Design and application of Delta VFD (Variable-frequency Drive) combined with PLC and man-machine interface on central air conditioner

I. Introduction?

The clean environment of the production workshop is provided by the purification central air-conditioning equipment, so that the temperature, humidity and pressure difference of each room in the production workshop can meet the requirements of the national GMP regulations. Due to seasonal changes and day and night changes, each room in the production workshop has obvious changes in demand for air volume, while the air volume and water flow of the pump fan are adjusted manually by the damper and throttle valve. When the demand for air volume and water flow decreases, the opening of the damper and valve decreases; when the demand for air volume and water flow increases, the opening of the damper and valve increases. Although this adjustment method is simple and easy to implement, it has become a habit, but it is at the cost of increasing the loss of the pipe network and consuming a large amount of energy on the damper and valve. Moreover, when the central air conditioner is working normally, most of the dampers and valves are opened at 50%-60%, which shows that the designed capacity of the existing central air conditioner water pump fan is much higher than the actual need, and there is a serious phenomenon of "big horses and small carts", resulting in a lot of waste of electric energy. In recent years, with the rapid development of electric power, electronic technology, and computer technology, frequency conversion speed regulation technology has become more and more mature. Therefore, we have installed 19 VFD (Variable-frequency Drive) on the company's central air-conditioning water pump fans for energy-saving transformation. In addition, due to the large dispersion of water pumps and fans, in order to reduce the inspection intensity of the personnel on duty and facilitate the timely grasp of the working status of the water pumps and fans and find faults, we have installed a frequency conversion monitoring system in the central monitoring room through the communication application of the PLC and the man-machine interface with the VFD (Variable-frequency Drive), so that the duty personnel can directly set the frequency value and start and stop each VFD (Variable-frequency Drive) on the man-machine interface, and can monitor the actual operating current and voltage of the pump fan motor in real time. , The size of the frequency, and has functions such as alarm.

2. Frequency conversion transformation plan for central air-conditioning water pump fan

1. Conditions of equipment before transformation

(1) The condition of the air-conditioning equipment in the genetic department

①The refrigeration hosts are Hitachi units, with a total of three units. ②Refrigeration pump: 11KW, 2 poles, 4 sets of full pressure start, head 30m, outlet water temperature 6°C, return water temperature 10°C, outlet water pressure 0.35Mpa, rated current of each motor is 21.8A, normal working current is 16.6A. Under normal circumstances, open two sets and prepare two sets. ③ Cooling pump: 15KW, 4 sets of 2-pole full-voltage start-up, lift 30m, outlet water temperature 32.5°C, return water temperature 28.2°C, outlet water pressure 0.38Mpa, rated current of each motor is 29.9A, normal working current is 18.0A. Under normal circumstances, open two sets and prepare two sets.

(2) Conditions of air-conditioning equipment in the air-conditioning machine room on the old second floor

①The refrigeration host is a Hitachi unit, a total of two. ②Refrigeration pump: 15KW, 3 sets of 2-pole full-pressure start, lift 30m, outlet water temperature 6.1°C, return water temperature 9.8°C, outlet water pressure 0.36Mpa, rated current of each motor is 29.9A, normal working current is 21A. Under normal circumstances, open one and prepare two. ③Cooling pump: 15KW, 3 sets of 2-pole full-pressure start, lift 30m, outlet water temperature 31.8°C, return water temperature 27.7°C, outlet water pressure 0.41Mpa, rated current of each motor is 29.9A, normal working current is 20.6A. Under normal circumstances, open one and prepare two.

(3) Conditions of air-conditioning equipment in sub-packaged air-conditioning machine rooms

①The refrigeration host is a Hitachi unit, a total of two. ②Refrigeration pump: 15KW, 2 poles, 3 sets of full pressure start, head 30m, outlet water temperature 5.8°C, return water temperature 9.3°C, outlet water pressure 0.38Mpa, rated current of each motor is 29.9A, normal working current is 20.2A. Under normal circumstances, open two and reserve one. ③Cooling pump: 15KW, 3 sets of 2-pole full-pressure start, head 30m, outlet water temperature 31.6°C, return water temperature 27.3°C, outlet water pressure 0.40Mpa, rated current of each motor is 29.9A, normal working current is 21.2A. Under normal circumstances, open two and reserve one.

(4) The company has a total of 13 air-conditioning cabinets. ① There are 7 air-conditioning cabinets in the genetic department, including 3 22KW fan motors, 2 11KW fan motors, and 1 15KW and 18.5KW fan motors. ② There are 3 air-conditioning cabinets on the old second floor, including 2 15KW fan motors and 1 11KW fan motor. ③ There are 3 air-conditioning cabinets in the quality inspection department, including 2 11KW fan motors and 1 7.5KW fan motor.

2. Water pump frequency conversion transformation plan

Since the temperature difference between the inlet and outlet water of the refrigeration pump and the cooling pump is less than 5°C, this shows that there is still a margin for the flow of chilled water and cooling water. In addition, the normal working current of the motor is less than the rated current (5-12A), which obviously has the phenomenon of "big horses and small carts". Therefore, we use one Delta VFD-P11KW VFD (Variable-frequency Drive) and one Delta VFD-P15KW VFD (Variable-frequency Drive) for the chilled water system and cooling water system of the genetic department respectively to implement one drive and three drives (as shown in Figure 1). According to the needs, PLC1 controls 3 chilled water pumps and 3 cooling water pumps to switch in turn (but one VFD (Variable-frequency Drive) can only drive one water pump motor at the same time), so that the amount of chilled water and cooling water can be controlled automatically in a flexible, convenient, timely and appropriate manner to meet the needs of the production process. Similarly, a Delta VFD-P15KW VFD (Variable-frequency Drive) is used for the chilled water system and the cooling water system of the air-conditioning machine room on the second floor and the sub-packaging air-conditioning machine room. The control method is the same as that of the chilled water system and the cooling water system of the Ministry of Genetics. The following is a description of the chilled water system of the Ministry of Genomics:

(1), closed-loop control

The chilled water system of the gene department adopts full-closed-loop automatic temperature difference control