District Heating - City Wide Heating And Cooling

District heating (also known as heat networks or 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 also biomass, although heat-only boiler stations, geothermal heating, heat pumps and central solar heating are also used, as well as nuclear power. District heating plants can provide higher efficiencies and better pollution control than localised boilers. According to some research, district heating with combined heat and power (CHPDH) is the cheapest method of cutting carbon emissions, and has one of the lowest carbon footprints of all fossil generation plants. CHPDH is being developed in Denmark as a store for renewable energy, particularly wind electric, that exceeds instantaneous grid demand via the use of heat pumps and thermal stores.

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Heat generation

Heat sources in use for various district heating systems include: geothermal heat; solar heat; industrial heat pumps which extract heat from seawater, river or lake water, sewage, or waste heat from industrial processes; power plants designed for combined heat and power (CHP, also called co-generation), including both combustion and nuclear power plants; and simple combustion of a fossil fuel or biomass.

Geothermal-sourced district heat

United States

Direct use geothermal district heating systems, which tap geothermal reservoirs and distribute the hot water to multiple buildings for a variety of uses, are uncommon in the United States, but have existed in America for over a century.

In 1890, the first wells were drilled to access a hot water resource outside of Boise, Idaho. In 1892, after routing the water to homes and businesses in the area via a wooden pipeline, the first geothermal district heating system was created.

As of a 2007 study, there were 22 geothermal district heating systems (GDHS) in the United States. As of 2010, two of those systems have shut down. The table below describes the 20 GDHS currently operational in America.

Solar-sourced district heat

Use of solar heat for district heating has been increasing in Denmark and Germany in recent years. The systems usually include interseasonal thermal energy storage for a consistent heat output day to day and between summer and winter. Good examples are in Braedstrup and Marstal, Denmark. These systems have been incrementally expanded to supply 10% and 40% of their villages' annual space heating needs. The solar-thermal panels are ground-mounted in fields. The heat storage is, respectively, in a borehole cluster and a pit storage. In Alberta, Canada the Drake Landing Solar Community has achieved a world record 97% annual solar fraction for heating needs, using solar-thermal panels on the garage roofs and thermal storage in a borehole cluster.

Heat pumps for district heat

Perhaps best illustrated by the Drammen Fjernvarme District Heating project in Norway which produces 14 MW from water at just 8 °C, industrial heat pumps are credible heat sources for district heating networks. Among the ways that industrial heatpump can be utilized are:

1. As the primary base load source where a low grade source of heat, e.g. river, fjord, datacentre, power station outfall, sewage treatment works outfall (all typically between 0 ?C and 25 ?C) are boosted up the network temperature of typically 60 ?C to 90 ?C. Such heat pumps, although consuming electricity, will deliver over 3× and perhaps 5× the heat output compared to the amount of electricity consumed. An example of a district system using a heat pump to source heat from raw sewage is one in Oslo, Norway that has a heat output of 18 MW(thermal).
2. As a means of recovering heat from the cooling loop of a power plant to increase either the level of flue gas heat recovery (as the district heating plant return pipe is now cooled by the heat pump) or by cooling the closed steam loop and artificially lowering the condensing pressure and thereby increasing the electricity generation efficiency.
3. As a means of cooling flue gas scrubbing working fluid (typically water) from 60 ?C post injection to 20 ?C pre-injection temperatures. The heat is recovered using a heat pump and sold into the network side of the facility at 80 ?C.
4. In situations where the network has reached capacity, large individual load users can be decoupled from the feed pipe at around 80 ?C and coupled to the return pipe at 40 ?C. By adding a heat pump locally to this user, the 40 ?C pipe is cooled to 20 ?C (the heat being delivered into the heat pump evaporator). The output from the heat pump is then a dedicated loop for the user at 40 ?C to 70 ?C. Therefore the overall network capacity has changed as the total delta T of the loop has changed from 80-40 ?C to 80 ?C-x (x being a value lower than 40 ?C).

A growing concern exists about the use of hydroflurocarbons as the working fluid (refrigerant) for large heat pumps. Whilst leakage is not usually measurable and is likely to be as low as 1% of total charge, a 30-megawatt heatpump will therefore leak (annually) around 75 kg of R134a or whatever working fluid is deployed. Given the high global warming potential of these HFCs this equates to over 800,000 kilometres (500,000 mi) of car travel per year.

