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According to the electricity tariff recently issued by the Italian government for the domestic heating systems fed with heat pumps (HP), an energy and economic analysis was carried out with the aim of investigating the effectiveness of the air-to-air heat pump systems (HPS) as an alternative to the traditional heating using domestic gas boilers systems (GBS). For the purpose of this study, the apartments of three residential buildings were examined. The hourly heating loads were calculated with the ASHRAE radiant time series and the coefficient of performance (COP) of the HPs was evaluated for each operating condition. The costs for the heating system installation and electricity and/or gas bills were combined with the benefits, related to the current promoting tax credit program. The study turned out that the time when the GBS convenience surpasses the HPS mainly depends on the amount of thermal energy consumed in the year, although other important features, such as the domestic electricity consumption and the kind of energy used to supply the domestic hot water system and the cookers, play a relevant role in making the best choice between HPS and GBS.

A combined cooling, heating and power system with hybrid chillers is designed, which mainly includes power generation unit, ground source heat pump system, boiler, absorption chiller, electric chiller and heating exchanger. In order to better reflect the actual operation of the system, the main devices of system are considered as off-design models. A novel parameter named start factor of off-design devices is proposed to improve devices efficiency. Under following electric load and following thermal load operating strategies, the optimal capacity and comprehensive performance of the system devices are obtained. By different off-design models, seven system models are built to analysis under two operating strategies. Moth flame optimization is selected as the optimization method to get model results. The results show that most start-factor system models can improve the system performance. Under the following electric load operating strategy, the typical start-factor model is compared with the traditional model (the energy saving: 8.25%; the cost saving: 7.47%; the carbon dioxide emission reduction: 7.22%). Under the following thermal load operating strategies operating strategy, the typical start-factor model is compared with the traditional model (the energy saving: 23.10%; the cost saving: 22.33%; the carbon dioxide emission reduction: 22.80%).

The use of district heating systems consisting of a combined heat and power (CHP) and a heat only boiler (HOB) is on the rise in South Korea. In this context, monopolistic district heating providers optimise cogeneration capacity composition to maximise their profits under price regulation. Building upon Joskow and Jones (1983), this study develops a theoretical framework to investigate the role of price regulation on the optimal capacity composition of a district heating system for a regional monopolist. Assuming varying heat demand, wherein the maximum heat load may exceed CHP capacity, the effects of price-cap and rate of return regulations on the optimal mix of the district heating system are examined and compared. The results show that the heat production mix is optimal for price-cap regulation. In contrast, the rate of return regulation hinders the monopolist's incentive to reduce costs. Finally, in case of internalising the environmental benefits of cogeneration, the optimal CHP size in the heat production mix should be increased; consequently, the energy efficiency for producing heat and electricity is likely to improve. This study, therefore, has far-reaching implications for policymakers and practitioners alike in terms of addressing the dual goals of energy efficiency and economic efficiency.

Heat pumps are promising for carbon neutrality. However, the existing vapor-compression heat pumps suffer from severe performance deterioration while the absorption heat pumps rely on toxic NH3-based fluids in sub-zero conditions. Therefore, a novel hybrid H2O/ionic liquid absorption and CO2 compression air-source heat pump is proposed for ultra-low ambient temperatures. The verified property and cycle models are used for performance optimization, characterization, and comparison. The coupling temperature that oppositely affects the efficiencies of the two sub-cycles is optimized to be 6 °C. With the ambient temperature rising from −30 °C to 0 °C, the primary energy efficiency (PEE) increases from 1.064 to 1.256, higher by 18–40% compared to a gas boiler. The heating capacity stably ranges in 94.0–102.9 kW, significantly increasing the reliability in cold climate. As the driving temperature rises from 96 °C to 130 °C, the PEE slightly varies in 1.155–1.190, while the exergetic coefficient of performance decreases from 0.609 to 0.600, encouraging the use of low-temperature heat sources (e.g., 100 °C). Compared to existing heat pumps, the hybrid heat pump efficiently operates at −30 °C, showing the highest PEE for most sub-zero conditions with much slower heating capacity deterioration. The advantage is much higher under colder conditions.

