electricity consumption finances the costs of cross-border

While the national taxation schemes might not have adjusted to sustain an allocative balance between local, national and



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Furthermore, the allocation of electricity system capacity costs through the way grid tariffs and feed-in tariffs is organised, incites long distance electricity trade at the dispense of short distance cross-sectoral integration. We thus have a governance system that hampers an optimal balance between investment in, on one hand, systems for the integration of heat and electricity and, on the other hand, investments in power transmission lines. The results of this distorted market are welfare losses and growing problems with integration of increasing shares of fluctuating renewable energy technologies. Therefore, there is a need for a set of new policies. The main goal of these policies is to establish a situation where local and regional integration of heat and electricity have equal competition conditions with electricity-to-electricity transmission lines. In the Danish case, these policies could be: A) A tax reform, where tax on wind and solar electricity for heat and cooling are at the same level or slightly lower than present taxes on biomass energy. B) A “user charge” for transmission services that includes the full costs of the marginal transmission service demand so that it competes with local infrastructure solutions. At the European level, C) If EU subsidises investments in transmission lines, similar subsidies for a district heating infrastructure with capacity for integration of fluctuating energy sources should be established. Furthermore, D) it should be recognised by the European Commission that the effect on electricity exchange prices from renewable resources necessitates a supplementing mechanism that internalises capacity costs in the international electricity trade. If capacity costs are not included in the transactions, economic misallocations will be the result. If the European energy system should develop fuel and cost efficiently, the European energy policies must at least provide a ‘plain field’ for the competition between different infrastructure solutions. The research shows that district heating is an important infrastructure that should play a central role in the European aspirations. With the recent heating and cooling strategy, the European Commission is starting to show an eye for this. However, if the European citizens are to enjoy the full potentials of district heating, the dawning attention for the district heating sector should develop into an integrated part of the concrete energy sector regulation. It requires deeper and concrete changes in old policies to adjust the energy system to the new visions.

electricity trade ( 2015). This means that short distance trade finances long distance trade. The full costs associated with international long distance electricity trade are therefore not internalised in the market. The investment costs in electricity grid expansion that the financial transactions in the electricity exchange necessitates therefore becomes an externality. An externality which for example may be held by electricity-to-heat consumers. This mechanism is thus a clear example of the in-built electricity sector bias which characterises theenergy systemwhen assessed in an international perspective. Dynamics between national feed-in tariffs and international electricity trade. Are the full costs of energy production fully internalised in the international energy trade? And to what extent are the electricity exchange price signals able to optimise allocation of energy? A further distortive mechanism is happening through the separation of capacity costs and energy markets. A lot of European countries are financing the built-up of (primarily) renewable electricity production capacity through feed-in tariffs. In Denmark, these capacity costs are currently placed on the electricity bill which must be preferable from an economic point of view. Some other countries have placed these costs on the state budget, which means that electricity production is subsidised and therefore the incentive for energy efficiency is weakened at a national level. When electricity is traded across borders, it is done so at the basis of the spot market prices which only reflects the short term marginal costs. In the long term, the short-term marginal costs of electricity production are pressed towards zero as wind power and photovoltaics replace thermal electricity generation. This development in spot market prices produces a long-term necessity of supplementing mechanisms that can finance production capacity; i.e. the long- term production costs. But while energy is traded internationally on basis of short term costs, national electricity trade includes the long-term costs; that is, market prices plus feed-in tariff. Electricity trade across borders are therefore structurally under- financed under the present regulation. A less efficient heating sector abroad thus gets access to below- cost imported energy while the domestic heating sector must pay the full costs of electricity production from nearby wind turbines. If the underlying national structures are not in place, international energy trade risks not to contribute with efficiency gains, as it should, but instead provides an international, European wide sub-optimisation. Summarising This transition from a district heating system based on fossil fuel CHPs to a system supplied by increasing shares of fluctuating renewable energy meets a set of institutional barriers. In the Danish case, high taxes on electricity (from wind turbines) for heat in combination with subsidies for transmission lines are pushing the system towards long distance electricity trade.