However, recent technical advances allow the use of natural heat pump refrigerants that have very low global warming potential (GWP). CO2 refrigerant (R744, GWP=1) or ammonia (R717, GWP=0) also have the benefit, depending on operating conditions, of resulting in higher heat pump efficiency than conventional refrigerants. An example is a 14 MW(thermal) district heating network in Drammen, Norway which is supplied by seawater-source heatpumps that use R717 refrigerant, and has been operating since 2011. 90 °C water is delivered to the district loop (and returns at 65 °C). Heat is extracted from seawater (from 60-foot (18 m) depth) that is 8 to 9 °C all year, giving an average coefficient of performance (COP) of about 3.15. In the process the seawater is chilled to 4 °C; however, this resource is not utilized. In a district system where the chilled water could be utilized for air conditioning, the effective COP would be considerably higher.

In the future industrial heatpumps will be further de-carbonised by using excess renewable electrical energy (otherwise spilled due to meeting of grid demand) from wind, solar, etc. and will have higher efficiencies by operating on the HV high voltage network.

Excess renewable electrical energy for district heat

With European countries such as Germany and Denmark moving to very high levels (80 & 100% by 2050) of renewable energy for all energy uses there will be increasing periods of excess production of renewable electrical energy. Storage of this energy as potential electrical energy e.g. pumped hydro, etc. is very costly, round trip efficiency is reduced and should be minimised. But storage as heat in District Heating for use in buildings where there is demand is significantly less costly. Whilst the quality of the electrical energy is degraded, high voltage grid MW sized heat pumps would maximise efficiency whilst not wasting excess renewable electricity.

District heat from combined heat and power or simple combustion

The core element of many district heating systems is 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, whereas a more advanced facility with the ability to recover waste heat can reach total energy efficiency of nearly 80%. or even exceeding 100% based on the lower heating value

Waste heat from nuclear power plants is sometimes 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.

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 generation was with the Ågesta Nuclear Power Plant in Sweden closed in 1974.

In Switzerland, the Beznau Nuclear Power Plant provides heat to about 20,000 people.

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Heat accumulators and storage

Increasingly large heat stores are being used with district heating networks to maximise efficiency and financial returns. This allows cogeneration units to be run at times of maximum electrical tariff, the electrical production having much higher rates of return than heat production, whilst storing the excess heat production. It also allows solar heat to be collected in summer and redistributed off season in very large but relatively low cost in ground insulated reservoirs or borehole systems.

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Heat distribution

After generation, the heat is distributed to the customer via a network of insulated pipes. District heating systems consist 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 or pressurized hot water, but steam is also 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.

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Heat metering

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 systems were installed under a socialist economy, and these were often not metered. This led 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.

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Size of systems

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 to 10 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.

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Pros and cons

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. This has the added benefit of reducing carbon emissions. 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.

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Ownership, monopoly issues and charging structures

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, for 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 PGNiG Termika owning the cogeneration unit, the Dalkia Polska owning 85% of the heat distribution, the rest of the heat distribution is owned by municipality and workers. Similarly all the large CHP/CH schemes in Denmark are of split ownership.

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Carbon footprint and cost of reduction

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.

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National variation

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.

Europe

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. A separate study, entitled Heat Roadmap Europe, has indicated that district heating can reduce the price of energy in the European Union between now and 2050. The legal framework in the member states of the European Union is currently influenced by the EU's CHP Directive.

Cogeneration in Europe

The EU 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." 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. 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.

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 an 80% 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. 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.

Austria

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.

Most of the 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.

Bulgaria

Bulgaria has district heating in around a dozen towns and cities. The largest system is in the capital Sofia, where there are four power plants (two CHPs and two boiler stations) providing heat to the majority of the city. The system dates back to 1949.^[8]

Czech Republic

The largest district heating system in the Czech Republic is in Prague owned and operated by Prazska teplarenska, serving 265,000 households and selling c. 13 PJ of heat annually. There are many smaller central heating systems spread around the country.

Denmark

In Denmark district heating covers more than 60% of space heating and water heating. 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. 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. The consumer price of heat from CTR is approximately EUR49 per MWh plus taxes (2009).

On the island of Samsø, three straw-fueled district heating plants are used (of which one is owned by the Danish energy company NRGi).

Finland

In Finland district heating accounts for about 50% of the total heating market, 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. Excess heat and power from pulp mill recovery boilers is a significant source in mill towns. 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.

In Helsinki, an underground datacenter next to the President's palace, will release the excess heat into the homes of the neighbours, producing enough heat to heat approximately 500 large houses.

Germany

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.

The largest district heating network is located in Berlin whereas the highest diffusion of district heating occurs in Flensburg with around 90% market share. In Munich about 70% of the electricity produced comes from district heating plants.

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.

