District Heating Pipelines Research Articles

Multi criteria dynamic design optimization of a small scale distributed energy system

The aim of this paper is to analyze the mutual interdependencies and trade-offs between heat storage and district heating network considering economic and ecological aspects. Therefore, a MILP (mixed integer linear programming) problem of a distributed energy system is formulated with a weighted multi-criteria objective function including profit and operational CO2 emissions. The considered components include CHP (combined heat and power) units of three different types, a thermal storage facility, a boiler, and district heating pipelines. In a single optimization step placement, quantity and capacity of all components as well as their operation is determined. The computed designs as well as the operation of the energy system are compared under varying weightings and different technology scenarios. We also conduct a sensitivity analysis of the investment costs associated with heat storage and of the piping costs for the district heating network. The results favor the construction of heat storage devices over a district heating network. This applies to both environmental impact and cost of energy supply and can be well explained by the decoupling of heat demand and electricity production, which is shown in a correlation analysis.

Optimum Siting and Sizing of Distributed Energy Resources Taking into Consideration Hourly Operating Strategies

In this paper, a distributed energy resource (DER) system plan and evaluation model is extended to include the design of district heating network. In the model, production and consumption of electric power and heat, power transmissions, transport of fuels to the production plants, transport of water in the district heating pipelines and storage of heat are taken into account. The problem is formulated as a mixed integer linear programming (MILP) model where the objective is to minimize the overall cost of the DER system. The solution gives the DER structure, i.e., which production units, heat transport lines and storages should be built as well as their locations, together with design parameters for plants and pipelines.

The concept of the system resilience within the infrastructure dimension: application to a Latvian case

Abstract Regarding the infrastructure systems resilience often means a capability of the system to recover its function and properties after a disruptive event. The evaluation of the resilience depends on the formulation of the resilience itself, the type of the system to be analysed and the methodology applied (i.e. quantitative or qualitative evaluations). The significance of this research field is crucial for optimizing recovery strategies and disaster risk management. This study provides a new methodological approach for selection of the most effective restoration strategy of a networked infrastructure system, utilizing both quantitative and qualitative (multi-criteria analysis) methods. The proposed methodology was summarized into a general algorithm and implemented into a programmed tool for practical application. The case of a real system was examined by the application of the developed methodology to the district heating pipeline system of Salaspils city (Latvia). This study also comprehends the main aspects to be considered when using the specific resilience metric as a function of time and involving economic components. The practical value of the current study is represented by the tool, which can be used by the stakeholders in the regional planning, organization of restoration and other processes, where high level efficiency in use of materials and time resources is required.

Absorption equipment for energy savings: A case study in Sicily

Abstract This paper considers a feasibility study on the recovery of the reject heat available from an electric utility with two units operating with 120-MW gas turbines; these units have a heat recovery system that feeds the district heating pipeline of an industrial consortium. Thus, feeding the expeller of the absorption equipment installed in a cooling plant for foodstuff stocking represents an opportunity for the feasibility study. This plant operates at both 0 °C and −18 °C. The feasibility study covers two aspects: (1) the technical feasibility of a suitable absorption cooling plant that uses two separate pieces of absorption equipment working with the pair ammonia–water and (2) the relevant economic venture analysis. The feasibility study pertains to both the optimal design of the absorption equipment and the energetic and exergetic analysis of the plant; moreover, the same type of analysis was performed for a reference case pertaining to a two-stage reciprocating compression refrigerating plant. An economic analysis of the venture demonstrated that the expected time of return on the differential investment is less than 4 years and that the specific investment costs expected given the differential costs between the two alternative options are 11.28 €/toe of primary energy savings and 15.84 c€/t(CO2,eq) of reduced greenhouse gas emissions.

