District heating (less commonly called teleheating) is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating. The heat is often obtained from a cogeneration plant burning fossil fuels but increasingly biomass, although heat-only boiler stations, geothermal heating and central solar heating are also used, as well as nuclear power. District heating plants can provide higher efficiencies and better pollution control than localized boilers. According to some research, District Heating with Combined Heat and Power (CHPDH) is the cheapest method of cutting carbon, and has one of the lowest carbon footprints of all fossil generation plants.[1]
The core element of a district heating system is as a minimum a heat-only boiler station. Additionally a cogeneration plant (also called combined heat and power, CHP) is often added in parallel with the boilers. Both have in common that they are typically based on combustion of primary energy carriers. The difference between the two systems is that, in a cogeneration plant, heat and electricity are generated simultaneously, whereas in heat-only boiler stations - as the name suggests - only heat is generated.
In the case of a fossil fueled cogeneration plant, the heat output is typically sized to meet half of the peak heat load but over the year will provide 90% of the heat supplied. The boiler capacity will be able to meet the entire heat demand unaided and can cover for breakdowns in the cogeneration plant. It is not economic to size the cogeneration plant alone to be able to meet the full heat load.
The combination of cogeneration and district heating is very energy efficient. A simple thermal power station can be 20-35% efficient,[2] whereas a more advanced facility with the ability to recover waste heat can reach total energy efficiency of nearly 80%.[2]
Other heat sources for district heating systems can be geothermal heat, solar heat, surplus heat from industrial processes, and nuclear power.
Nuclear energy can be used for district heating. The principles for a conventional combination of cogeneration and district heating applies the same for nuclear as it does for a thermal power station. Russia has several cogeneration nuclear plants which together provided 11.4 PJ of district heat in 2005. Russian nuclear district heating is planned to nearly triple within a decade as new plants are built.[3]
Other nuclear powered heating from cogeneration plants are in the Ukraine, the Czech Republic, Slovakia, Hungary, Bulgaria, and Switzerland, producing up to about 100 MW per power station. One use of nuclear heat (now closed) generation was with the Ågesta Nuclear Power Plant in Sweden.
In Switzerland, the Beznau Nuclear Power Plant provides heat to about 20,000 people.[4]
After generation, the heat is distributed to the customer via a network of insulated pipes. District heating systems consists of feed and return lines. Usually the pipes are installed underground but there are also systems with overground pipes. Within the system heat storages may be installed to even out peak load demands.
The common medium used for heat distribution is water, but also steam is used. The advantage of steam is that in addition to heating purposes it can be used in industrial processes due to its higher temperature. The disadvantage of steam is a higher heat loss due to the high temperature. Also, the thermal efficiency of cogeneration plants is significantly lower if the cooling medium is high temperature steam, causing smaller electric power generation. Heat transfer oils are generally not used for district heating, although they have higher heat capacities than water, as they are expensive, and have environmental issues.
At customer level the heat network is usually connected to the central heating of the dwellings by heat exchangers (heat substations). The water (or the steam) used in the district heating system is not mixed with the water of the central heating system of the dwelling. In the Odense system direct connection is used.
Typical annual loss of thermal energy through distribution is around 10%, as seen in Norway's district heating network.[5]
Often heat is metered to customers using a heat meter, to encourage economy and maximise the number of customers which can be served, but these are expensive. Many communist-era systems were not metered, leading to great inefficiencies - users simply opened windows when too hot - wasting energy and minimising the numbers of connectable customers. Due to the expense of heat metering, an alternative approach is simply to meter the water - water meters are much cheaper than heat meters, and have the advantage of encouraging consumers to extract as much heat as possible, leading to a very low return temperature, which increases the efficiency of power generation.
District heating systems can vary in size from covering entire cities such as Stockholm or Flensburg with a network of large meter diameter primary pipes linked to secondary pipes - 200 mm diameter perhaps, which in turn link to tertiary pipes of perhaps 25 mm diameter which might connect 10s to 50 houses.
Some district heating schemes might only be sized to meet the needs of a small village or area of a city in which case only the secondary and tertiary pipes will be needed.
