With the continuous development of my country’s national economy and the continuous improvement of people’s living standards, central air-conditioning has entered various fields such as hotels, restaurants, industrial and mining enterprises, and office buildings. The conventional central air-conditioning system is selected and designed according to the maximum cooling and heating load. The hottest and coldest weather in the year is only a few days. Therefore, most of the time, the central air conditioner is operated under the rated load of the unit, that is, the partial load state, resulting in a great waste of electric energy. With the development of science and technology, the frequency converter It has been widely used in all walks of life, with low price and mature technology, especially the energy-saving transformation of fans and pumps has been widely promoted in the industrial field, and the average power saving is more than 30%.
1. The best way to save energy in central air conditioning
Since the main equipment of the central air conditioner is the fan and the water pump, the best way to save energy is to use the frequency converter. At present, most of the intermediate air conditioners still use the old control method, that is, by changing the number of compressor units, water pumps, and fans to start and stop, in order to achieve the purpose of adjusting the temperature.
The shortcomings of this adjustment method are concentrated in the following points:
● The equipment is fully open or fully closed for a long time, running in turn, and the waste of electric energy is amazing.
● The motor starts directly at power frequency, and the inrush current is large, which seriously affects the service life of the equipment.
● The temperature control effect is not good. When the environment or the heating and cooling load changes, the indoor temperature can only be adjusted by increasing or decreasing the number of hot and cold water pumps or using a windshield. The temperature fluctuates greatly and the comfort is poor.
After the central air conditioner adopts the frequency converter, it has the following advantages:
● The frequency converter can soft start the motor, which greatly reduces the inrush current, reduces the motor bearing wear and prolongs the bearing life.
● Adjusting the flow and pressure of the pump and fan can be done directly by changing the operating frequency of the inverter
It can reduce or eliminate baffles and valves.
● The power consumption of the system is greatly reduced, and the noise is reduced.
● If the temperature closed-loop control method is adopted, the system can automatically adjust the air volume by detecting the ambient temperature, and automatically adjust with the change of weather and heat load, the temperature change is small, and the adjustment is rapid.
● The system can be networked with the central control room through the field bus to realize centralized remote monitoring.
2. Frequency conversion and energy saving transformation of water supply system
Whether it is the central air-conditioning system of lithium bromide unit or electric refrigeration (Freon) unit, the energy consumption of the host itself is controlled by the unit, and the power consumption group outside the unit cannot be controlled, and the cost of this part is quite high, but it is usually ignored. . Especially for lithium bromide units, the power consumption of external water pumps and cooling tower motors accounts for about 30% of the total energy consumption cost (calculated at 2 yuan per kilogram of oil and 1 yuan per kilowatt-hour of electricity). Whether from the perspective of environmental protection or the vital interests of users, the central air-conditioning system should be designed to be the most energy-efficient system. It is the simplest and most effective energy-saving measure to use the frequency converter to control the motor of the external water pump and the motor of the cooling tower. In general, it saves 20% to 50% of electricity, and it can save 12% to 20% of the total operating cost of the unit and system every year, which is amazing.
1. Frequency conversion control of cooling water pump
The power of the cooling water pump of the central air conditioner is designed according to the full load operation of the compressor of the air conditioner refrigeration unit. When the ambient temperature and various external factors, the refrigeration unit does not need to turn on all the compressor units. At this time, the cooling capacity required by the condensing system of the air conditioner It is also reduced accordingly. At this time, the speed of the cooling water pump can be adjusted by the variable frequency governor, and the circulation speed and flow of the cooling water can be reduced, so that the cooling load of the cooling water can be fully utilized by the condensing system, so as to achieve the purpose of energy saving. The following data is obtained from our company’s frequency conversion energy-saving transformation of central air conditioners. When the cooling water pump and cold and warm water pump operate at low flow rate, power can be greatly saved. The significance is even greater. Take the test data of BZ type direct combustion engine central air-conditioning system using Hailip inverter to control the water pump as an example:
When the cooling capacity is 75%, the cooling water flow required by the unit is 34%, and the power consumption of the pump is about 20%;
When the cooling capacity is 50%, the cooling water flow required by the unit is 22%, and the power consumption of the water pump is about 15%.
2. Frequency conversion control of cold and warm water pumps
The power of the refrigerant pump of the central air conditioner is designed according to the full load of the air conditioner. When the cooling or heat required by the hotel, hotel, and building does not reach the full load of the air conditioner, the frequency converter governor can be used to adjust the refrigerant pump. Speed, reduce the circulation speed of refrigerant water, make full use of cooling and heat, so as to achieve the purpose of energy saving. If cooling and heating share the same water pump, the flow rate of the water pump in winter only needs 50%, which can save electricity; 75%.
3. Frequency conversion control of cooling tower fan
The power of the fan is generally small, and the power saving is not as obvious as that of the water pump. However, the frequency conversion control of the fan can greatly contribute to the constant temperature of the cooling water, which is extremely critical for the cooling temperature of the unit; it can also stabilize the solution circulation of the unit and obtain the maximum fuel saving. The low-speed operation of cooling tower fans can also greatly reduce drifting water, save water sources, delay water quality deterioration, and reduce the impact of water mist on the surrounding environment.
4. Other benefits of using frequency converters
Since the start and stop process of the frequency converter is gradually increasing and decreasing, it can eliminate the impact of the motor start on the power grid. And can avoid the failure of the motor caused by overload.
Because the motor is often operated at low load, it can greatly extend the life of the motor, water pump and fan. At the same time, because there is no impact of starting and stopping, and the flow rate is reduced, the pressure on the pipeline and the impact force on the pipeline are reduced, so the pipeline is not affected. , valves, and terminal equipment also play a protective role. On the other hand, equipment noise and vibration are reduced, which protects the environment.
5. The control method of the inverter outside the central air-conditioning unit
● Change the speed of the water pump and adjust the flow according to the temperature of the cooling water outlet/inlet;
● Change the cooling tower fan speed and adjust the water temperature according to the cooling water inlet temperature;
● According to the temperature difference between the outlet/inlet of cold and warm water, change the speed of the water pump and adjust the flow;
● Change the speed of the water pump and adjust the flow according to the temperature of the cooling water outlet;
●Change the pump speed according to the return water temperature of the refrigerant water, and adjust the tax flow;
3. Central air-conditioning terminal equipment – frequency conversion control of variable air volume units
The variable air volume unit is also an important part of the central air-conditioning system. The pros and cons of its performance indicators (air volume, cooling capacity, noise, and electricity consumption) depend not only on the performance of the variable air volume unit itself, but also on the control mode, The performance and quality of the controller.
With the continuous popularization of central air conditioning, the variable air volume unit regulating controller has gone through three stages of development:
The first stage: damper adjustment. It can play a role in regulating the air volume, but the power consumption is large and the noise is large.
The second stage: thyristor voltage regulation and speed regulation. It can play the role of regulating air volume, cooling capacity and energy saving, and has a certain improvement on the noise of variable air volume units. Its disadvantages are large volume, low reliability and stability, and high failure rate.
The third stage: frequency conversion adjustment. It can meet the adjustment requirements of variable air volume units on air volume, cooling capacity and noise to the greatest extent, with more obvious energy-saving effect, small size, and high reliability and stability.
At present, the frequency conversion controller is favored by the people in the central air-conditioning industry due to its unique advantages.