For further information please contact:

Aalborg University Att.: Søren Djørup or Frede Hvelplund Sustainable Energy Planning Department of Development and Planning

Skibbrogade 5 DK-9000 Aalborg



Jan Eric Thorsen, Director, Danfoss Heating Segment Application Centre, Oddgeir Gudmundsson, Director Projects, Andre Hansen, Director Applications & Technology, Danfoss GmbH

Introduction Transforming the energy system towards a sustainable system based on a high share of often fluctuating renewable sources is a challenge. At the same time, building energy consumption is being reduced by energy renovations, which puts up challenges for the sustainability of traditional district heating (DH) systems. The district heating concept in general holds the key to address the fluctuating nature of renewables. To allowmaximal utilization, traditional DH temperature levels need to be reduced, which conveniently also solves the challenge of reduced energy demand in buildings. This development path is characterized as the 4th generation DH system. But how does this development path look and what can be learned from the transitions between older DH generations in order to manage the transition toward the 4th generation more efficiently? This article addresses some of the main learnings from the past transformation processes in order to advice on strategies towards the 4th generation. The generations of DH DH goes quite some years back. During the years, it has developed to fulfill the demands as they came up, e.g. the demand for reduced investment and heat costs, lower equipment space demands, and concerns of energy efficiency. Four generations are lined out, each indicating major changes in the technology. The main characteristic of the first generation DH systemwas the heat carrier of steam. Steamwas the obvious choice since electric motors were not yet available for more long-distance hot water distribution. The consumer groups were small urban industries using steam in their processes and large heat consumers such as hospitals and big residential complexes. Additionally, steamwas considered as a good heat carrier due to its high heat content. Furthermore, it was available from e.g. boilers or steam power plants, which did not run in a condensing mode and hence had high temperature steam available. This was when the concept of CHP was brought into operation. The first steam-based systems where built in the USA in the 1880s and became the normal DH design until 1930. Soon, the disadvantages of steam-based systems, including the high investment and operation costs, requirements for complex condensate system, and high heat losses due to high operating temperatures, became apparent.

The main characteristic of the 2nd generation DH system is heat transported by pressurized super-heated water at temperatures above 100°C. This is a significant difference compared to the 1st generation DH systems. By moving from steam, a number of benefits were achieved, for example: • Higher electrical efficiency of condensing heat plants. • Return water was easily returned and the low-grade energy in the return water was further used. • Better energy quality and energy usage match. • Simple to build and operate the system, even under varying load. • Simple way of metering heat consumption. • Large-scale thermal storage became possible, decoupling demand and supply. • Reduced risk and consequences in case of leakages. The 2nd generation DH was dominating in DH systems until the 1980s. The distribution network typically consisted of two steel pipes, a flow pipe and a return pipe. Another difference to the 1st generation steam based system was the centrally placed circulation pumps providing sufficient head to drive the water through the distribution network and allow heat extraction at the consumer site. Large pumps were available for the 2nd generation systems, leading to the situation that steam pressure based water circulation was not a precondition for DH systems anymore. The main benefit of the 2nd generation DH system compared to the 1st generation DH system is the increased energy efficiency due to lower operating temperatures and reduced risk and consequences in case of leakages. Furthermore, the challenges related to the corrosive condensate experienced in the 1st generation were eliminated.

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In the future, a higher focus will be on utilizing low grade renewable and waste heat sources to a larger extend. A common denominator for renewable low grade heat sources is that they tend to be difficult to access on a building level, either due to location, required investments or in general the economy of scale factor. To overcome the issues with both utilizing the low temperature renewable heat sources and the reduced heat demand of buildings, the DH networks can take advantage of the low-energy buildings and operate at even lower supply temperatures than commonly applied for 3rd generation DH systems. The reduced supply and return temperature not only increases the efficiency of the system but also increases the flexibility of the DH system towards potential new heat sources and towards the whole energy system.

The key characteristic of the 3rd generation DH system is the material and labor lean components applied combined with lower temperatures. The components consist of pre-insulated pipes buried directly into the ground and fixed without expansion loops, prefabricated compact substations, the use of compact brazed stainless steel plate heat exchangers and the use of material lean components such as combination valves. The 3rd generation DH is also referred to as the “Scandinavian” DH technology, since it was mainly driven by suppliers based in Scandinavia. Pressurized water is used as heat carrier, typically operated at temperatures below 100 °C. The 3rd generation DH was introduced in the 1970s and has been applied in almost all new schemes and renovation projects from approximately 1980. The motivation for this generation was the increased focus on lower construction cost and energy efficiency, e.g. triggered by the oil crises in the 1970s. Related factors were the security of supply aspect, where alternatives to oil found their way into the energy system. This included e.g. biomass and waste incineration. As a direct consequence of the oil crisis, CHP in Denmark became mandatory and was applied in many other countries as well. This boosted the deployment of DH heavily. The fuel mix has been altered by feeding in greener and renewable sources. The 3rd generation has made a huge contribution, and still has enormous potential, towards fulfilling the political energy goals. Currently, most DH schemes are 3rd generation systems starting a transition to the 4th generation to enable a future non-fossil and renewable based energy system. To meet these demands, existing DH schemes will develop towards focusing more on the integrated energy system, including buildings and integration of low quality fluctuating renewable and surplus energy sources. DH has to be seen as an integrated part of the future smart energy system, including district cooling, electricity and gas grids as well as buildings HVAC systems. A graphical comparison between the four generations of DH concepts / technology is shown in figure 1.