Some schemes may be designed to serve only a limited number of dwellings - 20 - 50 - in which case only tertiary sized pipes are needed.
District heating has various advantages compared to individual heating systems. Usually district heating is more energy efficient, due to simultaneous production of heat and electricity in combined heat and power generation plants. The larger combustion units also have a more advanced flue gas cleaning than single boiler systems. In the case of surplus heat from industries, district heating systems do not use additional fuel because they use heat (termed heat recovery) which would be dispersed to the environment.
District heating is a long-term commitment that fits poorly with a focus on short-term returns on investment. Benefits to the community include avoided costs of energy, through the use of surplus and wasted heat energy, and reduced investment in individual household or building heating equipment. District heating networks, heat-only boiler stations, and cogeneration plants require high initial capital expenditure and financing. Only if considered as long-term investments will these translate into profitable operations for the owners of district heating systems, or combined heat and power plant operators. District heating is less attractive for areas with low population densities, as the investment per household is considerably higher. Also it is less attractive in areas of many small buildings; e.g. detached houses than in areas with a few much larger buildings; e.g. blocks of flats, because each connection to a single-family house is quite expensive.
In many cases large combined heat and power district heating schemes are owned by a single entity. This was typically the case in the old Eastern bloc countries. However the majority of schemes the ownership of the cogeneration plant is separate from the heat using part.
Examples are Warsaw which has such split ownership with Vattenfall owning the cogeneration unit, and the municipality the heat distribution. Similarly all the large CHP/CH schemes in Denmark are of split ownership.
One study shows that District Heating with Combined Heat and Power has the lowest carbon footprint of any heating system, and it rapidly competes with extra insulation.[1]
Since conditions from city to city differ, every district heating system is uniquely constructed. In addition, nations have different access to primary energy carriers and so they have a different approach how to address the heating market within their borders. This leads not only to a different degree of diffusion but also to different district heating systems in general throughout the world.
Since 1954, district heating has been promoted in Europe by Euroheat & Power. They have compiled an analysis of district heating and cooling markets in Europe within their Ecoheatcool project supported by the European Commission. The legal framework in the member states of the European Union is currently influenced by the EU's CHP Directive.
Europe has actively incorporated cogeneration into its energy policy via the CHP Directive. In September 2008 at a hearing of the European Parliament’s Urban Lodgment Intergroup, Energy Commissioner Andris Piebalgs is quoted as saying, "security of supply really starts with energy efficiency."[6] Energy efficiency and cogeneration are recognized in the opening paragraphs of the European Union’s Cogeneration Directive 2004/08/EC. This directive intends to support cogeneration and establish a method for calculating cogeneration abilities per country. The development of cogeneration has been very uneven over the years and has been dominated throughout the last decades by national circumstances.
As a whole, the European Union currently generates 11% of its electricity using cogeneration, saving Europe an estimated 35 Mtoe per annum.[7] However, there are large differences between the member states, with energy savings ranging from 2% to 60%. Europe has the three countries with the world’s most intensive cogeneration economies: Denmark, the Netherlands and Finland.[8]
Other European countries are also making great efforts to increase their efficiency. Germany reported that, at present, over 50% of the country’s total electricity demand could be provided through cogeneration. Germany set a target to double its electricity cogeneration from 12.5% of the country’s electricity to 25% by 2020 and has passed supporting legislation accordingly in "Federal Ministry of Economics and Technology", (BMWi), Germany, August 2007. The UK is also actively supporting combined heat and power. In light of UK’s goal to achieve a 60% reduction in carbon dioxide emissions by 2050, the government had set the target to source at least 15% of government electricity from CHP by 2010.[9] Other UK measures to encourage CHP growth are financial incentives, grant support, a greater regulatory framework, and government leadership and partnership.
According to the IEA 2008 modelling of cogeneration expansion for the G8 countries, expansion of cogeneration in France, Germany, Italy and the UK alone would effectively double the existing primary fuel savings by 2030. This would increase Europe’s savings from today’s 155 TWh to 465 TWh in 2030. It would also result in a 16% to 29% increase in each country’s total cogenerated electricity by 2030.
