a， 1。 General situation of the project and contents of energy-saving transformation. A hotel in Shanghai is a large luxury five-star hotel, located in the center of Shanghai, which consists of a 43-storey main building and a 5-storey podium. The air-conditioning area of the hotel is 40000m2, and the central air-conditioning system is equipped with four air-conditioning units, with a total refrigeration capacity of 1 1,900 rt, including three centrifugal refrigeration units with a refrigeration capacity of 900 rt and a screw refrigeration unit with a refrigeration capacity of 1 400 rt. The chilled water circulation adopts a two-stage pump system, and both chilled water and cooling water circulation adopt constant flow. See table 1 for the detailed specifications and configuration of the main equipment of the central air-conditioning system, and see figure 1 ... The average annual electricity consumption of this constant flow system is about 3.9GWh, and the annual operating cost of the air-conditioning system is considerable. Because the air-conditioning cooling load of the hotel fluctuates greatly due to the occupancy rate of the room, there is rarely a full load condition under the design condition, which makes the use of constant flow system produce more cold waste, and also makes the power consumption of the air-conditioning system remain high, resulting in the waste of electric energy and operating expenses. In 2003, a company reformed the central air conditioning system of the hotel with variable flow and energy saving. Among them, the chilled water primary pump, the secondary pump, the cooling water pump and the cooling tower fan are all equipped with frequency converters, which change the original power frequency fixed-speed operation into variable-speed operation, so that the refrigeration capacity of the refrigerator is more matched with the air conditioning load in operation. 2 Detection and analysis of energy-saving benefits after transformation 2. 1 Energy-saving monitoring scheme and content The monitoring of frequency conversion energy-saving benefits of central air-conditioning system is mainly divided into two aspects: one is to test the actual air-conditioning load change under the condition of variable flow rate of refrigeration system, verify and ensure that the system load under the condition of variable flow rate and constant flow rate is similar, so that the monitoring data under the condition of variable flow rate and constant flow rate are comparable. It provides a prerequisite for future electricity consumption comparison. The second is to test the power consumption changes caused by the variable flow operation and constant flow operation of refrigeration host, chilled water pump, cooling water pump, cooling tower fan and other equipment in the air conditioning system, so as to calculate the energy saving rate and analyze its energy saving effect. According to the specific situation of central air conditioning distribution system, three groups of data are counted monthly in controlled variable flow equipment. In this way, the comparative data of power consumption and operating cost of air conditioning system under constant flow and variable flow conditions can be roughly obtained, so as to obtain the monthly power saving rate and the annual power saving benefit. 2.2 Analysis of energy-saving monitoring data By comparing the hourly load rate and supply and return water temperature of the refrigerator when the system is running under variable and constant flow conditions, and the hourly indoor temperature of the air-conditioned room under variable and constant flow conditions, the consistency of air-conditioning cooling load can be analogized. The hourly load rate of the system for two consecutive days under the conditions of variable flow and constant flow is shown in Figure 2. Figure 2 shows that the hourly variation of the refrigerator load rate is basically similar when the air conditioning system operates under variable flow and constant flow conditions respectively in the two adjacent monitoring days selected in the test, with the variation range of 95 %~ 10 1% and the fluctuation range of less than 5. 1%, indicating that the air conditioning load is basically the same under variable flow and constant flow conditions respectively in the two adjacent days. Next, we will compare the changes of various parameters in the air conditioning system when it runs under constant flow and variable flow conditions, and analyze some system and economic benefits that can be produced under variable flow conditions. Under the condition of variable and constant flow, the hourly supply and return water temperature of chilled water of the main engine is shown in Figure 3. Fig. 3 Comparison of chilled water supply and return temperature of the main engine under variable flow and constant flow conditions. As can be seen from Figure 3, the chilled water supply and return temperature of the refrigeration main engine is kept below 7℃ for two consecutive days under variable flow and constant flow conditions, and the average chilled water return temperature is about 1 1.7℃ under variable flow conditions, and the chilled water return temperature is relatively low under constant flow conditions. The average temperature is 10.5℃, which shows that the backwater temperature of chilled water under variable flow condition is about 1.2℃ higher than that under constant flow condition, which also shows that the cold energy transported by chilled water under variable flow condition is fully utilized to avoid the waste of cold energy caused by the reduction of terminal load