I. Introduction In the total energy consumption, building energy consumption accounts for a large proportion, among which lighting and air conditioning, especially air conditioning, account for the vast majority of building energy consumption. Therefore, it is of great significance to analyze the energy-saving potential of air conditioners. According to the analysis results, energy consumption can be reduced by designing air conditioning system or reforming existing air conditioning system. For areas with long refrigeration cycle, air conditioning energy consumption is high, so energy-saving work is particularly important and representative. This paper studies and discusses an office building in Shenzhen, with two floors underground and 20 floors above ground, with a total construction area of 39,200 square meters and air conditioning area of 30,000 square meters. Three centrifugal chillers with refrigeration capacity of 1336KW are selected for the air conditioning refrigeration system, but only two can meet the requirements. Both chilled water and cooling water systems operate at a constant flow rate. The indoor design parameters of the office building are: dry bulb temperature 24℃-26℃ and relative humidity 50%-60%. According to the actual investigation, the air conditioning system of the office building provides cooling all year round, and the running hours are 2530 hours. When the outdoor temperature drops in winter and refrigeration is not needed, the chiller stops running. Two, air conditioning load should be based on air conditioning load calculation for building energy consumption analysis and operation simulation. The design and operation energy consumption of air conditioning system is related to the dynamic load of air conditioning. In this paper, DOE-2, a large-scale energy consumption analysis software of the U.S. Department of Energy, is used to simulate the dynamic load of air conditioning in this office building, and the results are shown in figure 1. The simulated hourly peak load is 24 15KW, and the monthly average load shown in the figure is 1600KW. According to the calculation results, the office building needs refrigeration all year round.
Figure 1 After obtaining the dynamic load of the office building, in order to analyze the energy consumption of water chillers by using the load frequency method, according to a statistical method of air conditioning load throughout the year proposed in the reference [1], the dynamic load of air conditioning is converted into the relationship between load rate and time frequency. The annual average operating hours of the air conditioning system in the office building are 2530 hours, and the average time frequency of air conditioning cooling load is shown in Table 65438.
Air conditioning cooling load time frequency table 1
Loading rate (%)10 20 30 40 50 60 70 80 90 6 5438+000 Time frequency (%) 27.9 8.7 8.21.69.9 654 38+00.21/kloc.
Third, the energy saving analysis of the chiller in one year, because the air conditioning system runs for a long time under part load, the energy consumption in one year is related to the working characteristics of the chiller under part load. See Table 2[2] for the partial load performance of centrifugal water chillers. As can be seen from 2, compared with the load rate of 100%, the operation efficiency under partial load increases and decreases.
Part load performance parameter table of centrifugal chiller II
Unit load rate (%)
100
90
80
70
60
50
40
30
20
10
Percentage of unit power (%)
100
87.0
76.0
65.0
56.0
48.0
40.0
33.0
25.0
2 1.0
According to Table 2, the characteristic curve equation of typical centrifugal chillers is obtained by linear regression method, and the change of output power under different refrigeration capacity is calculated by load frequency method. The actual operation scheme of the refrigeration system is: firstly, start one water chiller to increase its refrigeration capacity from small to large to meet the actual load change, and then start another one until the output is insufficient. The first chiller is always at full load, while the second chiller is adjusted with the change of load. In this paper, the optimal operation scheme of water chillers is obtained according to the simulation optimization calculation (that is, the annual average output power of the units is the smallest). Because the centrifugal refrigerator surges when the design load is lower than 10 ~ 15%, this paper simulates the actual operation of the chiller, so that the minimum adjustment range of the chiller can not be lower than 15%, otherwise it will stop. The calculation results of the two operation schemes are shown in Table 3.
