Abstract
Within the current context of energy, there are several ways to meet the challenges of durable development. Efficiency in energy use, considered to be the fifth energy source, as well as the use of sustainable energy sources represent critical objectives. Nowadays, almost 50% of the total energy consumption in Europe is consumed by building heating and cooling. The current heat demand is mainly covered by conventional energy—fossil fuels. Consequently, there is a significant growth potential for the use of renewable energy sources (RES) in order to produce heat. One can expect in the near future that the energy systems would include a larger percentage of renewable sources, so the increase of the RES share is one of the main objectives of the thermoenergetic field. This chapter approaches heating system typology, the performance indicators used to asses the hybrid heating systems, and at the same time synthetising the assumptions of ensuring the optimum operating conditions.
TopIntroduction
The emergence and accelerated incurrence of centralized heating systems related to urban localities represent the superior stage of heating technique. This stage implied a ratiocination based on the prediction of the link between social and economic growth, the incurrence of urban congestion and the need for technological optimization and the adjustment of existing heating systems to the new demands of the population. Worldwide, 50% of the population lives in urban areas. This percentage is forecasted to increase to 60,8% by 2030 (Cohen, 2006). In Europe, 72% of the population lives in urban areas, with an increase of up to 84% by 2050 (Eicker, 2012).
Due to the significant impact of urban heating systems on the environment, the result of their span and the nature of traditional used fuels, the optimization of existing and future systems has become a priority with the awareness of the need for sustainable energy development. The technological development and the increase of the energetic consumption over the last two centuries have generated a number of unprecedented negative effects over the environment, such as air pollution in localities, soil and water pollution, greenhouse gas accumulation in the atmosphere, with an important role in climate change and the incurring of ecosystem imbalances, minimization of fossil energy resources, etc. Throughout history, the mankind has developed an energy intensive society, with negative impact on the environment, being necessary to focus all the efforts in trying to limit, reduce and minimize the negative effects and optimize actions in the field of energy. In the context of the exhaustion of traditional energy resources, it is imperative to bring major changes in terms of production, transport and last but not least, energy consumption. The competitiveness and security of energy supply, the moral and legal goals to mitigate the impact on the environment, and the fight against climate change require technological modernization and optimization of installations and increase efficiency throughout the entire energy - producing - transport - consumption chain. Reducing fossil energy consumption and eliminating energy wastage without adversely affecting indoor comfort in heated spaces and without compromising the users' ability to set their own comfort levels (indoor temperatures, durations, consumption levels, etc.) is one of the main objectives in the field. Thus, the following objectives are outlined: optimization of heating systems, development and diversification of alternative, clean and renewable energy harnessing technologies.
The followings are addressed by this chapter:
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Configurations associated with conventional heating systems.
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Identification of the optimization opportunities and trends for conventional heating systems, in order to increase variation of the energy mix and operational performances.
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Assessment of correspondence between energy efficiency improvement and harnessing energy from renewable sources.
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The identification and analysis of factors that influence the RES share in the production of thermal energy within heating systems.
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Assessment of thermo-energy performances of heating systems, by securing the specific performance indicators.
The conventional heating systems are presented and analysed within this chapter, together with the modern concepts as energetic hub that allows the association of one single energy output - energy demand, to several energy inputs - related to different energy sources (conventional, renewable or alternative). At the level of hybrid energy hub, the thermo-energy indicators used for assessing the performances of the heating systems are emphasized, together with a comparative assessment of the conventional heating systems, and of the hybrid heating systems, respectively.
Several measures are proposed for optimizing the heating system and increasing the annual thermo-energy efficiency:
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Increase of the buildings' energy performance class within urban areas.
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Reduction of operating temperatures within the existing district heating system.
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Configuration of hybrid heating systems by integrating renewable energy sources (RES).
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Increase of RES quota in the heat production mix.
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Integration of RES systems in the existing district heating systems, in a centralized manner - at the thermic source or in a non-centralized manner - within the heating systems.
Key Terms in this Chapter
Annual Efficiency of the Hybrid Heating System: Ratio between annual heat demand, or heat consumption in the case of an existing system and total amount of primary energy used at the auxiliary thermic source, based on conventional, fossil fuels.
Thermal-Solar Field: An assembly of technical systems with the role of collecting the solar energy, and converting it in the thermal energy, respectively.
Thermoenergetic Hub: Technological way of organising, that allows the association of one single energy output-energy demand, to several energy inputs related to different energy sources (conventional, renewable, clean or alternative).
Thermal Density: In the case of an urban area, it represents the ratio between thermal energy demand/consumption for space heating, domestic hot water preparation and industrial processes and considered territorial surface.
Conventional Thermic Source: The assembly of installations, technological equipments that produce heat in a centrally manner, by burning fossil fuels within outbreaks.
Performance Indicator: Numeric expression that quantifies the performance of a thermal system, at the present case.
Hybrid Heating System: A heating system that uses, to produce heat, a mix of conventional, regenerable or alternative energies and includes technologies for harness renewable and alternative energy sources, respectively.
Annual Solar Fraction: Percentage of annual demand/consumption of heat, covered through solar energy.