Study On The Applicability Domains Of Variable Chilled Water Temperature Adjustment In Central Air-conditioning System

As major energy consumer of central air-conditioning in modern architecture including offices, hotels and so on, reasonable energy-saving design application system plays an important role on energy conservation of the whole building.Many building owners began to in request of energy-saving renovation to air conditioning system with rising electricity prices.The air-conditioning system should have good regulation performance because air conditioners are under part load operation in most of the time. The regulation of Chilled water system concluded quantity adjustment and quality adjustment, frequency conversion of water supply pump belong to quantity adjustment and variable chilled water temperature belong to qualitative adjustment. Due to variable chilled water temperature adjustment have many prominent advantages such as it could be realized simply, needing less investment in the secondary energy-saving reform, and having on effect on the hydraulic characteristics of the water system and so on, the variable chilled water temperature adjustment got more and more research and application during recent years, and becoming one of the principal means of energy-saving in air-conditioning system.The energy-saving effect was more and more better with temperature rise, variable chilled water temperature adjustment would have no impact on the comfort of air-conditioning as long as regulating reasonably and making sure water supply can meet requirements of cooling load.In this paper,based on the transfer function method and typical annual meteorological data, the software of annual hourly air-conditioning cooling load calculation was compiled,then the air-conditioning load of four typical public buildings were simulated, including offices, hotels, public canteens and hospitals, and the relationships between the most unfavorable load rate and the averaged load rate were analyzed. The results indicated that the ratios of the most unfavorable load rate to the averaged load rate would be different for different buildings, the maximum and minimum ratios were 1.325 and 1 respectively. Furthermore,The ratios four one kind of building would change with time, The values were maximum in the morning and changed between 1.1 and 1.325, and less than 1.1 in the afternoon. Due to east rooms were influenced by solar radiation firstly during 8:00 to 11:00 every day, the load rate was quite different from any other orientations rooms, but in other period of time, the differences of load rate in all orientations rooms were not obvious.The most unfavorable load rate would reduce following the decreased trend of the averaged load rate, also the variable chilled water temperature adjustment technology was applicable when the load rate decreased.The best chiller water supply temperature was worked out through check calculation and optimization solution of surface air cooler. counting method based on heat efficiencyεl and contact coefficientε2 was used to the check calculation of surface air cooler.Taking office building for example, in the premise of comfort requirements in indoor environment was guaranteed, combined with the characteristic that variable chilled water temperature adjustment only applied to the situation when the most unfavorable load rate and average load rate changed consistent, the most unfavorable load rate and the averaged load rate were taken as optimization input load rate data respectively. The calculation results indicated that chilled inlet water temperature, supply air temperature and indoor relative humidity are all changed consistent, the differences of these parameters were all small when inputting these two different load rates, so the variable chilled water temperature adjustment technology was applicable to this typical public buildings.