Heating, Cooling and HVAC

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. District heating plants can provide higher efficiencies and better pollution control than localized boilers.

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…………………District heating pipe in Tübingen, Germany

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 less than approximately 50 % of the fuel input into electricity.[citation needed] The major part of the energy is wasted in form of heat and dissipated to the environment. A cogeneration plant recovers that heat and can reach total energy efficiency beyond 90 %.

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

A canceled Russian nuclear district heating plant in Fedyakovo, Nizhny Novgorod Oblast.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 Ã…gesta Nuclear Power Plant in Sweden. In Switzerland, the Beznau Nuclear Power Plant provides heat to about 20,000 people

Heat distribution:
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.
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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.

Advantages:
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 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 use additional fuel because they use heat (termed heat recovery) which would be disbursed to the environment.
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DISTRICT HEATING & DOMESTIC WATER SYSTEMS

Disadvantages:
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 houshold or building heating equipment. District heating network, heat-only boiler stations, and cogeneration plants require high initial capital expenditure and financing. Only if considered as long-term investments these may 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 investement per household is considerably higher.

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. The legal framework in the member states of the European Union is currently influenced by the EU-CHP Directive.

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. 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 [2]. In 1989 three people were also killed in a similar event . 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. Vancouver, Canada also has a sizable commercial system that heats and cools large parts of the downtown area.

Denmark
In Denmark district heating covers more than 60 % of space heating and water heating.[2] In 2005 82.4 % of this heat was produced on combined heat and power plants. Heat recovered from waste incineration accounted for 22.9 % of the total Danish district heat production.[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 Copenhagen area operated by CTR I/S and VEKS I/S. In central Copenhagen the CTR network covers 275.000 households (90-95 % of the areas population) through one network of 54 km district heating distribution pipes providing a peak delivery of 663 MW.[4] The consumer price of heat from CTR is approximately €42 per MWh plus taxes.

Finland
In Finland district heating accounts for about 50 per cent of the total heating market [6], 4/5 of which being produced from combined heat and power plants. Over 90 per cent 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 areas to 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. However, 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 insustrial by-product may sell otherwise waste heat to the network rather than release it to 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[7].

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.

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.

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

Norway
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.

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 .

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 . 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.

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

United Kingdom
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.

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.

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.

Market penetration of district heating:
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 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 (2003)
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%

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.

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.

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

Sources:http://en.wikipedia.org/wiki/District_heating