Filter monitoring: A crucial component for energy-efficient operation

If the careful use of ?energy? as a resource used to be for cost reasons, today addititionally there is increased environmental awareness. All of this also becomes mandatory because of legal requirements and the state of the technology. On this page you can read about how continuous filter monitoring crucially influences the energy efficiency of a system and supports you in complying with legal requirements.
Comparison: New filter ? used filter
Whether with air filters in ventilation and air-conditioning systems or oil filters in hydraulic circuits, in both cases, increasing contamination of the filter element causes a growing pressure drop. In order to keep the flow of the medium (air or oil) constant, the fan or the pump (respectively) must apply more power. The power consumption increases. Decadent monitoring signals the increasing pressure drop across a contaminated filter element. Replacing a fouled filter ensures the flow of the medium and thus prevents the energy usage of the fan or the pump from increasing.
Legal bases
With the adoption of the Kyoto Protocol in 1997, europe committed itself to reducing CO2 emissions. As a way to reach this climate goal, in 2005 it adopted the EuP (Energy using Products) directive. In 2009 2009, this was renamed the ErP directive (Energy-related Products directive) ? also called the Ecodesign directive.
Pressure gauge with switch contact, model PGS21
High resistance ? high energy consumption
You can easily recognize that a contaminated filter element is more resistant to the flow of a medium than a new, clean element. Physically, the pressure in the inlet (filter inlet) increases ? which may be monitored very well using a pressure measuring instrument ? and the flow rate is reduced. Since the required flow is specified, more energy should be introduced to compensate for the restriction in the filter.
Costs of filter change
Energy-related vs. cost-based considerations
From an energetic perspective, a lightly soiled filter should be replaced immediately. This conflicts with the fact that the exchange itself generates material and labour costs. Furthermore, the exchange can only just happen in the lack of both pressure and flow, and thus the machine or the process must be stopped. Predicated on these considerations, it is also clear that an exchange following a fixed amount of use, as we are aware of annual services on cars, for instance, is not an optimal solution.
Compromise: Filter monitoring
The compromise can be an acceptable degree of contamination ? meaning a specified maximum differential pressure across the filter. Normal limit values for the differential pressure (?P) of a hydraulic filter are between 1 and 5 bar. In ventilation systems, the limit values are between 50 to 5,000 Pa (0.5 to 50 mbar). Monitoring the pressure drop saves on operating costs, since changing out the filters only happens when close to reaching the accepted level of contamination of the filter. A further advantage is that, through continuous monitoring, the filter replacement could be scheduled in to the operational process.
Filter monitoring through measuring the pressure drop
In each case, the pressure drop across the filter is measured ? so ?P between the filter inlet and outlet. However, the pressure loss over the filter also increases with the volume flow. The ?P as a indicator of the contamination of the filter may therefore only be assessed in the defined operating state (flow and medium temperature). Filters for liquids can exceed the ?P limit due to brief pressure peaks. Due to inertia, these are not an issue for mechanical switches. For sensors, you should provide a short dead amount of time in the electronic evaluation (control).
Special case: Filter monitoring in hydraulic circuits
The return filters in a hydraulic circuit are a special case. As the name suggests, they are in the return line, just before the oil flows back to the tank. There is ambient pressure (atmospheric pressure) in the tank. Because of this ambient pressure is also present at the filter outlet. This simplifies monitoring, since a differential pressure sensor is now able to take over the measuring task. Punish has a favourable influence on the expenses of filter monitoring. On the one hand, these pressure sensors are less expensive than differential pressure sensors. On the other hand, you save on needing a pressure line from the filter outlet to the low-pressure connection of the ?P sensor. Temperature measurement of the oil is essential in hydraulic circuits. This permits the high viscosity of the hydraulic oil, which is still cold when starting, to be studied into account, thus avoiding false alerts. The hydraulic oil temperature is required to control the oil cooler. It includes a significant influence on the time over that your oil is used.
Calculation of the excessive differential pressure because of the high viscosity of cold oil
The trend in filter monitoring
Pressure sensor A-1200 with IO-Link
From ?preventive maintenance? to ?Industry 4.0? to IIoT cloud solutions ? there is a demand for data everywhere. This could be seen clearly in the change from traditional measuring instruments with optical displays to electrical sensors with analogue or digital output signals. When monitoring pressure filters, we can see the trend to displace the differential pressure sensor with gauge pressure sensors before and following the filter. Thus giving one both the system pressure and the pressure at the outlet of the filter, which a differential pressure sensor will not offer. The pressure drop, the difference between your two signals, is then calculated in the electronic control, in the edge computer or in the cloud.
Note
As well as pressure sensors for filter monitoring, the WIKA portfolio covers all relevant measurement parameters which are necessary for controlling and regulating the operating states of a machine or system. Further application examples can be found on our website in the ?Industries? section.
Also read our article
Safe filter monitoring with differential pressure gauges

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