Using Torque Sensor to Measure Efficiency and Actual Performance of Pumps as Turbines
for a Microhydro System
Rising temperatures, shifting precipitations, and increasing sea levels are among the main indicators that clearly show that climate change has already impacted our environment. There is no longer any doubt that the effect of climate change will continue and may even accelerate in the future, creating water scarcity in some geographical areas, in the years ahead.
Since the availability of water plays an important role in ecosystems and socio-economic activities, The EU and its member states are collaborating, to ensure better planning and management of water resources. This collaboration comes in many forms, such as effective legislation, adaptation of existing policies, improving knowledge base and developing new smart low-carbon technologies, to combat water scarcity in the future.
In the EU, for example, the European Regional Development Fund is created to reduce economic, environmental and social problems, with a special focus on sustainable urban development. Thus, the organisation is leading a number of investment projects, in education and research, of innovative water saving technologies.
One of the projects, partially funded by the ERDF and the Ireland Wales Co-operation programme 2014 – 2020 is Dŵr Uisce (which stands for Distributing our Water Resources: Utilising Integrated, Smart and Low Carbon Energy).
Comprised of academic and research staff from Trinity College in Dublin and Bangor University in Wales, the team is looking at improving the efficiency of water distribution in Ireland and Wales. The main objective of the project is to address the challenge of water availability, from a number of different perspectives. These include quantifying the economic and environmental impacts, examining methods, highlighting best practices for measuring water efficiency, and creating new technical solutions, aimed at ensuring a more water-efficient and water-saving economy.
As part of the project, the team proposed building two micro-hydro power installations. Instead of a costly ordinary hydro turbine, they used low-cost micro hydro power, with centrifugal pumps working in reverse as turbines, referred to as Pumps as Turbines (PaTs). This allowed the Trinity College team to reduce the cost of the micro-hydro power development by 4-5 times, compared to a conventional system.
Among the many proposed strategies to reduce the energy consumption and carbon intensity of the water sector, a prominent one is the adoption of small scale hydro turbines to recover the excess energy along the water distribution lines. Due to the reduced size and residual pressure requirement a standard hydro turbine is often impractical or too expensive to install in such locations. Therefore the research team has decided to investigate the use of PaTs, also known as pumps in reverse, as low cost and easy to maintain devices for distributed energy generation within water networks.
After the first phase of desk studies and theoretical modelling, the team at Trinity College decided to validate the performance of reverse running pumps by carrying out experimental testing. To evaluate a pump’s efficiency and working point, they needed to measure torque delivered by the turbine at different regimes, accurately and in real time.
To assess the performance of reverse running pumps under realistic conditions, the team was tasked with setting up a hydraulic test rig. At the heart of the test rig design was an inline M425 digital torque sensor, that was able to measure torque with high accuracy and reliability. Following thorough market research, the Trinity College team decided in favour of a Datum Electronics’ torque sensor, as compared to other torque sensors on the market, a Datum torque meter has two technical key advantages:
a) In addition to torque it can also measure (RPM) simultaneously, thus avoiding the need for a separate sensor to evaluate the shaft speed;
b) The Datum Universal Interface (DUI) ’s data acquisition card and intuitive PC interface are very flexible, with an extremely quick set up.
When installed axially into the driveline, connecting the hydraulic turbine to the generator, the torque sensor very accurately measures the mechanical power produced by the former and transfers the real time readings to a data logging PC, for further analysis.
PaTs can be a cost-effective alternative to traditional turbines, and when inserted in a water supply system with constant water availability they can generate power all year round. To measure the performance of PaTs under realistic conditions, it is fundamental to evaluate how the change of the shaft speed affects its efficiency.
To date, the team at the Trinity College in Dublin has finished testing the first PaT, with the results so far exceeding their expectations. They found that the actual PaT performance was around 71% efficient, which is almost 20 percentage points higher than stated by the manufacturer.
Although it’s still early days, and more testing needs to be completed, the results are promising and create a healthy potential, for the feasibility of the Dŵr Uisce Project. It also creates hope of preventing and mitigating water scarcity in the future, ensuring access to good quality water, in sufficient quantity, for remote rural areas in Ireland and Wales.