Forecasting of failures in district heating systems

This work presents the method of failures forecasting in district heating systems on the basis of time series analysis.Statistical data concerning the frequency of damage in communal heat distribution networks from a ten-year time period have been used in the article. The data were subjected to statistical analysis. The methods of exponential smoothing, ARIMA, homologous period trend estimation and seasonal indicators were applied as the most adequate for this type of data. Four forecast models of damage in district heating systems were formulated and the best optimal model for the system was selected.After verification, the methods of failure prediction in district heating systems can be applied in the operating process of a heat supply system. These methods give us answers to many questions about planning of repairs, maintenance emergency service, planning of finances and purposefulness of operational control.     

污水源热泵系统及其在成都地区应用的初步研究

介绍了城市污水的主要热能特性以及污水源热泵原理和分类,统计了成都市的污水处理厂及污水排放情况,并简单计算成都市污水中所蕴含的能量,分析了成都市发展污水源热泵的可行性,并简要介绍了目前成都地区应用污水源热泵需要解决的问题,分析结果表明污水源热泵在成都地区具有良好的发展及应用前景。     

Capacity-controlled ground source heat pumps in hydronic heating systems

The objective of this study was to investigate the energy-saving potential of using variable-speed capacity control instead of the conventional intermittent operation mode for domestic ground source heat pumps. Variable-speed capacity control is commonly used in air-to-air heat pumps, but not in ground source heat pumps for hydronic heating systems, even though the energy-saving potential may be greater for this application. A theoretical analysis indicates how the energy efficiency is influenced by variable-speed capacity control of the compressor. The analysis shows that, to take full advantage of the capacity control, care should be taken to achieve the correct relationship between refrigerant flow and heat transfer media flows. Intermittent control and variable-speed capacity control were compared by laboratory tests on two capacity-controlled heat pumps and one standard heat pump with a single-speed compressor. Test data were then used for seasonal performance factor (SPF) calculations. The SPF calculations show that despite improved performance at part load the variable-speed controlled heat pump did not improve the annual efficiency compared to the intermittently operated heat pump. This is mainly due to inverter and compressor motor efficiencies and the need for improved efficiency and control of pumps used in the heating and ground collector systems.     

Life cycle assessment of Irish district heating systems: a comparison of waste heat pump,biomass-based and conventional gas boiler

Clean Technologies and Environmental Policy - This paper presents a life cycle assessment of heat supply scenarios towards replacement of fossil-based energy systems through a case study focusing...     

System options for cooling of buildings making use of district heating heat

Issues stemming from district heating utilization during summer periods and the conversion of low-temperature heat into cold in adsorption chillers have been investigated in this paper. Due to the high vulnerability of adsorption chillers to ambient conditions, in the case of relatively low ambient temperatures, adsorption-based air-conditioning systems would be characterized by excessive cooling power. Moreover, adsorption chillers are also characterized by high investment costs and big time constants, and the vulnerabilities found in their regulatory processes have yet to be sufficiently investigated. The authors recommend the application of hybrid air-conditioning systems, consisting of adsorption and compressor chillers. The adsorption chiller works as a base while the compressor chiller contributes missing cooling power, working as a regulation unit. Sixteen configurations of the hybrid air-conditioning system have been analysed. It has been shown that 100 kW cooling power hybrid air-conditioning system, with respect to its configuration, enables the utilization of 0.5 to 0.9 TJ of low-temperature heat per year, while simultaneously providing comfortable air-conditioning. The authors have concluded that the adsorption share in the analysed hybrid system should not exceed 50%.     

Feasibility limits of using low-grade industrial waste heat in symbiotic district heating and cooling networks

Clean Technologies and Environmental Policy - Low-grade waste heat is an underutilized resource in process industries, which may consider investing in urban symbiosis projects that provide heating...     

湖南某区域污水源热泵系统的应用与分析

近年来,随着城镇化进程的加快,区域集中供冷在我国取得了较快的发展。同时,可持续发展已经引起各个方面的关注。采用污水源热泵系统回收城市污水中的热能,既开发了清洁能源,又降低了城市废热的排放,保护了环境。本文分析探讨了区域供冷中污水源热泵系统的特点,并以湖南某区域供冷项目为例,介绍了污水源热泵系统的规模、装机配置、组成等,同时进行了经济分析。对今后区域集中供冷中采用污水源热泵系统的建设提供了参考。     

可自动反冲洗的污水源热泵的应用研究

介绍一种带自动反冲洗功能的污水源热泵机组.增设此功能后,污水可以直接进入机组换热器,与带中间换热器的常规机组相比,减小传热温差.通过对整个系统进行优化设计,机组效率进一步提高,但设备成本有所增加.     

Effect of heating temperature on the sintering characteristics of sewage sludge ash

This study investigated and analyzed the effects of the heating temperature on the properties of the sintered sewage sludge ash. The results indicated that the water absorption rate of the sintered sewage sludge ash samples decreased when the firing temperature was increased from 800 to 900 degrees C. When the heating temperature reached 1000 degrees C, the absorption rate decreased significantly. The bulk density of the sewage sludge ash samples increased by 2.3g/cm3 when the heating temperature was increased from 900 to 1000 degrees C, indicating that the densification was affected by heating. The porosity of the sintered sewage sludge ash samples ranged from 36% to 39% when the heating temperature ranged from 600 to 900 degrees C. The least porosity occurred at 1000 degrees C; the sintered samples were well densified. When the temperature was between 900 and 1000 degrees C, the strength appeared to increase significantly, reaching 2040 kgf/cm2, implying an advance in densification due to sintering. The SEM observations were in general agreement with the trends shown by the density data.     

