The central air conditioning system is very common in modern enterprises and the improvement of the living environment, and a certain living environment or production process is necessary, that is, the so-called artificial environment, not only the temperature requirements, but also humidity, cleanliness and so on. So the central air conditioning system, the purpose is to improve product quality, improve people's comfort, centralized cooling and heating efficiency is high, then management, save investment and other reasons, for which almost enterprises, high-rise commercial buildings, business buildings, venues, theaters, offices, libraries, hotels, shopping malls, supermarkets, hotels, casinos, stadiums and other medium and large buildings are using central air conditioning. It is one of the indispensable supporting facilities of modern large buildings, the consumption of electricity is very large, it is a large electricity user, almost accounting for more than 50% of the electricity consumption, and the daily expenses are very large. Next, we have a detailed understanding of Kunshan central air conditioning maintenance.

The necessity of energy saving transformation of pump in central air conditioning system

Since the central air conditioning system is designed according to the large load and increases a certain margin, in fact, in a year, the full load operation is only more than ten days, or even more than ten hours, almost most of the time the load is running below 70%. Usually, the load of the refrigeration host in the central air conditioning system can automatically adjust the load with the change of seasonal temperature, and the refrigeration pump and cooling pump matched with the refrigeration host can not automatically adjust the load, almost long-term operation under the load, resulting in a great waste of energy, but also deteriorated the operating environment and operating quality of the central air conditioning. With the increasing maturity of frequency conversion technology, the organic combination of inverter, PLC, digital-to-analog conversion module, temperature sensor, temperature module and other devices constitutes a closed-loop automatic control system for temperature difference, which automatically adjusts the output flow of the pump. The use of frequency conversion speed regulation technology can not only maintain the market room temperature in the desired state, make people feel comfortable and satisfied, can make the whole system working state smooth and stable, more importantly, its energy saving effect of more than 30%, can bring good economic benefits.

First, the necessity of energy-saving transformation of water pump

Central air conditioning is a big power consumer in the building, and the annual electricity consumption of air conditioning accounts for about 60%, so the energy-saving transformation of central air conditioning is particularly important.

Due to the design, the central air conditioning system must be designed according to the hottest weather and large load, and leave 10-20% design margin, but in fact most of the time the air conditioning is not running at full load, there is a large surplus, so the potential for energy saving is larger, which can be loaded or unloaded according to the load change. Chilled water pump and cooling water pump can not be adjusted with the load changes, there is a lot of waste. The flow and pressure difference of the pump system is completed by the valve and by-pass adjustment, therefore, there is inevitably a large interception loss and large flow, high pressure, low temperature difference phenomenon, not only a large waste of electrical energy, but also cause the central air conditioning at the end of the reasonable effect. In order to solve these problems, the pump needs to adjust the water flow with the change of load and close the bypass. And because the pump is Y- △ starting mode, the motor's starting current is 3 to 4 times its rated current, a 90KW motor its starting current will reach 500A, in such a large current impact, contactor, motor service life greatly decreased, at the same time, starting mechanical impact and stop the pump when the water drop phenomenon, It is easy to cause damage to mechanical parts, bearings, valves, pipelines, etc., thus increasing the maintenance workload and spare parts, spare parts costs. The frequency converter control can adjust the speed of the pump motor according to the change of the load of the chilled water pump and the cooling water pump, and adjust the chilled water pump and the cooling water pump accordingly to meet the normal operation of the central air conditioning system, so as to achieve the purpose of energy saving. The speed of the pump motor decreases, and the electric energy absorbed by the motor from the grid will be greatly reduced.

Its reduced power consumption △ P=P0 [1-(N1/N0)3]

(1) Reduced flow △ Q=Q0 (1-(N1/N0))

(2) Where N1 is the changed speed, N0 is the original motor speed, P0 is the motor power consumption at the original motor speed, and Q0 is the pump flow generated at the original motor speed. It can be seen from the above formula that the reduction of flow is proportional to the first square of the reduction of speed, but the reduction of power consumption is proportional to the third square of the reduction of speed. Such as: Assuming that the original flow rate is 100 units and the energy consumption is 100 units, if the speed is reduced by 10 units, the flow rate can be obtained by equation (2) △ Q=Q0 [1-(N1/N0)] =100 * [1-(90/100)] =10. However, power consumption can be obtained from (1) equation △ P=P0[1-(N1/N0)3]=100 * [1-(90/100)3]= 27.1, the power will be reduced by 27.1 units, that is, 27.1% less than the original.

And because the frequency converter is a soft starting mode, after using the frequency converter to control the motor, the motor has no impact current during starting and running, and the impact current is the most important and direct factor affecting the service life of the contactor and the motor. At the same time, the frequency converter can also avoid the phenomenon of water sag after controlling the motor. Therefore, it can greatly extend the service life of motors, contactors and mechanical parts, bearings, valves and pipes.

Second, the central air conditioning system composition and working principle

1, refrigerating unit: the circulating water leading to each room is "internal heat exchange" by the refrigerating unit, so that the chilled water is cooled to 5~7 ° C. An external heat exchange source is provided to each air conditioning point through the circulating water system. The heat generated by the internal heat exchange is discharged into the air through the cooling water system in the cooling tower. The internal heat exchange system is the "cooling source" of the central air conditioning.

2, frozen water tower: used to provide "cooling water" for the refrigeration unit.

3, "external heat exchange" system: composed of two circulating water systems:

(1) The chilled water circulation system is composed of a refrigerated pump and a refrigerated pipeline. The chilled water flowing from the freezer unit is pressurized by the freezer pump into the chilled water pipeline, and the heat is exchanged in each room, taking away the heat in the room and reducing the temperature in the room.

(2) The cooling water circulation system is composed of cooling pump, cooling water pipe and cooling tower. Refrigeration unit for heat exchange, so that the water temperature cooling at the same time, will release a lot of heat, the heat is absorbed by the cooling water, the cooling water temperature rises, the cooling pump will rise the temperature of the cooling water pressure into the water tower, so that in the cooling tower and the atmosphere for heat exchange, and then the cooling water, sent back to the refrigeration unit, so constant circulation, take away the refrigerator composition of the release of heat.

4, cooling fan

(1) Indoor fan: installed in all rooms that need to be cooled, used to blow cold air cooled by chilled water into the room to accelerate the heat exchange in the room;

(2) Cooling tower fan is used to reduce the water temperature in the cooling tower and accelerate the heat brought back by the "return water" to the atmosphere.

All four parts of the central air conditioning system can be transformed to save electricity. However, the power saving effect of the refrigerated water unit and the cooling water unit is the most ideal. In this article, we will focus on the conversion speed regulation technology transformation of the refrigerated water unit and the cooling unit.