Daily Archives March 6, 2016

ENVIRONMENTAL IMPACT

High contents of dust, sulfur dioxide (SO2), and nitrogen oxides (NOx) in urban areas were among the first pollution problems to be identified. District heating improved the urban air quality in many towns since local heat boilers were replaced and high chimneys for heat-generation plants were required.

Acidification from SO2 and NOx is a major problem in many regions. District heating systems provide a centralized and cheap way to eliminate these emissions by separation, use of fuels with low sulfur content, have higher conversion efficiencies, and have higher combustion quality, resulting in lower NOx emissions.

Global warming due to the greenhouse gases is a problem more difficult to solve than the problems of urban air quality and acidification...

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METHODICAL ASPECTS

Examining such problems analytically requires cog­nitive information processing. The desired systematic procedures require application of methods to orga­nize and to extend our knowledge on complex systems. Generally, problem-specific combinations of methods are applied. Methodical problems and deficits usually emerge due to the complexity of the processes or of the impacts. Problems in describing complex dynamical systems are due to nonlinear impacts and boundary conditions, to boundary conditions that are time dependent and/or solution dependent, and to different time constants within the subsystems.

1.1 Deficit Analysis

Knowledge about technical systems is commonly gained by analyzing the underlying interactions. This is mainly characterized by the building of models...

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ENERGY SUPPLY

The base load heat-generation capacity in a district heating system must have a strong correlation with the five strategic resources discussed previously: cogeneration, refuse incineration, industrial waste heat, geothermal heat, and fuels difficult to manage. Internationally, the strongest driving force for district heating is the simultaneous generation of electricity and heat in cogeneration plants. Base load capacities are associated with low operating costs and high capital investment costs.

Conventional fossil fuels dominate the fuel supply for cogeneration, but the use of biomass is increasing in some countries. One example is the newly built biomass cogeneration plant in Eskilstuna, Sweden, which meets the majority of heat demand of a city with 65,000 inhabitants...

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CUSTOMER RELATIONS

The customers usually pay for the heat received according to a heat rate, which normally consists of one fixed portion related to the capacity needed and one variable portion related to the amount of heat bought. Sometimes, a water volume portion is also used in order to promote low return temperatures from the customer substations. The capacity portion is based on either the maximum heat load or the maximum water flow capacity. The amount of heat sold to the customer is recorded by integrating the product of water flow and the temperature difference between the supply and return pipes. A heat meter in each customer substation measures the district heating water flow, the supply temperature, and the return temperature...

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TECHNICAL DESIGN AND CONSTRUCTION

Heat is transferred from the network to the building heating systems by customer substations located in the connected buildings. A building has at least two internal distribution systems that must be heated— one system for supplying heat to the radiators and one system for distribution of domestic hot water. Some­times, a separate system also provides heat for heating the supply air in the mechanical ventilation system.

Each internal system is heated and regulated separately. The heat is often transferred by the use of heat exchangers, in which case the connection is indirect. There are also direct variants with only valves and elevator pumps. If domestic hot water is prepared by mixing district heating water and

TABLE I

Heat Flows through District Heating Systems for Various Countries...

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HISTORY OF DISTRICT HEATING

Birdsill Holly, an inventor and hydraulic engineer, is often credited with being the first to use district heating on a successful commercial basis. As a result of an experiment in 1876 involving a loop of steam pipes buried in his garden, Holly developed a steam supply system in October 1877. Several district heating systems were started in North American cities in the 1880s. The fuel source was steam coal. In New York, the Manhattan steam system went into operation in 1882. It exists today as the steam division of Consolidated Edison, and it delivered 29 PJ of heat during 2000.

The oldest district heating system still in operation is located in Chaudes-Aigues, France. It is based on a geothermal heat source with a temperature of 82°C and was in operation as early as the 14th century...

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MARKET PENETRATION

Citywide district heating systems exist in Helsinki, Stockholm, Copenhagen, Berlin, Munich, Hamburg, Paris, Prague, Moscow, Kiev, Warsaw, and other large cities. Many systems supply a downtown district (such as in New York, San Francisco,

Minneapolis, St. Paul, Seattle, Philadelphia, and other cities) or a university, military base, hospital complex, or an industrial area.

Total annual heat turnover is approximately 11EJ in several thousand district heating systems operating throughout the world. The amount of heat delivered corresponds to 3.5% of the total global final energy consumption (1999). The market penetration for district heating in various countries is presented in Table I which is based on international energy statistics...

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District Heating and Cooling

SVEN WERNER

Chalmers University of Technology Gothenburg, Sweden

district heating system: the suitable cheap heat source, the market heat demands, and the pipes as a connection between source and demands. These three elements must all be local in order to obtain short pipes for minimizing the capital investment in the distribution network. Suitable heat demands are space heating and preparation of domestic hot water for residential, public, and commercial buildings. Low-temperature industrial heat demands are also suitable.

1. FIVE STRATEGIC RESOURCES

The five suitable strategic local energy resources are useful waste heat from thermal power stations (cogeneration); heat obtained from refuse incineration; useful waste heat from industrial processes; natural geothermal heat sources; and fu...

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