Hybrid absorption heat pump with ammonia/water mixture – Some design guidelines and district heating application

An ammonia/water mixture can be used as an efficient working fluid in industrial-type heat recovery heat pumps and heat transformers. Several configurations of such systems are possible depending on the availability of the waste (thermal) and primary (thermal or electrical) energy sources. This article presents the configurations, the main thermodynamic and hydraulic parameters, and some design guidelines and operating experiences of a medium-temperature, ammonia/water-based compression/re-sorption heat recovery system for district domestic hot water production. In-field experiments have proven the advantages of the concept and its applicability limits in a particular economical environment, while hot water was produced at 55 °C with industrial cooling water at 36 °C as a waste heat source.     

Inverse heat transfer analysis of radiator central heating systems inside residential buildings using sensitivity analysis

In the present study, a novel inverse heat transfer methodology is presented for thermal energy analysis of residential buildings equipped with radiator Heating, Ventilation, Air Conditioning systems using a combination of numerical simulation and sensitivity analysis. With the use of numerical simulation, thermal analysis of building components is simulated in order to calculate temperature field in the computational domain. With inverse analysis technique, we perform the estimation of some thermal parameters with the use of Levenberg–Marquardt and conjugate gradient methods and reported the results with the use of sensitivity analysis inside the building. To confirm the accuracy of numerical simulation, the problem is also simulated with commercial software such as Carrier and Energy-Plus. Then, thermal parameter estimation results of inverse simulation are presented. The present study illustrates the sufficiency of inverse analysis in order to calculate building thermal design parameters with excellent accuracy and precision with the least possible financial design cost.     

Microwave heating in multiphase systems: evaluation of series solutions

The 1D electric field and heat-conduction equations are solved for a slab where the dielectric properties vary spatially in the sample. Series solutions to the electric field are obtained for systems where the spatial variation in the dielectric properties can be expressed as polynomials. The series solution is used to obtain electric-field distributions for a binary oil-water system where the dielectric properties are assumed to vary linearly within the sample. Using the finite-element method temperature distributions are computed in a three-phase oil, water and rock system where the dielectric properties vary due to the changing oil saturation in the rock. Temperature distributions predicted using a linear variation in the dielectric properties are compared with those obtained using the exact nonlinear variation.     

Microbiologically influenced corrosion in hydronic heating systems

Open-loop hydronic heating systems have been found to provide a breeding ground for bacteria, including bacteria associated with microbiologically influenced corrosion (MIC). Microbiologically influenced corrosion of brass fittings, which may contain up to 8% lead in potable water applications, has been linked to high copper and lead levels in water samples taken from the hydronic-loop tubing. The contamination is likely concentrated in slime deposits found within the tubing. These slime deposits can enter the potable water supply, resulting in potential copper and lead exposure levels considerably above Environmental Protection Agency (EPA) guidelines. The authors recommend that hydronic heating systems incorporate a closed-loop design to prevent personal exposure and to provide for use of corrosion-inhibiting additives.     

Cross field heating systems: influence of system parameters

A two-dimensional analysis of cross field heating systems is presented. An analytical method is used to obtain the impressed field in the air gap of the system without resorting to extensive calculations. The air-gap field in its turn makes it possible to calculate the power induced in the workpiece and provides some design guidelines. Expressions derived for the power induced in the workpiece are used to study the performance of the cross field systems as a function of parameters such as pole width, air-gap length, workpiece thickness, and supply frequency. The influence of the core permeability is also shown. The results indicate that the optimum value of the induced power in a system of given dimensions is almost independent of the workpiece thickness. The calculated value of the induced power shows good agreement with the measured value for a test system     

Influence of internal heat sources on nonstationary heat transfer in disperse systems

The influence of internal heat sources on the effective thermophysical properties of disperse media is examined and relaxation equations are obtained. It is shown that the heat-conduction equation can be both hyperbolic and elliptic in type.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 2, pp. 272–278, February, 1986.     

Failure analysis of a thermally insulated pipeline in a district heating system

Failure analysis of a thermally insulated pipeline which failed during operation in a district heating system was performed by utilizing optical and electron microscopy in addition to various mechanical tests. The fractographic investigation showed that a crack initiated at the inside of the pipe and propagated to the outside. The crack was initiated at the toe region of the weldment and propagated along the transverse direction of the weldment. In the mechanical tests, the low toughness and hydrogen sensitivity of the weldment affected the failure of the thermally-insulated pipeline. In short, the interaction of the multiple effects in the HAZ, including the lower mechanical properties, stress concentration, and hydrogen susceptibility, led to pipe failure.     

某医院污水源热泵系统应用分析

基于某医院项目中污水废热的回收利用,分析医院污水水质特征,阐明污水源热泵系统用于生活热水预热的技术可行性;参考同类项目中污水全年温度变化曲线,以某热泵产品运行参数为依据对该技术方案进行全年能耗计算分析,并与传统燃气锅炉供热系统进行经济性对比。结果表明,医院采用污水源热泵系统预热生活热水具有较大的节能优势和经济性。     

低温热水地板与热泵空调器采暖测试对比分析

通过对重庆地区一住宅内温水地板供暖系统的测试,分析对比了该系统与热泵空调器采暖方式对室内热舒适性的影响及运行费用的差别,同时对地板辐射和对流散热的综合效果进行分析,表明在长江流域等非采暖地区应用地板辐射采暖的可行性及优越性.