district heating

District heating pipe in Tübingen, Germany

District heating (less commonly called teleheating) is a system for distributing heat generated in a centralized location for residential and commercial heating requirements. The heat is often obtained from a cogeneration plant, although dedicated facilities called heat-only boiler stations are also used. A district heating plant can provide higher efficiencies and better pollution control than localized boilers.

Heat generation

The core element of a district heating system is usually a cogeneration plant (also called combined heat and power, CHP) or a heat-only boiler station. 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.

The combination of cogeneration and district heating is very energy efficient. A steam-electric power plant which generates only electricity can convert only up to 47 % of the fuel input into electricity. The major part of the energy is wasted in form of heat and dissipated to the environment. A cogeneration plant recovers that heat and thus has a degree of efficiency of around 90 %.

Other heat sources for district heating systems can be geothermal heat, solar power, surplus heat from industrial processes, and nuclear power.

Nuclear energy has been suggested to be used for district heating. The principals for a conventional combination of cogeneration and district heating applies the same for nuclear as it does for any steam-electric power plant. One use of nuclear heat generation was with the Ågesta Nuclear Power Plant in Sweden. In Switzerland, the Beznau Nuclear Power Plant provides heat to about 20,000 people.^[1]

Heat distribution

Insulated pipes to connect a new building to Warwick University's campus-wide combined heat and power system.

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 a smaller electric power generation.

At customer level the heat network is 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.

Pros and cons

District heating has various advantages compared to single heating systems. Usually district heating is more energy efficient due to simultaneous production of heat and electricity in CHP generation plants. In addition biomass or waste is being used for combustion. The larger combustors 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 need any fuel because they use heat which otherwise would be wasted to the environment.
For the consumers district heating is an easy and convenient solution to heat their houses.
Ecoheatcool, a study on district heating in Europe, showed some impressive results if more district heating would be used. The overall energy efficiency and the security of supply would increase considerably while the carbon dioxide emissions and the import dependence would decrease strongly.

One of the disadvantages of district heating are the high investment costs. A district heating network, a heat-only boiler station, or a cogeneration plant require high capital expenditures and need a long time before the investment pays off. Furthermore district heating is only suitable in urban areas. Where the population density is low, district heating will be too expensive.

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.

Russia

In most Russian cities, district-level combined heat and power plants (Russian: ТЭЦ, Тепло-электро централь) produce more than 50 % of the nation's electricity and simultaneously provide hot water for neighboring 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 ^{[verification needed]}.

Scandinavia

Scandinavian homes also use district heating for their hot water and heating needs.

Denmark

In Denmark district heating covers more than 60 % of space heating including hot water demand^[2]. 80 % of this heat is produced on combined heat and power plants^[3]. Most major cities in Denmark have big district heating networks including transmission networks operation 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 metropolitan area operated by CTR I/S and VEKS I/S

United Kingdom

District heating accumulator tower and workshops on the Churchill Gardens Estate, Pimlico, London. This plant once used waste heat piped from Battersea Power Station on the other side of the River Thames. (January 2006)

In the United Kingdom, district heating also 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 continued to expand up till about 1960. 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 CHP engines and 3 x 8 MW gas fired boilers. 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.

Serbia

In Serbia, district heating was used throughout the main cities, particularly in the capital, Belgrade. NATO targeted one of the main DH plants, the District Heating Plant of New Belgrade (JKP "Beogradske elektrane") during the Kosovo War [1][2]. This plant was deemed the beginning of the centralized heating supply to Belgrade, built in 1961 as a means to provide effective heating to the newly built suburbs of Novi Beograd. The district heating system of Belgrade possesses 112 heat sources of 2,454 MW capacity and by way of the pipelines more than 500 km long and 4365 connection stations, providing district heating to 240,000 apartments and 7,500 office/commercial buildings of the total floor area exceeding 17,000,000 square meters.

Italy

In Italy, district heating is used in some towns (Bergamo, Brescia, Reggio Emilia, Torino).

Sweden

Sweden has a long tradition for using district heating in urban areas. The city of Växjö have reduced its fossil fuel consumption by 30 % in 1993-2006 and aims at 50 % reduction in 2010. This is to a large extend to be achieved by way of biomass fired district heating^[4]

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.^[5]

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.