The hydraulic balance of heating network is considered as a pre-condition for the implementation of low temperature district heating (LTDH). Its imbalance result into high energy consumption and heat-losses in the network. In this study, a novel hydraulic model is presented which investigates hydraulic imbalance in the LTDH network, using real weather and hourly monitored operational heating data from an existing boiler based building. Analysis of delta t in space-heating system shows that the delta t is maximum when the outside air temperature is lowest and it decreases with increase in outside air temperature. Furthermore, the hydraulic imbalance is analysed for four different control scenarios with the aim to find an optimum scenario with minimum pumping power, energy consumption and heat-losses in the LTDH network. Results show that the hydraulic imbalance is due to the absence of flow-limiters and balancing valves on the return pipe, and thermostatic radiator valves (TRVs) alone are unable to maintain hydraulic balance in the space-heating system of buildings. Moreover, the control scenario with variable flow-rate and fixed supply water temperature from the sub-station is found to be optimum. Compared to the constant flow-rate scenario, the pumping power, energy consumption and heat-losses in the LTDH network are reduced by approximately 2%, 63% and 14%, respectively.

This paper presented a novel analytical method for the performance evaluation of various rural houses space heating systems and determination of the most appropriate system type, on the basis of Analytic Hierarchy Process (AHP) and Fuzzy Comprehensive Evaluation (FCE) methods. To initiate the system performance evaluation, a number of parametrical indexes, including three primary indexes namely, social benefit, environmental benefit and economic benefit, and nine secondary indexes namely, room temperature qualified rate, heating system reliability, smoke concentration, SO2 concentration, NOx concentration, energy consumption, initial investment, operational costs and policy incentives, were developed by running a dedicated specialists' questionnaire. These indexes were then applied to the performance assessment of the selected five rural houses space heating systems, i.e., hybrid solar/biomass boiler, biomass boiler, air source heat pump, hybrid solar/electrical heating and coal-fired boiler. As a result, the weights of different indexes for the five systems were determined using the AHP method and consequently, the priority order of the five systems was listed using FCE. The modelling results indicated that among the five selected systems, solar/biomass heating system presented the best performance, followed by the biomass boiler type, air source heat pump type, solar/electrical heating type, and coal-fired boiler type. The novelty of the research lies in the combined use of the AHP and FCE methods for solving the complex multi-factors inclusive equations. This combination can overcome the AHP's shortfall in subjective selection of the indicators, and meanwhile, prevent the FCE's drawback of ignoring the weights of the indexes, thus providing a realistic and effective method for selection of the best performing rural house space heating system. Wide deployment of research outcomes can help improve the living standard of the residents staying in wide range of rural areas in China and thus harvest greater social, environmental and economic benefits subsequently.

The availability of the power unit for electricity production is one of the most important issues of the power plant operator. Considering the power unit, boiler is the main source of its malfunction. Depending of the boiler construction, source of problem can be different. In case of usage of the circulating fluidized bed boiler the potential issue that can lead to interruption of the energy production is its failure caused by leakages of heating surfaces. In order to mitigate this risk different treatments or procedures are introduced. Nowadays, thanks to continuous development of mathematical tools its is possible to introduce a new solution to reduce the risk of heating surface erosion cause by the friction of solid material used in fluidization. One of possible option, that can help to resolve such a problem is application of machine learning technique. Based on real observation of the boiler operation and data analysis, it is believed that the uniform temperature distribution at the lower part of the combustion chamber should has positive impact on erosion reduction at the kick-out level where tapered walls changed to vertical one. This can be attain by careful manipulation of selected boiler operating parameters. Due to the reason that in order to find requires setup dozen of input data configuration need to be considered appropriate toll need to be developed. That is the main reason way the machine learning technique need to be applied for such purpose. Indeed, of this work is to develop artificial models that can help in adjustment boiler setup. In order to check models functionality, they were on-site tested by boiler operator. Developed model shows tremendous potential and confirm that it is worth to investigated this topic farther.

