Dimensioning and planning of 5GDHC networks
The dimensioning and planning of 5GDHC (anergy) networks is more complex than for normal heating networks. On this page, we give an overview of what has to be considered for the calculation and simulation.
What needs to be considered when planning for districts with 5GDHC / anergy network?
There are some planning steps that are carried out in most district projects. The planning steps are not carried out sequentially and once, but iteratively and several times, as the system design is refined gradually.
- Energy demands: Creation of an overview with all buildings to be supplied and, if necessary, creation of demand profiles for simulations.
- Calculate total energy loads: Simplified calculation of the heating and cooling demands to be covered for the entire district (load at the energy center)
- Heat sources: Analysis, which heat sources are available and can be used
- Energy simulation and simplified network calculation: To ensure the technical feasibility and economic viability of a district energy system, it is recommended to perform an energy simulation. The simulation results can be used to determine the dimensioning of the energy center or the required design capacities of the heat sources.
- Design of energy center: Depending on the heat sources, the planning of the energy center, which supplies the 5GDHC network, is more or less complex. The question of the optimal dimensioning of thermal storage (heat storage and/or cold storage) is one of the most complex issues.
- Network planning: The planning of the heating network includes decisions on the routing, pipe dimensioning and selection of a suitable pipe type.
Planning of the heating network: Network topology and routing
A number of different aspects have to be taken into account when planning a 5GDHC network. On the one hand, the choice of a suitable network topology is a fundamental decision. In most cases, star networks are planned which, starting from the energy center, branch out more and more in a tree structure and thus reach every building. Alternatively, depending on the geographic conditions of the neighborhood, a ring network can be advantageous. In ring networks, there is a closed ring of a warm and a cold pipe, from which branches go off to the buildings. The advantage of the ring network compared to a star network is that it has a higher redundancy and therefore a higher resilience against failures of individual pipes. The question of whether additional buildings or neighborhoods are to be connected to the heating network in the future is also important in determining an optimal network topology and a suitable route.
Simulation of energy demands
An important basis for the energy simulation and optimization of district energy systems in general and 5GDHC networks in particular are energy demand profiles. Energy demands should be created for heating, cooling and electricity as well as all other relevant heat sources or sinks. Profiles are often used for a single year with a temporal resolution of one hour. This allows for the consideration of fluctuations in energy production from renewable sources (photovoltaic, wind energy, solar thermal) as well as energy demands. Energy demand profiles can be generated in nPro for all important forms of energy: Space heating, domestic hot water demand, space air conditioning, process cooling, user electricity/general electricity, and charging profiles for electric mobility. While only space heating and domestic hot water demands are often relevant for the planning of conventional heating networks, all occurring energy demands of the neighborhood are of importance for the conceptual design of hybrid energy systems.
Simulation of 5GDHC networks
In order to analyze the thermo-hydraulic conditions (pressures and temperatures at different points in the network and at different times of the year) and thus optimize the network design, heat network simulations are often carried out. However, these can usually only be done in the detailed planning of a district, as a large number of input simulation parameters are required. For example, the route and the pipe diameters must be known. Furthermore, information on the type of pipe used, heat transfer fluid and planned network pumps is necessary. Since this information is not available in the early planning phase of districts, a quasi-static network simulation is carried out in the nPro tool, which requires fewer input values. Here, static heat losses and gains as well as pressure losses are determined.
Calculation and optimization
During the detailed planning phase, a preliminary design can be optimized with respect to various parameters. For this purpose, simulation models must be available for a district, which have been created either with commercial tools or with the help of modeling environments (such as Modelica). First, pipe diameters of the heating network can be optimized. This can be done by analyzing network slack points or performances of the network pumps calculated by the simulation. On the other hand, the charging and discharging behavior of thermal storages can be analyzed in order to optimize the capacity of storage tanks.
Dimensioning of heat storages
Achieving an optimal dimensioning of thermal storages for 5GDHC networks is usually not easy and requires good simulation methods as well as experience. This applies on the one hand to small decentralized storages in the buildings, but also to central storages on network level. The dimensioning of large thermal storages is complex, because many different optimization criteria have influence: On the one hand, the storage should be used as often as possible, i.e. one wants to maximize the full charge cycles over the year. On the other hand, the storage size must match the generation capacities of the plants so that certain cycle times of the generators are not undercut. Furthermore, the demands of heating and cooling loads in the neighborhood also play a role in order to maximize the balancing of heating and cooling demands through the use of central storages.
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