A district heating system based on absorption heat exchange with CHP systems

In order to decrease the energy consumption of large-scale district heating systems with cogeneration, a district heating system is presented in this paper based on absorption heat exchange in the cogeneration system named Co-ah cycle, which means that the cogeneration system is based on absorption heat exchange. In substations of the heating system, the temperature of return water of primary heat network is reduced to about 25°C through the absorption heat-exchange units. In the thermal station of the cogeneration plant, return water is heated orderly by the exhaust steam in the condenser, the absorption heat pumps, and the peak load heater. Compared with traditional heating systems, this system runs with a greater circuit temperature drop so that the delivery capacity of the heat network increases dramatically. Moreover, by recovering the exhausted heat from the condensers, the capacity of the district heating system and the energy efficiency of the combined heat and power system (CHP system) are highly developed. Therefore, high energy and economic efficiency can be obtained.     

A new type of district heating system based on distributed absorption heat pumps

Large district heating (DH) system accounts for 70% of urban building heating in China. In North China, this proportion is even higher (The North China is the north of the Huai River and Qinling Mountains). Many cities in North China can exploit various kinds of low-grade renewable energy. This paper presents a new heating method to realize renewable energy recovery by absorption heat pumps associated with municipal network. In the DH substations, absorption heat pumps are driven by the exergy-difference originated from the larger temperature difference of heat exchange between primary and secondary heat network. There are two configurations—type I and type II substations based on the temperature of renewable energy. A reasonable parameter setting of system is suggested. The equipment operational performance was optimized based on a practical example. The low-grade renewable energy can be recovered effectively in this method. As a result, both heating capacity and energy efficiency of the DH system can be improved. Furthermore, operating costs may be reduced remarkably, due to the reduction in both the coal consumption of heat production unit and the power consumption of delivery pump. Therefore, the system is superior in energy conservation and has a promising application prospect.     

吸收式热泵技术在热电联产供热系统中的应用

介绍热电联产相结合的吸收式热泵供热技术,并结合实例工程的计算与分析,指出该技术在理论和实际应用中的可行性,该方法可回收利用大量冷却水的低温余热,大大增加现有热源的供热能力。     

A model of district heating using a CHP plant

The paper presents a static linear programming model of a district heating system in which the base load is covered by a cogenerating station producing heat and electricity. The model provides optimal investment decisions (generating station, hot water accumulator, peak units, distribution network) as well as optimal operating rules. The reliability of the cogenerating station is taken explicitly into account by introducing shortage costs in case of failure. It is assumed the electricity produced is sold at time-variable transfer prices to the public grid. Numerical results are provided for a medium-size city.     

炼油装置余热回收汽暖改水暖集中供热方案研究

为回收炼厂丰富的低温余热用于生活区的集中供暖,本文对余热资源和生活区采暖热负荷分别进行了综合标定和统计计算,确定采用回收余热、汽暖改水暖的集中供热系统方案。技术经济分析表明,该方案的节能效果和经济效益十分显著。     

Design and performance of direct heat exchange geothermal district heating schemes

A variety of geothermal district heating scheme designs have been studied, differences of configuration have been identified and the design principles used to obtain maximum geothermal heat supply have been defined. The main principle is that return temperatures to the heat exchange must be as low as possible and to achieve this the network must be operated with variable temperature and flow in response to fluctuating demands. The location of back-up boilers, the type of sub-station and the inclusion of domestic water heating normally have small effects on performance. However, in some cases, water heating can have a detrimental effect.     

西安某小区供热系统气候补偿节能改造

以西安市某小区为例,对其进行气候补偿节能改造。通过调研提出其存在的其他问题,针对问题进行节能技术改造。主要采用了3种技术措施气候补偿、分时分区、加装自力式流量控制阀,达到节约能源的效果,并提高用户的舒适度。     

余热回收吸收式制冷集中空调方案研究

为回收大型炼油装置丰富的低温余热用于生活区的夏季集中空调,本文对余热资源状况和生活区集中空调建筑物供冷负荷分别进行了综合标定和统计计算,在分析比较的基础上确定采用余热热水型溴化锂吸收式制冷冷水机组和半集中式风机盘管全水型空调系统,并利用现有双管制热水集中供暖管网和泵站输送空调冷水,可以显著地节约投资。技术经济分析表明,该方案在技术上可行,节能效果和经济效益十分显著,而且可以大大改善厂区的热污染和居民的生活条件。     

Model-based influencing factors analysis of residential heat consumption in district heating systems

Abstract

A simplified and accurate hybrid model is proposed to analyze, evaluate, and predict space heating energy consumption and indoor temperature in residential buildings connected to district heating systems. With classical engineering equations of thermodynamic laws, this method uses physical and empirical modeling to describe heat exchangers in real-time. Furthermore, the model has optimized the cost of computation and enhanced the prediction accuracy. It is revealed this method can accurately predict the residential heat load and indoor temperature with the maximum error of ±10%. The architectural parameter, outdoor temperature, and wind velocity have decisive effects on the heat energy demand.     

