Pumping heat when cleaning parts

Energy efficiency and climate protection are key issues in the automotive industry. These issues impact products and how they are manufactured.

To exploit the existing potential when cleaning engine components, BMW Motoren GmbH’s BMW Group Plant Steyr in Steyr, Austria, replaced the electric water heating system in its Austrian works with a heat pump. This has resulted in electricity savings of about 70% per year.

The energy optimization of production lines and machinery for the manufacturing of core engine components like crankshafts and crankcases, cylinder heads and housings for the latest generation of electric drives has been on the agenda of BMW Group’s Steyr site for several years. This optimization also includes the cleaning machines for these components.

“To reduce energy consumption, we started with Ecoclean to equip the pumps of cleaning machines with variable-frequency drives in 2016,” said Gerhard Fuchs, the person in charge of the processes and energy officer at the Steyr facility. (Ecoclean Inc. is in Southfield, Michigan.)

In the search for further ways to save energy, consumption measurements showed that the electrical heating systems of the cleaning machines running in the three-shift operation consumed a large amount of electricity. Considerations on how energy could be saved to generate hot water resulted in the switch to a heat pump.

“I wanted to implement a pilot project to determine the energy savings potential we could achieve by replacing the previous electric heating system with a heat pump,” Fuchs said. “Due to the excellent cooperation we have had with Ecoclean, I asked the company whether they would join us as a general contractor. After they agreed, we chose a transfer cleaning machine of the manufacturer.”

To calculate the energy savings achievable by integrating a heat pump, an analysis was made first. The basis for it were the production, process and system data and previous energy consumption figures, as well as the modification concept prepared by Ecoclean.

“For reasons of neutrality, we hired an independent engineering office for the analysis,” Fuchs said. “They calculated savings of approximately 70% of the previous energy consumption.”

The solution is tailored to the situation at BMW Steyr. On the roof of the transfer system there is a tank holding 2,000 L (528.3 gal.) of clean water that is supplied to the cleaning process at 56° C (132.8° F). The required electrical heating system had a power draw of 39 kW. Cooling of the vacuum pumps and control cabinet was effected by a cold water circuit. Cooling water is provided at a supply temperature of 16° C (60.8° F) and returns at a temperature of 22° C (71.6° F).

This “warm water” serves as an energy source. It is supplied to the heat pump (power draw of 11.2 kW) where it is heated to 65° C (149° F). The heat transfer to the hot water supply of the cleaning machine is effected by a plate heat exchanger. A new circulating pump (power draw of 1.2 kW) delivers the heated process water to the hot water tank of the cleaning machine while a second new circulating pump (also with a 1.2 kW power draw) returns the water that has been cooled to 16 °C to the cold water circuit. This solution reduces the energy consumption from 39 kW to 13.6 kW. With a defined production time of 5,760 hours per year this adds up to more than 146 MWh.

Furthermore, another 23 MWh of power is saved in cold water generation since the cooling water now only needs to be cooled from a much lower return temperature to the required supply temperature.

As the project was to be implemented without interruption of production operations, the modification job was carried out during a two-week holiday. The heat pump, plate heat exchanger and the two new circulating pumps were installed on the shop floor near the machine, insulated and surrounded with guard fencing. The surface area required for this is about the size of two Euro pallets.

In addition, the modification required four new pipes. Two of them connect the clean water tank on the machine to the plate heat exchanger. The two other pipes transport the warm water from the cooling circuit to the heat pump and return it after cooling.

“We integrated a display for temperature and flow monitoring,” Fuchs said.

The company’s energy monitoring system includes an energy meter to verify the saved heating power. This monitoring, as well as measurements made by the independent engineering office after completion of the project, show that 100% of the predicted savings have been achieved.

Because of the saved current of a total of 169 MWh, the annual operating costs for cleaning have been reduced by about $20,492, or 19,000 Euros. In addition, about 34 fewer tons of CO2 emissions are emitted into the environment.

“It has been a good decision to involve Ecoclean as prime contractor for energy-efficient projects,” Fuchs said. “We are very happy with the results and their support and will continue our cooperation.”