Optimization Simulation Of The Central Air-conditioned Chilled Water System Based On Carbon Emissions

According to the International Energy Agency,the construction industry accounted for30%～40%of the global energy consumption and 30%of energy greenhouse gas emissions.Therefore,under the policy of"double carbon target",it has a great preasure.To achieve this,it is essential to optimize the high energy consuming system in the high-energy construction industry,which is the central air-conditioning system.In the central air-conditioning system,the chilled water system accounts more than half of the total energy consumption,and the energy waste is more common.Therefore,this article’s main object is the central air-conditioning chilled water system.At the beginning,this article describes the current status of domestic and foreign development and summarizes the method of carbon emissions calculation of the whole life cycle of the building.Established a mathematical model for the full life cycle of the central air-conditioning chilled water system.Considering the carbon emissions during the operation phase of the chilled water system,the production stage and the recycling stage of the end coil.And the building model established in this article carried out a dynamic load simulation throughout the year based on De ST software.First,in order to calculate the carbon emissions during the operation phase of the system,a central air-conditioning chilled water system operation simulation platform on the TRNSYS simulation software was set up based on the energy consumption model of the chilled water units,chilled water pumps and other major equipment,with the carbon emission accounting mathematical model embedded in.The platform can be divided into four functional areas of parameter input,result output,system circulation,and control module.Intimination found that the water saving effect of chilled water from 8℃to 9℃is the best,the chilled water units under the transition season of most of the load rate of 0.3～0.5 have great energy saving potential.Secondly,as increasing the chilled water supply temperature will have a negative impact on the end air supply in terms of insufficient dehumidification,this paper considers increasing the supply temperature while increasing the heat transfer area of the end coil to compensate for the end dehumidification capacity.Based on the mathematical model of the end coil area and the carbon emission calculation model,the relationship between the carbon emission of the whole life cycle of the central air-conditioning system and the end area is analysed:the carbon emission increased by the initial investment of the central air-conditioning chilled water system coil is only three thousandths of the carbon emission reduced by the operation of the chilled water system.For the virtual building rooms in this paper,at a load factor of 1 and a coil area of less than24.46m²,the total carbon emissions that can be reduced during the cooling period of a central air-conditioning chilled water system is approximately 24.04kg CO₂ for every 6%increase in coil area.Therefore,increasing the coil area to offset the side effect of increasing the chilled water supply temperature is still very economical.Thirdly,the relationship between whole-life carbon emissions and chilled water supply temperature is summarised to analyse the economic and environmental benefits of energy efficiency optimisation of chilled water systems.It is found that for the building model in this paper,increasing the water supply temperature by 1℃results in an average carbon saving of approximately 24.04kg CO₂ over a calculated time period of 2208 hours;as the water supply temperature increases,the change in total carbon emissions is decreasing and reaches a minimum value for this regulation method at t_g=10℃.In addition,the chilled water supply temperature was optimised for the complete carbon accounting model using the Python language based on the integrated optimisation solver Gourbi to find the optimum chilled water supply temperature for partial loads and the minimum total carbon emissions that can be achieved for different end design areas.It is found that increasing the chilled water supply temperature for load factors of 0.5,0.6 and 0.7 has the best economic and environmental benefits when meeting the end dehumidification requirements.