Tap water has existed since antiquity and was reachable for very limited people until 20th century when it began to be common in developed countries. It is known that publicly available clean water increases the life expectancy and improves public health. Although it is very crucial for our lives and it is available even in countryside, probably no one gives much of a thought about it. “Just open the tap and use it”. However, providing the clean water to large cities and towns requires a complicated system of collection, storage and distribution of water and planning. In this blog post, I will be showing how such a water pumping system can be established and simulated by using Claytex library in Dymola.
The Model
The system of a water well pump and distribution, simulates the water pumping from a water well to a reservoir of a city with a population of 11000. The well model is connected to a pump which pressurises the water and carries to a reservoir. The pump is controlled such that it will not pump water when the well water level is below 3 meters or when the reservoir water level exceeds the maximum height of the reservoir. Water is distributed to the city from the reservoir. According to the Water UK, an average person uses 142 litres of water in a day. 1562 m3 water is consumed by the city per day and the whole system provides the demanded volume of water to users without any interruption during the day. Moreover, the water pressure needs to be between 2.5 to 4.5 bar for the last users.
Figure 1: The model of water well pump and distribution system
List Of Components
- Water Well
- Submerged Water Pump and Electric Motor Array
- Reservoir
- Check Valve
- Linear Valves with Table based control
- Pipes
- Sewer
Water Well
The simple water well model is able to refill itself from the ground water table. The pressure gradient between the water table and the water well creates flow and water well is being filled. There are some assumptions that simplify the well model:
Assumptions
- The well is a vertical and cylindrical in cross section with a uniform diameter.
- The aquifer is a homogenous, isotropic, and unconfined layer of water.
- The aquifer water fills into the well from one point from the bottom and takes into account the hydrostatic pressure.
- The water level changes in the aquifer is neglected.
- The dynamic pressure for the aquifer is equal to 0.
Figure 2: The well model
Pump and Motor Array
Multiple pumps and electric motors are necessary to obtain required mass flow rate into reservoir because reservoir has to provide water to users at any time where it is required.
Figure 3: Electric motor and pump array.
As it is seen from Figure 3, submersible water pumps which can be characterised by altering the data, are used and run by the electric motors. Dymola allows us to run multiple number of pumps and electric motors in parallel by creating arrays, and different number of pumps and electric motors can be set in the model above. Also, Figure 3 indicates how each electric motor is controlled by a PID controller.
Model Setup
To be able to provide 1562 m3 water to town non-stop, 18 water wells and submersible water pumps are used. The depth of the wells was set to 200 meters and water table level could be reached at a depth of 130 meters. Reservoir is located 30 meters above the ground to have enough water pressure. There is also a controller for the pumps to keep water level at the desired level for both the well and reservoir. The water level pickup point should not be less than 3 meters inside the well to not pump all the sludge and small rocks into the pump which would compromise its operation and working order. In addition, water should not overflow the reservoir level. In both cases, the pumps need to be idle. A check valve is also needed before the reservoir inlet to avoid back flow when the pump is idle. Finally, water usage is controlled as a function of time by linear valve to model rush hours and low usage periods in a day.
Results
Figure 4: Total water consumption, Mass flow rate and Pressure during a day
As it is seen from Figure 4, 1564 m3 water was provided to households in a day with water pressure of around 4 bar at taps. These results are met with the requirements we had set ourselves. Also the mass flow rate graph indicates that water usage is relatively less at night times and increasing in the morning.
Figure 5: Level of water in reservoir and well, cumulative mass flow rate of the pumps during a day
There were 3 other requirements that the model needed to meet. First, the well model has to refill itself from the aquifer; there should always be water inside of reservoir and the level of water in the reservoir must not overflow. Figure 5 shows that, water inside the reservoir neither runs out or overflows. It can be seen that pumping stops when the water gets close to the maximum capacity of the reservoir. Furthermore, the well model periodically fills itself from the aquifer and keeps its level around 50 meters in height and never falls below 3 meter.
Conclusion
The World Health Organization claims that clean drinking water has significant health, economic and social effects on the public. Even if it has significant importance and influence on civilisation, people do not care much and do not know how the water reaches their kitchens, showers and toilets. The water is not coming to your house by itself, in reality, there are complicated multi-physics systems that are working in harmony to bring it to you. You can model and simulate these systems in Dymola.
The features below can be added or improved upon in future work:
- The well model can be developed to be more realistic: the aquifer should fill the well from various points and height.
- It is assumed that, all the wells and pumps, working in parallel are identical; however in reality, they could be of different specifications and controlled in different ways. This would also allow for the effects of fault injection to be investigated.
- Water consumption during the day can be made to be more realistic.
- A wind turbine system can be added to the model to supply the pump motors with electrical energy, thus renewable energy and grid energy power production and consumption can be observed, balanced and optimised.
Written by: Kadir Sahin – Project Engineer
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