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Article Technical paper

Title TitleDistribution of : 4th Generation

Jan Eric Thorsen, Oddgeir Gudmundsson, Marek Brand, Anders Dyrelund Author(s), Danfoss Published at ...

districtenergy. danfoss.com www.danfoss.com Jan Eric Thorsen, Oddgeir Gudmundsson, Marek Brand, Danfoss District Heating Application Centre, Anders Dyrelund, Senior Market Manager , Romboll, Denmark

Distribution of district heating: 4th Generation

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 demand for reduced investment and heat costs, but also lower equipment space demands, concerns of energy efficiency, environment, longer life-time, and lower fire risks. The development has been categorized in 4 generations which each indicate major changes in the technology. Currently most 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 . To meet the demands of the future energy system, existing DH schemes will develop into the next generation, the 4th and the most advanced generation with more focus on the integrated energy system including buildings and integration of low quality fluctuating sources and surplus heat. The intention of this series of articles is to describe the typical principles of each generation and discuss the motivation behind each generation and the main development drivers.

The fourth generation In the future a higher pressure will energy and cost effective solution for Transforming the energy system be on utilizing low grade renewable the overall energy system. Considering towards a sustainable system, based and sources to a larger the energy flexibility each sector on high share of fluctuating renewable extend. A common denominator for brings into the system will be a central sources for heating and cooling, and renewable low grade heat sources is mindset for the future. The energy at the same time reduced specific that they tend to be difficult to access flexibility is especially important due building energy consumption as well on a building level, either due to to the common intermittent nature of as supply and return temperatures, location, required investments or in renewable sources and in this respect calls for further development of general the economy of scale factor. To short and long term energy storage the DH and cooling concept. This overcome the issues with both utilizing become important. development path is characterized as the low temperature fluctuating the 4th generation DH. sources and the Sources of energy The concept of DH has to be seen reduced heat demand of buildings The concept of DH allows utilizing any as an integrated part of the future the district heating networks can take kind of thermal energy, including CHP, smart energy system, including advantage of the low-energy buildings surplus heat from industry, heat from also , electricity and operate at even lower supply waste to energy, geothermal, solar and gas grids as well as buildings temperatures than commonly used thermal and fluctuating electricity rd HVAC systems. The technology of today or applied for 3 generation via heat pumps and electric . DH must develop and be flexible DH systems. The reduced supply and Besides this, the process of converting to effectively position DH into the return temperature not only increases e.g. solid fuels into liquid future smart energy system. Even the efficiency of the system but also or gas phase fuels for the transport though some aspects of the 4th increases the flexibility of the district sector produces heat that can be generation DH concept are applied towards potential new also utilized in DH. In Denmark the in existing DH systems today, the heat sources and towards the whole high penetration of wind turbines general implementation or the energy system. have resulted in overproduction period of best available technology of electricity at periods of high is expected to be from year 2020. A Part of smart energy system wind speeds. The short term excess graphical comparison between the A smart energy system can be defined electricity could be absorbed by four generations of DH concepts / as a system where electricity, gas, electric boilers and the general high technology is shown in figure 1. The heating, cooling and transport systems level of wind based electricity could figure illustrates the typical applied in are combined and coordinated be used to supply large scale heat technologies, operational profile of to utilize synergies between them in pumps producing heat for the district each generation and the period of order to achieve an optimal solution heating systems while at the same best available technology. for each sector as well as the most time utilizing heat storages if the heat

2 A AA t A system, steam pipes Pressurised hot-water system Pre-insulated pipes Low energy demands in concrete ducts Heavy equipment Industrialised compact Smart energy (optimum Large ”build on site” stations substations (also with insulation) interaction of energy 200°C Metering and monitoring sources, distribution Temperature and consumption) level 2-way DH

100°C

100°C

50-0°C (70°C)

Energy Future energy Seasonal source heat storage

Large scale solar Biomass Large scale solar conversion d d i i r r g g

g g n

2-way n i i l t Biomass a District o e o h CHP Biomass c

t Heating t c c i Geothermal i r r t t s s i i D D PV, Wave Wind surplus CHP Industry surplus Electricity biomass Cold storage

Heat Heat Heat Centralised storage storage storage district cooling plant CHP waste Steam CHP CHP coal Centralised storage CHP oil CHP oil Industry surplus

Also Coal Coal Gas, Waste CHP waste low energy Waste Waste Oil, Coal buildings Local District Heating District Heating District Heating District Heating Develoment (District Heating generation) / Period of best available technology