Table 3 Operating Power Consumption of Chiller
Load rate (%)
10203040
50
60708090
100
Annual average value
Time frequency (%)
27.98.78.2 1 1.6
9.9
10.2 1 1.66.44.2
1.3
Real international transport case
Number of business entities
1
1
1
1
1
2
2
2
2
2
-
Refrigeration capacity (%)
1 set 18. 136.254.272.3
90.4
93.4 100 100 100
100
2 sets of 0000
15.026.544.662.7
80.8
Average power (kW)
19.248.84 1 1.522 1.64
23.77
32.004 1. 1425.02 17.97
6.29
207.43
The case of the best transportation company
Number of business entities
1 1 1 1
1
2222
2
-
Refrigeration capacity (%)
1 set 18. 136.254.272.3
90.4
54.263.372.38 1.3
90.4
2 sets of 0000
54.263.372.38 1.3
90.4
Average power (kW)
19.24
8.84
1 1.52
2 1.64
23.77
28.66
37.75
23.87
17.82
6.24
199.37
According to the results in Table 3, the optimal operation scheme is as follows: firstly, start one water chiller to increase its cooling capacity from small to large to meet the actual load change, and then start another one until the output is insufficient. When the two water chillers are started, the load is evenly distributed, and the cooling capacity of each water chiller meets the requirements of load change from small to large according to the above table. At this time, the total energy consumption is minimum.
Four. The energy-saving analysis of water system shows that the air-conditioning water system has the problems of large flow and small temperature difference. In summer, the temperature difference between supply and return water of cold water supply system is about 3℃, and the temperature difference is only 1 ~ 1.5℃. The circulating water volume is generally 1.5 times the design water volume. The cooling system of high-rise buildings is generally large in scale and consumes a lot of energy, but it also has great energy-saving potential. An energy-saving refrigeration system not only requires the performance and quantity of the selected equipment to adapt to the change of air conditioning system load, but also requires the whole system to keep the minimum energy consumption under various loads during operation. When the variable-flow operation of air-conditioning water system is carried out by using frequency conversion speed regulating device, the working point of the water pump can be moved along the pipeline characteristic curve without changing the pipeline characteristics, so that the water pump can always run at the highest efficiency point and achieve the maximum energy-saving effect. For a closed system, when the flow decreases, the actual power consumption decreases correspondingly in cubic ratio. This has obvious energy-saving significance for the situation that the design water volume of air conditioning water system is quite different from the actual water volume at present. Because the research focus of this paper is energy consumption, that is, how much energy-saving potential the air conditioning system can have in real-time operation and regulation, so as to guide the actual operation. This paper simulates the optimal speed regulation ratio and corresponding power consumption under different flow rates when two parallel pumps use frequency conversion devices to adjust the flow rate according to the load change. When calculating the average power of speed regulating pumps throughout the year, there is also the problem of optimal load distribution among running pumps when simulating the energy consumption of pumps. Our aim is to achieve the minimum energy consumption, that is, the minimum total power consumption of the pump, on the premise of satisfying the flow and lift as much as possible. This paper only calculates the energy consumption of chilled water pump and chilled water pump when the flow rate changes to meet part of the load requirements, and does not study the variable flow analysis of cooling water side. When calculating the operation energy consumption, it is assumed that the minimum critical water volume (load) is 50% of the total water volume, and the chilled water circulation flow of each unit in this project is 230m3/h, so the minimum critical water volume is 1 15m3/h ... Check the flow of the water pump during the simulation. If it is lower than this value, the speed regulation ratio of the water pump will remain unchanged. In this paper, various speed regulation schemes are calculated. The actual operation scheme of chilled water system is as follows: when the load is lower than 50%, one pump runs; When the load is 50%- 100%, start two pumps. Through the simulation and optimization calculation of various speed regulation schemes, this paper obtains the optimal operation scheme of the water chiller (that is, the average output power of the chilled water pump is the smallest): when the load is lower than 50%, start a water pump; When the load is 50%- 100%, start two pumps. The pump is operated in stages to adapt to the change of load rate. The calculation results of the two operation schemes are shown in Table 4.
