MIKE+ | WD working with Cost Analysis.
Description
The Cost analysis Tool provides an overall picture of the energy performance in the network by means of the computation of energy related metrics of a high detail level. This assessment enhances operators to evaluate the system performance and operational costs.
The cost and energy analysis provides two different aspects:
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Energy by pumping (*)
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Energy balance for the whole system (model) (**)
The traditional approach to save energy focuses on operational improvements such as pump efficiency and that is covered by the first part of the analysis (*). The purpose of the second part (**) is to calculate the energy balance of the water distribution system, compare it with the energy supplied to the system and determine where the energy is lost. This approach allows accounting for all the energy in the system, showing that the energy balance is maintained. This balance can be used to obtain performance indicators to assess the system from the energetic point of view. From these indicators, it is possible to identify the improvement actions that will make the system more efficient. These indicators are included in the energy balance:
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Natural input energy
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Shaft input energy
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Energy delivered to users
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Outgoing energy through leaks
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Friction energy losses on pipes
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Friction energy losses at valves
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Output energy
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Dissipated energy
Setting up the analysis is a straightforward process. The modeler first selects the currency (USD is default) and defines a global energy price for both pumps and turbines. This price represents the average cost per kilowatt hour (kW/hour) of operation. In the Patterns section, the modeler defines a time-varying price pattern describing how the energy cost changes throughout the day for the operated structure. A default efficiency for a single perfect pump/turbine efficiency must be specified (typically 75%) and it is used when no pump efficiency curve is provided. For pumps operations, it is required to specify a demand charge. This charge represents an added cost per maximum kilowatt (KW) usage during the simulation period. Optionally, the modeler can set Carbon Emission Factor, expressed as CO2 emissions per unit of energy consumed (CO2 per kWh), to support environmental impact analysis. The setup dialog for the Cost Analysis is presented in Figure 1.
Fig. 1- Setup of the Cost Analysis Tool.
The tool generates structured tabular outputs summarizing key indicators such as pump and turbine operation, power consumption and total energy cost over the simulation period. The output from this analysis is designed to support scenario comparisons, time lapse performance or asset's optimization, ensuring transparency and traceability of energy use. These tables can be exported into reports and be easily post-processed. In example, waterworks operators are concerned about their system energetic balance, by means of the tool report creating a quick overview of the system integrity is possible.
In Figure 2, a section of the Cost Analysis report is presented for a very simple model of one single pump, in this report it is possible to observe the system energy consumption and the operated structures summary (in this case for only one pump).
Fig. 2 - Cost Analysis Report, overview of the system's energy.
In addition to reports, the tool offers graphical visualizations to insights into pump and turbine utilization patterns, average power consumption or production, and its associated energy costs. In the time series tab, the output is available for efficiency, energy/volume, power generation and energy costs reports. In Figure 3, a representation of the energy cost of a pump performance time series is presented.
Fig. 3- Time series representation energy cost per pump.
The combination of detailed numerical data with graphical representations allows the Cost Analysis Tool to support the assessment of energy consumption and define strategies for operational optimization of the network. This special analysis helps quantifying energy consumption, conducted water production and the linked cost of operating such pumps or turbines. Allowing the modeler to compare the energy metrics to the simulated hydraulic conditions such as flow rates, heads and operation schemes.
In the Report tab the modeler can observe performance charts, these charts can be used for comparison between scenarios and consistency checks against modelling assumptions.
Let's consider that for the fictious model described before of one single pump, it is required to consider the impact of putting into work an old parallel pump that has been offline for a while. The idea is to evaluate if it is convenient to rehabilitate this old pump to work simultaneously together with the existing pump, the interest should be focus on cost efficiency. By means of Cost Analysis we can see what the utilization of one scenario is versus the other and also see what the economic impact is of putting two pumps to work instead of one single pump. In Figure 4 a comparative series of charts are presented for the utilization and cost efficiency for both scenarios.
Model calibration
Note, that the hydraulic model used for energy modeling needs to be calibrated for “energy” related components. In a typical network that includes energy by pumping, the following will be needed for the verification of energy calculations:
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Power per pump (ideally)
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Pump station cumulative energy over time during which the number of running pumps was constant
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Flow and head per pump (to correlate with the power reading)
Real case example
In this example, the system energy balance is used to evaluate zoning improvements to existing water distribution network. The system consists of a main water source with a pump station that pumps water into the main distribution zone (Zone 1). Parts of the network are situated in low elevation areas along the river, and they have unnecessary high pressure. The proposed zoning improvement will separate low elevation zones (Zone 2, Zone 3) from the main zone by several pressure reducing valves (PRV).
Both system state alternatives were simulated using the hydraulic model with system energy outputs, Table 1.
Table 1 Energy balance with selected energy components and indicators
Summary:
From the energy perspective, the pump energy is practically identical (that is because the pressure within the Zone 1 remains the same as before) and the only apparent change between these two states of the system is that 9% of the energy is dissipated at pressure reducing valves (as one would expect); originally, this part of the energy was delivered to user (higher service pressure than it is now).
Another change is that the energy delivered to users (demands) included leakage. This field is not estimated in the above table because we do not know the current amount of leakage. However, as pressures within the Zones 2 and 3 are smaller in the PRV scenario, the leakage will also be smaller, and some energy will be saved on pumping (less water to be delivered).
Conclusion:
Wrapping things together, combining numerical time series, tabulated results and graphical outputs gives the user consistent data to evaluate alternative operation strategies that will evaluate economical efficiencies and assess the cost implications of hydraulic designs and control decisions.
Two aspects of power and energy requirements can be evaluated, energy by pumping and energy balance for the whole system, including natural energy, energy by pumping, and energy supplied versus lost.
This tool allows the modeler to ensure that economic conclusions are directly related to the underlying hydraulic simulation results, making decision-making a technically sound and efficient process. Combined with the scenario manager, this tool allows for setting up and evaluating different operational strategies or network configurations and compare energy balance of the existing system vs proposed system configurations or future conditions.
FURTHER INFORMATION AND USEFUL LINKS
Manuals and User Guides
MIKE+ Water Distribution. Use Guide
[Release Notes]