Governments are being assisted in their CHP endeavors by organizations like COGEN Europe who serve as an information hub for the most recent updates within Europe’s energy policy. COGEN is Europe’s umbrella organization representing the interests of the cogeneration industry, users of the technology and promoting its benefits in the EU and the wider Europe. The association is backed by the key players in the industry including gas and electricity companies, ESCOs, equipment suppliers, consultancies, national promotion organisations, financial and other service companies.
The largest district heating system in Austria is in Vienna (Fernwärme Wien) - with many smaller systems distributed over the whole country.
District heating in Vienna is run by Wien Energie. In the business year of 2004/2005 a total of 5.163 GWh was sold, 1.602 GWh to 251.224 private apartments and houses and 3.561 GWh to 5211 major customers. The three large municipal waste incinerators provide 22 % of the total in producing 116 GWh electric power and 1.220 GWh heat. Waste heat from municipal power plants and large industrial plants account for 72 % of the total. The remaining 6 % is produced by peak heating boilers from fossil fuel. A biomass-fired power plant has produced heat since 2006.
In the rest of Austria the newer district heating plants are constructed as biomass plants or as CHP-biomass plants like the biomass district heating of Mödling or the biomass district heating of Baden.
The most older fossil fired district heating systems have a district heating accumulator, so that it is possible to produce the thermal district heating power only at that time where the electric power price is high.
The largest district heating system in the Czech Republic is in Prague owned and operated by Prazska teplarenska, serving 265 thousands households and selling ca. 13 PJ of heat annually. There are many smaller central heating systems spread around the country.<refname=tscr>Association for the District Heating of the Czech Republic</ref>
In Denmark district heating covers more than 60% of space heating and water heating.[10] In 2007, 80.5% of this heat was produced by combined heat and power plants. Heat recovered from waste incineration accounted for 20.4% of the total Danish district heat production.[11] Most major cities in Denmark have big district heating networks, including transmission networks operating with up to 125°C and 25 bar pressure and distribution networks operating with up to 95°C and between 6 and 10 bar pressure. The largest district heating system in Denmark is in the Copenhagen area operated by CTR I/S and VEKS I/S. In central Copenhagen, the CTR network serves 275,000 households (90-95% of the area's population) through a network of 54 km double district heating distribution pipes providing a peak capacity of 663 MW.[12] The consumer price of heat from CTR is approximately €49 per MWh plus taxes (2009).[13]
In Finland district heating accounts for about 50% of the total heating market,[14] 80% of which is produced by combined heat and power plants. Over 90% of apartment blocks, more than half of all terraced houses, and the bulk of public buildings and business premises are connected to a district heating network. Natural gas is mostly used in the south-east gas pipeline network, imported coal is used in areas close to ports, and peat is used in northern areas where peat is a natural resource. Other renewables, such as wood chips and other paper industry combustible by-products, are also used, as is the energy recovered by the incineration of municipal solid waste. Industrial units which generate heat as an industrial by-product may sell otherwise waste heat to the network rather than release it into the environment. In some towns waste incineration can contribute as much as 8% of the district heating heat requirement. Availability is 99.98% and disruptions, when they do occur, usually reduce temperatures by only a few degrees.[15] In Helsinki, an underground datacenter beneath the Uspenski Cathedral will release the excess heat into the homes of the neighbours,[16] producing enough heat to heat approximately 500 large houses.[17]
In Germany district heating has a market share of around 14 % in the residential buildings sector. The connected heat load is around 52.729 MW. The heat comes mainly from cogeneration plants (83 %). Heat-only boilers supply 16 % and 1 % is surplus heat from industry. The cogeneration plants use natural gas (42 %), coal (39 %), lignite (12 %) and waste/others (7 %) as fuel.[18]
The largest district heating network is located in Berlin whereas the highest diffusion of district heating occurs in Flensburg with around 90% market share.
District heating has rather little legal framework in Germany. There is no law on it as most elements of district heating are regulated in governmental or regional orders. There is no governmental support for district heating networks but a law to support cogeneration plants. As in the European Union the CHP Directive will come effective, this law probably needs some adjustment.
