How dynamic pressure management with Grundfos DDD helped achieve significant savings

The situation

Przedsiębiorstwo Gospodarki Komunalnej Sp. z o.o. (Communal Services Utility LTD) in Wolsztyn, Poland, delivers more than 1,800,000 m3 of water yearly to app. 30,000 citizens, as well as to production plants and public facilities throughout the Wolsztyn municipality. For many years the Water and Sewage Department has been successfully implementing innovative technical solutions such as the nationally unique Hydrox water treatment system, which carries out iron and manganese removal processes already in the aquifer. The company operates 220 km of clean water network. Originally the network utilised a water tower, which provided a buffer of 700 m3 of water which was crucial at high demand period, usually during summertime.

In 2014, PGK Wolsztyn was in need of an energy efficiency check of the main Wroniawy water treatment plant, and they turned to Grundfos for help, requesting an Energy Audit. At the time, their  pressure boosting set consisted of  six horizontal pumps, with 55 kW power each. It was significantly oversized and controlled in an inefficient way, and as a result consuming an average of 0.273 kWh for every m3 of clean water pumped into the network. 

The audit report clearly showed that the installation of 4 new NBG-100-65-200 pumps of 22 kW each and a control cabinet with frequency converters would allow delivery of the maximum required flow of 560 m3/h, as well as a reduction of specific energy to 0.216 kWh/m3. Considering the situation and the apparent benefits of choosing the Grundfos solution, PGK Wolsztyn decided to go ahead with the modernisation of the current installation. The achieved energy reduction was 30%, saving more than 98,000 kWh per year and with a return on investment of 2.7 years. The new system maintained constant pressure, smooth pump speed control, eliminated the water hammer effect and made daily work much easier for the operation team.

Switching between pumps was problematic; the operator had to close the throttle valve on one pump while opening on the other. This usually meant working with a stopwatch - throttle open at X% for Y seconds. Sometimes the network pressure instantly jumped up more than 0,5 bar. It occasionally happened that the throttle valve didn’t close and the flow to the network almost doubled. This problem was successfully solved with the refurbishment. The new control system automatically and smoothly controlled the speed of pumps, maintaining their equal operating hours, and the water hammer effect disappeared.
Mateusz Ziomek, Head of Water Supply and Sewage Systems Department

After a few years, a new challenge arose in Wolsztyn. The water tower had been working continuously since 1992, and in 2020 it failed when a large crack appeared at a height of 36 m above ground. PGK called a rock-climbing team, which performed 3D scan inside the tower. An expert analysis indicated that the upper tank had lost its tightness and that it required a major overhaul. This repair was only possible with an investment of 335,000 EUR. 

Water tower in Wolsztyn (left), city view from top of the water tower (middle), tank break (right).

The company was considering renovating the city's old buffer tanks and establishing an additional booster station. Potentially, this would mean another investment of 335,000 EUR, design work, obtaining the necessary approvals and fulfilling many formalities. Due to the very good experience with Grundfos in previous problem solving, PGK Wolsztyn again turned to Grundfos for consultancy and support.

The solution

Performing an Energy Audit with network analysis turned out to be the best approach. The audit involved measuring the current system’s work profile, efficiency, and specific energy, while recording pressure readings at measuring points located throughout the network. As a result of the study, Grundfos proposed disconnecting the damaged water tower and introducing a DDD pressure management solution.

Commissioning of the DDD solution. (left to right) Bartłomiej Kala (Senior Energy Optimization Specialist, Grundfos), Witold Zboralski and Mateusz Ziomek (PGK Sp. z o.o. Wolsztyn)

The proposed solution included control system modification and delivery of six new CR125-2 pumps. While the tower no longer provided a buffer of several hundred m3 for high flow situations, the new system can now deliver close to 1,000 m3/h. The booster controller wirelessly collects data from critical points located on the water supply network and automatically creates an optimal control curve. The discharge pressure adjusts to the current demand and the end-users experience constant water pressure, regardless of the time of the day or season. With these advanced features, the water tower could be disconnected without causing any impact to the users or to the network.

We even had questions from other waterworks: 'But how, you disconnected the tower and just kept working? That's impossible!' My answer is, 'come visit us and I’ll show you how!'
Mateusz Ziomek, Head of Water Supply and Sewage Systems Department

The outcome

The existing 4 NBG pumps of 22kW power were replaced with 6 new highly efficient CR125-2 pumps of 30 kW. Furthermore, the pump connection pipes were replaced with new ones, made of stainless steel. The control cabinets were equipped with two additional frequency converters, and a dedicated CU354 controller and measuring points have been installed on the water network. 

Stainless steel piping installation in progress (left), new 6 CR125-2 pump set (right).

All activities described above and the change from constant pressure control to intelligent DDD control, ensured a maximum flow of 978 m3/h, while significantly reducing the specific energy from 0.216 to 0.162 kWh/m3. The modernisation has reduced energy consumption by another 22%, with additional savings of almost 79,000 kWh per year. In addition, Grundfos DDD control stabilised the pressure on the water network, reducing the oscillations to approximately 0.1 bar. The return on investment was again less than 3 years. On top of all these benefits, PGK Sp. z o.o. in Wolsztyn avoided an investment of around 670,000 EUR for the renovation of water tower and potential the construction of a new pressure boosting station.

If I said a few years ago that we will be working without a water tower, many employees would have said "you're crazy, go get a new job, the tower has always been here, you can't do it in any other way". Suddenly, we disconnected the tower, switched on the DDD system and it turns out that everything works perfectly fine, while people have water at a stable pressure. For those who don’t believe that, we are proof that problems can always be solved in a better way, while saving a lot of money.
Mateusz Ziomek, Head of Water Supply and Sewage Systems Department