In the central heating industry, the upgrading and transformation of heat exchange station automation control systems is a systematic project that requires rigorous process management. Every step, from preliminary survey to final commissioning, affects the success or failure of the project. According to relevant technical regulations, the intelligent transformation of heating systems should generally follow the processes of survey and evaluation, design, construction and acceptance, and effect evaluation. As a professional control system integrator, Henan Rentai strictly follows this process to ensure the efficient and high-quality completion of transformation projects. Below, Henan Rentai will explain the complete implementation process of heat exchange station automation transformation from the stages of on-site research, scheme design, control cabinet production, construction and installation, and commissioning and operation.
1. On-site Survey and Demand Analysis
The starting point of the transformation work is in-depth on-site research. The project technical personnel will go to the heat exchange station to conduct on-site surveys of the existing control systems and equipment conditions. This includes understanding the primary side heat source parameters of the heat exchange station, the secondary side heating range, inventorying the types and installation positions of existing sensors, and the internal wiring and component conditions of the control cabinet. Since many old heat exchange stations may lack complete drawing materials, engineers will obtain first-hand information by taking on-site photos, recording equipment nameplates and terminal identifiers, etc. At the same time, fully communicate with the operation and maintenance personnel of the heat exchange station to understand the operation mode of the existing control logic, existing pain points, and the customer's functional requirements for the new system. For example, are there problems such as unstable temperature control of the secondary network heating and frequent start-stop of the pump that need to be solved? Through detailed on-site research, a reliable basis can be provided for subsequent scheme design to ensure that the transformation meets actual needs.
In the demand analysis stage, the engineering team will also evaluate which old equipment needs to be replaced and which can be reused. For example, check the performance of the original instruments and actuators: for components that are still in their service life and have reliable accuracy, they can be considered for retention to reduce transformation costs; on the contrary, sensors that are aging and inaccurate or control components with backward functions should be included in the replacement list. The demand analysis report will clarify the scope and objectives of the transformation, pointing out the direction for scheme design.
2. Technical Scheme Design and Planning
Based on the on-site research data, engineers start to formulate transformation schemes and design drawings. This step includes control strategy design, equipment selection, and system architecture planning. First, determine the architecture of the new control system: which PLC and its I/O modules to use, the supporting human-machine interface (HMI) model, network communication methods, etc. Professional engineers will select appropriate PLC models and module configurations according to the number of control points and functional requirements. For example, small heat exchange stations may use Siemens S7-200 SMART series PLCs, while medium and large stations may consider higher-performance PLCs or distributed control systems. Then, draw electrical schematics, indicating the wiring correspondence between all sensors, actuators and PLCs, as well as the layout of electrical components inside the control cabinet.
In terms of control strategies, the scheme design will provide the automation logic of each control loop of the heat exchange station. For example: the primary side regulating valve adjusts the opening degree using the PID algorithm according to the secondary side outlet water temperature; the circulating pump and make-up pump are controlled by the PLC through pressure or differential pressure feedback signals to start-stop and adjust the frequency conversion to maintain the stability of the secondary network pressure; and interlock protection logic under working conditions such as overpressure and overtemperature. These strategies should not only combine industry best practices but also be customized according to on-site characteristics to ensure that the new system is safe, reliable, efficient and energy-saving.
In addition to the control-level design, the scheme will also plan the steps and schedule for the implementation of the transformation. The construction organization plan will clarify when to carry out the demolition of old equipment, installation of new equipment, and when to carry out cold/heat commissioning, etc., to minimize the impact on heating. If conditions permit, Henan Rentai often adopts the strategy of "offline pre-installation and commissioning": first complete the assembly and simulation test of the new control cabinet in the factory to ensure that the program and hardware are basically reliable, and then transport it to the site to replace the original system, thereby compressing the on-site construction and commissioning time. This planning work is coordinated in the scheme design stage, laying the foundation for subsequent construction.
3. Control Cabinet Manufacturing and Testing
After the scheme is determined, enter the specific production link of the control cabinet. Henan Rentai has a professional electrical assembly workshop, which will assemble and wire the new PLC control cabinet according to the design drawings. The control cabinet usually includes PLC host and expansion modules, 24V DC power supply, contactors, relays, intermediate terminal blocks, and necessary circuit breakers, frequency converters and other components. In the manufacturing process, strictly follow electrical specifications: separate high-voltage parts from low-voltage control parts, use shielded wires for analog signal lines and single-point grounding, and all terminal blocks and wires are printed with numbers for correspondence. Such standardized assembly ensures the reliability and maintainability of the control cabinet.