FIGURE 1: Illustration of the concept of 4th Generation DH in comparison to the previous three generations production is higher than the demand. cooling systems. One advantage of To compensate for the intermediate Thus combined with the existing CHP such a tank is that it can availability of renewable sources and plants the district heating becomes reduce the maximal capacity by an increasing share of renewable a “very intelligent electric consumer” leveling the daily fluctuation. Another energy for heat and electricity, even responding on the weather conditions. advantage of large storages is that seasonal heat storages can be applied. Geothermal heat at temperature level the electric or heat pumps will For instance, Vojens consumer owned suitable to 4GDH can be accessed in be able to respond on the electricity district heating company in Denmark, most places with 2.000 to 3.500 meters prices and produce the cold or heat at put a 200.000 m3 underground deep boreholes. Currently there are periods of low cost electricity. That is in thermal storage into operation in more than 240 geothermal DH systems particular important in warm climate 2015 to increase the utilization of heat running in Europe. A particularly zones. District cooling with chilled from a solar thermal plant from 20% interesting heat source for DH is district water storages benefits from economy to 50% of the annual heat demand. cooling. By developing DH in symbiosis of scale and is probably the best way to Thereby Vojens DH utility is well with district cooling the heat extracted mitigate brown-outs at e.g. 1 pm due prepared for installation of electric from buildings by the district cooling to many uncontrolled electric chillers. boilers and heat pumps that can system can be used as an heat source for the district heating system, which results in very high efficiency of the cooling heat pump.

Storages Large heat storage tanks were introduced in the second generation of DH and it is a natural vital element in all third generation DH systems. In the fourth generation system, they will be more important and even larger and supplemented with several other types of thermal storages. Large storage tanks can also be designed for cold water for district FIGURE 2: Vojens solar heating plant and the storage pit under construction

3 take advantage of future fluctuating

electricity prices. Summer Cooling inter Elec. Heat In combined DHC systems the Aquifer (ATES) is of special interest, in particular in case it Cooling Heatpump is designed in a system in which the same heat pump is providing: 20 4-10 20 4-10 1) The cooling peak capacity is supplied by the , which replaces the peak load chillers and stores heat in the Hot Cold Hot Cold ground for the heating period 2) The heating peak capacity is supplied by the ground source heat Groundwater pump, which replaces the peak load boilers and stores cool in the ground for the cooling period. FIGURE 3: Aquifer thermal energy storage with heat pump By this four huge benefits are realized: Distribution Regarding DHW, one way to reduce 1. A heat storage of low temperature The introduction of lower supply DH supply temperature is to reduce heat the DHW temperature. However, when 2. A cold storage at low but use full temperatures will at the one hand reducing the DHW temperature special temperature increase the needed flow capacity, considerations should be put on the 3. A district cooling peak plant and but at the other hand also energy hygienic aspect regarding the legionella 4. A district heating peak plant consumption is expected to decrease due to energy renovation of existing bacteria. One way to reduce the risk In case of low temperature consumers buildings and due to lower energy of these bacteria is to minimize the and operation of the DH system at 70°C demands for new buildings. To volume of water in the DHW system during peak demand, the efficiency of overcome the hydraulic bottlenecks and make sure there is no still standing the heat pump will be fairly high. This in the network booster pumps can be water. The best way to achieve this is further reduces the reliance on fossil located decentral in the network to a to use instantaneous heat exchangers based heat sources, which are typically higher extend than applied today. The for DHW preparation, with special supplying the peak demand. benefit of lower supply temperatures is focus on the DHW volume in the The combination of: the reduced thermal distribution losses piping system. For larger buildings this • Efficient HVAC systems for low and the increased integration of low means decentralized instantaneous temperature heat and high grade energy sources. preparation of DHW in each flat by the temperature cold flat station concept. At the same time • DH grids with hot water storages, Building installations and as the system volume is minimized tanks and pits substations it becomes important to use highly • DC grids with cold water storages, The main criteria when it comes to efficient heat exchangers to reduce the tanks and pits the building installation is the ability temperature difference between the • Heat pumps to operate at low supply temperatures supply and the DHW temperatures. • Heat pumps with ATES for space heating and DHW and at • Electric boilers the same time reduce the return • Fast regulating CHP plants temperature. This is especially important • Biomass boilers for existing buildings, which will be has the ability to use huge amounts of the majority of buildings many years electricity when the prices are low and ahead. For energy renovated and avoid using electricity in longer periods new buildings the building heating of high electricity prices – even weeks. installation has to be designed to fulfill This system has the same impact on the requirements. Heating supply the power grid as an electrical battery, temperature below 40°C for floor but at fraction of the cost, even below heating or supply temperature of 50°C one hundredth of an electrical battery. for based space heating could This kind of an innovative idea could be a relevant future demand. In the be called a thermal/electric battery. period of high heat consumption the An obvious next stage is that such supply temperature can be increased. energy efficient and cost effective Studies have shown for Danish one battery will be a driver for extending family houses build in 1970 the supply the DH&C grids to replace uncontrolled temperature for space heating can be FIGURE 4: y-Booster substation installed electricity consumption from small heat as low as 50°C during 79% of the year, in a test house in the Northern pumps, chillers and . without any energy renovation required. area.