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. Consolidated Edison of New York (Con Ed) operates Con Edison Steam Operations, the largest commercial district heating system in the United States and world. [3] The system has operated continuously since March 1882 and serves Manhattan Island from the Battery through 96th Street. While operating smoothly for most of its time in service, incidents have occurred, On July 18 2007 one person was killed and numerous others injured when a steam pipe exploded on 41st Street and Lexington [4]. In 1989 three people were also killed in a similar event [5]. In addition to providing space and water heating, steam from the system is used in numerous restaurants for food preparation, process heat in laundries and dry cleaners, as well as to power absorption chillers for air conditioning.

Europe

Since 1954, district heating has been promoted in Europe by Euroheat & Power. They have recently compiled analysis of district heating and cooling markets in Europe within their Ecoheatcool project supported by the European Commission. [6]
The legal framework in the member states of the European Union is currently influenced by the EU-CHP Directive.

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. Across the Atlantic, 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.

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, completely lost interest in the district heating business and did not provide sufficient funding for maintenance of the systems. The systems and the service to the customer started to deteriorate. The result was that, after some years, the systems started to lose customers; the reliability for heat supply went down and finally the whole system closed down. For example, in Minnesota in the 1950s there were about 40 district steam systems; today only a few remain.[7]

Paris has been using groundwater from 1-2 kilometre's depth at 55-70 °C since the 1970's for domestic heating.[8] 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 between 15-20 % of the total heat-input into 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.[9][10].

Diffusion of district heating

Penetration of district heating (DH) into the heat market is very different by country. Penetration is influenced by different factors, including environmental conditions, availability heat sources and economic and legal framework.

In the year 2000 the percentage of houses supplied by heat from district heating in some European countries was as follows:

Iceland 95 %, Estonia 52 %, Poland 52 %, Denmark 51 %, Sweden 50 %, Slovakia 40 %,

Finland 49 %, Hungary 16 %, Austria 12.5 %, Germany 12 %, Netherlands, 3 %, UK 1 %

Source: Sabine Froning (Euroheat & Power): DHC/CHP/RES a smile for the environment, Kiev 2003

On 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 to stiff competition from natural gas supply.

Energy consumption

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.^[6]

Figures for Sweden suggest that the average Swede using district heating receives 4500 kWh/year from the system.^[7]

District cooling

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 that need to be cooled. In winter-time, the source for the cooling can often be sea water, so it is a cheaper resource than using electricity to run compressors to generate the cooling effect.

The Helsinki district cooling system uses otherwise wasted heat from summer time CHP power generation units to run condensers for cooling during summer time. Thus electricity usage for cooling is greatly reduced. 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. The idea is now being adopted in other Finnish cities.

In August 2004, Enwave Energy Corporation, a district energy company based in Toronto, Canada, started operation of an innovative system that uses water from Lake Ontario to cool a variety of 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 (refrigeration) (140 megawatts) of cooling—a significantly larger system than has been installed elsewhere. Another unique feature of the Enwave system is that it is integrated with the city of Toronto’s system for local drinking water supply, bringing benefits to the city in terms of improved drinking water supply.

Footnotes

1. ^ SUGIYAMA KEN'ICHIRO (Hokkaido Univ.) et al. Nuclear District Heating: The Swiss Experience
2. ^ Kort om elforsyning i Danmark, from the Homepage of Dansk Energi (in Danish).
3. ^ Danish Energy Stastistics 2005 by the Danish Ministry of Energy (in Danish).
4. ^ Fossil Fuel Free Växjö from the homepage of the Municipality of Växjö
5. ^ AGFW Branchenreport 2006, by the German Heat and Power Association -AGFW- (in German).
6. ^ Figures supplied by email to Alaric Hall, 28.5.2007.
7. ^ Chris Goodall, How to Live a Low-Carbon Life: The Individual's Guide to Stopping Climate Change (London: Earthscan, 2007), p. 85.

See also

• Central solar heating
• Geothermal heating
• Lists of public utilities
• New York City steam system
• Public utility
• Seasonal thermal store

External links

• Euroheat & Power: European District Heating & Cooling Association
• District Energy Library
• Towards Local Energy Systems: Revitalizing District Heating and Co-Generation in Central and Eastern Europe
• Technical description of district heating and district cooling at Munich Airport, Germany
• Helsinki district cooling system
• The Enwave Deep Lake Water System
• GST Group's homepage
• Sequoien - UK non-profit district heating

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