With 95% of all housing (mostly in the capital of Reykjavik) enjoying district heating services - mainly from geothermal energy, Iceland is the country with the highest penetration of district heating.
Most of Iceland's district heating comes from three geothermal power plants, producing over 800 MWth:[19]
In Italy, district heating is used in some cities (Bergamo, Brescia, Bolzano, Ferrara, Reggio Emilia, Terlan, Turin, Lodi and now Milan). The district heating of Turin is the biggest of the country and it supplies 550.000 people (55% of the whole city population).
In Norway district heating only constitutes approx. 2 % of energy needs for heating. This is a very low number compared to similar countries. One of the main reasons district heating has a low penetration in Norway is access to cheap hydro based electricity. However, there is district heating in the major cities.
The largest district heating system in Poland is in Warsaw owned and operated by SPEC distributing approx. 34 PJ annually.
The largest district heating system in Romania is in Bucharest owned and operated by RADET distributing approx. 24 PJ annually, serving 570 thousands households. Central heating system of RADET provides 72% of the heat in Bucharest (68% by the means of centralized heating system, 4% from block heating plants).
In most Russian cities, district-level combined heat and power plants (Russian: ТЭЦ, теплоэлектроцентраль) produce more than 50 % of the nation's electricity and simultaneously provide hot water for neighbouring city blocks. They mostly use coal and oil-powered steam turbines for cogeneration of heat. Now, gas turbines and combined cycle designs are beginning to be widely used as well. A Soviet-era approach of using very large central stations to heat large districts of a big city or entire small cities is fading away as due to inefficiency, much heat is lost in the piping network because of leakages and lack of proper thermal insulation.[20]
In Serbia, district heating is used throughout the main cities, particularly in the capital, Belgrade. The first district heating plant was built in 1961 as a means to provide effective heating to the newly built suburbs of Novi Beograd. Since then numerous plants were built to heat the ever growing city.As fuel they use natural gas,because it has less of an effect on the environment.The district heating system of Belgrade possesses 112 heat sources of 2,454 MW capacity and by pipelines more than 500 km long and 4365 connection stations, providing district heating to 240,000 apartments and 7,500 office/commercial buildings of total floor area exceeding 17,000,000 square meters.
Sweden has a long tradition for using district heating in urban areas. The city of Växjö reduced its fossil fuel consumption by 30% between 1993 and 2006, and aimed for a 50% reduction by 2010. This was to be achieved largely by way of biomass fired district heating[21]
90% of the energy in Swedish district heating systems are usually produced with renewable sources . The remaining 10% are only used when the weather is really cold and there is a very high energy demand. Because of the law forbidding landfill , waste is commonly used as a fuel.
In the United Kingdom, district heating became popular after World War II, but on a restricted scale, to heat the large residential estates that replaced areas devastated by the Blitz. The photo (right) shows the accumulator at the Pimlico District Heating Undertaking (PDHU), just north of the River Thames. The PDHU first became operational in 1950 and continues to expand to this day. The PDHU once relied on waste heat from the now-disused Battersea Power Station on the South side of the River Thames. It is still in operation, the water now being heated locally by a new energy centre which incorporates 3.1 MWe / 4.0 MWth of gas fired CHP engines and 3 x 8 MW gas fired boilers.
One of the United Kingdom's largest district heating schemes is EnviroEnergy in Nottingham. Plant initially built by Boots is now used to heat 4,600 homes, and a wide variety of business premises, including the Concert Hall, the Nottingham Arena, the Victoria Baths, the Broadmarsh Shopping Centre, the Victoria Centre and others. The heat source is a Waste-to-energy incinerator.[6] Scotland has several district heating systems with the first in the UK being installed at Aviemore and others following at Lochgilphead, Fort William and Forfar.
Another significant scheme is in Southampton.[22] It was originally built to use geothermal energy, but now also uses the heat from a gas fired CHP generator. It supplies heat to many large premises in the city, including the WestQuay shopping centre, the De Vere Grand Harbour hotel, the Royal South Hants Hospital and several housing schemes.
Many other such heating plants still operate on estates across Britain. Though they are said to be efficient, a frequent complaint of residents is that the heating levels are often set too high - the original designs did not allow for individual users to have their own thermostats.