Low temperature DH cases in Denmark – example of 4th generation DH

A number of pilot projects have been made supplying existing and new low-energy buildings with low-temperature DH. One example is the DH system in Lystrup/Denmark. 41 row house flats are successfully supplied with 50°C DH without decentralized boosting of the temperature. The concept is to apply instantaneous domestic hot water heat exchangers with sufficient thermal length to be able to produce 47°C domestic hot water at a supply temperature of 50°C while they still have a low primary return temperature. For the heating circuit radiators were installed with sufficient area for operating at 50°C supply temperature at design load. The target was to operate the heating system at a primary temperature set of 50/25°C.

Figure 2: Low-temperature DH supply for an area in Lystrup/Denmark.

The outcome of the project was very positive with a thermal distribution loss of 17%, which is to be considered low, given the

design energy consumption of 6 MWh/year/flat. A contributing factor was the design of the DH network, which was designed for media speeds up to 2 m/s and the pressure head of 6 bars for the 766m trench length. In case normal design rules and temperature levels were applied, the thermal distribution loss would have been around 40%.

Figure 1: Illustration of the concept of 4th Generation DH in comparison to the previous three generations



at the time of usage. Hereby, only a small volume of domestic hot water is held up in the pipes, leading to a higher level of hygiene e.g. in relation to bacteria growth, such as Legionella. As can be seen from figure 4, the concept reduces the number of distribution pipes in the building from five to three compared to the traditional distribution system.

Another example is an existing house area located in Sønderby/ Denmark. The area includes 75 one family houses built from 1997. Before the system renovation, the houses were equipped with domestic hot water storage tanks which were not adequate for low temperature operation. The renovation included new substations including instantaneous heat exchangers for domestic hot water preparation with long thermal length, replacement of the DH distribution pipe network and supply to the area from the existing DH network return pipe. The houses were equipped with floor heating operating at maximum 40°C, fitting well to the low temperature operation. The results showed that it was possible to operate the system at a supply temperature of 55°C, reducing the thermal distribution loss from 41% to 14%. The area was supplied from the existing DH network area return line to the maximum extent possible.

Figure 4: Traditional solution and flat station solution. Heat source can be DH.

A major benefit of the flat station concept is that it makes multi- apartment buildings suitable for operation at low DH supply temperatures, due to the reduced risk of bacteria in the domestic hot water system. The flat station concept is also a good option when renovating older buildings, leading to energy savings due to reduced hot distribution pipes and better match between supply and demand. Discussion The main challenge looking forward is the reduction of DH net temperatures. Looking historically on the temperatures, they have been going downwards and it is a matter of continuous focus and efforts on the short and long term. On the short term, monitoring of the building energy meter regarding weighted return temperature is relevant and widely applied. This temperature is the basis for a bonus system, motivating reduced return temperatures. In case the surface of the radiators is not sufficient for obtaining a low return temperature, the most exposed radiators can be replaced with larger ones. Investigations have shown that for a normal Danish one-family house from 1970, only 8,1% of the heating season duration the radiators need supply temperatures higher than 55°C. In case of installed new windows, this is reduced to 1,8%. In general, the radiator sizing should be sufficient for most of the season. For the preparation of domestic hot water it is a matter of the thermal length of the installed heat exchanger; in case this is not sufficient it can be replaced with a suitable one. By starting already today specifying heat exchanger with long thermal length, the DH system is made ready for reduced supply temperature once the time comes for low supply temperatures.

Figure 3: Low-temperature DH supply for an area in Sønderby/Denmark (75 houses).

The main learnings from the low temperature DH demonstration projects are: the network must be carefully designed to reduce distribution heat losses. This includes specifying pre-insulated DH pipes of a high insulation class and overall optimizing the pressure head utilization in terms of high media speeds. On the building level, the substation should be pre-insulated and domestic hot water should be prepared by instantaneous heat exchanger with a long thermal length. Besides this, the control valves should include automatic hydraulic balance, e.g. by means of combination valves. Hereby hydraulic balancing of the DH network is secured. The cases above focus on one-family houses/row houses. In case the buildings are multi-family houses, the concept of flat stations can be applied. The concept is to have a substation in each apartment, where fresh domestic hot water is prepared

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losses of the DH network and a higher utilization of the plants. The concept of low temperature DH in combination with renewable heat sources can be an important player for meeting the goals of limiting greenhouse effects set forth at the COP21 meeting and a feasible way towards achieving the future sustainable renewable energy system.

