introduction:

As a key energy-consuming equipment inside a building, the power consumption of the central air-conditioning system generally accounts for more than 40% of the power consumption of the entire building. The central air-conditioning unit is designed to meet the maximum cold and heat of the place of use. In practical applications, the majority of users have varying cooling and heating loads. Generally, there is a lot of The big difference is that more than 90% of all parts of the system are running in a non-full load rated state. Traditional central air-conditioning water and air systems all use valve or damper opening to adjust the water and air volume. The disadvantage of this adjustment method is not only that it consumes a lot of energy, but also the adjustment quality is difficult to achieve the ideal state, resulting in poor air conditioning comfort .

Apply AC frequency conversion technology to control and adjust the end air conditioner fan case, cooling tower fan, chilled water/cooling water pump, and even the speed of the main engine drive motor of the central air conditioner, so as to make the air volume, water flow and other load conditions of the air conditioning subsystems Timely adjustment according to the load situation can not only improve the adjustment quality of the system, but also achieve adjustment performance that cannot be compared with backward adjustment methods such as valve, damper/reflux adjustment, and pole-changing speed adjustment. It improves the comfort of air conditioning; it can also achieve savings. A large amount of electrical energy reduces equipment operating costs. With the maturity and development of frequency conversion technology, "one day's electricity cost two days' electricity" is no longer a fantasy. The frequency conversion energy-saving transformation of central air conditioners is a shortcut to reduce costs and increase efficiency. The composition and working principle of the central air conditioning system:

The refrigerator compresses the refrigerant into a liquid state through the compressor, and then sends it to the evaporator to exchange heat with the chilled water to cool the chilled water. The chilled water pump sends the chilled water to the cooling coils of the air outlets of the fans, and the fan blows cold air to cool down. the goal of. The evaporated refrigerant releases heat in the condenser and exchanges heat with the cooling circulating water. The cooling water pump sends the heat-carrying cooling water to the radiating water tower, which is sprayed and cooled by the water tower fan. Perform heat exchange between the two to radiate the heat to the atmosphere, as shown in the following figure:




Chilled water circulation system:

It consists of a refrigeration pump and a frozen water pipeline. The chilled water flowing out of the chiller is pressurized by the chiller pump and sent to the chilled water pipeline, and through the coils of each room, the heat in the room is taken away, and the temperature in the room is reduced. At the same time, the heat in the room is absorbed by the chilled water, which increases the temperature of the chilled water. The circulating water that has increased in temperature becomes chilled water after passing through the refrigerating host, and it circulates endlessly.

The chilled water flowing out of the freezing host and entering the room is referred to as "outlet water", and the chilled water returning to the freezing host after flowing through all rooms is referred to as "backwater". Undoubtedly, the temperature of the return water will be higher than that of the outlet water to form a temperature difference.

Cooling water circulation system:

It consists of cooling pump, cooling water pipeline and cooling tower. The refrigeration host will release a large amount of heat while performing heat exchange and cooling the water temperature. This heat is absorbed by the cooling water, which increases the temperature of the cooling water. The cooling pump presses the warmed cooling water into the cooling tower to exchange heat with the atmosphere in the cooling tower, and then sends the cooled cooling water back to the refrigeration unit. Such continuous circulation takes away the heat released by the refrigeration host.

The cooling water flowing into the refrigerating host is referred to as "inlet water", and the cooling water flowing from the refrigerating host back to the cooling tower is referred to as "backwater". Similarly, the temperature of the return water will be higher than the temperature of the inlet water to form a temperature difference.

