Energy efficiency offers water suppliers the prospect of much-needed reductions in energy costs and carbon emissions. But it is a different matter to identify a coherent set of changes and to justify investment in new or replacement infrastructure. Mathias Ernst and Marcus Beck report on how utilities in Berlin and Hamburg are progressing energy efficiency in groundwater collection – work that is forming the basis for guidance for the sector across Germany.
Seventy per cent of the water supplied in Germany comes from groundwater sources, meaning it is a vital resource in many locations in the country. The German water supply sector is focused on achieving reliability and high water quality using robust technology. However, specific measures to reduce energy consumption in water supply are rare, especially in groundwater extraction. This is despite the fact that one third of the total energy consumption in groundwater supply systems is for the submersible well pumps required, and that, typically, these have an overall energy efficiency of less than 50%.
Seeking efficiency in Berlin and Hamburg
Within this wider context, a four-year evaluation recently completed in Berlin and Hamburg looked at ways to increase energy efficiency at existing water works. This was undertaken jointly by Hamburg Water, Berlin Water Company, and DVGW-TUHH, the Hamburg research branch of the German Technical and Scientific Association for Gas and Water (DVGW).
The project included looking at the potential for energy saving measures relating to submersible pumps, the complete structure of wells, and to overall wellfield management. One particular innovative technology investigated was the new generation of submersible pumps that are fitted with a permanent magnet synchronous motor (PMSM). Data was collected before and after implementing the various technical options tested.
The tests in the two cities to assess pump efficiency compared conventional asynchronous motor (ASM) pumps, both speed controlled and non-speed controlled, with the PMSM pumps. This work focused on achieving overall maximum efficiency. The project also looked at bottlenecks, given that implementation of PMSM pumps by German water utilities is still limited.
The technology only entered the market in 2014 (see box, below), which contributes to suppliers having limited experience with this type of pump, or with the associated frequency converters used to implement variable speed control in wellfield applications. The latter allow pump outputs to be varied, contrasting with the traditional approach of operating pumps intermittently to deliver the required output.
Hamburg relies entirely upon groundwater. There, the work was undertaken at the Billbrook water treatment works, in Rothenburgsort, close to the river Elbe. The study well is 282m deep.
In Berlin, the tests were carried out at the Berlin-Tiefwerder water treatment works, in Spandau, West Berlin. The study well close to the river Havel is 42m deep.
The project also looked at the impact cleaning procedures have on energy efficiency, anticipating, for example, that cleaner pipes contribute to increased efficiency. Two raw water supply pipelines were studied in Hamburg and two collection pipelines were studied in Berlin, including one serving 37 wells at Tegel, site of a main treatment plant.
A number of wells at Tegel were retrofitted with PMSM pumps and state of the art data acquisition systems. The new wellfield is fully automated and integrated into the treatment work’s process control system. The PMSM pumps replaced fixed speed ASM pumps that were operated intermittently to achieve the desired flow rate.
In addition, the Tegel wellfield was modelled (using EPANET software), supported by collected energy optimisation data. Optimal solutions were identified by attaching the simulation to the Evolver genetic algorithm. Outcomes from the modelling – the number of PMSM pumps to operate in parallel, and the best pumping frequency – were applied in the real wellfield. Low and moderate flow pump scenarios were tested in real-life trials, and the electrical consumption was measured and compared to the simulation outcomes.
Data from parallel testing of the different pump types at Billbrook and Tiefwerder found the innovative PMSM pumps to significantly lower energy losses (for instance, higher global efficiencies) compared with reliable ASM pumps – even at the most efficient operating point. This led to a seven percentage point better performance in Berlin and a 10 percentage point improvement in Hamburg.