The technology of waste heat recovery from medium-low temperature flue gas has been widely studied in the past decade. In this paper, the principle and characteristics of the main technologies are extensively reviewed. The condensing boiler, as the primary waste heat recovery system, can achieve higher boiler efficiency by transferring waste heat to feedback water. As the temperature of feedback water is generally not cold enough to serve as the cold source, the waste heat recovery efficiency of condensing boilers is limited. More advanced waste heat recovery systems are proposed. The common principle of them is to enhance the difference between the cold source and the flue gas. Specific systems reviewed are classified according to working principles: (Ⅰ) to decrease the temperature of the cold source; (Ⅱ) to decrease the dew point temperature of the cold source; (Ⅲ) to increase the dew point temperature of the flue gas. System performances are analyzed involving efficiency, entransy dissipation, economic benefits and pollutant emissions. The heat recovery efficiency of several heat pump systems and vapor pump boiler systems can exceed 80 %. The vapor pump boiler system has a relatively short payback period (i.e. 1.4 years). Future perspectives and essential conclusions are presented in the end.

In this study, a novel swirl burner for industrial pulverized coal boiler was studied by laboratory experiments and industrial application tests. First, a cold flow experiment was carried out on a 1:3 scale model experimental platform. The cold air velocities of burner outlet were measured in detail. Moreover, the influence of the mass flow ratio of the inner and outer secondary air on the shape of the central reflux zone and the reflux rate at the burner outlet was analyzed. It was found that a stable central reflux zone can be formed at the burner outlet. In addition, an industry application test was carried out in a 29 MW hot water boiler. The flue gas temperature at the burner outlet and the composition of exhaust gas were obtained under different operating parameters. The influence of inner and outer secondary air damper opening on burner performance (ignition performance, NOx emission characteristics, stable combustion performance, and anti-slagging performance) was analyzed. The influence of inner secondary air damper opening on burner performance was found to be greater than that of outer secondary air damper opening. The maximum concentration of NOx emission at furnace outlet was 364.9 mg/m3, and low-NOx combustion was achieved for industrial pulverized coal boilers. The minimum load without natural gas support was 3 MW. The load regulation rate was close to 10:1, and low load combustion stability was achieved. During three heating seasons, the normal operation of the boiler was not affected by slagging.

Sustainable energy development in the farming sector is an essential strategy to respond the combined challenge of achieving a reliable and affordable solution but including mitigation and adaptation to climate change. Intensive breeding farms require maintaining an adequate indoor thermal environment that results in high energy demands, usually covered by fossil fuels and electricity. This paper addresses the application of the combined slurry technology for a particular pig farm that currently uses a diesel boiler to supply the piglet heating energy needs. The study also considers different options based on closed ground source heat pump systems. After the design of the slurry alternative and the geothermal ones, notable advantages are detected compared to the existing diesel system. Results show that the implementation of the slurry technology implies an important reduction of the operational costs, which, in turn, involves short amortization periods for this system in relation to the diesel one. Greenhouse gases emissions are also highly reduced in the slurry alternative based on the low electricity use of the heat pump. The environmental side is reinforced by the reduction of polluting substances such as methane of ammonia derived from the descent of temperature of the slurry.

In this study, two prediction models were developed to determine equilibrium compositions in the combustion products of a domestic boiler. These models are based on the Gibbs energy minimization and equilibrium constant methods. According to the domestic boiler standards (EN 15502–1 and EN 437), gaseous fuels (G20, G25, and NG) were selected to predict gaseous emissions. A novel investigation was realized for a domestic boiler's lean premixed burner in compliance with relevant standards. In the range of 0.6–0.9 equivalence ratio, the equilibrium compositions of the species were obtained. The proposed models were compared with CHEMKIN commercial software to verify the prediction of the results. Adiabatic flame temperatures and combustion products (NO, CO, N2, O2, CO2, and H2O) were estimated using prediction models. The estimated values showed good agreement with the results obtained from CHEMKIN software. Under efficient boiler operating conditions (ϕ=0.65, 0.7, and 0.75), minor deviations were observed comparing with the CHEMKIN results. For gaseous fuels, CO and NO emissions reach peak values near ϕ=0.9 and ϕ=0.85, respectively. Without using complex chemical kinetics mechanisms, models provide reliable estimates. The proposed models can be parametrically applied not only for boilers but also for other applications in combustion processes.

