Energy Consumption And Energy Flow Analysis Of Central Air Conditioning Systems With Water-cooled Chiller

There are three kinds of measures to reduce the energy consumption of central air conditioning system, that is, the use of energy-saving equipment, promoting the use of renewable energy and improving energy efficiency.Among them, the first two measures are mainly concentrated in the air conditioning system design and selection phase.Once the system was built and put into use, improving energy efficiency is the mian one.In the aspect of improving energy efficiency, the main ways are energy saving of equipment, the single equipment’s effective control and simulation.There still did not have ways to analysis energy consumption from a whole and complete air conditioning system.In addition, when central air conditioning systems were in actual operation, a lot of energy flow(such as the cold loss of water and air conveying system;the inefficiencies of water pump and fan;the energy loss of cold and heat source and so on)would have important influence on system energy consumption, cost and investment, and their environment,which has attracted widespread attention.But because of the lack of a benchmark, it is still unable to make quantitative analysis on it, and remains in the stage of qualitative analysis.Therefore, it is necessary to establish a benchmark for energy analysis method.In this method, it can not only analysis the energy consumption of system s each loop and the components, but also can provide a reference for the quantitative comparison of energy consumption of the system. From the point of view of the whole system with quantitative analysis, it is the way to analyze the whole air conditioning system energy efficiency, and to provide a solid theoretical support for energy saving for air conditioning system.This paper introduces a method of energy consumption analysis on the whole of central air-conditioning system with water-cooled chiller from a global view.Firstly, the establishment of the energy flow model for the system of extracting heat from cooling room and let it into environment through 5 consecutive sub-loop is put forward, and Sankey diagram is introduced to visualize energy flow.Then, real energy flow diagram of a 26 storey office building in Guangzhou for air conditioning system of constant air volume with water-cooled chiller in summer is drawn.Through the quantitative analysis, the variation of energy flow and energy flow relationship between them can be seen clearly.And the main flow of system’s is identified, that is fresh air load, the energy consumption of chiller and distribution system.Energy flow analysis can also provide the basis for the design and equipment selectionof a number of central air conditioning system.Based on the energy flow model of central air conditioning system with water-cooler chiller, the energy flow model for central air conditioning system of constant air volume with air-cooler chiller is further established.Then take a comprehensive building s air conditioning system of constant air volume in summer as example, the comparative analysis design energy flow and the difference of the two cold sources of the system is given, providing a reference for selection for the cold source of the system and energy saving design of the selected system.Energy flow analysis method can identify the main influence factors of the energy consumption of the system, but how these factors influence the energy consumption can not be reflected.Bacuse of the diversity of the factors, the analysis of their influences on the system energy consumption became complicated, so there give a simple energy analysis method called e-p analysis of air conditioning system.That is, to meet the regional thermal comfort conditions, the amount of energy per cooling capacity provided to the air conditioning area is as the foundation, and the energy per cooling capacity is analysised and decomposed.Apart from some very disturbance factors, the influencing factors of energy consumption of the system are divided into two categories:energy consumption of equipment per fluid flow e and conveying fluid flow per cooling capacity p, then analysis on effects of the factors on the energy consumption can transformed into the effects of the loop of e and p on the energy consumption, which greatly simplifies the analysis of the problem.A 26 storey office building in Guangzhou for air conditioning system of constant air volume with water-cooled chiller in summer is as a example, the e-p analysis method to analyze the energy consumption difference of the system between the actual and design condition.The results show that the energy consumption of the system between the actual and design condition has certain deviation, the deviation from the refrigerant loop is the largest, accounting for 84.88% of all;followed by air loop and the chilled water loop, respectively of the total deviation of 5.96% and 7.58%;cooling water loop accounted for 1.44%;the minimum deviation is cooling tower loop, accounted for only 0.14%.In addition, of the total energy consumption deviation, energy consumption of equipment per fluid flow e accounted for 20.33%, conveying fluid flow per cooling capacity p accounted for 79.67%.From the e-p analysis examples metioned above, the factors would effect on e and p of each loop, thus affect the energy consumption of the whole system.The degree of influence of these factors on e and p of each loop is difference, and that still can not judged, thus the benchmark energy consumption model is established to quantitative the effects of variousfactors on the system energy consumption.Also, a 26 storey office building in Guangzhou for air conditioning system of constant air volume with water-cooled chiller in summer is take as an example to analysis the changes of various factors caused by the energy consumption of the system.The analysis results show that maximum deviation is caused by the water chiller compressor due to inefficient, account for 89.5% of the total;followed by air loop pipe cold loss and the inefficient of chilled water pump, respectively account for 4.5% and 3.9%;the deviation caused by inefficient of the air loop fan is 1.1%;and the minimum part are chilled water pipe cold loss, efficiency of cooling water pump and cooling tower fan, the total three only account for 1%.Finally, based on the energy consumption deviation of the system existing between design and actual condition, the energy saving potential of various factors was calculated. Compressor inefficiency have the largest saving space, account for 81.88% of the total;followed by air loop pipe heat loss and water cooled pump s inefficiency, respectively 9.93% and 5%;air loop fan effiency also can not be ignored, account for 1.5%; other factors total energy saving space is 1.69%.And put forward relevant suggestions for the four main factors.