under constant flow condition. Figure 4 shows the hourly inlet and outlet temperatures of the cooling water of the main engine under the conditions of variable flow and constant flow. As can be seen from Figure 4, under the condition that the cooling water supply temperature of the refrigeration main engine is basically kept at about 30℃ under two working conditions, the cooling water outlet temperature of the refrigeration main engine is about 36℃ under variable flow condition, which is about 65438 0.6℃ higher than that under constant flow condition on average. It can be seen that the condenser of the refrigeration main machine can basically run under the rated working condition under the variable flow condition, and the cooling effect of the cooling tower can also be fully exerted. Let's compare the use effect of central air conditioning system under two flow conditions, and select the indoor temperature of hotel lobby for comparison. The specific comparison is shown in Figure 5. As can be seen from Figure 5, the indoor temperature of the hotel lobby is basically maintained at 25.65438 0℃ under constant flow conditions and 26℃ under variable flow conditions when the temperature of cold water return water changes under variable flow and constant flow conditions, that is, the indoor temperature is less than 3.7% higher than that under constant flow conditions, so it can be considered that the room temperature is basically unaffected, which proves that the central air conditioning system can meet the indoor comfort requirements under variable flow conditions. 3 Analysis of energy consumption and energy-saving rate of central air-conditioning system during the monitoring period When the system is operating under two different working conditions, namely variable flow and constant flow, the daily, monthly and annual data of power consumption can be obtained by recording the power consumption of central air-conditioning system hour by hour, and the changes of power consumption of the system after energy-saving transformation with variable flow are compared, as shown in Figure 6. Figure 6 shows that the monthly power consumption of the refrigeration main engine is lower than that of the constant current operation after the energy-saving transformation. In the monitoring days selected in the figure, it is calculated that the daily power consumption can be saved by more than 10%. By monitoring the hourly electricity consumption data and saving the daily electricity consumption data, according to the accumulated electricity consumption readings, we can further get the monthly energy-saving benefits and its changing trend generated by monthly variable flow operation compared with constant flow operation. The change of monthly electricity saving rate from 2004 to 2005 is shown in Figure 7. As can be seen from Figure 7, the power saving rate in winter and transition months is greater than that in summer. This is mainly because in summer, the cooling load of air conditioner is large and its hourly fluctuation is small. All equipment in the system basically runs at rated power and rated flow, and the system flow changes little, so there is little waste of cold energy, large power consumption base and small power saving potential. In the transitional season and winter, the load characteristics of hotel buildings determine that there is certain discontinuity and uncertainty in the area and time where cooling is needed, and the cooling load fluctuates greatly every hour, which makes the variable flow system after energy-saving transformation better match the fluctuation of load and basically realize the balance between supply and demand. In addition, the cooling hours in these seasons are much shorter than those in summer, and the electricity consumption base is smaller, so the energy-saving rate is higher and the energy-saving effect is more obvious. So in general, the energy-saving effect of variable flow energy-saving system in winter is better than that in summer. It should be noted that the monthly energy-saving rate listed in Figure 7 is obtained by the arithmetic average of the energy-saving rates measured in the first, middle and last three test periods of each month, that is, the following is the comparison of the system power consumption of the hotel central air-conditioning system when it is running under constant flow and variable flow conditions through annual monitoring. During the whole monitoring period from August 2005 to 65438+ in October 2006, its energy consumption is shown in Figure 8. As can be seen from Figure 8, the energy consumption is obviously reduced after the system is switched from the original flow operation to the variable flow fuzzy operation. The annual energy consumption of the original air-conditioning system in the hotel was about 3.7GWh when it was running at constant flow rate. However, after the energy-saving transformation with variable flow rate, the annual energy consumption of the system was basically kept below 3GWh, and the overall energy-saving rate reached more than 20%. According to statistics, from August 2004 to June 2006, the power saving rate was about 22. 1 0%. In actual operation, due to the influence of variable flow and constant flow, the above monitoring and calculation data may change slightly compared with environmental conditions. In a word, it can be considered that the comprehensive energy-saving rate of the central air-conditioning system is basically above 20% after the energy-saving transformation of variable flow, and the energy-saving effect is remarkable.

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