A comprehensive thermodynamic analysis of load‐flexible CHP plants using district heating network

Because of the rapid expansion of intermittent renewable energy, conventional coal‐fired power plants, including combined heat and power (CHP) plants, are required to improve the quick‐response ability to respond the changing demand of the grid. However, the flexibility of CHP plants is not easy to be improved because of the restriction of traditional load variation mechanism. This work presents a comprehensive thermodynamic analysis on the flexibility‐improving scheme using the thermal energy storage (TES) capacity of district heating (DH) network. A typical CHP plant and related DH network were selected as a case study. The flexibility demand under the context of renewables accommodation in the short timescale (counted by minutes) and the operational characteristics of CHP plants were analyzed on the basis of experimental data and thermodynamics. Besides, the influence of heat supply adjustment on heat users' indoor temperature was quantified with a dynamic model, and the thermal inertia of the DH network is discussed. Moreover, a thermodynamic model for the load variation processes simplified with operational characteristics was established to analyze the response ability improvement of CHP plants. Results of the case study show, the scheme can shorten approximately 34% of the response time while almost have no influence on the indoor temperature of heat users.     

Gas turbines in district heating combined heat and power systems: influence of performance on heating costs and emissions

Much work is currently focussed on identifying economically and environmentally optimal strategies for increasing gas turbine based combined heat and power (CHP). In many such studies, only a few fixed parameters are used to describe the CHP plant. These are typically total and electrical efficiencies, investment and running costs, minimum and maximum acceptable size, and minimum acceptable part-load. However, for gas turbine based systems these characteristics are clearly functions of the operating conditions, especially for part-load operation. This study examines the effects of varying performance of the gas turbine on the overall heat production costs and CO₂ emissions of a medium sized community district heating plant. Both single and double-shaft engines are considered in the study. The results show that the assumption of constant efficiencies for all operating conditions leads to an overestimation of the optimal CHP plant size, thereby underestimating the heat production costs and overestimating the CO₂ emissions of the plant. The results also show marked differences according to the type of gas turbine used and part-load operating strategy adopted. In particular, the paper discusses the part-load operating difficulties for CHP plants running gas turbines equipped with low emissions burners.     

Design of biomass district heating systems

The biomass exploitation takes advantage of the agricultural, forest, and manure residues and in extent, urban and industrial wastes, which under controlled burning conditions, can generate heat and electricity, with limited environmental impacts.Biomass can – significantly – contribute in the energy supplying system, if the engineers will adopt the necessary design changes to the traditional systems and become more familiar with the design details of the biomass heating systems.The aim of this paper is to present a methodology of the design of biomass district heating systems taking into consideration the optimum design of building structure and urban settlement around the plant. The essential energy parameters are presented for the size calculations of a biomass burning-district heating system, as well as for the environmental (i.e. Greenhouse Gas Emissions) and economic evaluation (i.e. selectivity and viability of the relevant investment). Emphasis has been placed upon the technical parameters of the biomass system, the economic details of the boiler, the heating distribution network, the heat exchanger and the Greenhouse Gas Emissions.     

Simulation of an absorption heat pump solar heating and cooling system

An absorption heat pump (AHP) is a heat driven heat pump utilizing the absorption process. A continuous, liquid absorbent AHP with chemical storage is modeled using mass and energy balances and assuming mass transfer equilibrium. This model is used with the TRNSYS program [5] to simulate the performance of an AHP in a residential solar-driven heating and cooling system. The effects of collector area for an AHP using the NaSCN---NH₃ chemical system are investigated for the Columbia, MO, Madison, WI, and Fort Worth, TX climates. The AHP system is compared to a conventional solar heating and cooling system and the effects of heat exchanger effectiveness, storage mass, additional thermal capacitance and alternative control strategies are studied for the Columbia climate.     