Economic and environmental impacts of insulation in district heating pipelines

The determination of optimum thickness of insulation is often applied to energy technologies and building projects. In this study, the energy, economic and environmental evaluations of thermal insulation in district heating pipeline are discussed. The optimum insulation thickness, energy saving over a lifetime of 10 years, payback period and emissions of CO 2, CO and SO 2 are calculated for nominal pipe sizes and fuel types based on heating loads in Afyonkarahisar/Turkey. The life cycle cost analysis is used to determine the optimum thickness of the pipeline material in order to take into account the change in inflation that directly affect both the cost of pipeline material and fuels depending on fuel type. The results show that the highest value of optimum insulation thickness, energy savings, emissions and the lowest payback period are reached for a nominal pipe size of 200 mm. About three times more energy saving results by making 200 mm nominal pipe instead of 50 mm. Considering the economical and environmental advantages, the geothermal energy is a better choice and then fuel-oil. When thermal insulation is done in a district heating pipeline, there will be a significant reduction of 21% in the amount of CO 2 emitted to the atmosphere.

Thermo-economic analysis of pipe insulation for district heating piping systems

Abstract In this study, the optimum insulation thickness of pipes used in district heating pipeline networks, energy savings over a lifetime of 10 years, and payback periods are calculated for the five different pipe sizes and four different fuel types in the city of Afyonkarahisar/Turkey. For this reason, an optimization model is performed depending on Life Cycle Cost (LCC) analysis via P 1 – P 2 method. Rock wool as insulation material and a system of pipelines (50–200 mm nominal sizes) with flow of hot water are considered. The results show that optimum insulation thicknesses vary between 0.085 and 0.228 m, energy savings vary between 10.041 $/m and 175.171 $/m, and payback periods vary between 0.442 and 0.808 years depending on the nominal pipe sizes and the fuel types. The highest value of energy savings is reached in 250 mm nominal pipe size for fuel-oil fuel type, while the lowest value is obtained in 50 mm for geothermal energy. Considering the economical and environmental advantages, the geothermal energy is a better choice and then natural gas.

10.2478/s11814-009-0159-x

This paper presents a scheme to achieve structural and operational optimization for the heat plant in a district energy system. A district energy system consists of energy suppliers and consumers, district heating pipelines and heat storage facilities in a region. Production and consumption of energy and transport of energy as well as storage of heat are taken into account in the model. The problem is formulated as a mixed integer linear programming (MILP) problem where the objective is to minimize the overall cost of the district energy system. Evaluation of the energy production cost is based on the daily operation for every season at the plant located at Suseo in Seoul, Korea. From the results of numerical simulations we can see that the district energy system is well approximated by the proposed model, and that the energy efficiency is improved by the application of the optimal operation conditions provided by the proposed model.

Optimal operation of the integrated district heating system with multiple regional branches

This paper presents an optimal production and distribution management for structural and operational optimization of the integrated district heating system (DHS) with multiple regional branches. A DHS consists of energy suppliers and consumers, district heating pipelines network and heat storage facilities in the covered region. In the optimal management system, production of heat and electric power, regional heat demand, electric power bidding and sales, transport and storage of heat at each regional DHS are taken into account. The optimal management system is formulated as a mixed integer linear programming (MILP) where the objectives is to minimize the overall cost of the integrated DHS while satisfying the operation constraints of heat units and networks as well as fulfilling heating demands from consumers. Piecewise linear formulation of the production cost function and stairwise formulation of the start-up cost function are used to compute nonlinear cost function approximately. Evaluation of the total overall cost is based on weekly operations at each district heat branches. Numerical simulations show the increase of energy efficiency due to the introduction of the present optimal management system.

Optimization of the heat plant of district energy systems

This paper presents a scheme to achieve structural and operational optimization for the heat plant in a district energy system. A district energy system consists of energy suppliers and consumers, district heating pipelines and heat storage facilities in a region. Production and consumption of energy and transport of energy as well as storage of heat are taken into account in the model. The problem is formulated as a mixed integer linear programming (MILP) problem where the objective is to minimize the overall cost of the district energy system. Evaluation of the energy production cost is based on the daily operation for every season at the plant located at Suseo in Seoul, Korea. From the results of numerical simulations we can see that the district energy system is well approximated by the proposed model, and that the energy efficiency is improved by the application of the optimal operation conditions provided by the proposed model.

