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Ideas and measures to improve energy station energy efficiency and system energy efficiency-Part 3
System Efficiency Improvement Measures
1. Cold source preparation
As mentioned above, the project builds the system based on the principle of overall system energy saving, and the end system makes reasonable use of high-temperature cold sources. The cold source of the air conditioner adopts a dual cold source method, that is, the energy station is equipped with a normal temperature chiller (5 °C/12 °C) and a high temperature chiller (15.5 °C/20.5 °C). The application of the high temperature chiller improves the average efficiency of the main engine.
2. Cold water distribution
The cold water transmission and distribution adopts a variable flow three-stage pump system. The primary and secondary pumps are installed in the energy station. Tertiary pumps are located in each service area. The way of direct series supply reduces the energy loss caused by setting plate heat exchangers, saves investment and ensures the temperature quality of cold water.
The primary pump is set in one-to-one correspondence with the chiller. There is a longer distance of the main pipe in the primary pump piping. When some main engines are turned on, the flow in the main pipe is lower than the full-load flow in the design working condition, and the pressure drop in the pipeline decreases. Therefore, the first-stage pump adopts the frequency conversion pump, and the rated flow rate of the main engine is used as the frequency conversion control target to adapt to the change of pipeline characteristics during operation and reduce the energy consumption of the first-stage pump. In addition, the existing conventional hosts can operate normally at 30% to 50% of the rated flow rate. In actual operation, under the premise of satisfying safety, the set flow rate can be appropriately reduced according to the performance of the host machine at extremely low load, and further energy saving can be achieved.
The normal temperature cold water frequency conversion secondary pump set adopts the way of high load and low load separately. The high-load pump set is configured according to the pipe network flow and resistance corresponding to the design load. The low-load pump set is configured according to the pipe network flow and resistance corresponding to 50% of the design load. In view of the large transmission and distribution flow rate of the project, the large annual transmission flow rate and the large change in the pressure drop of the pipeline network, the combination of high and low load pump group configuration and frequency conversion can further improve the matching degree between the pump operation and the change of the pipeline network characteristics, and adapt to the Changes in the flow and resistance of the pipe network during variable operating conditions improve the operating efficiency of the secondary pump under different load rates.
Normal temperature cold water three-stage pump sets, high temperature cold water three-stage pump sets and radiation mixed water pump sets are distributed according to service areas. The service area of each group of pumps is divided according to the transmission and distribution distance and load characteristics, which is convenient for start-stop and frequency modulation control. The radiant mixed water pump group close to the main ring network takes water directly from the high-temperature cold water secondary ring network, and the corridor radiant mixed water pump group takes water from the high-temperature cold water tertiary pump pipeline.
3. Cooling water distribution
Reducing the temperature of the cooling water supply can improve the operating conditions of the main engine, and a well-run cooling water system can ensure the operating conditions of the main engine, thereby improving the energy efficiency of the main engine. This case project is a single-built energy station, which has good layout conditions. The roof of the entire energy station can basically be equipped with cooling towers, and the arrangement of tower groups can ensure a reasonable spacing.
During partial load operation, the number control of the main engine and the cooling water pump implements the principle of one-to-one correspondence. The number of cooling towers is based on the principle of the lowest total energy consumption, that is, according to the performance parameters of the host, make full use of the heat dissipation capacity of the cooling tower in the system, try to obtain a lower cooling water temperature, and create conditions for the efficient operation of the host. In view of the large capacity of a single host, the power of the corresponding single cooling water pump is above 200 kW, and the cooling water pump adopts frequency conversion. Similar to the situation of the first-stage chilled water pump, the constant flow rate of the cooling water of the unit is used as the variable frequency control target, and the step variable constant flow mode can also be adopted according to the performance parameters of the main engine when the load is extremely low.
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