4 By introducing the concept of boosting the temperature locally, the temperature link between space heating and DHW preparation can be disconnected and the supply temperature of the DH system can be reduced to the temperature requirement of space heating system. First projects with decentralized electric boosting of the DH supply temperature have been already launched. The temperature can be boosted on the supply side or the FIGURE 5: Low temperature DH supply for an area in Lystrup/Denmark. Construction site and DHW side and the boosting can be area plan. done either by direct electric heater or by a heat pump. Depending on the weather compensator (building supply common situation today, where single- chosen solution primary or secondary temperature is controlled according to purpose organizations are owning and side storage tanks can be applied. the outdoor temperature). operating the systems. The concept of boosting the For the 4th generation DH, the control temperature for DHW is very will not only focus on the static heat Benefits interesting, especially seen in the demand of the buildings but also on DHC systems have an important role perspective of flexible use of heat and the energy flexibilities, e.g. provided to play in the future renewable energy electricity. But also a number of pilot by the passive thermal masses in the system, especially providing the projects have been made supplying building or by a heat storage capacity. capability of integrating intermittent existing and new low-energy buildings The aim is to avoid expensive and renewable and low grade energy with low-temperature DH. One inefficient peak load operation, sources at competitive costs. example is the DH system in Lystrup/ but also to bring the energy flexibilities Further energy flexibility across the Denmark. In Lystrup a group of 41 row in to play when dynamically optimizing energy carriers or sectors have to house flats where successfully supplied the energy system operation across the be integrated, as well as lower heat with 50°C DH without decentralized energy carriers. The intelligent control demands has to be taken into account. boosting of the temperature. will be based on model predictive To meet these demands of the future, The synergies between heating and control principles, where indirect the concept of DHC has to develop. cooling can also be utilized in the incentives like variable prices for The 4th generation DH is outlining building HVAC systems. Central hot energy will be a part of it. a path to go regarding the needed and cold water pipe systems in a development for the future. building can e.g. provide heating in Planning, cost and motivation winter and cooling in summer by structures the same ventilation coils and wall, An important aspect in regards to roof and floor tubes and thereby realizing the 4th generation DH concept improve and return is to ensure suitable planning, cost and temperatures. motivational structures in relation to the operation as well as to strategic Intelligent control investments. Beneficially investments The common way of controlling the could be done by multi-purpose heating system is by thermostatic organizations, able to identify the value radiator valves or thermostatic floor of integrated smart energy systems. heating valves in combination with a This is often in contradiction to the

5 References • Lund, H. et. al. (2014) 4th Generation District Heating (4GDH). Integrating Smart Thermal Grids into Future Systems. Energy 68(2014) 1-11. • Frederiksen, S. Werner, S. District Heating and Cooling , Studentlitteratur, Lund 2013. • O. Gudmundsson, O., Brand, M., Thorsen, J.E, Ultra-low temperature district heating and micro heat pump application – economic analysis. Proceedings of 14th International Symposium District Heating and Cooling, , , 2014. • Brand, M., Thorsen, J.E., Gudmundsson, O., Svendsen, S.,Traditional buildings supplied by low-temperature district heating. Proceedings of 14th International Symposium District Heating and Cooling , Stockholm, Sweden, 2014. • Christiansen, C. H., Dalla Rosa, A., Brand, M., Olsen, P. K., Thorsen, J.E., Results and Experiences From a 2-year Study With Measurements on a New Low-Temperature District Heating System for Low-Energy Buildings. Proceedings of 13th International Symposium District Heating and Cooling , Copenhagen, Denmark, 2012. • Thorsen, J.E., Analysis on Flat Station Concept. Proceedings of 12th International Symposium District Heating and Cooling, Tallinn, Estonia, 2010. • http://www.vojensfjernvarme.dk • www.ramboll.com

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