Greece

Greece has district heating mainly in the Province of Western Macedonia and the Peloponnese Province. The largest system is the city of Ptolemaida, where there are five power plants (Thermal power stations or TPS in particular) providing heat to the majority of the largest towns and cities of the area and some villages. The first small installation took place in Ptolemaida in 1960, offering heating to Proastio village of Eordaea using the TPS of Ptolemaida. Today District heating installations are also available in Kozani, Ptolemaida, Amyntaio, Philotas, and Megalopolis using nearby power plants.

Hungary

According to the 2011 census there were 607,578 dwellings (15.5% of all) in Hungary with district heating, mostly panel flats in urban areas. The largest district heating system located in Budapest, the municipality-owned F?táv Zrt. ("Metropolitan Teleheating Company") provides heat and piped hot water for 238,000 households and 7,000 companies.

Iceland

With 95% of all housing (mostly in the capital of Reykjavík) 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:

• Svartsengi combined heat and power plant (CHP)
• Nesjavellir CHP plant
• Hellisheiði CHP plant

Ireland

Tralee in Co Kerry has a 1MW district heating system providing heat to an apartment complex, sheltered housing for the elderly, a library and over 100 individual houses. The system is fuelled by locally produced wood chip.
In Glenstal Abbey in Co Limerick there exists a pond-based 150 kW heating system for a school.

Italy

In Italy, district heating is used in some cities (Bergamo, Brescia, Bolzano, Ferrara, Imola, 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).

Norway

In Norway district heating only constitutes approximately 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, and 80% of private electricity consumption goes to heat rooms and water. However, there is district heating in the major cities.

Poland

In 2009, 40% of Polish households used district heating, most of them in urban areas. Heat is provided primarily by combined heat and power plants, most of which burn hard coal. The largest district heating system is in Warsaw, owned and operated by Dalkia Warszawa, distributing approx. 34 PJ annually.

Romania

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).

Russia

In most Russian cities, district-level combined heat and power plants (Russian: ???, ????????????????????) 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.

Serbia

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

Sweden has a long tradition for using teleheating in urban areas. In 2015, about 60% of Sweden's houses (private and commercial) were heated by district heating, according to the Swedish association of district heating. 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 teleheating. Another example is the plant of Enköping, combining the use of short rotation plantations both for fuel as well as for phytoremediation.

47% of the heat generated in Swedish teleheating systems are produced with renewable bioenergy sources, as well as 16% in waste-to-energy plants, 7% is provided by heat pumps and 6% by industrial waste heat recovery. The remaining are mostly fossil fuels oil, natural gas, peat, and coal.

Because of the law forbidding landfill, waste is commonly used as a fuel.

United Kingdom

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. In 2013 there were 1,765 district heating schemes with 920 based in London alone. In total around 210,000 homes and 1,700 businesses are supplied by heat networks in the UK.

The Pimlico District Heating Undertaking (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. The 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. 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.

Sheffield's district heating network was established in 1988 and is still expanding today. It saves an equivalent 21,000 plus tonnes of CO2 each year when compared to conventional sources of energy - electricity from the national grid and heat generated by individual boilers. There are currently over 140 buildings connected to the district heating network. These include city landmarks such as the Sheffield City Hall, the Lyceum Theatre, Sheffield University, Sheffield Hallam University, hospitals, shops, offices and leisure facilities plus 2,800 homes. More than 44 km of underground pipes deliver energy which is generated at Sheffield's Energy Recovery Facility. This converts 225,000 tonnes of waste into energy, producing up to 60 MWe of thermal energy and up to 19 MWe of electrical energy.

The Southampton District Energy Scheme was originally built to use just geothermal energy, but now also uses the heat from a gas fired CHP generator. It supplies heating and district cooling 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.

Lerwick District Heating Scheme is of note because it is one of the few schemes where a completely new system was added to a previously existing small town.

A map of district heating installations can be viewed here.

Spain

The largest district heating system in Spain is located in Soria. It is called "Ciudad del Medio Ambiente" (Environmental Town) and will receive 41MW from a biomass power plant.

North America

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.

Canada

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:

• Montreal, QC has a district heating and cooling system in the downtown core.
• Toronto, ON - Enwave provides district heating and cooling within the downtown core of Toronto, including deep lake cooling technology, which circulates cold water from Lake Ontario through heat exchangers to provide cooling for many buildings in the city.
• Calgary, AB: ENMAX is currently building its Calgary Downtown District Energy Centre which will provide heating to up to 10,000,000 square feet (930,000 m²) of new and existing residential and commercial buildings. Construction of the Calgary Downtown District Energy Centre has begun with commercial operation anticipated for March 2010.
• Vancouver, BC:
  • Central Heat Distribution Ltd. Since 1968 operates a central heating plant in the downtown core of Vancouver, British Columbia. In addition to heating 180 buildings, the Central Heat Distribution network also drives a steam clock.
  • A large scale district heating system known as the Neighbourhood Energy Utility in the South East False Creek area is in initial operations with natural gas boilers and serves the 2010 Olympic Village. The commissioning of an innovative untreated sewage heat recovery system anticipated for January 2010 is expected to supply 70% of annual energy demands and reduce greenhouse gas emissions.
• Windsor, ON has a district heating and cooling system in the downtown core.
• Drake Landing, AB, is small in size (52 homes) but notable for having the only central solar heating system in North America.
• London, Ontario and Charlottetown, PEI have district heating co-generation systems owned and operated by Veresen.
• Sudbury, Ontario has a district heating cogeneration system in its downtown core, as well as a standalone cogeneration plant for the Sudbury Regional Hospital. In addition, Naneff Gardens, a new residential subdivision off Donnelly Drive in the city's Garson neighbourhood, features a geothermal district heating system using technology developed by a local company, Renewable Resource Recovery Corporation.
• Ottawa, Ontario, contains a significant district heating and cooling system serving the large number of federal government buildings in the city. The system loop contains nearly a million gallons of chilled or heated water at any time.
• Cornwall, Ontario operates a district heating system which serves a number of city buildings and schools.

Many Canadian universities operate central campus heating plants.

United States

• Consolidated Edison of New York (Con Ed) operates the New York City steam system, the largest commercial district heating system in the United States. The system has operated continuously since March 3, 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.

The city of Milwaukee, Wisconsin has been using district heating for its central business district since the Valley Power Plant commenced operations in 1968.[9] Amazingly, the air quality in the immediate vicinity of the plant, based on the sensor located on César Chavez Drive, qualifies as the best in Southeastern Wisconsin, at least with regard to ozone concentration. The recent (2012) conversion of the plant, which changed the fuel input from coal to natural gas, is expected to further improve air quality at both the local César Chavez sensor as well as Antarctic sensors [10]. Interesting to note about Wisconsin power plants is their dual use as breeding grounds for peregrines [11].

• Denver's district steam system is the oldest continuously operated commercial district heating system in the world. It began service November 5, 1880 and continues to serve 135 customers. The system is partially powered by the Xcel Energy Zuni Cogeneration Station, which was originally built in 1900.
• NRG Energy operates district systems in the cities of San Francisco, Harrisburg, Minneapolis, Omaha, Pittsburgh, and San Diego.
• Seattle Steam Company operates a district system in Seattle.
• Hamtramck Energy Services (HES) operates a district system in Detroit that started operation at the Willis Avenue Station in 1903.
• Lansing Board of Water and Light, a municipal utility system in Lansing, MI operates a heated and chilled water system from their existing coal plant. They have announced their new natural gas cogeneration plant will continue to provide this service.
• Cleveland Thermal operates a district steam (since 1894) from the Canal Road plant near The Flats and district cooling system (since 1993) from Hamilton Avenue plant on the bluffs east of downtown.
• Fort Chicago Energy Partners L.P. operate district heating/co-generation plants in Ripon, California and San Gabriel, California.
• Veolia Energy, a successor of the 1887 Boston Heating Company, operates a 26-mile (42 km) district system in Boston and Cambridge, Massachusetts, and also operates systems in Philadelphia PA, Baltimore MD, Kansas City MO, Tulsa OK, Houston TX and other cities.
• District Energy St. Paul operates the largest hot water district heating system in North America and generates the majority of its energy from an adjacent biomass-fueled combined heat and power plant. In March 2011, a 1 MWh thermal solar array was integrated into the system, consisting of 144 20' x 8' solar panels installed on the roof of a customer building, RiverCentre.
• The California Department of General Services runs a central plant providing district heating to four million square feet in 23 state-owned buildings, including the State Capitol, using high-pressure steam boilers.

District heating is also used on many college campuses, often in combination with district cooling and electricity generation. Colleges using district heating include the University of Texas at Austin; Cornell University, which also employs deep water source cooling using the waters of nearby Cayuga Lake,; Purdue University,; University of Notre Dame; Michigan State University; Case Western Reserve University; Iowa State University; University of Delaware; and University of Maryland, College Park. MIT installed a cogeneration system in 1995 that provides electricity, heating and cooling to 80% of its campus buildings. 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. North Dakota State University (NDSU) in Fargo, North Dakota has used district heating for over a century from their coal-fired heating plant.

Asia

Japan

87 district heating enterprises are operating in Japan, serving 148 districts.

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.

China

In southern China, there are no district heating systems. In northern China, district heating systems are common. As air pollution in China has become quite serious, many cities are now using natural gas rather than coal in district heating system. There is also some amount of geothermal heating and sea heat pump systems.

History

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.

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.

Market penetration

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:

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.

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