Necessity of energy-saving transformation of central air-conditioning:

Due to the design, the central air-conditioning system must be designed according to the hottest weather and maximum load, and a design margin of 10-20% is reserved. However, in fact, most of the time, the air-conditioning system will not run at full load. Surplus, so the potential for energy saving is greater. Among them, the refrigeration host can be loaded or unloaded according to the load change, but the chilled water pump and the cooling water pump cannot be adjusted accordingly with the load change, and there is a lot of waste. The flow and pressure difference of the water pump system used to be adjusted by valves and bypasses. Therefore, there are inevitably large interception losses and large flow, high pressure, and low temperature differences, which not only wastes a lot of electricity, but also causes central air conditioning The situation where reasonable results cannot be achieved at the very end. In order to solve these problems, it is necessary to make the water pump adjust the water flow and close the bypass as the load changes. Because the water pump adopts the Y-△ starting method, the starting current of the motor is 3 to 4 times of its rated current on average. Under such a large current impact, the service life of the contactor and the motor is greatly reduced. At the same time, the Mechanical shock and water hammer when the pump is stopped can easily cause damage to mechanical parts, bearings, valves, pipelines, etc., thereby increasing the maintenance workload and the cost of spare parts and spare parts.

Energy saving system introduction:

Adopting Anbangxin G7 series inverters to realize intelligent fuzzy control, and automatic frequency conversion operation according to the temperature difference of the refrigerating and cooling return water. While meeting the demand for air-conditioning, it can achieve the maximum power saving rate, which can reach more than 60%.

The refrigeration system is thermostatically controlled. The return water temperature signal is used as the target signal, so that the target value of the pressure difference can be appropriately adjusted according to the return water temperature within a certain range. That is to say, when the room temperature is low, the target value of the pressure difference is appropriately reduced, the average speed of the refrigeration pump is reduced, and the energy saving effect is improved. In this way, the environmental temperature is taken into account and the energy saving effect is improved.

The specific method is to determine the minimum operating frequency of a refrigeration pump inverter under the premise of ensuring the required flow of chilled water in the refrigeration unit, which can be set as the lower limit frequency. The frequency adjustment of the water pump motor is to measure the return water temperature through a temperature sensor installed on the system pipe. The thermostat compares it with the set value. When the refrigerated return water temperature is greater than the set value, the inverter outputs the upper limit frequency and the water pump motor runs at high speed; when the refrigerated return water temperature is less than the set temperature, the motor will work with the set frequency curve. The system diagram is as follows:

The cooling system uses the differential pressure signal as the feedback signal to perform constant pressure differential control. The system is shown in the figure:

The main functions are:

* Frequency conversion/power frequency switching function

If the conversion K1 switch is placed in the "stop" position, the operation of the original control cabinet will not be changed. If the frequency conversion operation is required, the conversion 1 switch must be placed in the "No. 1" position

*Closed loop automatic operation function

Set the changeover switch K1 to the "1" position, and the "frequency conversion operation" indicator light is on. At this time, the operation frequency of the inverter is automatically given by the PID, without manual adjustment.

*Open loop adjustment function

Set the changeover switch K1 to the "1" position, and the "frequency conversion operation" indicator light is on. At this time, the operating frequency of the inverter can be set manually by adjusting the potentiometer by setting the inverter parameter F12=1. From the perspective of operation, after the frequency conversion energy saving transformation:

* Significant energy saving effect;

*Realize the soft start, the motor starting current is greatly reduced, avoiding the impact on the power grid when the motor starts;

*The equipment runs more smoothly, eliminating the water hammer effect during start-up and shutdown;

*Realize closed-loop fully automatic control, improve the level of automation, safe and reliable operation, unattended.

Conclusion:

The frequency converter has energy-saving automatic operation, which can continuously optimize the efficiency of the motor to achieve the greatest energy-saving effect. At the same time, the built-in PID regulator is convenient for automatic control. Generally, the overall power saving effect is 30% to 60%, which is safe and reliable, and simple to operate.

Central air conditioning is an indispensable facility for modern property buildings, hotels and shopping malls. It can bring people a warm and comfortable day all year round. The energy-saving transformation of central air conditioning not only saves a lot of electricity, but also protects the environment. The most important thing is to bring huge economic benefits to the enterprise and greatly strengthen the competitiveness of the enterprise!