The paper describes the analysis of the Gentofte District Heating Company as it will be when extended with consumers converted from natural gas in the coming years. The project’s objective was to recommend the hydraulically and economically most favorable configuration of the transmission pipelines and distribution networks. Furthermore, a preliminary financial analysis of the planned investment was performed. The task was completed using software dedicated to district heating (DH) networks analysis: the recognized Termis and the innovative Comsof Heat.
By Thomas Andreas Østergaard, Market director, COWI and Adam Frechowicz, Project Manager, COWI
Extending a DH network is a long-term process that needs to be planned well in terms of hydraulics and timeframe. One of the first steps is pipeline routing, which usually utilizes streets. Future consumers need to be identified regarding location, heating- and hot tap water requirements. The process is followed by many pipe dimensioning – leading to a preliminary determination of costs and economic effects. Although these stages are only a tentative and estimative part of the entire investment, they are a prerequisite to investment planning and budgeting. At the same time, they require a considerable amount of time. Fortunately, there is a way to shorten this process using Comsof Heat Designer. This software can become a valuable part of any DH planner’s toolbox. The Gentofte DH Company expansion project is practical evidence.
The expansion of the Gentofte DH Company will provide heat supply to approximately 6,000 new consumers with an expected annual energy demand of 192 gWh. The completion of the investment is planned for 2027. The study’s main objective was to determine the preliminary routings and the diameters of the future transmission and distribution pipelines. The analysis included a calculation of the key economic parameters of the investment.
Part of the planned distribution areas has no access to the existing DH network. Therefore, the task required determining the routes and diameters of new transmission pipelines. Furthermore, developing capacity from the heat central (NYC) owned by CTR (Centralkommunernes Transmissionsselskab I/S) provided an additional challenge to the task. Since the heat central is located at the outer edge of the network, it was necessary to propose a solution that would not create an imbalance in the system. Therefore, from among several transmission pipelines configurations, the optimum one had to be singled out to ensure the whole network’s proper functioning. That is fully effective operation both under standard operating conditions and flexible in case of the potential partial indisposition of one of the heating centrals.
The routings of the new distribution networks must coincide with existing streets due to the dense development in the Gentofte Municipality. Routing a network under the streets provides numerous viable trace configurations. Determined by the chosen routing, the upcoming network’s investment costs, rates, and hydraulic conditions can differ. Variant analyses under each aspect were needed to define the optimal solution.
Transmission pipelines – the initial work
Gentofte DH company determined possible routings for the new transmission pipelines. Considering the annual energy consumption of the new areas and potential points of connection, several hydraulic simulations were performed in the Termis software. The outcome made it possible to select the optimal configuration and diameters for the new main pipelines.
The conducted analyses proved the necessity of installing a booster pump station in the extended DH network. The operation of the boosting station will be crucial to secure sufficient hydraulic conditions in the areas located in the north of the city. Moreover, the construction of the booster pump station will lower the total pressure in the whole network leading to lower operation costs.
New distribution networks – input data
For the project, the Comsof Heat Designer software has been used to conduct the process of distribution pipes routing and dimensioning. The software can simultaneously calculate a specific variant’s hydraulic and economic parameters. Thereby, selecting the optimum configuration in vast areas becomes a feasible task utilizing the Comsof Heat application.
The basis data required for the calculations is the information on the future consumers. It is necessary to have the locations of the upcoming consumers in the form of points or building contours on a map. This project data was obtained from the Danish “Bygnings- og Boligregistret register” (BBR). The annual energy demand and peak demand are used for calculations as well. The accurate information about consumer’s types and the yearly energy consumption is a bottom-line for correct simulations.
The software requires street centreline data as well. However, Comsof also provides an option to supplement manual trace. This function can be utilized when routing should go through green areas. All data can be imported in, e.g., shape format. The software is an add-on to a QGIS and ArcGIS application.
The planned extension of the system includes densely built-up urban areas of the Gentofte Municipality. That forced a network design based mainly on the street grid. The tool offered by Comsof was extremely useful in this case. That is because it enables the generation of the new network configuration, for a given street grid, in a short time. Consequently, the software has significantly reduced and simplified the process required to complete this study phase.