In the longer run, building energy renovations, like replacement of windows and typically insulation of ceilings, lead to a reduced energy consumption, allowing reduction of the DH net temperatures from the perspective of energy capacity. Anyhow, low temperature DH focuses on the general temperature level, but increasing the temperatures in the network when the ambient is very cold is an obvious option to optimize the network investment and operational costs. Conclusion 4th generation DH is an important step leading to increased efficiency of the system, including reduced thermal distribution

For further information please contact:

Danfoss A/S Att.: Andre Hansen, Jan Eric Thorsen, Oddgeir Gudmundsson Nordborgvej 81 DK-6430 Nordborg

Phone +45 7488 2222

It is hardly a secret that the sun does not always shine in Denmark. That is why the construction of a seasonal thermal store, where the energy can be deposited until needed, is valuable. On sunny days, the heat is absorbed in water in a pit and saved for district heating consumers to use during autumn and winter. This 200-million- litre/5.3-million-gallon pit, the largest in the world, has been designed for Vojens District Heating by Ramboll.


See how solar heating builds resilience at




By Construction, Environment and Energy Director Hans-Henrik Høg, Municipality of Albertslund and Chief Project Manager Theodor Møller Moos, COWI A/S

The residence is made ready for low-temperature district heating by installing a radiator with double wall.

Albertslund is a district heating town District heating is firmly established, and has been an essential part of Albertslund’s DNA since the 1960s and 70s, but it has always moved with the times. The district heating was initially based on oil. In the late 1980s, a transmission network was established in Greater Copenhagen to use surplus heat from the big central combined heat & power plants – CHP plants - and waste incineration plants. Together with a user group, the authorities in Albertslund have been working constantly since 1980 to improve the service and implement many energy-saving measures. Among other things, these have resulted in individual metering and incentive/ cooling tariffs. Green Accounts have been drawn up, including ‘Small Green Accounts’ for each residential district. In 2008, Albertslund adopted an energy-saving action plan based on a national order on fixed annual energy-reduction requirements. The plan was drawn up to support local energy savings only. In return, providers receive a generous subsidy per MWh saved. Each year, the municipal council adopts a new, revised plan with targeted actions towards Albertslund Forsyning’s energy-saving efforts for the city’s homes, businesses and public institutions, including the development of the ‘Albertslund concept’ (a wide- ranging development and demonstration project in Albertslund) with renovated show homes in the residential districts. The producer is running internal projects to develop the metering system, renovate the pipe network and optimise district heating delivery from the CHP plant and the VEKS transmission system, as well as conducting energy-saving campaigns and providing energy advice.

After a successful phase 1, Albertslund is now moving on to the next phases, in which around 1,500 homes will be converted. Albertslund has now also decided that the whole city should switch to low-temperature district heating by 2026. In Albertslund (a suburb of Copenhagen, DK, built in the 1960s), a large renovation programme is underway. The aim is to energy-renovate the city’s homes and other properties and to convert the existing 90° C district heating network to a new 4th generation (4DH) system with low-temperature district heating. Phase 1 covered 544 dwellings; it started in 2013 and finished in 2015. The project was described in Hot Cool 1/2015 in the article ‘Low-temperature district heating is a reality’. The 544 homes in Albertslund South have now been thoroughly renovated and their residents have moved back in. The results are right up to expectations: heat demand has fallen by around 57 %, and the homes are supplied with district heating at a supply temperature of 50-55° C, while the return temperature is in the region of 30-35° C. Hot tap water is produced via district heating units (flat stations) in the individual homes. The users are happy to have moved back into their light and friendly homes, and are finding them warm and cosy. Therefore, it seems the low-temperature heat supply is working without any problems. The BO-VEST Housing Association and Albertslund Forsyning (the energy supplier) have now launched the next phases, which involve energy-renovating around 1,500 homes; these are either in progress or at the planning stage. The projects are building on the good experience gained from phase 1; for example, an external equipment box is being installed on the front of the building to accommodate all the new technical installations (ventilation with heat recovery, flat station for hot water, and connections for tap water, district heating, electricity and cabling). The design parameters for the low-temperature district heating are unchanged.

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