The largest district heating system in Spain is located in Soria.[23] It is called 'Ciudad del Medio Ambiente' (Environmental Town) and will receive 41MW from a biomass power plant.
In North America, district heating systems fall into two general categories. Those that are owned by and serve the buildings of a single entity are considered institutional systems. All others fall into the commercial category.
District Heating is becoming a growing industry in Canadian cities, with many new systems being built in the last ten years. Some of the major systems in Canada include:
Many Canadian universities operate central campus heating plants.
Consolidated Edison of New York (Con Ed) operates the New York City steam system, the largest commercial district heating system in the United States.[27] The system has operated continuously since March 1882 and serves Manhattan Island from the Battery through 96th Street. In addition to providing space- and water-heating, steam from the system is used in numerous restaurants for food preparation, for process heat in laundries and dry cleaners, and to power absorption chillers for air conditioning. On July 18, 2007, one person was killed and numerous others injured when a steam pipe exploded on 41st Street at Lexington.[28] On August 19, 1989, three people were killed in an explosion in Gramercy Park.[29]
District heating is also used on many college campuses, Including the University of Texas at Austin, which also provides district cooling and can generate all of the electricity used on campus, the University of Notre Dame, Michigan State University, University of Maryland, College Park, which produce over half their own electricity and all of their heating needs from a single plant on their respective campuses. MIT installed a cogeneration system in 1995 that provides electricity, heating and cooling to 80% of its campus buildings.[34] The University of New Hampshire has a cogeneration plant run on methane from an adjacent landfill, providing the University with 100% of its heat and power needs without burning oil or natural gas.[35]
87 district heating enterprises are operating in Japan, serving 148 districts.[36]
Many companies operate district cogeneration facilities that provide steam and/or hot water to many of the office buildings. Also, most operators in the Greater Tokyo serve district cooling.
District heating traces its roots to the hot water-heated baths and greenhouses of the ancient Roman Empire. District systems gained prominence in Europe during the Middle Ages and Renaissance, with one system in France in continuous operation since the 14th century. The U.S. Naval Academy in Annapolis began steam district heating service in 1853.
Although these and numerous other systems have operated over the centuries, the first commercially successful district heating system was launched in Lockport, New York, in 1877 by American hydraulic engineer Birdsill Holly, considered the founder of modern district heating.
Paris has been using geothermal heating from a 55-70 °C source 1–2 km below the surface since the 1970s for domestic heating.[37]
In the 1980s Southampton began utilising combined heat and power district heating, taking advantage of geothermal heat "trapped" in the area. The geothermal heat provided by the well works in conjunction with the Combined Heat and Power scheme. Geothermal energy provides 15-20 %, fuel oil 10 %, and natural gas 70 % of the total heat input for this scheme and the combined heat and power generators use conventional fuels to make electricity. "Waste heat" from this process is recovered for distribution through the 11 km mains network.[37][38]
The future of many of these systems are in doubt. The same kind of problems many district heating operations in former Soviet Union and Eastern Europe have today, many North American steam district heating systems began to experience in the 1960s and 1970s. In North America, the owners (in many cases power utilities) lost interest in the district heating business and provided insufficient funding for maintenance, and the systems and service to customers started to deteriorate. The result was that the systems started losing customers. The reliability decreased and finally the whole system closed down. For example, in Minnesota in the 1950s there were about 40 district steam systems, but today only a few remain.[39]
Penetration of district heating (DH) into the heat market varies by country. Penetration is influenced by different factors, including environmental conditions, availability of heat sources, economics, and economic and legal framework.
In the year 2000 the percentage of houses supplied by district heat in some European countries was as follows:
| Country | Penetration (2000)[40] |
|---|---|
| Iceland | 95% |
| Denmark | 60% (2005)[10] |
| Estonia | 52% |
| Poland | 52% |
| Sweden | 50% |
| Czech Rep. | 49% |
| Finland | 49% |
| Slovakia | 40% |
| Hungary | 16% |
| Austria | 12.5% |
| Germany | 12% |
| Netherlands | 3% |
| UK | 1% |
In Iceland the prevailing positive influence on DH is availability of easily captured geothermal heat. In most East European countries energy planning included development of cogeneration and district heating. Negative influence in The Netherlands and UK can be attributed partially to milder climate and also competition from natural gas supply.