The traditional combined heat and power (CHP) units restrict the operational flexibility and causes serious wind power curtailment. To study the wind power accommodation ability and coal consumption, a new method is proposed to calculate the heat–power characteristic of CHP units with different decoupling technologies. A series of mathematical models are established to quantitatively compare the wind power accommodation ability, coal consumption and pollutant emissions. The results show that the minimum electric power of traditional CHP units can be decreased equipped with a heat storage tank only under high heating load but it can be decreased when installed with an electric boiler and high pressure-low pressure (HP-LP) bypass heating under any heating load. With the increase of heating load, the wind power accommodation ability of CHP units with three typical decoupling technologies decreases. The amount of coal consumption of CHP units with HP-LP bypass heating saves twice more than with electric boiler, and saves 30 times more than with heat storage tank. Furthermore, HP-LP bypass heating technology can reduce pollutant emissions efficiently. In engineering practice, the optimal decoupling technology should consider the CHP unit self condition, wind power load, electric power generation and heating demands.

Clean heating is a powerful solution for satisfying the building heat demand by synergizing energy efficiency and carbon emission. For satisfying the newly increased heat load, this paper constructs an alternative integrated electricity and heat energy system (IEHES) to consider different clean heating supply modes, namely electrical-heating mode (EH, electric boiler or electric heat pump), CHP unit with high back-pressure turbine heating mode (HBP–CHP), and auxiliary heat source heating mode (AHS, coal-fired boiler or gas-fired boiler). An optimal configuration planning and dispatch model is proposed for comparing the performance of the three heating modes. Wherein, a new comprehensive energy-carbon price is proposed as the optimization objective to minimize this system's total production costs and carbon emission costs. The results show that the HBP-CHP mode is the optimal solution when the heat load growth rate λ is lower than 14%, followed by the electric heat pump heating way under the EH mode. However, the HBP-CHP mode will limit the flexibility of the IEHES when λ is larger than 8%. Therefore, we propose a combined heating mode by introducing the electric heat pump into the HBP-CHP heating mode that facilitates the flexibility of the IEHES and brings the optimal system coal-saving effect.

The paper presents a new method of determining optimum temperature variations of the fluid during heating and cooling of cylindrical thick-walled components weakened by holes. The temperature of the fluid located or flowing through the pressure component is equal to the saturation temperature. The stress concentration factors at the edges of the holes were determined using the Finite Element Method (FEM) to represent the real construction of the junction between the element and the spigot. Optimum fluid temperature variations were determined so that the maximum equivalent stress at the edge of the opening is equal to the permissible stress determined concerning thermal fatigue. The equivalent stress at the hole edge at the point of its concentration includes thermal stress and stress due to pressure. Optimum temperature changes of hot water and steam-water mixture were determined during heating up and cooling down of the boiler drum, i.e., during boiler start-up and shutdown. Three-dimensional computations of the transient field of temperature and stress were carried out for the junction of the drum and downcomer to show that the equivalent stress at the edge of the hole does not exceed the allowable stress if the optimum temperature of the fluid was estimated by the proposed method.

In this paper, a steady-state 1D computer model of a complete sugarcane bagasse-fired boiler system is presented, which pays special attention to the different heat transfer phenomena encountered in the boiler heat exchangers. The model solves the mass, momentum and energy balance equations for water, flue gas and air streams in an integrated manner which utilizes fundamental equations and empirical correlations for pressure drop, radiative heat transfer and convection. The integrated model is successfully applied to model a 105 t/h industrial watertube boiler at three different load cases namely 100 t/h, 65 t/h and 35 t/h. The model results are validated using typical plant measurements. The mean relative predicted gas temperature errors are 1.47%, 0.58% and 4.84% respectively for the different load cases simulated, and for the water circuit temperature predictions the mean errors are 1.48%, 0.85% and 5.31% respectively. Additionally, a sensitivity analysis is performed on the integrated model, which investigates the influence of selected modelling parameters such as flame height on key boiler output variables such as the furnace exit gas temperature.