Evaluation of Approaches for Modeling Temperature Wave Propagation in District Heating Pipelines

The limitations of a pseudo-transient approach for modeling temperature wave propagation in district heating pipes were investigated by comparing numerical predictions with experimental data. The performance of two approaches, namely a pseudo-transient approach implemented in the finite element code ANSYS and a node method, was examined for a low turbulent Reynolds number regime and small velocity fluctuations. Both approaches are found to have limitations in predicting the temperature response time and predicting the peak values of the temperature wave, which is further hampered by the fact that the fluid is represented as an ideal fluid. The approaches failed to adequately predict the temperature wave propagation in the case of rapid inlet temperature changes. The overall conclusion from this case study was that in order to improve the prediction of the transient temperature, attention has to be given to the detailed modeling of the turbulent flow characteristics.

Structural and operational optimisation of distributed energy systems

A distributed energy system (DES) is a system comprising a set of energy suppliers and consumers, district heating pipelines, heat storage facilities and power transmission lines in a region. Distributed energy production has got an increasingly important role in the energy market. In this paper, a model for structural and operational optimisation of DES is presented. In the model, production and consumption of electrical power and heat, power transmissions, transport of fuels to the production plants, transport of water in the district heating pipelines and storage of heat are taken into account. The problem is formulated as a mixed integer linear programming (MILP) problem where the objective is to minimise the overall cost of DES, i.e., the sum of the running costs for the included operations and the annualised investment costs of the included equipment. An illustrative example is presented for a complex DES situation. The solution gives the DES structure, i.e., which production units, heat transport lines and storages should be built as well as their locations be, together with design parameters for plants and pipelines. The model enables the involved parties—suppliers, consumers, designers and authorities—to form a joint view of different situations as a basis for the decision making. A tool based on the model is built, which can be used in design, in creating guidelines for regional energy policies and for versatile what-if analyses.

THERMO-HYDRAULIC FINITE ELEMENT MODELLING OF DISTRICT HEATING NETWORK BY THE UNCOUPLED APPROACH

The modelling of uncoupled fluid flow and heat transfer problems of a district heating network using the finite element method (FEM) is presented. Since the standard thermo-hydraulic pipe elements cannot be directly used for modelling insulation, the main attention was paid to discretisation of multilayered structure of pipes and surrounding by one-dimensional thermal elements. In addition, validity of the finite element method was verified numerically by solving fluid flow and heat transfer problems in district heating pipelines. Verification analysis involves standard single pipe problems and simulation of fragment of district heating in Vilnius. Pressure and temperature results obtained by finite element method are compared with those by other approaches.

THERMO-HYDRAULIC FINITE ELEMENT MODELLING OF DISTRICT HEATING NETWORK BY THE UNCOUPLED APPROACH

Abstract The modelling of uncoupled fluid flow and heat transfer problems of a district heating network using the finite element method (FEM) is presented. Since the standard thermo-hydraulic pipe elements cannot be directly used for modelling insulation, the main attention was paid to discretisation of multilayered structure of pipes and surrounding by one-dimensional thermal elements. In addition, validity of the finite element method was verified numerically by solving fluid flow and heat transfer problems in district heating pipelines. Verification analysis involves standard single pipe problems and simulation of fragment of district heating in Vilnius. Pressure and temperature results obtained by finite element method are compared with those by other approaches.

Analysis Of Fluid Flow And Heat Transfer In District Heating Pipelines Using The Finite Element Method

The finite element method is applied to solve coupled steady-state fluid flow and heat transfer problems in insulated pipes of district heating networks. The main advantage of the finite element method involved here is the standard discretization and solution technique for both coupling of temperature-dependent physical properties in the thermo-hydraulic flow and for description of the multilayered structure of insulation, which may also be situated in the environment, such as soil or air. In order to describe the above problem in a standard manner, the complex thermo-hydraulic macroelement has been proposed. This element presents a combination of a standard hydraulic pipe element and one-dimensional thermal elements of the ANSYS code. The proposed approach is used to investigate temperature-dependent fluid properties and the role of the coupling in district heating pipelines. (Less)

