In central air – conditioning system, The capacity of chilled water pumps and cooling water pump is based on the maximum design heat load of buildings to select, and there is certain design margin. In the system without using speed governing, pump is running at full speed under power frequency throughout the year, have to use throttling or return to regulate the flow, generate a lot of throttle or recirculation loss. And for pump motor, because it is running at full speed under the frequency, causing a significant waste of energy. It is enumerated that 67% engineering designs of thermal load are 94-165w/m2, but only 83% of the heat load meet 58-93 w/m2. Practice has proved that the circulatory system in central air – conditioning ( cooling pump and freezing pump ) insert frequency conversion system, by using frequency conversion technology can change the motor speed to adjust the flow rate and pressure change to replace the valve controls flow to save energy.
2. Energy-saving principle
From the working principle of fluid transfer equipment, water pump and fan, we can know that pump or fan’s flow rate ( volume ) is proportional to its speed, its pressure (lift) proportional to the square of its speed, its shaft power is equal to the product of flow and pressure. Thus we get a result : reduce the speed of water pump, fan, pump and fan power can fall even more. Use frequency converter ( Air ) control, you can save a lot of power, Soft start function of the inverter and the smooth speed control feature can achieve smooth adjustment to the system, make the system work stably, and extend the life of the machine set and network management.
3. The performance of frequency control of air conditioning system after modification
1) Use of Inverter closed – loop control, according to the need for software configuration and PID adjust the set temperature, to make the motor’s output power varies with the heat load, on the premise of meeting the requirements to achieve the maximum energy saving.
2) Because spin down run and soft-starting, reduces vibration, noise and wear, can extend the period of equipment maintenance and service life, improve equipment MTBF (Mean Time to Repair) value and reduce the impact of the Power Grid, improve the reliability of the system.
3) The system has a variety of protective measures, make the system work rate and the safety & reliability greatly improved.
4) Frequency closed – loop control system with the original frequency control system interlock each other, does not affect the original system’s running. Primary frequency control system can be running properly when frequency closed – loop control system in maintenance or failure.