A proposed system consists of a combined cooling, heating, and power (CCHP) system driven by a gas turbine prime mover and an auxiliary boiler (CCHP-Boiler) system in a dairy factory. The CCHP-Boiler system optimized based on three different objective functions. In the 1st method, the system is considered as the combined CCHP-Boiler system. However, in the 2nd and 3rd methods, the optimization process has been carried out to the combined CCHP-Boiler system which has power transfer with the central power plant (CPP). The first objective function in the 1st method is the exergy efficiency of the CCHP-Boiler system. The second objective function is the annual total cost of the CCHP-Boiler system. In the 2nd and 3rd methods, the comprehensive objective function (CO), is the single-objective function. The results indicate that the base design requires a higher pressure ratio of air compressor (RP), which is equal to 14.79, and consequently, the existence of APH and LPG2 is recommended. But, optimization with all the methods for the CCHP-Boiler system leads to low RP values, which is approximately equal to 6. Meanwhile, it can be concluded that the existence of air pre-heater (APH) is not necessary and it should be removed.

A novel burner arrangement scheme with annularly combined multiple airflows (ACMA) was previously proposed for wall-tangentially fired boiler (WTFB), and its superiority over traditional WTFB had been proved. However, coal-fired boilers are often required to play the role of peak-shaving. To this, low load performances of ACMA boiler were investigated in this work to test whether ACMA can still work well under low boiler thermal load (BTL) conditions. Results show that ACMA boiler performance is still better than that of traditional WTFB under low BTL condition, with smaller airflow deflection, improved coal combustion behavior and alleviated thermal deviation on suspended heating surfaces. Besides, NOx emission characteristic of ACMA boiler under low BTL is more desirable. Furthermore, the location of non-service burners has significant effects on coal combustion and heat transfer processes under 440 MW load conditions, and closing the upper burner group is the optimal choice in terms of the comprehensive boiler performance. These findings deepen the understanding of ACMA boiler and provide theoretical and practical guidance in its application in power plants.

The article discusses the theoretical and practical foundations of the study of the possibility of obtaining volatile combustible substances released during special heat treatment of coal, with the aim of replacing ignition fuel oil at thermal power plants. The results of an experimental study of the coals of the Saryadyr field of three Kazakhstan deposits with the aim of obtaining volatile combustible substances, as well as the possibility of using these combustible substances as starting fuel, are presented. The results of calculating the heat of combustion of the gas obtained from the presented coal samples at different heating temperatures showed that with an increase in the heating temperature, the heat of combustion of combustible gases obtained from coal samples also increases. For all the coal samples under consideration, the maximum value of the heat of combustion is traced at a heating temperature of 600 °C. The greatest value is observed for the coal of the Shubarkul deposit - 22.1 MJ/m3, and the minimum value for the brown coal of the Saryadyr deposit is 13.5 MJ/m3. According to the results of experimental studies, we can conclude that of the three presented coals for producing combustible gas, the most suitable are the coals of the Shubarkul and Maikuben deposits. For use in the boiler unit as a starting fuel, it is sufficient to heat coal to temperatures of 350–450 °C.

Carrying out structural and parametric design and performance optimization of boiler economizer is important to improve comprehensive performance of supercharged boiler. By application of constructal theory, the design of a boiler economizer is conducted in this paper. Firstly, a complex function composed of linear weighted sum of heat transfer rate and power consumption rate is minimized. The total heat transfer area is given, and outer diameter, group number and row number of the serpentine tubes are taken as design variables, respectively. The optimal performance of the boiler economizer is gained. It reveals that in the limited ranges of the design variables, the optimal dimensionless outer diameter, optimal group number and optimal row number of the serpentine tubes are 0.92, 16 and 8, respectively, which individually lead to the minimum complex function. The complex functions derived by individually optimizing the outer diameter, group number and row number of the serpentine tubes are decreased by 5.7%, 4.9% and 5.0%, respectively. Secondly, multi-objective optimization based on non-dominated sorting genetic algorithm (NSGA-II) is also conducted, and the Pareto frontier is obtained. The research results of this paper will provide certain theoretical guidelines for structural and parametric designs of various boiler economizers.

