I. Introduction
As the key energy-consuming equipment in the building, the power consumption of the central air-conditioning system generally accounts for more than 40% of the entire building's power consumption. The central air-conditioning unit is designed to meet the maximum cold heat of the place of use. However, in actual applications, the vast majority of users use cold and heat loads, which are generally different from the maximum design cooling heat. For large differences, more than 90% of all parts of the system are operating at non-full load ratings. The traditional central air-conditioning water and air systems adjust the water volume and air volume by adjusting the valve or damper opening. The disadvantage of this adjustment method is not only the consumption of a large amount of energy, but also the adjustment quality is difficult to achieve the desired state, resulting in poor comfort of the air conditioner. .
The use of frequency converters controls and adjusts the speeds of the central air conditioner's terminal air-conditioning cabinets, chilled water/cooling water pumps, cooling tower fans, and even the host drive motors, so that the air condition, sub-system air volume, water flow and other load operating parameters can be The timely adjustment of the load condition can not only improve the adjustment quality of the system, but also achieve the adjustment performance that cannot be compared with the backward adjustment methods such as valve, damper/return adjustment, pole-changing speed regulation, etc., and improve the comfort of the air conditioner; it can also save a lot of electric energy. .
Second, the composition and working principle of the central air conditioning system
The chiller compresses the refrigerant into a liquid evaporative compressor through a compressor and exchanges 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 cool air is blown by the blower to achieve cooling. 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 cooling water with heat to the cooling water tower and is sprayed and cooled by the water tower fan, and the air is cooled. The heat exchange between the two, dissipates the heat to the atmosphere,
As shown below:
Chilled water circulation system: It consists of a freezing pump and a chilled water pipeline. The chilled water that flows out of the freezing machine is sent to the chilled water pipeline under pressure by a freezing pump, passes through the coils in each room, and takes away the heat in the room to lower the temperature in the room. At the same time, the heat in the room is absorbed by the chilled water and the temperature of the chilled water rises. The circulating water that has risen in temperature has become chilled water after it has been frozen by the main engine. This cycle is endless. The chilled water that flows from the freezing machine into the room is abbreviated as "water", and the chilled water that flows back to the freezing machine after flowing through all the rooms is abbreviated as "backwater". It is no doubt that the temperature of the return water will be higher than the temperature of the outflow to create a temperature difference.
Cooling water circulation system: It consists of cooling pump, cooling water pipe and cooling tower. When the refrigeration host performs heat exchange and cools the water temperature, it will certainly release a lot of heat. This heat is absorbed by the cooling water and raises 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 returns the cooled cooling water to the refrigeration unit. This cycle continues, taking away the heat released from the freezing unit. The cooling water flowing into the freezing machine is abbreviated as "water inflow", and the cooling water flowing from the freezing machine back to the cooling tower is simply referred to as "backwater." Also, the temperature of the return water will be higher than the temperature of the incoming water to create a temperature difference.
Third, the central air-conditioning converter energy-saving reform
Due to the design, the central air-conditioning system must be designed with the hottest weather and maximum load, and leave a design margin of 10-20%. However, in reality most of the time, the air-conditioning system will not operate under full load. The surplus, so the potential for energy saving is relatively large. Among them, the freezing machine can be loaded or deloaded according to the load changes. The chilled water pump and the cooling water pump can not be adjusted accordingly with the load change, and there is a great waste. The flow rate and pressure difference of the water pump system were previously accomplished by valves and bypass adjustment. Therefore, the phenomenon of large cut-off loss, large flow, high pressure, and low temperature difference inevitably existed, which not only wastes a lot of electric energy, but also causes central air conditioning. The end of the case does not achieve reasonable results. To solve these problems, the water pump needs to adjust the water flow and close the bypass as the load changes. Because the water pump adopts the Y-â–³ starting method, the starting current of the motor is 3 to 4 times of its rated current. Under the impact of such large current, the service life of the contactor and the motor is greatly reduced. At the same time, the starting time The water hammer phenomenon during mechanical shock and pump stop is easy to cause damage to mechanical parts, bearings, valves, pipes, etc., thereby increasing maintenance workload, spare parts and spare parts costs.
1. Reconstruction of the refrigeration system
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 properly adjusted according to the return water temperature within a certain range. That is, when the room temperature is lower, the target value of the pressure difference is appropriately decreased, the average rotation speed of the refrigeration pump is reduced, and the energy saving effect is improved. In this way, both the environmental temperature factor and the energy saving effect are improved. The specific method is as follows: Under the premise of ensuring the chilled water flow of the chiller, the minimum operating frequency of a chilled pump frequency converter is determined and it can be set as the lower limit frequency. The frequency regulation of the pump motor is measured by the temperature sensor installed on the system pipe. The thermostat compares it with the setpoint. When the temperature of the frozen return water is greater than the set value, the inverter outputs the upper limit frequency, and the pump motor runs at high speed; when the frozen return water temperature is less than the set temperature, the motor operates at the set frequency.
2. Reconstruction of cooling system
The frequency conversion of the cooling system adopts two temperature sensors to measure the inlet temperature and return water temperature of the cooling water. When the inlet and return water temperature difference is large, the cooling water pump and the cooling fan accelerate the operation, so that the temperature difference between the inlet and return water is kept at 5°C. Left and right; When the temperature difference between inlet and return water is small, reduce the speed of cooling water pump and cooling fan to achieve the purpose of energy saving.
Fourth, the conclusion