The hidden champions of energy efficiency: energy savings with pumps and fans
Saving energy in pump and fan applications
Rising energy prices, political and social pressure for more environmental protection, less energy consumption and lower CO₂ emissions, better competitiveness through reduced production costs or a greener image – corporate reasons for energy optimization are manifold.
Flow machines such as pumps, fans and compressors, which control numerous necessary processes in buildings, consume a lot of energy. Nevertheless, they have to work reliably day by day. Because without, e.g, ventilation and cooling in buildings, our lives would be much less comfortable. But in times of rising energy prices, the operation of flow machines unfortunately also increases the electricity bill. Owners and operators of buildings are therefore looking for solutions for a more sensible use of energy in factory and production halls, in data centers as well as in residential and office buildings. The good news is, there is plenty of potential for saving energy in building automation. One of the key technologies for improved energy efficiency is electric drive technology. It helps to optimize processes and currently offers the most effective way to save energy and costs.
Energy savings of pumps and fans with quadratic load characteristics
Excellent savings can be achieved with pumps and fans, and a large number of them are used in building services in particular. This is because more than half of the applications in industrial buildings driven by electric motors are flow machines. Especially centrifugal pumps and fans, i.e. flow machines with a quadratic load characteristic, reduce energy consumption to the third power when the speed is reduced. A drive system running at half speed accordingly consumes only 12.5% of its rated power.
100% * 0,83 = 51%: Speed reduction of 20% results in savings of 49%.
100% * 0,53 = 12,5%: Speed reduction of 50% results in savings of 87.5
A widely used solution is to equip devices with a quadratic characteristic curve with modern frequency converters and thus optimally adapt their speed to the respective power requirement. This is because, in most cases, pumps and fans in building services are engineered for the worst case scenario; air conditioning systems, for example, for the hottest day of the year, when they then have to deliver their nominal output. For the rest of the operating time, however, they run at partial load. This also applies, for example, to pressure boosting systems in high-rise buildings. The figure shows the typical load profile of a room ventilation system. 85% of the time the fan runs in partial load mode.
And this is where frequency converters come into play. Another factor in favor of frequency converters is that decreasing product prices are making them increasingly attractive. But beware: not all pumps and fans are equally suitable for speed control.
Speed control as a saving factor
Swirl dampers, throttles or three-way valves are still used in many pumps and fans in older systems, but also in new systems, in order to adjust the pressure or the volume flow within the application to power requirements.
If a centrifugal pump is controlled by means of a throttle valve, the throttling shifts the operating point of the machine along the pump characteristic curve. There is only a minimal reduction in the energy required compared to the nominal operating point of the pump.
In the case of pump control via the speed, the operating point shifts along the system characteristic curve. The required energy is reduced in the third power compared to throttle control!
This relationship applies analogously to all turbomachines with a quadratic characteristic curve. Fans, for example, require only one-eighth of the power at half speed.
Efficiency curves for turbomachinery
In the characteristic curve diagram, in addition to the pump and system characteristic curve, some efficiency limits are also shown. Both throttle control and speed control move the operating point out of the efficiency optimum.
However, speed control provides the better energy balance in each scenario. Nevertheless, users should determine the energy-optimal frequency for each system so that additional losses do not exceed the savings from speed control.
Already in the project planning phase, please note that changing the speed also changes the operating point and thus the efficiency of turbomachinery.
Speed control of pumps and fans offers many other advantages
If the difference between the maximum power required and the average part-load operation is too great, you as the operator should consider the solution of multi-unit operation. With the so-called cascading of pumps, a speed-controlled pump covers the base load. If the consumption increases, the frequency converter switches on further pumps one after the other. The pumps thus operate at their optimum efficiency as far as possible. The control of a pump always ensures the best utilization of the system in terms of energy. The same system can also control fans analogously. Corresponding cascade controllers are available as external modules or already integrated in the most intelligent frequency converters.
Gentle machine operation
The use of speed control drastically reduces the number of starts and stops with full speed change. In addition, gentle start-up and deceleration ramps avoid unnecessary mechanical and electrical stress on plant components.
The frequency converter does not require any maintenance. When operating at reduced speeds, the system service life is increased. Load shocks that occur when motors are switched on directly are eliminated, which avoids damage to plant components caused by these shocks.
Reduced impact on process controls
Intelligent frequency converters can take over subtasks from programmable controls decentrally on site in the drive unit and perform smaller control and monitoring tasks themselves. This reduces the required storage space and size in the central controller and increases its speed.
Optimum system efficiency: Take the overall system perspective
Even though controlling turbomachinery with modern, intelligent frequency converters is a first step towards reducing energy costs and CO₂ emissions, it does not guarantee maximum savings. This is because a total of four factors play a key role, particularly in ventilation systems such as those in the case study on Volkswagen’s production site in Navarra, Spain:
- the efficiency of the fan,
- the motor efficiency,
- the coupling efficiency, and
- the efficiency of the speed control.
Sustainable ventilation technology: VW saves 20% energy and 350 tons of CO₂
Volkswagen relies on the EC+ concept from Danfoss and Novenco for the ventilation of one of the largest assembly halls at the Navarra plant. EC+’ stands for the intelligent interaction of the optimally selected system components such as AC drive, motor and fan. In this way, the new air handling system at the VW plant offers maximum energy and cost efficiency. Because ultimately, drive technology is the key technology for greater energy efficiency in fans and pumps through speed control.
Compared with the previous ventilation system, the 6 new AHUs have a combined total savings potential – based on nominal operation per year – of 747,429 kWh of electrical energy, 350 tons of CO₂ and 199,115 € in electricity costs in the first year. This calculation results for an energy price of 26.64 Cents/kWh. Other underlying assumptions of the calculation are the CO₂ emission factor of 468 g/kWh and 8,760 annual operating hours.
In addition to these significant energy and cost savings, the new units are also 30 percent shorter and lighter.
Discover your energy efficiency champions!
Energy is and will remain expensive. In addition, companies must reduce CO₂ emissions as part of their ESG targets. Many companies therefore invest in renewable energies such as photovoltaics on the roof or purchase green electricity.
But is that enough? Discover the hidden energy efficiency champions in your building with this online simulation tool. You will learn which settings will save you the most energy, costs and emissions at the same time.
By the way, the example building in our online tool has the same dimensions as the Danfoss production site in Graasten, Denmark. All value quantities of the savings and the related calculations are related to the dimensions of this building. Start playing your energy efficiency match now!
Talk to experts
Whether it’s a new construction project or an existing building, commercial buildings need to ensure a precise balance between dynamic growth and sustainable management. Whether in hotels, offices, data centers or public facilities, Danfoss products and solutions for speed-controlling pumps and fans can help you achieve significant energy savings, emissions reductions and cost reductions. We support you with expert advice on specific applications and on holistic solutions for optimum efficiency in your building. Do you have questions about energy efficiency with drive technology in your building? Then simply book an appointment in the online expert calendar.
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