Pipe cleaning was shown to reduce pressure losses. The submersible well pumps adapted their operating points and supplied more water after cleaning. For both pipe-well systems, these higher volumes meant lower energy demand per unit of water supplied and lower costs, with reductions of up to 3%. However, the benefits of cleaning depend heavily on the raw water quality and pipe diameter. At one location in Berlin, iron hydroxide deposits were found to grow back nearly 20mm annually. The cost of such cleaning and disposal is often not economic, although it can be necessary to meet the required water demand.
Assessment of other associated equipment, such as hydro-stops, fittings, and non-optimised valves, revealed an extra 2% of potential energy efficiencies.
The modelling results indicated a potential energy saving of 24% under a low flow scenario, and 26% at moderate flows. The real-life tests found that the projections were quite good for low flows and still reasonably close at moderate flows. For the moderate flow scenario, annual savings of between €6000 and €10,000 were predicted under certain circumstances.
Overall, the study results revealed that the energy efficiency of groundwater collection systems is currently around 50% on average. It was concluded that energy savings of up to 30% are possible for larger well fields having to meet a varying water demand.
Prospects for Berlin and Hamburg
The project has identified some new opportunities for the two water utilities.
Energy measurements for every individual well was initiated as part of the project. This will be continued on all existing wellfields in order to monitor real energy consumption. In Hamburg, this data will be integrated within the utility’s operational control system. This is basically useful for planning new measures linked to the project results.
The results relating to energy efficient well structures and equipment have been combined to create a new well concept. Hamburg Water and Berlin Water Company are going to apply this for all future well constructions.
Both suppliers are to consider operational aspects and calculated life-cycle costs to an even greater extent than before. Most new pumps will be PMSM, because of their high energy efficiency. They expect to achieve relatively short payback periods, depending on the well location.
In addition, based on the positive results in the Tegel waterworks, Berlin Water Company is to adapt the concept of overall variable speed operation to wellfields in other locations.
A further outcome is that both of the suppliers are to invest in new sensors to measure energy related data in wells and wellfields. This offers the prospect of digital monitoring of the collection process, allowing investment measures to be identified clearly.
Preparation of guidance
Based on the experience gained in the project, the core team from Hamburg Water, Berlin Water Company and DVGW-TUHH is bringing the results together in a guidance document for the German water industry, including details on best practice and lessons learned.
It will also feature suggestions for an adapted energy measurement concept. This is a field in which many errors can lead to incorrect power measurements, directly influencing the information an organisation gathers on energy savings. The document will also have recommendations for an optimised well concept, raw water pipe cleaning protocols, and wellfield operation strategies where PMSM pumps are installed.
Pump efficiency progress
- Up to 90% of life-cycle costs relate to electrical energy during well pump operation (project outcome)
- Using well pumps with high total efficiency reduces energy consumption, cutting supplier energy costs and carbon dioxide emissions for all (helping the community)
- Since 2014, new PMSM technology has become available for well pumps, offering a big step to increase total well-pump efficiency and cross the 70% limit (project outcome)
- PMSM motors use permanent magnets instead of typical rotor windings. This creates synchronous rotating magnetic fields with no slippage, resulting in a 10% increase of PMSM maximum efficiency compared with ASM at best operation point
- The results from the Hamburg-Billbrook well show a global efficiency increase from 0.652 to 0.72, and a power consumption reduction from 17.55kW to 16.08kW. Total energy consumption dropped from 140,425kWh/year to 126,811kWh/year and energy costs from €22,889 per annum to €20,670 per annum for one single well
- Pump operation using variable speeds via a frequency converter is interesting for well fields with large varying capacities. Lower water demand usually means fewer operating pumps, but running with lower efficiency. With decreasing speed, the pumps were adapted to lower raw water system pressure, leading to considerable energy savings of up to 25% (project outcome)
Dr Mathias Ernst is professor at the Institute for Water Resources and Water Supply
at the Technical University of Hamburg (TUHH), which hosts the DVGW-Research
Centre TUHH. Dr Marcus Beck is with the DVGW-Research Centre TUHH.