District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes (network, grid) for residential and commercial heating requirements such as space heating and water heating (also domestic hot water (DHW)
Today is counted four generation of district Heating (DH). Most common is third generation, started from 70-s. The third generation uses prefabricated, pre-insulated pipes, which are directly buried into the ground and operates with lower temperatures, usually below 100 °C. In many cases 90/70°C, it means supplyo temerature is 90 °C and return temperatuure 70 °C.
Currently, the 4th generation is being developed. Compared to the previous generations the temperature levels have been reduced to increase the energy efficiency of the system, with supply side temperatures of 70 °C and lower. Potential heat sources are waste heat from industry, CHP plants burning waste, biomass power plants, geothermal and solar thermal energy (central solar heating), large scale heat pumps, waste heat from cooling purposes and data centers and other sustainable energy sources. With those energy sources and large scale thermal energy storage, including seasonal thermal energy storage, 4th generation district heating systems are expected to provide flexibility for balancing wind and solar power generation, for example by using heat pumps to integrate surplus power as heat when there is much wind energy or providing electricity by biomass plants when back-up power is needed.
Operating hours(unit h in periode) means time in hours in certain perioode like day, month or year, when DH plant supply heatenergy to consumers (network).
Heat load (unit: MWh )- Heat load refers to the amount of heat energy that supplied to consumer (network) in certain time perioode like hour, day, month or year.
RiL- relative importance of losses (unit: %) is the amount of heat loss consumed by the network. Its ratio of energy losses in pipes, pluss electricity for delivering energy to network to energy delivered to consumer (network)
PEF- primary energy factor, PEF quantifies the primary energy use of a district heating network. It express the ratio of the amount of input energy (primary energy consumed, plus electricity consumed) to the amount of energy supplied to network.
Also, its definition is given by equation where Ej is the amount of the jth primary energy consumed by the network, Eaux is the amount of electricity needed to deliver power and heat to the consumers (e.g. pump consumption, lighting of the heat plant, ...), ECHP is the amount of electricity provided by the combined heat and power plant (CHP) if any is installed, fp,j is the primary energy factor related to an energy source, fp,el is the primary energy factor for the power plants and Edel is the amount of energy delivered to the consumers. This is a major factor allowing people to compare in an efficient manner two heating technologies e.g. district heating network and conventional boiler. But this indicator is not enough to assess the whole energy use of district heating networks. The value of this parameter can be negative if a large CHP plant has been installed and can also hide the effects of the use of fossil fuels or great amounts of heat loss. These two statements led us to define three new energy parameters in order to add complementary information on their energy performances.
The district heating global efficiency, parameter is defined as a general efficiency: the ratio between all provided energies and all the necessary energies.
Operating temperature range of DH (unit: ˚C/˚C), supply and return temperatuures in network (exampl. 90/70 ˚C).
Consumption density (unit: MWh/m), is the amount of heat sold in MWh per running meter of the heat network
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