When supplying compressed air to industrial production systems, it is important to ensure a sufficient air volume for all machine processes at a constant system pressure and to reliably prevent the air from falling below the dew point. The measurement technology used enables the leakage to be determined and provides information on system optimization and permanent energy cost reduction. Intelligent, time-optimized activation of the individual consumer machines allows the total amount of air consumed to be kept within economically sensible limits (measured against the graduated energy prices for maximum consumption). The targeted heat recovery of the compressor systems for room ventilation technology fulfils a further point of energy saving in accordance with DIN EN ISO 50001. The system process data and the individual consumption values must be automatically monitored at all times to ensure compressed air quality and production availability and the processes must be documented - clearly visible on site and can be called up decentrally in the company communication network.

Used as a central energy management system, the GHM-ONE multifunctional unit equipped with a color touch display clearly shows the system operator the status of the process data and trend curves (short and long-term) for efficiency assessment.

Tried and tested solution

The sensors are connected directly - for example a dew point transmitter (measuring range -20 to +30° Ctd, optionally -40 to +30° Ctd), a pressure transmitter (0..16 bar) for the system pressure and a volumetric flow meter that reliably calculates the consumed volume from the flow velocity and gas density.

The start screen of the GHM-ONE multifunctional device provides an overview of the connected system.

© GHM

The supply and exhaust air, including recirculated air from the central compressor station and, for example, the adjoining room, are controlled using associated temperature sensors and motors (e.g. for fans or dampers).

In addition to the connection of logic signals for the start and interlock signals, a number of energy meters (kW/h), which can also be easily extended to the individual consumers, completes the complete process data acquisition in the GHM-ONE.

The modular device system technology and the directly connectable industrial network topology (e.g. fieldbus and Ethernet) allow for individual adaptation. The multifunctional device is based on a powerful processor which, together with a relay card and the power supply card, forms the basic device. The basic device is adapted to the application with a communication card and up to two I/O cards. The number of physical inputs and outputs can be expanded via the communication card. This modular design allows the hardware to be specifically adapted to the automation task.

Fast customization

Real compressed air consumption curves for several machines in a production plant. The red curve in the graph shows the total volume flow - during the 5-minute recording interval alone, this fluctuates between 55 and 20 m³/min.

© GHM

The software components are quickly adapted to individual customer requirements using the intuitive GHM-CAT tool. It essentially consists of the function block diagram, HMI and menu editor, the simulation and commissioning support consisting of a debug function and online diagrams.

The core of the application creation is the function block diagram editor with the function block library. The user creates his application with the help of the function blocks; no programming knowledge is required. The library contains more than 100 tested functions that can be easily placed on the user interface and wired using the computer mouse. There is no need to declare variables or assign complex functions. In this way, the user can effectively simulate his system or process from ready-made modules.

The operating and monitoring pages of the application are created using an integrated designer. This can be used to create specific information for the employee on site or more detailed pages for the service technician. These pages can be freely designed - it is even possible to integrate process images or other graphics. In addition, the user can create text-based operating pages to enable the rapid input of multiple process data.

Simulation of the application

Once the application has been created, it is tested in GHM-CAT. With the simulation, the software offers an exact replica of the device including all functions. Even the inputs and outputs of the hardware can be simulated. The user can thus test the application in the first step - without any risk to the system. During commissioning, the user is further supported by the GHM-CAT software with various forcing and debugging functions as well as a sophisticated online display of analog and digital values. With this variety of information and intervention options, nothing stands in the way of efficient commissioning.

The GHM-ONE library offers the option of implementing a data logger and a data recorder in the device.

Data recording and trend display

The data logger is configured via function blocks directly in the GHM-CAT application. It is possible to log digital and analog signals in different time intervals.

Block diagram of the typical system components with sensors and the GHM-ONE multifunctional device.

© GHM

The analog data can be recorded as minimum, maximum or average values over specific time frames. The data is stored in the device on an eMMC chip and can be read out via the Ethernet port via FTP and via the USB port on the front. The device has 2 GB available for data storage. The read-out data is available to the user in a standard ASCII format (csv) for further processing and analysis. The trend display on the device takes place on predefined operating pages. Up to four hydrographs can be displayed in one trend.

Different time grids can be displayed by cascading the function. As the trend block can be called up several times in the visualization, it is possible to use the GHM-ONE as a multi-channel recorder. The trend display is independent of the logger function. This means that different process signals can be displayed and recorded. The library also provides alarm management functions. A function block can be used to display alarm lists in plain text on the device. Alarm management also includes an acknowledgement function.

Concrete results

With this equipment, the user determines both the individual consumption processes of his individual production machines and the leakage rate in the entire system. Based on the process data analysis obtained from this, the necessary number of screw compressors to be activated, the reduction/reduction of the buffer tanks used on the machines and the measures to eliminate leaks are optimized. The aim is to ensure that the entire volume of compressed air to be provided by the system is reliably sufficient at all times thanks to an intelligent, individual machine start and a process that is optimally adapted to the current energy price scales for maximum withdrawals.

The idea behind this is implemented in practice in such a way that consumption peaks are reduced by intelligently delaying the activation of a single large consumer. After mathematical calculation, the GHM-ONE specifies the machine release. As each machine has a small buffer tank, it is also possible to elegantly reduce the direct inflow of compressed air supply by means of a simple control valve in order to dampen the sudden flow peaks in the system. With a small buffer tank in the machines, the direct inflow of the compressed air supply can be reduced by means of a simple control valve in order to dampen the abrupt flow peaks in the system.

50,000 euros saved per year

In one specific case, a maximum compressor output of 65 m³/min was installed. Thanks to the harmonization carried out, however, this maximum output was no longer required. The system pressure was reduced by 0.2 bar to 7.8 bar - whereby 1 bar corresponds to a cost reduction of around 6 %. With a requirement of 35 m³/min for regular operation, the old, calculated size of the compressed air storage tank of 90 m³ could also be reduced by 15 to 20 m³ by delaying the connection of the consumers. Determining the leakage resulted in a loss of 0.4 to 0.5 m³/min per machine, which, after eliminating the causes at energy costs of 2 ct/m³, generates an additional daily profit of several euros per shift and, with thirteen machines in 3-shift operation, accumulates to almost 50,000 euros per year. Depending on the compressor, a heat output of up to around 50 kW per hour is available for heat recovery.

Facility management of the entire compressed air system is handled by the GHM-ONE multifunctional device. The graphical representation of the current energy management via trend graphics on the on-site display and the simple communication with mobile and stationary computers connected via the company network (with MES and ERM coupling) as well as the low-cost investment requirements proved to be decisive factors for its use.

This makes the GHM-ONE a profitable solution for the system supplier, which can be tailored to the specific requirements of production companies and supports the tasks of consulting, planning, installation, energy efficiency, maintenance, service and customer service. For the production plant, the use of the technology means cost-efficient and reliable implementation that provides transparency in the process flow of all machines and the compressed air supply system at all times.

Author: Torsten Obermann is responsible for Application & Services Industrial Electronics at the GHM Group.