1.Overview
Central air conditioning can be cooled in summer and heated in winter. The key to achieve stable cooling or heating is to control the circulating pump to make the appropriate flow of hot water (winter) or cold water (summer). When the control switch of the benefit room is opened, the coil fan to the indoor hot air (winter) or cold air (summer), so that the room is stable in a comfortable temperature range. For example, in winter, the heat provided by the CCAC to all rooms is directly related to the flow of circulating water and the temperature difference between effluent and backwater. In order to ensure the stability of indoor temperature, the temperature difference between outlet water and return water should be relatively stable. If the temperature difference is too large, the indoor temperature is low and the circulating water flow increases; if the temperature difference is too small, the opposite is true. The traditional method is to adjust the opening of the valve in the pipeline according to the temperature difference between the outlet and the return water when the circulating pump is running.
2.Implementation plans
In the central air conditioning system of an office building of a company, FGI FD300 series frequency inverter 45kW fan pump, combined with LU-906H intelligent instrument temperature thermometer, is used to control the circulating water of the central air conditioning, realizing the positive effect of saving manpower, energy and stabilizing indoor temperature.
The FD300 series frequency inverter cooperates with the intelligent instrument thermograph to control the automatic operation of the central air conditioning system. The LU-906H instrument of Anton Company has the input terminal of two Pt100 temperature sensors, namely the temperature sensor t 1 on the outlet pipe and the temperature sensor t2 on the backwater pipe. By setting the instrument parameters, it outputs the PID control signal of 4 to 20 mA at the output end and sends it to the frequency control end of the frequency converter to adjust the output frequency of the frequency converter. Realize the closed-loop feedback control of the water pump rotation speed. It should be noted here that the intelligent instrument temperature thermometer has the PID control function, and has been opened to use, so there is no need to enable the PID control function of the frequency converter.
3. Application advantage
(1)Significant energy saving effect
Reduce the circulation pump speed through the frequency inverter, which can save 30% -50% power compared with the conventional constant speed pump operation.
(2)Precise control of the flow rate and the pressure
It can accurately adjust the flow rate and pressure of the circulating pump according to the feedback signals such as the temperature sensor and the pressure sensor. For example, in some places with strict temperature and humidity requirements.
(3)Soft start and soft stop protection devices
The frequency inverter adopts the soft start mode, which can make the motor slowly accelerate to the rated speed, and the starting current can be controlled in about 1.5-2 times of the rated current. It can also slow down slowly when stopping, avoiding the water hammer phenomenon caused by the sudden stop of the pump. This plays an important role in extending the service life of the motor and water pump and protecting the pipeline system.