Techno-economic analysis of a coal-fired CHP based combined heating system with gas-fired boilers for peak load compensation

Combined heat and power (CHP) plants dominate the heating market in China. With the ongoing energy structure reformation and increasing environmental concerns, we propose gas-fired boilers to be deployed in underperforming heating substations of heating networks for peak load compensation, in order to improve both energy efficiency and environmental sustainability. However, due to the relatively high price of gas, techno-economic analysis is required for evaluating different combined heating scenarios, characterized by basic heat load ratio (β). Therefore, we employ the dynamic economics and annual cost method to develop a techno-economic model for computing the net heating cost of the system, considering the current state of the art of cogeneration systems in China. The net heating cost is defined as the investment costs and operations costs of the system subtracted by revenues from power generation. We demonstrate the model in a real-life combined heating system of Daqing, China. The results show that the minimum net heating cost can be realized at β=0.75 with a cost reduction of 16.8% compared to coal heating alone. Since fuel cost is the dominating factor, sensitivity analyses on coal and gas prices are discussed subsequently.     

A review of heat pump water heating systems

A heat pump water heater (HPWH) operates on an electrically driven vapor-compression cycle and pumps energy from the air in its surroundings to water in a storage tank, thus raising the temperature of the water. HPWHs are a promising technology in both residential and commercial applications due to both improved efficiency and air conditioning benefits.Residential HPWH units have been available for more than 20 years, but have experienced limited success in the marketplace. Commercial-scale HPWHs are also a very promising technology, while their present market share is extremely low.This study dealt with reviewing HPWH systems in terms of energetic and exergetic aspects. In this context, HPWH technology along with its historical development was briefly given first. Next, a comprehensive review of studies conducted on them were classified and presented in tables. HPWHs were then modeled for performance evaluation purposes by using energy and exergy analysis methods. Finally, the results obtained were discussed. It is expected that this comprehensive review will be very beneficial to everyone involved or interested in the energetic and exergetic design, simulation, analysis, performance assessment and applications of various types of HPWH systems.     

Validation of a computer model for solar assisted district heating systems with seasonal hot water heat store

The TRNSYS XST-model for the calculation of the thermal behaviour of ground buried hot water heat stores was validated. For the validation procedure measured data of the seasonal hot water heat store in Hannover (Germany) were used. In contrast to previous investigations the temperatures of the surrounding ground were also taken into consideration. The determination of the heat store parameters was carried out using TRNSYS in combination with the parameter identification software DF. The deviation between measured and calculated temperatures is less than ±3%. The measured and calculated heat quantities are also in good agreement (annual deviation less than 2%). The validated XST-model was integrated into a TRNSYS model to calculate the thermal behaviour of the solar assisted district heating system in Hannover in 2002. The deviations between measured and calculated heat quantities do not exceed 5%.     

Fuzzy comprehensive evaluation of district heating systems

Selecting the optimal type of district heating (DH) system is of great importance because different heating systems have different levels of efficiency, which will impact the system economics, environment and energy use. In this study, seven DH systems were analysed and evaluated by the fuzzy comprehensive evaluation method. The dimensionless number—goodness was introduced into the calculation, the economics, environment and energy technology factors were considered synthetically, and the final goodness values were obtained. The results show that if only one of the economics, environment or energy technology factors are considered, different heating systems have different goodness values. When all three factors were taken into account, the final ranking of goodness values was: combined heating and power>gas-fired boiler>water-source heat pump>coal-fired boiler>ground-source heat pump>solar-energy heat pump>oil-fired boiler. The combined heating and power system is the best choice from all seven systems; the gas-fired boiler system is the best of the three boiler systems for heating purpose; and the water-source heat pump is the best of the three heat pump systems for heating and cooling.     

A multicriteria approach to evaluate district heating system options

District energy systems, in which renewable energy sources may be utilized, are centralized systems to provide energy to residential and commercial buildings. The aim of this paper is to evaluate and rank energy sources available for a case of district heating system in Vancouver, Canada, based on multiple criteria and the view points of different stakeholders, and to show how communication would affect the ranking of alternatives. The available energy sources are natural gas, biomass (wood pellets), sewer heat, and geothermal heat. The evaluation criteria include GHG emissions, particulate matter emissions, maturity of technology, traffic load, and local source. In order to rank the energy options the PROMETHEE method is used. In this paper, two different scenarios were developed to indicate how the communication between the stakeholders would affect their preferences about criteria weights and would change the ranking of alternatives. The result of this study shows that without communication the best energy source for the considered district energy system is different for different stakeholders. While, addressing concerns through efficient communication would result in a general consensus. In this case, wood pellet is the best energy alternative for all the stakeholders.