Central air conditioners can be refrigerated in summer, and it can be heated in winter. The key to achieving stable refrigeration or heating is to control the circulating water pump to make the appropriate flow of hot water (winter) or cold water (summer) flow through all benefit rooms, when the control switch of the benefit room is opened, the coil fan blows the water pipe to indoors. Release hot air (winter) or cold air (summer), so that indoors are stable in a comfortable temperature range. Taking winter as an example, the central air conditioning system provides heat from the flow of the circulating water and the flow of water, the temperature difference of the return water. In order to ensure that the indoor temperature is stable, it should ensure the relatively stable temperature difference of the returning water. If the temperature difference value is too large, the indoor temperature is low, and the flow of circulating water is needed; if the temperature difference value is too small, the situation is just the opposite. The conventional method is to perform the flow of the valve in the conduit according to the water, the temperature difference of the returning water, and control the flow of the circulating water in accordance with the temperature difference of the returning water, and the temperature difference of the return water. This is a waste of manpower and cannot guarantee the stability of the temperature and waste electricity. The central air conditioning system of a office building uses Fuji brand FRN30P11S-4CX type 45KW fan pump special inverter, with UL-906H intelligent instrument temperature difference, control of central air-conditioning circulating water, achieving saving, saving energy, stability The active effect of indoor temperature. The control circuit is shown in Figure 1. The inverter cooperates with the intelligent instrument temperature difference, and controls the automatic operation of the central air conditioning system. The temperature difference is selected using a UL-906H type instrument, the instrument input (9 to 14 terminals of the temperature difference in Figure 1), two PT100 temperature sensors, the temperature sensor T1 on the water pipe T1 and the temperature of the returned pipeline The sensor T2, by setting the measurement result of the instrument parameter and the temperature sensor, outputs 4-20 mA of the PID control signal at its output (15 and 16 terminals of the temperature difference) of the instrument (Fig. 1 medium temperature difference). Send the frequency control terminal of the inverter for regulating the output frequency of the inverter. Realization of closed loop feedback control of pump speed. It should be noted here that the intelligent meter temperature difference has a PID control function and has been used in this control scheme, so there is no need to enable the PID control function of the drive. In the circuit, the buttons SB1 and SB2 are used as the closing and fractal control of contactor contacts on the power source side of the inverter. Buttons SB3 and SB4 are used as a turning power control of the intermediate relay 1KA coil. When the 1kA coil is electrically, the contact is closed, turned on the terminal FWD and CM of the inverter, the inverter starts to run; when the 1kA coil is powered, the inverter stops running. Diangon.com All rights reserved! The terminals 30b and 30c of the inverter are the normally closed contacts of the exit relay. When the system runs anomalies, the contact is open, the intermediate relay 2ka coil is discharged, the contact is disconnected, and the contactor Km is turned off, and the contact of the contactor km is cut off. The device is released, the inverter is powered off, and the equipment is protected. The temperature difference and the inverter are intelligent instrument devices that can only be operated at the optimal state of the correct parameter settings. The temperature difference setting is shown in Table 1 in the parameter setting of the site. Table 1 On-site debug parameters of the temperature difference: 1. The temperature difference is displayed by the LED, the display effect is limited, and the parameter symbol is used in case. 2. Parameters in Table 1 "Cool" Cool for the choice of summer cooling and winter heating. The parameter setting effect is the opposite control logic for the adjustment of the frequency converter output frequency. The parameter setting of the inverter is shown in Table 2. Table 2 The field debug parameter of the inverter needs to be described, in the parameters of the inverter, "lower limit frequency" cannot be set to zero (see Table 2), and the factory value cannot be used by default because the default factory value of this parameter is zero, Here is 25 Hz. After setting the lower limit of zero, even if the frequency control command sent by the temperature difference is zero, the frequency converter is still running the following frequency. This is to prevent the pump motor from being stopped. Once the air conditioning circulating water stops the flow, the temperature sensor T1 and T2 measurements have lost practical significance to the PID control signal output after the temperature difference. The principle of the "lower frequency" parameter setting is that the pump motor continues to operate in the "lower limit frequency", and the heat is not enough to make the temperature of the air-conditioned room to reach the temperature, and the temperature cannot be made to the right value, at this time, The temperature difference value of T1 and T2 increases, and the control signal output of the temperature difference is increased, the frequency converter output frequency is increased, and the flow rate of circulating water is increased, and the indoor temperature is adjusted. Thereafter, the inverter changes the temperature difference of the temperature difference of the temperature difference, adjusting the temperature and flow of the water pump at any time, controlling the temperature of the air conditioner. This case successfully applies the inverter and temperature difference to the central air conditioning circulating water flow control. The pump belongs to the secondary law load. When the no-load power is ignored, the power of the load is proportional to the speed of the speed, so that the load power will drop much as long as the speed is slightly reduced. Compared to traditional programs, the motor is always running at full speed, with a valve to adjust the flow, with a large energy-saving space. After actual measurement, the power saving effect of this program reached 28%. At the same time, there are also many benefits that saving human, stable air-conditioning rooms, and extending equipment life. Read more
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