To improve the performance of tangentially-fired pulverized boiler, a new burner arrangement scheme with annularly combined multiple airflows is proposed and its performance is thoroughly investigated with a previously validated 660 MW lignite boiler model. Results show that compared with conventional wall-tangentially fired boiler, the in-furnace aerodynamic field under the proposed burner arrangement scheme is obviously improved, embodying as reduced airflow deflections, increased furnace fullness and alleviated phenomenon of airflow scouring furnace walls. Besides, coal combustion behavior is also improved, resulting in increased combustion temperature and enhanced heat transfer process in the main burners’ region. Furthermore, the reduced flue gas swirling intensity mitigates the deviations of flue gas velocity and temperature in the upper furnace region, which finally lowers the unevenness of heat absorption on the suspended heating surfaces. With the improvement of the abovementioned aspects, the safety and economy of tangentially-fired boilers can be largely increased. Considering the increasingly enlarged boiler capacity and the widespread use of low-rank coal, the proposed burner arrangement scheme can be of great use in retrofitting the existing boilers and designing new ones.

The integration of large solar heating systems in district heating (DH) networks with large combined heat and power (CHP) plants is rarely considered. This is often due to low costs for heat but also due to subsidies for the electricity by CHP plants. Possible changes in subsidies and requirements in the reduction of fossil fuel based CO2 emissions raise an awareness of improving the operational flexibility of fossil fuelled CHP plants. This paper provides a rather simple but detailed methodology of including large solar heating systems in an existing district heating system, where heat is supplied by a large CHP plant. It uses hourly data of load and temperature patterns as well as radiation data and collector efficiency data to determine collector field size and storage size. The possibility of largely independent operation of sub-networks is analysed, which allows different system temperatures. It is demonstrated that a sub-network can operate without a back-up boiler and that both network parts benefit from the interaction. (C) 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Integrating gas, electricity and residential heating sectors through hybrid heating technologies equipped with smart controls could provide energy system planning and operational benefits. Hybrid heaters combine different heating appliances in one device and can switch between those appliances during operation. Different configurations are possible: B-R (gas boiler-resistance), HP-B (heat pump-gas boiler), and HP-R (heat pump-resistance) heaters. A linear programming investment model is formulated and applied to an Irish test system with 40% wind energy generation to determine the optimal capacities and dispatch for the power and residential heat systems, including thermal storage. No technology is a silver bullet, but this paper finds that the widespread deployment of hybrid HP-B systems delivers a wide range of cost and strategic benefits: This hybrid technology minimises total system cost, reduces gas consumption and CO2 emissions compared to B-only, and, compared to HP-only, reduces power generation capacity requirements and heater capital cost. Other hybrid heaters are effective in addressing a specific challenge, although with drawbacks: Hybrid B-Rs considerably reduce wind curtailment, but increase the use of carbon-intensive coal generation; HP-Rs mainly only benefit consumers by reducing heater capital cost compared to HPs and require more generation capacity additions and thermal storage tanks.

Space and water heating are two major components of household energy consumption, and a number of work has been done to combine multiple residential heating technologies to develop hybrid heating solutions that are more flexible, efficient and economical. This paper studied and modelled a smart home with a novel hybrid heating system, which consists of a wall-hung gas boiler (for both space and water heating) that is connected to a water tank with an auxiliary electric resistance heater (for water heating), and auxiliary split air conditioners (for space heating). A multi-objective optimization was further formulated to optimally schedule the gas and electricity consumption of a smart home equipped with the hybrid heating system as well as an onsite photovoltaic (PV) system, a battery energy storage system, an electric vehicle and various types of flexile loads. Two objectives, i.e. the minimization of operating energy cost (including both electricity and gas payment) and the maximization of thermal comfort, were considered. The optimization problem was finally transformed to a single objective mixed integer linear programming problem that can be solved by existing optimization solvers. Simulation results verified the operational performance of the studied hybrid heating system and the effectiveness of the proposed scheduling method. Sensitivity analysis was conducted considering various levels of electricity/gas prices, onsite PV capacity, battery capacity and outdoor air temperature, and it shows that in all the scenarios the operating energy cost of the smart home with the hybrid heating system was always lower than that with the pure electricity or pure gas heating systems. The performance under various uncertainties and the benefits of adopting model predictive control were also demonstrated. It is noted that this paper only focuses on the optimal scheduling and operation costs of the hybrid heating system. Optimal configuration and sizing of the heating system with the initial investment (i.e. capital expenditures) considered are identified as research directions in the future.