High-resolution thermophysical measurements using staring infrared detector arrays

Infrared thermal imaging by means of a staring focal-plane-array infrared camera system is now available for civil applications in environmental, industrial, and medical areas. The high sensitivity (ΔT < 0.01 K) and the high speed (At < 5 ms) of such camera systems open up wide new fields for applications. Infrared systems are demonstrated which can detect flaws in solar-grade semiconductor material. Microscope infrared lenses permit localisation of material defects with a resolution of 10 μm. Other applications are the detection of weak spots in the insulation of district heating pipelines and the real-time visualisation of methane gas distributions emitted into the atmosphere from leaky gas pipelines. The high temporal resolution (5 ms) of time-dependent temperature variations by the infrared camera systems even permits the capture of a frame sequence of the solution heat trace created by a methanol droplet falling into and rebounding out of a water surface until it eventually dissolves in the water after 100 ms.

96/00823 Examination of the condition of district heating pipelines in east Germany

96/00823 Examination of the condition of district heating pipelines in east Germany

Pre-insulated district-heating pipelines: Design and operational advice

Steady-state temperature distributions have been measured within a cylindrical duct enclosing two different diameter pipes—one for district heating and the other for the supply of domestic hot-water; the gaps between the pipes being filled with well-packed fibrous thermal insulant. The procedure was repeated successively with each of three sets of different-diameter pipes. The recommended configuration was with the DH pipe coaxial with the centre of the pipeline and the DHW one located vertically below it: this corresponded to the minimum rate of heat loss from the district-heating pipe under the considered conditions. An overall improvement of ∼8% in the thermal insulation of the DH pipe has been achieved compared with the current conventional practice of installing the DHW pipe above the DH pipe.

Underground district heating mains: Causes of failure

This report highlights the principal causes of failure of underground district heating pipelines installed in the UK over the last 20 years. Standard UK practice is to use prefabricated pipe in pipe conduit systems. Both steel and plastic cased systems have suffered from penetration of the outer conduit, especially at the location of the main joints. This has enabled moisture to enter the systems and corrode the hot steel carrier pipes within. An improvement in site supervision and the introduction of a registered training scheme for completing conduit closures could increase the reliability of future installations. This is vital if the UK is to benefit from the potential energy savings of city-wide CHP schemes.

Optimal location of a district-heating pipeline within a rectangular duct

The steady-state rate of heat transfer from a horizontal hot-water pipe (of a district-heating system) within an air-filled, relatively cold horizontal rectangular trench has been measured. The optimal configuration, which results in the minimum rate of heat loss from the pipe under the considered conditions being achieved, has been deduced. The procedure was repeated successively with each of three different diameters of the pipe. For the range of 0·15 < D X < 0·35 , the optimal displacement ratio E equals 0·70 ± 0·03 (the pipe being in the upper region of the trench), and an improvement of approximately 9% in the thermal insulation provided by the entrapped air was achieved compared with the current conventional practice (i.e. with E = 0).

District Heating and/or District Cooling Distribution Pipelines: Optimal Configurations

Factors influencing the steady state heat transfers from a horizontal hot-water (or to a chilled-water) pipeline within a relatively cold (or hot) horizontal rectangular trench filled with either (a) atmospheric pressure air or (b) hollow plastic spheres or Lytag in order to simulate a buried district heating (or cooling) distribution network have been considered. A series of experimental measurements as well as finite element and finite difference predictive analyses revealed the optimal configuration, for each set of considered circumstances, is that which achieves the minimum steady state rate of heat exchange between the supply pipes and their surroundings under the considered conditions. The recommended configuration for both the district heating and cooling systems is to place the two pipelines one above the other in the trench, the hotter pipe being the upper member. This differs radically from the arrangement of the pipelines traditionally adopted in district heating or district cooling designs (the pipes being placed side by side), and its adoption leads to at least a 4 per cent improvement in energy thrift. Such a saving can be achieved with no extra constructional costs, and the savings should be significant over the lifetime of either the district heating or cooling system.