The following to Figure 8, for example, calculate the different load distribution under different control modes required pump head. In order to simplify the analysis, the calculation assumes that the user design load is equal, and the flow rate replaces the user load change. The calculation results are shown in Table 1 and Figure 9. Fig. 8 Air-conditioning water system with 6 identical ends Fig. 8 Pump head required for different load distribution with different control modes (unit: kPa) Table 1 Flow rate User 6 Stationary pressure difference User 1 Stationary pressure difference load concentrated on the proximal end The load is concentrated on the remote proportional load 0 m3 / h 48.00 48.00 48.00 84.00 45 m3 / h 48.67 58.57 49.65 84.66 90 m3 / h 50.91 71.67 54.66 86.67 135 m3 / h 55.34 83.55 63.00 90.00 180 m3 / h 63.67 92.52 74.67 94.68 225 m3 / h is the pump curve; OQ is the system curve; OAN is the constant pressure differential at the far end, the load is concentrated on the control curve of the proximal end; OCN is the constant pressure at the distal end OBN is the control curve when the proportional load changes; the closed area composed by the curve OANCO is the range of the system working point when the remote fixed pressure difference control; the ODM is the proximal fixed Pressure control curve. Fig. 9 Control curve of different user load distribution Through the above analysis and calculation, the following conclusions can be drawn: (1) When the pressure drop near the system is fixed, the pump head demand depends only on the load and has nothing to do with the load distribution; , Pump head demand is not only related to the size of the load, but also with the load distribution. â‘¡ In addition to the user fully open or fully off the two conditions, the remote set pressure when the system needs less pressure than the proximal, the system is more energy-efficient operation. This is because the system has the largest variable head when the pressure drop is set at the far end. (3) when the system is set to a fixed pressure at the far end, the user needs to be concentrated in the near-end when the system needs less lift than the proportional load, and when the load is concentrated on the far end, the system needs to be larger than the proportional load. This is because the remote load requires large transport energy consumption. Conclusion In the design of air conditioning variable water system, the domestic use of sub-catchment pressure differential bypass control of the primary pump system abroad often with bridge pump secondary pump system. In this paper, the secondary pump system form, load regulation and differential pressure control strategy are discussed, the following conclusions: The secondary pump system by setting the bridge, not only effectively solve the contradiction of the constant flow rate load variable flow and achieve The hydraulic conditions of all parts of the system isolation, and has the characteristics of distributed water pump hydraulic stability; when the cooling system capacity and load wide range of changes, the use of multi-pump parallel variable speed operation can reduce operating energy consumption in the Low load system can still maintain a high efficiency. Pump speed control with constant pressure at the far end, the system has the largest variable lift, operating energy than the pressure control near the end to be small. Remote head pressure demand control is not only related to load size, but also with the load distribution. References [1] Lu Yaoqing practical heating air conditioning design manual Beijing: China Building Industry Press 1993.6 [2] Luther K. Variable Volume Pumping Fundamentals HPAC August 1998. [3] Luther K. Applying variable volume pumping HPAC October 1998 [ 4] Weinstein Taylor and Associates The PST System Hydronic circuitry for high efficiency. Http: // [5] Jiang Yi with variable speed pump and variable speed fan instead of regulating valve with water valve HVAC 1997 27 (2) [6] Qin Xu Zhongjiang ASHRAE. 1995. 1995 ASHRAE handbook? HVAC applications, Chap. 34 Testing, Adjusting and Balancing. Atlanta: American Society of Heating, Refrigerating and Heating Systems, Air Conditioning 1998 28 (3) [7] Air ~ Conditioning Engineering, Inc. [8] Hegberg, RA 1997. Selecting control and balancing valves in variable flow system. ASHRAE Journal. June, pp53-62 [9] Petijean, RT 1992. Total balancing. Tour & Anderson. ] Shi Junliang control valve selection Beijing: China Building Industry Press 1986.12 About the Author Li Jianxing, male, born in 1972, Han nationality, Shanxi Yuanpingren, Tianjin University lecturer, doctor of engineering, involved in the preparation of a book, has published more than 10 papers, is now engaged in construction environment and equipment engineering teaching and research work. Address: Nankai District, Tianjin Wei Jin Road 92, School of Environmental Science and Engineering, Tianjin University, 300072 Tel: 022 ~ E-mail: Flow 6 users at a fixed pressure differential User 1 pressure differential load concentrated in the near End load concentrated on remote proportional load 0 m3 / h 48.00 48.00 48.00 84.00 45 m3 / h 48.67 58.57 49.65 84.66 90 m3 / h 50.91 71.67 54.66 86.67 135 m3 / h 55.34 83.55 63.00 90.00 180 m3 / h 63.67 92.52 74.67 94.68 225 m3 / h 78.71 100.68 89.67 100.97 270 m3 / h 108.00 108.00 108.00 108.00
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