New distribution networks – a variety of features
Pipe dimensioning can be done following user-defined simultaneity factors or with the Danish Standard DS439. Furthermore, pipe design parameters such as maximum velocity, gradient, or pressure limit are considered. Moreover, the software provides complete pipe tables of major manufacturers, making the design of networks accurate and based on actual parameters.
In the project, twin pipes were used for the new distribution areas, and all three criteria were applied. The maximum network pressure of 10 bar was assumed to ensure low-pressure levels. The specified network criteria fulfilment has been verified in a further phase of the analysis performed in Termis.
One of the advantages of the Comsof tool is the ability to define the unit costs of pipelines construction on a given street type. The user can specify these costs depending on any property (e.g., the density of the utilities in the ground). In addition, service pipes and heat exchangers are part of the calculation. With this approach, the calculated investment costs can be brought significantly closer to reality. The software provides a vast number of ways of routing so that the calculations are as accurate as possible. For example, the trace can be carried in the middle of the road or sideways, depending on the declared construction costs.
Using this feature, it was possible to certain network configurations effectively, both construction and operating costs. The project covers approximately 6,000 new consumers, of which a significant percentage are single-family houses. Therefore, it was pragmatic to dimension the service pipes and calculate their construction costs.
The verification stage
After completing the calculations in a Comsof Heat, all new distribution networks were transferred into Termis software. This activity aimed to verify the diameters of the designed distribution pipes and the preliminary diameters of the transmission pipelines when combined with the existing network. This was performed by inspecting the whole system’s velocities, gradients, and pressures. Analyzing the system and the developed distribution networks also allowed obtaining a variety of new knowledge. First, it provided a complete view of the conditions in the future network operation. Moreover, it enabled to proper study of the cases involving the partial failure of one or more of the heating centrals.
Simulations of the developed network revealed that the diameter of some of the planned transmission pipes in the new areas could be reduced while maintaining the maximum system pressure of 10 bar. These operating conditions required an increase in the booster station pump head. However, without implementing the new distribution networks into the calculation model, these conclusions could not have been reached. Furthermore, this phase confirmed that the previously selected dimensioning criteria in the Comsof software were fulfilled.
The economics of the new system was determined by the revenues to be earned from heating tariffs and the costs to be covered by Gentofte DH Company. In this field, the Comsof software offers a wide configuration of opportunities. Depending on the adopted criteria, it is possible to include different heat tariffs for consumers in the calculations. The evaluation of costs and revenues has a multi-year character and is calculated over the considered network lifetime. The heat and electrical power purchase costs and their fluctuations over the years can be evaluated.
All new 18 areas with 6,000 consumers were included in the analysis. The investment costs were determined with Comsof separately for each location and broken down by specific pipe diameters or heat exchanger capacities. Each distribution network operating cost was determined for the lifetime expected by Gentofte Dh Company.
The calculated cost of constructing all new distribution areas was confirmed by other analyses conducted for this project and considered credible by GF.
In conclusion, two different software were used for the task performed for Gentofte Dh Company: the well-recognized in District Heating world Termis software and the new Comsof Heat Designer software. The use of the tool provided by Comsof has significantly simplified the work related to creating the routing in distribution areas. It allowed obtaining the network design, the investment, and variable costs at one time. Therefore, the time required for creating new routings and financial calculations has been saved.
The simultaneity of these calculations also made it possible to speed up selecting the optimal route. Furthermore, the verification of hydraulic parameters performed with Termis confirmed the correctness of the proposed designs and gave a complete overview of the future network operation.
The entire task could not be fulfilled in Comsof Heat nor Termis only. The synergy of both solutions was the key to success in this case. In addition, it should be emphasized that the Comsof Heat Designer is quick to learn. It means that municipalities can make preliminary designs and heat planning that at a later stage can be verified in Termis.
For further information please contact: Thomas Andreas Østergaard, firstname.lastname@example.org