| With the increasing public building area in China and the urgent need for indoor comfortable environment,central air-conditioning water system,as an essential part of the central air-conditioning system in public buildings,has formed the characteristics of large number and large increment in the number of applications.In building energy consumption,air-conditioning energy consumption accounts for about40%-50%,while central air-conditioning water system energy consumption accounts for 39%of air-conditioning energy consumption.Air-conditioning water system has great energy-saving potential.In the design of central air-conditioning water system,more attention has been paid to the energy consumption of air-conditioning water system.For example,in the Standard for Energy Conservation Design of Public Buildings?GB50189-2015?,the cooling/heat ratio of power consumption for pumps in air-conditioning cold/hot water systems is stipulated.In addition,low management level,low operation efficiency and high energy consumption often occur in the operation and maintenance management of central air-conditioning water system,which leads to the failure of energy-saving operation of central air-conditioning water system.Therefore,how to improve the quality of commissioning,operation and maintenance management of central air-conditioning water system and how to optimize the energy-saving of central air-conditioning water system on the premise of ensuring the comfort of indoor staff are very important.This paper investigates the water system of central air conditioning in six typical public building projects,explores the problems that are not conducive to the energy-saving operation of the water system of central air conditioning,and puts forward suggestions for improvement.In the aspect of design,it is suggested that the Variable primary flow system should be used in central air conditioning water system,and the circulating water pump should be set separately in winter and summer as far as possible.The different conditions of central air-conditioning water system in winter and summer should be taken into account in the selection of control mode for pump variable speed design.In the aspect of operation and maintenance,it is suggested to increase the inspection of automatic control system and terminal equipment of central air-conditioning water system,to train the operation and maintenance personnel of central air conditioning water system in regular time.In the aspect of construction debugging,it is suggested that the pipeline network should be thoroughly flushed before debugging,and the debugging work of hydraulic balance should be emphasized.In the process of studying the temperature difference,flow rate,power consumption and EH?C?R-a of water supply and return system of central air-conditioning in winter and summer of a public building complex project in Xi'an,the concept of maximum frequency operation flow during heating period?cooling period?is put forward.The results show that the circulating water system of central air conditioning in winter and summer of this project has the phenomenon of"small temperature difference and large flow"and the terminal is in low load operation for a long time.In addition,EHR-a of the central air-conditioning water system in the winter of the project cannot meet the Design Standard for Energy Efficiency of Public Buildings?GB50189-2015?.This paper holds that the reason for this phenomenon is that the circulating water system of the air-conditioning system of the project does not adopt the measures of separating pumps in winter and summer,which results in the selection of pumps not in line with the winter working conditions.And on the other hand,the control mode of variable speed adjustment of pumps in the central air-conditioning water system is not suitable.Finally,using MATLAB software to fit and calculate the characteristic curves of the five energy-saving optimization modes of central air-conditioning water system,it is found that the energy-saving rate of the pump in the user-side valve optimization method is negative?-2.7%?,which is not conducive to the energy-saving of the pump.Under the condition that the frequency of pump motor is not less than 30Hz,the energy-saving rate of water pumps is sorted from large to small as constant temperature difference control method?47.9%?,terminal valve position control method?36.6%?,terminal constant pressure difference control method?24.6%?and trunk pipe constant pressure difference control method?19.3%?.In the aspect of EHR-a of central air-conditioning water system,the variable speed optimization strategy of water pump is an effective way to reduce the energy consumption of central air-conditioning water system in existing public buildings.In the variable speed control strategies of pumps,the EHR-a value of the central air-conditioning water system is ranked from small to large by constant temperature difference control?0.00675?,terminal valve position control method?0.00850?,terminal constant pressure difference control method?0.01009?,trunk pipe constant pressure difference control method?0.01080?.From the conclusion of the study,it can be seen that the constant temperature difference control method has obvious advantages,but the actual use of the constant temperature difference control method can not fully guarantee the most disadvantageous user's air-conditioning effect.It is suggested that the control mode of pump variable speed regulation should be considered comprehensively before choosing.For the optimization method of variable speed regulation of pump controlled by trunk pipe constant pressure difference control,the larger value of?P,the larger EHR-a value of the system,the more unfavorable to the operation and energy saving of the transmission and distribution system.Therefore,when choosing the value of differential pressure,we should choose the smaller?P value as far as possible under the condition of meeting the most disadvantageous economic specific frictional resistance of the central air-conditioning water system. |
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