According to Helsingin Energia, consumption of energy by district heating in Helsinki since 1970 peaked in 1971, at 67 kWh/m³/year, falling to 43 kWh/m³/year in 1997, since when it has not fluctuated greatly.[41]
Figures for Sweden suggest that the average Swede using district heating receives 4500 kWh/year from the system.[42]
The opposite of district heating is district cooling. Working on broadly similar principles to district heating, district cooling delivers chilled water to buildings like offices and factories needing cooling. In winter, the source for the cooling can often be sea water, so it is a cheaper resource than using electricity to run compressors for cooling.
The Helsinki district cooling system uses otherwise wasted heat from summer time CHP power generation units to run absorption refrigerators for cooling during summer time, greatly reducing electricity usage. In winter time, cooling is achieved more directly using sea water. The adoption of district cooling is estimated to reduce the consumption of electricity for cooling purposes by as much as 90 per cent and an exponential growth in usage is forecast.[43] The idea is now being adopted in other Finnish cities. The use of district cooling grow also rapidly in Sweden in a similar way.[44]
Cornell University's Lake Source Cooling System uses Cayuga Lake as a heat sink to operate the central chilled water system for its campus and to also provide cooling to the Ithaca City School District. The system has operated since the summer of 2000 and was built at a cost of $55–60 million. It cools a 14,500 tons load.
In August 2004, Enwave Energy Corporation, a district energy company based in Toronto, Canada, started operating a system that uses water from Lake Ontario to cool downtown buildings, including office towers, the Metro Toronto Convention Centre, a small brewery and a telecommunications centre. The process has become known as Deep Lake Water Cooling (DLWC). It will provide for over 40,000 tons (140 megawatts) of cooling—a significantly larger system than has been installed elsewhere. Another feature of the Enwave system is that it is integrated with Toronto’s drinking water supply. The Toronto drinking water supply required a new intake location that would be further from shore and deeper in the lake. This posed two problems for the utility that managed the city's drinking water supply: 1. the capital cost of moving the water intake location and additionally, the new location would supply water that was so cold it would require heating before it could be distributed. The cooperation of the district cooling agency, Enwave, solved both problems: Enwave paid for the cost of moving the water intake and also supplied the heat to warm the drinking water supply to acceptable levels by effectively extracting the heat from the buildings it served. Contact between drinking water and the Enwave cooling system is restricted to thermal contact in a heat exchanger. Drinking water does not circulate through the Enwave cooling systems.
In January 2006, PAL technology is one of the emerging project management companies in UAE involved in the diversified business of desalination, sewage treatment and district cooling system. More than 400,000 Tons of district cooling projects are planned. The Palm Jumeirah utilises district cooling to provide air conditioning.
In 2006, a district cooling system came online in Amsterdam's Zuidas, drawing water from the Nieuwe Meer[45][46]
On the 10th of November 2010, The world's largest district cooling plant opened at The Pearl-Qatar. It is capable of cooling a load of 130,000 tons. [47]
If the other renewable alternatives are too warm during the summer or too expensive, cold storage can be investigated. In large scale applications underground and snow storage are the most likely alternatives. In an underground storage the winter cold is heat exchanged from the air and loaded into the bedrock or an aquifer by one or more bore holes. In a snow storage frozen water (snow and/or ice) is saved in some kind of storage (pile, pit, cavern etc). The cold is utilized by pumping melt water to the cooling object, directly in a district cooling system or indirect by a heat exchanger. The lukewarm melt water is then pumped back to the snow where it gets cooled and mixed with new melt water. Snow cooling works as a single cold source but can also be used for peak cooling since there is no relevant cooling limit.[48] In Sweden there is one snow cooling plant in Sundsvall, built and owned by the county. The cooling load in Sundsvall is about 2000 kW (570 000 tons of refrigeration) and 1500 MWh/year.[49]