After the production is completed, the new control cabinet will undergo functional testing before leaving the factory. Engineers use simulation signals or connect actual sensors to verify each logic of the PLC program one by one. For example, given an analog temperature signal, observe the control effect of the PID algorithm on the regulating valve output; simulate the water tank level change to verify whether the make-up pump start-stop logic is correct; manually create overpressure conditions to check whether alarms and interlocks are activated. At the same time, measure the on-off of each wire inside the control cabinet to ensure that the wiring is consistent with the drawings without omissions or wrong connections. Once problems are found in the indoor test, they are rectified immediately and tested again until all functions work normally in the simulated environment.
Through sufficient factory testing, the new control cabinet is equivalent to completing pre-commissioning and is sent to the site with "zero defects". This greatly reduces problems during on-site commissioning and improves the first-time success rate after installation.
4. On-site Construction, Installation and Wiring
On-site construction is usually carried out during the non-heating period or shutdown maintenance period to avoid affecting heating. The construction team first removes the old control cabinet and related old equipment (if needed), and then positions and installs the new control cabinet. If the on-site space is limited and the old and new cabinets cannot be placed at the same time, the engineering personnel will adopt the strategy of "install first, then remove": first install the new cabinet and wire it next to the old one, and after commissioning, switch over and quickly remove the old cabinet to reduce the heating interruption time.
Wiring work is crucial, especially when information is missing, so it is necessary to be extremely careful. The construction personnel will connect the cables of all on-site sensors and actuators to the new control cabinet terminals one by one according to the design drawings and make marks. To avoid control logic confusion caused by wrong wiring, Henan Rentai emphasizes the principle of checking each loop and commissioning item by item: after connecting each signal line, use a multimeter or tester to confirm that it is connected to the correct PLC channel; after completing the control wiring of one loop, energize and test the function of that loop separately to confirm it is correct before proceeding to the next one. During the wiring process, special attention will also be paid to interface adaptation issues. The sensor output signals of many old heat exchange stations may be different, and the new PLC may need signal conversion modules to be compatible. Therefore, during on-site installation, if it is found that, for example, a pressure transmitter outputs 0-10V while the PLC only supports 4-20mA, a conversion module will be added on-site; or if an actuator needs AC 220V drive and the PLC relay cannot directly drive it, an intermediate relay will be added for amplification. These detailed treatments ensure that the old and new equipment are completely matched electrically, laying a good foundation for the physical connection of the system.
5. System Commissioning and Final Operation
After the installation is completed, the project enters the critical on-site commissioning stage. First, cold commissioning is carried out: verify and calibrate each function of the control system one by one without heat medium. The commissioning engineer will repeatedly check the correspondence between the PLC program and on-site equipment, and monitor the data of each measuring point through the touch screen or computer to see if they are reasonable. For example, manually change the outdoor temperature sensor reading to see if the PLC can adjust the secondary side water supply set temperature accordingly to realize the automatic correction of the heating curve; manually switch the standby circulating pump to verify the interlock logic to ensure that the two pumps can alternate normally; trigger the low liquid level switch to check whether the make-up pump starts automatically, etc. Each alarm and interlock protection is also tested at this stage to ensure that the system will shut down safely according to the design in case of overpressure, overtemperature and other conditions. After cold testing confirms that the logic is correct and the equipment operates reliably, hot commissioning begins.
Hot commissioning is carried out under the condition of actual heating medium operation. Gradually increase the temperature and pressure to make the heat exchange station enter the heating operation state, and continuously observe the adjustment effect. During this process, experienced commissioning engineers will closely monitor the supply and return water temperature and pressure curves and optimize the control parameters. For example, when it is found that the secondary water supply temperature fluctuates greatly, adjust the PID parameters in time; if the circulating pump starts and stops too frequently, modify the control strategy to add a delay or adjust the trigger threshold to improve system stability. Through continuous fine-tuning, until all performance indicators meet the design requirements. In addition, the operation under different working conditions (such as low load at night and peak load during the day) will be simulated to verify the self-adaptive ability of the system.
When the commissioning engineer confirms that the new system is running stably, the transformation project can enter the operation stage: formally switch the heat exchange station to the new PLC automatic control mode. At this time, the technical personnel of the owner unit are usually invited to participate in the acceptance together. Both parties confirm item by item according to the initial design function list that all control and monitoring functions have been realized and the operating parameters meet the standards. If there are any detailed problems, the program will be finalized after on-site adjustment. At the same time, necessary operation training and maintenance guidance will be provided to the customer. At this point, the automation transformation project of the heat exchange station is successfully completed, and the new system begins to play a role in the entire heating season.
As finishing work, Henan Rentai will also provide technical support and inspection in the early stage of operation to ensure the long-term reliable operation of the system. Under the strict control and professional execution of the entire process, all links of the heat exchange station from preliminary research to installation and commissioning are connected in an orderly manner, and the transformed system is put into operation stably and achieves the expected energy-saving and efficiency-increasing effects. For more information, please contact Henan Rentai Electric immediately: Phone: 17638563962 / 0371-56520104 and Email: info@hnrentai.com.