Geothermal energy has been successfully applied in many district heating systems. In order to promote better use of geothermal energy, it is important to analyze the operation strategy of geothermal heating system. This study proposes a comprehensive and systematic operation strategy for a geothermal step utilization heating system (GSUHS). Calculation models of radiator heating system (RHS), radiant floor heating system (RFHS), heat pump (HP), gas boiler (GB), plate heat exchanger (PHE) and pump are first established. Then the operation strategy of the GSUHS is analyzed with the aim to substantially reduce the conventional energy consumption of the whole system. Finally, the energy efficiency and geothermal tail water temperature are analyzed. With the operation strategy in this study, the geothermal energy provides the main heating amount for the system. The heating seasonal performance factor is 15.93. Compared with coal-fired heating, 75.1% of the standard coal equivalent can be saved. The results provide scientific guidance for the application of an operation strategy for a geothermal step utilization heating system.

Natural gas can be used for satisfying population needs for heating, either directly by bringing the gas to the dwellings through the gas distribution system and combusting it in the domestic boiler (gas distribution system—G) or indirectly by combusting the natural gas in the heating plant and distributing the heat energy to the dwellings through the district-heating (DH) system. The selection of a certain type of heating system is made according to the disposition of buildings in the area, their number, size, insulation quality, etc. Based on these characteristics, calculations of investments and exploitation costs have been made for both heating systems and a comparison has been made for all of the 96 presented cases. Almost each type of real settlement can be represented by one of the types of the conditional urban area that are introduced in the paper. The main goal of this paper is to establish a general model to achieve coordinated development of centralized energy supply systems fueled by natural gas, based on defined and accepted criteria. A structure analysis of centralized systems for energy supply has been done with accent on their pipelines.

District heating systems using cogeneration, as well as local fuel-based and electric heating systems for detached houses, are analysed. The analysis includes the whole energy system, from the natural resource to the end user, with respect to primary energy use, emission and cost. The end-use technologies studied are heat pumps, resistance heaters and boilers. It was assumed that the base-load electricity, except for the cogenerated electricity, was produced in stand-alone power plants using wood chips or natural gas, while peak-load electricity and fuel used for transportation were produced from crude oil. The heat pump and district heating systems are found to be most energy efficient, followed by the local fuel-based systems. The wood-fuel-based systems emit about one tenth of the greenhouse gases emitted by the natural-gas-based systems. The sulphur and nitrogen oxide emission, however, is higher for wood-fuel-based systems. Systems based on natural gas are less expensive than the corresponding wood-fuel-based systems. Decarbonization and carbon dioxide sequestration, however, do not reduce the carbon dioxide emission to the low level of the wood-fuel-based systems and, in addition, make the natural-gas-based systems more expensive than the wood-fuel-based systems.

An experimental facility consisting of two identical 3×4.4×3.8 m3 rooms has been built. Each room has a gas-fired boiler supplying hot water to the radiant-floor heating system. An electrically heated storage tank installed in the circuit ensures that hot water to the floor slab is supplied directly from the storage tank. The facility serves for instantaneous comparisons of two different control strategies implemented in separate rooms. Two flow-control schemes were tested and evaluated. We used (i) a conventional on–off control for a valve controlled by feedback from the room thermostat and (ii) a two-parameter switching control (TPSC) with switching intervals ranging from 30 s to 60 min. With this strategy and a switching time of 10 min, the valve is operated in the on–off mode for the first 10 min based on feedback signals received from the slab-temperature sensor and during the next 10 min, air-temperature signals from the thermostat control the valve. This latter strategy is shown to be better for radiant heat control under continuous and intermittent modes of operation than to conventional on–off control.