Table 4 Operating power consumption of chilled water system
Load rate (%)
10
20
30
40
50
60
70
80
90
100
Annual average value
Time frequency (%)
27.9
8.7
8.2
1 1.6
9.9
10.2
1 1.6
6.4
4.2
1.3
Actual operation scheme
Number of business entities
1
1
1
1
1
2
2
2
2
2
-
Speed ratio (%)
1 unit
1
1
1
1
1
1
1
1
1
1
2 sets
1
1
1
1
1
Average power (kW)
12.58
3.90
3.70
5.2 1
4.46
9.2 1
10.42
5.76
3.74
1. 17
60. 15
Optimal operation scheme
Number of business entities
1
1
1
1
1
2
2
2
2
2
-
Speed ratio (%)
1 unit
0.35
0.35
0.35
0.47
0.59
0.35
0.4 1
0.47
0.53
0.59
2 sets
0.35
0.4 1
0.47
0.53
0.59
Average power (kW)
0.55
0. 17
0. 16
0.54
0.9 1
0.4 1
0.73
0.60
0.56
0.24
4.87
After inspection, the water quantity of each unit is always above the minimum critical water quantity when the two pumps are running at variable speed. From the above two schemes, it can be seen that the energy saving effect of variable frequency speed regulating pump is very significant compared with that of constant speed pump under partial load. 5. There are many factors that affect the energy consumption of air conditioning system by indoor air parameters and building energy consumption. In view of the office building studied in this paper, according to the existing actual conditions and capabilities, this project analyzes the building energy consumption from the perspective of selecting design standards. In air conditioning design, indoor design parameters should be determined first, which is related to comfort standards and hygiene requirements. Reasonable indoor design temperature and humidity should strive to reduce energy consumption on the premise of meeting the requirements of thermal comfort. Dry bulb temperature is 22 ~ 27℃ and relative humidity is 30% ~ 70%, which is generally considered as a comfort zone. According to the indoor design parameters of the office building, through the calculation of six design points, the corresponding human response to the thermal environment and power consumption can be obtained, as shown in Table 5.
Power consumption of air conditioning system under different indoor parameters Table 5
design point
Dry bulb temperature (℃)
Relative humidity (%)
Comfort level
Power consumption (kWh)
1
24
50%
Slight icing
864 700
2
25
50%
comfortable
824 900
three
26
50%
comfortable
784 600
four
24
60%
comfortable
855 900
five
25
60%
comfortable
8 15 900
six
26
60%
comfortable
775 900
As can be seen from Table 5, the increase of temperature and relative humidity will reduce energy consumption. The above design points are basically in the comfort zone, but the power consumption is different. It can be seen that changing the interior design standards has great potential for energy saving. Therefore, on the premise of meeting the comfort requirements, we can choose to increase the indoor temperature and relative humidity to reduce the energy consumption of the air conditioning system. According to the actual situation of the office building, the energy-saving measures of the air conditioning system in the office building are put forward and analyzed through research. If only the energy-saving effect and economic benefit brought by the first three transformations are considered, the comprehensive effect is shown in Table 6. List of Energy Saving Potential Analysis of Air Conditioning System Table 6
modification works
Increase investment (yuan)
Power consumption (kWh)
Energy saving rate (%)
Save operating expenses ① (yuan/year)
convalescence
Gacey
After the change
Optimal operation scheme of water chiller
-
524 798
504 406
3.9
20 392
The constant water flow operation of chilled water pump is changed to variable water flow operation.
Frequency converter and auxiliary equipment 80 000
152 180
12 32 1
9 1.9
139 859
1 year
total
80 000
676 978
5 16 727
23.7
159 85 1
1 year
① The electricity price in Shenzhen is 1 yuan/(kWh). From the data in Table 6, it can be seen that considerable energy-saving effect and a large amount of operating expenses can be achieved by transforming the existing cold source system of artificial air conditioning with less investment. Because some energy-saving measures are difficult to operate for the system that has been built and operated, it would be better if the energy-saving problems of the system can be fully considered in the design stage. Seven. Conclusion By analyzing the energy-saving potential of air conditioning system in an office building in Shenzhen, we can see that the existing air conditioning system has great energy-saving potential. Only from the perspective of optimal operation of refrigeration system and chilled water system, the energy-saving potential of operation is very great, and the energy-saving rate can reach 23.7%. If the energy-saving problem of the system can be fully considered in the system design, better energy-saving and economy can be obtained. Reference 1 sheet, single season flat. Discussion on capacity matching of refrigerator from the perspective of energy-saving operation. HVAC,1990,20 (1):14 ~172 Cao Qi, Zhang Hua. Calculation and correct selection of part load performance parameters of water chillers. HVAC HVAC HVAC.
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